Norbert Pelc

All Publications

• Spectral optimization using fast kV switching and filtration for photon counting CT with realistic detector responses: a simulation study. Journal of medical imaging (Bellingham, Wash.) Wang, S., Yang, Y., Pal, D., Yin, Z., Maltz, J. S., Pelc, N. J., Wang, A. S. 2024; 11 (Suppl 1): S12805

  Abstract

  Photon counting CT (PCCT) provides spectral measurements for material decomposition. However, the image noise (at a fixed dose) depends on the source spectrum. Our study investigates the potential benefits from spectral optimization using fast kV switching and filtration to reduce noise in material decomposition.The effect of the input spectra on noise performance in both two-basis material decomposition and three-basis material decomposition was compared using Cramer-Rao lower bound analysis in the projection domain and in a digital phantom study in the image domain. The fluences of different spectra were normalized using the CT dose index to maintain constant dose levels. Four detector response models based on Si or CdTe were included in the analysis.For single kV scans, kV selection can be optimized based on the imaging task and object size. Furthermore, our results suggest that noise in material decomposition can be substantially reduced with fast kV switching. For two-material decomposition, fast kV switching reduces the standard deviation (SD) by ∼ 10 % . For three-material decomposition, greater noise reduction in material images was found with fast kV switching (26.2% for calcium and 25.8% for iodine, in terms of SD), which suggests that challenging tasks benefit more from the richer spectral information provided by fast kV switching.The performance of PCCT in material decomposition can be improved by optimizing source spectrum settings. Task-specific tube voltages can be selected for single kV scans. Also, our results demonstrate that utilizing fast kV switching can substantially reduce the noise in material decomposition for both two- and three-material decompositions, and a fixed Gd filter can further enhance such improvements for two-material decomposition.

  View details for DOI 10.1117/1.JMI.11.S1.S12805

  View details for PubMedID 39072221

  View details for PubMedCentralID PMC11272100

• The effects of intra-detector Compton scatter on low-frequency DQE for photon-counting CT using edge-on-irradiated silicon detectors. Medical physics Grönberg, F., Yin, Z., Maltz, J. S., Pelc, N. J., Persson, M. 2024

  Abstract

  Edge-on-irradiated silicon detectors are currently being investigated for use in full-body photon-counting computed tomography (CT) applications. The low atomic number of silicon leads to a significant number of incident photons being Compton scattered in the detector, depositing a part of their energy and potentially being counted multiple times. Even though the physics of Compton scatter is well established, the effects of Compton interactions in the detector on image quality for an edge-on-irradiated silicon detector have still not been thoroughly investigated.To investigate and explain effects of Compton scatter on low-frequency detective quantum efficiency (DQE) for photon-counting CT using edge-on-irradiated silicon detectors.We extend an existing Monte Carlo model of an edge-on-irradiated silicon detector with 60 mm active absorption depth, previously used to evaluate spatial-frequency-based performance, to develop projection and image domain performance metrics for pure density and pure spectral imaging tasks with 30 and 40 cm water backgrounds. We show that the lowest energy threshold of the detector can be used as an effective discriminator of primary counts and cross-talk caused by Compton scatter. We study the developed metrics as functions of the lowest threshold energy for root-mean-square electronic noise levels of 0.8, 1.6, and 3.2 keV, where the intermediate level 1.6 keV corresponds to the noise level previously measured on a single sensor element in isolation. We also compare the performance of a modeled detector with 8, 4, and 2 optimized energy bins to a detector with 1-keV-wide bins.In terms of low-frequency DQE for density imaging, there is a tradeoff between using a threshold low enough to capture Compton interactions and avoiding electronic noise counts. For 30 cm water phantom, 4 energy bins, and a root-mean-square electronic noise of 0.8, 1.6, and 3.2 keV, it is optimal to put the lowest energy threshold at 3, 6, and 1 keV, which gives optimal projection-domain DQEs of 0.64, 0.59, and 0.52, respectively. Low-frequency DQE for spectral imaging also benefits from measuring Compton interactions with respective optimal thresholds of 12, 12, and 13 keV. No large dependence on background thickness was observed. For the intermediate noise level (1.6 keV), increasing the lowest threshold from 5 to 35 keV increases the variance in a iodine basis image by 60%-62% (30 cm phantom) and 67%-69% (40 cm phantom), with 8 bins. Both spectral and density DQE are adversely affected by increasing the electronic noise level. Image-domain DQE exhibits similar qualitative behavior as projection-domain DQE.Compton interactions contribute significantly to the density imaging performance of edge-on-irradiated silicon detectors. With the studied detector topology, the benefit of counting primary Compton interactions outweighs the penalty of multiple counting at all lowest threshold energies. Compton interactions also contribute significantly to the spectral imaging performance for measured energies above 10 keV.

  View details for DOI 10.1002/mp.17122

  View details for PubMedID 38753884

• Empirical optimization of energy bin weights for compressing measurements with realistic photon counting x-ray detectors. Medical physics Yang, Y., Wang, S., Pal, D., Yin, Z., Pelc, N. J., Wang, A. S. 2023

  Abstract

  BACKGROUND: Photon counting detectors (PCDs) provide higher spatial resolution, improved contrast-to-noise ratio (CNR), and energy discriminating capabilities. However, the greatly increased amount of projection data in photon counting computed tomography (PCCT) systems becomes challenging to transmit through the slip ring, process, and store.PURPOSE: This study proposes and evaluates an empirical optimization algorithm to obtain optimal energy weights for energy bin data compression. This algorithm is universally applicable to spectral imaging tasks including 2 and 3 material decomposition (MD) tasks and virtual monoenergetic images (VMIs). This method is simple to implement while preserving spectral information for the full range of object thicknesses and is applicable to different PCDs, for example, silicon detectors and CdTe detectors.METHODS: We used realistic detector energy response models to simulate the spectral response of different PCDs and an empirical calibration method to fit a semi-empirical forward model for each PCD. We numerically optimized the optimal energy weights by minimizing the average relative Cramer-Rao lower bound (CRLB) due to the energy-weighted bin compression, for MD and VMI tasks over a range of material area density rho A , m ${\rho }_{A,m}$ (0-40g/cm2 water, 0-2.16g/cm2 calcium). We used Monte Carlo simulation of a step wedge phantom and an anthropomorphic head phantom to evaluate the performance of this energy bin compression method in the projection domain and image domain, respectively.RESULTS: The results show that for 2 MD, the energy bin compression method can reduce PCCT data size by 75% and 60%, with an average variance penalty of less than 17% and 3% for silicon and CdTe detectors, respectively. For 3 MD tasks with a K-edge material (iodine), this method can reduce the data size by 62.5% and 40% with an average variance penalty of less than 12% and 13% for silicon and CdTe detectors, respectively.CONCLUSIONS: We proposed an energy bin compression method that is broadly applicable to different PCCT systems and object sizes, with high data compression ratio and little loss of spectral information.

  View details for DOI 10.1002/mp.16590

  View details for PubMedID 37401203

• Early CT physics research at massachusetts general hospital. Medical physics Pelc, N. J., Chesler, D. A. 2023

  View details for DOI 10.1002/mp.16229

  View details for PubMedID 36681879

• Empirical Optimization of Energy Bin Weights for Compressing Measurements with Photon Counting X-ray Detectors Yang, Y., Wang, S., Pal, D., Pelc, N. J., Wang, A. S., Zhao, W., Yu, L. SPIE-INT SOC OPTICAL ENGINEERING. 2022

  View details for DOI 10.1117/12.2611555

  View details for Web of Science ID 000836294000013

• A Methodology to Train a Convolutional Neural Network-Based Low-Dose CT Denoiser With an Accurate Image Domain Noise Insertion Technique IEEE ACCESS Kim, B., Divel, S. E., Pelc, N. J., Baek, J. 2022; 10: 86395-86407

  View details for DOI 10.1109/ACCESS.2022.3198948

  View details for Web of Science ID 000844074400001

• Fast kV Switching for Improved Material Decomposition with Photon Counting X-ray Detectors Wang, S., Yang, Y., Pal, D., Pelc, N. J., Wang, A. S., Zhao, W., Yu, L. SPIE-INT SOC OPTICAL ENGINEERING. 2022

  View details for DOI 10.1117/12.2611601

  View details for Web of Science ID 000836294000014

• How CT happened: the early development of medical computed tomography. Journal of medical imaging (Bellingham, Wash.) Schulz, R. A., Stein, J. A., Pelc, N. J. 2021; 8 (5): 052110

  Abstract

  As we arrive at the 50th anniversary of the first computed tomography (CT) scan of a live patient, we take this opportunity to revisit the history of early CT development. It is not an exaggeration to say that the invention of CT may represent the greatest revolution in medical imaging since the discovery of x-rays. We cover events over a period of about two decades that started with the realization that accurate cross-sectional soft-tissue detail is possible and could be a significant advance. We describe in some detail the development of the first CT system and then the rapid technical advances during the following years that included the entry of many companies into the field and the circumstances that led many of those entrants to exit the field. Rather than focusing on the specific technical details (which can be found elsewhere), we include stories and events in the hope that broader lessons can be learned. As the first x-ray-based digital imaging modality, CT brought into common use an exceptional tool that benefits countless patients every day. It also introduced dramatic changes to biomedical imaging as a field that continues to influence progress to this day.

  View details for DOI 10.1117/1.JMI.8.5.052110

  View details for PubMedID 34729383

• Special Section Guest Editorial: Computed tomography (CT) at 50 years. Journal of medical imaging (Bellingham, Wash.) La Riviere, P. J., Fahrig, R., Pelc, N. J. 2021; 8 (5): 052101

  Abstract

  Guest editors Patrick La Riviere, Rebecca Fahrig, and Norbert Pelc introduce the JMI Special Section Celebrating X-Ray Computed Tomography at 50.

  View details for DOI 10.1117/1.JMI.8.5.052101

  View details for PubMedID 34738026

• Findings of the AAPM Ad Hoc committee on magnetic resonance imaging in radiation therapy: Unmet needs, opportunities, and recommendations. Medical physics McGee, K. P., Tyagi, N., Bayouth, J. E., Cao, M., Fallone, B. G., Glide-Hurst, C. K., Goerner, F. L., Green, O. L., Kim, T., Paulson, E. S., Yanasak, N. E., Jackson, E. F., Goodwin, J. H., Dieterich, S., Jordan, D. W., Hugo, G. D., Bernstein, M. A., Balter, J. M., Kanal, K. M., Hazle, J. D., Pelc, N. J. 2021

  Abstract

  The past decade has seen the increasing integration of magnetic resonance (MR) imaging into radiation therapy (RT). This growth can be contributed to multiple factors, including hardware and software advances that have allowed the acquisition of high-resolution volumetric data of RT patients in their treatment position (also known as MR simulation) and the development of methods to image and quantify tissue function and response to therapy. More recently, the advent of MR-guided radiation therapy (MRgRT) - achieved through the integration of MR imaging systems and linear accelerators - has further accelerated this trend. As MR imaging in RT techniques and technologies, such as MRgRT, gain regulatory approval worldwide, these systems will begin to propagate beyond tertiary care academic medical centers and into more community-based health systems and hospitals, creating new opportunities to provide advanced treatment options to a broader patient population. Accompanying these opportunities are unique challenges related to their adaptation, adoption, and use including modification of hardware and software to meet the unique and distinct demands of MR imaging in RT, the need for standardization of imaging techniques and protocols, education of the broader RT community (particularly in regards to MR safety) as well as the need to continue and support research, and development in this space. In response to this, an ad hoc committee of the American Association of Physicists in Medicine (AAPM) was formed to identify the unmet needs, roadblocks, and opportunities within this space. The purpose of this document is to report on the major findings and recommendations identified. Importantly, the provided recommendations represent the consensus opinions of the committee's membership, which were submitted in the committee's report to the AAPM Board of Directors. In addition, AAPM ad hoc committee reports differ from AAPM task group reports in that ad hoc committee reports are neither reviewed nor ultimately approved by the committee's parent groups, including at the council and executive committee level. Thus, the recommendations given in this summary should not be construed as being endorsed by or official recommendations from the AAPM.

  View details for DOI 10.1002/mp.14996

  View details for PubMedID 34231224

• Spectral Photon Counting CT: Imaging Algorithms and Performance Assessment. IEEE transactions on radiation and plasma medical sciences Wang, A. S., Pelc, N. J. 2021; 5 (4): 453-464

  Abstract

  Photon counting x-ray detectors (PCDs) with spectral capabilities have the potential to revolutionize computed tomography (CT) for medical imaging. The ideal PCD provides accurate energy information for each incident x-ray, and at high spatial resolution. This information enables material-specific imaging, enhanced radiation dose efficiency, and improved spatial resolution in CT images. In practice, PCDs are affected by non-idealities, including limited energy resolution, pulse pileup, and cross talk due to charge sharing, K-fluorescence, and Compton scattering. In order to maximize their performance, PCDs must be carefully designed to reduce these effects and then later account for them during correction and post-acquisition steps. This review article examines algorithms for using PCDs in spectral CT applications, including how non-idealities impact image quality. Performance assessment metrics that account for spatial resolution and noise such as the detective quantum efficiency (DQE) can be used to compare different PCD designs, as well as compare PCDs with conventional energy integrating detectors (EIDs). These methods play an important role in enhancing spectral CT images and assessing the overall performance of PCDs.

  View details for DOI 10.1109/trpms.2020.3007380

  View details for PubMedID 35419500

  View details for PubMedCentralID PMC9000208

• A dynamic simulation framework for CT perfusion in stroke assessment built from first principles. Medical physics Divel, S. E., Christensen, S., Segars, W. P., Lansberg, M. G., Pelc, N. J. 2021

  Abstract

  PURPOSE: Physicians utilize cerebral perfusion maps (e.g., cerebral blood flow, cerebral blood volume, transit time) to prescribe the plan of care for stroke patients. Variability in scanning techniques and post-processing software can result in differences between these perfusion maps. To determine which techniques are acceptable for clinical care, it is important to validate the accuracy and reproducibility of the perfusion maps. Validation using clinical data is challenging due to the lack of a gold standard to assess cerebral perfusion and the impracticality of scanning patients multiple times with different scanning techniques. In contrast, simulated data from a realistic digital phantom of the cerebral perfusion in acute stroke patients would enable studies to optimize and validate the scanning and post-processing techniques.METHODS: We describe a complete framework to simulate CT perfusion studies for stroke assessment. We begin by expanding the XCAT brain phantom to enable spatially varying contrast agent dynamics and incorporate a realistic model of the dynamics in the cerebral vasculature derived from first principles. A dynamic CT simulator utilizes the time concentration curves to define the contrast agent concentration in the object at each time point and generates CT perfusion images compatible with commercially available post-processing software. We also generate ground truth perfusion maps to which the maps generated by post-processing software can be compared.RESULTS: We demonstrate a dynamic CT perfusion study of a simulated patient with an ischemic stroke and the resulting perfusion maps generated by post-processing software. We include a visual comparison between the computer-generated perfusion maps and the ground truth perfusion maps. The framework is highly tunable; users can modify the perfusion properties (e.g., occlusion location, CBF, CBV, and MTT), scanner specifications (e.g., focal spot size and detector configuration), scanning protocol (e.g., kVp and mAs), and reconstruction parameters (e.g., slice thickness and reconstruction filter).CONCLUSIONS: This framework provides realistic test data with the underlying ground truth that enables a robust assessment of CT perfusion techniques and post-processing methods for stroke assessment.

  View details for DOI 10.1002/mp.14887

  View details for PubMedID 33877693

• CNN-based CT denoising with an accurate image domain noise insertion technique Kim, B., Divel, S. E., Pelc, N. J., Baek, J., Bosmans, H., Zhao, W., Yu, L. SPIE-INT SOC OPTICAL ENGINEERING. 2021

  View details for DOI 10.1117/12.2580997

  View details for Web of Science ID 000672731900135

• Simulation of contrast agent dynamics in digital brain phantom for CT perfusion optimization Divel, S. E., Christensen, S., Lansberg, M. G., Pelc, N. J., Chen, G. H., Bosmans, H. SPIE-INT SOC OPTICAL ENGINEERING. 2021

  View details for DOI 10.1117/12.2549741

  View details for Web of Science ID 000671890600039

• Analytical model for pulse pileup in photon counting detectors with seminonparalyzable behavior Yang, Y., Pelc, N. J., Wang, A. S., Bosmans, H., Zhao, W., Yu, L. SPIE-INT SOC OPTICAL ENGINEERING. 2021

  View details for DOI 10.1117/12.2581145

  View details for Web of Science ID 000672731900060

• Detective quantum efficiency of photon-counting CdTe and Si detectors for computed tomography: a simulation study. Journal of medical imaging (Bellingham, Wash.) Persson, M., Wang, A., Pelc, N. J. 2020; 7 (4): 043501

  Abstract

  Purpose: Developing photon-counting CT detectors requires understanding the impact of parameters, such as converter material, thickness, and pixel size. We apply a linear-systems framework, incorporating spatial and energy resolution, to study realistic silicon (Si) and cadmium telluride (CdTe) detectors at a low count rate. Approach: We compared CdTe detector designs with 0.5 * 0.5 mm 2 and 0.225 * 0.225 mm 2 pixels and Si detector designs with 0.5 * 0.5 mm 2 pixels of 30 and 60mm active thickness, with and without tungsten scatter blockers. Monte-Carlo simulations of photon transport were used together with Gaussian charge sharing models fitted to published data. Results: For detection in a 300-mm-thick object at 120kVp, the 0.5- and 0.225-mm pixel CdTe systems have 28% to 41% and 5% to 29% higher detective quantum efficiency (DQE), respectively, than the 60-mm Si system with tungsten, whereas the corresponding numbers for two-material decomposition are 2% lower to 11% higher DQE and 31% to 54% lower DQE compared to Si. We also show that combining these detectors with dual-spectrum acquisition is beneficial. Conclusions: In the low-count-rate regime, CdTe detector systems outperform the Si systems for detection tasks, whereas silicon outperforms one or both of the CdTe systems for material decomposition.

  View details for DOI 10.1117/1.JMI.7.4.043501

  View details for PubMedID 32715022

• Principles and Applications of Multi-energy CT Report of AAPM Task Group 291. Medical physics McCollough, C. H., Boedeker, K. n., Cody, D. n., Duan, X. n., Flohr, T. n., Halliburton, S. n., Hsieh, J. n., Layman, R. n., Pelc, N. J. 2020

  Abstract

  In x-ray computed tomography (CT), materials with different elemental compositions can have identical CT number values, depending on the mass density of each material and the energy of the detected x-ray beam. Differentiating and classifying different tissue types and contrast agents can thus be extremely challenging. In multi-energy CT, one or more additional attenuation measurements are obtained at a second, third or more energy. This allows the differentiation of at least two materials. Commercial dual-energy CT systems (only two energy measurements) are now available either using sequential acquisitions of low- and high-tube potential scans, fast tube-potential switching, beam filtration combined with spiral scanning, dual-source, or dual-layer detector approaches. The use of energy-resolving, photon-counting detectors is now being evaluated on research systems. Irrespective of the technological approach to data acquisition, all commercial CT multi-energy systems today provide dual-energy data. Material decomposition algorithms are then used to identify specific materials according to their effective atomic number and/or to quantitate mass density. These algorithms are applied to either projection or image data. Since 2006, a number of clinical applications have been developed for commercial release, including those that automatically 1) remove the signal from bony anatomy and/or calcified plaque; 2) create iodine concentration maps from contrast-enhanced CT data and/or quantify absolute iodine concentration; 3) create virtual non-enhanced images from contrast-enhanced scans; 4) identify perfused blood volume in lung parenchyma or the myocardium; and 5) characterize materials according to their elemental compositions, which can allow in vivo differentiation between uric-acid and non-uric-acid urinary stones or uric acid (gout) or non-uric-acid (calcium pyrophosphate) deposits in articulating joints and surrounding tissues. In this report, the underlying physical principles of multi-energy CT are reviewed and each of the current technical approaches described. In addition, current and evolving clinical applications are introduced. Finally, the impact of multi-energy CT technology on patient radiation dose is summarized.

  View details for DOI 10.1002/mp.14157

  View details for PubMedID 32215937

• Acoustic Attenuation: Multifrequency Measurement and Relationship To CT and MR Imaging. IEEE transactions on ultrasonics, ferroelectrics, and frequency control Webb, T. D., Leung, S. A., Ghanouni, P. n., Dahl, J. J., Pelc, N. J., Pauly, K. B. 2020; PP

  Abstract

  Transcranial magnetic resonance guided focused ultrasound (tcMRgFUS) is gaining significant acceptance as a non-invasive treatment for motion disorders and shows promise for novel applications such as blood brain barrier opening for tumor treatment. A typical procedure relies on CT derived acoustic property maps to simulate the transfer of ultrasound through the skull. Accurate estimates of the acoustic attenuation in the skull are essential to accurate simulations, but there is no consensus about how attenuation should be estimated from CT images and there is interest in exploring MR as a predictor of attenuation in the skull. In this study we measure the acoustic attenuation at 0.5, 1, and 2.25 MHz in 89 samples taken from two ex-vivo human skulls. CT scans acquired with a variety of x-ray energies, reconstruction kernels, and reconstruction algorithms and MR images acquired with ultra short and zero echo time sequences are used to estimate the average Hounsfield unit value, MR magnitude, and T2* value in each sample. The measurements are used to develop a model of attenuation as a function of frequency and each individual imaging parameter.

  View details for DOI 10.1109/TUFFC.2020.3039743

  View details for PubMedID 33226938

• Spectral modulator with flying focal spot for cone-beam CT: a feasibility study. SPIE Medical Imaging 2020: Physics of Medical Imaging Gao, H., Zhou, H., Zhu, L., Pelc, N., Bennett, R., Wang, A. 2020

  View details for DOI 10.1117/12.2548954

• Spectral Photon Counting CT: Imaging Algorithms and Performance Assessment. IEEE Transactions on Radiation and Plasma Medical Sciences Wang, A. S., Pelc, N. J. 2020

  View details for DOI 10.1109/TRPMS.2020.3007380

• Implementation of a piecewise-linear dynamic attenuator JOURNAL OF MEDICAL IMAGING Shunhavanich, P., Bennett, N., Hsieh, S. S., Pelc, N. J. 2019; 6 (2)

  View details for DOI 10.1117/1.JMI.6.2.023502

  View details for Web of Science ID 000481890500009

• Accurate image domain noise insertion in CT images. IEEE transactions on medical imaging Divel, S. E., Pelc, N. J. 2019

  Abstract

  Tools to simulate lower dose, noisy computed tomography (CT) images from existing data enable protocol optimization by quantifying the trade-off between patient dose and image quality. Many studies have developed and validated noise insertion techniques; however, most of these tools operate on proprietary projection data which can be difficult to access and can be time consuming when a large number of realizations is needed. In response, this work aims to develop and validate an image domain approach to accurately insert CT noise and simulate low dose scans. In this framework, information from the image is utilized to estimate the variance map and local noise power spectra (NPS). Normally distributed noise is filtered within small patches in the image domain using the inverse Fourier transform of the square root of the estimated local NPS to generate noise with the appropriate spatial correlation. The patches are overlapped and element-wise multiplied by the standard deviation map to produce locally varying, spatially correlated noise. The resulting noise image is scaled based on the relationship between the initial and desired dose and added to the original image. The results demonstrate excellent agreement between traditional projection domain methods and the proposed method, both for simulated and real data sets. This new framework is not intended to replace projection domain methods; rather, it fills a gap in CT noise simulation tools and is an accurate alternative when projection domain methods are not practical, for example, in large scale repeatability or detectability studies.

  View details for DOI 10.1109/TMI.2019.2961837

  View details for PubMedID 31870981

• Fluid-filled dynamic bowtie filter: Description and comparison with other modulators MEDICAL PHYSICS Shunhavanich, P., Hsieh, S. S., Pelc, N. J. 2019; 46 (1): 127–39

  View details for DOI 10.1002/mp.13272

  View details for Web of Science ID 000455029900014

• Simulation model for evaluating energy-resolving photon-counting CT detectors based on generalized linear-systems framework Persson, M., Pelc, N. J., Schmidt, T. G., Chen, G. H., Bosmans, H. SPIE-INT SOC OPTICAL ENGINEERING. 2019

  View details for DOI 10.1117/12.2512593

  View details for Web of Science ID 000483585700063

• Noise reduction in photon-counting CT using frequency-dependent optimal weighting Persson, M., Pelc, N. J., Matej, S., Metzler, S. D. SPIE-INT SOC OPTICAL ENGINEERING. 2019

  View details for DOI 10.1117/12.2534911

  View details for Web of Science ID 000535354300062

• Detective Efficiency of Photon Counting Detectors with Spectral Degradation and Crosstalk. Medical physics Rajbhandary, P. L., Persson, M. n., Pelc, N. J. 2019

  Abstract

  Charge sharing and migration of scattered and fluorescence photons in an energy discriminating photon counting detector (PCD) degrade the detector's energy response and can cause a single incident photon to be registered as multiple events at different energies among neighboring pixels, leading to spatio-energetic correlation. Such a correlation in conventional linear, space-invariant imaging system can be usefully characterized by the frequency dependent detective quantum efficiency DQE(f). Defining and estimating DQE(f) for PCDs in a manner consistent with that of conventional detectors is complicated because the traditional definition of DQE(f) does not address spectral information.We introduce the concept of presampling spectroscopic detective quantum efficiency, DQEs (f), and present an analysis of it for CdTe PCDs using a spatial domain method that starts from a previously described analytic computation of spatio-energetic crosstalk. DQEs (f) is estimated as the squared signal-to-noise ratio of the amplitude of a small-signal sinusoidal modulation of the object (cortical bone) thickness at frequency f estimated using data from the detector under consideration compared that obtained from the photon distribution incident on the detector. DQEs for material decomposition (spectral) and effective monoenergetic imaging tasks for different pixel pitch is studied based on the multi-pixel Cramér-Rao lower bound (CRLB) that accounts for inter pixel basis material correlation. Effective monoenergetic DQEs is estimated from the CRLB of a linear weighted combination of basis materials, and its energy dependence is also studied.Zero frequency DQEs for the spectral task was ~18%, 25% and 34% for 250 μm, 500 μm and 1 mm detector pixels, respectively. Inter pixel signal correlation results in positive noise correlation between same basis material estimates of neighboring pixels, resulting in least impact on DQEs at the detector's Nyquist frequency. Effective monoenergetic DQEs (0) at the optimal energy is relatively tolerant of spectral degradation (85-91% depending on pixel size), but is highly dependent on the selected effective energy, with maximum variation (in 250 μm pixels) of 17% to 85% for effective energy between 30 to 120 keV.Our results show that spatio-energetic correlations degrade DQEs (f) beyond what is lost by poor spectral response in a single detector element. The positive correlation between computed single basis material values in neighboring pixels results in the penalty to DQEs (f) to be the least at the Nyquist frequency of the detector. It is desirable to reduce spectral degradation and crosstalk to minimize the impact on system performance. Larger pixels sizes have better spatio-energetic response due to lower of charge sharing and escape of scatter and K-fluorescence photons, and therefore higher DQEs (0). Effective monoenergetic DQEs (0) at the optimal energy is much less affected by spectral degradation and crosstalk compared to DQEs for spectral tasks.

  View details for DOI 10.1002/mp.13889

  View details for PubMedID 31665541

• A framework for performance characterization of energy-resolving photon-counting detectors MEDICAL PHYSICS Persson, M., Rajbhandary, P. L., Pelc, N. J. 2018; 45 (11): 4897–4915

  View details for DOI 10.1002/mp.13172

  View details for Web of Science ID 000449995900026

• Fluid-filled dynamic bowtie filter: description and comparison with other modulators. Medical physics Shunhavanich, P., Hsieh, S. S., Pelc, N. J. 2018

  Abstract

  PURPOSE: A dynamic bowtie filter can modulate flux along both fan and view angles for reduced patient dose, scatter, and required photon flux, which is especially important for photon counting detectors (PCDs). Among the proposed dynamic bowtie designs, the piecewise-linear attenuator (Hsieh and Pelc, Med Phys 2013) offers more flexibility than conventional filters, but relies on analog positioning of a limited number of wedges. In this work, we study our previously proposed dynamic attenuator design, the fluid-filled dynamic bowtie filter (FDBF) that has digital control. Specifically, we use computer simulations to study fluence modulation, reconstructed image noise, and radiation dose and to compare it to other attenuators. FDBF is an array of small channels each of which, if it can be filled with dense fluid or emptied quickly, has a binary effect on the flux. The cumulative attenuation from each channel along the x-ray path contributes to the FDBF total attenuation.METHODS: An algorithm is proposed for selecting which FDBF channels should be filled. Two optimization metrics are considered: minimizing the maximum-count-rate for PCDs and minimizing peak-variance for energy-integrating detectors (EIDs) at fixed radiation dose (for optimizing dose efficiency). Using simulated chest, abdomen, and shoulder data, the performance is compared with a conventional bowtie and a piecewise-linear attenuator. For minimizing peak-variance, a perfect-attenuator (hypothetical filter capable of adjusting the fluence of each ray individually) and flat-variance attenuator are also included in the comparison. Two possible fluids, solutions of zinc bromide and gadolinium chloride, were tested.RESULTS: To obtain the same SNR as routine clinical protocols, the proposed FDBF reduces the maximum-count-rate (across projection data, averaged over the test objects) of PCDs to 1.2 Mcps/mm2 , which is 55.8 and 3.3 times lower than the max-count-rate of the conventional bowtie and the piecewise-linear bowtie, respectively. (Averaged across objects for FDBF, the max-count-rate without object and FDBF is 2063.5 Mcps/mm2 , and the max-count-rate with object without FDBF is 749.8 Mcps/mm2 .) Moreover, for the peak-variance analysis, the FDBF can reduce entrance-energy-fluence (sum of energy incident on objects, used as a surrogate for dose) to 34% of the entrance-energy-fluence from the conventional filter on average while achieving the same peak noise level. Its entrance-energy-fluence reduction performance is only 7% worse than the perfect-attenuator on average and is 13% better than the piecewise-linear filter for chest and shoulder. Furthermore, the noise-map in reconstructed image domain from the FDBF is more uniform than the piecewise-linear filter, with 3 times less variation across the object. For the dose reduction task, the zinc bromide solution performed slightly poorer than stainless steel but was better than the gadolinium chloride solution.CONCLUSIONS: The FDBF allows finer control over flux distribution compared to piecewise-linear and conventional bowtie filters. It can reduce the required maximum count rate for PCDs to a level achievable by current detector designs and offers a high dose reduction factor. This article is protected by copyright. All rights reserved.

  View details for PubMedID 30383310

• A framework for performance characterization of energy-resolving photon-counting detectors. Medical physics Persson, M., Rajbhandary, P. L., Pelc, N. J. 2018

  Abstract

  PURPOSE: Photon-counting energy resolving detectors are subject to intense research interest, and there is a need for a general framework for performance assessment of these detectors. The commonly used linear-systems theory framework, which measures detector performance in terms of noise-equivalent quanta (NEQ) and detective quantum efficiency (DQE) is widely used for characterizing conventional X-ray detectors but does not take energy-resolving capabilities into account. The purpose of this work is to extend this framework to encompass energy-resolving photon-counting detectors and elucidate how the imperfect energy response and other imperfections in real-world detectors affect imaging performance, both for feature detection and for material quantification tasks.METHOD: We generalize NEQ and DQE to matrix-valued quantities as functions of spatial frequency, and show how these matrices can be calculated from simple Monte Carlo simulations. To demonstrate how the new metrics can be interpreted, we compute them for simplified models of fluorescence and Compton scatter in a photon-counting detector and for a Monte Carlo model of a CdTe detector with 0.5 * 0.5 mm2 pixels.RESULTS: Our results show that the ideal-linear-observer performance for any detection or material quantification task can be calculated from the proposed generalized NEQ and DQE metrics. We also demonstrate that the proposed NEQ metric is closely related to a generalized version of the Cramer-Rao lower bound commonly used for assessing material quantification performance. Off-diagonal elements in the NEQ and DQE matrices are shown to be related to loss of energy information due to imperfect energy resolution. The Monte Carlo model of the CdTe detector predicts a zero-frequency dose efficiency relative to an ideal detector of 0.86 and 0.65 for detecting water and bone, respectively. When the task instead is to quantify these materials, the corresponding values are 0.34 for water and 0.26 for bone.CONCLUSIONS: We have developed a framework for assessing the performance of photon-counting energy-resolving detectors and shown that the matrix-valued NEQ and DQE metrics contain sufficient information for calculating the dose efficiency for both detection and quantification tasks, the task having any spatial and energy dependence. This framework will be beneficial for the development and optimization of photon-counting X-ray detectors. This article is protected by copyright. All rights reserved.

  View details for PubMedID 30191571

• Photon-counting CT: Technical Principles and Clinical Prospects. Radiology Willemink, M. J., Persson, M., Pourmorteza, A., Pelc, N. J., Fleischmann, D. 2018: 172656

  Abstract

  Photon-counting CT is an emerging technology with the potential to dramatically change clinical CT. Photon-counting CT uses new energy-resolving x-ray detectors, with mechanisms that differ substantially from those of conventional energy-integrating detectors. Photon-counting CT detectors count the number of incoming photons and measure photon energy. This technique results in higher contrast-to-noise ratio, improved spatial resolution, and optimized spectral imaging. Photon-counting CT can reduce radiation exposure, reconstruct images at a higher resolution, correct beam-hardening artifacts, optimize the use of contrast agents, and create opportunities for quantitative imaging relative to current CT technology. In this review, the authors will explain the technical principles of photon-counting CT in nonmathematical terms for radiologists and clinicians. Following a general overview of the current status of photon-counting CT, they will explain potential clinical applications of this technology.

  View details for PubMedID 30179101

• Modeling charge transport in photon-counting detectors NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Fang, Y., Xu, C., Yao, Y., Pelc, N., Danielsson, M., Badano, A. 2018; 899: 115–21

  View details for DOI 10.1016/j.nima.2018.05.027

  View details for Web of Science ID 000436488100018

• Effect of Spectral Degradation and Spatio-Energy Correlation in X-Ray PCD for Imaging IEEE TRANSACTIONS ON MEDICAL IMAGING Rajbhandary, P. L., Hsieh, S. S., Pelc, N. J. 2018; 37 (8): 1910–19

  Abstract

  Charge sharing, scatter, and fluorescence events in a photon counting detector can result in counting of a single incident photon in multiple neighboring pixels, each at a fraction of the true energy. This causes energy distortion and correlation of data across energy bins in neighboring pixels (spatio-energy correlation), with the severity depending on the detector pixel size and detector material. If a "macro-pixel" is formed by combining the counts from multiple adjacent small pixels, it will exhibit correlations across its energy bins. Understanding these effects can be crucial for detector design and for model-based imaging applications. This paper investigates the impact of these effects in basis material and effective monoenergetic estimates using the Cramér-Rao Lower Bound. To do so, we derive a correlation model for the multi-counting events. CdTe detectors with grids of pixels with side length of $250~\mu \text{m}$ , $500~\mu \text{m}$ , and 1 mm were compared, with binning of $4\times4$ , $2\times2$ , and $1\times1$ pixels, respectively, to keep the same net 1 mm2 aperture constant. The same flux was applied to each. The mean and covariance matrix of measured photon counts were derived analytically using spatio-energy response functions precomputed from Monte Carlo simulations. Our results show that a 1 mm2 macro-pixel with $250\times 250\,\,\mu \text{m}^{\textsf {2}}$ sub-pixels shows 35% higher standard deviation than a single 1 mm2 pixel for material-specific imaging, while the penalty for effective monoenergetic imaging is <10% compared with a single 1 mm $^{\textsf {2}}$ pixel. Potential benefits of sub-pixels (higher spatial resolution and lower pulse pile-up effects) are important but were not investigated here.

  View details for DOI 10.1109/TMI.2018.2834369

  View details for Web of Science ID 000440805800016

  View details for PubMedID 29993882

• Measurements of the Relationship Between CT Hounsfield Units and Acoustic Velocity and How It Changes With Photon Energy and Reconstruction Method IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL Webb, T. D., Leung, S. A., Rosenberg, J., Ghanouni, P., Dahl, J. J., Pelc, N. J., Pauly, K. 2018; 65 (7): 1111–24

  Abstract

  Transcranial magnetic resonance-guided focused ultrasound continues to gain traction as a noninvasive treatment option for a variety of pathologies. Focusing ultrasound through the skull can be accomplished by adding a phase correction to each element of a hemispherical transducer array. The phase corrections are determined with acoustic simulations that rely on speed of sound estimates derived from CT scans. While several studies have investigated the relationship between acoustic velocity and CT Hounsfield units (HUs), these studies have largely ignored the impact of X-ray energy, reconstruction method, and reconstruction kernel on the measured HU, and therefore the estimated velocity, and none have measured the relationship directly. In this paper, 91 ex vivo human skull fragments from two skulls are imaged by 80 CT scans with a variety of energies and reconstruction methods. The average HU from each fragment is found for each scan and correlated with the speed of sound measured using a through transmission technique in that fragment. As measured by the -squared value, the results show that CT is able to account for 23%-53% of the variation in velocity in the human skull. Both the X-ray energy and the reconstruction technique significantly alter the -squared value and the linear relationship between HU and speed of sound in bone. Accounting for these variations will lead to more accurate phase corrections and more efficient transmission of acoustic energy through the skull.

  View details for DOI 10.1109/TUFFC.2018.2827899

  View details for Web of Science ID 000436933000004

  View details for PubMedID 29993366

• Spectral resolution and high-flux capability tradeoffs in CdTe detectors for clinical CT MEDICAL PHYSICS Hsieh, S. S., Rajbhandary, P. L., Pelc, N. J. 2018; 45 (4): 1433–43

  Abstract

  Photon-counting detectors using CdTe or CZT substrates are promising candidates for future CT systems but suffer from a number of nonidealities, including charge sharing and pulse pileup. By increasing the pixel size of the detector, the system can improve charge sharing characteristics at the expense of increasing pileup. The purpose of this work is to describe these considerations in the optimization of the detector pixel pitch.The transport of x rays through the CdTe substrate was simulated in a Monte Carlo fashion using GEANT4. Deposited energy was converted into charges distributed as a Gaussian function with size dependent on interaction depth to capture spreading from diffusion and Coulomb repulsion. The charges were then collected in a pixelated fashion. Pulse pileup was incorporated separately with Monte Carlo simulation. The Cramér-Rao lower bound (CRLB) of the measurement variance was numerically estimated for the basis material projections. Noise in these estimates was propagated into CT images. We simulated pixel pitches of 250, 350, and 450 microns and compared the results to a photon counting detector with pileup but otherwise ideal energy response and an ideal dual-energy system (80/140 kVp with tin filtration). The modeled CdTe thickness was 2 mm, the incident spectrum was 140 kVp and 500 mA, and the effective dead time was 67 ns. Charge summing circuitry was not modeled. We restricted our simulations to objects of uniform thickness and did not consider the potential advantage of smaller pixels at high spatial frequencies.At very high x-ray flux, pulse pileup dominates and small pixel sizes perform best. At low flux or for thick objects, charge sharing dominates and large pixel sizes perform best. At low flux and depending on the beam hardness, the CRLB of variance in basis material projections tasks can be 32%-55% higher with a 250 micron pixel pitch compared to a 450 micron pixel pitch. However, both are about four times worse in variance than the ideal photon counting detector. The optimal pixel size depends on a number of factors such as x-ray technique and object size. At high technique (140 kVp/500 mA), the ratio of variance for a 450 micron pixel compared to a 250 micron pixel size is 2126%, 200%, 97%, and 78% when imaging 10, 15, 20, and 25 cm of water, respectively. If 300 mg/cm2 of iodine is also added to the object, the variance ratio is 117%, 91%, 74%, and 72%, respectively. Nonspectral tasks, such as equivalent monoenergetic imaging, are less sensitive to spectral distortion.The detector pixel size is an important design consideration in CdTe detectors. Smaller pixels allow for improved capabilities at high flux but increase charge sharing, which in turn compromises spectral performance. The optimal pixel size will depend on the specific task and on the charge shaping time.

  View details for PubMedID 29418004

• Frequency Dependent DQE of Photon Counting Detector with Spectral Degradation and Cross-talk Rajbhandary, P. L., Persson, M., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2293922

  View details for Web of Science ID 000436173700036

• Effect of Electronic Noise and Lowest Energy Threshold Selection in Photon Counting Detectors Rajbhandary, P. L., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2293929

  View details for Web of Science ID 000436173700163

• Energy dependence of SNR and DQE for effective monoenergetic imaging in spectral CT Rajbhandary, P. L., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2293932

  View details for Web of Science ID 000436173700049

• Implementation of a Piecewise-linear Dynamic Attenuator Shunhavanich, P., Bennett, N., Hsieh, S. S., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2293525

  View details for Web of Science ID 000436173700028

• Generalized linear-systems framework for performance assessment of energy-resolving photon-counting detectors Persson, M., Rajbhandary, P. L., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/2.2293402

  View details for Web of Science ID 000436173700044

• Can image-domain filtering of FBP CT reconstructions match low-contrast performance of iterative reconstructions? Divel, S. E., Hsieh, S. S., Wang, J., Pelc, N. J., Lo, J. Y., Schmidt, T. G., Chen, G. H. SPIE-INT SOC OPTICAL ENGINEERING. 2018

  View details for DOI 10.1117/12.2292599

  View details for Web of Science ID 000436173700038

• Segmented targeted least squares estimator for material decomposition in multibin photon-counting detectors. Journal of medical imaging (Bellingham, Wash.) Rajbhandary, P. L., Hsieh, S. S., Pelc, N. J. 2017; 4 (2): 023503-?

  Abstract

  We present a fast, noise-efficient, and accurate estimator for material separation using photon-counting x-ray detectors (PCXDs) with multiple energy bin capability. The proposed targeted least squares estimator (TLSE) is an improvement of a previously described A-table method by incorporating dynamic weighting that allows the variance to be closer to the Cramér-Rao lower bound (CRLB) throughout the operating range. We explore Cartesian and average-energy segmentation of the basis material space for TLSE and show that, compared with Cartesian segmentation, the average-energy method requires fewer segments to achieve similar performance. We compare the average-energy TLSE to other proposed estimators-including the gold standard maximum likelihood estimator (MLE) and the A-table-in terms of variance, bias, and computational efficiency. The variance and bias were simulated in the range of 0 to 6 cm of aluminum and 0 to 50 cm of water with Monte Carlo methods. The Average-energy TLSE achieves an average variance within 2% of the CRLB and mean absolute error of [Formula: see text]. Using the same protocol, the MLE showed variance within 1.9% of the CRLB ratio and average absolute error of [Formula: see text] but was 50 times slower in our implementations. Compared with the A-table method, TLSE gives a more homogenously optimal variance-to-CRLB ratio in the operating region. We show that variance in basis material estimates for TLSE is lower than that of the A-table method by as much as [Formula: see text] in the peripheral region of operating range (thin or thick objects). The TLSE is a computationally efficient and fast method for material separation with PCXDs, with accuracy and precision comparable to the MLE.

  View details for DOI 10.1117/1.JMI.4.2.023503

  View details for PubMedID 28560242

• Special Section Guest Editorial: Positron Emission Tomography: History, Current Status, and Future Prospects. Journal of medical imaging (Bellingham, Wash.) Pelc, N. J., Kinahan, P. E., Pettigrew, R. I. 2017; 4 (1): 011001-?

  View details for DOI 10.1117/1.JMI.4.1.011001

  View details for PubMedID 28401172

• Improvements in low contrast detectability with iterative reconstruction and the effect of slice thickness Hsieh, S. S., Pelc, N. J., Flohr, T. G., Lo, J. Y., Schmidt, T. G. SPIE-INT SOC OPTICAL ENGINEERING. 2017

  View details for DOI 10.1117/12.2253937

  View details for Web of Science ID 000405562100174

• Sensitivity Analysis of Pulse Pileup Model Parameter in Photon Counting Detectors Shunhavanich, P., Pelc, N. J., Flohr, T. G., Lo, J. Y., Schmidt, T. G. SPIE-INT SOC OPTICAL ENGINEERING. 2017

  View details for DOI 10.1117/12.2255665

  View details for Web of Science ID 000405562100128

• Effect of Spatio-energy Correlation in PCD due to Charge Sharing, Scatter and Secondary Photons Rajbhandary, P. L., Hsieh, S. S., Pelc, N. J., Flohr, T. G., Lo, J. Y., Schmidt, T. G. SPIE-INT SOC OPTICAL ENGINEERING. 2017

  View details for DOI 10.1117/12.2254999

  View details for Web of Science ID 000405562100030

• Image quality comparison between single energy and dual energy CT protocols for hepatic imaging. Medical physics Yao, Y., Ng, J. M., Megibow, A. J., Pelc, N. J. 2016; 43 (8): 4877-?

  Abstract

  Multi-detector computed tomography (MDCT) enables volumetric scans in a single breath hold and is clinically useful for hepatic imaging. For simple tasks, conventional single energy (SE) computed tomography (CT) images acquired at the optimal tube potential are known to have better quality than dual energy (DE) blended images. However, liver imaging is complex and often requires imaging of both structures containing iodinated contrast media, where atomic number differences are the primary contrast mechanism, and other structures, where density differences are the primary contrast mechanism. Hence it is conceivable that the broad spectrum used in a dual energy acquisition may be an advantage. In this work we are interested in comparing these two imaging strategies at equal-dose and more complex settings.We developed numerical anthropomorphic phantoms to mimic realistic clinical CT scans for medium size and large size patients. MDCT images based on the defined phantoms were simulated using various SE and DE protocols at pre- and post-contrast stages. For SE CT, images from 60 kVp through 140 with 10 kVp steps were considered; for DE CT, both 80/140 and 100/140 kVp scans were simulated and linearly blended at the optimal weights. To make a fair comparison, the mAs of each scan was adjusted to match the reference radiation dose (120 kVp, 200 mAs for medium size patients and 140 kVp, 400 mAs for large size patients). Contrast-to-noise ratio (CNR) of liver against other soft tissues was used to evaluate and compare the SE and DE protocols, and multiple pre- and post-contrasted liver-tissue pairs were used to define a composite CNR. To help validate the simulation results, we conducted a small clinical study. Eighty-five 120 kVp images and 81 blended 80/140 kVp images were collected and compared through both quantitative image quality analysis and an observer study.In the simulation study, we found that the CNR of pre-contrast SE image mostly increased with increasing kVp while for post-contrast imaging 90 kVp or lower yielded higher CNR images, depending on the differential iodine concentration of each tissue. Similar trends were seen in DE blended CNR and those from SE protocols. In the presence of differential iodine concentration (i.e., post-contrast), the CNR curves maximize at lower kVps (80-120), with the peak shifted rightward for larger patients. The combined pre- and post-contrast composite CNR study demonstrated that an optimal SE protocol has better performance than blended DE images, and the optimal tube potential for SE scan is around 90 kVp for a medium size patients and between 90 and 120 kVp for large size patients (although low kVp imaging requires high x-ray tube power to avoid photon starvation). Also, a tin filter added to the high kVp beam is not only beneficial for material decomposition but it improves the CNR of the DE blended images as well. The dose adjusted CNR of the clinical images also showed the same trend and radiologists favored the SE scans over blended DE images.Our simulation showed that an optimized SE protocol produces up to 5% higher CNR for a range of clinical tasks. The clinical study also suggested 120 kVp SE scans have better image quality than blended DE images. Hence, blended DE images do not have a fundamental CNR advantage over optimized SE images.

  View details for DOI 10.1118/1.4959554

  View details for PubMedID 27487905

• Multisource inverse-geometry CT. Part I. System concept and development. Medical physics De Man, B., Uribe, J., Baek, J., Harrison, D., Yin, Z., Longtin, R., Roy, J., Waters, B., Wilson, C., Short, J., Inzinna, L., Reynolds, J., Neculaes, V. B., Frutschy, K., Senzig, B., Pelc, N. 2016; 43 (8): 4607-?

  Abstract

  This paper presents an overview of multisource inverse-geometry computed tomography (IGCT) as well as the development of a gantry-based research prototype system. The development of the distributed x-ray source is covered in a companion paper [V. B. Neculaes et al., "Multisource inverse-geometry CT. Part II. X-ray source design and prototype," Med. Phys. 43, 4617-4627 (2016)]. While progress updates of this development have been presented at conferences and in journal papers, this paper is the first comprehensive overview of the multisource inverse-geometry CT concept and prototype. The authors also provide a review of all previous IGCT related publications.The authors designed and implemented a gantry-based 32-source IGCT scanner with 22 cm field-of-view, 16 cm z-coverage, 1 s rotation time, 1.09 × 1.024 mm detector cell size, as low as 0.4 × 0.8 mm focal spot size and 80-140 kVp x-ray source voltage. The system is built using commercially available CT components and a custom made distributed x-ray source. The authors developed dedicated controls, calibrations, and reconstruction algorithms and evaluated the system performance using phantoms and small animals.The authors performed IGCT system experiments and demonstrated tube current up to 125 mA with up to 32 focal spots. The authors measured a spatial resolution of 13 lp/cm at 5% cutoff. The scatter-to-primary ratio is estimated 62% for a 32 cm water phantom at 140 kVp. The authors scanned several phantoms and small animals. The initial images have relatively high noise due to the low x-ray flux levels but minimal artifacts.IGCT has unique benefits in terms of dose-efficiency and cone-beam artifacts, but comes with challenges in terms of scattered radiation and x-ray flux limits. To the authors' knowledge, their prototype is the first gantry-based IGCT scanner. The authors summarized the design and implementation of the scanner and the authors presented results with phantoms and small animals.

