- Diagnostic Radiology
- Pediatric and Abdominal MRI
- Cardiovascular Diagnostic Techniques
Co-Director of MRI, Stanford (2011 - Present)
Chief, Body MRI, Stanford (2011 - Present)
Honors & Awards
Tashia and John Morgridge Faculty Endowed Scholar in Pediatric Translational Medicine, Child Health Research Institute
Fellowship:Stanford University - Fellowship (2007) CA
Residency:Stanford University - Fellowship (2006) CA
Fellowship:Children's Hospital Medical Center (2006) OH
Internship:Stanford University - Dept of Surgery (2002) CA
Medical Education:Stanford University School of Medicine (2001) CA
Board Certification: Diagnostic Radiology, American Board of Radiology (2006)
Board Certification: Pediatric Radiology, American Board of Radiology (2008)
Fellowship:Hospital for Sick Children (2007) Canada
Current Research and Scholarly Interests
Our group is focused on developing new MRI techniques, and in particular, developing novel applications for children. We take a comprehensive approach, exploring novel hardware, MRI pulse sequence techniques, and motion correction methods. These approaches are then evaluated for cardiovascular, abdominal, and musculoskeletal pediatric MRI exams. Additionally, we seek to develop quantitative MRI methods, including those for cardiovascular function, renal function, and tumor perfusion.
A Study to Evaluate Sildenafil for the Treatment of Lymphatic Malformations
There is an unsatisfied medical need for a first-line treatment of lymphatic malformations with a good benefit/risk profile. Based on a patient experience in the institution, the investigators plan to verify whether or not the medication sildenafil has a beneficial effect on lymphatic malformations. The investigators plan to do this by treating patients with lymphatic malformations with the medication sildenafil for a 20 week period. This is an investigator initiated study funded by an Innovations in Patient Care grant and a SPARK grant.
Stanford is currently not accepting patients for this trial. For more information, please contact Andrea Tichy, Ph.D., 650-724-1982.
PET/CT and Whole-Body MRI for Detection of Skeletal and Soft Tissue Metastases
Fluorine-18 Fluorodeoxyglucose (F-18 FDG) PET/CT is established as a powerful imaging tool for cancer detection and monitoring response to therapy. However, not all cancers are identified reliably due to variable rates of glucose metabolism. Whole-body MRI emerges currently as an excellent modality for morphological characterization of soft tissue and skeletal lesions. Sodium Fluorine-18 (F-18) was used in the 1970's for bone scanning and can be used as a skeletal tracer in current PET/CT scanners. The direct comparison of F-18/F-18 FDG PET/CT and whole-body MRI for skeletal metastases detection was not attempted to date. However, such an approach has the potential to improve cancer diagnosis, staging, prognosis, and therapy monitoring. The combination of these technologies may also allow for improved screening or earlier cancer detection. We will attempt a pilot study with 10 patients to acquire the preliminary results needed to proceed with additional 90 subjects.
Feasibility of Using Real-time Cine-MRI for Treating Moving & Deforming Tumors
This study aims to investigate and optimize imaging sequences and parameters of rapid real-time MRI in order to obtain adequate guidance for accurately and precisely delivering radiation to moving abdominal and thoracic tumors.
Stanford is currently not accepting patients for this trial. For more information, please contact Melody Chung, (650) 736 - 0798.