  View details for DOI 10.1118/1.4954846

  View details for PubMedID 27487877

  View details for PubMedCentralID PMC4958105

• Multisource inverse-geometry CT. Part II. X-ray source design and prototype. Medical physics Neculaes, V. B., Caiafa, A., Cao, Y., De Man, B., Edic, P. M., Frutschy, K., Gunturi, S., Inzinna, L., Reynolds, J., Vermilyea, M., Wagner, D., Zhang, X., Zou, Y., Pelc, N. J., Lounsberry, B. 2016; 43 (8): 4617-?

  Abstract

  This paper summarizes the development of a high-power distributed x-ray source, or "multisource," designed for inverse-geometry computed tomography (CT) applications [see B. De Man et al., "Multisource inverse-geometry CT. Part I. System concept and development," Med. Phys. 43, 4607-4616 (2016)]. The paper presents the evolution of the source architecture, component design (anode, emitter, beam optics, control electronics, high voltage insulator), and experimental validation.Dispenser cathode emitters were chosen as electron sources. A modular design was adopted, with eight electron emitters (two rows of four emitters) per module, wherein tungsten targets were brazed onto copper anode blocks-one anode block per module. A specialized ceramic connector provided high voltage standoff capability and cooling oil flow to the anode. A matrix topology and low-noise electronic controls provided switching of the emitters.Four modules (32 x-ray sources in two rows of 16) have been successfully integrated into a single vacuum vessel and operated on an inverse-geometry computed tomography system. Dispenser cathodes provided high beam current (>1000 mA) in pulse mode, and the electrostatic lenses focused the current beam to a small optical focal spot size (0.5 × 1.4 mm). Controlled emitter grid voltage allowed the beam current to be varied for each source, providing the ability to modulate beam current across the fan of the x-ray beam, denoted as a virtual bowtie filter. The custom designed controls achieved x-ray source switching in <1 μs. The cathode-grounded source was operated successfully up to 120 kV.A high-power, distributed x-ray source for inverse-geometry CT applications was successfully designed, fabricated, and operated. Future embodiments may increase the number of spots and utilize fast read out detectors to increase the x-ray flux magnitude further, while still staying within the stationary target inherent thermal limitations.

  View details for DOI 10.1118/1.4954847

  View details for PubMedID 27487878

  View details for PubMedCentralID PMC4958104

• A prototype piecewise-linear dynamic attenuator PHYSICS IN MEDICINE AND BIOLOGY Hsieh, S. S., Peng, M. V., May, C. A., Shunhavanich, P., Fleischmann, D., Pelc, N. J. 2016; 61 (13): 4974-4988

  Abstract

  The piecewise-linear dynamic attenuator has been proposed as a mechanism in CT scanning for personalizing the x-ray illumination on a patient- and application-specific basis. Previous simulations have shown benefits in image quality, scatter, and dose objectives. We report on the first prototype implementation. This prototype is reduced in scale and speed and is integrated into a tabletop CT system with a smaller field of view (25 cm) and longer scan time (42 s) compared to a clinical system. Stainless steel wedges were machined and affixed to linear actuators, which were in turn held secure by a frame built using rapid prototyping technologies. The actuators were computer-controlled, with characteristic noise of about 100 microns. Simulations suggest that in a clinical setting, the impact of actuator noise could lead to artifacts of only 1 HU. Ring artifacts were minimized by careful design of the wedges. A water beam hardening correction was applied and the scan was collimated to reduce scatter. We scanned a 16 cm water cylinder phantom as well as an anthropomorphic pediatric phantom. The artifacts present in reconstructed images are comparable to artifacts normally seen with this tabletop system. Compared to a flat-field reference scan, increased detectability at reduced dose is shown and streaking is reduced. Artifacts are modest in our images and further refinement is possible. Issues of mechanical speed and stability in the challenging clinical CT environment will be addressed in a future design.

  View details for DOI 10.1088/0031-9155/61/13/4974

  View details for Web of Science ID 000378094000015

  View details for PubMedID 27284705

  View details for PubMedCentralID PMC4937875

• Improving pulse detection in multibin photon-counting detectors. Journal of medical imaging (Bellingham, Wash.) Hsieh, S. S., Pelc, N. J. 2016; 3 (2): 023505-?

  Abstract

  Energy-discriminating, photon-counting (EDPC) detectors are attractive for their potential for improved detective quantum efficiency and for their spectral imaging capabilities. However, at high count rates, counts are lost, the detected spectrum is distorted, and the advantages of EDPC detectors disappear. Existing EDPC detectors identify counts by analyzing the signal with a bank of comparators. We explored alternative methods for pulse detection for multibin EDPC detectors that could improve performance at high count rates. The detector signal was simulated in a Monte Carlo fashion assuming a bipolar shape and analyzed using several methods, including the conventional bank of comparators. For example, one method recorded the peak energy of the pulse along with the width (temporal extent) of the pulse. The Cramer-Rao lower bound of the variance of basis material estimates was numerically found for each method. At high count rates, the variance in water material (bone canceled) measurements could be reduced by as much as an order of magnitude. Improvements in virtual monoenergetic images were modest. We conclude that stochastic noise in spectral imaging tasks could be reduced if alternative methods for pulse detection were utilized.

  View details for DOI 10.1117/1.JMI.3.2.023505

  View details for PubMedID 27284548

  View details for PubMedCentralID PMC4888744

• A limit on dose reduction possible with CT reconstruction algorithms without prior knowledge of the scan subject. Medical physics Hsieh, S. S., Chesler, D. A., Fleischmann, D., Pelc, N. J. 2016; 43 (3): 1361-?

  Abstract

  To find an upper bound on the maximum dose reduction possible for any reconstruction algorithm, analytic or iterative, that result from the inclusion of the data statistics. The authors do not analyze noise reduction possible from prior knowledge or assumptions about the object.The authors examined the task of estimating the density of a circular lesion in a cross section. Raw data were simulated by forward projection of existing images and numerical phantoms. To assess an upper bound on the achievable dose reduction by any algorithm, the authors assume that both the background and the shape of the lesion are completely known. Under these conditions, the best possible estimate of the density can be determined by solving a weighted least squares problem directly in the raw data domain. Any possible reconstruction algorithm that does not use prior knowledge or make assumptions about the object, including filtered backprojection (FBP) or iterative reconstruction methods with this constraint, must be no better than this least squares solution. The authors simulated 10 000 sets of noisy data and compared the variance in density from the least squares solution with those from FBP. Density was estimated from FBP images using either averaging within a ROI, or streak-adaptive averaging with better noise performance.The bound on the possible dose reduction depends on the degree to which the observer can read through the possibly streaky noise. For the described low contrast detection task with the signal shape and background known exactly, the average dose reduction possible compared to FBP with streak-adaptive averaging was 42% and it was 64% if only the ROI average is used with FBP. The exact amount of dose reduction also depends on the background anatomy, with statistically inhomogeneous backgrounds showing greater benefits.The dose reductions from new, statistical reconstruction methods can be bounded. Larger dose reductions in the density estimation task studied here are only possible with the introduction of prior knowledge, which can introduce bias.

  View details for DOI 10.1118/1.4941954

  View details for PubMedID 26936720

  View details for PubMedCentralID PMC4769269

• Digital Tomosynthesis System Geometry Analysis Using Convolution-Based Blur-and-Add (BAA) Model IEEE TRANSACTIONS ON MEDICAL IMAGING Wu, M., Yoon, S., Solomon, E. G., Star-Lack, J., Pelc, N., Fahrig, R. 2016; 35 (1): 131-143

  Abstract

  Digital tomosynthesis is a three-dimensional imaging technique with a lower radiation dose than computed tomography (CT). Due to the missing data in tomosynthesis systems, out-of-plane structures in the depth direction cannot be completely removed by the reconstruction algorithms. In this work, we analyzed the impulse responses of common tomosynthesis systems on a plane-to-plane basis and proposed a fast and accurate convolution-based blur-and-add (BAA) model to simulate the backprojected images. In addition, the analysis formalism describing the impulse response of out-of-plane structures can be generalized to both rotating and parallel gantries. We implemented a ray tracing forward projection and backprojection (ray-based model) algorithm and the convolution-based BAA model to simulate the shift-and-add (backproject) tomosynthesis reconstructions. The convolution-based BAA model with proper geometry distortion correction provides reasonably accurate estimates of the tomosynthesis reconstruction. A numerical comparison indicates that the simulated images using the two models differ by less than 6% in terms of the root-mean-squared error. This convolution-based BAA model can be used in efficient system geometry analysis, reconstruction algorithm design, out-of-plane artifacts suppression, and CT-tomosynthesis registration.

  View details for DOI 10.1109/TMI.2015.2458983

  View details for Web of Science ID 000367624800012

• Limits to dose reduction from iterative reconstruction and the effect of through-slice blurring Hsieh, S. S., Pelc, N. J., Kontos, D., Flohr, T. G., Lo, J. Y. SPIE-INT SOC OPTICAL ENGINEERING. 2016

  View details for DOI 10.1117/12.2216889

  View details for Web of Science ID 000378352900046

• Lossless Compression of Projection Data from Photon Counting Detectors Shunhavanich, P., Pelc, N. J., Kontos, D., Flohr, T. G., Lo, J. Y. SPIE-INT SOC OPTICAL ENGINEERING. 2016

  View details for DOI 10.1117/12.2217231

  View details for Web of Science ID 000378352900053

• "Conventional" CT images from spectral measurements Rajbhandary, P. L., Pelc, N. J., Kontos, D., Flohr, T. G., Lo, J. Y. SPIE-INT SOC OPTICAL ENGINEERING. 2016

  View details for DOI 10.1117/12.2216988

  View details for Web of Science ID 000378352900060

• Upper-Bound on Dose Reduction in CT Reconstruction for Nodule Detection IEEE ACCESS De Man, R., Wang, G., Kalra, M. K., Otrakji, A., Hsieh, S., Pelc, N. 2016; 4: 4247-4253

  View details for DOI 10.1109/ACCESS.2016.2592941

  View details for Web of Science ID 000382777400027

• Raw data normalization for a multi source inverse geometry CT system OPTICS EXPRESS Baek, J., De Man, B., Harrison, D., Pelc, N. J. 2015; 23 (6): 7514-7526

  Abstract

  A multi-source inverse-geometry CT (MS-IGCT) system consists of a small 2D detector array and multiple x-ray sources. During data acquisition, each source is activated sequentially, and may have random source intensity fluctuations relative to their respective nominal intensity. While a conventional 3^rd generation CT system uses a reference channel to monitor the source intensity fluctuation, the MS-IGCT system source illuminates a small portion of the entire field-of-view (FOV). Therefore, it is difficult for all sources to illuminate the reference channel and the projection data computed by standard normalization using flat field data of each source contains error and can cause significant artifacts. In this work, we present a raw data normalization algorithm to reduce the image artifacts caused by source intensity fluctuation. The proposed method was tested using computer simulations with a uniform water phantom and a Shepp-Logan phantom, and experimental data of an ice-filled PMMA phantom and a rabbit. The effect on image resolution and robustness of the noise were tested using MTF and standard deviation of the reconstructed noise image. With the intensity fluctuation and no correction, reconstructed images from simulation and experimental data show high frequency artifacts and ring artifacts which are removed effectively using the proposed method. It is also observed that the proposed method does not degrade the image resolution and is very robust to the presence of noise.

  View details for DOI 10.1364/OE.23.007514

  View details for Web of Science ID 000351765900048

  View details for PubMedID 25837090

  View details for PubMedCentralID PMC4408891

• A Dynamic Attenuator Improves Spectral Imaging With Energy-Discriminating, Photon Counting Detectors IEEE TRANSACTIONS ON MEDICAL IMAGING Hsieh, S. S., Pelc, N. J. 2015; 34 (3): 729-739

  Abstract

  Energy-discriminating, photon counting (EDPC) detectors have high potential in spectral imaging applications but exhibit degraded performance when the incident count rate approaches or exceeds the characteristic count rate of the detector. In order to reduce the requirements on the detector, we explore the strategy of modulating the X-ray flux field using a recently proposed dynamic, piecewise-linear attenuator. A previous paper studied this modulation for photon counting detectors but did not explore the impact on spectral applications. In this work, we modeled detection with a bipolar triangular pulse shape (Taguchi et al., 2011) and estimated the Cramer-Rao lower bound (CRLB) of the variance of material selective and equivalent monoenergetic images, assuming deterministic errors at high flux could be corrected. We compared different materials for the dynamic attenuator and found that rare earth elements, such as erbium, outperformed previously proposed materials such as iron in spectral imaging. The redistribution of flux reduces the variance or dose, consistent with previous studies on benefits with conventional detectors. Numerical simulations based on DICOM datasets were used to assess the impact of the dynamic attenuator for detectors with several different characteristic count rates. The dynamic attenuator reduced the peak incident count rate by a factor of 4 in the thorax and 44 in the pelvis, and a 10 Mcps/mm (2) EDPC detector with dynamic attenuator provided generally superior image quality to a 100 Mcps/mm (2) detector with reference bowtie filter for the same dose. The improvement is more pronounced in the material images.

  View details for DOI 10.1109/TMI.2014.2360381

  View details for Web of Science ID 000350870700005

  View details for PubMedID 25265628

• Multivariate Gaussian Model Based Cramer-Rao Lower Bound Evaluation of the In-Depth PCXD Yao, Y., Pelc, N. J., Hoeschen, C., Kontos, D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2082111

  View details for Web of Science ID 000355581700036

• Pulse detection logic for multibin photon counting detectors: beyond the simple comparator Hsieh, S. S., Pelc, N. J., Hoeschen, C., Kontos, D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2081479

  View details for Web of Science ID 000355581700033

• First results from a prototype dynamic attenuator system Hsieh, S. S., Peng, M. V., May, C. A., Shunhavanich, P., Pelc, N. J., Hoeschen, C., Kontos, D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2081482

  View details for Web of Science ID 000355581700055

• Statistical bias in material decomposition in low photon statistics region Rajbhandary, P. L., Pelc, N. J., Hoeschen, C., Kontos, D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2081326

  View details for Web of Science ID 000355581700159

• Fluid-filled Dynamic Bowtie Filter: a Feasibility Study Shunhavanich, P., Hsieh, S. S., Pelc, N. J., Hoeschen, C., Kontos, D. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2081673

  View details for Web of Science ID 000355581700053

• An algorithm to estimate the object support in truncated images. Medical physics Hsieh, S. S., Nett, B. E., Cao, G., Pelc, N. J. 2014; 41 (7): 071908-?

  Abstract

  Truncation artifacts in CT occur if the object to be imaged extends past the scanner field of view (SFOV). These artifacts impede diagnosis and could possibly introduce errors in dose plans for radiation therapy. Several approaches exist for correcting truncation artifacts, but existing correction algorithms do not accurately recover the skin line (or support) of the patient, which is important in some dose planning methods. The purpose of this paper was to develop an iterative algorithm that recovers the support of the object.The authors assume that the truncated portion of the image is made up of soft tissue of uniform CT number and attempt to find a shape consistent with the measured data. Each known measurement in the sinogram is interpreted as an estimate of missing mass along a line. An initial estimate of the object support is generated by thresholding a reconstruction made using a previous truncation artifact correction algorithm (e.g., water cylinder extrapolation). This object support is iteratively deformed to reduce the inconsistency with the measured data. The missing data are estimated using this object support to complete the dataset. The method was tested on simulated and experimentally truncated CT data.The proposed algorithm produces a better defined skin line than water cylinder extrapolation. On the experimental data, the RMS error of the skin line is reduced by about 60%. For moderately truncated images, some soft tissue contrast is retained near the SFOV. As the extent of truncation increases, the soft tissue contrast outside the SFOV becomes unusable although the skin line remains clearly defined, and in reformatted images it varies smoothly from slice to slice as expected.The support recovery algorithm provides a more accurate estimate of the patient outline than thresholded, basic water cylinder extrapolation, and may be preferred in some radiation therapy applications.

  View details for DOI 10.1118/1.4881521

  View details for PubMedID 24989386

• An algorithm to estimate the object support in truncated images. Medical physics Hsieh, S. S., Nett, B. E., Cao, G., Pelc, N. J. 2014; 41 (7): 071908-?

  View details for DOI 10.1118/1.4881521

  View details for PubMedID 24989386

• The piecewise-linear dynamic attenuator reduces the impact of count rate loss with photon-counting detectors. Physics in medicine and biology Hsieh, S. S., Pelc, N. J. 2014; 59 (11): 2829-2847

  Abstract

  Photon counting x-ray detectors (PCXDs) offer several advantages compared to standard energy-integrating x-ray detectors, but also face significant challenges. One key challenge is the high count rates required in CT. At high count rates, PCXDs exhibit count rate loss and show reduced detective quantum efficiency in signal-rich (or high flux) measurements. In order to reduce count rate requirements, a dynamic beam-shaping filter can be used to redistribute flux incident on the patient. We study the piecewise-linear attenuator in conjunction with PCXDs without energy discrimination capabilities. We examined three detector models: the classic nonparalyzable and paralyzable detector models, and a 'hybrid' detector model which is a weighted average of the two which approximates an existing, real detector (Taguchi et al 2011 Med. Phys. 38 1089-102 ). We derive analytic expressions for the variance of the CT measurements for these detectors. These expressions are used with raw data estimated from DICOM image files of an abdomen and a thorax to estimate variance in reconstructed images for both the dynamic attenuator and a static beam-shaping ('bowtie') filter. By redistributing flux, the dynamic attenuator reduces dose by 40% without increasing peak variance for the ideal detector. For non-ideal PCXDs, the impact of count rate loss is also reduced. The nonparalyzable detector shows little impact from count rate loss, but with the paralyzable model, count rate loss leads to noise streaks that can be controlled with the dynamic attenuator. With the hybrid model, the characteristic count rates required before noise streaks dominate the reconstruction are reduced by a factor of 2 to 3. We conclude that the piecewise-linear attenuator can reduce the count rate requirements of the PCXD in addition to improving dose efficiency. The magnitude of this reduction depends on the detector, with paralyzable detectors showing much greater benefit than nonparalyzable detectors.

  View details for DOI 10.1088/0031-9155/59/11/2829

  View details for PubMedID 24819415

• Control algorithms for dynamic attenuators. Medical physics Hsieh, S. S., Pelc, N. J. 2014; 41 (6): 061907-?

  Abstract

  The authors describe algorithms to control dynamic attenuators in CT and compare their performance using simulated scans. Dynamic attenuators are prepatient beam shaping filters that modulate the distribution of x-ray fluence incident on the patient on a view-by-view basis. These attenuators can reduce dose while improving key image quality metrics such as peak or mean variance. In each view, the attenuator presents several degrees of freedom which may be individually adjusted. The total number of degrees of freedom across all views is very large, making many optimization techniques impractical. The authors develop a theory for optimally controlling these attenuators. Special attention is paid to a theoretically perfect attenuator which controls the fluence for each ray individually, but the authors also investigate and compare three other, practical attenuator designs which have been previously proposed: the piecewise-linear attenuator, the translating attenuator, and the double wedge attenuator.The authors pose and solve the optimization problems of minimizing the mean and peak variance subject to a fixed dose limit. For a perfect attenuator and mean variance minimization, this problem can be solved in simple, closed form. For other attenuator designs, the problem can be decomposed into separate problems for each view to greatly reduce the computational complexity. Peak variance minimization can be approximately solved using iterated, weighted mean variance (WMV) minimization. Also, the authors develop heuristics for the perfect and piecewise-linear attenuators which do not require a priori knowledge of the patient anatomy. The authors compare these control algorithms on different types of dynamic attenuators using simulated raw data from forward projected DICOM files of a thorax and an abdomen.The translating and double wedge attenuators reduce dose by an average of 30% relative to current techniques (bowtie filter with tube current modulation) without increasing peak variance. The 15-element piecewise-linear dynamic attenuator reduces dose by an average of 42%, and the perfect attenuator reduces dose by an average of 50%. Improvements in peak variance are several times larger than improvements in mean variance. Heuristic control eliminates the need for a prescan. For the piecewise-linear attenuator, the cost of heuristic control is an increase in dose of 9%. The proposed iterated WMV minimization produces results that are within a few percent of the true solution.Dynamic attenuators show potential for significant dose reduction. A wide class of dynamic attenuators can be accurately controlled using the described methods.

  View details for DOI 10.1118/1.4875727

  View details for PubMedID 24877818

  View details for PubMedCentralID PMC4032442

• Control algorithms for dynamic attenuators. Medical physics Hsieh, S. S., Pelc, N. J. 2014; 41 (6): 061907-?

  Abstract

  The authors describe algorithms to control dynamic attenuators in CT and compare their performance using simulated scans. Dynamic attenuators are prepatient beam shaping filters that modulate the distribution of x-ray fluence incident on the patient on a view-by-view basis. These attenuators can reduce dose while improving key image quality metrics such as peak or mean variance. In each view, the attenuator presents several degrees of freedom which may be individually adjusted. The total number of degrees of freedom across all views is very large, making many optimization techniques impractical. The authors develop a theory for optimally controlling these attenuators. Special attention is paid to a theoretically perfect attenuator which controls the fluence for each ray individually, but the authors also investigate and compare three other, practical attenuator designs which have been previously proposed: the piecewise-linear attenuator, the translating attenuator, and the double wedge attenuator.The authors pose and solve the optimization problems of minimizing the mean and peak variance subject to a fixed dose limit. For a perfect attenuator and mean variance minimization, this problem can be solved in simple, closed form. For other attenuator designs, the problem can be decomposed into separate problems for each view to greatly reduce the computational complexity. Peak variance minimization can be approximately solved using iterated, weighted mean variance (WMV) minimization. Also, the authors develop heuristics for the perfect and piecewise-linear attenuators which do not require a priori knowledge of the patient anatomy. The authors compare these control algorithms on different types of dynamic attenuators using simulated raw data from forward projected DICOM files of a thorax and an abdomen.The translating and double wedge attenuators reduce dose by an average of 30% relative to current techniques (bowtie filter with tube current modulation) without increasing peak variance. The 15-element piecewise-linear dynamic attenuator reduces dose by an average of 42%, and the perfect attenuator reduces dose by an average of 50%. Improvements in peak variance are several times larger than improvements in mean variance. Heuristic control eliminates the need for a prescan. For the piecewise-linear attenuator, the cost of heuristic control is an increase in dose of 9%. The proposed iterated WMV minimization produces results that are within a few percent of the true solution.Dynamic attenuators show potential for significant dose reduction. A wide class of dynamic attenuators can be accurately controlled using the described methods.

  View details for DOI 10.1118/1.4875727

  View details for PubMedID 24877818

  View details for PubMedCentralID PMC4032442

• A multi-source inverse-geometry CT system: initial results with an 8 spot x-ray source array PHYSICS IN MEDICINE AND BIOLOGY Baek, J., De Man, B., Uribe, J., Longtin, R., Harrison, D., Reynolds, J., Neculaes, B., Frutschy, K., Inzinna, L., Caiafa, A., Senzig, R., Pelc, N. J. 2014; 59 (5)

  Abstract

  We present initial experimental results of a rotating-gantry multi-source inverse-geometry CT (MS-IGCT) system. The MS-IGCT system was built with a single module of 2 × 4 x-ray sources and a 2D detector array. It produced a 75 mm in-plane field-of-view (FOV) with 160 mm axial coverage in a single gantry rotation. To evaluate system performance, a 2.5 inch diameter uniform PMMA cylinder phantom, a 200 µm diameter tungsten wire, and a euthanized rat were scanned. Each scan acquired 125 views per source and the gantry rotation time was 1 s per revolution. Geometric calibration was performed using a bead phantom. The scanning parameters were 80 kVp, 125 mA, and 5.4 µs pulse per source location per view. A data normalization technique was applied to the acquired projection data, and beam hardening and spectral nonlinearities of each detector channel were corrected. For image reconstruction, the projection data of each source row were rebinned into a full cone beam data set, and the FDK algorithm was used. The reconstructed volumes from upper and lower source rows shared an overlap volume which was combined in image space. The images of the uniform PMMA cylinder phantom showed good uniformity and no apparent artifacts. The measured in-plane MTF showed 13 lp cm(-1) at 10% cutoff, in good agreement with expectations. The rat data were also reconstructed reliably. The initial experimental results from this rotating-gantry MS-IGCT system demonstrated its ability to image a complex anatomical object without any significant image artifacts and to achieve high image resolution and large axial coverage in a single gantry rotation.

  View details for DOI 10.1088/0031-9155/59/5/1189

  View details for Web of Science ID 000331950000007

  View details for PubMedID 24556567

• Efficacy of fixed filtration for rapid kVp-switching dual energy x-ray systems. Medical physics Yao, Y., Wang, A. S., Pelc, N. J. 2014; 41 (3): 031914-?

  Abstract

  Dose efficiency of dual kVp imaging can be improved if the two beams are filtered to remove photons in the common part of their spectra, thereby increasing spectral separation. While there are a number of advantages to rapid kVp-switching for dual energy, it may not be feasible to have two different filters for the two spectra. Therefore, the authors are interested in whether a fixed added filter can improve the dose efficiency of kVp-switching dual energy x-ray systems.The authors hypothesized that a K-edge filter would provide the energy selectivity needed to remove overlap of the spectra and hence increase the precision of material separation at constant dose. Preliminary simulations were done using calcium and water basis materials and 80 and 140 kVp x-ray spectra. Precision of the decomposition was evaluated based on the propagation of the Poisson noise through the decomposition function. Considering availability and cost, the authors chose a commercial Gd2O2S screen as the filter for their experimental validation. Experiments were conducted on a table-top system using a phantom with various thicknesses of acrylic and copper and 70 and 125 kVp x-ray spectra. The authors kept the phantom exposure roughly constant with and without filtration by adjusting the tube current. The filtered and unfiltered raw data of both low and high energy were decomposed into basis material and the variance of the decomposition for each thickness pair was calculated. To evaluate the filtration performance, the authors measured the ratio of material decomposition variance with and without filtration.Simulation results show that the ideal filter material depends on the object composition and thickness, and ranges across the lanthanide series, with higher atomic number filters being preferred for more attenuating objects. Variance reduction increases with filter thickness, and substantial reductions (40%) can be achieved with a 2× loss in intensity. The authors' experimental results validate the simulations, yet were overall slightly worse than expectation. For large objects, conventional (non-K-edge) beam hardening filters perform well.This study demonstrates the potential of fixed K-edge filtration to improve the dose efficiency and material decomposition precision for rapid kVp-switching dual energy systems.

  View details for DOI 10.1118/1.4866381

  View details for PubMedID 24593732

• Efficacy of fixed filtration for rapid kVp-switching dual energy x-ray systems. Medical physics Yao, Y., Wang, A. S., Pelc, N. J. 2014; 41 (3): 031914-?

  View details for DOI 10.1118/1.4866381

  View details for PubMedID 24593732

• Dose reduction using a dynamic, piecewise-linear attenuator. Medical physics Hsieh, S. S., Fleischmann, D., Pelc, N. J. 2014; 41 (2): 021910-?

  Abstract

  The authors recently proposed a dynamic, prepatient x-ray attenuator capable of producing a piecewise-linear attenuation profile customized to each patient and viewing angle. This attenuator was intended to reduce scatter-to-primary ratio (SPR), dynamic range, and dose by redistributing flux. In this work the authors tested the ability of the attenuator to reduce dose and SPR in simulations.The authors selected four clinical applications, including routine full field-of-view scans of the thorax and abdomen, and targeted reconstruction tasks for an abdominal aortic aneurysm and the pancreas. Raw data were estimated by forward projection of the image volume datasets. The dynamic attenuator was controlled to reduce dose while maintaining peak variance by solving a convex optimization problem, assuminga priori knowledge of the patient anatomy. In targeted reconstruction tasks, the noise in specific regions was given increased weighting. A system with a standard attenuator (or "bowtie filter") was used as a reference, and used either convex optimized tube current modulation (TCM) or a standard TCM heuristic. The noise of the scan was determined analytically while the dose was estimated using Monte Carlo simulations. Scatter was also estimated using Monte Carlo simulations. The sensitivity of the dynamic attenuator to patient centering was also examined by shifting the abdomen in 2 cm intervals.Compared to a reference system with optimized TCM, use of the dynamic attenuator reduced dose by about 30% in routine scans and 50% in targeted scans. Compared to the TCM heuristics which are typically used withouta priori knowledge, the dose reduction is about 50% for routine scans. The dynamic attenuator gives the ability to redistribute noise and variance and produces more uniform noise profiles than systems with a conventional bowtie filter. The SPR was also modestly reduced by 10% in the thorax and 24% in the abdomen. Imaging with the dynamic attenuator was relatively insensitive to patient centering, showing a 17% increase in peak variance for a 6 cm shift of the abdomen, instead of an 82% increase in peak variance for a fixed bowtie filter.A dynamic prepatient x-ray attenuator consisting of multiple wedges is capable of achieving substantial dose reductions and modest SPR reductions.

  View details for DOI 10.1118/1.4862079

  View details for PubMedID 24506631

• Dose reduction using a dynamic, piecewise-linear attenuator. Medical physics Hsieh, S. S., Fleischmann, D., Pelc, N. J. 2014; 41 (2): 021910-?

  View details for DOI 10.1118/1.4862079

  View details for PubMedID 24506631

• Recent and Future Directions in CT Imaging ANNALS OF BIOMEDICAL ENGINEERING Pelc, N. J. 2014; 42 (2): 260-268

  Abstract

  Computed tomography (CT) has made enormous technical advances since its introduction into clinical use. The engineering improvements have in turn led to important clinical applications and large impact in patient care. This paper reviews the technology development trends in CT since its introduction and uses these trends to help illuminate likely future progress. The prediction is that significant further improvements in speed, spatial resolution and dose efficiency can be expected in the next decade.

  View details for DOI 10.1007/s10439-014-0974-z

  View details for Web of Science ID 000331976300003

  View details for PubMedID 24435658

  View details for PubMedCentralID PMC3958932

• Use of Depth Information from In-depth Photon Counting Detectors for X-ray Spectral Imaging: A Preliminary Simulation Study Medical Imaging - Physics of Medical Imaging Yao, Y., Bornefalk, H., Hsieh, S. S., Danielsson, M., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2014

  View details for DOI 10.1117/12.2042839

  View details for Web of Science ID 000338775800117

• UTILIZATION OF IN-DEPTH PHOTON COUNTING DETECTORS TOWARDS X-RAY SPECTRAL IMAGING: THE BENEFITS FROM THE DEPTH INFORMATION Yao, Y., Bornefalk, H., Hsieh, S. S., Danielsson, M., Pelc, N. J., IEEE IEEE. 2014: 1156–59

  View details for Web of Science ID 000392750900287

• Enabling Photon Counting Detectors with Dynamic Attenuators Medical Imaging - Physics of Medical Imaging Hsieh, S. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2014

  View details for DOI 10.1117/12.2042533

  View details for Web of Science ID 000338775800122

• Algorithms for Optimizing CT Fluence Control Medical Imaging - Physics of Medical Imaging Hsieh, S. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2014

  View details for DOI 10.1117/12.2042542

  View details for Web of Science ID 000338775800019

• Segmented Targeted Least Squares Estimator for Material Decomposition in Multi-Bin PCXDs Medical Imaging - Physics of Medical Imaging Rajbhandary, P. L., Hsieh, S. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2014

  View details for DOI 10.1117/12.2043198

  View details for Web of Science ID 000338775800042

• To bin or not to bin? The effect of CT system limiting resolution on noise and detectability PHYSICS IN MEDICINE AND BIOLOGY Baek, J., Pineda, A. R., Pelc, N. J. 2013; 58 (5): 1433-1446

  Abstract

  We examine the noise advantages of having a computed tomography (CT) detector whose spatial resolution is significantly better (e.g. a factor of 2) than needed for a desired resolution in the reconstructed images. The effective resolution of detectors in x-ray CT is sometimes degraded by binning cells because the small cell size and fine sampling are not needed to achieve the desired resolution (e.g. with flat panel detectors). We studied the effect of the binning process on the noise in the reconstructed images and found that while the images in the absence of noise can be made identical for the native and the binned system, for the same system MTF in the presence of noise, the binned system always results in noisier reconstructed images. The effect of the increased noise in the reconstructed images on lesion detection is scale (frequency content) dependent with a larger difference between the high resolution and binned systems for imaging fine structure (small objects). We show simulated images reconstructed with both systems for representative objects and quantify the impact of the noise on the detection of the lesions based on mathematical observers. Through both subjective assessment of the reconstructed images and the quantification using mathematical observers, we show that for a CT system where the photon noise is dominant, higher resolution in the detectors leads to better noise performance in the reconstructed images at any resolution.

  View details for DOI 10.1088/0031-9155/58/5/1433

  View details for Web of Science ID 000315191400017

  View details for PubMedID 23399724

• The feasibility of an inverse geometry CT system with stationary source arrays. Medical physics Hsieh, S. S., Heanue, J. A., Funk, T., Hinshaw, W. S., Wilfley, B. P., Solomon, E. G., Pelc, N. J. 2013; 40 (3): 031904-?

  Abstract

  Inverse geometry computed tomography (IGCT) has been proposed as a new system architecture that combines a small detector with a large, distributed source. This geometry can suppress cone-beam artifacts, reduce scatter, and increase dose efficiency. However, the temporal resolution of IGCT is still limited by the gantry rotation time. Large reductions in rotation time are in turn difficult due to the large source array and associated power electronics. We examine the feasibility of using stationary source arrays for IGCT in order to achieve better temporal resolution. We anticipate that multiple source arrays are necessary, with each source array physically separated from adjacent ones.Key feasibility issues include spatial resolution, artifacts, flux, noise, collimation, and system timing clashes. The separation between the different source arrays leads to missing views, complicating reconstruction. For the special case of three source arrays, a two-stage reconstruction algorithm is used to estimate the missing views. Collimation is achieved using a rotating collimator with a small number of holes. A set of equally spaced source spots are designated on the source arrays, and a source spot is energized when a collimator hole is aligned with it. System timing clashes occur when multiple source spots are scheduled to be energized simultaneously. We examine flux considerations to evaluate whether sufficient flux is available for clinical applications.The two-stage reconstruction algorithm suppresses cone-beam artifacts while maintaining resolution and noise characteristics comparable to standard third generation systems. The residual artifacts are much smaller in magnitude than the cone-beam artifacts eliminated. A mathematical condition is given relating collimator hole locations and the number of virtual source spots for which system timing clashes are avoided. With optimization, sufficient flux may be achieved for many clinical applications.IGCT with stationary source arrays could be an imaging platform potentially capable of imaging a complete 16-cm thick volume within a tenth of a second.

  View details for DOI 10.1118/1.4789918

  View details for PubMedID 23464319

  View details for PubMedCentralID PMC3585759

• The feasibility of an inverse geometry CT system with stationary source arrays MEDICAL PHYSICS Hsieh, S. S., Heanue, J. A., Funk, T., Hinshaw, W. S., Wilfley, B. P., Solomon, E. G., Pelc, N. J. 2013; 40 (3)

  Abstract

  Inverse geometry computed tomography (IGCT) has been proposed as a new system architecture that combines a small detector with a large, distributed source. This geometry can suppress cone-beam artifacts, reduce scatter, and increase dose efficiency. However, the temporal resolution of IGCT is still limited by the gantry rotation time. Large reductions in rotation time are in turn difficult due to the large source array and associated power electronics. We examine the feasibility of using stationary source arrays for IGCT in order to achieve better temporal resolution. We anticipate that multiple source arrays are necessary, with each source array physically separated from adjacent ones.Key feasibility issues include spatial resolution, artifacts, flux, noise, collimation, and system timing clashes. The separation between the different source arrays leads to missing views, complicating reconstruction. For the special case of three source arrays, a two-stage reconstruction algorithm is used to estimate the missing views. Collimation is achieved using a rotating collimator with a small number of holes. A set of equally spaced source spots are designated on the source arrays, and a source spot is energized when a collimator hole is aligned with it. System timing clashes occur when multiple source spots are scheduled to be energized simultaneously. We examine flux considerations to evaluate whether sufficient flux is available for clinical applications.The two-stage reconstruction algorithm suppresses cone-beam artifacts while maintaining resolution and noise characteristics comparable to standard third generation systems. The residual artifacts are much smaller in magnitude than the cone-beam artifacts eliminated. A mathematical condition is given relating collimator hole locations and the number of virtual source spots for which system timing clashes are avoided. With optimization, sufficient flux may be achieved for many clinical applications.IGCT with stationary source arrays could be an imaging platform potentially capable of imaging a complete 16-cm thick volume within a tenth of a second.

  View details for DOI 10.1118/1.4789918

  View details for Web of Science ID 000316369400027

  View details for PubMedID 23464319

  View details for PubMedCentralID PMC3585759

• The feasibility of a piecewise-linear dynamic bowtie filter MEDICAL PHYSICS Hsieh, S. S., Pelc, N. J. 2013; 40 (3)

  Abstract

  The prepatient attenuator (or "bowtie filter") in CT is used to modulate the flux as a function of fan angle of the x-ray beam incident on the patient. Traditional, static bowtie filters are tailored only for very generic scans and for the average patient. The authors propose a design for a dynamic bowtie that can produce a time-dependent piecewise-linear attenuation profile. This dynamic bowtie may reduce dynamic range, dose or scatter, but in this work they focus on its ability to reduce dynamic range, which may be particularly important for systems employing photon-counting detectors.The dynamic bowtie is composed of a set of triangular wedges. Each wedge is independently moved in order to produce a time-dependent piecewise-linear attenuation profile. Simulations of the bowtie are conducted to estimate the dynamic range reduction in six clinical datasets. The control of the dynamic bowtie is determined by solving a convex optimization problem, and the dose is estimated using Monte Carlo techniques. Beam hardening artifacts are also simulated.The dynamic range is reduced by factors ranging from 2.4 to 27 depending on the part of the body studied. With a dynamic range minimization objective, the dose to the patient can be reduced from 6% to 33% while maintaining peak image noise. Further reduction in dose may be possible with a specific dose reduction objective. Beam hardening artifacts are suppressed with a two-pass algorithm.A dynamic bowtie producing a time-dependent, piecewise-linear attenuation profile is possible and can be used to modulate the flux of the scanner to the imaging task. Initial simulations show a large reduction in dynamic range. Several other applications are possible.

  View details for DOI 10.1118/1.4789630

  View details for Web of Science ID 000316369400033

  View details for PubMedID 23464325

  View details for PubMedCentralID PMC3598818

• Novel motor design for rotating anode x-ray tubes operating in the fringe field of a magnetic resonance imaging system MEDICAL PHYSICS Lillaney, P., Shin, M., Hinshaw, W., Bennett, N. R., Pelc, N., Fahrig, R. 2013; 40 (2)

  Abstract

  Using hybrid x-ray∕MR (XMR) systems for image guidance during interventional procedures could enhance the diagnosis and treatment of neurologic, oncologic, cardiovascular, and other disorders. The authors propose a close proximity hybrid system design in which a C-arm fluoroscopy unit is placed immediately adjacent to the solenoid magnet of a MR system with a minimum distance of 1.2 m between the x-ray and MR imaging fields of view. Existing rotating anode x-ray tube designs fail within MR fringe field environments because the magnetic fields alter the electron trajectories in the x-ray tube and act as a brake on the induction motor, reducing the rotation speed of the anode. In this study the authors propose a novel motor design that avoids the anode rotation speed reduction.The proposed design replaces the permanent magnet stator found in brushed dc motors with the radial component of the MR fringe field. The x-ray tube is oriented such that the radial component of the MR fringe field is orthogonal to the cathode-anode axis. Using a feedback position sensor and the support bearings as electrical slip rings, the authors use electrical commutation to eliminate the need for mechanical brushes and commutators. A vacuum compatible prototype of the proposed motor design was assembled, and its performance was evaluated at various operating conditions. The prototype consisted of a 3.1 in. diameter anode rated at 300 kHU with a ceramic rotor that was 5.6 in. in length and had a 2.9 in. diameter. The material chosen for all ceramic components was MACOR, a machineable glass ceramic developed by Corning Inc. The approximate weight of the entire assembly was 1750 g. The maximum rotation speed, angular acceleration, and acceleration time of the motor design were investigated, as well as the dependence of these parameters on rotor angular offset, magnetic field strength, and field orientation. The resonance properties of the authors' assembly were also evaluated to determine its stability during acceleration, and a pulse width modulation algorithm was implemented to control the rotation speed of the motor.At a magnetic flux density of 41 mT orthogonal to the axis of rotation (on the lower end of the expected flux density in the MR suite) the maximum speed of the motor was found to be 5150 revolutions per minute (rpm). The acceleration time necessary to reach 3000 rpm was found to be approximately 10 s at 59 mT. The resonance frequency of the assembly with the anode attached was 1310 rpm (21.8 Hz) which is far below the desired operating speeds. Pulse width modulation provides an effective method to control the speed of the motor with a resolution of 100 rpm.The proposed design can serve as a direct replacement to the conventional induction motor used in rotating anode x-ray tubes. It does not suffer from a reduced rotation speed when operating in a MR environment. The presence of chromic steel bearings in the prototype prevented testing at the higher field strengths, and future iterations of the design could eliminate this shortcoming. The prototype assembly demonstrates proof of concept of the authors' design and overcomes one of the major obstacles for a MR compatible rotating anode x-ray tube.

  View details for DOI 10.1118/1.4773313

  View details for Web of Science ID 000314727700045

  View details for PubMedID 23387764

  View details for PubMedCentralID PMC3562343

• Optimized control of a dynamic, pre-patient attenuator Hsieh, S. S., Pelc, N., J. 2013
• Dynamic bowtie for fan-beam CT JOURNAL OF X-RAY SCIENCE AND TECHNOLOGY Liu, F., Wang, G., Cong, W., Hsieh, S. S., Pelc, N. J. 2013; 21 (4): 579-590

  Abstract

  A bowtie is a filter used to shape an x-ray beam and equalize its flux reaching different detector channels. For development of spectral CT with energy discriminating photon-counting (EDPC) detectors, here we propose and evaluate a dynamic bowtie for performance optimization based on a patient model or a scout scan. With a mechanical rotation of a dynamic bowtie and an adaptive adjustment of an x-ray source flux, an x-ray beam intensity profile can be modulated. First, a mathematical model for dynamic bowtie filtering is established for an elliptical section in fan-beam geometry, and the contour of the optimal bowtie is derived. Then, numerical simulation is performed to compare the performance of the dynamic bowtie in the cases of an ideal phantom and a realistic cross-section relative to the counterparts without any bowtie and with a fixed bowtie respectively. Our dynamic bowtie can equalize the expected numbers of photons in the case of an ideal phantom. In practical cases, our dynamic bowtie can effectively reduce the dynamic range of detected signals inside the field of view. Although our design is optimized for an elliptical phantom, the resultant dynamic bowtie can be applied to a real fan-beam scan if the underlying cross-section can be approximated as an ellipse. Furthermore, our design methodology can be applied to specify an optimized dynamic bowtie for any cross-section of a patient, preferably using rapid prototyping technology.

  View details for DOI 10.3233/XST-130386

  View details for Web of Science ID 000326747000012

  View details for PubMedID 24191994

• Truncation artifact correction by support recovery Conference on Medical Imaging - Physics of Medical Imaging Hsieh, S. S., Cao, G., Nett, B. E., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2013

  View details for DOI 10.1117/12.2008224

  View details for Web of Science ID 000322002700124

• Optimized control of a dynamic, prepatient attenuator Conference on Medical Imaging - Physics of Medical Imaging Hsieh, S. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2013

  View details for DOI 10.1117/12.2008229

  View details for Web of Science ID 000322002700058

• Liver Imaging: Image Quality Evaluation and Comparison between Single and Dual Energy Protocols Conference on Medical Imaging - Physics of Medical Imaging Yao, Y., Megibow, A. J., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2013

  View details for DOI 10.1117/12.2008363

  View details for Web of Science ID 000322002700063

• Dynamic Bowtie for Fan-beam CT (PMID: 24191994). X-Ray Sci Technol Liu, F., Wang, G., Cong, W., Hsieh, S. S., Pelc, N., J. 2013; 4 (21): 579-90
• Liver imaging: image quality evaluation and comparison between single and dual energy protocols Yao, Y., Megibow, A. J., Pelc, N., J. 2013
• Truncation artifact correction by support recovery Hsieh, S. S., Cao, G., Nett, B. E., Pelc, N., J. 2013
• Image-based synthetic CT: simulating arbitrary low dose single and dual energy protocols from dual energy images Wang, A., Feng, C., Pelc, N., J. 2012
• A comparison of dual kV energy integrating and energy discriminating photon counting detectors for dual energy x-ray imaging Conference on Medical Imaging - Physics of Medical Imaging Wang, A. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.912030

  View details for Web of Science ID 000304768000029

• Image-based Synthetic CT: simulating arbitrary low dose single and dual energy protocols from dual energy images Conference on Medical Imaging - Physics of Medical Imaging Wang, A. S., Feng, C., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.912163

  View details for Web of Science ID 000304768000048

• A volumetric reconstruction algorithm for stationary source inverse-geometry CT Conference on Medical Imaging - Physics of Medical Imaging Hsieh, S. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.912490

  View details for Web of Science ID 000304768000126

• Data normalization method for a multi-source inverse geometry CT system Conference on Medical Imaging - Physics of Medical Imaging Baek, J., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.912029

  View details for Web of Science ID 000304768000078

• Efficacy of Fixed Filtration for Rapid kVp-Switching Dual Energy X-ray Systems: Experimental Verification Conference on Medical Imaging - Physics of Medical Imaging Yao, Y., Wang, A. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.913222

  View details for Web of Science ID 000304768000047

• Initial results with a multi-source inverse-geometry CT system Conference on Medical Imaging - Physics of Medical Imaging Baek, J., Pelc, N. J., Deman, B., Uribe, J., Harrison, D., Reynolds, J., Neculaes, B., Inzinna, L., Caiafa, A. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.912207

  View details for Web of Science ID 000304768000042

• Frequency-combined extended 3D reconstruction for multiple circular cone-beam CT scans. Grimmer, R., Baek, J., Pelc, N., J., Kachelriess, M. 2012
• Data normalization method for a multisource inverse geometry CT system Baek, J., Pelc, N., J. 2012
• Efficacy of fixed filtration for rapid kVp-switching dual energy x-ray systems: experimental verification Yao, Y., Wang, A., Pelc, N., J. 2012
• A volumetric reconstruction algorithm for stationary source inverse-geometry CT Hsieh, S. S., Pelc, N., J. 2012
• Initial results with a multisource inverse-geometry CT system Baek, J., Uribe, J., Harrison, D., Reynolds, J., Neculaes, B., Inzinna, L., Pelc, N. J. 2012
• A Review of Dual Energy CT: Principles, Applications, and Future Outlook (Chinese Journal of) CT Theory and Applications Wang, A., S., Hsieh, S., S., Pelc, N., J. 2012; 3 (21): 367-386
• A comparison of dual kV energy integrating and energy discriminating photon counting detectors for dual energy x-ray imaging Wang, A., Pelc, N., J. 2012
• Synthetic CT: Simulating low dose single and dual energy protocols from a dual energy scan MEDICAL PHYSICS Wang, A. S., Pelc, N. J. 2011; 38 (10): 5551-5562

  Abstract

  The choice of CT protocol can greatly impact patient dose and image quality. Since acquiring multiple scans at different techniques on a given patient is undesirable, the ability to predict image quality changes starting from a high quality exam can be quite useful. While existing methods allow one to generate simulated images of lower exposure (mAs) from an acquired CT exam, the authors present and validate a new method called synthetic CT that can generate realistic images of a patient at arbitrary low dose protocols (kVp, mAs, and filtration) for both single and dual energy scans.The synthetic CT algorithm is derived by carefully ensuring that the expected signal and noise are accurate for the simulated protocol. The method relies on the observation that the material decomposition from a dual energy CT scan allows the transmission of an arbitrary spectrum to be predicted. It requires an initial dual energy scan of the patient to either synthesize raw projections of a single energy scan or synthesize the material decompositions of a dual energy scan. The initial dual energy scan contributes inherent noise to the synthesized projections that must be accounted for before adding more noise to simulate low dose protocols. Therefore, synthetic CT is subject to the constraint that the synthesized data have noise greater than the inherent noise. The authors experimentally validated the synthetic CT algorithm across a range of protocols using a dual energy scan of an acrylic phantom with solutions of different iodine concentrations. An initial 80/140 kVp dual energy scan of the phantom provided the material decomposition necessary to synthesize images at 100 kVp and at 120 kVp, across a range of mAs values. They compared these synthesized single energy scans of the phantom to actual scans at the same protocols. Furthermore, material decompositions of a 100/120 kVp dual energy scan are synthesized by adding correlated noise to the initial material decompositions. The aforementioned noise constraint also allows us to compute feasible mAs values that can be synthesized for each kVp.The single energy synthesized and actual reconstructed images exhibit identical signal and noise properties at 100 kVp and at 120 kVp, and across a range of mAs values. For example, the noise in both the synthesized and actual images at 100 kVp increases by 2 when the mAs is halved. The synthesized and actual material decompositions of a dual energy protocol show excellent agreement when the decomposition images are linearly weighted to form monoenergetic images at energies from 40 to 100 keV. For simulated single energy protocols with kVp between 80 and 140, the highest feasible mAs exceeds that of either initial scan.This work describes and validates the synthetic CT theory and algorithm by comparing its results to actual scans. Synthetic CT is a powerful new tool that allows users to realistically see how protocol selection affects CT images and enables radiologists to retrospectively identify the lowest dose protocol achievable that provides diagnostic quality images on real patients.