- Introduction to Imaging and Image-based Human Anatomy
BIOE 220, RAD 220 (Win)
Independent Studies (6)
- Directed Reading in Radiology
RAD 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Radiology
RAD 280 (Aut, Win, Spr, Sum)
- Graduate Research
RAD 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
RAD 370 (Aut, Win, Spr, Sum)
- Readings in Radiology Research
RAD 101 (Aut, Win, Spr, Sum)
- Undergraduate Research
RAD 199 (Aut, Win, Spr, Sum)
- Directed Reading in Radiology
Graduate and Fellowship Programs
Classification of Hypervascular Liver Lesions Based on Hepatic Artery and Portal Vein Blood Supply Coefficients Calculated from Triphasic CT Scans
JOURNAL OF DIGITAL IMAGING
2015; 28 (2): 213-223
Perfusion CT of the liver typically involves scanning the liver at least 20 times, resulting in a large radiation dose. We developed and validated a simplified model of tumor blood supply that can be applied to standard triphasic scans and evaluated whether this can be used to distinguish benign and malignant liver lesions. Triphasic CTs of 46 malignant and 32 benign liver lesions were analyzed. For each phase, regions of interest were drawn in the arterially enhancing portion of each lesion, as well as the background liver, aorta, and portal vein. Hepatic artery and portal vein blood supply coefficients for each lesion were then calculated by expressing the enhancement curve of the lesion as a linear combination of the enhancement curves of the aorta and portal vein. Hepatocellular carcinoma (HCC) and hypervascular metastases, on average, both had increased hepatic artery coefficients compared to the background liver. Compared to HCC, benign lesions, on average, had either a greater hepatic artery coefficient (hemangioma) or a greater portal vein coefficient (focal nodular hyperplasia or transient hepatic attenuation difference). Hypervascularity with washout is a key diagnostic criterion for HCC, but it had a sensitivity of 72 % and specificity of 81 % for diagnosing malignancy in our diverse set of liver lesions. The sensitivity for malignancy was increased to 89 % by including enhancing lesions that were hypodense on all phases. The specificity for malignancy was increased to 97 % (p = 0.039) by also examining hepatic artery and portal vein blood supply coefficients, while maintaining a sensitivity of 76 %.
View details for DOI 10.1007/s10278-014-9725-9
View details for Web of Science ID 000351242500012
View details for PubMedID 25183580
Robust 4D Flow Denoising Using Divergence-Free Wavelet Transform
MAGNETIC RESONANCE IN MEDICINE
2015; 73 (2): 828-842
To investigate four-dimensional flow denoising using the divergence-free wavelet (DFW) transform and compare its performance with existing techniques.DFW is a vector-wavelet that provides a sparse representation of flow in a generally divergence-free field and can be used to enforce "soft" divergence-free conditions when discretization and partial voluming result in numerical nondivergence-free components. Efficient denoising is achieved by appropriate shrinkage of divergence-free wavelet and nondivergence-free coefficients. SureShrink and cycle spinning are investigated to further improve denoising performance.DFW denoising was compared with existing methods on simulated and phantom data and was shown to yield better noise reduction overall while being robust to segmentation errors. The processing was applied to in vivo data and was demonstrated to improve visualization while preserving quantifications of flow data.DFW denoising of four-dimensional flow data was shown to reduce noise levels in flow data both quantitatively and visually. Magn Reson Med 73:828-842, 2015. © 2014 Wiley Periodicals, Inc.
View details for DOI 10.1002/mrm.25176
View details for Web of Science ID 000348139500043
View details for PubMedID 24549830
Inlet and outlet valve flow and regurgitant volume may be directly and reliably quantified with accelerated, volumetric phase-contrast MRI.
Journal of magnetic resonance imaging
2015; 41 (2): 376-385
To determine whether it is feasible to use solely an accelerated 4D phase-contrast magnetic resonance imaging (4D-PC MRI) acquisition to quantify net and regurgitant flow volume through each of the cardiac valves.Accelerated, 4D-PC MRI examinations performed between March 2010 through June 2011 as part of routine MRI examinations for congenital, structural heart disease were retrospectively reviewed and analyzed using valve-tracking visualization and quantification algorithms developed in Java and OpenGL. Excluding patients with transposition or single ventricle physiology, a total of 34 consecutive pediatric patients (19 male, 15 female; mean age 6.9 years; age range 10 months to 15 years) were identified. 4D-PC flow measurements were compared at each valve and against routine measurements from conventional cardiac MRI using Bland-Altman and Pearson correlation analysis.Inlet and outlet valve net flow were highly correlated between all valves (P = 0.940-0.985). The sum of forward flow at the outlet valve and regurgitant flow at the inlet valve were consistent with volumetric displacements in each ventricle (P = 0.939-0.948). These were also highly consistent with conventional planar MRI measurements with net flow (P = 0.923-0.935) and regurgitant fractions (P = 0.917-0.972) at the outlet valve and ventricular volumes (P = 0.925-0.965).It is possible to obtain consistent measurements of net and regurgitant blood flow across the inlet and outlet valves relying solely on accelerated 4D-PC. This may facilitate more efficient clinical quantification of valvular regurgitation. J. Magn. Reson. Imaging 2015;41:376-385.© 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24578
View details for PubMedID 24677253
Fast pediatric 3D free-breathing abdominal dynamic contrast enhanced MRI with high spatiotemporal resolution.