  View details for DOI 10.1118/1.3633895

  View details for Web of Science ID 000295617400030

  View details for PubMedID 21992373

• Effect of detector lag on CT noise power spectra MEDICAL PHYSICS Baek, J., Pelc, N. J. 2011; 38 (6): 2995-3005

  Abstract

  The authors examined the effect of detector lag on the noise power spectrum (NPS) of CT images reconstructed with filtered backprojection (FBP).The authors derived an analytical expression of the NPS with detector lag, and then verified it using computer simulations with parallel beam and fan beam geometries. The dependence of the NPS on the amount of lag, location within the scanned field of view (FOV), and the number of views used in the reconstruction (samples per rotation) was investigated using constant and view dependent noise in the raw data.Detector lag introduces noise correlation in the azimuthal direction. The effect on the NPS is a frequency dependent reduction in amplitude. In small regions of the image, the effect is primarily in the frequencies corresponding to the azimuthal direction. The noise blurring and NPS filtering increases with increasing radial distance, and therefore regions at larger radial distances have lower noise power. With the same detector lag response function, the amount of noise correlation and NPS filtering decreases with increasing number of views.The shape of the NPS depends on the detector lag coefficients, location of the region, and the number of views used in the reconstruction. In general, the noise correlation caused by detector lag decreased the amplitude of the NPS.

  View details for DOI 10.1118/1.3589135

  View details for Web of Science ID 000291405200018

  View details for PubMedID 21815373

  View details for PubMedCentralID PMC3162307

• Local and global 3D noise power spectrum in cone-beam CT system with FDK reconstruction MEDICAL PHYSICS Baek, J., Pelc, N. J. 2011; 38 (4): 2122-2131

  Abstract

  The authors examine the nonstationary noise behavior of a cone-beam CT system with FDK reconstruction.To investigate the nonstationary noise behavior, an analytical expression for the NPS of local volumes and an entire volume was derived and quantitatively compared to the NPS estimated from experimental air and water images.The NPS of local volumes at different locations along the z-axis showed radial symmetry in the f(x)-f(y) plane and different missing cone regions in the f(z) direction depending on the tilt angle of rays through the local volumes. For local volumes away from the z-axis, the NPS of air and water images showed sharp transitions in the f(x)-f(y) and f(y)-f(z) planes and lack of radial symmetry in the f(x)-f(y) plane. These effects are mainly caused by varying magnification and different noise levels from view to view. In the NPS of the entire volume, the f(x)-f(y) plane showed radial symmetry because the nonstationary noise behaviors of local volumes were averaged out. The nonstationary sharp transitions were manifested as a high-frequency roll-off.The results from noise power analysis for local volumes and an entire volume demonstrate the spatially varying noise behavior in the reconstructed cone-beam CT images.

  View details for DOI 10.1118/1.3556590

  View details for Web of Science ID 000289153500039

  View details for PubMedID 21626945

  View details for PubMedCentralID PMC3078160

• Sufficient Statistics as a Generalization of Binning in Spectral X-ray Imaging IEEE TRANSACTIONS ON MEDICAL IMAGING Wang, A. S., Pelc, N. J. 2011; 30 (1): 84-93

  Abstract

  It is well known that the energy dependence of X-ray attenuation can be used to characterize materials. Yet, even with energy discriminating photon counting X-ray detectors, it is still unclear how to best form energy dependent measurements for spectral imaging. Common ideas include binning photon counts based on their energies and detectors with both photon counting and energy integrating electronics. These approaches can be generalized to energy weighted measurements, which we prove can form a sufficient statistic for spectral X-ray imaging if the weights used, which we term μ-weights, are basis attenuation functions that can also be used for material decomposition. To study the performance of these different methods, we evaluate the Cramér-Rao lower bound (CRLB) of material estimates in the presence of quantum noise. We found that the choice of binning and weighting schemes can greatly affect the performance of material decomposition. Even with optimized thresholds, binning condenses information but incurs penalties to decomposition precision and is not robust to changes in the source spectrum or object size, although this can be mitigated by adding more bins or removing photons of certain energies from the spectrum. On the other hand, because μ-weighted measurements form a sufficient statistic for spectral imaging, the CRLB of the material decomposition estimates is identical to the quantum noise limited performance of a system with complete energy information of all photons. Finally, we show that μ-weights lead to increased conspicuity over other methods in a simulated calcium contrast experiment.

  View details for DOI 10.1109/TMI.2010.2061862

  View details for Web of Science ID 000285844900008

  View details for PubMedID 20682470

• A comparison of four algorithms for metal artifact reduction in CT imaging Conference on Medical Imaging 2011 - Physics of Medical Imaging Golden, C., Mazin, S. R., Boas, F. E., Tye, G., Ghanouni, P., Gold, G., Sofilos, M., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2011

  View details for DOI 10.1117/12.878896

  View details for Web of Science ID 000294178500097

• Use of sphere phantoms to measure the 3D MTF of FDK reconstructions Conference on Medical Imaging 2011 - Physics of Medical Imaging Baek, J., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2011

  View details for DOI 10.1117/12.878850

  View details for Web of Science ID 000294178500010

• An inverse geometry CT system with stationary source arrays Conference on Medical Imaging 2011 - Physics of Medical Imaging Hsieh, S. S., Heanue, J. A., Funk, T., Hinshaw, W. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2011

  View details for DOI 10.1117/12.878801

  View details for Web of Science ID 000294178500063

• Synthetic CT: simulating arbitrary low dose single and dual energy protocols Conference on Medical Imaging 2011 - Physics of Medical Imaging Wang, A. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2011

  View details for DOI 10.1117/12.878771

  View details for Web of Science ID 000294178500058

• Frequency-Combined Extended 3D Reconstruction for Multiple Circular Cone-Beam CT Scans IEEE Nuclear Science Symposium/Medical Imaging Conference (NSS/MIC)/18th International Workshop on Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors Grimmer, R., Baek, J., Pelc, N., Kachelriess, M. IEEE. 2011: 4089–4092

  View details for Web of Science ID 000304755604065

• An inverse geometry CT system with stationary source arrays. Hsieh, S. S., Heanue, J. A., Funk, T., Hinshaw, W. S., Pelc, N., J. 2011
• A comparison of four algorithms for metal artifact reduction in CI imaging. Golden, C., Mazin, S. R., Boas, F. E., Tye, G., Ghanouni, P., Sofilos, M., Pelc, N. J. 2011
• Synthetic CT: simulating arbitrary low dose single and dual energy protocols. Wang, A. S., Pelc, N., J. 2011
• Design for a Dynamic Bowtie Achieving a Piecewise-Linear Attenuation Profile Hsieh, S. S., Pelc, N., J. 2011
• Effect of detector lag on CT noise power spectra (PMCID: PMC3162307). Med Phys Baek, J., Pelc, N., J. 2011; 38: 2995-3005
• Efficacy of Fixed Filtration for Rapid KVp-Switching Dual Energy X-Ray Systems Yao, Y., Wang, A., Pelc, N., J. 2011
• Use of sphere phantoms to measure the 3D MTF of FDK reconstructions. Baek, J., Pelc, N., J. 2011
• Synthetic CT: Simulating Low Dose Single and Dual Energy Protocols from a Dual Energy Scan (PMID: 21992373). Med Phys Wang, A., S., Pelc, N., J. 2011; 38: 5551-62
• A new method to combine 3D reconstruction volumes for multiple parallel circular cone beam orbits MEDICAL PHYSICS Baek, J., Pelc, N. J. 2010; 37 (10): 5351-5360

  Abstract

  This article presents a new reconstruction method for 3D imaging using a multiple 360 degrees circular orbit cone beam CT system, specifically a way to combine 3D volumes reconstructed with each orbit. The main goal is to improve the noise performance in the combined image while avoiding cone beam artifacts.The cone beam projection data of each orbit are reconstructed using the FDK algorithm. When at least a portion of the total volume can be reconstructed by more than one source, the proposed combination method combines these overlap regions using weighted averaging in frequency space. The local exactness and the noise performance of the combination method were tested with computer simulations of a Defrise phantom, a FORBILD head phantom, and uniform noise in the raw data.A noiseless simulation showed that the local exactness of the reconstructed volume from the source with the smallest tilt angle was preserved in the combined image. A noise simulation demonstrated that the combination method improved the noise performance compared to a single orbit reconstruction.In CT systems which have overlap volumes that can be reconstructed with data from more than one orbit and in which the spatial frequency content of each reconstruction can be calculated, the proposed method offers improved noise performance while keeping the local exactness of data from the source with the smallest tilt angle.

  View details for DOI 10.1118/1.3484058

  View details for Web of Science ID 000283483700023

  View details for PubMedID 21089770

  View details for PubMedCentralID PMC2955728

• In vivo hemodynamic analysis of intracranial aneurysms obtained by magnetic resonance fluid dynamics (MRFD) based on time-resolved three-dimensional phase-contrast MRI NEURORADIOLOGY Isoda, H., Ohkura, Y., Kosugi, T., Hirano, M., Takeda, H., Hiramatsu, H., Yamashita, S., Takehara, Y., Alley, M. T., Bammer, R., Pelc, N. J., Namba, H., Sakahara, H. 2010; 52 (10): 921-928

  Abstract

  Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to perform in vivo hemodynamic analysis of unruptured intracranial aneurysms of magnetic resonance fluid dynamics using time-resolved three-dimensional phase-contrast MRI (4D-Flow) at 1.5 T and to analyze relationships between hemodynamics and wall shear stress (WSS) and oscillatory shear index (OSI).This study included nine subjects with 14 unruptured aneurysms. 4D-Flow was performed by a 1.5-T magnetic resonance scanner with a head coil. We calculated in vivo streamlines, WSS, and OSI of intracranial aneurysms based on 4D-Flow with our software. We evaluated the number of spiral flows in the aneurysms and compared the differences in WSS or OSI between the vessel and aneurysm and between whole aneurysm and the apex of the spiral flow.3D streamlines, WSS, and OSI distribution maps in arbitrary direction during the cardiac phase were obtained for all intracranial aneurysms. Twelve aneurysms had one spiral flow each, and two aneurysms had two spiral flows each. The WSS was lower and the OSI was higher in the aneurysm compared to the vessel. The apex of the spiral flow had a lower WSS and higher OSI relative to the whole aneurysm.Each intracranial aneurysm in this study had at least one spiral flow. The WSS was lower and OSI was higher at the apex of the spiral flow than the whole aneurysmal wall.

  View details for DOI 10.1007/s00234-009-0635-3

  View details for Web of Science ID 000281792600008

  View details for PubMedID 20012431

• Comparison of hemodynamics of intracranial aneurysms between MR fluid dynamics using 3D cine phase-contrast MRI and MR-based computational fluid dynamics NEURORADIOLOGY Isoda, H., Ohkura, Y., Kosugi, T., Hirano, M., Alley, M. T., Bammer, R., Pelc, N. J., Namba, H., Sakahara, H. 2010; 52 (10): 913-920

  Abstract

  Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to compare hemodynamics of intracranial aneurysms of MR fluid dynamics (MRFD) using 3D cine PC MR imaging (4D-Flow) at 1.5 T and MR-based computational fluid dynamics (CFD).4D-Flow was performed for five intracranial aneurysms by a 1.5 T MR scanner. 3D TOF MR angiography was performed for geometric information. The blood flow in the aneurysms was modeled using CFD simulation based on the finite element method. We used MR angiographic data as the vascular models and MR flow information as boundary conditions in CFD. 3D velocity vector fields, 3D streamlines, shearing velocity maps, wall shear stress (WSS) distribution maps and oscillatory shear index (OSI) distribution maps were obtained by MRFD and CFD and were compared.There was a moderate to high degree of correlation in 3D velocity vector fields and a low to moderate degree of correlation in WSS of aneurysms between MRFD and CFD using regression analysis. The patterns of 3D streamlines were similar between MRFD and CFD. The small and rotating shearing velocities and higher OSI were observed at the top of the spiral flow in the aneurysms. The pattern and location of shearing velocity in MRFD and CFD were similar. The location of high oscillatory shear index obtained by MRFD was near to that obtained by CFD.MRFD and CFD of intracranial aneurysms correlated fairly well.

  View details for DOI 10.1007/s00234-009-0634-4

  View details for Web of Science ID 000281792600007

  View details for PubMedID 19967532

• The noise power spectrum in CT with direct fan beam reconstruction MEDICAL PHYSICS Baek, J., Pelc, N. J. 2010; 37 (5): 2074-2081

  Abstract

  The noise power spectrum (NPS) is a useful metric for understanding the noise content in images. To examine some unique properties of the NPS of fan beam CT, the authors derived an analytical expression for the NPS of fan beam CT and validated it with computer simulations. The nonstationary noise behavior of fan beam CT was examined by analyzing local regions and the entire field-of-view (FOV). This was performed for cases with uniform as well as nonuniform noise across the detector cells and across views. The simulated NPS from the entire FOV and local regions showed good agreement with the analytically derived NPS. The analysis shows that whereas the NPS of a large FOV in parallel beam CT (using a ramp filter) is proportional to frequency, the NPS with direct fan beam FBP reconstruction shows a high frequency roll off. Even in small regions, the fan beam NPS can show a sharp transition (discontinuity) at high frequencies. These effects are due to the variable magnification and therefore are more pronounced as the fan angle increases. For cases with nonuniform noise, the NPS can show the directional dependence and additional effects.

  View details for DOI 10.1118/1.3378673

  View details for Web of Science ID 000277242800014

  View details for PubMedID 20527540

  View details for PubMedCentralID PMC2871306

• Fourier properties of the fan-beam sinogram MEDICAL PHYSICS Mazin, S. R., Pelc, N. J. 2010; 37 (4): 1674-1680

  Abstract

  P. R. Edholm, R. M. Lewitt, and B. Lindholm, "Novel properties of the Fourier decomposition of the sinogram," in Proceedings of the International Workshop on Physics and Engineering of Computerized Multidimensional Imaging and Processing [Proc. SPIE 671, 8-18 (1986)] described properties of a parallel beam projection sinogram with respect to its radial and angular frequencies. The purpose is to perform a similar derivation to arrive at corresponding properties of a fan-beam projection sinogram for both the equal-angle and equal-spaced detector sampling scenarios.One of the derived properties is an approximately zero-energy region in the two-dimensional Fourier transform of the full fan-beam sinogram. This region is in the form of a double-wedge, similar to the parallel beam case, but different in that it is asymmetric with respect to the frequency axes. The authors characterize this region for a point object and validate the derived properties in both a simulation and a head CT data set. The authors apply these results in an application using algebraic reconstruction.In the equal-angle case, the domain of the zero region is (q,k) for which / k/(k-q) / > R/L, where q and k are the frequency variables associated with the detector and view angular positions, respectively, R is the radial support of the object, and L is the source-to-isocenter distance. A filter was designed to retain only sinogram frequencies corresponding to a specified radial support. The filtered sinogram was used to reconstruct the same radial support of the head CT data. As an example application of this concept, the double-wedge filter was used to computationally improve region of interest iterative reconstruction.Interesting properties of the fan-beam sinogram exist and may be exploited in some applications.

  View details for DOI 10.1118/1.3366253

  View details for Web of Science ID 000276211200031

  View details for PubMedID 20443488

• Synthetic CT: Generating Images of Arbitrary CT Protocols Using a Dual Energy Scan. RSNA 2010 Annual Meeting. Wang, A., S., Pelc, N., J. 2010: SSC14-09
• High Power Distributed X-ray Source Conference on Medical Imaging - Physics of Medical Imaging Frutschy, K., Neculaes, B., Inzinna, L., Caiafa, A., Reynolds, J., Zou, Y., Zhang, X., Gunturi, S., Cao, Y., Waters, B., Wagner, D., De Man, B., McDevitt, D., Roffers, R., Lounsberry, B., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2010

  View details for DOI 10.1117/12.843743

  View details for Web of Science ID 000285047200051

• Impact of Photon Counting Detector Spectral Response on Dual Energy Techniques Conference on Medical Imaging - Physics of Medical Imaging Wang, A. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2010

  View details for DOI 10.1117/12.840052

  View details for Web of Science ID 000285047200122

• Multisource Inverse-Geometry CT - Prototype System Integration IEEE Nuclear Science Symposium (NSS)/Medical Imaging Conference (MIC)/17th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors Uribe, J., Reynolds, J. L., Inzinna, L. P., Longtin, R., Harrison, D. D., De Man, B., Neculaes, B., Caiafa, A., Waters, W., Frutschy, K. J., Senzig, R., Baek, J., Pelc, N. IEEE. 2010: 2578–2581

  View details for Web of Science ID 000306402902159

• In vivo hemodynamic analysis of intracranial aneurysms obtained by magnetic resonance fluid dynamics (MRFD) based on time-resolved three-dimensional phase-contrast MRI. Neuroradiology Isoda, H., Ohkura, Y., Kosugi, T., Hirano, M., Takeda, H., Hiramatsu, H., Pelc, N. J. 2010; 10: 921-8
• Impact of photon counting detector spectral response on dual energy approaches. Wang, A. S., Pelc, N., J. 2010
• High power distributed x-ray source. Frutschy, K., Neculaes, B., Inzinna, L., Caiafa, A., Reynolds, J., Zou, Y., Pelc, N. J. 2010
• Distributed X-ray Source Development. Frutschy, K., Neculaes, B., Inzinna, L., Mani, V., Caiafa, A., Reynolds, J., Pelc, N. J. 2010
• Multisource inverse-geometry CT — Prototype system integration Uribe, J., Reynolds, J. L., Inzinna, L. P., Longtin, R., Harrison, D. D., De Man, B., Pelc, N. J. 2010
• First Imaging with Gantry-based Multisource Inverse Geometry CT scanner. Uribe, J., Reynolds, J., Longtin, R., Harrison, D., Waters, W., De Man, B., Pelc, N. J. 2010
• A High Power Distributed X-ray Source for Multisource Inverse Geometry CT. Neculaes, B. V., Inzinna, L., Caiafa, A., Reynolds, J., Frutschy, K., De Man, B., Pelc, N. J. 2010
• Emission Guided Radiation Therapy System: A Feasibility Study. Mazin, S., Nanduri, A., Pelc, N., J. 2010
• Understanding and controlling the effect of lossy raw data compression on CT images MEDICAL PHYSICS Wang, A. S., Pelc, N. J. 2009; 36 (8): 3643-3653

  Abstract

  The requirements for raw data transmission through a CT scanner slip ring, through the computation system, and for storage of raw CT data can be quite challenging as scanners continue to increase in speed and to collect more data per rotation. Although lossy compression greatly mitigates this problem, users must be cautious about how errors introduced manifest themselves in the reconstructed images. This paper describes two simple yet effective methods for controlling the effect of errors in raw data compression and describe the impact of each stage on the image errors. A CT system simulator (CATSIM, GE Global Research Center, Niskayuna, NY) was used to generate raw CT datasets that simulate different regions of human anatomy. The raw data are digitized by a 20-bit ADC and companded by a log compander. Lossy compression is performed by quantization and is followed by JPEG-LS (lossless), which takes advantage of the correlations between neighboring measurements in the sinogram. Error feedback, a previously proposed method that controls the spatial distribution of reconstructed image errors, and projection filtering, a newly proposed method that takes advantage of the filtered backprojection reconstruction process, are applied independently (and combined) to study their intended impact on the control and behavior of the additional noise due to the compression methods used. The log compander and the projection filtering method considerably reduce image error levels, while error feedback pushes image errors toward the periphery of the field of view. The results for the images are a compression ratio (CR) of 3 that keeps peak compression errors under 1 HU and a CR of 9 that increases image noise by only 1 HU in common CT applications. Lossy compression can substantially reduce raw CT data size at low computational cost. The proposed methods have the flexibility to operate at a wide range of compression ratios and produce predictable, object-independent, and often imperceptible image artifacts.

  View details for DOI 10.1118/1.3158738

  View details for Web of Science ID 000268440600029

  View details for PubMedID 19746798

• Simulations of Virtual PET/CT 3-D Bronchoscopy Imaging Using a Physical Porcine Lung-Heart Phantom MOLECULAR IMAGING AND BIOLOGY Yerushalmi, D., Mullick, R., Quon, A., Fahrig, R., Pelc, N. J., Fann, J. I., Gambhir, S. S. 2009; 11 (4): 275-282

  Abstract

  We present a systematic approach for studying positron emission tomography-computed tomography (PET/CT) 3-D virtual fly-through endoscopy and for assessing the accuracy of this technology for visualizing and detecting endobronchial lesions as a function of focal lesion morphology and activity.Capsules designed to simulate endobronchial lesions were filled with activity and introduced into a porcine lung-heart phantom. PET/CT images were acquired, reconstructed, and volume rendered as 3-D fly-through and fly-around visualizations. Anatomical positioning of lesions seen on the 3-D-volume-rendered PET/CT images was compared to the actual position of the capsules.Lesion size was observed to be highly sensitive to PET threshold parameter settings and careful opacity and color transfer function parameter assignment.We have demonstrated a phantom model for studies of PET/CT 3-D virtual fly-through bronchoscopy and have applied this model for understanding the effect of PET thresholding on the visualization and detection of lesions.

  View details for DOI 10.1007/s11307-009-0201-8

  View details for Web of Science ID 000266830700010

  View details for PubMedID 19434462

• Direct two-dimensional reconstruction algorithm for an inverse-geometry CT system MEDICAL PHYSICS Baek, J., Pelc, N. J. 2009; 36 (2): 394-401

  Abstract

  An inverse-geometry computed tomography (IGCT) system uses a large source array opposite a smaller detector array. A previously described IGCT reconstruction algorithm uses gridding, but this gridding step produces blurring in the reconstructed image. In this article, the authors describe a two-dimensional (2D) IGCT reconstruction algorithm without gridding. In the transverse direction, the raw data of the IGCT system can be viewed as being composed of many fan beams. Because the spacing between source spots is larger than the spot width, each fan beam has undersampled projection data, but the missing samples are effectively provided by other undersampled fan beam views. In the proposed method, a direct fan beam reconstruction algorithm is used to process each undersampled fan beam. Initial images with this method showed ring artifacts caused by nonuniform sampling in the radial direction as compared to an ideal fan beam. A new method for correcting this effect was developed. With this correction, high quality images were obtained. The noise performance of the proposed 2D IGCT reconstruction algorithm was investigated, and it was comparable to that of the fan beam system. A MTF study showed that the proposed method achieves better resolution than the gridding method.

  View details for DOI 10.1118/1.3050160

  View details for Web of Science ID 000262852600012

  View details for PubMedID 19291978

  View details for PubMedCentralID PMC2673672

• Analytical construction of 3D NPS for a cone beam CT system. Baek, J., Pelc, N., J. 2009
• Multi-source inverse-geometry CT: from system concept to research prototype IEEE Nuclear Science Symposium Conference 2009 De Man, B., Caiafa, A., Cao, Y., Frutschy, K., Harrison, D., Inzinna, L., Longtin, R., Neculaes, B., Reynolds, J., Roy, J., Short, J., Uribe, J., Waters, W., Yin, Z., Zhang, X., Zou, Y., Senzig, B., Baek, J., Pelc, N. IEEE. 2009: 3531–3533

  View details for Web of Science ID 000280505102033

• Multi-source inverse-geometry CT: From system concept to research prototype De Man, B., Caiafa, B. A., Cao, Y., Frutschy, K. J., Harrison, D. D., Inzinna, L., Pelc, N. J. 2009
• Optimal energy thresholds and weights for separating materials using photon counting x-ray detectors with energy discriminating capabilities. Wang, A., Pelc, N., J. 2009
• Balanced SSFP Cisternography in the Cerebellopontine (CP) Angle: Inconsistent Vessel Contrast and a Possible Remedy. Wu, P. H., Lin, C. Y., Cheng, C. C., Chung, H. W., Wu, W. C., Hargreaves, B. A., Pelc, N. J. 2009
• Metal Artifact Reduction Algorithm for X-Ray CT Using a Three-Pass Approach. Mazin, S., Pelc, N., J. 2009
• SNR efficient 3D reconstruction algorithm for multi-source inverse geometry CT system. Baek, J., Pelc, N., J. 2009
• Fourier rebinning algorithm for inverse geometry CT MEDICAL PHYSICS Mazin, S. R., Pelc, N. J. 2008; 35 (11): 4857-4862

  Abstract

  Inverse geometry computed tomography (IGCT) is a new type of volumetric CT geometry that employs a large array of x-ray sources opposite a smaller detector array. Volumetric coverage and high isotropic resolution produce very large data sets and therefore require a computationally efficient three-dimensional reconstruction algorithm. The purpose of this work was to adapt and evaluate a fast algorithm based on Defrise's Fourier rebinning (FORE), originally developed for positron emission tomography. The results were compared with the average of FDK reconstructions from each source row. The FORE algorithm is an order of magnitude faster than the FDK-type method for the case of 11 source rows. In the center of the field-of-view both algorithms exhibited the same resolution and noise performance. FORE exhibited some resolution loss (and less noise) in the periphery of the field-of-view. FORE appears to be a fast and reasonably accurate reconstruction method for IGCT.

  View details for DOI 10.1118/1.2986155

  View details for Web of Science ID 000260484400012

  View details for PubMedID 19070219

  View details for PubMedCentralID PMC2673599

• Shimming with permanent magnets for the x-ray detector in a hybrid x-ray/MR system MEDICAL PHYSICS Wen, Z., Fahrig, R., Williams, S. T., Pelc, N. J. 2008; 35 (9): 3895-3902

  Abstract

  In this x-ray/MR hybrid system an x-ray flat panel detector is placed under the patient cradle, close to the MR volume of interest (VOI), where the magnetic field strength is approximately 0.5 T. Immersed in this strong field, several electronic components inside the detector become magnetized and create an additional magnetic field that is superimposed on the original field of the MR scanner. Even after linear shimming, the field homogeneity of the MR scanner remains disrupted by the detector. The authors characterize the field due to the detector with the field of two magnetic dipoles and further show that two sets of permanent magnets (NdFeB) can withstand the main magnetic field and compensate for the nonlinear components of the additional field. The ideal number of magnets and their locations are calculated based on a field map measured with the detector in place. Experimental results demonstrate great promise for this technique, which may be useful in many settings where devices with magnetic components need to be placed inside or close to an MR scanner.

  View details for DOI 10.1118/1.2963994

  View details for Web of Science ID 000258773000009

  View details for PubMedID 18841840

  View details for PubMedCentralID PMC2673662

• Noise considerations of three-point water-fat separation imaging methods MEDICAL PHYSICS Wen, Z., Reeder, S. B., Pineda, A. R., Pelc, N. J. 2008; 35 (8): 3597-3606

  Abstract

  Separation of water from fat tissues in magnetic resonance imaging is important for many applications because signals from fat tissues often interfere with diagnoses that are usually based on water signal characteristics. Water and fat can be separated with images acquired at different echo time shifts. The three-point method solves for the unknown off-resonance frequency together with the water and fat densities. Noise performance of the method, quantified by the effective number of signals averaged (NSA), is an important metric of the water and fat images. The authors use error propagation theory and Monte Carlo simulation to investigate two common reconstructive approaches: an analytic-solution based estimation and a least-squares estimation. Two water-fat chemical shift (CS) encoding strategies, the symmetric (-theta, 0, theta) and the shifted (0, theta, 2theta) schemes are studied and compared. Results show that NSAs of water and fat can be different and they are dependent on the ratio of intensities of the two species and each of the echo time shifts. The NSA is particularly poor for the symmetric (-theta, 0, theta) CS encoding when the water and fat signals are comparable. This anomaly with equal amounts of water and fat is analyzed in a more intuitive geometric illustration. Theoretical prediction of NSA matches well with simulation results at high signal-to-noise ratio (SNR), while deviation arises at low SNR, which suggests that Monte Carlo simulation may be more appropriate to accurately predict noise performance of the algorithm when SNR is low.

  View details for DOI 10.1118/1.2952644

  View details for Web of Science ID 000258038900021

  View details for PubMedID 18777920

  View details for PubMedCentralID PMC2673650

• Design, performance, and applications of a hybrid X-Ray/MR system for interventional guidance PROCEEDINGS OF THE IEEE Fahrig, R., Ganguly, A., Lillaney, P., Bracken, J., Rowlands, J. A., Wen, Z., Yu, H., Rieke, V., Santos, J. M., Pauly, K. B., Sze, D. Y., Frisoli, J. K., Daniel, B. L., Pelc, N. J. 2008; 96 (3): 468-480

  View details for DOI 10.1109/JPROC.2007.913506

  View details for Web of Science ID 000253299600007

• Optimal multi-energy binning in photon counting detectors with energy discrimination capabilities. RSNA '08 Wang, A., S., Pelc, N., J. 2008: 1061
• Effect of the frequency content and spatial location of raw data errors on CT images MEDICAL IMAGING 2008: PHYSICS OF MEDICAL IMAGING, PTS 1-3 Wang, A. S., Xie, Y., Pelc, N. J. 2008; 6913

  View details for DOI 10.1117/12.770552

  View details for Web of Science ID 000256660300107

• Lossy raw data compression in computed tomography with noise shaping to control image effects Medical Imaging 2008 Conference Xie, Y., Wang, A. S., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2008

  View details for DOI 10.1117/12.769954

  View details for Web of Science ID 000256660300105

• Propagation of quantum noise in multiplexed x-ray imaging Medical Imaging 2008 Conference De Man, B., Pelc, N. J., Dumoulin, C., Bernstein, T. SPIE-INT SOC OPTICAL ENGINEERING. 2008

  View details for DOI 10.1117/12.773126

  View details for Web of Science ID 000256660300062

• A Fourier rebinning algorithm for cone beam CT Medical Imaging 2008 Conference Mazin, S. R., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2008

  View details for DOI 10.1117/12.769575

  View details for Web of Science ID 000256660300071

• On the angular dependence of Bremsstrahlung x-ray emission Medical Imaging 2008 Conference GANGULY, A., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2008

  View details for DOI 10.1117/12.773235

  View details for Web of Science ID 000256660300158

• A new reconstruction method to improve SNR for an inverse geometry CT system Medical Imaging 2008 Conference Baek, J., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2008

  View details for DOI 10.1117/12.769606

  View details for Web of Science ID 000256660300102

• On the angular dependence of Bremsstrahlung x-ray emission. Ganguly, A., Pelc, N., J. 2008
• A Fourier rebinning algorithm for conebeam CT. Mazin, S., Pelc, N., J. 2008
• A Fourier Rebinning Algorithm for Cone Beam CT. Med Phys, (PMCID: PMC2673599). Mazin, S, R., Pelc, N., J. 2008; 35: 4857-62
• Lossy raw data compression in computed tomography with noise shaping to control image effects. Xie, Y., Wang, A., S., Pelc, N., J. 2008
• Effect of the frequency content and spatial location of raw data errors on CT images. Wang, A. A., Xie, Y., Pelc, N., J. 2008
• Fundamentals of flow and hemodynamics. In Magnetic Resonance Imaging of the Brain and Spine Pelc, N., J., Alley, M., T., Listerud, J., Atlas, S., W. edited by Atlas, S., W. Lippincott Williams and Wilkins, Philadelphia. 2008; Fourth Edition: 71–93
• A new reconstruction method to improve SNR for an inverse geometry CT system. Baek, J., Pelc, N., J. 2008
• Analytical derivation of the noise power spectrum for a fan-beam CT system. Baek, J., Pelc, N., J. 2008
• Propagation of quantum noise in multiplexed x-ray imaging, Bruno De Man. De Man, B., Pelc, N., J., Bernstein, T. 2008
• Investigation of electron trajectories of an x-ray tube in magnetic fields of MR scanners MEDICAL PHYSICS Wen, Z., Fahrig, R., Conolly, S., Pelc, N. J. 2007; 34 (6): 2048-2058

  Abstract

  A hybrid x-ray/MR system combining an x-ray fluoroscopic system and an open-bore magnetic resonance (MR) system offers advantages from both powerful imaging modalities and thus can benefit numerous image-guided interventional procedures. In our hybrid system configurations, the x-ray tube and detector are placed in the MR magnet and therefore experience a strong magnetic field. The electron beam inside the x-ray tube can be deflected by a misaligned magnetic field, which may damage the tube. Understanding the deflection process is crucial to predicting the electron beam deflection and avoiding potential damage to the x-ray tube. For this purpose, the motion of an electron in combined electric (E) and magnetic (B) fields was analyzed theoretically to provide general solutions that can be applied to different geometries. For two specific cases, a slightly misaligned strong field and a perpendicular weak field, computer simulations were performed with a finite-element method program. In addition, experiments were conducted using an open MRI magnet and an inserted electromagnet to quantitatively verify the relationship between the deflections and the field misalignment. In a strong (B > E/c; c: speed of light) and slightly misaligned magnetic field, the deflection in the plane of E and B caused by electrons following the magnetic field lines is the dominant component compared to the deflection in the E X B direction due to the drift of electrons. In a weak magnetic field (B < or = E/c), the main deflection is in the E x B direction and is caused by the perpendicular component of the magnetic field.

  View details for DOI 10.1118/1.2733798

  View details for Web of Science ID 000247479600022

  View details for PubMedID 17654908

• Imaging with distributed source arrays 49th Annual Meeting of the American-Association-of-Physicists-in-Medicine Pelc, N. AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS. 2007: 2518–18

  View details for Web of Science ID 000247479600855

• Inverse-geometry volumetric CT system with multiple detector arrays for wide field-of-view imaging MEDICAL PHYSICS Mazin, S. R., Star-Lack, J., Bennett, N. R., Pelc, N. J. 2007; 34 (6): 2133-2142

  Abstract

  Current volumetric computed tomography (CT) methods require seconds to acquire a thick volume (>8 cm) with high resolution. Inverse-geometry CT (IGCT) is a new system geometry under investigation that is anticipated to be able to image a thick volume in a single gantry rotation with isotropic resolution and no cone-beam artifacts. IGCT employs a large array of source spots opposite a smaller detector array. The in-plane field of view (FOV) is primarily determined by the size of the source array, in much the same way that the FOV is determined by the size of the detector array in a conventional CT system. Thus, the size of the source array can be a limitation on the achievable FOV. We propose adding additional detector arrays, spaced apart laterally, to increase the in-plane FOV while still using a modestly sized source array. We determine optimal detector placement to maximize the FOV while obtaining relatively uniform sampling. We also demonstrate low wasted radiation of the proposed system through design and simulation of a pre-patient collimator. Reconstructions from simulated projection data show no artifacts when combining the data from the detector arrays. Finally, to demonstrate feasibility of the concept, an anthropomorphic thorax phantom containing a porcine heart was scanned on a prototype table-top system. The reconstructed axial images demonstrate a 45 cm in-plane FOV using a 23 cm source array.

  View details for DOI 10.1118/1.2737168

  View details for Web of Science ID 000247479600030

  View details for PubMedID 17654916

• Quantitative evaluation of the relaxivity effects of iodine on Gd-DTPA enhanced MR arthrography JOURNAL OF MAGNETIC RESONANCE IMAGING Ganguly, A., Gold, G. E., Pauly, K. B., Mayer, D., Moseley, M. M., Pelc, N. J., Fahrig, R. 2007; 25 (6): 1219-1225

  Abstract

  To quantify the effect of iodine on the gadolinium (Gd) contrast-enhanced signal in MR arthrography.Saline solutions of Gd contrast agent (0-1 mmol/liter) were mixed with iodinated contrast agent (0-185 mmol/liter). The T1 and T2 relaxation constants of these solutions were measured at 1.5T. Different types of commonly used iodinated contrast agents as well as sodium iodide (NaI) solutions were also analyzed.Iodine caused significant T2 shortening and some T1 shortening in Gd contrast solutions. Both contrast agents independently obeyed the standard relaxation relation, and their mixture obeyed a modified version of this relation. The side chains in various iodine molecules and their viscosities affected the relaxation properties differently. For various spin-echo (SE) sequences, the signal from synovial fluid containing different concentrations of the two contrast agents was calculated. The T2-weighted signal appeared to be most affected by the increase in iodine concentrations. In the absence of Gd contrast, all SE sequences showed an initial increase in signal from iodine contrast.A generalized relation for the relaxivities of Gd contrast in the presence of iodine was established. The side chains of iodine contrast were found to alter the relaxivities of Gd contrast. Imaging with proton density (PD)-weighted SE with only iodine contrast agent was found to be feasible.

  View details for DOI 10.1002/jmri.20934

  View details for Web of Science ID 000246824100017

  View details for PubMedID 17520728

• Visualization of hemodynamics in intracranial arteries using time-resolved three-dimensional phase-contrast MRI 13th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine Yamashita, S., Isoda, H., Hirano, M., Takeda, H., Inagawa, S., Takehara, Y., Alley, M. T., Markl, M., Pelc, N. J., Sakahara, H. JOHN WILEY & SONS INC. 2007: 473–78

  Abstract

  To visualize the hemodynamics of the intracranial arteries using time-resolved three-dimensional phase-contrast (PC)-MRI (4D-Flow).MR examinations were performed with a 1.5T MR unit on six healthy volunteers (22-50 years old, average = 30 years). 4D-Flow was based on a radiofrequency (RF)-spoiled gradient-echo sequence, and velocity encoding (VENC) was performed along all three spatial directions. Measurements were retrospectively gated to the electrocardiogram (ECG), and cine series of three-dimensional (3D) data sets were generated. The voxel size was 1 x 1 x 1 mm, and acquisition time was 30-40 minutes. 4D data sets were calculated into time-resolved images of 3D streamlines, 3D particle traces, and 2D velocity vector fields by means of flow visualization software.We were able to see the 3D streamlines from the circle of Willis to the bilateral M2 segment of the middle cerebral arteries (MCAs). Time-resolved images of 3D particle traces also clearly demonstrated intracranial arterial flow dynamics. 2D velocity vector fields on the planes traversing the carotid siphon or the basilar tip were clearly visualized. These results were obtained in all six volunteers.4D-Flow helped to elucidate the in vivo 3D hemodynamics of human intracranial arteries. This method may be a useful noninvasive means of analyzing the hemodynamics of intracranial arteries in vivo.

  View details for DOI 10.1002/jmri.20828

  View details for Web of Science ID 000244698800003

  View details for PubMedID 17279504

• Study of increased radiation when an x-ray tube is placed in a strong magnetic field MEDICAL PHYSICS Wen, Z., Pelc, N. J., Nelson, W. R., Fahrig, R. 2007; 34 (2): 408-418

  Abstract

  When a fixed anode x-ray tube is placed in a magnetic field (B) that is parallel to the anode-cathode axis, the x-ray exposure increases with increasing B. It was hypothesized that the increase was caused by backscattered electrons which were constrained by B and reaccelerated by the electric field onto the x-ray tube target. We performed computer simulations and physical experiments to study the behavior of the backscattered electrons in a magnetic field, and their effects on the radiation output, x-ray spectrum, and off-focal radiation. A Monte Carlo program (EGS4) was used to generate the combined energy and angular distribution of the backscattered electrons. The electron trajectories were traced and their landing locations back on the anode were calculated. Radiation emission from each point was modeled with published data (IPEM Report 78), and thus the exposure rate and x-ray spectrum with the contribution of backscattered electrons could be predicted. The point spread function for a pencil beam of electrons was generated and then convolved with the density map of primary electrons incident on the anode as simulated with a finite element program (Opera-3d, Vector Fields, UK). The total spatial distribution of x-ray emission could then be calculated. Simulations showed that for an x-ray tube working at 65 kV, about 54% of the electrons incident on the target were backscattered. In a magnetic field of 0.5 T, although the exposure would be increased by 33%, only a small fraction of the backscattered electrons landed within the focal spot area. The x-ray spectrum was slightly shifted to lower energies and the half value layer (HVL) was reduced by about 6%. Measurements of the exposure rate, half value layer and focal spot distribution were acquired as functions of B. Good agreement was observed between experimental data and simulation results. The wide spatial distribution of secondary x-ray emission can degrade the MTF of the x-ray system at low spatial frequencies for B < 0.5 T.

  View details for DOI 10.1118/1.2404618

  View details for Web of Science ID 000244424200005

  View details for PubMedID 17388157

• Localized Quantification of Geometry, Hemodynamics, and Histology in a Rat Model of Abdominal Aortic Aneurysm. Greve, J. M., Sho, E., Tedesco, M. M., Draney Blomme, M. T., Wilson, N. M., Dalman, R. L., Pelc, N. J. 2007
• Inverse geometry CT: The next-generation CT architecture? IEEE Nuclear Science Symposium/Medical Imaging Conference De Man, B., Basu, S., Fitzgerald, P., Harrison, D., Iatrou, M., Khare, K., LeBlanc, J., Senzig, B., Wilson, C., Yin, Z., Pelc, N. IEEE. 2007: 2715–2716

  View details for Web of Science ID 000257380402034

• Multi-source inverse geometry CT : a new system concept for X-ray computed tomography Medical Imaging 2007 Conference De Man, B., Basu, S., Beque, D., Claus, B., Edic, P., Iatrou, M., LeBlanc, J., Senzig, B., Thompson, R., Vermilyea, M., Wilson, C., Yin, Z., Pelc, N. SPIE-INT SOC OPTICAL ENGINEERING. 2007

  View details for DOI 10.1117/12.712854

  View details for Web of Science ID 000247292100016

• Two-dimensional reconstruction algorithm of an inverse-geometry volumetric CT system Medical Imaging 2007 Conference Baek, J., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2007

  View details for DOI 10.1117/12.709027

  View details for Web of Science ID 000247292100189

• A fast 3D reconstruction algorithm for inverse-geometry CT based on an exact PET rebinning algorithm Medical Imaging 2007 Conference Mazin, S. R., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2007

  View details for DOI 10.1117/12.708961

  View details for Web of Science ID 000247292100179

• Implementation of the Derivative Back Projection - Finite Hilbert Inverse algorithm in projection reconstruction MRI IEEE Nuclear Science Symposium/Medical Imaging Conference Barral, J. K., Pelc, N. J., Pauly, J. A., Nishimura, D. G. IEEE. 2007: 4083–4089

  View details for Web of Science ID 000257380403049

• A fast 3D reconstruction algorithm for inverse-geometry CT based on an exact PET rebinning algorithm Mazin, S., Pelc, N., J. 2007
• the Next Generation CT Architecture? De Man, B., Basu, S., Fitzgerald, P., Harrison, D., Iatrou, M., Khare, K., Pelc, N. J. 2007
• Study of increased radiation when an x-ray tube is placed in a strong magnetic field. Med. Phys. Wen, Z., Pelc, N., J., Nelson, W., R., Fahrig, R. 2007; 34: 408-18
• Implementation of the Derivative Back Projection - Finite Hilbert Inverse Algorithm in Projection Reconstruction MRI. Barral, J. K., Pelc, N., J., Pauly, J., M., Nishimura, D. G. 2007
• Accurate Reconstruction in PR-MRI Despite Truncated Data. Barral, J. K., Wu, H. G., Gold, G. E., Pelc, N., J., Pauly, J. M., Nishimura, D. G. 2007
• Promises and Limitations of Dual-Energy CT in Lower Extremity CT Angiography Annual Scientific Meeting, SCBT/MR, Orlando, Fl, 3/07 (Moncada In-training Award). Tran, D., N., Roos, J., E., Straka, M., Sandner, D., Razavi, H., Chang, M., Pelc, N. J. 2007
• Multi-source inverse geometry CT: a new system concept for x-ray computed tomography. De Man, B., Basu, S., Bequé, S., Claus, B., Edic, P., Iatrou, M., Pelc, N. J. 2007
• Allometric scaling of wall shear stress from mice to humans: quantification using cine phase-contrast MRI and computational fluid dynamics AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Greve, J. M., Les, A. S., Tang, B. T., Blomme, M. T., Wilson, N. M., Dalman, R. L., Pelc, N. J., Taylor, C. A. 2006; 291 (4): H1700-H1708

  Abstract

  Allometric scaling laws relate structure or function between species of vastly different sizes. They have rarely been derived for hemodynamic parameters known to affect the cardiovascular system, e.g., wall shear stress (WSS). This work describes noninvasive methods to quantify and determine a scaling law for WSS. Geometry and blood flow velocities in the infrarenal aorta of mice and rats under isoflurane anesthesia were quantified using two-dimensional magnetic resonance angiography and phase-contrast magnetic resonance imaging at 4.7 tesla. Three-dimensional models constructed from anatomic data were discretized and used for computational fluid dynamic simulations using phase-contrast velocity imaging data as inlet boundary conditions. WSS was calculated along the infrarenal aorta and compared between species to formulate an allometric equation for WSS. Mean WSS along the infrarenal aorta was significantly greater in mice and rats compared with humans (87.6, 70.5, and 4.8 dyn/cm(2), P < 0.01), and a scaling exponent of -0.38 (R(2) = 0.92) was determined. Manipulation of the murine genome has made small animal models standard surrogates for better understanding the healthy and diseased human cardiovascular system. It has therefore become increasingly important to understand how results scale from mouse to human. This noninvasive methodology provides the opportunity to serially quantify changes in WSS during disease progression and/or therapeutic intervention.

  View details for DOI 10.1152/ajpheart.00274.2006

  View details for Web of Science ID 000240509700025

  View details for PubMedID 16714362

• T-1- and T-2-weighted fast spin-echo imaging of the brachial plexus and cervical spine with IDEAL water-fat separation JOURNAL OF MAGNETIC RESONANCE IMAGING Reeder, S. B., Yu, H., Johnson, J. W., Shimakawa, A., Brittain, J. H., Pelc, N. J., Beaulieu, C. F., Gold, G. E. 2006; 24 (4): 825-832

  Abstract

  To compare the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method with fat-saturated T1-weighted (T1W) and T2W fast spin-echo (FSE) and short-TI inversion recovery (STIR) imaging of the brachial plexus and cervical spine.Images acquired at 1.5T in five volunteers using fat-saturated T1W and T2W FSE imaging and STIR were compared with T1W and T2W IDEAL-FSE images. Examples of T1W and T2W IDEAL-FSE images acquired in patients are also shown.T1W and T2W IDEAL-FSE demonstrated superior fat suppression (P<0.05) and image quality (P<0.05), compared to T1W and T2W fat-saturated FSE, respectively. SNR performance of T1W-IDEAL-FSE was similar to T1W FSE in the spinal cord (P=0.250) and paraspinous muscles (P=0.78), while T2W IDEAL-FSE had superior SNR in muscle (P=0.02) and CSF (P=0.02), and marginally higher cord SNR (P=0.09). Compared to STIR, T2W IDEAL-FSE demonstrated superior image quality (P<0.05), comparable fat suppression (excellent, P=1.0), and higher SNR performance (P<0.001).IDEAL-FSE is a promising method for T1W and T2W imaging of the brachial plexus and cervical spine.

  View details for DOI 10.1002/jmri.20721

  View details for Web of Science ID 000240882000013

  View details for PubMedID 16969792

• Articular cartilage of the knee: Rapid three-dimensional MR imaging at 3.0 T with IDEAL balanced steady-State free precession - Initial experience RADIOLOGY Gold, G. E., Reeder, S. B., Yu, H., Kornaat, P., Shimakawa, A. S., Johnson, J. W., Pelc, N. J., Beaulieu, C. F., Brittain, J. H. 2006; 240 (2): 546-551

  Abstract

  Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. In this study, iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) balanced steady-state free precession (bSSFP), fat-suppressed bSSFP, and fat-suppressed spoiled gradient-echo (GRE) sequences for 3.0-T magnetic resonance (MR) imaging of articular knee cartilage were prospectively compared in five healthy volunteers. Cartilage and fluid signal-to-noise ratio (SNR), cartilage-fluid contrast-to-noise ratio (CNR), SNR efficiency, CNR efficiency, image quality, and fat suppression were compared. Fat-suppressed bSSFP and IDEAL bSSFP had higher SNR efficiency of cartilage (P < .01) than did GRE. IDEAL bSSFP had higher cartilage-fluid CNR efficiency than did fat-suppressed bSSFP or GRE (P < .01). Fat-suppressed bSSFP and IDEAL bSSFP had higher image quality than did GRE (P < .01). GRE and IDEAL bSSFP had significantly better fat-water separation or fat saturation than did fat-suppressed bSSFP (P < .05). IDEAL bSSFP is a promising method for imaging articular knee cartilage.

  View details for DOI 10.1148/radiol.2402050288

  View details for Web of Science ID 000239242600029

  View details for PubMedID 16801369

• A prototype table-top inverse-geometry volumetric CT system MEDICAL PHYSICS Schmidt, T. G., Star-Lack, J., Bennett, N. R., Mazin, S. R., Solomon, E. G., Fahrig, R., Pelc, N. J. 2006; 33 (6): 1867-1878

  Abstract

  A table-top volumetric CT system has been implemented that is able to image a 5-cm-thick volume in one circular scan with no cone-beam artifacts. The prototype inverse-geometry CT (IGCT) scanner consists of a large-area, scanned x-ray source and a detector array that is smaller in the transverse direction. The IGCT geometry provides sufficient volumetric sampling because the source and detector have the same axial, or slice direction, extent. This paper describes the implementation of the table-top IGCT scanner, which is based on the NexRay Scanning-Beam Digital X-ray system (NexRay, Inc., Los Gatos, CA) and an investigation of the system performance. The alignment and flat-field calibration procedures are described, along with a summary of the reconstruction algorithm. The resolution and noise performance of the prototype IGCT system are studied through experiments and further supported by analytical predictions and simulations. To study the presence of cone-beam artifacts, a "Defrise" phantom was scanned on both the prototype IGCT scanner and a micro CT system with a +/-5 cone angle for a 4.5-cm volume thickness. Images of inner ear specimens are presented and compared to those from clinical CT systems. Results showed that the prototype IGCT system has a 0.25-mm isotropic resolution and that noise comparable to that from a clinical scanner with equivalent spatial resolution is achievable. The measured MTF and noise values agreed reasonably well with theoretical predictions and computer simulations. The IGCT system was able to faithfully reconstruct the laminated pattern of the Defrise phantom while the micro CT system suffered severe cone-beam artifacts for the same object. The inner ear acquisition verified that the IGCT system can image a complex anatomical object, and the resulting images exhibited more high-resolution details than the clinical CT acquisition. Overall, the successful implementation of the prototype system supports the IGCT concept for single-rotation volumetric scanning free from cone-beam artifacts.

  View details for DOI 10.1118/1.2192887

  View details for Web of Science ID 000238688500036

  View details for PubMedID 16872094

• Visualization of hemodynamics in a silicon aneurysm model using time-resolved, 3D, phase-contrast MRI 43rd Annual Meeting of the American-Society-of-Neuroradiology Isoda, H., Hirano, M., Takeda, H., Kosugi, T., Alley, M. T., Markl, M., Pelc, N. J., Sakahara, H. AMER SOC NEURORADIOLOGY. 2006: 1119–22

  Abstract

  We performed time-resolved 3D phase-contrast MR imaging by using a 1.5T MR scanner to visualize hemodynamics in a silicon vascular model with a middle cerebral aneurysm. We ran an aqueous solution of glycerol as a flowing fluid with a pulsatile pump. Time-resolved images of 3D streamlines and 2D velocity vector fields clearly demonstrated that the aneurysm had 3D complex vortex flows within it during systolic phase. This technique provided us with time-resolved 3D hemodynamic information about the intracranial aneurysm.

  View details for Web of Science ID 000237602000037

  View details for PubMedID 16687555

• Single acquisition water-fat separation: Feasibility study for dynamic imaging 13th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine Yu, H. Z., Reeder, S. B., McKenzie, C. A., Brau, A. C., Shimakawa, A., Brittain, J. H., Pelc, N. J. JOHN WILEY & SONS INC. 2006: 413–22

  Abstract

  Water-fat separation can be challenging in the presence of field inhomogeneities. Three-point (3-pt) water-fat separation methods achieve robust performance by measuring and compensating for field inhomogeneities; however, they triple the scan time. The "1+-pt" water-fat separation method proposed in this article for dynamic or repetitive imaging situations combines 3-pt methods' ability to correct for field inhomogeneities with the scan efficiency of a single acquisition method to achieve high temporal and spatial resolutions and robust water-fat separation. Single-echo data are collected with water and fat at a relative phase shift of an odd multiple of pi/2. To correct for undesired phase modulation, phase maps are estimated from a 3-pt calibration scan acquired prior to dynamic imaging. The phase maps are assumed to be slowly varying in time, so they may be used for correcting the phase of the subsequent single-echo signals at the same imaging location. Noise performance was investigated and shown to be equivalent to a single excitation acquisition. The 1+-pt method can also be used in conjunction with parallel imaging. In this situation, the calibration scans required by both methods can be integrated into a shared calibration scan. Promising results were obtained in breast, abdominal, and cardiac imaging applications.

  View details for DOI 10.1002/mrm.20771

  View details for Web of Science ID 000235326500024

  View details for PubMedID 16372279

• Allometric Scaling of Wall Shear Stress from Mouse to Man: Quantification using Cine Phase-Contrast MRI and Computational Fluid Dynamics. Am. J. Physiol.: Heart Circ Physiol Greve, J., M., Les, A., S., Tang, B., T., Draney Blomme, M. T., Wilson, N. M., Dalman, R. L., Pelc, N. J. 2006; 291: H1700-8
• Motion artifacts from an inverse-geometry CT system with multiple detector arrays - art. no. 61420G Mazin, S., Pele, N., Flynn, M. J., Hsieh, J. SPIE-INT SOC OPTICAL ENGINEERING. 2006: G1420

  View details for DOI 10.1117/12.653863

  View details for Web of Science ID 000238049700014

• Adaptation of a Fast 3D PET Reconstruction Algorithm to an Inverse-Geometry CT System 15th International Workshop on Room-Temperature Semiconductor X- and Gamma-Ray Detectors/ 2006 IEEE Nuclear Science Symposium Mazin, S. R., Pelc, N. J. IEEE. 2006: 2268–2275

  View details for Web of Science ID 000288875602070

• IDEAL Water-Fat Separation with Simultaneous T2* Estimation. Yu, H., McKenzie, C. A., Shimakawa, A., Pelc, N. J., Brittain, J. H., Reeder, S. B. 2006
• Time Constant Sensitivity of Eddy Current Characterizing Pulse Sequence. Ennis, D. B., Alley, M. T., Hargreaves, B. A., Pelc, N, J. 2006
• Adaptation of a fast 3D PET reconstruction algorithm to an inverse geometry CT system Mazin, S. R., Pelc, N. J. 2006
• Single Quadrature Echo Water-Fat Separation with Robust Phase Correction. Yu, H., Reeder, S. B., McKenzie, C. A., Shimakawa, A., Brau, A., Pelc, N. J. 2006
• PET-CT Fly-through Virtual Bronchoscopy: A Model for Systematic Investigation of 3D Visualization. Yerushalmi, D., Quon, A., Fahrig, R., Pelc, N., J., Fann, J., Gambhir, S. S. 2006
• Implementation, Validation, and Application of Cine PCMRI for Quantifying Blood Flow in Small Animal Models of Cardiovascular Disease. Greve, J. M., Draney, M. T., Les, A. S., Wilson, N., Pelc, N. J., Taylor, C. A. 2006
• Single acquisition water-fat separation: Feasibility study for dynamic imaging. Mag Res Med Yu., H., Reeder, S., B., McKenzie, C., A., Brau, A. C., Shimakawa, A., Brittain, J. H., Pelc, N. J. 2006; 55
• Segmentation and Characterization of Vortical Flow Patterns in MRI Phase-Contrast Velocity Data. Wigström, L., Hope, T., Draney, M. T., Heiberg, E., Bolger, A. F., Alley, M, T., Pelc, N. J. 2006
• Motion artifacts from an inverse-geometry CT system with multiple detector arrays. Mazin, S., Pelc, N., J. 2006
• Preliminary Study of Wall Shear Stress of an Intracranial Aneurysmal Model Based on the Data of Time-Resolved Three-Dimensional Phase-Contrast MRI. Isoda, H., Yamashita, S., Ohkura, Y., Kosugi, T., Takeda, H., Takehara, Y., Pelc, N. J. 2006
• Assessment of the Wall Shear Stress (WSS) of the Abdominal Aortic Aneurysm Using Time-Resolved Three-Dimensional Phase-Contrast MRI (4D-Flow) and a New WSS Mapping Application (Flova). Takehara, Y., Isoda, H., Yamashita, S., Takeda, H., Ohkura, Y., Kosugi, T., Pelc, N. J. 2006
• A three-dimensional reconstruction algorithm for an inverse-geometry volumetric CT system MEDICAL PHYSICS Schmidt, T. G., Fahrig, R., Pelc, N. J. 2005; 32 (11): 3234-3245

  Abstract

  An inverse-geometry volumetric computed tomography (IGCT) system has been proposed capable of rapidly acquiring sufficient data to reconstruct a thick volume in one circular scan. The system uses a large-area scanned source opposite a smaller detector. The source and detector have the same extent in the axial, or slice, direction, thus providing sufficient volumetric sampling and avoiding cone-beam artifacts. This paper describes a reconstruction algorithm for the IGCT system. The algorithm first rebins the acquired data into two-dimensional (2D) parallel-ray projections at multiple tilt and azimuthal angles, followed by a 3D filtered backprojection. The rebinning step is performed by gridding the data onto a Cartesian grid in a 4D projection space. We present a new method for correcting the gridding error caused by the finite and asymmetric sampling in the neighborhood of each output grid point in the projection space. The reconstruction algorithm was implemented and tested on simulated IGCT data. Results show that the gridding correction reduces the gridding errors to below one Hounsfield unit. With this correction, the reconstruction algorithm does not introduce significant artifacts or blurring when compared to images reconstructed from simulated 2D parallel-ray projections. We also present an investigation of the noise behavior of the method which verifies that the proposed reconstruction algorithm utilizes cross-plane rays as efficiently as in-plane rays and can provide noise comparable to an in-plane parallel-ray geometry for the same number of photons. Simulations of a resolution test pattern and the modulation transfer function demonstrate that the IGCT system, using the proposed algorithm, is capable of 0.4 mm isotropic resolution. The successful implementation of the reconstruction algorithm is an important step in establishing feasibility of the IGCT system.

  View details for DOI 10.1118/1.2064827

  View details for Web of Science ID 000233385800002

  View details for PubMedID 16370414

• Field map estimation with a region growing scheme for iterative 3-point water-fat decomposition MAGNETIC RESONANCE IN MEDICINE Yu, H. Z., Reeder, S. B., Shimakawa, A., Brittain, J. H., Pelc, N. J. 2005; 54 (4): 1032-1039

  Abstract

  Robust fat suppression techniques are required for many clinical applications. Multi-echo water-fat separation methods are relatively insensitive to B(0) field inhomogeneity compared to the fat saturation method. Estimation of this field inhomogeneity, or field map, is an essential and important step, which is well known to have ambiguity. For an iterative water-fat decomposition method recently proposed, ambiguities still exist, but are more complex in nature. They were studied by analytical expressions and simulations. To avoid convergence to incorrect field map solutions, an initial guess closer to the true field map is necessary. This can be achieved using a region growing process, which correlates the estimation among neighboring pixels. Further improvement in stability is achieved using a low-resolution reconstruction to guide the selection of the starting pixels for the region growing. The proposed method was implemented and shown to significantly improve the algorithm's immunity to field inhomogeneity.

  View details for DOI 10.1002/mrm.20654

  View details for Web of Science ID 000232348000034

  View details for PubMedID 16142718

• Stroke volume and cardiac output in juvenile elephant seals during forced dives JOURNAL OF EXPERIMENTAL BIOLOGY Thornton, S. J., Hochachka, P. W., Crocker, D. E., Costa, D. P., LeBoeuf, B. J., Spielman, D. M., Pelc, N. J. 2005; 208 (19): 3637-3643

  Abstract

  The aim of this study was to examine the effect of forced diving on cardiac dynamics in a diving mammal by evaluating cardiac output and heart rate. We used MR Imaging and phase contrast flow analysis to obtain accurate flow measurements from the base of the aorta. Heart rate (fh) and cardiac output (Q) were measured before, during and after dives in four restrained juvenile northern elephant seals, Mirounga angustirostris, and stroke volume (Vs) was calculated (Vs=Q/fh). Mean Q during diving (4011+/-387 ml min(-1)) and resting (6530+/-1018 ml min(-1)) was not significantly different (paired t-test; P<0.055). Diving was accompanied by a 20% increase in Vs over the pre-dive level. Pre-dive, post-dive or diving fh was not significantly correlated with Vs during any state. Diving Vs correlated negatively with the bradycardic ratio (diving fh to pre-dive fh). In this study, the degree of bradycardia during diving was less than in previous pinniped studies, suggesting that the reduction in vagal input may contribute to the observed increase in Vs.

  View details for DOI 10.1242/jeb.01789

  View details for Web of Science ID 000233127200011

  View details for PubMedID 16169941

• Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): Application with fast spin-echo imaging MAGNETIC RESONANCE IN MEDICINE Reeder, S. B., Pineda, A. R., Wen, Z. F., Shimakawa, A., Yu, H. Z., Brittain, J. H., Gold, G. E., Beaulieu, C. H., Pelc, N. J. 2005; 54 (3): 636-644

  Abstract

  Chemical shift based methods are often used to achieve uniform water-fat separation that is insensitive to Bo inhomogeneities. Many spin-echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time-dependent phase shifts caused by water-fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water-fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed "iterative decomposition of water and fat with echo asymmetric and least-squares estimation" (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least-squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2pi/3, with the middle echo centered at pi/2+pik (k=any integer), i.e., (-pi/6+pik, pi/2+pik, 7pi/6+pik). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil-water phantom was observed, demonstrating that the iterative least-squares decomposition method is an efficient estimator.

  View details for DOI 10.1002/mrm.20624

  View details for Web of Science ID 000231494000015

  View details for PubMedID 16092103

• Truly hybrid x-ray/MR imaging: Toward a streamlined clinical system 5th International Interventional MRI Symposium Ganguly, A., Wen, Z. F., Daniel, B. L., Butts, K., Kee, S. T., Rieke, V., Do, H. M., Pelc, N. J., Alley, M. T., Fahrig, R. ELSEVIER SCIENCE INC. 2005: 1167–77

  Abstract

  We have installed an improved X-ray/MR (XMR) truly hybrid system with higher imaging signal-to-noise ratio (SNR) and versatility than our first prototype. In our XMR design, a fixed anode X-ray fluoroscopy system is positioned between the two donut-shaped magnetic poles of a 0.5T GE Signa-SP magnet (SP-XMR). This paper describes the methods for increased compatibility between the upgraded x-ray and MR systems that have helped improve patient management.A GE OEC 9800 system (GE OEC Salt Lake City, UT) was specially reconfigured for permitting X-ray fluoroscopy inside the interventional magnet. A higher power X-ray tube, a new permanent tube mounting system, automatic exposure control (AEC), remote controlled collimators, choice of multiple frame rates, DICOM image compatibility, magnetically shimmed X-ray detector, X-ray compatible MR coil, and better RF shielding are the highlights of the new system. A total of 23 clinical procedures have been conducted with SP-XMR guidance of which five were performed using the new system.The 70% increased power for fluoroscopy, and a new 6 times higher power single frame imaging mode, has improved imaging capability. The choice of multiple imaging frame rates, AEC, and collimator control allow reduction in X-ray exposure to the patient. The DICOM formatting has permitted easy transfer of clinical images over the hospital PACS network. The increased MR compatibility of the detector and the X-ray transparent MR coil has enabled faster switching between X-ray and MR imaging modes.The improvements introduced in our SP-XMR system have further streamlined X-ray/MR hybrid imaging. Additional clinical procedures could benefit from the new SP-XMR imaging.

  View details for DOI 10.1016/j.acra.2005.03.076

  View details for PubMedID 16099685

• Cramer-Rao bounds for three-point decomposition of water and fat MAGNETIC RESONANCE IN MEDICINE Pineda, A. R., Reeder, S. B., Wen, Z. F., Pelc, N. J. 2005; 54 (3): 625-635

  Abstract

  The noise analysis for three-point decomposition of water and fat was extended to account for the uncertainty in the field map. This generalization leads to a nonlinear estimation problem. The Crámer-Rao bound (CRB) was used to study the variance of the estimates of the magnitude, phase, and field map by computing the maximum effective number of signals averaged (NSA) for any choice of echo time shifts. The analysis shows that the noise properties of the reconstructed magnitude, phase, and field map depend not only on the choice of echo time shifts but also on the amount of fat and water in each voxel and their alignment at the echo. The choice of echo time shifts for spin-echo, spoiled gradient echo, and steady-state free precession imaging techniques were optimized using the CRB. The noise analysis for the magnitude explains rough interfaces seen clinically in the boundary of fat and water with source images obtained symmetrically about the spin-echo. It also provides a solution by choosing appropriate echo time shifts (-pi/6+pik, pi/2+pik, 7pi/6+pik), with k an integer. With this choice of echo time shifts it is possible to achieve the maximum NSA uniformly across all fat:water ratios. The optimization is also carried out for the estimation of phase and field map. These theoretical results were verified using Monte Carlo simulations with a newly developed nonlinear least-squares reconstruction algorithm that achieves the CRB.

  View details for DOI 10.1002/mrm.20623

  View details for Web of Science ID 000231494000014

  View details for PubMedID 16092102

• Co-registration of x-ray and MR fields of view in a hybrid XMR system 11th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine Yu, H. Z., Fahrig, R., Pelc, N. J. JOHN WILEY & SONS INC. 2005: 291–301

  Abstract

  To validate one possible function of a real-time x-ray/MR (XMR) interface in a hybrid XMR system using x-ray images as "scouts" to prescribe the MR slices.The registration process consists of two steps: 1) calibration, in which the system's geometric parameters are found from fiducial-based registration; and 2) application, in which the x-ray image of a target structure and the estimated geometric parameters are used to prescribe an MR slice to observe the target structure. Errors from the noise in the location of the fiducial markers, and MR gradient nonlinearity were studied. Computer simulations were used to provide guidelines for fiducial marker placement and tolerable error estimation. A least-squares-based correction method was developed to reduce errors from gradient nonlinearity.In simulations with both sources of errors and the correction for gradient nonlinearity, the use of 16 fiducial markers yielded a mean error of about 0.4 mm over a 7200 cm(3) volume. Phantom scans showed that the prescribed target slice hit most of the target line, and that the length visualized was improved with the least-squares correction.The use of 16 fiducial markers to co-register XMR FOVs can offer satisfactory accuracy in both simulations and experiments.

  View details for DOI 10.1002/jmri.20376

  View details for Web of Science ID 000230812900017

  View details for PubMedID 16028248

• Estimation of renal extraction fraction based on postcontrast venous and arterial differential T-1 values: An error analysis MAGNETIC RESONANCE IN MEDICINE Levin, Y. S., Chow, L. C., Pec, N. J., Sommer, F. G., Spielman, D. M. 2005; 54 (2): 309-316

  Abstract

  An error analysis for quantifying single kidney extraction fraction (EF) via differential T1 measurements in the renal vein (RV) and renal artery (RA) is presented. Sources of error include blood flow effects, the effect of a short repetition time (TR), and the impact of uncertainties in the T1 estimates on the final EF calculations. Blood flow effects were investigated via simulation. For a range of blood velocities in the renal vein that may be found in kidney disease, incomplete refreshment of blood between readouts results in significant errors in T1 estimation. For a .5-cm slice, 110-ms sampling interval, and T1 of 600 ms, T1 estimation to within 5% of true T1 requires an average through-plane velocity of 6.75 cm/s for parabolic flow, and 3.5 cm/s for plug flow. Improvement can be achieved by accurately estimating the fraction of blood that has not refreshed between readouts (f(old)), while the quality of the T1 estimate varies with the accuracy of f(old) estimation. Shortening of the TR was investigated using phantom and in vivo studies. T1 was estimated to within 3% of the true value on phantoms, and within 5% of the true value for flowing blood for TR = 2T1. The estimated EF is shown to be very sensitive to the difference between T(1RA) and T(1RV). To achieve 10% or 20% uncertainty in the EF estimate, T1 in the renal vein and renal artery must be estimated to within approximately 1% or 2%. Because of limitations on measurement accuracy and precision, this method appears to be impractical at this time.

  View details for Web of Science ID 000230765700008

  View details for PubMedID 16032662

• Time-resolved three-dimensional magnetic resonance velocity mapping of aortic flow in healthy volunteers and patients after valve-sparing aortic root replacement 30th Annual Meeting of the Western-Thoracic-Surgical-Association Markl, M., Draney, M. T., Miller, D. C., Levin, J. M., Williamson, E. E., Pelc, N. J., Liang, D. H., Herfkens, R. J. MOSBY-ELSEVIER. 2005: 456–63

  Abstract

  To provide more complete characterization of ascending aortic blood flow, including vortex formation behind the valve cusps, in healthy subjects and patients after valve-sparing aortic root replacement (David reimplantation).Time-resolved 3-dimensional magnetic resonance imaging velocity mapping was performed to analyze pulsatile blood flow by using encoded 3-directional vector fields in the thoracic aortas of 10 volunteers and 12 patients after David reimplantation using a cylindrical tube graft (T. David I) and two versions of neosinus recreation (T. David-V and T. David-V-S mod ). Aortic flow was evaluated by using 3-dimensional time-resolved particle traces and velocity vector fields reformatted onto 2-dimensional planes. Semiquantitative data were derived by using a blinded grading system (0-3: 0, none; 1, minimal; 2, medium; 3, prominent) to analyze the systolic vortex formation behind the cusps, as well as retrograde and helical flow in the ascending aorta.Systolic vortices were seen in both coronary sinuses of all volunteers (greater in the left sinus [2.5 +/- 0.5] than the right [1.8 +/- 0.8]) but in only 4 of 10 noncoronary sinuses (0.7 +/- 0.9). Comparable coronary vortices were detected in all operated patients. Vorticity was minimal in the noncoronary cusp in T. David-I repairs (0.7 +/- 0.7) but was prominent in T. David-V noncoronary graft pseudosinuses (1.5 +/- 0.6; P = .035). Retrograde flow (P = .001) and helicity (P = .028) were found in all patients but were not distinguishable from normal values in the T. David-V-S mod patients.Coronary cusp vorticity was preserved after David reimplantation, regardless of neosinus creation. Increased retrograde flow and helicity were more prominent in T. David-V patients. These novel magnetic resonance imaging methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing various types of valve-sparing aortic root replacement.

  View details for DOI 10.1016/j.jtcvs.2004.08.056

  View details for PubMedID 16077413

• Robust x-ray tubes for use within magnetic fields of MR scanners MEDICAL PHYSICS Wen, Z. F., Fahrig, R., Pelc, N. J. 2005; 32 (7): 2327-2336

  Abstract

  A hybrid system that combines an x-ray fluoroscopic system and a magnetic resonance (MR) system can provide physicians with the synergy of exquisite soft tissue contrast (from MR) and high temporal and spatial resolutions (from x ray), which may significantly benefit a number of image-guided interventional procedures. However, the system configuration may require the x-ray tube to be placed in a magnetic field, which can hinder the proper functioning of the x-ray tube by deflecting its electron beam. From knowledge of how the magnetic field affects the electron trajectories, we propose creating another magnetic field along the cathode-anode axis using either solenoids or permanent magnets to reduce the deflection of the electron beam for two cases: a strong and slightly misaligned field or a weak field that is arbitrary in direction. Theoretical analysis is presented and the electron beam is simulated in various external magnetic fields with a finite element modeling program. Results show that both correction schemes enhance the robustness of the x-ray tube operation in an externally applied magnetic field.

  View details for DOI 10.1118/1.1944267

  View details for Web of Science ID 000230542600018

  View details for PubMedID 16121589

• Robust x-ray tubes for use within magnetic fields of MR scanners. Medical physics Wen, Z., Fahrig, R., Pelc, N. J. 2005; 32 (7Part1): 2327-2336

  Abstract

  A hybrid system that combines an x-ray fluoroscopic system and a magnetic resonance (MR) system can provide physicians with the synergy of exquisite soft tissue contrast (from MR) and high temporal and spatial resolutions (from x ray), which may significantly benefit a number of image-guided interventional procedures. However, the system configuration may require the x-ray tube to be placed in a magnetic field, which can hinder the proper functioning of the x-ray tube by deflecting its electron beam. From knowledge of how the magnetic field affects the electron trajectories, we propose creating another magnetic field along the cathode-anode axis using either solenoids or permanent magnets to reduce the deflection of the electron beam for two cases: a strong and slightly misaligned field or a weak field that is arbitrary in direction. Theoretical analysis is presented and the electron beam is simulated in various external magnetic fields with a finite element modeling program. Results show that both correction schemes enhance the robustness of the x-ray tube operation in an externally applied magnetic field.

  View details for DOI 10.1118/1.1944267

  View details for PubMedID 28493583

• Cardiac CINE imaging with IDEAL water-fat separation and steady-state free precession JOURNAL OF MAGNETIC RESONANCE IMAGING Reeder, S. B., Markl, M., Yu, H. Z., Hellinger, J. C., Herfkens, R. J., Pelc, N. J. 2005; 22 (1): 44-52

  Abstract

  To decompose multicoil CINE steady-state free precession (SSFP) cardiac images acquired at short echo time (TE) increments into separate water and fat images, using an iterative least-squares "Dixon" (IDEAL) method.Multicoil CINE IDEAL-SSFP cardiac imaging was performed in three volunteers and 15 patients at 1.5 T.Measurements of signal-to-noise ratio (SNR) matched theoretical expectations and were used to optimize acquisition parameters. TE increments of 0.9-1.0 msec permitted the use of repetition times (TRs) of 5 msec or less, and provided good SNR performance of the water-fat decomposition, while maintaining good image quality with a minimum of banding artifacts. Images from all studies were evaluated for fat separation and image quality by two experienced radiologists. Uniform fat separation and diagnostic image quality was achieved in all images from all studies. Examples from volunteers and patients are shown.Multicoil IDEAL-SSFP imaging can produce high quality CINE cardiac images with uniform water-fat separation, insensitive to Bo inhomogeneities. This approach provides a new method for reliable fat-suppression in cardiac imaging.

  View details for DOI 10.1002/jmri.20327

  View details for Web of Science ID 000230128900006

  View details for PubMedID 15971192

• Performance of a static-anode/flat-panel x-ray fluoroscopy system in a diagnostic strength magnetic field: A truly hybrid x-ray/MR imaging system MEDICAL PHYSICS Fahrig, R., Wen, Z., GANGULY, A., DECRESCENZO, G., Rowlands, J. A., Stevens, G. M., Saunders, R. F., Pelc, N. J. 2005; 32 (6): 1775-1784

  Abstract

  Minimally invasive procedures are increasing in variety and frequency, facilitated by advances in imaging technology. Our hybrid imaging system (GE Apollo flat panel, custom Brand x-ray static anode x-ray tube, GE Lunar high-frequency power supply and 0.5 T Signa SP) provides both x-ray and MR imaging capability to guide complex procedures without requiring motion of the patient between two distant gantries. The performance of the x-ray tube in this closely integrated system was evaluated by modeling and measuring both the response of the filament to an externally applied field and the behavior of the electron beam for field strengths and geometries of interest. The performance of the detector was assessed by measuring the slanted-edge modulation transfer function (MTF) and when placed at zero field and at 0.5 T. Measured resonant frequencies of filaments can be approximated using a modified vibrating beam model, and were at frequencies well below the 25 kHz frequency of our generator for our filament geometry. The amplitude of vibration was not sufficient to cause shorting of the filament during operation within the magnetic field. A simple model of electrons in uniform electric and magnetic fields can be used to estimate the deflection of the electron beam on the anode for the fields of interest between 0.2 and 0.5 T. The MTF measured at the detector and the DQE showed no significant difference inside and outside of the magnetic field. With the proper modifications, an x-ray system can be fully integrated with a MR system, with minimal loss of image quality. Any x-ray tube can be assessed for compatibility when placed at a particular location within the field using the models. We have also concluded that a-Si electronics are robust against magnetic fields. Detailed knowledge of the x-ray system installation is required to provide estimates of system operation.

  View details for DOI 10.1118/1.1915016

  View details for Web of Science ID 000229908600036

  View details for PubMedID 16013735

• X-ray compatible radiofrequency coil for magnetic resonance imaging MAGNETIC RESONANCE IN MEDICINE Rieke, V., GANGULY, A., Daniel, B. L., Scott, G., Pauly, J. M., Fahrig, R., Pelc, N. J., Butts, K. 2005; 53 (6): 1409-1414

  Abstract

  The range of RF coils that can be used in combined X-ray/MR (XMR) systems is limited because many conventional coils contain highly X-ray attenuating materials that are visible in the X-ray images and potentially obscure patient anatomy. In this study, an X-ray compatible coil design that has minimal X-ray attenuation in the field of view (FOV) of the X-ray image is presented. In this design, aluminum is used for the loop conductor and discrete elements of the coil are eliminated from the X-ray FOV. A surface coil and an abdominal phased array coil were built using the X-ray compatible design. X-ray attenuation and MR imaging properties of the coils were evaluated and compared to conventional coils. The X-ray compatible phased array coil was used to image patients during two interventional procedures in the XMR system. The X-ray compatible coils allowed for fluoroscopic X-ray image acquisition, without degradation by the coil, while maintaining excellent MR imaging qualities.

  View details for DOI 10.1002/mrm.20494

  View details for PubMedID 15906285

• MR-guided transjugular intrahepatic portosystemic shunt creation with use of a hybrid radiography/MR system 29th Annual Meeting of the Society-of-Interventional-Radiology (SIR) Kee, S. T., GANGULY, A., Daniel, B. L., Wen, Z. F., Butts, K., Shimikawa, A., Pelc, N. J., Fahrig, R., Dake, M. D. ELSEVIER SCIENCE INC. 2005: 227–34

  Abstract

  To evaluate the performance of a combined hybrid radiography/magnetic resonance (MR) unit to guide portal vein (PV) puncture during human transjugular intrahepatic portosystemic shunt (TIPS) creation.Fourteen patients undergoing TIPS creation were studied during standard clinical applications. Patients were anesthetized and then positioned in an open MR unit containing a flat-panel radiographic fluoroscopic unit. With use of a combination of fluoroscopy and MR imaging, the PV was accessed and the TIPS procedure was performed. A noncovered nitinol stent or a covered stent-graft was placed in the TIPS tract. Number of punctures required, total procedure time, fluoroscopy time, procedural success rate, complications, and ultrasonographic and clinical follow-up were recorded.Clinical success was obtained in 13 of 14 patients. In one patient, extrahepatic puncture of the PV occurred, resulting in hemorrhage and requiring placement of a covered stent to control the bleeding. The mean number of punctures required to access the PV was 2.6 +/- 1.7, and the total procedure time was 2.5 hours +/- 0.6. Mean fluoroscopy time was 22.3 minutes +/- 5.5. Results of clinical and ultrasonographic follow-up compare favorably to previously published reports.TIPS creation with a combination hybrid radiography/MR unit is feasible and may reduce the number of needle passes required and radiation exposure, with similar overall outcomes compared with studies reported in the literature.

  View details for DOI 10.1097/01.RVI.0000143766.08029.6E

  View details for PubMedID 15713923

• Reply to "Comment on 'an inverse-geometry volumetric CT system with a large-area scanned source: A feasibility study' [Med. Phys. 32, 635 (2005)] MEDICAL PHYSICS Schmidt, T. G., Fahrig, R., Pelc, N. J., Solomon, E. G. 2005; 32 (2): 636-636

  View details for DOI 10.1118/1.1851913

  View details for Web of Science ID 000227420800039

• Wider Field-of-View Inverse-Geometry CT with Multiple Detector Arrays: Initial Experimental Results. RSNA '05 Mazin, S. R., Bennet, N. R., Schmidt, T. G., Pelc, N., J. 2005: 391
• Estimating 0(th) and 1(th) moments in C-arm CT data for extrapolating truncated projections Medical Imaging 2005 Conference Starman, J., Pelc, N., Strobel, N., Fahrig, R. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 378–387

  View details for DOI 10.1117/12.596041

  View details for Web of Science ID 000230109600039

• 2D simulations of an inverse-geometry volumetric CT system with multiple detector arrays Medical Imaging 2005 Conference Mazin, S., Star-Lack, J., Schmidt, T. G., Pelc, N. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 889–897

  View details for DOI 10.1117/12.595947

  View details for Web of Science ID 000229929500093

• MTF analysis of a prototype table-top inverse-geometry volumetric CT system Medical Imaging 2005 Conference Schmidt, T. G., Bennett, N. R., Mazin, S. R., Star-Lack, J., Solomon, E. G., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 171–178

  View details for DOI 10.1117/12.596083

  View details for Web of Science ID 000229929500018

• Cardiac Cine Imaging with "Dixon" Fat-Water Separation and Steady-State Free Precession. J Magn. Reson. Imag Reeder, S., B., Markl, M., Yu, H., Hellinger, J. C., Herfkens, R. J., Pelc, N., J. 2005; 22: 44-52
• Two-dimensional simulations of an inverse geometry CT system with multiple detector arrays. Mazin, S, R., Star-Lack, J., Schmidt, T. G., Pelc, N., J. 2005
• Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-squares Estimation (IDEAL): Application with Fast Spin-echo Imaging. Mag Res Me Reeder, S., B., Pineda, A., R., Wen, Z., Shimakawa, A., H, Y., Brittain, J. H., Pelc, N. J. 2005; 54: 636-44
• Parallel Imaging Accelerated Single Acquisition Water-Fat Separation for Dynamic Imaging H, Y., McKenzie, C. A., Shimakawa, A., Brau, A. C., Pineda, A. R., Pelc, N., J. 2005
• In-Vivo Hemodynamic Analysis of Splanchnic Arteries Affected by Aortic Dissection Using Time-resolved 3D Phase-contrast MR Imaging. Takehara, Y., Isoda, H., Hirano, M., Alley, M. T., Markl, M., Pelc, N., J. 2005
• Investigation of Increase in Radiation When an X-ray Tube Is Placed in a Magnetic Field. Wen, Z., Pelc, N., J., Nelson, W. R., Fahrig, R. 2005
• Water-Fat Separation with IDEAL-SPGR Reeder, S. B., Pineda, A. R., Yu, H., McKenzie, C. A., Brau, A., GE, G., Pelc, N. J. 2005
• Determination of Electronic and Quantum Noise Dominated Regions in a CT System. RSNA '05 Dormo, J., Pelc, N., J. 2005: 211
• Cramér-Rao Bounds for 3-Point Dixon Imaging. Mag Res Med Pineda, A., R., Reeder, S., B., Wen, Z., Pelc, Norbert, J. 2005; 54: 625-35
• MTF analysis of a prototype table-top inverse-geometry volumetric CT system. Schmidt, T. G., Bennet, N. R., Mazin, S. R., Pelc, N. J. 2005
• Investigation of a Prototype Table-top Inverse-geometry Volumetric CT System. Schmidt, T. G., Star-Lack, J., Bennet, N. R., Solomon, E. G., Mazin, S. R., Pelc, N., J. 2005
• Optimization of Echo Time Shifts for 3-Pt Fat/Water Separation Pineda, A., R., Reeder, S., B., Wen, Z., Pelc, N., J. 2005
• MR Imaging for Polymethylmethacralate During a Percutaneous Vertebroplasty Procedure H, Y., Fahrig, R., Butts, K., Ganguly, A., Adalsteinsson, E., Mayer, D., Pelc, N. J. 2005
• Estimating 0th and 1st moments in C-arm CT data for extrapolating projections. Starman, J. D., Strobel, N., Pelc, N., J., Fahrig, R. 2005
• Cartilage Morphology at 1.5T: Comparison of 3D FS-SPGR and IDEAL SPGR Imaging Gold, G. E., Reeder, S. B., Yu, H., Shimakawa, A., Johnson, J. W., Pelc, N., J. 2005
• On flow effects in balanced steady-state free precession imaging: Pictorial description, parameter dependence, and clinical implications JOURNAL OF MAGNETIC RESONANCE IMAGING Markl, M., Pelc, N. J. 2004; 20 (4): 697-705

  Abstract

  To present a pictorial description of the origin of flow effects in balanced steady-state free precession (SSFP) imaging that can result in considerable frequency offset-dependent signal changes originating from outflow of spins that can still contribute to the total SSFP signal (out-of-slice contributions), to analyze the parameter dependence and slice broadening associated with outflow effects, and to illustrate clinical implications such as frequency offset-dependent flow artifacts and spatial misencoding.Computer simulations were used to create a pictorial description of flow effects that illustrates the origin and parameter dependence of the observed signal changes and links their frequency dependency to the phase distribution of spins flowing in and out of the imaging slice. Slice broadening associated with out-of-slice contributions and flow-related signal enhancement was characterized by an effective slice thickness, which depends on flow rate, the T2* decay of signal magnitude from spins that have left the imaging slice, and the ratio of the net out-of-slice magnetization relative to the thickness of the imaging slice.Both simulated SSFP signal intensities and effective slice broadening vary with flip angle and demonstrate a nonlinear dependence on inflow. Simulations with bloodlike T1 and T2 show that the effective slice thickness can be as large as 15 times the prescribed slice thickness. These effects can have significant clinical implications such as large frequency offset-dependent signal enhancement, pulsatile flow artifacts, and spatial misrepresentation of blood signal that has already left the imaging slice.Flow-related signal changes in SSFP imaging exhibit highly complex parameter dependence, which predominantly has to be associated with frequency offset-dependent outflow effects and a resulting broadening of the slice thickness.

  View details for DOI 10.1002/jmri.20163

  View details for Web of Science ID 000224219000019

  View details for PubMedID 15390233

• An inverse-geometry volumetric CT system with a large-area scanned source: A feasibility study MEDICAL PHYSICS Schmidt, T. G., Fahrig, R., Pelc, N. J., Solomon, E. G. 2004; 31 (9): 2623-2627

  Abstract

  We propose an inverse-geometry volumetric CT system for acquiring a 15-cm volume in one rotation with negligible cone-beam artifacts. The system uses a large-area scanned source and a smaller detector array. This note describes two feasibility investigations. The first examines data sufficiency in the transverse planes. The second predicts the signal-to-noise ratio (SNR) compared to a conventional scanner. Results showed sufficient sampling of the full volume in less than 0.5 s and, when compared to a conventional scanner operating at 24 kW with a 0.5-s voxel illumination time (e.g., 0.5-s gantry rotation and pitch of one), predicted a relative SNR of 76%.

  View details for DOI 10.1118/1.1786171

  View details for Web of Science ID 000224117400031

  View details for PubMedID 15487745

• Quantification of vessel wall motion and cyclic strain using cine phase contrast MRI: In vivo validation in the porcine aorta MAGNETIC RESONANCE IN MEDICINE Draney, M. T., Arko, F. R., Alley, M. T., Markl, M., Herfkens, R. J., Pelc, N. J., Zarins, C. K., Taylor, C. A. 2004; 52 (2): 286-295

  Abstract

  Artery wall motion and strain play important roles in vascular remodeling and may be important in the pathogenesis of vascular disease. In vivo observations of circumferentially nonuniform wall motion in the human aorta suggest that nonuniform strain may contribute to the localization of vascular pathology. A velocity-based method to investigate circumferential strain variations was previously developed and validated in vitro; the current study was undertaken to determine whether accurate displacement and strain fields can be calculated from velocity data acquired in vivo. Wall velocities in the porcine thoracic aorta were quantified with PC-MRI and an implanted coil and were then time-integrated to compute wall displacement trajectories and cyclic strain. Displacement trajectories were consistent with observed aortic wall motion and with the displacements of markers in the aortic wall. The mean difference between velocity-based and marker-based trajectory points was 0.1 mm, relative to an average pixel size of 0.4 mm. Propagation of error analyses based on the precision of the computed displacements were used to demonstrate that 10% strain results in a standard deviation of 3.6%. This study demonstrates that it is feasible to accurately quantify strain from low wall velocities in vivo and that the porcine thoracic aorta does not deform uniformly.

  View details for DOI 10.1002/mrm.20137

  View details for Web of Science ID 000223121400008

  View details for PubMedID 15282810

• Time-resolved 3-dimensional velocity mapping in the thoracic aorta - Visualization of 3-directional blood flow patterns in healthy volunteers and patients JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY Markl, M., Draney, M. T., Hope, M. D., Levin, J. M., Chan, F. P., Alley, M. T., Pelc, N. J., Herfkens, R. J. 2004; 28 (4): 459-468

  Abstract

  An analysis of thoracic aortic blood flow in normal subjects and patients with aortic pathologic findings is presented. Various visualization tools were used to analyze blood flow patterns within a single 3-component velocity volumetric acquisition of the entire thoracic aortaTime-resolved, 3-dimensional phase-contrast magnetic resonance imaging (3D CINE PC MRI) was employed to obtain complete spatial and temporal coverage of the entire thoracic aorta combined with spatially registered 3-directional pulsatile blood flow velocities. Three-dimensional visualization tools, including time-resolved velocity vector fields reformatted to arbitrary 2-dimensional cut planes, 3D streamlines, and time-resolved 3D particle traces, were applied in a study with 10 normal volunteers. Results from 4 patient examinations with similar scan prescriptions to those of the volunteer scans are presented to illustrate flow features associated with common pathologic findings in the thoracic aorta.Previously reported blood flow patterns in the thoracic aorta, including right-handed helical outflow, late systolic retrograde flow, and accelerated passage through the aortic valve plane, were visualized in all volunteers. The effects of thoracic aortic disease on spatial and temporal blood flow patterns are illustrated in clinical cases, including ascending aortic aneurysms, aortic regurgitation, and aortic dissection.Time-resolved 3D velocity mapping was successfully applied in a study of 10 healthy volunteers and 4 patients with documented aortic pathologic findings and has proven to be a reliable tool for analysis and visualization of normal characteristic as well as pathologic flow features within the entire thoracic aorta.

  View details for PubMedID 15232376

• Steady-state free precession MR imaging: Improved myocardial tag persistence and signal-to-noise ratio for analysis of myocardial motion 88th Scientific Assembly and Annual Meeting of the Radiological-Society-of-North-America Markl, M., Reeder, S. B., Chan, F. P., Alley, M. T., Herfkens, R. J., Pelc, N. J. RADIOLOGICAL SOC NORTH AMERICA. 2004: 852–61

  Abstract

  Tagging with balanced steady-state free-precession (SSFP) magnetic resonance (MR) imaging by using a steady-state storage scheme for myocardial motion analysis was evaluated. Signal-to-noise ratio (SNR), blood-tissue contrast, and tag persistence in volunteers and phantoms showed improved performance of SSFP imaging with tagging compared with that of radiofrequency spoiled gradient-echo (SPGR) MR imaging with tagging. Choice of flip angle with SSFP imaging involved a trade-off among SNR, blood-tissue contrast, and tag persistence. Increased SNR and tag persistence can be achieved simultaneously with SSFP imaging compared with SPGR tagging methods. As a result, the proposed technique may be useful for analysis of diastolic ventricular function.

  View details for DOI 10.1148/radiol.2303030181

  View details for Web of Science ID 000189186500037

  View details for PubMedID 14990847

• Multicoil Dixon chemical species separation with an iterative least-squares estimation method MAGNETIC RESONANCE IN MEDICINE Reeder, S. B., Wen, Z. F., Yu, H. Z., Pineda, A. R., Gold, G. E., Markl, M., Pelc, N. J. 2004; 51 (1): 35-45

  Abstract

  This work describes a new approach to multipoint Dixon fat-water separation that is amenable to pulse sequences that require short echo time (TE) increments, such as steady-state free precession (SSFP) and fast spin-echo (FSE) imaging. Using an iterative linear least-squares method that decomposes water and fat images from source images acquired at short TE increments, images with a high signal-to-noise ratio (SNR) and uniform separation of water and fat are obtained. This algorithm extends to multicoil reconstruction with minimal additional complexity. Examples of single- and multicoil fat-water decompositions are shown from source images acquired at both 1.5T and 3.0T. Examples in the knee, ankle, pelvis, abdomen, and heart are shown, using FSE, SSFP, and spoiled gradient-echo (SPGR) pulse sequences. The algorithm was applied to systems with multiple chemical species, and an example of water-fat-silicone separation is shown. An analysis of the noise performance of this method is described, and methods to improve noise performance through multicoil acquisition and field map smoothing are discussed.

  View details for Web of Science ID 000188041500007

  View details for PubMedID 14705043

• Noise simulations for an inverse-geometry volumetric CT system Medical Imaging 2004 Conference Schmidt, T. G., Fahrig, R., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2004: 420–427

  View details for DOI 10.1117/12.535932

  View details for Web of Science ID 000222012700046

• Geometry analysis of an inverse-geometry volumetric CT system with multiple detector arrays Medical Imaging 2004 Conference Mazin, S., Schmidt, T. G., Solomon, E., Fahrig, R., Pelc, N. SPIE-INT SOC OPTICAL ENGINEERING. 2004: 320–329

  View details for DOI 10.1117/12.536032

  View details for Web of Science ID 000222012700035

• Collimator for a Multiple-Eye Inverse-Geometry Volumetric CT System. Mazin, S. R., Schmidt, T. G., Pelc, N., J. 2004
• X-Ray Compatible RF-Coil for MR Imaging Rieke, V., Ganguly, A., Scott, G. C., Daniel, B. L., Pauly, J, M., Fahrig, R., Pelc, N. J. 2004
• TIPS using Truly Hybrid X-Ray/MR Guidance Fahrig, R., Kee, S. T., Daniel, B. L., Ganguly, A., Wen, Z., Butts, K., Pelc, N. J. 2004
• Parallel Cardiac CINE Imaging: Application to "Dixon" Water-Fat Separation and Steady-State Free Precession Reeder, S. B., McKenzie, C. A., Markl, M., Yu, H., Pelc, N. J., Brittain, J. H. 2004
• Implementation and Noise Analysis of Chemical Shift Correction for Fast Spin Echo Dixon Imaging. Yu, H., Reeder, S. B., Shimakawa, A., Gold, G. E., Pelc, N. J., Brittain, J. H. 2004
• Dixon Water-Fat Separation for Musculoskeletal Imaging with Fast Spin-Echo at 3T. Reeder, S. B., Yu, H., Shimakawa, A., Brittain, J. H., Johnson, J. W., Pelc, N. J. 2004
• Abdominal Three Point Dixon Imaging with Self Calibrating Parallel MRI. McKenzie, C. A., Reeder, S. B., Shimakawa, A., Pelc, N. J., Jean, B. 2004
• First Images from a Table-top Inverse Geometry Volumetric CT System with a Large-area Scanned Source. Schmidt, T. G., Bennet, N. R., Mazin, S. R., Star-Lack, J., Solomon, E. G., Pelc, N., J. 2004
• Permanent Magnet Shimming for the X-Ray Detector in a Hybrid X-Ray/MR System Wen, Z., Fahrig, R., Pelc, N. J. 2004
• Noise simulations for an inverse geometry volumetric CT system. Schmidt, T. G., Fahrig, R., Pelc, N., J. 2004
• Cramér-Rao Bounds for 3-Point Dixon Imaging Pineda, A. R., Wen, Z., Reeder, S. B., Yu, H., Pelc, N. J. 2004
• Contrast Agent Optimization for Imaging with MR/X-Ray Hybrid Systems Ganguly, A., Mayer, D., Fahrig, R., Pelc, N. J. 2004
• Pictorial Description, Parameter Dependence and Clinical Implications. J Magn Reson Imaging Markl, M., Pelc, N., J. 2004; 20: 697-705
• Asymmetric Echoes for Optimal SNR Performance of “Dixon” Water-Fat Separation with Fast Spin-Echo Imaging. Reeder, S. B., Pineda, A., H, Y., Wen, Z., Shimakawa, A., Pelc, N., J. 2004
• Time-Resolved 3D Magnetic Resonance Velocity Mapping Of Aortic Outflow In Volunteers And Patients After Valve Sparing Aortic Root Replacement. Markl, M., Draney, M. T., Levin, J. M., Williamson, E. E., Pelc, N. J., Liang, D. 2004
• Single Acquisition Water Fat Separation for SSFP Cardiac CINE Imaging: Feasibility Study Yu, H., Reeder, S. B., Markl, M., Pelc, N. J. 2004
• Rapid Cartilage Morphology at 3.0T: Comparison of FS-SPGR, FS-SSFP, and "Dixon" SSFP Imaging Gold, G. E., Reeder, S. B., Yu, H., Shimakawa, A., Johnson, J. W., Pelc, N. J. 2004
• Geometry analysis of an inverse geometry volumetric CT system with multiple detector arrays. Mazin, S. R., Schmidt, T. G., Solomon, E. G., Fahrig, R., Pelc, N., J. 2004
• Cardiac CINE Imaging with "Dixon" Water-Fat Separation and Steady-State Free Precession Reeder, S. B., Markl, M., Yu, H., Hellinger, J. C., Herfkens, R. J., Pelc, N. J. 2004
• Extrapolating Truncated Projections Using 0th and 1st Moment Constraints. Starman, J., Strobel, N., Pelc, N., J., Fahrig, R. 2004
• Time-Resolved 3D Velocity Mapping in the Thoracic Aorta: Three-Directional Blood Flow Patterns in Healthy Volunteers and Patients. Markl, M., Draney, M. T., Hope, M. D., Levin, J. M., Alley, M. T., Chan, F. P., Pelc, N. J. 2004
• Robust Field Map Estimation in a Dixon Water-Fat Separation Algorithm with Short Echo Time Increments Yu, H., Reeder, S. B., Shimakawa, A., Brittain, J. H., Pelc, N. J. 2004
• Asymmetric Echoes for Robust Fast Spin-Echo "Dixon" Water-Fat Separation Reeder, S. B., Wen, Z., Yu, H., Pineda, A. R., Shimakawa, A., Brittain, J. H., Pelc, N. J. 2004
• “Musculoskeletal Imaging with “Dixon” Water-Fat Separation at 3T” Reeder, S. B., Gold, G. E., Yu, H., Shimakawa, A., Brittain, J. H., Pelc, N. J. 2004
• To Bin or Not to Bin? A Question Regarding the Noise Properties of CT Reconstructions with or without Binned Projections. RSNA '04 Pineda, A., R., Pelc, N., J. 2004: 354
• Time-Resolved 3D Velocity Mapping in the Thoracic Aorta: Visualization of Three-Directional Blood Flow Patterns in Healthy Volunteers and Patients. J Comput Assist Tomogr Markl, M., Draney, M., T., Hope, M., D., Levin, J. M., Chan, F. P., Alley, M. T., Pelc, N. J. 2004; 28: 459-468
• Measurement of renal extraction fraction using contrast-enhanced computed tomography MEDICAL PHYSICS Sommer, G., Chow, L., Pelc, N. 2004; 31 (1): 37-38

  Abstract

  Renal extraction fraction (EF) is the percentage of plasma entering the glomerulus which is filtered. Contrast agents which are freely filtered and neither secreted nor reabsorbed, may be used as markers for renal filtration, allowing EF to be calculated from computed tomography (CT) measurements of systemic vessels and renal veins. CT scans of 10 adult patients having no known renal disease were studied in this manner, giving EF values averaging 12.6% and 12.3% for the right and left kidneys, respectively, compared to the accepted value of 15%-20%. EF measurement using CT may provide noninvasive evaluation of renal function, complementing CT-derived morphologic information.