Journal of magnetic resonance imaging
2015; 41 (2): 460-473
To develop a method for fast pediatric 3D free-breathing abdominal dynamic contrast enhanced (DCE) magnetic resonance imaging (MRI) and investigate its clinical feasibility.A combined locally low rank parallel imaging method with soft gating is proposed for free-breathing DCE MRI acquisition. With Institutional Review Board (IRB) approval and informed consent/assent, 23 consecutive pediatric patients were recruited for this study. Free-breathing DCE MRI with ∼1 mm(3) spatial resolution and a 6.5-sec frame rate was acquired on a 3T scanner. Undersampled data were reconstructed with a compressed sensing method without motion correction (FB-CS) and the proposed method (FB-LR). A follow-up respiratory-triggered acquisition (RT-CS) was performed as a reference standard. The reconstructed images were evaluated independently by two radiologists. Wilcoxon tests were performed to test the hypothesis that there was no significant difference between different reconstructions. Quantitative evaluation of contrast dynamics was also performed.The mean score of overall image quality of FB-LR was 4.0 on a 5-point scale, significantly better (P < 0.05) than FB-CS reconstruction (mean score 2.9), and similar to RT-CS (mean score 4.1). FB-LR also matched the temporal fidelity of contrast dynamics with a root mean square error less than 5%.Fast 3D free-breathing DCE MRI with high scan efficiency and image quality similar to respiratory-triggered acquisition is feasible in a pediatric clinical setting.J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24551
View details for PubMedID 24375859
Simultaneous Whole-Body Time-of-Flight F-18-FDG PET/MRI A Pilot Study Comparing SUVmax With PET/CT and Assessment of MR Image Quality
CLINICAL NUCLEAR MEDICINE
2015; 14 (1): 1-8
View details for Web of Science ID 000346633400023
Clinical Performance of Contrast Enhanced Abdominal Pediatric MRI With Fast Combined Parallel Imaging Compressed Sensing Reconstruction
JOURNAL OF MAGNETIC RESONANCE IMAGING
2014; 40 (1): 13-25
To deploy clinically, a combined parallel imaging compressed sensing method with coil compression that achieves a rapid image reconstruction, and assess its clinical performance in contrast-enhanced abdominal pediatric MRI.With Institutional Review Board approval and informed patient consent/assent, 29 consecutive pediatric patients were recruited. Dynamic contrast-enhanced MRI was acquired on a 3 Tesla scanner using a dedicated 32-channel pediatric coil and a three-dimensional SPGR sequence, with pseudo-random undersampling at a high acceleration (R = 7.2). Undersampled data were reconstructed with three methods: a traditional parallel imaging method and a combined parallel imaging compressed sensing method with and without coil compression. The three sets of images were evaluated independently and blindly by two radiologists at one siting, for overall image quality and delineation of anatomical structures. Wilcoxon tests were performed to test the hypothesis that there was no significant difference in the evaluations, and interobserver agreement was analyzed.Fast reconstruction with coil compression did not deteriorate image quality. The mean score of structural delineation of the fast reconstruction was 4.1 on a 5-point scale, significantly better (P < 0.05) than traditional parallel imaging (mean score 3.1). Fair to substantial interobserver agreement was reached in structural delineation assessment.A fast combined parallel imaging compressed sensing method is feasible in a pediatric clinical setting. Preliminary results suggest it may improve structural delineation over parallel imaging. J. Magn. Reson. Imaging 2014;40:13-25. © 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24333
View details for Web of Science ID 000337640700003
View details for PubMedID 24127123
Enhancement of Respiratory Navigator-Gated Three-Dimensional Spoiled Gradient-Recalled Echo Sequence with Variable Flip Angle Scheme
MAGNETIC RESONANCE IN MEDICINE
2014; 72 (1): 172-177
To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection.A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners.Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts.The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study.