  View details for DOI 10.1118/1.1631092

  View details for Web of Science ID 000188383500005

  View details for PubMedID 14761018

• Flow effects in balanced steady state free precession imaging MAGNETIC RESONANCE IN MEDICINE Markl, M., Alley, M. T., Elkins, C. J., Pelc, N. J. 2003; 50 (5): 892-903

  Abstract

  An analysis of the effect of flow on 2D fully balanced steady state free precession (SSFP) imaging is presented. Transient and steady-state SSFP signal intensities in the presence of steady and pulsatile flow were simulated using a matrix formalism based on the Bloch equations. Various through-plane flow waveforms and rates were modeled numerically considering factors such as the excitation slice profile and both in- and out-flow effects. Phantom measurements in an experimental setup that allowed the assessment of SSFP signal properties as a function of frequency offset and flow rate demonstrated that the computer simulations provided a suitable description of the effects of flow in SSFP imaging. A volunteer scan was performed to provide in vivo validations. For accurate modeling of SSFP signal intensities it is crucial to include effects such as imperfect slice profiles and, more importantly, "out-of-slice" contributions to the signal. Both simulations and experiments show that there can be considerably large-frequency offset dependent-signal contributions from flowing spins that have already left the imaging slice but still add to the SSFP signal. Although spins leaving the slice do not experience additional RF-excitation, gradient activity is not confined to the region of excitations and the balanced nature of the SSFP imaging gradients allows "out-of-slice" transverse magnetization to contribute to the total SSFP signal, effectively by broadening the slice thickness for flowing spins. This results in a frequency dependence of in-flow related signal enhancement and flow artifacts.

  View details for DOI 10.1002/mrm.10631

  View details for Web of Science ID 000186326400002

  View details for PubMedID 14586999

• First use of a truly-hybrid X-ray/MR imaging system for guidance of brain biopsy ACTA NEUROCHIRURGICA Fahrig, R., Heit, G., Wen, Z., Daniel, B. L., Butts, K., Pelc, N. J. 2003; 145 (11): 995-997

  Abstract

  The use of a new hybrid imaging system for guidance of a brain biopsy is described. The system combines the strengths of MRI (soft-tissue contrast, arbitrary plane selection) with those of x-ray fluoroscopy (high-resolution real-time projection images, clear portrayal of bony structures) and allows switching between the imaging modalities without moving the patient. The biopsy was carried out using x-ray guidance for direction of the needle through the foramen ovale and MR guidance to target the soft-tissue lesion. Appropriate samples were acquired. The system could be particularly effective for guidance of those cases where motion, swelling, resection and other intra-operative anatomical changes cannot be accounted for using traditional stereotactic-based imaging approaches.

  View details for DOI 10.1007/s00701-003-0138-7

  View details for Web of Science ID 000186686300020

  View details for PubMedID 14628205

• Generalized reconstruction of phase contrast MRI: Analysis and correction of the effect of gradient field distortions MAGNETIC RESONANCE IN MEDICINE Markl, M., Bammer, R., Alley, M. T., Elkins, C. J., Draney, M. T., Barnett, A., Moseley, M. E., Glover, G. H., Pelc, N. J. 2003; 50 (4): 791-801

  Abstract

  To characterize gradient field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous gradient fields can introduce deviations from the nominal gradient strength and orientation, and therefore spatially-dependent first gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative gradient field deviations derived from a theoretical model of local gradient field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45 degrees. Results of phantom measurements demonstrate that effects of gradient field nonuniformity on PC-MRI can be corrected with the proposed method.

  View details for DOI 10.1002/mrm.10582

  View details for Web of Science ID 000185698000019

  View details for PubMedID 14523966

• Analysis and generalized correction of the effect of spatial gradient field distortions in diffusion-weighted imaging MAGNETIC RESONANCE IN MEDICINE Bammer, R., Markl, M., Barnett, A., Acar, B., Alley, M. T., Pelc, N. J., Glover, G. H., Moseley, M. E. 2003; 50 (3): 560-569

  Abstract

  Nonuniformities of magnetic field gradients can cause serious artifacts in diffusion imaging. While it is well known that nonlinearities of the imaging gradients lead to image warping, those imperfections can also cause spatially dependent errors in the direction and magnitude of the diffusion encoding. This study shows that the potential errors in diffusion imaging are considerable. Further, we show that retrospective corrections can be applied to reduce these errors. A general mathematical framework was formulated to characterize the contribution of gradient nonuniformities to diffusion experiments. The gradient field was approximated using spherical harmonic expansion, and this approximation was employed (after geometric distortions were eliminated) to predict and correct the errors in diffusion encoding. Before the corrections were made, the experiments clearly revealed marked deviations of the calculated diffusivity for fields of view (FOVs) generally used in diffusion experiments. These deviations were most significant farther away from the magnet's isocenter. For an FOV of 25 cm, the resultant errors in absolute diffusivity ranged from approximately -10% to +20%. Within the same FOV, the diffusion-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the gradient nonuniformities are not considered. With the proposed correction scheme, most of the errors introduced by gradient nonuniformities can be removed.

  View details for DOI 10.1002/mrm.10545

  View details for Web of Science ID 000185174500015

  View details for PubMedID 12939764

• Circular tomosynthesis: Potential in imaging of breast and upper cervical spine - Preliminary phantom and in vitro study 86th Scientific Assembly and Annual Meeting of the Radiological-Society-of-North-America (RSNA) Stevens, G. M., Birdwell, R. L., Beaulieu, C. F., Ikeda, D. M., Pelc, N. J. RADIOLOGICAL SOC NORTH AMERICA. 2003: 569–75

  Abstract

  Phantom and in vitro studies were performed to evaluate the potential application of digital circular tomosynthesis in imaging of the breast and upper cervical spine. A prototype volumetric x-ray system was used to image a mammographic phantom, a fresh mastectomy specimen, and a head phantom containing the upper cervical spine. Results show that breast tissue visualization is improved by the ability to produce sectional images that blur overlying structures and yield three-dimensional information about calcification clusters. In upper cervical spine imaging, digital circular tomosynthesis effectively blurs overlying jaw and skull structures so that C1 and C2 can be visualized in a standard anteroposterior view.

  View details for DOI 10.1148/radiol.2282020295

  View details for Web of Science ID 000184381100041

  View details for PubMedID 12821770

• Fast algorithms for GS-model-based image reconstruction in data-sharing Fourier imaging IEEE TRANSACTIONS ON MEDICAL IMAGING Liang, Z. P., Madore, B., Glover, G. H., Pelc, N. J. 2003; 22 (8): 1026-1030

  Abstract

  Many imaging experiments involve acquiring a time series of images. To improve imaging speed, several "data-sharing" methods have been proposed, which collect one (or a few) high-resolution reference(s) and a sequence of reduced data sets. In image reconstruction, two methods, known as "Keyhole" and reduced-encoding imaging by generalized-series reconstruction (RIGR), have been used. Keyhole fills in the unmeasured high-frequency data simply with those from the reference data set(s), whereas RIGR recovers the unmeasured data using a generalized series (GS) model, of which the basis functions are constructed based on the reference image(s). This correspondence presents a fast algorithm (and two extensions) for GS-based image reconstruction. The proposed algorithms have the same computational complexity as the Keyhole algorithm, but are more capable of capturing high-resolution dynamic signal changes.

  View details for DOI 10.1109/TMI.2003.815896

  View details for Web of Science ID 000184567100011

  View details for PubMedID 12906256

• Balanced phase-contrast steady-state free precession (PC-SSFP): A novel technique for velocity encoding by gradient inversion 10th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine (ISMRM) Markl, M., Alley, M. T., Pelc, N. J. JOHN WILEY & SONS INC. 2003: 945–52

  Abstract

  A technique for measuring velocity is presented that combines cine phase contrast (PC) MRI and balanced steady-state free precession (SSFP) imaging, and is thus termed PC-SSFP. Flow encoding was performed without the introduction of additional velocity encoding gradients in order to keep the repetition time (TR) as short as in typical SSFP imaging sequences. Sensitivity to through-plane velocities was instead established by inverting (i.e., negating) all gradients along the slice-select direction. Velocity sensitivity (VENC) could be adjusted by altering the first moments of the slice-select gradients. Disturbances of the SSFP steady state were avoided by acquiring different flow echoes in consecutively (i.e., sequentially) executed scans, each over several cardiac cycles, using separate steady-state preparation periods. A comparison of phantom measurements with those from established 2D-cine-PC MRI demonstrated excellent correlation between both modalities. In examinations of volunteers, PC-SSFP exhibited a higher intrinsic signal-to-noise ratio (SNR) and consequently low phase noise in measured velocities compared to conventional PC scans. An additional benefit of PC-SSFP is that it relies less on in-flow-dependent signal enhancement, and thus yields more uniform SNRs and better depictions of vessel geometry throughout the whole cardiac cycle in structures with slow and/or pulsatile flow.

  View details for DOI 10.1002/mrm.10451

  View details for Web of Science ID 000182642400021

  View details for PubMedID 12704778

• 4D Magnetic resonance velocimetry for mean velocity measurements in complex turbulent flows EXPERIMENTS IN FLUIDS Elkins, C. J., Markl, M., Pelc, N., Eaton, J. K. 2003; 34 (4): 494-503

  View details for DOI 10.1007/S00348-003-0587-z

  View details for Web of Science ID 000183198800006

• Time-resolved three-dimensional phase-contrast MRI 10th Annual Meeting of the International-Society-for-Magnetic-Resonance-in-Medicine (ISMRM) Markl, M., Chan, F. P., Alley, M. T., Wedding, K. L., Draney, M. T., Elkins, C. J., Parker, D. W., Wicker, R., Taylor, C. A., Herfkens, R. J., Pelc, N. J. JOHN WILEY & SONS INC. 2003: 499–506

  Abstract

  To demonstrate the feasibility of a four-dimensional phase contrast (PC) technique that permits spatial and temporal coverage of an entire three-dimensional volume, to quantitatively validate its accuracy against an established time resolved two-dimensional PC technique to explore advantages of the approach with regard to the four-dimensional nature of the data.Time-resolved, three-dimensional anatomical images were generated simultaneously with registered three-directional velocity vector fields. Improvements compared to prior methods include retrospectively gated and respiratory compensated image acquisition, interleaved flow encoding with freely selectable velocity encoding (venc) along each spatial direction, and flexible trade-off between temporal resolution and total acquisition time.The implementation was validated against established two-dimensional PC techniques using a well-defined phantom, and successfully applied in volunteer and patient examinations. Human studies were performed after contrast administration in order to compensate for loss of in-flow enhancement in the four-dimensional approach.Advantages of the four-dimensional approach include the complete spatial and temporal coverage of the cardiovascular region of interest and the ability to obtain high spatial resolution in all three dimensions with higher signal-to-noise ratio compared to two-dimensional methods at the same resolution. In addition, the four-dimensional nature of the data offers a variety of image processing options, such as magnitude and velocity multi-planar reformation, three-directional vector field plots, and velocity profiles mapped onto selected planes of interest.

  View details for DOI 10.1002/jmri.10272

  View details for Web of Science ID 000182453200016

  View details for PubMedID 12655592

• Rapid MR imaging of articular cartilage with steady-state free precession and multipoint fat-water separation. AJR. American journal of roentgenology Reeder, S. B., Pelc, N. J., Alley, M. T., Gold, G. E. 2003; 180 (2): 357-362

  Abstract

  To obtain high-quality high-resolution images of articular cartilage with reduced imaging time, we combined a novel technique of generalized multipoint fat-water separation with three-dimensional (3D) steady-state free precession (SSFP) imaging.The cartilage of 10 knees in five healthy volunteers was imaged with 3D SSFP imaging and a multipoint fat-water separation method capable of separating fat and water with short TE increments. Fat-saturated 3D spoiled gradient-echo (SPGR) images were obtained for comparison.High-quality images of the knee with excellent fat-water separation were obtained with 3D SSFP imaging. Total imaging time required was 58% less than that required for 3D SPGR imaging with a comparable cartilage signal-to-noise ratio and spatial resolution. Unlike 3D SPGR images, 3D SSFP images exhibited bright synovial fluid, providing a potential arthrographic effect.High-quality high-resolution images of articular cartilage with improved fat-water separation, bright synovial fluid, and markedly reduced acquisition times can be obtained with 3D SSFP imaging combined with a fat-water separation technique.

  View details for PubMedID 12540434

• Rapid imaging cartilage with precession and of articular steady-state free multipoint fat water separation AMERICAN JOURNAL OF ROENTGENOLOGY Reeder, S. B., Pelc, N. J., Alley, M. T., Gold, G. E. 2003; 180 (2): 357-362

  Abstract

  To obtain high-quality high-resolution images of articular cartilage with reduced imaging time, we combined a novel technique of generalized multipoint fat-water separation with three-dimensional (3D) steady-state free precession (SSFP) imaging.The cartilage of 10 knees in five healthy volunteers was imaged with 3D SSFP imaging and a multipoint fat-water separation method capable of separating fat and water with short TE increments. Fat-saturated 3D spoiled gradient-echo (SPGR) images were obtained for comparison.High-quality images of the knee with excellent fat-water separation were obtained with 3D SSFP imaging. Total imaging time required was 58% less than that required for 3D SPGR imaging with a comparable cartilage signal-to-noise ratio and spatial resolution. Unlike 3D SPGR images, 3D SSFP images exhibited bright synovial fluid, providing a potential arthrographic effect.High-quality high-resolution images of articular cartilage with improved fat-water separation, bright synovial fluid, and markedly reduced acquisition times can be obtained with 3D SSFP imaging combined with a fat-water separation technique.

  View details for Web of Science ID 000180753200014

• A Novel Technique for Velocity Encoding by Gradient Inversion Magn. Res. Med Markl, M., Alley, M., T., Pelc., N., J. 2003; 49: 945-952
• Three-dimensional reconstruction algorithm for a reverse geometry volumetric CT system with a large array scanned source Medical Imaging 2003 Conference Gilat, T., Fahrig, R., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2003: 103–111

  View details for Web of Science ID 000184199600010

• X-ray tube in parallel magnetic fields Medical Imaging 2003 Conference Wen, Z. F., Fahrig, R., Pelc, N. J. SPIE-INT SOC OPTICAL ENGINEERING. 2003: 972–979

  View details for Web of Science ID 000184199600100

• Lithographic flare measurements of EUV full-field projection optics Conference on Emerging Lithographic Technologies VII Lee, S. H., Naulleau, P., KRAUTSCHIK, C., Chandhok, M., Chapmad, H. N., O'Connell, D. J., Goldstein, M. SPIE-INT SOC OPTICAL ENGINEERING. 2003: 103–111

  View details for Web of Science ID 000184179100011

• A 3D Reconstruction Algorithm for an Inverse Geometry Volumetric CT System with a Large Array Scanned Source Gilat, T., Fahrig, R., Pelc, N., J. 2003
• Multi-Coil “Dixon” Fat-Water Separation with SSFP Imaging Reeder, S., B., Wen, Z., Gold, G., E., Pelc, N., J. 2003
• Investigating UNFOLD with Factors Greater Than 2 Lew, C., Chan, F., P., Pelc, N., J. 2003
• Three-dimensional reconstruction algorithm for a reverse geometry volumetric CT system with a large array scanned source. Gilat, T., Fahrig, R., Pelc, N., J. 2003
• Generalized Modeling of Gradient Field Non-Linearities and Reconstruction of Phase Contrast MRI Measurements Markl, M., Bammer, R., Alley, M., T., Moseley, M., E., Glover, G., H., Pelc, N., J. 2003
• X-ray tube in parallel magnetic fields. Wen, Z., Fahrig, R., Pelc, N., J. 2003
• Hybrid x-ray/MR system and other hybrid imaging modalities. Pelc, N., J. 2003
• Technical Development: First use of a truly-hybrid X-ray/MR imaging system for guidance of brain biopsy. Acta Neurochir (Wien) Fahrig, R., Heit, G., Wen, Z., Daniel, B., L., Butts, K., Pelc, N., J. 2003; 145: 995-997
• Noise Performance Study of Symmetric Three Point Dixon Method Wen, Z., Reeder, S., B., Pineda, A., R., Glover, G., H., Pelc, N., J. 2003
• Multi-Point "Dixon" Fat-Water Separation with Steady-State Free Precession at 3T: Application to Musculoskeletal Imaging Reeder, S. R., Shimakawa, A., Brittain, J., Yu, H., Pelc, N., J., Gold, G. 2003
• Application of Cine Phase Contrast Magnetic Resonance Imaging and SPAMM-Tagging for Assessment of Endoleaks and Aneurysm Sac Motion Hellinger, J., Draney, M., Markl, M., Pelc, N., J., Herfkens, R. J. 2003
• Initial Clinical Experience using a Truly Hybrid X-ray/MR Imaging System Fahrig, R., Wen, Z., Daniel, B., L., Butts, K., Kee, S., T., Heit, G., Pelc, N. J. 2003
• Imaging of Articular Cartilage at 3T with Multi-Point “Dixon” Fat-Water Separation and SSFP Reeder, S., B., Brittain, J., H., Shimakawa, A., Wen, Z., Gold, G., E., Pelc, N., J. 2003
• Fast tomosynthesis for lung cancer detection using the SBDX geometry. Fahrig, R., Pineda, A., R., Solomon, E., G., Leung, A., N., Pelc, N., J. 2003
• Combined Evaluation of Ventricular Wall Motion and Delayed Myocardial Enhancement Using a 3D-CINE Technique Chan, F., P., Levin, J., M., Alley, M., T., Herfkens, R., J., Pelc, N., J. 2003
• Artifacts Caused by Transient Effects in Multi-Shot EPI Lew, C., Pelc, N., J. 2003
• A Method for MR Eddy Current Characterization and Compensation Alley, M., T., Pineda, A., R., Bammer, R., Markl, M., Pelc, N., J. 2003
• X-ray Image Quality Assessment in X-ray/MR Hybrid System. RSNA '03 Ganguly, A., Fahrig, R., Wen, Z., Pelc, N., J. 2003: 391
• Magnetic Resonance Velocimetry for Mean Velocity Measurements in Complex Turbulent Flows. Experiments in Fluids Elkins, C., J, Markl, M., Pelc, N., J., Eaton, J., K. 2003; 34: 494–503
• Generalized reconstruction of phase contrast MRI: Analysis and correction of the effect of gradient field distortions. Mag Reson Med Markl, M., Bammer, R., Alley, M., T., Elkins, C., J., Draney, M., T., Barnett, A., Pelc, N. J. 2003; 50: 791-801
• Multi-point "Dixon" fat-water separation and steady-state free precession 88th Scientific Assembly and Annual Meeting of the Radiological-Society-of-North-America Reeder, S. B., Wen, Z., Gold, G. E., Alley, M. T., Markl, M., Pelc, N. J. RADIOLOGICAL SOC NORTH AMERICA. 2002: 313–313

  View details for Web of Science ID 000178825100793

• Integrated-modality imaging: The best of both worlds ACADEMIC RADIOLOGY von Schulthess, G. K., Pec, N. J. 2002; 9 (11): 1241–44

  View details for DOI 10.1016/S1076-6332(03)80556-1

  View details for Web of Science ID 000179023000001

  View details for PubMedID 12449355

• Development of a hybrid X-ray/MR system for interventional guidance: Verification of x-ray tube behavior in large magnetic fields produces surprising results 88th Scientific Assembly and Annual Meeting of the Radiological-Society-of-North-America Fahrig, R., Wen, Z., Nelson, W. R., Pelc, N. J. RADIOLOGICAL SOC NORTH AMERICA. 2002: 545–545

  View details for Web of Science ID 000178825101689

• Quantification of vessel wall cyclic strain using cine phase contrast magnetic resonance imaging ANNALS OF BIOMEDICAL ENGINEERING Draney, M. T., Herfkens, R. J., Hughes, T. J., Pelc, N. J., Wedding, K. L., Zarins, C. K., Taylor, C. A. 2002; 30 (8): 1033-1045

  Abstract

  In vivo quantification of vessel wall cyclic strain has important applications in physiology and disease research and the design of intravascular devices. We describe a method to calculate vessel wall strain from cine PC-MRI velocity data. Forward-backward time integration is used to calculate displacement fields from the velocities, and cyclic Green-Lagrange strain is computed in segments defined by the displacements. The method was validated using a combination of in vitro cine PC-MRI and marker tracking studies. Phantom experiments demonstrated that wall displacements and strain could be calculated accurately from PC-MRI velocity data, with a mean displacement difference of 0.20 +/- 0.16 mm (pixel size 0.39 mm) and a mean strain difference of 0.01 (strain extent 0.20). A propagation of error analysis defined the relationship between the standard deviations in displacements and strain based on original segment length and strain magnitude. Based on the measured displacement standard deviation, strain standard deviations were calculated to be 0.015 (validation segment length) and 0.045 (typical segment length). To verify the feasibility of using this method in vivo, cyclic strain was calculated in the thoracic aorta of a normal human subject. Results demonstrated nonuniform deformation and circumferential variation in cyclic strain, with a peak average strain of 0.08 +/- 0.11.

  View details for DOI 10.1114/1.1513566

  View details for Web of Science ID 000179121200005

  View details for PubMedID 12449764

• In vivo validation of numerical prediction of blood flow in arterial bypass grafts ANNALS OF BIOMEDICAL ENGINEERING Ku, J. P., Draney, M. T., Arko, F. R., Lee, W. A., Chan, F. P., Pelc, N. J., Zarins, C. K., Taylor, C. A. 2002; 30 (6): 743-752

  Abstract

  In planning operations for patients with cardiovascular disease, vascular surgeons rely on their training, past experiences with patients with similar conditions, and diagnostic imaging data. However, variability in patient anatomy and physiology makes it difficult to quantitatively predict the surgical outcome for a specific patient a priori. We have developed a simulation-based medical planning system that utilizes three-dimensional finite-element analysis methods and patient-specific anatomic and physiologic information to predict changes in blood flow resulting from surgical bypass procedures. In order to apply these computational methods, they must be validated against direct experimental measurements. In this study, we compared in vivo flow measurements obtained using magnetic resonance imaging techniques to calculated flow values predicted using our analysis methods in thoraco-thoraco aortic bypass procedures in eight pigs. Predicted average flow rates and flow rate waveforms were compared for two locations. The predicted and measured waveforms had similar shapes and amplitudes, while flow distribution predictions were within 10.6% of the experimental data. The average absolute difference in the bypass-to-inlet blood flow ratio was 5.4 +/- 2.8%. For the aorta-to-inlet blood flow ratio, the average absolute difference was 6.0 +/- 3.3%.

  View details for DOI 10.1114/1.1496086

  View details for Web of Science ID 000177640900001

  View details for PubMedID 12220075

• New approach to 3D time-resolved angiography MAGNETIC RESONANCE IN MEDICINE Madore, B., Pelc, N. J. 2002; 47 (5): 1022-1025

  Abstract

  TRICKS is an acquisition and reconstruction method capable of generating 3D time-resolved angiograms. Arguably, the main problem with TRICKS is the way it handles the outer regions of the k-space matrix, leading to artifacts at the edges of blood vessels. An alternative to the data- processing stage of TRICKS, designed to better represent edges and small vessels, is presented here. A weakness of the new approach is an increased sensitivity to motion compared to TRICKS. Since this method can use the same data as TRICKS, a hybrid reconstruction method could conceivably be developed where the advantages of both approaches are combined. Magn Reson Med 47:1022-1025, 2002.

  View details for DOI 10.1002/mrm.10151

  View details for Web of Science ID 000175346100025

  View details for PubMedID 11979584

• Measurement of vessel wall strain using cine phase contrast MRI 9th Annual Meeting of the ISMRM Wedding, K. L., Draney, M. T., Herfkens, R. J., Zarins, C. K., Taylor, C. A., Pelc, N. J. JOHN WILEY & SONS INC. 2002: 418–28

  Abstract

  To determine the feasibility of using magnetic resonance imaging (MRI) to non-invasively measure strain in the aortic wall.Cine phase contrast MRI was used to measure the velocity of the aortic wall and calculate changes in circumferential strain over the cardiac cycle. A deformable vessel phantom was used for initial testing and in vitro validation. Ultrasonic sonomicrometer crystals were attached to the vessel wall and used as a gold standard.In the in vitro validation, MRI-calculated wall displacements were within 0.02 mm of the sonomicrometer measurements when maximal displacement was 0.28 mm. The measured maximum strain in vitro was 0.02. The in vivo results were on the same order as prior results using ultrasound echo-tracking.Results of in vivo studies and measurement of cyclic strain in human thoracic and abdominal aortas demonstrate the feasibility of the technique.

  View details for DOI 10.1002/jmri.10077

  View details for Web of Science ID 000174759700008

  View details for PubMedID 11948831

• Noninvasive measurement of extraction fraction and single-kidney glomerular filtration rate with MR imaging in swine with surgically created renal artery stenoses RADIOLOGY Coulam, C. H., Lee, J. H., Wedding, K. L., Spielman, D. M., Pelc, N. J., Kee, S. T., Hill, B. B., Bouley, D. M., Derby, G. C., Myers, B. D., Sawyer-Glover, A. M., Sommer, F. G. 2002; 223 (1): 76-82

  Abstract

  To test whether magnetic resonance (MR) imaging enables accurate measurement of extraction fraction (EF) in swine with unilateral renal ischemia and to evaluate effects of renal arterial stenosis on EF and single-kidney glomerular filtration rate.High-grade unilateral renal arterial stenoses were surgically created in eight pigs. Direct measurements of renal venous and arterial inulin concentration provided reference standard estimates of single-kidney EF. Pigs were imaged with a 1.5-T imager to estimate EF, renal blood flow, and glomerular filtration rate. A breath-hold inversion-recovery spiral sequence was used to measure T1 of blood in the infrarenal inferior vena cava and renal veins after intravenous administration of gadopentetate dimeglumine, and these data were used to calculate EF. Cine-phase contrast material-enhanced imaging of the renal arteries provided quantitative renal blood flow measurements. Bilateral single-kidney glomerular filtration rate was then determined: glomerular filtration rate = renal blood flow x (1 - hematocrit level) x EF.A statistically significant linear correlation was found between EF, as determined with MR imaging, and inulin (r = 0.77). As compared with kidneys without renal arterial stenosis, kidneys with renal arterial stenosis showed 50% (0.14/0.28) EF reduction (P <.01) and 59% glomerular filtration rate reduction (P <.01).MR imaging shows promise for in vivo measurement of EF and glomerular filtration rate, which may be useful in assessing the clinical importance of renal arterial stenosis.

  View details for DOI 10.1148/radiol.2231010420

  View details for PubMedID 11930050

• Rapid Cartilage Imaging with SSFP and Four-Point Dixon Techniques Reeder, S. B., Alley, M. T., Pelc, N. J., Gold, G. E. 2002
• Improved image reconstruction from sensitivity-encoded data by wavelet denoising and Tikhonov regularization IEEE International Symposium on Biomedical Imaging Liang, Z. P., Bammer, R., Ji, J., Pelc, N. J., Glover, G. H. IEEE. 2002: 493–496

  View details for Web of Science ID 000178000400124

• X-ray tube for Use in Magnetic Fields Wen, Z., Fahrig, R., Wang, N. S., Pelc, N. J. 2002
• Recovery of Signal Acquired through UNFOLD with Slice Interleaving Lew, C., Chan, F. P., Alley, M. T., Pelc, N. J. 2002
• Four point Dixon fat-water separation and steady-state free precession. Radiology 255(P) Reeder, S., B., Wen, Z., Gold, G., E., Alley, M. T., Markl, M., Pelc, N., J. 2002: 313
• Integrated-modality imaging: the best of both worlds. Acad. Radiol. von Schultess, G., K., Pelc, N., J. 2002; 9: 1241-4
• Making Better SENSE: Wavelet Denoising, Tikhonov Regularization, and Total Least Squares Liang, Z. P., Bammer, R., Ji, J., Pelc, N., J., Glover, G. H. 2002
• Analysis and Correction of the Effect of Spatial Gradient Field Distortions on Velocity Measurements with Phase Contrast MRI Markl, M., Draney, M. T., Pelc, N. J. 2002
• Volumetric CT with a large array scanned source. Radiology 255(P) Gilat, T., Fahrig, R., Pelc, N. J. 2002: 404
• Improved image reconstruction from sensitivity-encoded data by wavelet denoising and Tikhonov regularization. In IEEE EMBS Summer School Book Series Liang, Z. P., R, R. B., Ji, J., Pelc, N. J., Glover, G. H. edited by M, A. IEEE Press and John Wiley & Sons, Somerset, NJ. 2002: 493–496
• Time Resolved 3D Phase-Contrast MRI (4D Flow): Assessment of Three Directional Velocity Vector Fields Markl, M., Chan, F. P., Alley, M. T., Wedding, K. L., Draney, M. T., Elkins, C., Pelc, N. J. 2002
• In Vivo Quantification of Porcine Aortic Wall Motion Using Cine PC-MRI Draney, M. T., Arko, F. R., Alley, M. T., Markl, M., Herfkens, R. J., Pelc, N. J. 2002
• Dynamic Breast Cancer Imaging with High Spatiotemporal Resolution by Reduced-Encoding Stables, L. A., Glover, G. H., Pelc, N. J., Liang, Z. P. 2002
• Clinical Assessment and Applications of 4D-Flow Imaging Chan, F. P., Markl, M., Alley, M. T., Daniel, B. L., Herfkens, R. J., Pelc, N. J. 2002
• Assessment of Gradient Field Distortion in Diffusion-Weighted Imaging Bammer, R., Markl, M., Pelc, N. J., Moseley, M. E. 2002
• Development of a hybrid x-ray/MR system for interventional guidance: verification of x-ray tube behavior in large magnetic fields produces surprising results. Radiology 255(P) Fahrig, R., Wen, Z., Nelson, W., R., Pelc, N., J. 2002: 545
• Balanced SSFP and myocardial tagging for improved tag-tissue contrast and SNR. Radiology 255(P) Markl, M., Reeder, S., B., Alley, M., T., Herfkens, R. J., Pelc, N., J. 2002: 539
• Improved Image Reconstruction from Sensitivity-Encoded Data by Wavelet Denoising and Tikhonov Regularization. Liang, Z. P., Bammer, R., Ji, J., Pelc, N., J., Glover, G. H. 2002
• Velocity Encoding in the Steady State: Combining Phase Contrast MRI and Balanced Steady State Free Precession (PC-SSFP) Markl, M., Alley, M. T., Pelc, N., J. 2002
• Water and Fat SSFP Imaging with Four-Point Dixon Techniques Reeder, S. B., Alley, M. T., Pelc, N. J. 2002
• Truly hybrid interventional MR/x-ray system: Investigation of in vivo applications ACADEMIC RADIOLOGY Fahrig, R., Butts, K., Wen, Z. F., Saunders, R., Kee, S. T., Sze, D. Y., Daniel, B. L., Laerum, F., Pelc, N. J. 2001; 8 (12): 1200-1207

  Abstract

  The purpose of this study was to provide in vivo demonstrations of the functionality of a truly hybrid interventional x-ray/magnetic resonance (MR) system.A digital flat-panel x-ray system (1,024(2) array of 200 microm pixels, 30 frames per second) was integrated into an interventional 0.5-T magnet. The hybrid system is capable of MR and x-ray imaging of the same field of view without patient movement. Two intravascular procedures were performed in a 22-kg porcine model: placement of a transjugular intrahepatic portosystemic shunt (TIPS) (x-ray-guided catheterization of the hepatic vein, MR fluoroscopy-guided portal puncture, and x-ray-guided stent placement) and mock chemoembolization (x-ray-guided subselective catheterization of a renal artery branch and MR evaluation of perfused volume).The resolution and frame rate of the x-ray fluoroscopy images were sufficient to visualize and place devices, including nitinol guidewires (0.016-0.035-inch diameter) and stents and a 2.3-F catheter. Fifth-order branches of the renal artery could be seen. The quality of both real-time (3.5 frames per second) and standard MR images was not affected by the x-ray system. During MR-guided TIPS placement, the trocar and the portal vein could be easily visualized, allowing successful puncture from hepatic to portal vein.Switching back and forth between x-ray and MR imaging modalities without requiring movement of the patient was demonstrated. The integrated nature of the system could be especially beneficial when x-ray and MR image guidance are used iteratively.

  View details for Web of Science ID 000172759200002

  View details for PubMedID 11770916

• Effects of forced diving on the spleen and hepatic sinus in northern elephant seal pups PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Thornton, S. J., Speilman, D. M., Pelc, N. J., Block, W. F., Crocker, D. E., Costa, D. P., LeBoeuf, B. J., Hochachka, P. W. 2001; 98 (16): 9413-9418

  Abstract

  In phocid seals, an increase in hematocrit (Hct) accompanies diving and periods of apnea. The variability of phocid Hct suggests that the total red cell mass is not always in circulation, leading researchers to speculate on the means of blood volume partitioning. The histology and disproportionate size of the phocid spleen implicates it as the likely site for RBC storage. We used magnetic resonance imaging on Northern elephant seals to demonstrate a rapid contraction of the spleen and a simultaneous filling of the hepatic sinus during forced dives (P < 0.0001, R(2) = 0.97). The resulting images are clear evidence demonstrating a functional relationship between the spleen and hepatic sinus. The transfer of blood from the spleen to the sinus provides an explanation for the disparity between the timing of diving-induced splenic contraction ( approximately 1-3 min) and the occurrence of peak Hct (15-25 min). Facial immersion was accompanied by an immediate and profound splenic contraction, with no further significant decrease in splenic volume after min 2 (Tukey-Kramer HSD, P = 0.05). At the conclusion of the dive, the spleen had contracted to 16% of its predive volume (mean resting splenic volume = 3,141 ml +/- 68.01 ml; 3.54% of body mass). In the postdive period, the spleen required 18-22 min to achieve resting volume, indicating that this species may not have sufficient time to refill the spleen when routinely diving at sea, which is virtually continuous with interdive surface intervals between 1 and 3 min.

  View details for Web of Science ID 000170216900090

  View details for PubMedID 11481497

  View details for PubMedCentralID PMC55435

• Alignment of a volumetric tomography system MEDICAL PHYSICS Stevens, G. M., Saunders, R., Pelc, N. J. 2001; 28 (7): 1472-1481

  Abstract

  A test-bed system has been developed for imaging phantoms with tomosynthesis and volumetric computed tomography. This system incorporates an amorphous silicon flat panel detector on a movable gantry and a computer-controlled rotational positioning stage. In this paper, an analysis of the sensitivity of reconstructed images to geometrical misalignment is presented. Application of this method to circular digital tomosynthesis is examined, with spatial resolution in the focal plane as the criterion for evaluating the effect of misalignment. A software-based method is presented for correcting data for imperfect system alignment prior to image reconstruction. Experimental results yield reconstructed images with spatial resolution approaching the theoretical limit based on detector pixel size and accounting for data interpolation.

  View details for Web of Science ID 000169991000021

  View details for PubMedID 11488581

• SMASH and SENSE: Experimental and numerical comparisons MAGNETIC RESONANCE IN MEDICINE Madore, B., Pelc, N. J. 2001; 45 (6): 1103-1111

  Abstract

  Three parallel-imaging methods were implemented and compared in terms of artifact and noise content: original SMASH, Cartesian SENSE, and an extremely simple method called here the "scissors method." These methods represent very different approaches to the parallel-imaging problem. The experimental and numerical comparisons presented here aim at shedding light on the whole spectrum of parallel-imaging methods, not just the three methods actually implemented. In our results, SMASH images had an artifact level significantly higher than SENSE images for all acceleration factors. The SNR in SENSE images was nearly optimal at low acceleration factors. As acceleration was increased, the noise content in SENSE images eventually sharply departed from optimal values, while the artifact content remained low.

  View details for Web of Science ID 000168878900021

  View details for PubMedID 11378889

• Filtered backprojection for modifying the impulse response of circular tomosynthesis MEDICAL PHYSICS Stevens, G. M., Fahrig, R., Pelc, N. J. 2001; 28 (3): 372-380

  Abstract

  A filtering technique has been developed to modify the three-dimensional impulse response of circular motion tomosynthesis to allow the generation of images whose appearance is like those of some other imaging geometries. In particular, this technique can reconstruct images with a blurring function which is more homogeneous for off-focal plane objects than that from circular tomosynthesis. In this paper, we describe the filtering process, and demonstrate the ability to alter the impulse response in circular motion tomosynthesis from a ring to a disk. This filtering may be desirable because the blurred out-of-plane objects appear less structured.

  View details for Web of Science ID 000167593100012

  View details for PubMedID 11318319

• A truly hybrid interventional MR/X-ray system: Feasibility demonstration 8th Annual Meeting of the ISMRM Fahrig, R., Butts, K., Rowlands, J. A., Saunders, R., Stanton, J., Stevens, G. M., Daniel, B. L., Wen, Z. F., Ergun, D. L., Pelc, N. J. JOHN WILEY & SONS INC. 2001: 294–300

  Abstract

  A system enabling both x-ray fluoroscopy and MRI in a single exam, without requiring patient repositioning, would be a powerful tool for image-guided interventions. We studied the technical issues related to acquisition of x-ray images inside an open MRI system (GE Signa SP). The system includes a flat-panel x-ray detector (GE Medical Systems) placed under the patient bed, a fixed-anode x-ray tube overhead with the anode-cathode axis aligned with the main magnetic field and a high-frequency x-ray generator (Lunar Corp.). New challenges investigated related to: 1) deflection and defocusing of the electron beam of the x-ray tube; 2) proper functioning of the flat panel; 3) effects on B0 field homogeneity; and 4) additional RF noise in the MR images. We have acquired high-quality x-ray and MR images without repositioning the object using our hybrid system, which demonstrates the feasibility of this new configuration. Further work is required to ensure that the highest possible image quality is achieved with both MR and x-ray modalities.

  View details for Web of Science ID 000171295900018

  View details for PubMedID 11169837

• Filtered backprojection for modifying the impulse response of circular tomosynthesis. Medical Physics Stevens, G., M., Fahrig, R., Pelc, N., J. 2001; 28: 372-380
• Phase contrast measurements of aortic wall strain in vivo. Wedding, K. L., Draney, M. T., Herfkens, R. J., Zarins, C. K., Taylor, C. A., Pelc, N. J. 2001
• Left ventricular function measurement and visualization of endocardium using noncontrast-enhanced cardiac cine SSFP imaging. Chan, F. P., Alley, M. T., Coulam, C., Shimakawa, A., Wedding, K. L., Pelc, N. J. 2001
• Fundamentals of flow and motion. In Magnetic Resonance Imaging of the Brain and Spine Pelc, N., J., Alley, M., T., Listerud, J., Atlas, S., W. edited by Atlas, S., W. Lippincott Williams and Wilkins, Philadelphia. 2001; Third Edition: 101–125
• Sampling strategies for flow quantification with phase contrast MRI Markl, M. 2001
• Investigation of electron trajectories of an x-ray tube in a magnetic field. Wen, Z., Fahrig, R., Pelc, N. J. 2001
• Calculation of Time-Dependent Vessel Strain from Cine Phase Contrast Magnetic Resonance Imaging Data. Draney, M. T., Pelc, N. J., Zarins, C. K., Taylor, C. A. 2001
• A truly hybrid x-ray/MR system for guidance of minimally invasive procedures: In vivo validation. Fahrig, R., Butts, K., Wen, Z., Saunders, R., Kee, S., Pelc, N. J. 2001
• Myocardial Spatiotemporal Tracking. In Measurement of Cardiac Deformations from MRI: Physical and Mathematical Models Zhu, Y., Pelc, N., J. edited by Amini, A., A., Prince, J., L. Kluwer Academic Publishers, Dordrecht, the Netherlands. 2001: 257–288
• Partial fat-saturated contrast-enhanced three-dimensional MR angiography compared with non-fat-saturated and conventional fat-saturated MR angiography RADIOLOGY Hilfiker, P. R., Herfkens, R. J., Heiss, S. G., Alley, M. T., Fleischmann, D., Pelc, N. J. 2000; 216 (1): 298-303

  Abstract

  Abdominal three-dimensional magnetic resonance angiography was performed in 35 patients in the equilibrium phase without fat saturation, with conventional fat saturation, and with fast partial fat saturation. Qualitative and quantitative evaluation demonstrated significantly better vessel visualization with both fat-saturated techniques. The partial fat-saturated technique provided water-specific images within a breath hold, reducing motion artifacts significantly.

  View details for Web of Science ID 000087829500044

  View details for PubMedID 10887265

• Depth-segmented detector for x-ray absorptiometry MEDICAL PHYSICS Stevens, G. M., Pelc, N. J. 2000; 27 (5): 1174-1184

  Abstract

  A new energy-dependent multi-cell detector, which is a generalization of the conventional front-back detector, was studied using computer simulations. The noise performance of the detector for bone quantitation was examined in comparison to an ideal energy discriminating detector, and front-back detectors with and without inter-detector filters. The front-back detectors were optimized for a reference object composed of water and bone, and then compared to the new detector over a range of object compositions. In this paper, precision in calculated bone thickness is used as the criterion for evaluating detector performance. Simulations show that the segmented detector always performs better than the front-back detector without an inter-detector filter. It outperforms the detector incorporating a filter by an amount that depends on the heterogeneity of the x-ray spectrum. In addition, for single component radiographic images, this multi-cell detector retains information which is lost in the front-back detector with a filter layer.

  View details for Web of Science ID 000087212200043

  View details for PubMedID 10841425

• A reduced field-of-view method to increase temporal resolution or reduce scan time in cine MRI MAGNETIC RESONANCE IN MEDICINE Madore, B., Fredrickson, J. O., Alley, M. T., Pelc, N. J. 2000; 43 (4): 549-558

  Abstract

  In some dynamic applications of MRI, only a part of the field-of-view (FOV) actually undergoes dynamic changes. A class of methods, called reduced-FOV (rFOV) methods, convert the knowledge that some part of the FOV is static or not very dynamic into an increase in temporal resolution for the dynamic part, or into a reduction in the scan time. Although cardiac imaging is an important example of an imaging situation where changes are concentrated in a fraction of the FOV, the rFOV methods developed up to now are not compatible with one of the most common cardiac sequences, the so-called retrospective cine method. The present work is a rFOV method designed to be compatible with cine imaging. An increase by a factor n in temporal resolution or a decrease by n in scan time is obtained in the case where only one nth of the FOV is dynamic (the rest being considered static). Results are presented for both Cartesian and spiral imaging.

  View details for Web of Science ID 000086214400009

  View details for PubMedID 10748430

• Three-dimensional cardiac cine magnetic resonance imaging with an ultrasmall superparamagnetic iron oxide blood pool agent (NC100150) JOURNAL OF MAGNETIC RESONANCE IMAGING Amano, Y., Herfkens, R. J., Shifrin, R. Y., Alley, M. T., Pelc, N. J. 2000; 11 (2): 81-86

  Abstract

  The purpose of this study was to assess image quality of three-dimensional (3D) cardiac cine magnetic resonance (MR) imaging before and after administration of a T1-shortening ultrasmall superparamagnetic iron oxide blood pool agent (NC100150). 3D cardiac cine MR imaging was performed in 13 volunteers using a radiofrequency-spoiled cardiac-gated 3D cine gradient-echo sequence with short repetition and echo times. Compared with precontrast images, postcontrast images showed no enhancement in fat and skeletal muscle, moderate enhancement in myocardium, and significant enhancement in ventricular cavity. After contrast injection, the signal ratio of the ventricular chamber to the myocardium significantly increased, and dramatic improvements were seen in the quality of the cineangiographic images and the depiction of cardiac valves. This quantitative study has shown that 3D cardiac cine MR imaging using a blood pool agent provided MR ventriculography and cineangiography with excellent image quality.

  View details for Web of Science ID 000086078100002

  View details for PubMedID 10713938

• Filtered-Backprojection for Improved Blurring in Circular Tomosynthesis Radiology 217(P) Stevens, G. M., Fahrig, R., Pelc, N. J. 2000: 314
• On the feasibility of using the scanning-beam digital X-ray system (SBDX) for lung nodule screening 22nd Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society Fahrig, R., Stevens, G. M., Solomon, E. G., Pelc, N. J. IEEE. 2000: 1652–1655

  View details for Web of Science ID 000166896300456

• On the Feasibility of Integrating a Flat-Panel X-Ray Fluoroscopy System into an Open MRI System Fahrig, R., Butts, K., Rowlands, J. A., Saunders, R., Ergun, D. L., Stanton, J., Pelc, N. J. 2000
• Measurement of T1 of flowing blood, extraction fraction of Gd-DTPA and single-kidney GFR using interleaved spiral acquisition. Sommer, F. G., Alley, M. T., Kee, S. T., Coulam, C. H., Spielman, D. M., Fredrickson, J. O., Pelc, N. J. 2000
• SMASH vs SENSE Madore, B., Pelc, N. J. 2000
• A New Way to Perform 3D Time-Resolved Angiography Madore, B., Pelc, N. J. 2000
• A truly hybrid interventional MR/x-ray system: Feasibility demonstration. JMRI Fahrig, R., Butts, K., Rowlands, J., A., Saunders, R., Stanton, J., Stevens, G., M., Pelc, N. J. 2000; 13: 294-300
• On the Feasibility of Using the Scanning-Beam Digital X-Ray System (SBDX) for Lung Nodule Screening. Fahrig, R., Stevens, G. M., Solomon, E. G., Pelc, N. J. 2000
• Measurements of In Vivo Vessel Wall Motion and Strain with Cine Phase Contrast MRI Wedding, K. L., Draney, M. T., Herfkens, R. J., Zarins, C. K., Taylor, C. A., Pelc, N. J. 2000
• Integrating a Flat-Panel X-ray Fluoroscopy System into an Open MRI System: Technical Considerations Radiology 217(P) Fahrig, R., Rowlands, J. A., Pelc, N. J., Stanton, J. P., Saunders, R. F., Stevens, G. M. 2000: 348
• Unaliasing by Fourier-encoding the overlaps using the temporal dimension (UNFOLD), applied to cardiac imaging and fMRI MAGNETIC RESONANCE IN MEDICINE Madore, B., Glover, G. H., Pelc, N. J. 1999; 42 (5): 813-828

  Abstract

  In several applications, MRI is used to monitor the time behavior of the signal in an organ of interest; e.g., signal evolution because of physiological motion, activation, or contrast-agent accumulation. Dynamic applications involve acquiring data in a k-t space, which contains both temporal and spatial information. It is shown here that in some dynamic applications, the t axis of k-t space is not densely filled with information. A method is introduced that can transfer information from the k axes to the t axis, allowing a denser, smaller k-t space to be acquired, and leading to significant reductions in the acquisition time of the temporal frames. Results are presented for cardiac-triggered imaging and functional MRI (fMRI), and are compared with data obtained in a conventional way. The temporal resolution was increased by nearly a factor of two in the cardiac-triggered study, and by as much as a factor of eight in the fMRI study. This increase allowed the acquisition of fMRI activation maps, even when the acquisition time for a single full time frame was actually longer than the paradigm cycle period itself. The new method can be used to significantly reduce the acquisition time of the individual temporal frames in certain dynamic studies. This can be used, for example, to increase the temporal or spatial resolution, increase the spatial coverage, decrease the total imaging time, or alter sequence parameters e.g., repetition time (TR) and echo time (TE) and thereby alter contrast. Magn Reson Med 42:813-828, 1999.

  View details for Web of Science ID 000083447900001

  View details for PubMedID 10542340

• A spatiotemporal model of cyclic kinematics and its application to analyzing nonrigid motion with MR velocity images IEEE TRANSACTIONS ON MEDICAL IMAGING Zhu, Y. D., Pelc, N. J. 1999; 18 (7): 557-569

  Abstract

  We present a method (DMESH) for nonrigid cyclic motion analysis using a series of velocity images covering the cycle acquired, for example, from phase-contrast magnetic resonance imaging. The method is based on fitting a dynamic finite-element mesh model to velocity samples of an extended region, at all time frames. The model offers a flexible tradeoff between accuracy and reproducibility with controllable built-in spatiotemporal smoothing, which is determined by the fineness of the initially defined mesh and the richness of included Fourier harmonics. The method can further provide a prediction of the analysis reproducibility, along with the estimated motion and deformation quantities. Experiments have been conducted to validate the method and to verify the reproducibility prediction. Use of the method for motion analysis using displacement information (e.g., from magnetic resonance tagging) has also been explored.

  View details for Web of Science ID 000082713800001

  View details for PubMedID 10504090

• Fast 3D cardiac cine MR imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Alley, M. T., Napel, S., Amano, Y., Paik, D. S., Shifrin, R. Y., Shimakawa, A., Pelc, N. J., Herfkens, R. J. 1999; 9 (5): 751-755

  Abstract

  We describe a technique for three-dimensional cine MR imaging. By using short repetition times (TR) and interleaved slice encoding, volumetric cine data can be acquired throughout the cardiac cycle with a temporal resolution of approximately 80 msec. A T1-shortening agent is used to produce contrast between blood and myocardium. A comparison between the acquisition times of this and several other two-dimensional techniques is presented.

  View details for Web of Science ID 000083418000021

  View details for PubMedID 10331775

• Three-dimensional motion tracking with volumetric phase contrast MR velocity imaging JOURNAL OF MAGNETIC RESONANCE IMAGING Zhu, Y. D., Pelc, N. J. 1999; 9 (1): 111-118

  Abstract

  Motion tracking based on single-slice cine-phase contrast magnetic resonance imaging data has limitations. In the presence of nontrivial three-dimensional motion and deformation, volumetric data are necessary for accurate reconstruction of material point trajectories. A three-dimensional Fourier tracking method that uses volumetric data for motion tracking is presented. The method reconstructs a material point trajectory by computing its various harmonics. For any given temporal sampling rate, a frequency domain perspective of the tracking problem indicates that the method is accurate in estimating all reconstructible harmonics of a trajectory. The algorithm incorporates an intra-voxel linear spatial model into the integration to address potential tracking performance degradation due to possibly reduced spatial resolution, which may be most relevant in the slice direction (z) if the volumetric data are obtained as multiple two-dimensional slices. The tracking method was evaluated on computer-generated data sets that simulated various motion patterns. The method was also tested with two sets of in vitro data obtained using a phantom, one acquired as multiple two-dimensional slices and the other using a three-dimensional sequence capable of higher spatial resolution in the z direction. These studies demonstrated that the algorithm can achieve high sub-voxel tracking accuracy.

  View details for Web of Science ID 000080144300015

  View details for PubMedID 10030658

• Haemodynamics of the phocid spleen as determined by Magnetic Resonance Imaging (MRI). Comparative Biochemistry and Physiology Part A Molecular & Integrative Physiology Thornton, S. J., Block, W. F., Spielman, D. M., Crocker, D. E., Costa, D. P., Pelc, N. J. 1999; 124: S22
• Fast Fat Suppression for 3D Angiographic Imaging. Alley, M. T., Heiss, S. G., Pelc, N., J., Herfkens, R. J. 1999
• System Alignment for a Volumetric Tomography System Radiology 213(P) Stevens, G., M., Pelc, N., J. 1999; 320
• Measurement of Gd-DTPA Concentration in Flowing Blood. Fredrickson, J. O., Sommer, F. G., Pelc, N. J. 1999
• An In Vivo Method for Measuring Vessel Wall Motion and Cyclic Strain Using Magnetic Resonance Imaging. Draney, M. T., Wedding, K. L., Taylor, C. A., Pelc, N. J. 1999
• A Reduced FOV Method for Spiral Cine Cardiac MR Imaging Radiology 213(P) Madore, B., Fredrickson, J. O., Alley, M. T., Pelc, N. J. 1999; 136
• Vessel Wall Strain with Cine Phase Contrast MR Imaging Radiology 213(P) Wedding, K. L., Draney, M. T., Taylor, C. A., Pelc, N. J. 1999; 478
• UNFOLD used to Speed Up Cardiac Imaging and fMRI. Madore, B., Glover, G, H., Pelc., N, J. 1999
• Comparison of PC-MRI to Computational Simulations and Digital Particle Image Velocimetry. Wedding, K. L., Draney, M. T., Fredrickson, J. O., Taylor, C. A., Pelc, N. J. 1999
• 3D myocardial motion tracking with volumetric MR velocity imaging. JMRI Zhu, Y., Pelc, N., J. 1999; 9: 111-118
• A Reduced-FOV Method for CINE MRI. Madore, B., Alley, M. T., Fredrickson, J. O., Pelc, N. J. 1999
• In vitro verification of myocardial motion tracking from phase-contrast velocity data MAGNETIC RESONANCE IMAGING Drangova, M., Zhu, Y. D., Bowman, B., Pelc, N. J. 1998; 16 (8): 863-870

  Abstract

  The ability to track motion from cine phase-contrast (PC) magnetic resonance (MR) velocity measurements was investigated using an in vitro model. A computer-controlled deformable phantom was used for the characterization of the accuracy and precision of the forward-backward and the compensated Fourier integration techniques. Trajectory accuracy is limited by temporal resolution when the forward-backward technique is used. With this technique the extent of the calculated trajectories is underestimated by an amount related to the motion period and the sequence repetition time, because of the band-limiting caused in the cine interpolation step. When the compensated Fourier integration technique is used, trajectory accuracy is independent of temporal resolution and is better than 1 mm for excursions of less than 15 mm, which are comparable to those observed in the myocardium. Measurement precision is dominated by the artifact level in the phase-contrast images. If no artifacts are present precision is limited by the inherent signal-to-noise ratio of the images. In the presence of artifacts, similar in magnitude to those observed in vivo, the reproducibility of tracking a 2.2 x 2.2 mm2 region of interest is better than 0.5 mm. When the Fourier integration technique is used, the improved accuracy is accompanied by a reduction in precision. We verified that tracking three-dimensional (3D) motion from velocity measurements of a single slice can lead to underestimations of the trajectory if there is a through-plane component of the motion that is not truly represented by the measured velocities. This underestimation can be overcome if volumetric cine phase-contrast velocity data are acquired and full three-dimensional analysis is performed.

  View details for Web of Science ID 000076700900002

  View details for PubMedID 9814767

• Renal blood flow: Measurement in vivo with rapid spiral MR imaging RADIOLOGY Sommer, G., Corrigan, G., Fredrickson, J., Sawyer-Glover, A., Liao, J. R., Myers, B., Pelc, N. 1998; 208 (3): 729-734

  Abstract

  To assess the ability of three cine phase-contrast magnetic resonance (MR) imaging techniques to measure normal human renal blood flow (RBF) in vivo.Eighteen healthy volunteers were studied with three cine phase-contrast MR imaging techniques: breath-hold, segmented k-space, two-dimensional, Fourier transform technique (ie, time-resolved imaging with automatic data segmentation, or TRIADS); a breath-hold rapid spiral acquisition; and a non-breath-hold rapid spiral acquisition that allowed resolution of both cardiac and respiratory cycles. In each case, total arterial RBF and blood flow per unit of renal volume were calculated. For each subject, RBF was measured with a standard technique of p-aminohippuric acid (PAH)-clearance hematocrit on the same day as the MR imaging examination was performed.The range of agreement (2 standard deviations, or 95% confidence interval) between RBF measurements obtained with the PAH-clearance hematocrit technique and the various cine phase-contrast techniques varied from +/- 17.6% to +/- 26.5%. The best agreement was obtained with non-breath-hold rapid spiral data, by using data from the end-expiratory phase of respiration.Findings with cine phase-contrast MR imaging employing rapid spiral acquisition are in good agreement with measurements made with PAH-clearance hematocrit and give the promise of clinical measurements of RBF.

  View details for Web of Science ID 000075488200028

  View details for PubMedID 9722853

• Gradient characterization using a Fourier-transform technique MAGNETIC RESONANCE IN MEDICINE Alley, M. T., Glover, G. H., Pelc, N. J. 1998; 39 (4): 581-587

  Abstract

  This paper describes a technique for characterizing the gradient subsystem of a magnetic resonance (MR) system. The technique uses a Fourier-transform analysis to directly measure the k-space trajectory produced by an arbitrary gradient waveform. In addition, the method can be easily extended to multiple dimensions and can be adapted to measuring residual gradient effects such as eddy currents. Several examples of gradient waveform and eddy-current measurements are presented. Also, it is demonstrated how the eddy-current measurements can be parameterized with an impulse-response formalism for later use in system tuning. When compared to a peak-fitting analysis, this technique provides a more direct extraction of the k-space measurements, which reduces the possibility of analysis error. This approach also has several advantages as compared to the conventional eddy-current measurement technique, including the ability to measure very short time constant effects.

  View details for Web of Science ID 000072700900010

  View details for PubMedID 9543420

• Ultrafast contrast-enhanced three-dimensional MR angiography: State of the art 83rd Scientific Assembly and Annual Meeting of the Radiological-Society-of-North-America Alley, M. T., Shifrin, R. Y., Pelc, N. J., Herfkens, R. J. RADIOLOGICAL SOC NORTH AMERICA. 1998: 273–85

  Abstract

  Ultrafast breath-hold contrast material-enhanced magnetic resonance (MR) angiography can be performed with a flexible imaging sequence. With the current generation of high-speed imaging gradients, it is possible to achieve sequence repetition times of 4 msec or less. These repetition times make it possible to obtain high-resolution (512 x 512 x 64) images in under 30 seconds. Applications of this versatile technique include imaging of aortic dissection, thoracic and abdominal aortic aneurysm, pulmonary embolus, carotid stenosis, and peripheral vascular disease. The administration of contrast material must be tailored to the vascular anatomy under examination to avoid venous enhancement. The rapid data acquisition times can be used to image multiple temporal phases or multiple locations. With this technique and administration of a T1-shortening contrast agent, high-quality MR angiography can be routinely performed in a variety of vascular regions (eg, thoracic and abdominal aorta, pulmonary arteries, carotid arteries, lower extremities).

  View details for Web of Science ID 000072493100003

  View details for PubMedID 9536477

• Concomitant gradient terms in phase contrast MR: Analysis and correction MAGNETIC RESONANCE IN MEDICINE Bernstein, M. A., Zhou, X. H., Polzin, J. A., King, K. F., Ganin, A., Pelc, N. J., Glover, G. H. 1998; 39 (2): 300-308

  Abstract

  Whenever a linear gradient is activated, concomitant magnetic fields with non-linear spatial dependence result. This is a consequence of Maxwell's equations, i.e., within the imaging volume the magnetic field must have zero divergence, and has negligible curl. The concomitant, or Maxwell field has been described in the MRI literature for over 10 years. In this paper, we theoretically and experimentally show the existence of two additional lowest-order terms in the concomitant field, which we call cross-terms. The concomitant gradient cross-terms only arise when the longitudinal gradient Gz is simultaneously active with a transverse gradient (Gx or Gy). The effect of all of the concomitant gradient terms on phase contrast imaging is examined in detail. Several methods for reducing or eliminating phase errors arising from the concomitant magnetic field are described. The feasibility of a joint pulse sequence-reconstruction method, which requires no increase in minimum TE, is demonstrated. Since the lowest-order terms of the concomitant field are proportional to G2/B0, the importance of concomitant gradient terms is expected to increase given the current interest in systems with stronger gradients and/or weaker main magnetic fields.

  View details for Web of Science ID 000071665800017

  View details for PubMedID 9469714

• In-vitro comparative study by MRI and DPIV of flow through normal and thrombosed bileaflet aortic valve: Velocity and vorticity mapping and shear stress analysis Rambod, E., Gharib, M., Zarandi, M., Pelc, N., Sahn, D. J. ELSEVIER SCIENCE INC. 1998: 111A–111A

  View details for Web of Science ID 000071920600458

• Development of Volumetric Tomosynthesis and Tomography System. Radiology 209(P) Stevens, G. M., Saunders, R. F., Pelc, N. J. 1998: 280
• Outer Limits of Contrast-Enhanced MRA, Revisited. Pelc, N., J., Alley, M., T., Shifrin, R., Y., Herfkens, R., J. 1998
• Measurement of Renal Blood Flow in-vivo Using Rapid Spiral Acquisition. Radiology Sommer, F., G, Corrigan, G., Fredrickson, J., O, Sawyer-Glover, A., M., Liao, J. R., Meyers, B., Pelc, N. J. 1998; 208: 729-734
• Gradient characterization using a Fourier transform technique. Magn. Res. Med. Alley, M., T., Glover, G., H., Pelc, N., J. 1998; 39: 581-587
• Contrast Enhanced 4D Phase Contrast Imaging. Fredrickson, J., O., Alley, M., T., Moseley, M., E., Herfkens, R., J., Pelc, N., J. 1998
• A Lagrangian Strain Approach to Velocity-Based Quantification of Myocardial Function and Tissue Deformation. Zhu, Y., Herfkens, R. J., Pappas, G., Drace, J. E., Pelc, N., J. 1998
• 3D Cine Cardiac Ventriculography with a Iron Oxide Blood Pool Agent. Alley, M., T., Amano, Y., Shifrin, R. Y., Pelc, N., J., Herfkens, R. J. 1998
• Estimation of deformation gradient and strain from cine-PC velocity data IEEE TRANSACTIONS ON MEDICAL IMAGING Zhu, Y. D., Drangova, M., Pelc, N. J. 1997; 16 (6): 840-851

  Abstract

  Phase contrast magnetic resonance imaging (MRI) can provide in vivo myocardial velocity field measurements. These data allow densely spaced material points to be tracked throughout the whole heart cycle using, for example, the Fourier tracking algorithm. To process the tracking results for myocardial deformation and strain quantification, we developed a method that is based on fitting the tracking results to an appropriate local deformation model. We further analyzed the accuracy and precision of the method and provided performance predictions for several local models. In order to validate the method and the theoretical performance analysis, we conducted controlled computer simulations and a phantom study. The results agreed well with expectations. Human heart data were also acquired and analyzed, and provided encouraging results. At the signal-to-noise ratio (SNR) level and spatial resolution expected in clinical settings, the study predicts strain quantification accuracy and precision that may allow the technique to become a practical and powerful noninvasive approach for the study of cardiac function, although clinically acceptable data acquisition strategies for three-dimensional (3-D) data are still a challenge.

  View details for Web of Science ID 000072458500014

  View details for PubMedID 9533584

• MRI using piecewise-linear spiral trajectory MAGNETIC RESONANCE IN MEDICINE Liao, J. R., Pauly, J. M., Pelc, N. J. 1997; 38 (2): 246-252

  Abstract

  A new generation of high power gradient systems which allow much faster MR imaging as well as shorter echo times has recently become available. Some of these high-speed gradient systems impose limits on the percentage of time during which the gradient can change in amplitude (slewing duty cycle). While this limitation may be immaterial to many 2DFT and echo planar imaging methods, a traditional circular spiral trajectory is difficult to use on these systems because its gradient waveforms change during the entire course of the trajectory so that the slewing duty cycle during the readout period is 100%. We describe a piecewise-linear spiral trajectory which is composed of linear segments and rounded corners. This trajectory reduces the slewing duty cycle while maintaining the desirable imaging properties of circular spirals including interleaving by simple gradient rotation. For one representative example, the slewing duty cycle is reduced to 46%. A conventional gridding method was used for image reconstruction, but a new numerical algorithm to calculate the density compensation factor was required. Use of piecewise-linear spiral trajectories reduces the impact imposed by limited gradient slewing duty cycle.

  View details for Web of Science ID A1997XN62100012

  View details for PubMedID 9256104

• Effect of artifacts due to flowing blood on the reproducibility of phase-contrast measurements of myocardial motion JOURNAL OF MAGNETIC RESONANCE IMAGING Drangova, M., Zhu, Y. D., Pelc, N. J. 1997; 7 (4): 664-668

  Abstract

  The reproducibility of myocardial motion trajectories calculated from cine phase-contrast (PC) velocity data is reduced by artifacts due to the inconsistent motion of intracardiac blood. Spatial presaturation reduces these artifacts but requires a longer sequence TR, with a potentially negative effect on trajectory accuracy and reproducibility. We investigated the effect of spatial presaturation on trajectory reproducibility. A mid-ventricular transaxial slice was imaged in five normal volunteers. The same slice was imaged three times each with sequences using spatial presaturation or not. Because the most serious artifacts originate in the heart chambers and propagate in the phase-encoded direction, myocardial regions that were in line with the heart chambers (in the phase-encode direction) had the highest artifact level in the scans without spatial presaturation. The reproducibility of trajectories for regions placed in these areas (the anterior wall, septum and posterior wall in the transaxial scans with phase encoding in the anterior-posterior direction) improved by a factor of two when presaturation was used (P < .001). In areas that were not in line with the heart chambers (eg, the anterior aspect of the lateral wall in the transaxial scans), the effect of presaturation was not significant. These results correlate well with the measured reduction in artifact level. The reproducibility of myocardial motion trajectories over large areas of the heart is improved to approximately 1 mm when presaturation is used. Therefore, use of presaturation is recommended for myocardial motion studies using cine PC velocity data.

  View details for Web of Science ID A1997XL78100008

  View details for PubMedID 9243385

• Reduction of motion artifacts in cine MRI using variable-density spiral trajectories MAGNETIC RESONANCE IN MEDICINE Liao, J. R., Pauly, J. M., Brosnan, T. J., Pelc, N. J. 1997; 37 (4): 569-575

  Abstract

  Dynamic cardiac imaging in MRI is a very challenging task. To obtain high spatial resolution, temporal resolution, and signal-to-noise ratio (SNR), single-shot imaging is not sufficient. Use of multishot techniques resolves this problem but can cause motion artifacts because of data inconsistencies between views. Motion artifacts can be reduced by signal averaging at some cost in increased scan time. However, for the same increase in scan time, other techniques can be more effective than simple averaging in reducing the artifacts. If most of the energy of the inconsistencies is limited to a certain region of kappa-space, increased sampling density (oversampling) in this region can be especially effective in reducing motion artifacts. In this work, several variable-density spiral trajectories are designed and tested. Their efficiencies for artifact reduction are evaluated in computer simulations and in scans of normal volunteers. The SNR compromise of these trajectories is also investigated. The authors conclude that variable-density spiral trajectories can effectively reduce motion artifacts with a small loss in SNR as compared with a uniform density counterpart.

  View details for Web of Science ID A1997WQ66700013

  View details for PubMedID 9094079

• Angiographic imaging with 2D RF pulses MAGNETIC RESONANCE IN MEDICINE Alley, M. T., Pauly, J. M., Sommer, F. G., Pelc, N. J. 1997; 37 (2): 260-267

  Abstract

  Magnetic resonance angiography (MRA) was performed by using RF pulses designed to excite a limited spatial extent in two orthogonal directions. The restriction in the second spatial dimension can be used to increase inflow enhancement and to improve small field-of-view imaging. A rectangular excitation was produced with an "echo-planar" k-space trajectory and a sinc-modulated RF waveform. In vivo images have demonstrated that vessels are more clearly delineated with the two-dimensional excitation. Aliasing artifacts in small field-of-view imaging are significantly reduced, although in some cases complete elimination is not possible due to the nature of the gradient trajectory.

  View details for Web of Science ID A1997WD27200016

  View details for PubMedID 9001151

• A Fast 3D-Cine Acquisition for Cardiac Imaging. Alley, M., T., Shifrin, R., Y., Pelc, N., J., Herfkens, R., J. 1997
• A spatiotemporal finite element mesh model of cyclical deforming motion and its application in myocardial motion analysis using phase contrast MR images International Conference on Image Processing Zhu, Y. D., Pelc, N. J. I E E E, COMPUTER SOC PRESS. 1997: 117–120

  View details for Web of Science ID A1997BJ90B00030

• Optimisation of flip angle for T1 dependent contrast: A closed form solution (Letter). Magn Res Med Pelc, N., J. 1997; 38: 518
• Vascular Flow Dynamics in a Diving Elephant Seal (Mirounga angustirostric) Thornton, S., J., Pelc, N., J., Liao, J. R., Costa, D., P., Spielman, D., M., Crocker, D., E. 1997
• On the Use of Spiral Ring Trajectories for Dynamic Imaging. Liao, J. R., Pelc, N., J. 1997
• A Method for MR Gradient Characterization in Four Dimensions. Alley, M., T., Pelc, N., J. 1997
• Ultrafast Contrast Enhanced 3D Magnetic Resonance Angiography: State of the Art. Radiology 205P Shifrin, R., Y, Alley, M., T., Herfkens, R., J., Pelc, N., J. 1997: 552
• In Vivo Renal Blood Flow Measurement with Rapid Spiral Acquisition Techniques. Sommer, F., G., Corrigan, G., Sawyer, A., M., Fredrickson, J., O., Liao, J. R., Myers, B., Pelc, N. J. 1997
• Shading Artifacts in Phase Contrast Angiography Induced by Maxwell Terms: Analysis and Correction. Bernstein, M., A., Zhou, X., King, K., F., Ganin, A., Pelc, N., J., Glover, G., H. 1997
• Sampling Density Optimization for Motion Artifact Reduction in Variable-Density Spiral Scanning. Liao, J. R., Pelc, N., J. 1997
• An Improved Method for Coronary Flow Measurement Using Simultaneous Resolution Of The Cardiac And Respiratory Cycles. Drangova, M., Fredrickson, J., O., Pelc, N., J. 1997
• Reduction of motion artifacts in cine MRI using variable-density spiral trajectories. Mag Res Med Liao, J. R., Pauly, J., M., Brosnan, T., J., Pelc, N., J. 1997; 37: 569-575
• A Rapid 3D Cine MR Sequence for Cardiac Imaging. Radiology 205P Alley, M., T., Shifrin, R., Y., Pelc, N., J., Herfkens, R., J. 1997: 212
• Myocardial Function Analysis Using a Spatial Temporal Finite Element Mesh Model and Cine-PC Velocity Data. Zhu, Y., Pelc, N., J. 1997
• MR Imaging in a Diving Seal. Thornton, S., J., Spielman, D., M., Block, W., F., Hochachka, P., W., Crocker, D., E., Le Boeuf, B., J., Pelc, N. J. 1997
• Flow Effects of Spectral Spatial Excitation. Fredrickson, J., O, Meyer, C., H., Pelc, N., J. 1997
• Diminishing Variance Algorithm Respiratory Compensation for Fast Spin Echo. Block, W., F., Sachs, T., S., Thornton, S., J., Spielman, D., M., Nishimura, D., G., Pelc, N., J. 1997
• A Spatiotemporal Finite Element Mesh Model of Cyclical Deforming Motion and Its Application in Myocardial Motion Analysis Using Phase Contrast MR Images. Zhu, Y., Pelc, N., J. 1997
• Dynamic contrast-enhanced breath-hold MR imaging of thoracic malignancy using cardiac compensation JOURNAL OF MAGNETIC RESONANCE IMAGING Low, R. N., Sigeti, J. S., Song, S. Y., Shimakawa, A., Pelc, N. J. 1996; 6 (4): 625-631

  Abstract

  The purpose of this paper was to evaluate the use of dynamic gadopentetate dimeglumine-enhanced, breath-hold spoiled gradient-recalled (SPGR) MR imaging with cardiac compensation (CMON) compared to spin-echo MR imaging in patients with thoracic malignancy. We retrospectively reviewed MR images from 29 patients with thoracic tumors. MR imaging included axial electrocardiogram (ECG)-gated T1-weighted, fast spin echo (FSE) T2-weighted, and contrast-enhanced breath-hold fast multiplanar SPGR imaging with CMON, which selects the phase-encoding gradient based on the phase within the cardiac cycle. Images were reviewed for lung masses, mediastinal or hilar tumor, disease of the pleura, chest wall, and bones and vascular compression or occlusion. Contrast-enhanced fast multiplanar SPGR imaging with CMON produces images of the chest that are free of respiratory artifact and have diminished vascular pulsation artifact. ECG-gated T1-weighted images were preferred for depicting mediastinal and hilar tumor. The gadopentetate dimeglumine-enhanced fast multiplanar SPGR images were useful for depicting chest wall tumor, vascular compression or thrombosis, osseous metastases, and in distinguishing a central tumor mass from peripheral lung consolidation. Pleural tumor was depicted best on the FSE T2-weighted images and the contrast-enhanced SPGR images. As an adjunct to spin echo T1-weighted and T2-weighted imaging, contrast-enhanced fast multiplanar SPGR imaging with CMON is useful in the evaluation of thoracic malignancy.

  View details for Web of Science ID A1996UY96400010

  View details for PubMedID 8835956

• Physiologic motion phantom for MRI applications JOURNAL OF MAGNETIC RESONANCE IMAGING Drangova, M., Bowman, B., Pelc, N. J. 1996; 6 (3): 513-518

  Abstract

  To address the need for a complex physiologic motion phantom for use in MR applications, such as the verification of techniques for measuring myocardial motion dynamics and motion insensitive pulse sequences, a computer-controlled motion phantom has been designed. The phantom, which consists of a deformable silicone gel annulus mounted on a translation stage, can undergo a range of bulk motions and deformations. Available motions include bulk rotation and translation, rotational shear, axial shear, and combinations of some or all of these motions. In this paper, the capability of the phantom to produce accurate constant and time-varying waveforms is demonstrated. In the current implementation, peak linear translation and rotation rates are 175 mm s-1 and 10 rad s-1, respectively. Cycle-to-cycle reproducibility is excellent, with variations of less than .003 radians over the period of hours while undergoing rotational shear. The phantom has been designed in a flexible fashion so that various test objects can be scanned while undergoing bulk translation and can be adapted to produce different deformations.

  View details for Web of Science ID A1996UM58400013

  View details for PubMedID 8724418

• Fourier tracking of myocardial motion using Cine-PC data MAGNETIC RESONANCE IN MEDICINE Zhu, Y. D., Drangova, M., Pelc, N. J. 1996; 35 (4): 471-480

  Abstract

  A closed-form integration method is derived and analyzed for computing motion trajectories from velocity field data, particularly as measured by phase contrast (PC) cine MR imaging. By modeling periodic motion as composed of Fourier harmonics and integrating the material velocity of the tracked point in the frequency domain, this method gives an unbiased trajectory estimate in the presence of white measurement noise and eddy current effects. When applied to cine PC data, the method can incorporate compensation for the frequency response of the cine interpolation, offering a further improvement on the tracking accuracy. In simulation and phantom studies, the estimated trajectories were in excellent agreement with the true trajectories. Encouraging results have also been obtained on data from volunteers.

  View details for Web of Science ID A1996UD31600005

  View details for PubMedID 8992196

• Temporal resolution improvement in dynamic imaging MAGNETIC RESONANCE IN MEDICINE Fredrickson, J. O., Pelc, N. J. 1996; 35 (4): 621-625

  Abstract

  In some dynamic imaging applications, only a fraction, 1/n, of the field of view (FOV) may show considerable change during the motion cycle. A method is presented that improves the temporal resolution for a dynamic region by a factor, n, while maintaining spatial resolution at a cost of square root of n in signal-to-noise ratio (SNR). Temporal resolution is improved, or alternatively, total imaging time is reduced by reducing the number of phase encodes acquired for each temporal frame by 1/n. To eliminate aliasing, a representation of the signal from the static outer portion of the FOV is constructed using all the raw data. The k-space data derived from this representation is subtracted from the original data sets, and the differences correspond to the dynamic portion of the FOV. Improved resolution results are presented in phantom studies, and in vivo phase contrast quantitative flow imaging.

  View details for Web of Science ID A1996UD31600025

  View details for PubMedID 8992216

• Artifacts and signal loss due to flow in the presence of B-0 inhomogeneity MAGNETIC RESONANCE IN MEDICINE Drangova, M., Pelc, N. J. 1996; 35 (1): 126-130

  Abstract

  An in vitro study was performed to investigate the effects of B(o) inhomogeneity on magnetic resonance images of flow. Controlled inhomogeneity gradients (Gi) were applied and the magnitude of the artifacts produced was quantified for different echo delay times (TE). Both steady and pulsatile flows were examined. In the presence of an inhomogeneity gradient, signal loss is apparent if the flow is pulsatile and/or if the slice thickness is large. The signal loss increases with increasing TE and Gi. With pulsatile flow, ghosting artifacts are also generated. These increase in intensity with increasing TE and Gi. In vivo, field inhomogeneity due to susceptibility variations is large enough to produce these effects. Representative time-of-flight images obtained of a normal volunteer with two different TEs demonstrate the effect in vivo. Flow-related signal loss and artifacts, therefore, increase with increasing TE independent of the moments of the applied gradients.

  View details for Web of Science ID A1996TN36800015

  View details for PubMedID 8771030

• Improved Temporal Resolution with View Ordered Phase Contrast Magnetic Resonance Imaging. Sheehan, F., Fredrickson, J., Pelc, N., Zhu, Y., Drace, J. 1996
• Image Reconstruction of Generalized Spiral Trajectory. Liao, J., R., Pelc, N., J. 1996
• Performance Assessment of a Cine-Phase-Contrast-Velocity-Data-Based Strain Estimation Method. Radiology 201P Zhu, Y., Pelc, N., J. 1996: 404
• Fast Gradient Characterization and K-Space Measurement Technique. Radiology 201P Alley, M., T., Kerr, A., B., Pelc, N., J., Glover, G., H. 1996: 152
• Estimation of Deformation Gradient and Strain from Densely Sampled Velocity Data. Zhu, Y., Pelc, N. 1996
• Fourier tracking of myocardial motion using Cine-PC data. Mag Res Med Y, Y., Zhu, Drangova, M., Pelc, N., J. 1996; 35: 471-480
• MR Imaging Using Piecewise-Linear Spiral Trajectory. Liao, J., R., Pauly, J., M., Pelc, N., J. 1996
• Simultaneous Resolution of Cardiac and Respiratory Motion with a Rapid Spiral Acquisition. Frederickson, J., O., Drangova, M., Liao, J., R., Pelc, N., J. 1996
• Application of Phase Contrast MR Imaging to the Study of Musculoskeletal Motion. Drace, J., E., Sheehan, F., T., Pelc, N., J. 1996
• Measurement of Renal Blood Flow In Vivo using Simultaneous Resolution of Cardiac and Respiratory Motion. Radiology 201P Sommer, F., G., Merchant, N., Fredrickson, J., O., Drangova, M., Liao, J. R., Pelc, N., J. 1996: 217
• Artifacts and signal loss due to flow in the presence of Bo inhomogeneity. Mag Res Med Drangova, M., Pelc, N., J. 1996; 35: 126-130
• CINE SPIRAL IMAGING MAGNETIC RESONANCE IN MEDICINE Liao, J. R., Sommer, F. G., Herfkens, R. J., Pelc, N. J. 1995; 34 (3): 490-493

  Abstract

  Interleaved spiral scanning of k-space is an efficient and fast method for imaging dynamic processes. In this article, a cine version of interleaved spiral imaging is presented. The method is shown to overcome the "lightning-flash" artifacts of the conventional triggered (gated) method. Compared with the segmented k-space 2DFT method, it achieves better temporal resolution in a comparable or shorter scan time. Preliminary human studies show that the method is a promising tool for imaging dynamic processes.

  View details for Web of Science ID A1995RR68700029

  View details for PubMedID 7500891

• Flow quantification and analysis methods. Magnetic resonance imaging clinics of North America Pelc, N. J. 1995; 3 (3): 413-424

  Abstract

  The sensitivity of nuclear magnetic resonance to motion can be harnessed to produce quantitative measurements of low flow velocity and volume flow rate. MR flow quantification is noninvasive, can be performed in arbitrary locations and in any image orientation, and is fairly rapid. This article discusses the basic techniques with particular attention to phase contrast quantitation of volume flow rate, especially the determinants of accuracy and reproducibility in these measurements.

  View details for PubMedID 7584247

• T-1-WEIGHTED SIGNAL CONTRAST OPTIMIZATION BY RF PULSE SEQUENCES - RESPONSE MAGNETIC RESONANCE IN MEDICINE Pelc, N. J., Sumanaweera, T. S. 1995; 34 (1): 134-135

  View details for Web of Science ID A1995RF76800020

• TRACKING OF CYCLIC MOTION WITH PHASE-CONTRAST CINE MR VELOCITY DATA JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Pelc, N. J., Drangova, M., Pelc, L. R., Zhu, Y., Noll, D. C., BOWMAN, B. S., Herfkens, R. J. 1995; 5 (3): 339-345

  Abstract

  A method of computing trajectories of objects by using velocity data, particularly as acquired with phase-contrast magnetic resonance (MR) imaging, is presented. Starting from a specified location at one time point, the method recursively estimates the trajectory. The effects of measurement noise and eddy current-induced velocity offsets are analyzed. When the motion is periodic, trajectories can be computed by integrating in both the forward and backward temporal directions, and a linear combination of these trajectories minimizes the effect of velocity offsets and maximizes the precision of the combined trajectory. For representative acquisition parameters and signal-to-noise ratios, the limitations due to measurement noise are acceptable. In a phantom with reciprocal rotation, the measured and true trajectories agreed to within 3.3%. Sample trajectory estimates of human myocardial regions are encouraging.

  View details for Web of Science ID A1995QZ28100015

  View details for PubMedID 7633112

• PHASE UNWRAPPING OF MR PHASE IMAGES USING POISSON EQUATION IEEE TRANSACTIONS ON IMAGE PROCESSING Song, S. M., Napel, S., Pelc, N. J., Glover, G. H. 1995; 4 (5): 667-676

  Abstract

  The authors have developed a technique based on a solution of the Poisson equation to unwrap the phase in magnetic resonance (MR) phase images. The method is based on the assumption that the magnitude of the inter-pixel phase change is less than pi per pixel. Therefore, the authors obtain an estimate of the phase gradient by "wrapping" the gradient of the original phase image. The problem is then to obtain the absolute phase given the estimate of the phase gradient. The least-squares (LS) solution to this problem is shown to be a solution of the Poisson equation allowing the use of fast Poisson solvers. The absolute phase is then obtained by mapping the LS phase to the nearest multiple of 2 K from the measured phase. The proposed technique is evaluated using MR phase images and is proven to be robust in the presence of noise. An application of the proposed method to the 3-point Dixon technique for water and fat separation is demonstrated.

  View details for Web of Science ID A1995QV84500012

  View details for PubMedID 18290015

• SIMULTANEOUS TEMPORAL RESOLUTION OF CARDIAC AND RESPIRATORY MOTION IN MR-IMAGING RADIOLOGY Fredrickson, J. O., WEGMULLER, H., Herfkens, R. J., Pelc, N. J. 1995; 195 (1): 169-175

  Abstract

  To evaluate a magnetic resonance (MR) imaging method that allows for simultaneous resolution of both the cardiac and respiratory cycles.Conventional and phase-contrast cine sequences were modified to provide additional resolution of the respiratory cycle. Data were collected in 11 healthy volunteers during MR imaging of the heart and portal vein. The imaging time was increased over that of a conventional cine acquisition by a factor equal to the number of frames in the respiratory cycle. Data were compared with those from comparable sequences in which only one motion cycle was resolved.In the heart, motion due to cardiac dynamics was separated from respiration-induced excursions. The extent of motion could be measured, and artifacts were minimized. Changes in flow rate as a function of both motion cycles were resolved and quantified in both the portal vein and superior vena cava.This method allows for simultaneous resolution of cardiac and respiratory motion cycles and helps provide a more physiologic view of the effects of cardiac and respiratory variations.

  View details for Web of Science ID A1995QM66300033

  View details for PubMedID 7892461

• 3-POINT PHASE-CONTRAST VELOCITY-MEASUREMENTS WITH INCREASED VELOCITY-TO-NOISE RATIO MAGNETIC RESONANCE IN MEDICINE Lee, A. T., Pike, G. B., Pelc, N. J. 1995; 33 (1): 122-126

  Abstract

  We describe a technique to increase the velocity-to-noise ratio (VNR) of phase-contrast magnetic-resonance velocity images based on making three measurements/flow encoding axis rather than the usual two. A phase-aliased high first moment data set and a nonaliased low first moment data set are acquired, and the high-moment data are phase unwrapped using the low-moment data. The VNR of the resulting measurement is given by that of the high-moment measurement and increases linearly with the first moment. A factor of 4 gain in VNR was observed with only a 50% increase in scan time. Thus, this method is a much more efficient way to increase VNR than simple averaging.

  View details for Web of Science ID A1995PZ80800018

  View details for PubMedID 7891526

• Dual echo "DIET" fast spin echo imaging". Butts, K., Pauly, J., M., Glover, G., H., Pelc, N., J. 1995
• Phase contrast MRI assessment of pedal blood flow. Eur. Radiol. Debatin, J., F., Dalman, R., Herfkens, R., J., Harris, E., J., Pelc, N., J. 1995; 5: 36-42
• Linear interpolation of local velocity field in myocardial tracking from Cine-PC data. Radiology 197P Zhu, Y., Drangova, M., Pelc, N., J. 1995: 256
• Improved angiographic imaging with 2D spatially selective RF pulses. Alley, M., T., Pauly, J., M., Sommer, F., G., Pelc, N., J. 1995
• Preoperative planning of muscle-tendon transfers with phase-contrast MR imaging. Radiology 197P Drace, J., E., Sheehan, F., T., Pelc, N., J. 1995: 296
• Three-point phase-contrast velocity measurements with increased velocity-to-noise ratio. Mag Res Med Lee, A., T., Pike, G., B., Pelc, N., J. 1995; 33: 122-126
• Simultaneous temporal resolution of cardiac and respiratory motion. Radiology Fredrickson, J., O., Wegmüller, H., Herfkens, R., J., Pelc, N., J. 1995; 195: 169-175
• Reply to T1 weighted signal contrast optimization by RF pulses (Letter). Mag Res Med Pelc, N., J., Sumanaweera, T. 1995; 34: 134-135
• View order phase contrast magnetic resonance imaging: A new technique for measuring in-vivo muscle kinematics and kinetics. Sheehan, F., T., Fredrickson, J., O., Pelc, N., J., Zajac, F., E., Drace, J., E. 1995
• Validation of cine phase-contrast for motion analysis. JMRI Lingamneni, A., Hardy, P., A., Powell, K., A., Pelc, N., J., White, R., D. 1995; 5: 331-338
• Retrospective flow measurement from 3D all-direction phase-contrast MR imaging. Radiology 197P Brosnan, T., J., Drangova, M., Pelc, N., J., Enzmann, D., R., Napel, S., A. 1995: 391
• Flow-induced spatial displacement artifact in phase-contrast imaging. Fredrickson, J., O., Drangova, M., Pelc, N., J. 1995
• Improved temporal resolution of phase-contrast imaging of muscle dynamics by using view ordering. Radiology 197P Drace, J., E., Sheehan, F., T., Pelc, N., J. 1995: 389
• Concentric, eccentric, and isometric muscle contraction with electromyography and phase-contrast MR imaging. Radiology 197P Drace, J., E., Sheehan, F., T., Pelc, N., J. 1995: 296
• Impact of spatial resolution and interpolation on myocardial tracking from Cine-PC data. Zhu, Y., Drangova, M., Pelc, N., J. 1995
• Impact of artifacts due to flowing blood on the reproducibility of phase-contrast measurements of myocardial motion. Drangova, M., Pelc, N., J. 1995
• Tracking of cyclical motion using phase contrast cine MRI velocity data. JMRI Pelc, N., J., Drangova, M., Pelc, L., R., Zhu, Y., Noll, D., C., Bowman, B., S. 1995; 5: 339-345
• PHASE-CONTRAST MRI ASSESSMENT OF PEDAL BLOOD-FLOW EUROPEAN RADIOLOGY Debatin, J. F., Dalman, R., Herfkens, R. J., Harris, E. J., Pelc, N. J. 1995; 5 (1): 36-42

  View details for Web of Science ID A1995QK12800007

• EVALUATION OF MYOCARDIAL MOTION TRACKING WITH CINE-PHASE CONTRAST MAGNETIC-RESONANCE-IMAGING INVESTIGATIVE RADIOLOGY Pelc, L. R., Sayre, J., Yun, K., Castro, L. J., Herfkens, R. J., Miller, D. C., Pelc, N. J. 1994; 29 (12): 1038-1042

  Abstract

  The accuracy of myocardial motion measurements, computed from cine-phase contrast (cine-PC) magnetic resonance (MR) velocity data, was compared with directly visualized motion of MR signal voids caused by implanted tantalum markers in anesthetized dogs.Magnetic resonance imaging (MRI) data were electrocardiogram-gated and divided into 16 phases per cardiac cycle. Myocardial trajectories as a function of time in the cardiac cycle were measured using both methods for four to seven markers in each of eight animals.The peak observed in-plane excursion was 4.0 +/- 2.1 mm. The average deviation between displacements derived from velocity data versus displacements visualized directly was 1.1 +/- 0.7 mm (27.5% of the peak displacement). The difference was less if three separate MR scans were used to measure each velocity component in the cine-PC method. This improvement is probably caused by improved temporal resolution.Cine-PC MRI offers a noninvasive method for accurate quantification of myocardial motion.

  View details for PubMedID 7721545

• MAGNETIC-RESONANCE-IMAGING EVALUATION OF PULMONARY VASCULAR MALFORMATIONS CHEST Silverman, J. M., JULIEN, P. J., Herfkens, R. J., Pelc, N. J. 1994; 106 (5): 1333-1338

  Abstract

  The purpose of our study was to establish magnetic resonance imaging (MRI) criteria for the diagnosis of pulmonary vascular malformations (PVMs).Since 1987, 11 patients have been referred for chest MRI at our institution because of findings suggestive of a PVM. They were evaluated with a 1.5-T MRI system, incorporating a combination of spin-echo, gradient-recalled echo (GRE) cine, and 2-D phase contrast (PC) cine sequences. We used the following MRI criteria to diagnose PVM: (1) flow void or intermediate gray signal on spine-echo sequences; (2) bright signal on GRE cine sequences; and (3) bright signal consistent with flow detected on PC cine sequences using relatively low velocity ranges. Twelve patients not suspected of having a PVM served as controls; all had both MRI and pulmonary angiography to evaluate for central pulmonary embolus.Eight patients in the study group had PVM as determined with MRI using these criteria. In four of these patients, a PVM was confirmed by subsequent pulmonary angiography. Three patients did not have PVM utilizing these criteria; two had neoplasms and one had presumed mucus plugging and/or atelectasis that resolved spontaneously. The smallest vascular malformation detected by MRI was 1 cm. None of the control patients had PVM by MRI or pulmonary angiography.Utilizing these criteria, we believe that MRI is potentially an excellent noninvasive modality to evaluate PVM, and we stress that some form of PC cine sequence must be performed to determine if indeed there is blood flow within a suspicious lesion.

  View details for Web of Science ID A1994PR29300009

  View details for PubMedID 7956380

• SKELETAL-MUSCLE CONTRACTION - ANALYSIS WITH USE OF VELOCITY DISTRIBUTIONS FROM PHASE-CONTRAST MR-IMAGING RADIOLOGY Drace, J. E., Pelc, N. J. 1994; 193 (2): 423-429

  Abstract

  Velocity gradient data from phase-contrast magnetic resonance (MR) imaging were tested for the ability to calculate tensile strain and shear strain (deformation) during cyclical motion of skeletal muscle.Strain data were derived from in vitro and in vivo phase-contrast MR velocity maps. A motion phantom designed to cyclically compress and expand a specimen of skeletal muscle provided a standard of reference to validate deformation, translation, and rotation measurements. The authors studied anterior and posterior muscle compartments of the lower extremity in three healthy volunteers during ankle dorsiflexion and plantar flexion against various resistances and the forearms of five healthy volunteers during flexion and extension of the fingers.The mean in vitro tracking error was 0.5 mm. The gastrocnemius muscle area in vivo changed 20% for both the minimum and maximum force conditions and therefore did not appear to be a good predictor of force.Phase-contrast MR imaging provides quantitative data on muscle contraction and demonstrates that shear and tensile strain can be measured and separated from translation and rotation of muscle.

  View details for Web of Science ID A1994PN94700032

  View details for PubMedID 7972757

• TRACKING THE MOTION OF SKELETAL-MUSCLE WITH VELOCITY-ENCODED MR-IMAGING JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Drace, J. E., Pelc, N. J. 1994; 4 (6): 773-778

  Abstract

  Phase-contrast magnetic resonance velocity-encoding techniques were used to track two-dimensional movement of skeletal muscle tissue. Axial and longitudinal planes in the forearms of five healthy volunteers were imaged during cyclic flexion and extension of the fingers, and the resulting data were used to plot the trajectories of the motion of pieces of muscle tissue. A phantom that produced complex two-dimensional trajectories validated the accuracy of the imaging and analysis techniques; after adjustments for phase errors, two-dimensional trajectories were tracked with an root-mean-square error of 0.1 cm. Preliminary results indicate that velocity-encoded image data can characterize motion trajectories and that refinements in data acquisition and analysis techniques may make it possible to correlate the movements of different regions within a muscle, characterize muscle contraction, and quantify longitudinal strain. This ability to track velocity vectors may provide a foundation for quantitative analysis of muscle motion.

  View details for Web of Science ID A1994PR94400003

  View details for PubMedID 7865936

• MAGNETIC-RESONANCE VELOCITY IMAGING USING A FAST SPIRAL PHASE-CONTRAST SEQUENCE MAGNETIC RESONANCE IN MEDICINE Pike, G. B., Meyer, C. H., Brosnan, T. J., Pelc, N. J. 1994; 32 (4): 476-483

  Abstract

  Time-resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin-warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k-space data acquisition that permits time-resolved, three-direction velocity imaging within a breath-hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in-line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.

  View details for Web of Science ID A1994PJ32300008

  View details for PubMedID 7997113

• RECONSTRUCTIONS OF PHASE-CONTRAST, PHASED-ARRAY MULTICOIL DATA MAGNETIC RESONANCE IN MEDICINE Bernstein, M. A., Grgic, M., Brosnan, T. J., Pelc, N. J. 1994; 32 (3): 330-334

  Abstract

  We present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.

  View details for Web of Science ID A1994PE25900007

  View details for PubMedID 7984065

• QUANTITATIVE MAGNETIC-RESONANCE FLOW IMAGING MAGNETIC RESONANCE QUARTERLY Pelc, N. J., Sommer, F. G., Li, K. C., Brosnan, T. J., Herfkens, R. J., Enzmann, D. R. 1994; 10 (3): 125-147

  Abstract

  Time-of-flight and phase shift methods have both been used for vascular imaging with magnetic resonance. Phase methods, and phase contrast in particular, are well suited to quantitative measurements of velocity and volume flow rate. The most robust methods for measuring flow encode through-plane velocity into phase shift and compute flow by integrating the measured velocity over the vessel lumen. The accuracy of the flow data can be degraded by the effects of acceleration and eddy currents and by partial volume effects, including the effects of finite slice thickness and resolution, pulsatile waveforms, motion, and chemical shift. The reproducibility depends on the signal-to-noise of the data and the strength of the flow encoding and can be degraded by inconsistent definition of the vessel boundary. The adjustable flow sensitivity inherent in this method is a particular asset, allowing phase contrast flow measurement to operate over a dynamic range exceeding 10(5). Recently developed rapid imaging methods are helpful in applications that would be compromised by respiratory motion. With care, excellent quantitative data can be quickly obtained in vivo, and the resulting flow information is valuable for the diagnosis and management of a variety of conditions.

  View details for Web of Science ID A1994PM96800001

  View details for PubMedID 7811608

• SINGLE BREATH-HOLD PULMONARY MAGNETIC-RESONANCE ANGIOGRAPHY - OPTIMIZATION AND COMPARISON OF 3 IMAGING STRATEGIES INVESTIGATIVE RADIOLOGY Rubin, G. D., Herfkens, R. J., Pelc, N. J., Foo, T. K., Napel, S., Shimakawa, A., Steiner, R. M., Bergin, C. J. 1994; 29 (8): 766-772

  Abstract

  Ultrafast gradient-recalled-echo techniques for obtaining high-quality pulmonary magnetic resonance angiograms within a single breath-hold were optimized.Fourteen subjects were imaged with both the body coil and a phased-array surface coil, using three gradient-recalled-echo pulse sequences: 1) two-dimensional sequential; 2) two-dimensional interleaved; and 3) volumetric acquisitions. Image quality was assessed with varied flip angle, receiver bandwidth, slice thickness/number, and matrix size. Cardiac compensation diminished ghost artifacts in the interleaved sequence. Individual sagittal sections and maximum intensity projections were reviewed.Pulmonary magnetic resonance angiograms acquired with volumetric and two-dimensional interleaved gradient-recalled-echo pulse sequences benefit greatest from intravenous gadolinium and result in greater pulmonary arterial visualization than traditional time-of-flight techniques. Phased-array coils result in improved vessel detection.High-quality breath-held pulmonary magnetic resonance angiography can be obtained with an intravenous contrast-enhanced gradient-recalled-echo acquisition; however, image quality is dependent on the pulse sequence.

  View details for Web of Science ID A1994PE81100006

  View details for PubMedID 7960627

• THE ANATOMY OF THE POSTERIOR COMMUNICATING ARTERY AS A RISK FACTOR FOR ISCHEMIC CEREBRAL INFARCTION NEW ENGLAND JOURNAL OF MEDICINE Schomer, D. F., Marks, M. P., Steinberg, G. K., Johnstone, I. M., Boothroyd, D. B., Ross, M. R., Pelc, N. J., Enzmann, D. R. 1994; 330 (22): 1565-1570

  Abstract

  After the occlusion of an internal carotid artery the principal source of collateral flow is through the arteries of the circle of Willis, but the size and patency of these arteries are quite variable. Study of the anatomy of the collateral pathways in patients with internal-carotid-artery occlusion with or without infarction in the watershed area of the deep white matter may identify patterns that afford protection from ischemic infarction.Using conventional magnetic resonance imaging and three-dimensional phase-contrast magnetic resonance angiography, we evaluated 29 consecutive patients (32 hemispheres at risk) with angiographically proved occlusion of the internal carotid artery. Four collateral pathways to the occluded vessel were evaluated: the proximal segment of the anterior cerebral artery, the posterior communicating artery, the ophthalmic artery, and leptomeningeal collateral vessels from the posterior cerebral artery.Only features of the ipsilateral posterior communicating artery were related to the risk of watershed infarction. The presence of posterior communicating arteries measuring at least 1 mm in diameter was associated with the absence of watershed infarction (13 hemispheres, no infarcts; P < 0.001). Conversely, there were 4 watershed infarcts in the 6 hemispheres with posterior communicating arteries measuring less than 1 mm in diameter and 10 infarcts in the 13 hemispheres with no detectable flow in the ipsilateral posterior communicating artery.A small (< 1 mm in diameter) or absent ipsilateral posterior communicating artery is a risk factor for ischemic cerebral infarction in patients with internal-carotid-artery occlusion.

  View details for PubMedID 8177246

• ELASTIC-DEFORMATION IN TENDONS AND MYOTENDINOUS TISSUE - MEASUREMENT BY PHASE-CONTRAST MR-IMAGING RADIOLOGY Drace, J. E., Pelc, N. J. 1994; 191 (3): 835-839

  Abstract

  To determine whether phase-contrast magnetic resonance (MR) imaging can be used to measure stretch in the myotendinous junction and tendon.Velocity-encoded cine MR images obtained during cyclic motion were used to measure strain in myotendinous tissue and indirectly in tendons in gastrocnemius muscle-tendon sutured to a motion phantom. Videotapes of the experiments were digitized and used as a standard of reference for validation of MR measurements. Strain, rotation, and translation of the myotendinous junction were calculated from the phase-contrast MR data and indirectly in the tendon.Strain as determined from the MR imaging experiments agreed with the measurements from the video reference, with linear correlation coefficients of .987 for tendon strain and .992 for strain in the myotendinous junction.Measurement of tendon and myotendinous stretch during movement may provide insight into tendon ability to store energy and a means of noninvasive measurement of muscle force.