View details for DOI 10.1002/mrm.24902
View details for Web of Science ID 000337624400020
View details for PubMedID 23904390
An open-label study to evaluate sildenafil for the treatment of lymphatic malformations
JOURNAL OF THE AMERICAN ACADEMY OF DERMATOLOGY
2014; 70 (6): 1050-1057
Lymphatic malformations can be challenging to treat. Mainstay interventions including surgery and sclerotherapy are invasive and can result in local recurrence and complications.We sought to assess the effect of 20 weeks of oral sildenafil on reducing lymphatic malformation volume and symptoms in children.Seven children (4 boys, 3 girls; ages 13-85 months) with lymphatic malformations were given oral sildenafil for 20 weeks in this open-label study. The volume of the lymphatic malformation was calculated blindly using magnetic resonance imaging performed before and after 20 weeks of sildenafil. Lymphatic malformations were assessed clinically on weeks 4, 12, 20, and 32. Both the physician and parents evaluated the lymphatic malformation in comparison with baseline.Four subjects had a lymphatic malformation volume decrease (1.0%-31.7%). In 2 subjects, despite a lymphatic malformation volume increase (1.1%-3.7%), clinical improvement was noted while on sildenafil. One subject had a 29.6% increase in lymphatic malformation volume and no therapeutic response. Lymphatic malformations of all 6 subjects who experienced a therapeutic response on sildenafil softened and became easily compressible. Adverse events were minimal.A randomized controlled trial will be necessary to verify the effects of sildenafil on lymphatic malformations.Sildenafil can reduce lymphatic malformation volume and symptoms in some children.
View details for DOI 10.1016/j.jaad.2014.02.005
View details for Web of Science ID 000336030400023
View details for PubMedID 24656411
Perforated appendicitis: an underappreciated mimic of intussusception on ultrasound
2014; 44 (5): 535-541
We encountered multiple cases in which the US appearance of ruptured appendicitis mimicked intussusception, resulting in diagnostic and therapeutic delay and multiple additional imaging studies.To explore the clinical and imaging discriminatory features between the conditions.Initial US images in six children (age 16 months to 8 years; 4 boys, 2 girls) were reviewed independently and by consensus by three pediatric radiologists. These findings were compared and correlated with the original reports and subsequent US, fluoroscopic, and CT images and reports.All initial US studies demonstrated a multiple-ring-like appearance (target sign, most apparent on transverse views) with diagnostic consensus supportive of intussusception. In three cases, US findings were somewhat discrepant with clinical concerns. Subsequently, four of the six children had contrast enemas; two were thought to have partial or complete intussusception reduction. Three had a repeat US examination, with recognition of the correct diagnosis. None of the US examinations demonstrated definite intralesional lymph nodes or mesenteric fat, but central echogenicity caused by debris/appendicolith was misinterpreted as fat. All showed perilesional hyperechogenicity that, in retrospect, represented inflamed fat "walling off" of the perforated appendix. There were four CTs, all of which demonstrated a double-ring appearance that correlated with the US target appearance, with inner and outer rings representing the dilated appendix and walled-off appendiceal rupture, respectively. All six children had surgical confirmation of perforated appendicitis.Contained perforated appendicitis can produce US findings closely mimicking intussusception. Clinical correlation and careful multiplanar evaluation should allow for sonographic suspicion of perforated appendicitis, which can be confirmed on CT if necessary.
View details for DOI 10.1007/s00247-014-2873-8
View details for Web of Science ID 000334513800004
View details for PubMedID 24463638
- ESPIRiT-An Eigenvalue Approach to Autocalibrating Parallel MRI: Where SENSE Meets GRAPPA MAGNETIC RESONANCE IN MEDICINE 2014; 71 (3): 990-1001
Investigating the feasibility of rapid MRI for image-guided motion management in lung cancer radiotherapy.
BioMed research international
2014; 2014: 485067-?