  View details for Web of Science ID A1994NM66800045

  View details for PubMedID 8184075

• DETERMINATION OF BLOOD-FLOW TO THE TRANSPLANTED KIDNEY - A NOVEL APPLICATION OF PHASE-CONTRAST, CINE MAGNETIC-RESONANCE-IMAGING TRANSPLANTATION Myers, B. D., Sommer, F. G., Li, K., Tomlanovich, S., Pelc, N., McDonnell, C., PAGTALUNAN, E., Newton, L., Jamison, R. 1994; 57 (10): 1445-1450

  Abstract

  There is at present no noninvasive method that reliably measures blood flow in the poorly functioning renal allograft. The present study was designed to evaluate phase-contrast cine magnetic resonance imaging (PC-cine-MRI) for this purpose. We recruited for study 18 patients who had received kidney transplants 13-66 months earlier from closely related living donors. As judged by the glomerular filtration rate, which was elevated for a single kidney (76 +/- 4 ml/min 1.73 m2), allograft function was excellent, permitting the assumption of unimpaired renal extraction of paminohippuric acid (PAH). Allograft blood flow was determined consecutively on the same day, first by the standard PAH clearance technique and they by the product of the velocity of protons and renal vein cross-sectional area using PC-cine-MRI. MRI determinations could not be completed because of claustrophobia in two patients and failure to image the terminus of the allograft vein another two. Comparison of blood flow in the remaining 14 subjects revealed the two techniques to be strongly related (r = 0.91, P < 0.001). On the average, the renal blood flow rate was similar by each method; 732 +/- 62 by PAH clearance and 703 +/- 69 ml/min by PC-cine-MRI, but the agreement among individuals between the two methods was only modest, with a 95% confidence interval of agreement from -214 to +254 ml/min. We conclude that PC-cine-MRI provides a fairly accurate and noninvasive method for determining the rate of blood flow in the transplanted kidney. With further refinement it should permit the role of depressed blood flow in a variety of acute and chronic forms of human allograft dysfunction to be elucidated in humans for the first time.

  View details for Web of Science ID A1994NP05700007

  View details for PubMedID 8197605

• MEASUREMENT OF SKELETAL-MUSCLE MOTION IN-VIVO WITH PHASE-CONTRAST MR-IMAGING JOURNAL OF MAGNETIC RESONANCE IMAGING Drace, J. E., Pelc, N. J. 1994; 4 (2): 157-163

  Abstract

  The ability to measure skeletal muscle motion with phase-contrast magnetic resonance (MR) imaging was tested with a motion phantom that simulated muscle activity. Quantitative analytic data on unidimensional, bidirectional skeletal muscle motion measured in vivo was obtained in four healthy volunteers. MR images of the subjects' forearms were obtained during flexion and extension of the fingers and of the anterior and posterior muscle compartments of the lower leg with various resistances to ankle dorsiflexion and plantar flexion. It was necessary to correct the data for the effects of eddy currents. In vitro evaluation of the technique was done by studying through-plane sinusoidal motion of solid objects. The largest error was underestimation of the peak excursion of 11.5 mm by 0.09 mm (the root mean square error for the cycle was 0.04 mm) In vivo experiments demonstrated the contraction of muscles in relation to each other. Data acquisition and analysis techniques must be refined, but measuring skeletal muscle motion with phase-contrast MR imaging should enhance the understanding of bioengineering fundamentals and muscular changes in disease and adaptation.

  View details for Web of Science ID A1994NC12500007

  View details for PubMedID 8180454

• TIME-RESOLVED MR-IMAGING BY AUTOMATIC DATA SEGMENTATION JOURNAL OF MAGNETIC RESONANCE IMAGING Fredrickson, J. O., Pelc, N. J. 1994; 4 (2): 189-196

  Abstract

  A method for time-resolved imaging that provides a flexible trade-off between imaging time and temporal resolution is presented. It is based on a view order selection technique that automatically segments the acquired raw data into appropriate temporal frames. When used with cardiac monitoring and phase-contrast imaging, data similar to that obtained with a conventional gated phase-contrast sequence are acquired rapidly. For many applications, the temporal resolution can be reduced enough to permit imaging within a breath-hold interval, while still allowing accurate time-averaged flow quantitation. This is a general technique that can be implemented within a variety of pulse sequences and can resolve other motion cycles, including the respiratory cycle.

  View details for Web of Science ID A1994NC12500013

  View details for PubMedID 8180460

• RENAL-ARTERY BLOOD-FLOW - QUANTITATION WITH PHASE-CONTRAST MR-IMAGING WITH AND WITHOUT BREATH-HOLDING RADIOLOGY Debatin, J. F., Ting, R. H., WEGMULLER, H., Sommer, F. G., Fredrickson, J. O., Brosnan, T. J., BOWMAN, B. S., Myers, B. D., Herfkens, R. J., Pelc, N. J. 1994; 190 (2): 371-378

  Abstract

  To compare the accuracy of 16-frame cine phase-contrast (PC) magnetic resonance (MR) imaging with those of two breath-hold PC techniques in the measurement of renal artery blood flow.In vitro flow measurements were performed in a segment of harvested human artery embedded in gel. For the cine PC acquisition, respiratory motion was simulated. In eight subjects with recently obtained para-amino-hippurate-clearance renal blood flow data, renal artery flow measurements were subsequently performed with two breath-hold imaging techniques and with cine PC imaging during shallow respiration.Breath-hold sequences were significantly more accurate than conventional cine PC sequences both in vitro (P < .005) and in vivo (P < .05). Cine PC imaging tended to overestimate flow (in vivo mean, 24.47% +/- 9.94), reflecting artifactual enlargement of the apparent vessel size.Reliable blood flow measurements in the renal artery are possible with breath-hold PC MR imaging.

  View details for Web of Science ID A1994MW44400017

  View details for PubMedID 8284383

• SHUNT FLOW MEASUREMENT AND EVALUATION OF VALVE OSCILLATION WITH A SPIN-ECHO PHASE-CONTRAST MR SEQUENCE RADIOLOGY Norbash, A. M., Pelc, N. J., Shimakawa, A., Enzmann, D. R. 1994; 190 (2): 560-564

  Abstract

  To present a spin-echo phase-contrast (SEPC) magnetic resonance pulse sequence designed to measure the very slow flow in ventricular shunt tubing.A flow phantom constructed of shunt tubing and incorporating no valve or a high-, medium-, or low-pressure valve was connected to a flow pump. Flow rates were 0.05-1.00 mL/min (72-1,440 mL/d). Flow measurement was performed with the thin-section SEPC sequence.The flow rates measured with SEPC imaging correlated closely with the pump flow rate for the entire physiologic spectrum of shunt flow rates. This was true for all valves, resulting in overall R2s of .974 at 4 cm/sec and .980 at 2 cm/sec. Shunt flow was pulsatile with valves in place. There was a linear relationship between flow rate and the frequency of valve opening and closing.The SEPC technique is an accurate and noninvasive method of measuring shunt flow.

  View details for Web of Science ID A1994MW44400050

  View details for PubMedID 8284416

• BLOOD-FLOW IN MAJOR CEREBRAL-ARTERIES MEASURED BY PHASE-CONTRAST CINE MR AMERICAN JOURNAL OF NEURORADIOLOGY Enzmann, D. R., Ross, M. R., Marks, M. P., Pelc, N. J. 1994; 15 (1): 123-129

  Abstract

  To measure mean blood flow in individual cerebral arteries (carotid, basilar, anterior cerebral, middle cerebral, and posterior cerebral) using a cine phase contrast MR pulse sequence.Ten healthy volunteers (22 to 38 years of age) were studied. The cine phase-contrast section was positioned perpendicular to the vessel of interest using oblique scanning planes. This pulse sequence used a velocity encoding range of 60 to 250 cm/sec. From the velocity and area measurements on the cine images, mean blood flow was calculated in milliliters per minute and milliliters per cardiac cycle. In the same subjects, transcranial Doppler measurements of blood velocity in these same vessels were also obtained.There was no difference in blood flow in the paired cerebral arteries. Carotid arteries had mean blood flow in the range of 4.8 +/- 0.4 ml/cycle, the basilar artery 2.4 +/- 0.2 ml/cycle, the middle cerebral artery 1.8 +/- 0.2 ml/cycle, the distal anterior cerebral artery 0.6 +/- 0.1 ml/cycle, and the posterior cerebral artery 0.8 +/- 0.1 ml/cycle. Overall, there was poor correlation between MR-measured and transcranial Doppler-measured peak velocity.Although careful attention to technical detail is required, mean blood flow measurements in individual cerebral vessels is feasible using a cine phase-contrast MR pulse sequence.

  View details for PubMedID 8141043

• Tracking the motion of skeletal muscle with velocity-encoded MR Imaging. JMRI Drace, J., E., Pelc, N., J. 1994; 4: 773-778
• Simultaneous temporal resolution of cardiac and respiratory motion. JMRI, 4P Fredrickson, J., O., Wegmüller, H., Herfkens, R., J., Pelc, N., J. 1994: 85
• Phase-contrast quantitation of renal arterial blood flow. Radiology 193P Debatin, J., F., Ting, R., Krestin, G., P., Fredrickson, J., O., Sommer, F., G., Pelc., N., J. 1994: 302
• Comparison of lesion enhancement on spin-echo and gradient-echo images. AJNR Chappell, P., M., Pelc, N., J., Foo, T., K.F., Glover, G., H., Haros, S., P., Enzmann., D., R. 1994; 15: 37-44
• In Vitro Validation of Phase-contrast Measurements of Myocardial Wall Motion. Drangova, M., Zhu, Y., Bowman, B., S., Pelc, N., J. 1994
• Cine Spiral Imaging. Liao, J., R., Sommer, F., G., Pelc, N., J. 1994
• Renal arterial blood flow: Quantitation with phase-contrast MR imaging with and without breath-holding. Radiology Debatin, J., F., Ting, R., H., Wegmüller, H., Sommer, F., G., Fredrickson, J., O., Brosnan, T., J., Pelc, N. J. 1994; 190: 371-378
• Quantitative Magnetic Resonance flow imaging. Magn Reson Quarterly Pelc, N., J., Sommer, F., G., Li, K., C.P., Brosnan, T., J., Herfkens, R., J., Enzmann, D., R. 1994; 10: 125-147
• Voxel Size Effects on Vascular Shear Measurement. Strang, J., Herfkens, R., J., Pelc, N., J. 1994
• MR Signal Loss due to Flow in the Presence of Bo Inhomogeneities. Drangova, M., Pelc, N., J. 1994
• Quantitative Patellar Tracking with MR velocity distributions. Radiology 193P Drace, J., E., Sheehan, F., T., Pelc., N., J. 1994: 370
• Verification of myocardial wall motion tracking from phase-contrast velocity data. Radiology 193P Drangova, M., Zhu, Y., Bowman, B., S., Pelc, N., J. 1994: 199
• Phase-contrast phased array reconstruction. Soc. Mag. Res. WIP Supplement Bernstein, M., A., Grgic, M., Brosnan, T., J., Pelc, N., J. 1994: S9
• Differences in CSF Flow and Brain Motion in Atrophy and Hydroecphalus. ASNR Norbash, A., M., Pelc, N., J., Enzmann., D., R. 1994
• Cine phase-contrast MRI assessment of pedal blood flow. JMRI, 4P Debatin, J., F., Dalman, R., Pelc, N., J., Harris, E., J. 1994: 66
• Breath-hold phase-contrast MR quantification of renal artery blood flow. JMRI, 4P Debatin, J., F., Ting, R., H., Wegmüller, H., Sommer, F., G, Fredrickson, J., O., Brosnan, T., J., Pelc, N. J. 1994: 44
• Phase-contrast velocity measurements with increased signal-to-noise ratio. JMRI, 4P Lee, A., T., Pelc, N., J. 1994: 45
• Influence of respiratory motion on cine phase contrast based flow measurements. JMRI, 4P Debatin, J., F., Wegmüller, H., Bowman, B., S., Sommer, F., G, Pelc, N., J., Herfkens, R., J. 1994: 44
• Quantitative 3D time-resolved phase contrast MR imaging. Fredrickson, J., O., Irarrazabal, P., Pelc, N., J. 1994
• Time resolved MR imaging by automatic data segmentation. JMRI Fredrickson, J., O., Pelc, N., J. 1994
• Elastic deformation in tendons and myotendinous tissue: Measurement by phase contrast MR imaging. Radiology Drace, J., E., Pelc, N., J. 1994; 191: 835-839
• CSF Dynamics in Chiari I Syringomyelia. ASNR Ginier, B., L., Chappell, P., M., Pelc, N., J., Enzmann., D., R. 1994
• CHRONIC MESENTERIC ISCHEMIA - EVALUATION WITH PHASE-CONTRAST CINE MR-IMAGING RADIOLOGY Li, K. C., Whitney, W. S., McDonnell, C. H., Fredrickson, J. O., Pelc, N. J., Dalman, R. L., Jeffrey, R. B. 1994; 190 (1): 175-179

  Abstract

  To compare superior mesenteric artery (SMA) blood flow in healthy volunteers and patients with stenoses in the fasting state and after food intake by using phase-contrast (PC) cine magnetic resonance (MR) imaging.Ten healthy subjects, four asymptomatic patients (three with 50% stenosis, one with 70% stenosis), and one symptomatic patient (with 80% stenosis) were studied. All subjects were studied after fasting at least 8 hours and 15, 30, and 45 minutes after ingesting a standard meal.In healthy volunteers, SMA blood flow at all postprandial intervals increased significantly compared with that obtained after fasting (P < or = .0005). The percentage change in SMA blood flow 30 minutes after food intake provided the best distinction between the healthy subjects, the asymptomatic patients, and the symptomatic patient.Cine PC MR imaging is an effective, noninvasive technique for measuring SMA blood flow.

  View details for Web of Science ID A1994MW25300035

  View details for PubMedID 8259400

• VELOCITY AND FLOW QUANTITATION IN THE SUPERIOR SAGITTAL SINUS WITH UNGATED AND CINE (GATED) PHASE-CONTRAST MR-IMAGING JOURNAL OF MAGNETIC RESONANCE IMAGING Jordan, J. E., Pelc, N. J., Enzmann, D. R. 1994; 4 (1): 25-28

  Abstract

  Normal blood flow and velocity in the superior sagittal sinus were measured in 30 patients. A fast two-dimensional ungated phase-contrast (PC) pulse sequence was compared with a peripherally gated cine PC technique for velocity and flow quantitation. The same imaging parameters were used for both methods. Measured values for mean velocity and flow obtained with the two methods were compared by using regression analysis and t testing. For blood flow, the correlation coefficient was .976. For velocity measurements, r was .950. Mean flow was 285 mL/min +/- 19 with the ungated PC method and 281 mL/min +/- 19 with the cine PC method. The mean velocities measured with the two methods were 12.94 cm/sec +/- 1.1 and 13.59 cm/sec +/- 1.1, respectively. There was no significant difference (paired t test) between the methods for mean flow or velocity data. This was true even though flow in the superior sagittal sinus is moderately pulsatile, as shown with the cine PC technique. The ungated PC method provided these data in 13 seconds versus 3.5 minutes for the cine PC method.

  View details for Web of Science ID A1994NA66700005

  View details for PubMedID 8148552

• COMPARISON OF LESION ENHANCEMENT ON SPIN-ECHO AND GRADIENT-ECHO IMAGES AMERICAN JOURNAL OF NEURORADIOLOGY CHAPPELL, P. M., Pelc, N. J., Foo, T. K., Glover, G. H., HAROS, S. P., Enzmann, D. R. 1994; 15 (1): 37-44

  Abstract

  To compare lesion enhancement after injection of gadopentetate dimeglumine on spin-echo and gradient-echo T1-weighted images.A total of 48 contrast-enhancing intracranial lesions were evaluated using a spin-echo and two gradient-echo T1-weighted pulse sequences. Percent contrast, contrast-to-noise, and signal-to-noise measurements were made on the spin-echo T1-weighted, three-dimensional gradient-echo, and multiplanar gradient-echo sequences.The measurements were somewhat different for the following categories of lesions: extraaxial, intraaxial with edema, and intraaxial without edema. The latter group provided the greatest diagnostic challenge: three of 19 such lesions 1 cm in size or smaller could not be identified on three-dimensional gradient-echo images, and one could not be identified on multi-planar gradient-echo images. The spin-echo T1-weighted sequence demonstrated significantly higher percent contrast (P < .05) and greater contrast to noise (P < .03) than either gradient-echo sequence for these small intraaxial lesions without edema. For extraaxial and intraaxial lesions with edema, percent C was similar for spin-echo T1-weighted and three-dimensional gradient-echo images, while contrast to noise was greater for spin-echo T1-weighted images. This reflected greater tissue noise with gradient-echo sequences.The T1-weighted spin-echo sequence was preferred for detecting the full spectrum of contrast-enhancing lesions of the central nervous system.

  View details for Web of Science ID A1994MT25700007

  View details for PubMedID 8141064

• QUANTITATIVE DIFFERENTIAL PULMONARY PERFUSION - MR-IMAGING VERSUS RADIONUCLIDE LUNG-SCANNING 1992 ANNUAL SCIENTIFIC ASSEMBLY OF THE RADIOLOGICAL-SOC-OF-NORTH-AMERICA Silverman, J. M., JULIEN, P. J., Herfkens, R. J., Pelc, N. J. RADIOLOGICAL SOC NORTH AMERICA. 1993: 699–701

  Abstract

  To compare the results of quantitative analysis of differential pulmonary artery blood flow performed with phase-contrast cine magnetic resonance (MR) images with those of differential radionuclide pulmonary perfusion scanning in preoperative lung transplantation patients.Forty preoperative lung transplantation patients underwent prospective, quantitative analysis of differential pulmonary artery blood flow performed with MR imaging and radionuclide pulmonary perfusion scanning. MR imaging analysis was performed at 1.5 T with a phase-contrast cine pulse sequence to acquire data perpendicular to each central pulmonary artery.Comparative analysis of differential pulmonary perfusion showed excellent correlation between the two modalities in all patients (P = .0001). MR imaging enabled calculation of the pulmonary artery blood flow to each lung; radionuclide lung scanning enabled only calculation of relative perfusion to each lung.MR imaging is as effective as radionuclide lung scanning in assessment of relative, and superior for determination of absolute differential, pulmonary perfusion.

  View details for Web of Science ID A1993MH58600014

  View details for PubMedID 8234693

• CEREBROSPINAL-FLUID FLOW MEASURED BY PHASE-CONTRAST CINE MR AMERICAN JOURNAL OF NEURORADIOLOGY Enzmann, D. R., Pelc, N. J. 1993; 14 (6): 1301-1307

  Abstract

  This prospective study was designed to establish the temporal and quantitative relationship between blood flow and cerebrospinal fluid (CSF) flow using a phase-contrast cine MR pulse sequence.A cine phase-contrast MR pulse sequence using peripheral gating was used to measure CSF flow direction and velocity. Data were acquired continuously and interpolated into 16 images throughout the cardiac cycle.The timing of systolic CSF flow in the cervical subarachnoid space (SAS) correlated very closely to the brain arteriovenous blood flow difference during the cardiac cycle. This arteriovenous difference was a measure of brain expansion. Aqueduct CSF flow during the cardiac cycle differed from SAS flow in that systolic flow was delayed in comparison with systolic cervical SAS flow. The normal aqueductal oscillatory flow volume was 1.7 +/- .4 mL/min or 0.03 +/- 0.01 mL per cardiac cycle. This represented 14.5% +/- 3.1% of the total CSF flow and tissue displacement through the incisura which was 14.5 +/- 2.2 mL/min or 0.22 +/- 0.03 mL per cycle. CSF oscillatory flow volume in the cervical SAS was 39.0 +/- 4.0 mL/min or 0.65 +/- 0.08 mL per cycle.CSF flow can be measured. Results in healthy subjects show relatively low oscillatory flow through the aqueduct which is slightly out of phase (delayed) compared with SAS CSF flow.

  View details for Web of Science ID A1993MG53700005

  View details for PubMedID 8279323

• COMPARISON OF CEREBRAL-ARTERY BLOOD-FLOW MEASUREMENTS WITH GATED CINE AND UNGATED PHASE-CONTRAST TECHNIQUES JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Enzmann, D. R., Marks, M. P., Pelc, N. J. 1993; 3 (5): 705-712

  Abstract

  Cine phase-contrast (PC) magnetic resonance (MR) pulse sequences have been used to measure blood flow in a variety of vessels. Because the cine PC sequence is time-consuming, this prospective study was undertaken to compare it with an ungated PC technique for measuring average blood flow in individual cerebral arteries to potentially achieve substantial time savings. The following cerebral arteries were studied in 10 healthy volunteers: carotid, basilar, middle cerebral, anterior cerebral, and posterior cerebral. Imaging planes were placed perpendicular to the vessel of interest, and velocity encoding, ranging from 40 to 250 cm/sec, was matched to individual arteries. Good correlation between cine and ungated PC blood flow measurements was obtained for both high- and low-flow vessels, with an overall correlation coefficient of .978. The ungated PC sequence, because of its short imaging time, allows measurement of the blood volume flow rate in the circle of Willis in approximately 20 minutes, a clinically acceptable time.

  View details for Web of Science ID A1993LX79600003

  View details for PubMedID 8400555

• NOISE-REDUCTION IN 3-DIMENSIONAL PHASE-CONTRAST MR VELOCITY-MEASUREMENTS JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Song, S. M., Napel, S., Glover, G. H., Pelc, N. J. 1993; 3 (4): 587-596

  Abstract

  The authors have developed a method to reduce noise in three-dimensional (3D) phase-contrast magnetic resonance (MR) velocity measurements by exploiting the property that blood is incompressible and, therefore, the velocity field describing its flow must be divergence-free. The divergence-free condition is incorporated by a projection operation in Hilbert space. The velocity field obtained with 3D phase-contrast MR imaging is projected onto the space of divergence-free velocity fields. The reduction of noise is achieved because the projection operation eliminates the noise component that is not divergence-free. Signal-to-noise ratio (S/N) gains on the order of 15%-25% were observed. The immediate effect of this noise reduction manifests itself in higher-quality phase-contrast MR angiograms. Alternatively, the S/N gain can be traded for a reduction in imaging time and/or improved spatial resolution.

  View details for Web of Science ID A1993LM78100006

  View details for PubMedID 8347951

• MR CHARACTERIZATION OF BLOOD-FLOW IN NATIVE AND GRAFTED INTERNAL MAMMARY ARTERIES JOURNAL OF MAGNETIC RESONANCE IMAGING Debatin, J. F., Strong, J. A., Sostman, H. D., NEGROVILAR, R., Paine, S. S., Douglas, J. M., Pelc, N. J. 1993; 3 (3): 443-450

  Abstract

  In the postoperative patient with anginal symptoms, differentiation between bypass graft compromise and nonischemic causes has until now been accomplished only by means of x-ray angiography. A non-invasive test is clearly desirable. The authors used a cine phase-contrast (PC) magnetic resonance (MR) imaging technique to characterize blood flow in native and grafted internal mammary arteries (IMAs). Ten volunteers and 15 patients who had recently undergone IMA coronary artery bypass grafting were imaged. Cine PC MR imaging was performed in the transaxial plane at the level of the pulmonary artery bifurcation. Flow in both IMAs was quantified and expressed as a percentage of cardiac output measured in the ascending aorta. In the 15 patients, flow analysis was performed in both the native and grafted IMAs. In the volunteers, IMA blood flow ranged from 2.1% to 4.3% of cardiac output on the left (mean, 3.5%) and 2.1% to 5.1% (mean, 3.5%) on the right. There was considerable intersubject variability, with coefficients of variation of 10.7% for the left and 12.3% for the right IMA. Intrasubject variability was limited, with estimated common standard deviations of 0.45% of cardiac output (range, 0.2%-1.1%) for the left and 0.39% (range, 0.1%-0.6%) for the right IMA. Flow in grafted IMAs was identified in 13 of 15 patients. In one of two patients without demonstrable IMA graft flow, cardiac catheterization confirmed lack of flow. IMA graft flow varied from 28 to 164 mL/min (mean, 80.3 mL/min). This study shows the feasibility of using cine PC MR imaging as a quantitative method of evaluating blood flow in IMA coronary artery bypass grafts.

  View details for Web of Science ID A1993LC10000002

  View details for PubMedID 8324302

• OPTIMIZATION OF FLIP ANGLE FOR T1 DEPENDENT CONTRAST IN MRI MAGNETIC RESONANCE IN MEDICINE Pelc, N. J. 1993; 29 (5): 695-699

  Abstract

  The flip angle which maximizes contrast between materials with different T1 can be calculated from the root of a cubic expression. A simple closed form expression can be used if contrast is defined in a differential sense and results in only slight contrast loss even with large T1 differences.

  View details for Web of Science ID A1993KZ52500018

  View details for PubMedID 8505908

• FAST MULTIPLANAR SPOILED GRADIENT-RECALLED IMAGING OF THE LIVER - PULSE SEQUENCE OPTIMIZATION AND COMPARISON WITH SPIN-ECHO MR IMAGING AMERICAN JOURNAL OF ROENTGENOLOGY Low, R. N., Francis, I. R., Herfkens, R. J., Jeffrey, R. B., Glazer, G. M., Foo, T. K., Shimakawa, A., Pelc, N. J. 1993; 160 (3): 501-509

  Abstract

  The purpose of this study was to optimize a new rapid-acquisition MR pulse sequence, called fast multiplanar spoiled gradient-recalled (FMPSPGR) imaging, for breath-hold imaging of the liver and to compare unenhanced and contrast-enhanced FMPSPGR with standard spin-echo imaging in detecting liver tumors.The pulse sequence was optimized at 1.5 T with a healthy volunteer. Various scanning parameters were evaluated, and liver-spleen signal difference/noise measurements were used to estimate lesion contrast-to-noise ratios. We examined 24 patients with hepatic masses using the optimized sequence with spin-echo T1-weighted and T2-weighted imaging as well as unenhanced and gadopentetate dimeglumine-enhanced FMPSPGR imaging. The contrast-to-noise ratio for the hepatic tumors was determined for each sequence. Three radiologists who did not know the biopsy or test results reviewed all images for lesion conspicuity, lesion tissue specificity, and overall image quality.A comparison of unenhanced FMPSPGR images with spin-echo T1-weighted images showed a 40% improvement in mean contrast-to-noise ratio and a 70% improvement in liver signal-to-noise ratio for the FMPSPGR images. A comparison of gadopentetate dimeglumine-enhanced FMPSPGR images with spin-echo T1- and T2-weighted images showed a superior contrast-to-noise ratio for the enhanced FMPSPGR images in 17 (68%) of 25 hepatic lesions, which included all hepatic cysts (n = 3) and all hepatomas (n = 6), and in six of 12 patients with other liver tumors. The results of contrast-to-noise ratio for four patients with hemangiomas were mixed. For the remaining eight lesions, the contrast-to-noise ratio for spin-echo T1- and T2-weighted images predominated in three and five cases, respectively. Contrast-enhanced FMPSPGR images revealed a 40% and 300% increase in contrast-to-noise ratio compared with T2- and T1-weighted images, respectively. All three radiologists preferred the contrast-enhanced FMPSPGR images for overall image quality. For lesion conspicuity and specificity, however, the three radiologists differed, with a preference for the FMPSPGR images in 52%, 80%, and 40% of cases for lesion conspicuity and in 68%, 40%, and 60% of cases for lesion specificity.FMPSPGR is a new, ultrafast MR sequence that provides T1-weighted images of the liver during suspended respiration. Contrast-to-noise ratio and liver signal-to-noise ratio are significantly improved over those on conventional spin-echo T1-weighted images. The combination of breath-hold FMPSPGR with gadopentetate dimeglumine is an excellent technique that can be used to rapidly evaluate the liver with superior overall image quality. Contrast-to-noise ratios are generally superior to T2-weighted spin-echo images, making this technique a useful adjunct to conventional spin-echo MR imaging.

  View details for Web of Science ID A1993KM93500009

  View details for PubMedID 8381572

• MAGNETIC-RESONANCE-IMAGING OF BLOOD-FLOW WITH A PHASE SUBTRACTION TECHNIQUE - INVITRO AND INVIVO VALIDATION INVESTIGATIVE RADIOLOGY Evans, A. J., Iwai, F., GRIST, T. A., Sostman, H. D., Hedlund, L. W., Spritzer, C. E., NEGROVILAR, R., Beam, C. A., Pelc, N. J. 1993; 28 (2): 109-115

  Abstract

  One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity-encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers.In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of +/- 12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r2 = .99; P = .0001).Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was +/- 70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r2 = .99; P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms.Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.

  View details for Web of Science ID A1993KL82100002

  View details for PubMedID 8444566

• QUALITATIVE PHASE-CONTRAST MRA IN THE NORMAL AND ABNORMAL CIRCLE OF WILLIS AMERICAN JOURNAL OF NEURORADIOLOGY Ross, M. R., Pelc, N. J., Enzmann, D. R. 1993; 14 (1): 19-25

  Abstract

  To determine the direction of blood flow in the circle of Willis using a 3-D phase contrast MR angiographic (MRA) technique with high spatial resolution.Fifty healthy subjects and 15 patients with occlusive disease were studied using 3-D phase contrast MRA.In the 50 normal subjects, 39 (78%) had detectable flow in one or both posterior communicating arteries. In 24 (48%) of these subjects, flow was detected in both posterior communicating arteries, whereas unilateral flow was detected in 15 (30%). In 36 (92%) of the 39 normal subjects, flow in the posterior communicating artery was from anterior to posterior with only 3 (8%) showing reverse flow from posterior to anterior. The A1 segment of both anterior cerebral arteries was identified in 100% of normal subjects with flow in the expected direction from carotid to the A2 segment. In patients with carotid occlusion, the pattern of flow in the circle of Willis was altered with reversed flow in the ipsilateral posterior communicating artery and sometimes in the ipsilateral A1 segment. An ipsilateral posterior communicating artery was present in 10 of 17 occluded carotid arteries, all showing reversed flow.3-D phase contrast MRA provides useful information about the hemodynamics of normal and abnormal blood flow in the circle of Willis.

  View details for Web of Science ID A1993KJ75600004

  View details for PubMedID 8427087

• A LEAST-SQUARES BASED PHASE UNWRAPPING ALGORITHM FOR MRI Nuclear Science Symposium and Medical Imaging Conference (NSS-MIC 93) Song, S. M., Napel, S., Pelc, N. J., Glover, G. H. IEEE. 1993: 1784–1788

  View details for Web of Science ID A1993BA79S00365

• CSF Dynamics in Chiari I Syringomyelia. Enzmann, D., R., Chappell, P., M., Pelc, N., J. 1993
• Spiral phase-contrast velocity MR imaging. 93 RSNA, Radiology 189P Pike, G., B., Meyer, C., H., McDonnell, C., Pelc, N., J. 1993: 291
• Rapid quantitative flow imaging using a spiral phase contrast sequence. Pike, G., B., Meyer, C., H., Pelc, N., J. 1993
• Dynamic range extension of phase contrast velocity measurements. Song, S., M., Napel, S., Pike, G., B., Pelc, N., J., Glover., G., H. 1993
• Cine phase contrast versus respiratory resolved TRIADS in the portal vein. Flow quantification and flow profile analysis. Wegmüller, H., Fredrickson, J., O., Brosnan, T., J., Pelc, N., J., Debatin, J., F., Herfkens., R., J. 1993
• High-resolution phase-contrast sequence for very slow flow. Soc. Mag. Res. Imaging Pelc, N., J., Norbash, A., M., Shimakawa, A., Enzmann, D., R. 1993: S31
• Breathheld phase contrast MRI flow quantification in the portal vein. Wegmüller, H., Fredrickson, J., O., Brosnan, T., J., Pelc, N., J., Debatin, J., F., Herfkens., R., J. 1993
• Portal venous flow analysis with respiratory-resolved phase-contrast MR imaging. 93 RSNA, Radiology 189P Wegmüller, H., Fredrickson, J., O., Brosnan, T., J., Pelc, N., J., Debatin, J., F., Herfkens, R., J. 1993: 306
• Optimization of xenon-enhanced helical CT for acquisition of 3D regional cerebral blood flow maps of the brain. 93 RSNA, Radiology 189P Napel, S., A., Marks, M., P., Pelc, N., J. 1993: 217
• Phase sensitive flow imaging. In Magnetic Resonance Angiography: Concepts and Applications Dumoulin, C., L., Souza, S., P., Pelc, N., J. edited by Potchen, E., J., Siebert, J., E., Haacke, E., M. Mosby, St. Louis. 1993: 173–186
• SE phase-contrast sequence for measurement of cerebrospinal fluid shunt flow. 93 RSNA, Radiology 189P Pelc, N., J., Shimakawa, A., Norbash, A., Enzmann, D., R. 1993: 292
• Determination of shunt flow with SE phase-contrast MR imaging. '93 RSNA Radiology 189P Norbash, A., M., Pelc, N., J., Shimakawa, A., Enzmann, D., R. 1993: 223
• Cerebrospinal fluid flow in hydrocephalus and atrophy. Enzmann, D., R., Norbash, A., M., Pelc, N., J. 1993
• A least squares based phase unwrapping algorithm for MRI Song, S., M., Napel, N., Pelc, N., J., Glover, G., H. 1993
• A stroll through k-space. In The Physics of MRI Pelc, N., J., Glover, G., H. edited by Sprawls, P., Bronskill, M., J. AAPM, Woodbury NY. 1993: 771–784
• Spin preparation and manipulation techniques. In The Physics of MRI Pelc, N., J. edited by Sprawls, P., Bronskill, M., J. AAPM, Woodbury NY. 1993: 268–287
• Phase-contrast cine MR imaging determination of renal blood flow in the transplanted kidney JMRI 3P Sommer, F., G., Li, K., C.P, Pelc, N., J., Meyers, B., Jamison, R., Pagtalunan, E. 1993: 55
• Obtaining spatial pressure distributions from phase-contrast velocity data. 93 RSNA, Radiology 189P Song, S., M., Hu, B., S., Napel, S., A., Pelc, N., J., Glover, G., H. 1993: 270
• MR imaging of blood flow with a phase subtraction technique: In-vitro and in-vivo validation. Invest. Radiol. Evans, A., J., Iwai, F., Grist, T., A., Sostman, H., D., Hedlund, L., A., Spritzer, C., E., Pelc, N. J. 1993; 28: 109-115
• ARTERIAL AND VENOUS-BLOOD FLOW - NONINVASIVE QUANTITATION WITH MR IMAGING RADIOLOGY Pelc, L. R., Pelc, N. J., Rayhill, S. C., Castro, L. J., Glover, G. H., Herfkens, R. J., Miller, D. C., Jeffrey, R. B. 1992; 185 (3): 809-812

  Abstract

  Quantitative measurements of arterial and venous blood flow were obtained with phase-contrast cine magnetic resonance (MR) imaging and compared with such measurements obtained by means of implanted ultrasound (US) blood flow probes in anesthetized dogs. The US flowmeter was enabled during a portion of each MR imaging sequence to allow virtually simultaneous data acquisition with the two techniques. MR imaging data were gated by means of electrocardiography and divided into 16 phases per cardiac cycle. The rates of portal venous blood flow measured with MR imaging and averaged across the cardiac cycle (710 mL/min +/- 230 [standard deviation]) correlated well with those measured with the flowmeter and averaged in like fashion (751 mL/min +/- 238) (r = .995, slope = 1.053). The correspondence in arterial blood flow was almost as good. No statistically significant difference existed between the paired measurements of blood flow obtained with MR imaging and the implanted probe. It is concluded that, as a noninvasive means of accurate quantification of blood flow, phase-contrast MR imaging may be especially useful in deep blood vessels in humans.

  View details for PubMedID 1438767

• BRAIN MOTION - MEASUREMENT WITH PHASE-CONTRAST MR IMAGING RADIOLOGY Enzmann, D. R., Pelc, N. J. 1992; 185 (3): 653-660

  Abstract

  Brain motion during the cardiac cycle was measured prospectively in 10 healthy volunteers by using a phase-contrast cine magnetic resonance (MR) pulse sequence. The major cerebral lobes, diencephalon, brain stem, cerebellum, cerebellar tonsils, and spinal cord were studied. The overall pattern of brain motion showed caudal motion of the central structures (diencephalon, brain stem, and cerebellar tonsils) shortly after carotid systole, with concurrent cephalic motion of the major cerebral lobes and posterior cerebellar hemisphere. Peak brain displacement was in the range of 0.1-0.5 mm for all the structures except the cerebellar tonsils, which had greater displacement (0.4 mm +/- 0.16 [mean +/- standard error of mean]). Caudal motion of the central structures did not occur simultaneously but progressed in a caudal-to-rostral and posterior-to-anterior sequence, being seen first in the cerebellar tonsils and then later in the diencephalon (hypothalamus). Caudal motion of the low brain stem and cerebellar tonsil was simultaneous with caudal motion of cerebrospinal fluid in the cervical subarachnoid space. Oscillatory flow in the aqueduct was delayed compared with brain stem motion.

  View details for Web of Science ID A1992JZ34700012

  View details for PubMedID 1438741

• MINIMIZING TE IN MOMENT-NULLED OR FLOW-ENCODED 2-DIMENSIONAL AND 3-DIMENSIONAL GRADIENT-ECHO IMAGING JMRI-JOURNAL OF MAGNETIC RESONANCE IMAGING Bernstein, M. A., Shimakawa, A., Pelc, N. J. 1992; 2 (5): 583-588

  View details for Web of Science ID A1992JP25600014

• Minimizing TE in moment-nulled or flow-encoded two- and three-dimensional gradient-echo imaging. Journal of magnetic resonance imaging : JMRI Bernstein, M. A., Shimakawa, A., Pelc, N. J. 1992; 2 (5): 583-588

  Abstract

  A method for minimizing field-echo delay in moment-nulled gradient-echo imaging is presented. Even though ramps are accounted for, the analysis yields simple closed-form solutions. The method is then generalized to the section-select waveform for three-dimensional volume imaging and to flow encoding for phase-contrast imaging. Three strategies for first-moment selection in phase-contrast imaging are discussed, including a new strategy that always yields the minimum echo delay. Trapezoidal and triangular gradient lobe shapes are analyzed.

  View details for PubMedID 1392252

• NORMAL RENAL BLOOD-FLOW MEASUREMENT USING PHASE-CONTRAST CINE MAGNETIC-RESONANCE-IMAGING INVESTIGATIVE RADIOLOGY Sommer, G., NOORBEHESHT, B., Pelc, N., Jamison, R., Pinevich, A. J., Newton, L., Myers, B. 1992; 27 (6): 465-470

  Abstract

  This study assesses the ability of a cardiac-gated phase-contrast magnetic resonance imaging (MRI) technique to measure renal blood flow (RBF) noninvasively in humans.In nine normal volunteers, total RBF in the renal arteries and in the left renal vein was estimated by MRI and correlated with RBF determined by the clearance of para-aminohippuric acid (CPAH) and the hematocrit level.Correlation of RBF estimated from left renal vein flow, with RBF by CPAH-hematocrit, yielded r = .86 (P less than .003). Repeated measurement of RBF by MRI demonstrated a high degree of reproducibility, with coefficients of variation ranging from 4.8% to 8.9%. However, the MRI measurements of arterial flow did not significantly correlate with the standard measurements.Reproducible noninvasive measurement of normal RBF is possible with the phase-contrast MRI technique used to measure renal venous blood flow.

  View details for Web of Science ID A1992HX03500010

  View details for PubMedID 1607260

• DETERMINATION OF CEREBRAL BLOOD-FLOW WITH A PHASE-CONTRAST CINE MR IMAGING TECHNIQUE - EVALUATION OF NORMAL SUBJECTS AND PATIENTS WITH ARTERIOVENOUS-MALFORMATIONS RADIOLOGY Marks, M. P., Pelc, N. J., Ross, M. R., Enzmann, D. R. 1992; 182 (2): 467-476

  Abstract

  This study evaluated a phase-contrast cine magnetic resonance (MR) imaging technique capable of simultaneously allowing determination of velocity and volume flow rate (VFR) in both carotid arteries and the basilar artery. Forty patients were studied; 24 were neurologically normal, and 16 had intracerebral arteriovenous malformations (AVMs). In the normal group, mean basilar flow was significantly less than mean carotid flow. Mean velocity and VFR showed a significant decline with age in the basilar artery. Carotid artery flow and total cerebral blood flow did not decline with age. In the AVM patients, flow and velocity measurements were significantly elevated in all three arteries. Flow in the carotid artery ipsilateral to the AVM was significantly greater than flow in the contralateral carotid artery. VFR increased in all three arteries with increasing AVM volume. Four patients underwent partial embolization, and a corresponding decrease in flow was observed. Phase-contrast cine MR imaging provides rapid, simultaneous, noninvasive velocity and VFR measurement in the major intracranial arteries.

  View details for Web of Science ID A1992HA58600033

  View details for PubMedID 1732966

• Elastic properties of tendon and myotendinous tissue: Measurement with phase-contrast MR imaging. '92 RSNA Radiology 185P Drace, J., E., Herfkens, R., J., Pelc, N., J. 1992: 177
• Renal blood flow measurement using phase-contrast cine MRI: Preliminary report. Invest. Radiol Sommer, F., G., Noorbehesht, B., Pelc, N., J., Jamison, R., Pinevich, A., Newton, L. 1992; 27: 465-470
• Phase-contrast cine MR imaging for measuring superior mesenteric artery blood flow. 92 RSNA, Radiology 185P Li, K., C.P., Whitney, W., S., MacDonnell, C., H., Van Dalsem, W., J., Fredrickson, J., O., Pelc et al, N., J. 1992: 235
• Evaluation of Cerebral Blood Flow in Patients with Ischemic White Matter Disease and Carotid Occulsive Disease Utilizing Phase Contrast Cine MR. Book of Absrtacts ASNR Marks, M., P., Pelc, N., J., Liddell, R., P., Enzmann, D., R. 1992: 101
• Veolocity Imaging and Flow Quantitation in the Superior Sagittal and Dural Venous Sinuses with Ungated and Cine Gated 2D Phase Contrast MR. Book of Absrtacts ASNR Jordan, J., E., Pelc, N., J., Enzmann, D., R. 1992: 58
• Improvement in vessel conspicuity of 3D phase contrast MRI by application of a divergence-free constraint. Book of Abstracts SMRM Song, S., M., Napel, S., A., Pelc, N., J. 1992: 474
• Flexible and rapid time-resolved imaging by view-order selection. Book of Abstracts SMRM Fredrickson, J., O., Shimakawa, A., Pelc, N., J. 1992: 3921
• 3D analysis of myocardial motion and deformation with phase contrast cine MRI. Book of Abstracts SMRM Pelc, N., J., Herfkens, R., J., Pelc, L., R. 1992: 18
• Evaluation of cerebral blood flow with phase-contrast cine MR in patients with atherosclerotic carotid artery disease. 92 RSNA, Radiology 185P Marks, M., P., Liddell, R., P., Pelc, N., J., Enzmann, D., R. 1992: 181
• Comparison of ungated and cine-gated 2D phase contrast MR measurements of blood flow in major cerebral arteries. 92 RSNA, Radiology 185P Enzmann, D., R., Pelc, N., J. 1992: 182
• Brain motion: measurement with phase-contrast MR Imaging. Radiology Enzmann, D., R., Pelc, N., J. 1992; 185: 653-660
• Quantitative differential pulmonary perfusion: MR imaging versus radionuclide scanning versus lung scanning. Silverman, J., M., Julien, P., J., Herfkens, R., J., Pelc, N., J. 1992
• Right ventricular strain measured by phase contrast MRI. Book of Abstracts SMRM Herfkens, R., J., Pelc, N., J., Pelc, L., R., Sayre, J., R. 1992: 163
• MR imaging displacement and velocity profiles in skeletal muscle correlate with developed force. 92 RSNA, Radiology 185P Drace, J., E., Herfkens, R., J., Pelc, N., J. 1992: 332
• Phase contrast cine magnetic resonance imaging. Magnetic resonance quarterly Pelc, N. J., Herfkens, R. J., Shimakawa, A., Enzmann, D. R. 1991; 7 (4): 229-254

  Abstract

  Phase contrast cine magnetic resonance imaging (MRI) combines the flow-dependent contrast of phase contrast MRI with the ability of cardiac cine imaging to produce images throughout the cardiac cycle. Two pulse sequence types are used for sensitivity to flow in one direction, whereas four are needed for sensitivity in all directions. Several alternatives for synchronization of the data to the cardiac cycle exist. Retrospectively interpolated methods can image the entire cardiac cycle efficiently. Rapid interleaving of the various sequence types ensures immunity to motion misregistration. The technique produces images in which contrast is related to flow velocity as well as magnitude images such as those of conventional cine MRI. The data can be interpreted qualitatively to demonstrate the presence, magnitude, and direction of flow, and quantitatively to provide estimates of flow velocity, volume flow rate, and displaced volumes. Phase contrast cine MRI is helpful in the diagnosis of aortic dissections, in the study of flow distributions in large vessels such as pulmonary arteries, as well as in smaller vessels such as carotid and basilar arteries, and in the evaluation of complex anatomical variants. Future developments are expected to reduce imaging time and expand the quantitative applications.

  View details for PubMedID 1790111

• ENCODING STRATEGIES FOR 3-DIRECTION PHASE-CONTRAST MR IMAGING OF FLOW JOURNAL OF MAGNETIC RESONANCE IMAGING Pelc, N. J., Bernstein, M. A., Shimakawa, A., Glover, G. H. 1991; 1 (4): 405-413

  Abstract

  Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase-contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six-point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four-point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six-point method. An alternate, balanced four-point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four-point method is more efficient and is preferred over the six-point approach.

  View details for Web of Science ID A1991HA76600003

  View details for PubMedID 1790362

• SIMULTANEOUS ACQUISITION OF PHASE-CONTRAST ANGIOGRAMS AND STATIONARY-TISSUE IMAGES WITH HADAMARD ENCODING OF FLOW-INDUCED PHASE-SHIFTS JOURNAL OF MAGNETIC RESONANCE IMAGING Dumoulin, C. L., Souza, S. P., Darrow, R. D., Pelc, N. J., Adams, W. J., Ash, S. A. 1991; 1 (4): 399-404

  Abstract

  A technique for the simultaneous acquisition of three-dimensional phase-contrast angiograms and stationary-tissue images is described. Hadamard multiplexed encoding of flow information permits image acquisition times that are a third shorter than those of previous phase-contrast methods. The encoding scheme described also enables differentiation of flow-induced phase shifts from phase shifts due to resonance offset conditions such as field inhomogeneities and chemical shift. Display strategies that combine this phase information with the flow image are described.

  View details for Web of Science ID A1991HA76600002

  View details for PubMedID 1790361

• DURAL SINUS OCCLUSION - EVALUATION WITH PHASE-SENSITIVE GRADIENT-ECHO MR IMAGING AMERICAN JOURNAL OF ROENTGENOLOGY Tsuruda, J. S., Shimakawa, A., Pelc, N. J., Saloner, D. 1991; 157 (1): 139-146

  View details for Web of Science ID A1991FR86800031

• DURAL SINUS OCCLUSION - EVALUATION WITH PHASE-SENSITIVE GRADIENT-ECHO MR IMAGING AMERICAN JOURNAL OF NEURORADIOLOGY Tsuruda, J. S., Shimakawa, A., Pelc, N. J., Saloner, D. 1991; 12 (3): 481-488

  Abstract

  The purpose of this study was to evaluate the usefulness of limited-flip-angle, phase-sensitive velocity imaging with gradient-recalled-echo (VIGRE) MR when combined with spin-echo MR in the diagnosis of dural sinus thrombosis. The VIGRE sequence consists of a rapid single-slice acquisition, 50/15/2 (TR/TE/excitations), and 30 degrees flip angle. At each slice position, a total of four images were reconstructed; these consisted of one magnitude image and three images sensitive to proton motion in each orthogonal direction. The flow direction and flow velocity (cm/sec) were obtained from each of the phase images, and results were correlated with data obtained from a phantom experiment. In normal controls, dural sinus velocities ranged from a mean of 9.9 to 14.4 cm/sec for the transverse and superior sagittal sinuses, respectively. Three patients with proved dural sinus occlusion were studied with spin-echo images at 1.5 T. Three-dimensional time-of-flight MR angiography was also performed in one patient. The presence of dural sinus occlusion was determined by the lack of flow void on the spin-echo images, the absence of phase shift on the VIGRE study, and the presence of retrograde flow on the phase image in the sinus proximal to the occluded segment. Time-of-flight angiography overestimated the extent of the thrombosis caused by spin saturation. Follow-up VIGRE studies detected the formation of collateral flow in one patient and recanalization with the establishment of normal antegrade sinus flow in the other. We conclude that phase-sensitive MR imaging is helpful in establishing the diagnosis and extent of dural sinus occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

  View details for Web of Science ID A1991FJ90400021

  View details for PubMedID 2058498

• NORMAL FLOW PATTERNS OF INTRACRANIAL AND SPINAL CEREBROSPINAL-FLUID DEFINED WITH PHASE-CONTRAST CINE MR IMAGING RADIOLOGY Enzmann, D. R., Pelc, N. J. 1991; 178 (2): 467-474

  Abstract

  A phase-contrast cine magnetic resonance (MR) imaging technique was used to study normal dynamics of cerebrospinal fluid (CSF) in 10 healthy volunteers and four patients with normal MR images. This pulse sequence yielded 16 quantitative flow-encoded images per cardiac cycle (peripheral gating). Flow encoding depicted craniocaudal flow as high signal intensity and caudo-cranial flow as low signal intensity. Sagittal and axial images of the head, cervical spine, and lumbar spine were obtained, and strategic sites were analyzed for quantitative CSF flow. The onset of CSF systole in the subarachnoid space was synchronous with the onset of systole in the carotid artery. CSF systole and diastole at the foramen of Monro and aqueduct were essentially simultaneous. The systolic and diastolic components were different in the subarachnoid space, where systole occupied approximately 40% and diastole 60% of the cardiac cycle, compared with the ventricular system, where they were equal. This difference results in systole in the intracranial and spinal subarachnoid spaces preceding that in the ventricular system; the same is true for diastole. The fourth ventricle and cisterna magna serve as mixing chambers. The high-velocity flow in the cervical spine and essentially no flow in the distal lumbar sac indicate that a portion of the capacitance necessary in this essentially closed system resides in the distal spinal canal.

  View details for Web of Science ID A1991EU03500034

  View details for PubMedID 1987610

• EVALUATION OF ACUTE-RENAL-FAILURE WITH MAGNETIC-RESONANCE-IMAGING USING GRADIENT-ECHO AND GD-DTPA INVESTIGATIVE RADIOLOGY Munechika, H., SULLIVAN, D. C., Hedlund, L. W., Beam, C. A., Sostman, H. D., Herfkens, R. J., Pelc, N. J. 1991; 26 (1): 22-27

  Abstract

  Detection of acute renal failure (ARF) using fast-scan magnetic resonance imaging (MRI) with Gd-DTPA was studied in a dog model. ARF was produced in five dogs by infusion of norepinephrine (0.75 micrograms/kg/min) into the renal arteries for 40 minutes. MRI was performed 1 hour later and compared with baseline (pre-ARF) MRI. There was no significant difference in the ratios of signal intensity-vs.-time curves from 0 to 35 seconds after injection of Gd-DTPA. However, a difference between the outer and inner medulla was significant in the time period of 5 to 20 minutes after Gd-DTPA injection. These later signal intensity differences by fast-scan (gradient-echo) technique may be useful in the evaluation of ARF.

  View details for Web of Science ID A1991ER52500005

  View details for PubMedID 2022449

• Phase contrast Magnetic Resonance Imaging accurately tracks myocardial motion in a canine model. Sayre, J., R., Pelc, L., R., Herfkens, R., J., Castro, L., J., Rayhill, S., R., Miller, D., C. 1991
• Brain motion during the cardiac cycle. Enzmann, D., R., Pelc, N., J. 1991
• Noninvasive quantitation of arterial and venous blood flow with MR imaging. Radiology 181P Pelc, L., R., Pelc, N., J., Rayhill, S., C., Castro, L., J., Glover, G., H., Jeffrey et al, R., B. 1991: 263
• Initial experience with myocardial motion analysis by means of phase-contrast MR imaging. 91 RSNA, Radiology 181P Herfkens, R., J., Pelc, N., J., Sayre, J., R., Pelc, L., R. 1991: 219
• Dural sinus occlusion: evaluation with phase sensitive gradient echo MR imaging. AJNR Tsuruda, J., S., Shimakawa, A., Pelc, N., J., Saloner, D. 1991; 12: 481-488
• Determination of cerebral blood flow with a phase-contrast cine MR technique: Evaluation of normal and AVM patients. Society of Magnetic Resonance in Medicine Marks, M., P., Pelc, N., J., Enzmann, D., R. 1991: 260
• Improved diagnostic accuracy of aortic dissection with phase contrast cine MRI. Herfkens, R., J., Trefelner, E., Jeffrey, R., B., Steiner, R., M., Francis, I., R., Pelc, N., J. 1991
• Simultaneous acquisition of phase-contrast angiograms and stationary-tissue images with Hadamard encoding of flow-induced phase shifts. JMRI Dumoulin, C., L., Souza, S., P., Darrow, R., D., Pelc, N., J., Adams, W., J., Ash, S., A. 1991; 1: 399-404
• Reduced pulsatility artifacts in MR angiography. Society of Magnetic Resonance in Medicine Pelc, N., J., Shimakawa, A. 1991: 821
• Phase-contrast MR imaging measurement of myocardial motion. JMRI Pelc, N., J., Herfkens, R., J., Pelc, L., R. 1991; 1: 181
• MR imaging of the pulmonary vasculature: Optimization with a breath-holding spoiled gradient-echo technique. 91 RSNA, Radiology 181P Rubin, G., D., Steiner, R., M., Pelc, N., J., Herfkens, R., J., Francis, I., R., Low, R., N. 1991: 156
• Measurement of cerebrospinal fluid flow with phase-contrast cine MR. 91 RSNA, Radiology 181P Enzmann, D., R., Pelc, N., J. 1991: 171
• Aortic dissection: Velocity encoded pulse sequence improves diagnostic accuracy. Society of Computed Body Tomography. Am. J. Roentg Herfkens, R., J., Jeffrey, R., B, Trefelner, E., Pelc, N., J., Lucas:, D. 1991; 157: 616
• Renal blood flow measurement using phase-contrast cine MRI. Society of Magnetic Resonance in Medicine Sommer, F., G., Noorbehesht, B., Pelc, N., J., Jamison, R., L., Pinevich, A., J., Newton, L. 1991: 966
• Myocardial motion analysis with phase contrast cine MRI. Society of Magnetic Resonance in Medicine Pelc, N., J. 1991: 17
• Measurement of CSF flow using a phase-contrast cine MR pulse sequence. Society of Magnetic Resonance in Medicine Enzmann, D., R., Ross, M., R., Pelc, N., J. 1991: 155
• Angiography of the portal venous system: Optimizing technique. Society of Computed Body Tomography. Am. J. Roentg Jeffrey, R., B., Pelc, N., J., Trefelner, E. 1991; 157: 616
• Accuracy and precision of phase-contrast flow measurements. Radiology 181P Pelc, N., J., Sommer, F., G., Enzmann, D., R., Pelc, L., R., Glover, G., H. 1991: 189
• RAPID MR IMAGING OF BLOOD-FLOW WITH A PHASE-SENSITIVE, LIMITED-FLIP-ANGLE, GRADIENT RECALLED PULSE SEQUENCE - PRELIMINARY EXPERIENCE RADIOLOGY Spritzer, C. E., Pelc, N. J., Lee, J. N., Evans, A. J., Sostman, H. D., Riederer, S. J. 1990; 176 (1): 255-262

  Abstract

  To assess blood flow rapidly, a limited-flip-angle, gradient recalled pulse sequence was modified to acquire two views at the same phase-encoding step in successive repetitions. One view is obtained with first-moment flow compensation, while the second view is obtained with selectable flow encoding (non-zero first moment) along one direction. Blood flowing along the encoded direction acquires a phase difference between the two views, resulting in signal dependent on both direction and speed of flow. Stationary tissues undergo no phase change. Therefore, the phase shift between the two views produces an image that spatially renders flow direction and velocity. With a 24-msec repetition time, a 256 X 128 matrix, and two excitations, data acquisition is completed in 13 seconds per location (both a magnitude image and a flow image are produced at each location). Images generated with flow phantoms confirmed the accuracy of this method. Preliminary clinical evidence in 23 human subjects suggests that this method is useful in evaluating portal hypertension, distinguishing arterial from venous flow, distinguishing between slow flow and clot, and confirming the presence of clot. This method appears to be a fast, easy way to assess blood flow in large vessels.

  View details for Web of Science ID A1990DJ99600053

  View details for PubMedID 2353099

• ANALYSIS OF T2 LIMITATIONS AND OFF-RESONANCE EFFECTS ON SPATIAL-RESOLUTION AND ARTIFACTS IN ECHO-PLANAR IMAGING MAGNETIC RESONANCE IN MEDICINE Farzaneh, F., Riederer, S. J., Pelc, N. J. 1990; 14 (1): 123-139

  Abstract

  Several aspects of blipped echo-planar imaging (EPI) are treated mathematically. An expression relating the necessary readout gradient strength and sampling time to the spatial resolution and readout duration is derived. It is shown how the net spatial resolution may be limited by the object's T2 characteristics and B0 field homogeneity, irrespective of the number of sampled points. Additionally, off-resonance effects result in a loss of spatial resolution and image distortion to a considerably greater degree than in conventional two-dimensional Fourier transform imaging. The extent of these effects is directly related to the time required to acquire the data matrix, and is therefore amplified when EPI is implemented on a standard commercial whole-body system which because of limited gradient performance uses necessarily longer sampling durations. Specific hardware modifications to a standard commercial imager are considered to allow successful EPI implementation. EPI image characteristics are compared quantitatively with those of conventional methods.

  View details for Web of Science ID A1990CZ23000011

  View details for PubMedID 2352469

• Methods to achieve very short echo times for volume magnetic resonance angiography. Radiology Schmalbrock, P., Yuan, C., Charkeres, D., W., Kohli, J., Pelc, N., J. 1990; 175: 861-865
• Reduced scan time with improved signal-to-noise in phase-contrast flow MR imaging. Radiology, 177P Pelc, N., J., Bernstein, M., A. 1990: 171
• Measurement of myocardial motion dynamics with phase-contrast cine MRI. Radiology, 177P Pelc, N., J., Pelc, L., R., Herfkens, R., J., Glover, G., H. 1990: 171
• Application of velocity imaging and gradient-recalled echo in neuroimaging. Radiology, 177P Boyko, O., B., Pelc, N., J., Shimakawa, A. 1990: 256
• Multiphase respiratory gated MRI - Study of normal respiratory motion. Pelc, N., J., Fitzpatrick, M., E., Shimakawa, A., Herfkens, R., J. 1990
• MR measurement of portal blood flow in chronic liver disease: Application to predicting clinical outcome. Book of Abstracts SMRM Rubin, D., L, Herfkens, R., J., Pelc, N., J., Jeffrey, R., B. 1990: 90
• Modeling of hand function by mapping the motion of individual muscle voxels with MR velocity tagging. Radiology, 177P Drace, J., Pelc, N., J., Herfkens, R., J. 1990: 224
• Optimized encoding for phase contrast flow measurement. Book of Abstracts SMRM Pelc, N., J., Bernstein, M., A. 1990: 475
• Preliminary experience with rapid MR blood flow imaging using a phase sensitive limited flip angle gradient refocussed pulse sequence. Radiology Spritzer, C., E., Pelc, N., J., Lee, J., N., Evans, A., J., Sostman, H., D., Riederer, S., J. 1990; 176: 255-262
• Normal CSF flow dynamics in the brain and spine. American Society of Neuroradiology, Los Angeles Enzmann, D., R., Pelc, N., J. 1990
• FLOW-COMPENSATED LIMITED FLIP ANGLE MR ANGIOGRAPHY MAGNETIC RESONANCE IN MEDICINE Lee, J. N., Riederer, S. J., Pelc, N. J. 1989; 12 (1): 1-13

  Abstract

  A method of subtraction angiography that has an acquisition time of 8 s per slice is described. Flow-compensated and uncompensated measurements are acquired in an interleaved fashion using limited flip angles and gradient refocusing. Magnitude images are reconstructed and subtracted to generate the angiogram. Results were generated in vivo in the imaging of the carotid bifurcation of several human volunteers. Susceptibility and inhomogeneity induced artifacts are prominent in thick slices, but can be greatly reduced by imaging several thin slices and adding them together. Thin slices do not require dephasing gradients to reduce the dynamic range, and there is no signal cancellation in overlapping vessels. The method is ideal for acquiring scout angiograms, and with averaging may produce images of diagnostic quality.

  View details for Web of Science ID A1989AT67000001

  View details for PubMedID 2691835

• Cine phase contrast maps of cervical cerebrospinal fluid motion. Radiology, 173P Enzmann, D., R., Rubin, J., Pelc, N., J. 1989: 157
• A new transceiver for MR imaging and spectroscopy. Book of Abstracts SMRM Stormont, R., S., Noonan, J., P., Pelc et. al., N., J. 1989: 962
• Detection of iron in hemorrhage using a combined spin echo and gradient echo acquisition. American Society of Neuro Radiology, Orlando Boyko, O., B., Pelc, N., J., Curnes et. al., J., T. 1989
• Cine phase contrast technique for the determination of cerebral blood flow. Radiology, 173P Marks, M., P., Pelc, N., J., Enzmann, D., R. 1989: 186
• Reduction of motion artifacts in computed tomography. Crawford, C., R., Godwin, J., D., Pelc, N., J. edited by Kim, Y., Spelman, F., A. 1989
• Visualization of supratentorial perivascular spaces with VB pulse sequence. Society of Magnetic Resonance Imaging, Los Angeles Boyko, O., B., Pelc, N., J., Shimakawa et. al., A. 1989
• Phase contrast cine MRI. Book of Abstracts SMRM Pelc, N., J., Shimakawa, A., Glover, G., H. 1989: 101
• MRI of normal/ abnormal brain iron using a combined spin and gradient echo acquisition. Society of Magnetic Resonance Imaging, Los Angeles Boyko, O., B., Pelc, N., J., Herfke et al, R., J. 1989
• Flow compensated limited flip angle MR angiography. Mag. Res. Med. Lee, J., N., Riederer, S., J., Pelc, N., J. 1989; 12: 1-13
• CSF dynamics in normal and syringomyelia patients using phase contrast cine MR. Book of Abstracts SMRM Enzmann, D., R., Pelc, N., J. 1989: 11
• Cine velocity encoded MR imaging: Initial clinical experience. Radiology, 173P Herfkens, R., J., Pelc, N., J., Shimakawa, A. 1989: 275
• VALVULAR REGURGITATION - DYNAMIC MR IMAGING RADIOLOGY UTZ, J. A., Herfkens, R. J., HEINSIMER, J. A., Shimakawa, A., Glover, G., Pelc, N. 1988; 168 (1): 91-94

  Abstract

  Cine magnetic resonance (MR) imaging is a new technique that combines short repetition times, limited flip angles, gradient refocused echoes, and cardiac gating. This technique has a temporal resolution of up to 32 time frames per cardiac cycle and accentuates signal from flowing blood. Cine MR images of 56 valves in 27 patients were evaluated and compared with either Doppler echocardiograms or cardiac catheterization images. An area of decreased signal that correlated spatially and temporally with regurgitant blood flow was seen in all instances in which valvular incompetence was demonstrated on either Doppler echocardiograms or cardiac catheterization images (20 valves). This abnormality was seen in nine of 36 cases without valvular incompetence. Cine MR imaging may be sensitive to turbulence and thus sensitive to valvular regurgitation.

  View details for Web of Science ID A1988N942700016

  View details for PubMedID 3380987

• A software approach to variable bandwidth multiecho imaging. Book of Abstracts SMRM Pelc, N., J., Shimakawa, A. 1988: 1048
• A rapid-gated cine MRI technique. Magnetic resonance annual Glover, G. H., Pelc, N. J. 1988: 299-333

  View details for PubMedID 3079300

• A rapid gated cine MRI technique. In Magnetic Resonance Annual 1988 Glover, G., H., Pelc, N., J. edited by Kressel, H., Y. Raven Press, New York. 1988: 299–333
• Correction for spatially dependent phase shifts for partial Fourier imaging. Mag. Res. Imag. MacFall, J., R., Pelc, N., J., Vavrek, R. 1988; 6: 143-155
• A method for mapping T2' and for improved T2 measurements. Book of Abstracts SMRM. Pelc, N., J., Shimakawa, A., Boyko, O., B. 1988: 746
• A rapid flow imaging method. Radiology, 169P Pelc, N., J., Spritzer, C., E., Lee, J., N. 1988: 343
• High speed reprojection and its applications. Crawford, C., R., Colsher, J., G., Pelc, N., J. 1988
• Preliminary experience with a rapid phase sensitive limited flip angle gradient refocussed pulse sequence to determine blood flow. Radiology, 169P Spritzer, C., E., Pelc, N., J., Lee et. al., J., N. 1988: 108
• Improved magnetic resonance images of the brain using a variable bandwidth pulse sequence. American Society of Neuro Radiology, Chicago Curnes, J., T., Boyko, O., B., Yeates, A., E., Pelc, N., J., Shimakawa, A. 1988
• Clinical experience of detecting hemorrhage using an acquisition combining gradient and spin echo imaging generating T2 prime maps. Book of Abstracts SMRM Boyko, O., B., Pelc, N., J., Herfkens et al, R., J. 1988: 74
• CINE MR DETERMINATION OF LEFT-VENTRICULAR EJECTION FRACTION AMERICAN JOURNAL OF ROENTGENOLOGY UTZ, J. A., Herfkens, R. J., HEINSIMER, J. A., Bashore, T., Califf, R., Glover, G., Pelc, N., Shimakawa, A. 1987; 148 (5): 839-843

  Abstract

  Cine MR imaging provides tomographic images of the heart with both high spatial and high temporal resolution. As many as 32 images per cardiac cycle can be acquired with up to four separate anatomic slices and a total imaging time of 128 cardiac cycles. End-diastolic and end-systolic volumes were determined in 11 patients, and ejection fractions were calculated. The results correlated linearly with those from cardiac catheterization (correlation coefficient of .88). We conclude that cine MR imaging can be used to obtain quantitative information about the heart and has the potential to become a valuable noninvasive means of cardiac evaluation.

  View details for Web of Science ID A1987G945000001

  View details for PubMedID 3495115

• 2-SECOND MR IMAGES - COMPARISON WITH SPIN-ECHO IMAGES IN 29 PATIENTS AMERICAN JOURNAL OF ROENTGENOLOGY UTZ, J. A., Herfkens, R. J., Johnson, C. D., Shimakawa, A., Pelc, N., Glover, G., Johnson, G. A., Spritzer, C. E. 1987; 148 (3): 629-633

  Abstract

  MR images can be obtained with a 2-sec scan time when an extremely short repetition rate (22 msec), limited flip angle (30 degrees), and gradient refocused echoes are used. Comparison of 415 such images obtained in 29 patients with routine T1-weighted (TR 500, TE 25) and T2-weighted (TR 2000, TE 80) images showed that images free of respiratory artifacts could be obtained in all patients. Although abdominal organs were well seen with 2-sec scan time, overall evaluation of these organs was better on routine T1-weighted images. Vascular structures, however, were seen as well or better on the 2-sec images in 60% of cases. The images were extremely sensitive to field nonhomogeneity, and metallic artifact was exaggerated in five patients with surgical clips. Two-sec MR images provide a rapid method of localizing abdominal organs for further evaluation. The sensitivity to blood flow may assist in the assessment of vascular patency.

  View details for Web of Science ID A1987G131300036

  View details for PubMedID 3492897

• RAPID CALCULATION OF T1 USING VARIABLE FLIP ANGLE GRADIENT REFOCUSED IMAGING MAGNETIC RESONANCE IMAGING Fram, E. K., Herfkens, R. J., Johnson, G. A., Glover, G. H., Karis, J. P., Shimakawa, A., PERKINS, T. G., Pelc, N. J. 1987; 5 (3): 201-208

  Abstract

  We present a method for rapid measurement of T1 relaxation times using gradient refocused images at limited flip angles and short repetition times. This "variable nutation" techniques was investigated using a T1 phantom. There was a high correlation between measurements obtained with the variable nutation and partial saturation techniques. The ability of this method to create calculated T1 images is also demonstrated. We conclude that the variable nutation method may allow measurement of T1 relaxation times with a significant reduction in acquisition time compared to partial saturation techniques.

  View details for Web of Science ID A1987J432400007

  View details for PubMedID 3626789

• Applications of high speed reprojection algorithms. Crawford, C., R., Colsher, J., G., Pelc, N., J. edited by et al, L. 1987
• Grass movie technique for gated studies. Glover, G., H., Pelc, N., J., Shimakawa, A. 1987
• Rapid calculation of T1 using variable flip angle gradient refocused imaging. Magn Reson Imaging Fram, E., K., Herfkens, R., J., Johnson, G., A., Glover, G., H., Karis, J., P., Shimakawa, A., Pelc, N. J. 1987; 5: 201-8
• Principles of x-ray computed tomography. In Radiology Pelc, N., J., Colsher, J., G. edited by Taveras, J., M., Ferrucci, J., T. J. B. Lippincott Co., Philadelphia. 1987: 1
• Two-second MR images: Comparison with spin-echo images in 29 patients. AJR Utz, J., A., Herfkens, R., J., Johnson, C., D., Shimakawa, A., Pelc, N., J., Glover, G., H. 1987; 148: 629-633
• Applications of high speed reprojection algorithms. Computer Assisted Radiology International Symposium and Exhibition, Berlin, 1987. Crawford, C., R., Colsher, J., G., Pelc, N., J. edited by et al, L. Springer Verlag, Berlin. 1987: 142
• Computed tomography systems and performance. In Radiology Colsher, J., G., Pelc, N., J. edited by Taveras, J., M., Ferrucci, J., T. J. B. Lippincott Co., Philadelphia. 1987: 1
• CT reconstruction with angular integration and inter-projection correlation. Radiology, 161P Crawford, C., R., Pelc, N., J. 1986: 244
• Dynamic MR imaging of the heart. Radiology, 161P Utz, J., A., Herfkens, R., J., Glover, G., H., Pelc, N., J., Shimakawa, A. 1986: 185
• An attenuated projector-backprojector for iterative SPECT reconstruction. Phys. Med. Biol. Gullberg, G., T., Huesman, R., H., Malko, J., A., Pelc, N., J., Budinger, T., F. 1985; 30: 799-816
• CHEMICAL-SHIFT MAGNETIC-RESONANCE IMAGING OF 2-LINE SPECTRA BY GRADIENT REVERSAL MAGNETIC RESONANCE IN MEDICINE Axel, L., Glover, G., Pelc, N. 1985; 2 (5): 428-436

  Abstract

  A method of chemical-shift imaging is described using the invariance of chemical shifts to changes in magnetic field gradients used for frequency encoding of position in imaging. This enables separation of the effects on the observed signal of chemical shift from the effects of different positions along the imaging gradient when the signal is observed with different gradients. A simple implementation for a two-line spectrum is presented using signals observed with normal and reversed imaging gradients. This is used to create "fat" and "water" images of the thigh.

  View details for Web of Science ID A1985ATJ1100002

  View details for PubMedID 4094557

• COMPARISON OF LINEAR AND CIRCULAR-POLARIZATION FOR MAGNETIC-RESONANCE IMAGING JOURNAL OF MAGNETIC RESONANCE Glover, G. H., Hayes, C. E., Pelc, N. J., Edelstein, W. A., Mueller, O. M., HART, H. R., Hardy, C. J., ODONNELL, M., Barber, W. D. 1985; 64 (2): 255-270

  View details for Web of Science ID A1985AQW9800008

• Respiration artifacts in MRI. Pelc, N., J., Glover, G., H., Charles, H., C. 1985
• Comparison of linear and circular polarization for magnetic resonance imaging. J. Mag. Res. Glover, G., H., Hayes, C., E., Pelc, N., J., Edelstein, W., A., Mueller, O., M., Hart, H., R. 1985; 64: 2
• Chemical shift magnetic resonance imaging of two-line spectra by gradient reversal. Mag. Res. Med. Axel, L., Glover, G., H., Pelc, N., J. 1985; 2: 428-436
• Progress in ECG gated CT. Testing with a motion phantom and comparison with the Imatron 50 msec scanner. Radiology, 153P Godwin, J., D., Pelc, N., J., Johnson et. al., G., A. 1984: 268
• Statistical aspects of digital x-ray imaging. In Electronic Imaging in Medicine Pelc, N., J. edited by et al, F. AAPM Monograph 11, Am. Inst. Phys., New York. 1984: 1
• Improved cardiac gated CT using a GE CT-9800. Association of University Radiologists Pelc, N., J., Godwin, J., D., Teeter, B., C. 1984
• Retrospective cardiac gating with a CT-9800. International Workshop on cardiac reconstruction.Santa Cruz, 1983, J. Comput. Assist. Tomogr. Pelc, N., J. 1984; 8: 361-2
• INTRAARTERIAL DIGITAL SUBTRACTION SPINAL ANGIOGRAPHY AMERICAN JOURNAL OF NEURORADIOLOGY Enzmann, D. R., Brody, W. R., DJANG, W. T., Riederer, S., Keyes, G., Collins, W., Pelc, N. 1983; 4 (1): 25-26

  View details for Web of Science ID A1983PV95600004

  View details for PubMedID 6402899

• Spectral variations in tissues and phantoms. Ultrasound in medicine and biology FLAX, S. W., Glover, G. H., Pelc, N. J., Gutmann, F. D., McLachlan, M. 1983: 127-131

  Abstract

  This paper is concerned with the characterization of attenuation in tissue. A simple method for measuring frequency dependent attenuation is demonstrated. The effects of frequency dependent scatter on the measurement of attenuation are also considered in order to determine the theoretical and practical ramifications of this interfering effect. Finally, a means of placing definitive error bounds on the statistical reliability of the measurement is discussed.

  View details for PubMedID 6400227

• SPECTRAL CHARACTERIZATION AND ATTENUATION MEASUREMENTS IN ULTRASOUND ULTRASONIC IMAGING FLAX, S. W., Pelc, N. J., Glover, G. H., Gutmann, F. D., McLachlan, M. 1983; 5 (2): 95-116

  Abstract

  Various means of characterizing ultrasonic attenuation in tissue are reviewed. A simple method for estimating frequency-dependent attenuation via measurement of the zero crossing density of the signal is presented and validated. Both the effects of the frequency dependence of scatter and stochastic variability of the measurement are considered and discussed. Results of measurements made in phantoms, animals and humans are presented and compared to the theoretical model. The technique is shown to be technically feasible.

  View details for Web of Science ID A1983QS87600001

  View details for PubMedID 6683894

• Textural variations in B-mode ultrasonography. Flax, S., W., Pelc, N., J. 1983
• Spectral variations in tissues and phantoms. Ultrasound Med Biol Flax, S., W., Glover, G., H., Pelc, N., J., Gutmann, F., D., McLachlan, M. 1983; 2: 127-131
• Spectral characterization and attenuation measurements in ultrasound. Ultrason Imaging Flax, S., W., Pelc, N., J., Glover, G., H., Gutmann, F., D., McLachlan, M. 1983; 5: 95-116
• The application of matched filtering to x-ray exposure reduction in digital subtraction angiography: clinical results. Radiology Riederer, S., J., Enzmann, D., R., Hall, A., L., Pelc, N., J., Djang, W., T. 1983; 146: 349-354
• Experimental retrospective cardiac gating using a G.E. CT 9800 scanner. Radiology, 149P Pelc, N., J., Godwin, J., D., Cann, C., E., Teeter, B., C. 1983: 239
• THE APPLICATION OF MATCHED FILTERING TO X-RAY-EXPOSURE REDUCTION IN DIGITAL SUBTRACTION ANGIOGRAPHY - CLINICAL-RESULTS RADIOLOGY Riederer, S. J., Enzmann, D. R., Hall, A. L., Pelc, N. J., DJANG, W. T. 1983; 146 (2): 349-354

  Abstract

  This new digital fluorography processing method of matched filtering generates a set of images that have been acquired at continuous video-frame rates (30 per second) over the temporal extent of the bolus (10 seconds), and it combines them to produce the equivalent of a single digital subtraction angiography (DSA) image. Because of the extensive temporal averaging used, the method can provide substantial x-ray exposure reduction per run as compared with conventional techniques for an equivalent signal-to-noise ratio in the final image. The matched filtering technique was compared with conventional pulsed (one per second) DSA images of both extracranial and intracranial arteries, and the results are presented. Matched filtered images provided image quality that was equivalent to that of conventional DSA images at about one-fourth the patient exposure per run for both carotid artery and cerebral vessel studies. Despite long integration times, patient motion irretrievably corrupted image quality in only two of five carotid artery studies and in none of three intracranial studies. Compensation for patient motion is demonstrated, and additional applications and limitations of the technique are discussed.

  View details for Web of Science ID A1983PZ13800012

  View details for PubMedID 6336846

• THE TECHNICAL CHARACTERISTICS OF MATCHED FILTERING IN DIGITAL SUBTRACTION ANGIOGRAPHY MEDICAL PHYSICS Riederer, S. J., Hall, A. L., Maier, J. K., Pelc, N. J., Enzmann, D. R. 1983; 10 (2): 209-217

  Abstract

  The technical characteristics of a new digital fluorographic image processing method called matched filtering are presented. This technique, a type of extensive temporal integration, takes a weighted sum of images acquired during passage of a contrast bolus through some area of interest. The weight of each image is governed by the magnitude of the contrast bolus in that image. An essential requirement of the matched filter is that its integral be zero. It is shown for equal exposure rates and typical bolus characteristics that matched filtering provides a factor of two higher signal-to-noise ratio (SNR) than conventional methods for bolus transit times of 10 s or higher. Equilvalently, matched filtering can yield images with quality comparable to conventional digital subtraction angiography (DSA) at a factor of four less patient exposure. The SNR obtained with matched filtering is shown to be within 30% of an ideal bound. Comparisons of matched filtering to standard recursive methods and simple integration are made. Experimental canine studies are presented which compare matched filtering with conventional DSA.

  View details for Web of Science ID A1983QM15000012

  View details for PubMedID 6346033

• INTRA-CRANICAL INTRAVENOUS DIGITAL SUBTRACTION ANGIOGRAPHY NEURORADIOLOGY Enzmann, D. R., Brody, W. R., Riederer, S., Keyes, G., Collins, W., Pelc, N. 1982; 23 (5): 241-251

  Abstract

  Intravenous digital subtraction angiography (iDSA) promises to significantly alter the use of conventional cerebral angiography in the workup of neurological patients. Understanding its diagnostic potential and its limitations are important in incorporating this new examination into the diagnostic thought process of neuroradiologic tests. Different image processing techniques such as integration of mask and contrast images promise to improve image quality for neuroradiologic application. At present, iDSA is suitable for the diagnosis and follow-up of vascular lesions (atherosclerosis, aneurysms, arteriovenous malformations, venous sinus occlusion), and tumor (meningioma). Although limited, the spatial resolution of iDSA studies is capable of demonstrating diffuse vascular disease such as arteritis and vasospasm after subarachnoid hemorrhage. In some patients in conjunction with the CT scan, iDSA may prove sufficient as the primary and only diagnostic angiographic test necessary, supplanting conventional angiography.

  View details for Web of Science ID A1982PK53500002

  View details for PubMedID 7121819

• CONTRAST SENSITIVITY OF DIGITAL FLUOROGRAPHIC SYSTEMS PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS Riederer, S. J., Hall, A. L., KEYES, G. S., Pelc, N. J. 1982; 372: 66-73

  View details for Web of Science ID A1982RL28700009

• INTRAVENOUS ARTERIOGRAPHY USING DIGITAL SUBTRACTION TECHNIQUES JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION Brody, W. R., Enzmann, D. R., Miller, D. C., GUTHANER, D. F., Pelc, N. J., KEYES, G. S., Riederer, S. J. 1982; 248 (6): 671-674

  Abstract

  The application of digital computers to electronic x-ray imaging devices has rejuvenated interest in the field of intravenous arteriography. By utilizing computer image subtraction techniques, digital roentgenographic systems based on fluoroscopy or computed tomography (scanned projection radiography) provide significantly improved vascular imaging compared with conventional film subtraction methods. Digital subtraction angiography schemes isolate contrast media in the vessel by detecting differences in images obtained before and after the injection of contrast medium or changes in the relative attenuation of contrast media at different x-ray energies. Present applications include carotid and peripheral arteriography, thoracic and abdominal aortography, pulmonary arteriography, and ventriculography. Future applications may include intracerebral and coronary arteriography. These systems should provide low-risk outpatient screening arteriography.

  View details for Web of Science ID A1982PA67300016

  View details for PubMedID 7047776

• DUAL-KVP RADIOGRAPHY PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS Brody, W. R., Sommer, F. G., LEHMANN, L. A., Macovski, A., Alvarez, R. E., Pelc, N. J., Riederer, S. J., Hall, A. 1981; 273: 239-243

  View details for Web of Science ID A1981NF93100037

• TEXTURAL VARIATIONS IN B-MODE ULTRASONOGRAPHY - A STOCHASTIC-MODEL ULTRASONIC IMAGING FLAX, S. W., Glover, G. H., Pelc, N. J. 1981; 3 (3): 235-257

  View details for Web of Science ID A1981LY68200002

• AN ALGORITHM FOR THE REDUCTION OF METAL CLIP ARTIFACTS IN CT RECONSTRUCTIONS MEDICAL PHYSICS Glover, G. H., Pelc, N. J. 1981; 8 (6): 799-807

  Abstract

  Implanted surgical metal clips often produce objectionable artifacts in CT reconstructions. The artifacts appear as streaks which emanate radially from the site of the clip. It is shown in this paper that these artifacts stem primarily from motion of the clip during the scan. An algorithm is described which reduces the intensity of these artifacts. The procedure attempts to remove the metal object entirely from the scan data by replacing the measured projection values of rays that passed through a neighborhood of the clip with calculated values consistent with an object whose density is an average of the surround. Examples are given for head and body scans as well as for computer simulations which show substantial reduction of the streak intensity.

  View details for Web of Science ID A1981MT75600007

  View details for PubMedID 7322078

• Performance characteristics of a digital fluorographic system. Riederer, S., J., DiBianca, F., A., Georges, J, P.J., Jensen, G., A., Keyes, G., S., Pelc, N., J. 1981
• Textural variations in B-mode ultrasonography: a stochastic model. Ultrasonic Imag. Flax, S., W., Glover, G., H., Pelc, N., J. 1981; 3: 235-257
• An algorithm for the reduction of metal clip artifacts in CT reconstructions. Med. Phys. Glover, G., H., Pelc, N., J. 1981; 8: 6
• Experimental system for dual energy scanned projection radiography. Hall, A., L., Pelc, N., J., Riederer, S., J., Keyes, G., S., Brody, W., R., Lehmann, L., A. 1981
• Generalized image combinations in dual kVp digital radiography. Med. Phys. Lehmann, L., A., Alvarez, R., E., Macovski, A., Pelc, N., J., Riederer, S., J., Hall, A., L. 1981; 8: 5
• IODINE SENSITIVITY OF DIGITAL IMAGING-SYSTEMS PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS Riederer, S. J., BELANGER, B. F., KEYES, G. S., Pelc, N. J. 1981; 314: 132-139

  View details for Web of Science ID A1981NF95200021

• AN UNDERSTANDING OF DIGITAL RADIOGRAPHY THROUGH IMAGE COMPUTER-SIMULATION PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS GEORGES, J. P., KEYES, G. S., Pelc, N. J., Riederer, S. J. 1981; 273: 96-102

  View details for Web of Science ID A1981NF93100016

• PERFORMANCE-CHARACTERISTICS OF A DIGITAL FLUOROGRAPHIC SYSTEM PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS Riederer, S. J., DiBianca, F. A., GEORGES, J. P., Jensen, G. A., KEYES, G. S., Pelc, N. J., STEINIKE, E. R., WESBEY, W. H. 1981; 273: 88-95

  View details for Web of Science ID A1981NF93100015

• INTRAVENOUS ARTERIOGRAPHY USING SCANNED PROJECTION RADIOGRAPHY RADIOLOGY Brody, W. R., Macovski, A., Pelc, N. J., Lehmann, L., Joseph, R. A., Edelheit, L. S. 1981; 141 (2): 509-514

  Abstract

  Visualization of arteries using intravenous injections of contrast material requires an imaging system capable of (a) excellent sensitivity to dilute concentrations of contrast media and (b) adequate temporal resolution to minimize the effects of motion during the exposure. A line-scanned radiography system based on a CT fan-beam detector (high-pressure xenon ionization chamber) was used for phantom and animal studies of intravenous arteriography to demonstrate the potential advantages of this method. Even though line-scanned systems require long scan times compared to existing radiographic methods, they are capable of showing rapidly moving arteries without blurring. Concentrations of 3 mg/ml of iodine could be seen in vessels 2 mm in diameter. Phantom studies using kVp switching showed that bone or soft tissue could be selectively cancelled.

  View details for Web of Science ID A1981MM65400042

  View details for PubMedID 7027311

• BEAM HARDENING, NOISE, AND CONTRAST CONSIDERATIONS IN SELECTIVE IODINE DIGITAL RADIOGRAPHY IEEE TRANSACTIONS ON NUCLEAR SCIENCE Riederer, S. J., Pelc, N. J., GEORGES, J. P., KEYES, G. S., LEHMANN, L. A., Hall, A. L. 1981; 28 (1): 213-218

  View details for Web of Science ID A1981LH26700037

• DUAL-KVP RADIOGRAPHY Brody, W. R., Sommer, F. G., Macovski, A., Lehmann, L., Alvarez, R., Pelc, N., Hall, A. AMER ROENTGEN RAY SOC. 1981: 1277–77

  View details for Web of Science ID A1981LU08900088

• EXCRETORY UROGRAPHY USING DUAL-ENERGY SCANNED PROJECTION RADIOGRAPHY RADIOLOGY Sommer, F. G., Brody, W. R., Gross, D., Macovski, A., Hall, A., Pelc, N. 1981; 141 (2): 529-532

  View details for Web of Science ID A1981MM65400046

  View details for PubMedID 7027312

• GENERALIZED IMAGE COMBINATIONS IN DUAL KVP DIGITAL RADIOGRAPHY MEDICAL PHYSICS LEHMANN, L. A., Alvarez, R. E., Macovski, A., Brody, W. R., Pelc, N. J., Riederer, S. J., Hall, A. L. 1981; 8 (5): 659-667

  Abstract

  Dual energy basis decomposition techniques apply to single projection radiographic imaging. The high and low energy images are non-linearly transformed to generate two energy-independent images characterizing the integrated Compton/photoelectric attenuation components. Characteristic linear combinations of these two basis images identify unknown materials, cancel known materials, and generate synthesized monoenergetic images. The problems of intervening materials and material displacement are solved in general for a wide class of clinical imaging tasks. The basis projection angle identifies one from a family of energy selective imaging tasks, and such performance measures as the contrast enhancement factor (CEF) and signal to noise ratio (SNR) are expressed as functions of this angle. Algorithms for the decomposition of high and low energy measurements are compared and experimental images are included.

  View details for Web of Science ID A1981MJ52300006

  View details for PubMedID 7290019

• EXPERIMENTAL SYSTEM FOR DUAL ENERGY SCANNED PROJECTION RADIOGRAPHY PROCEEDINGS OF THE SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS Hall, A. L., Pelc, N. J., Riederer, S. J., KEYES, G. S., Brody, W. R., LEHMANN, L. A., Macovski, A., Alvarez, R. E. 1981; 314: 155-159

  View details for Web of Science ID A1981NF95200025

• DUAL-ENERGY PROJECTION RADIOGRAPHY - INITIAL CLINICAL-EXPERIENCE AMERICAN JOURNAL OF ROENTGENOLOGY Brody, W. R., CASSEL, D. M., Sommer, F. G., LEHMANN, L. A., Macovski, A., Alvarez, R. E., Pelc, N. J., Riederer, S. J., Hall, A. L. 1981; 137 (2): 201-205

  View details for Web of Science ID A1981LZ80100001

  View details for PubMedID 6789622

• INTRAVENOUS CAROTID ARTERIOGRAPHY USING LINE-SCANNED DIGITAL RADIOGRAPHY RADIOLOGY Brody, W. R., Enzmann, D. R., Deutsch, L. S., Hall, A., Pelc, N. 1981; 139 (2): 297-300

  Abstract

  Digital subtraction and an experimental system for line-scanned radiography were used to image the bifurcations of the carotid arteries. The subtracted images were obtained before and after injections of contrast media. The anatomy of the extracranial carotid arteries was demonstrated in most patients, and verified by selective catheter arteriograms. Unsuccessful studies were attributed to improper timing while obtaining the images, and to venous occlusion. Artifacts produced by motion limit the temporal subtraction method.

  View details for Web of Science ID A1981LP62400005

  View details for PubMedID 7012922

• DUAL ENERGY DIGITAL RADIOGRAPHY Pelc, N. J., Riederer, S. J., GEORGES, J. P., KEYES, G. S., Macovski, A., LEHMANN, L. A., Alvarez, R. E., Brody, W. R. LIPPINCOTT-RAVEN PUBL. 1981: 944–45

  View details for Web of Science ID A1981MP56900059

• SOURCE LIMITATIONS IN SCANNED PROJECTION RADIOGRAPHY LEHMANN, L. A., Brody, W. R., Macovski, A., STRUHL, B., DIBIANCA, R. A., Pelc, N. AMER ROENTGEN RAY SOC. 1980: 853–54

  View details for Web of Science ID A1980JM11100047

• NON-LINEAR PARTIAL VOLUME ARTIFACTS IN X-RAY COMPUTED-TOMOGRAPHY MEDICAL PHYSICS Glover, G. H., Pelc, N. J. 1980; 7 (3): 238-248

  Abstract

  Dark streaks connecting the petrous bones are often observed in cranial transverse section CT reconstructions. These artifacts are usually only slightly diminished by two-pass beam hardening corrections. However, it is found that by narrowing the slice thickness the artifacts are substantially reduced. In this paper, it is shown that axial partial volume effects can account for the presence of the artifacts. These axial partial volume effects occur when, at any point in the slice, the object has axial variations in attenuation. In such cases the logarithm of the integrated intensity measured by the detector is not a linear function of the integrated attenuation (even for monochromatic beams). This nonlinearity causes inconsistencies in the data set which in turn can cause streaks in the image. We have studied the partial volume effect using computer simulation. Algorithms are presented whose purpose is to correct for these effects by estimating the axial variation using neighboring slices. These correction algorithms are successful in computer simulation cases but failed with clinical data. It is concluded that no practical correction method is viable unless overlap scanning is employed. However, thin-slice scanning for sections where these artifacts are common is perhaps a more preferable solution.

  View details for Web of Science ID A1980LE70800010

  View details for PubMedID 7393149

• A higher resolution fan-beam reconstruction algorithm for rotate-rotate CT systems. J. Comput. Assist. Tomogr. Pelc, N., J., Glover, G., H., Griffie, T., R. 1980; 5: 4
• Recent improvements in transmission CT reconstruction algorithms. 3-rd Symp. on Phys. and Tech. Aspects of Trans. and Emis. Comput. Tomog., Tokyo Pelc, N., J., Glover, G., H. 1980
• Non-linear partial volume artifacts in x-ray computed tomography. Med. Phys. Glover, G., H., Pelc, N., J. 1980; 7 (3)
• Removal of "starburst" artifacts from metal clips in CT reconstruction. Glover, G., H., Pelc, N., J. 1980
• A dynamically switching dual kVp digital scanned projection radiography system. Pelc, N., J., Joseph, R., A., Daniels et al, H., E. 1980
• Generalized image combination in dual kVp digital radiography. Lehmann, L., A., Pelc, N., J., Riederer et al, S., J. 1980
• Removal of "metal-clip" artifacts in CT reconstruction. J. Comput. Assist. Tomogr. Glover, G., H., Pelc, N., J. 1980; 5: 4
• INTRAVENOUS CAROTID ARTERIOGRAPHY USING SCANNED PROJECTION RADIOGRAPHY Brody, W. R., ENZMANN, D., Deutsch, L. S., Macovski, A., Pelc, N., Joseph, R., Edelheit, L. S. LIPPINCOTT-RAVEN PUBL. 1980: 409–

  View details for Web of Science ID A1980KK17000073

• UTILIZATION OF CROSS-PLANE RAYS FOR 3-DIMENSIONAL RECONSTRUCTION BY FILTERED BACK-PROJECTION JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY Pelc, N. J., CHESLER, D. A. 1979; 3 (3): 385-395

  Abstract

  Present popular computed tomography (CT) algorithms reconstruct an object from the ray measurements lying on a set of parallel planes. This paper presents an algorithm that can also utilize "cross-plane" rays (i.e., rays that cross through many planes) to reconstruct the object. In this reconstruction algorithm, the ray measurements are grouped into two-dimensional projections, filtered, and stored. The filtered projections can then be back-projected onto a three-dimensional matrix or any plane through the three-dimensional volume. General theoretical aspects are presented and then applied to the special case in which ray measurements have been made in all directions. The algorithm is tested using computer-generated data. Expressions for the noise power spectrum and the variance in the reconstruction are derived. It is shown that the noise-to-signal ratio per detected photon for this reconstruction method is close to a theoretical limit, as it also is for normal CT. The ability to use ray measurements that cross many planes is especially useful in emission CT, where order-of-magnitude improvements in image quality per unit dose can be achieved.

  View details for Web of Science ID A1979GT73100015

  View details for PubMedID 438380

• A higher resolution reconstruction algorithm for third generation CT systems. Pelc, N., J., Glover, G., H., Griffie, T., R., Acharya, K., C. 1979
• Three dimensional reconstruction using "in-plane" and "cross-plane" rays. V Intl Conf on Med. Phys., Jerusalem Pelc, N., J., Chesler, D., A. 1979
• The non-linear partial volume artifact. J. Comput. Assist. Tomogr. Glover, G., H., Pelc, N., J. 1979; 3: 4
• Comparison of computed radiography, standard radiography, and computed tomography. J. Comput. Assist. Tomogr. DiBianca, F., A., Carmean, R., E., Pelc, N., J., Cohen, G. 1979; 3: 4
• Non-linear partial volume artifacts. V Intl Conf on Med. Phys., Jerusalem Pelc, N., J., Glover, G., H. 1979
• Utilization of cross-plane rays for three-dimensional reconstruction by filtered backprojection. J. Comput. Assist. Tomog. Pelc, N., J., Chesler, D., A. 1979; 3 (3): 385
• A reconstruction algorithm for higher sensitivity positron emission tomography. J. Comput. Assist.Tomogr. Pelc, N., J., Chesler, D., A. 1979; 3: 4
• NOISE POWER SPECTRUM IN COMPUTED X-RAY TOMOGRAPHY PHYSICS IN MEDICINE AND BIOLOGY Riederer, S. J., Pelc, N. J., CHESLER, D. A. 1978; 23 (3): 446-454

  Abstract

  An expression is derived showing that the two-dimensional noise power spectrum of computed X-ray tomography is proportional to [G(k)]2/k where k is the radial spatial frequency and G(k) is the one-dimensional corrective filter used in the filtered back-projection reconstuction technique. It is shown that predicted noise power spectra compare well with those estimated from CT reconstructions of simulated noise for both the ramp filter and the Hanning-weighted ramp filter. A consequence of the non-uniform shape of the noise power spectrum is that statistical noise in CT reconstructions is correlated from point to point. Because of this correlation when the reconstructed CT values are averaged over some region, the uncertainty of the average depends on the shape of the region as well as its area. This dependence is confirmed by computer simulations.

  View details for Web of Science ID A1978EZ47600008

  View details for PubMedID 674361

• Three dimensional reconstruction from rays not lying on parallel planes. J. Comput. Assist.Tomogr. Pelc, N., J., Chesler, D., A. 1978; 2: 3
• The noise power spectrum in computed x-ray tomography. Phys. Med. Biol. Riederer, S., J., Pelc, N., J., Chesler, D., A. 1978; 23 (3): 446
• Comparison of transmission detection CT systems with scatter detection CT systems. J. Comput. Assist. Tomogr. Chesler, D., A., Pelc, N., J. 1978; 2: 3
• NOISE DUE TO PHOTON-COUNTING STATISTICS IN COMPUTED X-RAY TOMOGRAPHY JOURNAL OF COMPUTER ASSISTED TOMOGRAPHY CHESLER, D. A., Riederer, S. J., Pelc, N. J. 1977; 1 (1): 64-74

  Abstract

  A general expression is derived for the noise due to photon counting statistics in computed X-ray tomography. The variance is inversely proportional to the cube of the resolution distance. For scanners using a water box, the noise in the reconstructed image depends inversely on the number of detected primary photons, summed over all angles, that have passed through a resolution element. Predictions of this formula agree well with the results of computer simulations. It is shown how this formula can be used to determine such parameters as required X-ray flux, detector counting rate, and dose, with special emphasis on tradeoffs between these parameters and resolution. It is also shown that to determine the X-ray attenuation coefficient of a resolution element to a given precision, the number of photons required by computed X-ray tomography is close to a theoretical limit.

  View details for Web of Science ID A1977DD54200008

  View details for PubMedID 615896

• The contribution of x-ray tube focal spots to the resolution of CT systems. J. Comput. Assist. Tomogr. Pelc, N., J., Chesler, D., A. 1977; 1: 3
• Statistical properties and simulation studies of transverse section algorithms. In Reconstruction Tomography in Diagnostic Radiology and Nuclear Medicine Chesler, D., A., Aronow, S., Correll, J., E., Riederer, S., J., Pelc, N., J. edited by Ter Pogossian et. al., M., M. University Park Press, Baltimore, MD. 1977: 1
• Results of computer simulation studies of computerized tomography. Pelc, N., J., Chesler, D., A., Riederer, S., J. 1976
• Statistical aspects of computed x-ray tomography. Chesler, D., A., Riederer, S., J., Pelc, N., J. 1976
• The progress in dual photon absorptiometry of bone. Mazess, R., B., Hanson, J., Kan, W., Madsen, M., Pelc, N., J., Wilson, C., R. edited by Schmelling, P. 1974
• Simple groups of orders less than 1000. J. Undergrad. Math. Cornell, G., Pelc, N., J., Wage, M., L. 1973; 5 (2)
• Breathheld phase-contrast MR for the diagnosis of mesenteric ischemia. VanDalsem, W., J., Li, K., C.P., McDonnell, C., H., Fredrickson, J., O., Pelc, N., J., Whitney, W., S.
• Human Tissue X-Ray Diffraction: Breast, Brain, and Prostate World Congress on Medical Physics and Biomedical Engineering (Chicago) FR-Ea325-06. Lazarev, P., Paukshto, M., Pelc, N., Sakharova, A.
• Measurement of Myocardial Motion and Deformation with Phase Contrast Cine MRI. Association for the Advancement of Medical Instrumentation Bethesda, MD Pelc, N., J., Herfkens, R., J., Pelc, L., R., Ni, C., Sayre, J., R., Miller, D., C.
• Method for decreasing CT simulation time of complex phantoms and systems through separation of material specific projection data SPIE Medical Imaging 2017: Physics of Medical Imaging Divel, S. E., Christensen, S., Wintermark, M., Lansberg, M. G., Pelc, N. J. 2017: 1013259

  View details for DOI 10.1117/12.2254076

• Development of a realistic, dynamic digital brain phantom for CT Perfusion validation SPIE Medical Imaging 2016: Physics of Medical Imaging Divel, S. E., Segars, W. P., Christensen, S., Wintermark, M., Lansberg, M. G., Pelc, N. J. 2016

  View details for DOI 10.1117/12.2214997

• Image-domain insertion of spatially correlated, locally varying noise in CT images SPIE Medical Imaging 2019: Physics of Medical Imaging Divel, S. E., Pelc, N. J. 2019

  View details for DOI 10.1117/12.2512453