Cycle-to-cycle variations in respiratory motion can cause significant geometric and dosimetric errors in the administration of lung cancer radiation therapy. A common limitation of the current strategies for motion management is that they assume a constant, reproducible respiratory cycle. In this work, we investigate the feasibility of using rapid MRI for providing long-term imaging of the thorax in order to better capture cycle-to-cycle variations. Two nonsmall-cell lung cancer patients were imaged (free-breathing, no extrinsic contrast, and 1.5 T scanner). A balanced steady-state-free-precession (b-SSFP) sequence was used to acquire cine-2D and cine-3D (4D) images. In the case of Patient 1 (right midlobe lesion, ~40 mm diameter), tumor motion was well correlated with diaphragmatic motion. In the case of Patient 2, (left upper-lobe lesion, ~60 mm diameter), tumor motion was poorly correlated with diaphragmatic motion. Furthermore, the motion of the tumor centroid was poorly correlated with the motion of individual points on the tumor boundary, indicating significant rotation and/or deformation. These studies indicate that image quality and acquisition speed of cine-2D MRI were adequate for motion monitoring. However, significant improvements are required to achieve comparable speeds for truly 4D MRI. Despite several challenges, rapid MRI offers a feasible and attractive tool for noninvasive, long-term motion monitoring.
View details for DOI 10.1155/2014/485067
View details for PubMedID 24524077
- Investigating the Feasibility of Rapid MRI for Image-Guided Motion Management in Lung Cancer Radiotherapy BIOMED RESEARCH INTERNATIONAL 2014
Improvement of Gadoxetate Arterial Phase Capture With a High Spatio-Temporal Resolution Multiphase Three-Dimensional SPGR-Dixon Sequence
JOURNAL OF MAGNETIC RESONANCE IMAGING
2013; 38 (4): 938-945
PURPOSE: To determine whether a multiphase method with high spatiotemporal resolution (STR) by means of a combination of parallel imaging, pseudorandom sampling and temporal view sharing improves the capture and intensity of gadoxetate arterial phase images as well as lesion enhancement. MATERIALS AND METHODS: Thirty-seven patients were imaged with a conventional spoiled gradient echo acquisition and 48 with a high STR multiphase acquisition after the administration of gadoxetate. Arterial phase capture, image quality, and quality of fat suppression were qualitatively graded. Fourteen lesions in the conventional group and 28 in the high STR multiphase group were imaged, including 34 focal nodular hyperplasias. The ratio of lesion to parenchyma enhancement as well as relative hepatic artery enhancement were calculated. Chi-squared, Mann-Whitney U and student t-tests were used to compare differences. RESULTS: The high STR multiphase acquisition included the arterial phase more frequently than conventional acquisitions (P < 0.001), with the arterial phase missed in 17% (95% CI of 4-28%) of patients with conventional acquisition compared with 2% (95% CI of 0-6%) with the high STR multiphase acquisition. There was no loss of image quality or degree of fat saturation. Additionally, there was increased relative intensity of the hepatic arteries (P < 0.001) as well as lesion enhancement (P = 0.01). CONCLUSION: The high STR multiphase acquisition resulted in more reliable gadoxetate arterial phase capture compared with a conventional acquisition while preserving image quality with robust fat saturation J. Magn. Reson. Imaging 2013. © 2013 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.24048
View details for Web of Science ID 000328224900021
Noncontrast-enhanced renal angiography using multiple inversion recovery and alternating TR balanced steady-state free precession
MAGNETIC RESONANCE IN MEDICINE
2013; 70 (2): 527-536
Noncontrast-enhanced renal angiography techniques based on balanced steady-state free precession avoid external contrast agents, take advantage of high inherent blood signal from the $T_2/T_1$ contrast mechanism, and have short steady-state free precession acquisition times. However, background suppression is limited; inflow times are inflexible; labeling region is difficult to define when tagging arterial flow; and scan times are long. To overcome these limitations, we propose the use of multiple inversion recovery preparatory pulses combined with alternating pulse repetition time balanced steady-state free precession to produce renal angiograms. Multiple inversion recovery uses selective spatial saturation followed by four nonselective inversion recovery pulses to concurrently null a wide range of background $T_1$ species while allowing for adjustable inflow times; alternating pulse repetition time steady-state free precession maintains vessel contrast and provides added fat suppression. The high level of suppression enables imaging in three-dimensional as well as projective two-dimensional formats, the latter of which has a scan time as short as one heartbeat. In vivo studies at 1.5 T demonstrate the superior vessel contrast of this technique. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
View details for DOI 10.1002/mrm.24480
View details for Web of Science ID 000322128300025
View details for PubMedID 23172805
Pediatric Hepatobiliary Magnetic Resonance Imaging
RADIOLOGIC CLINICS OF NORTH AMERICA
2013; 51 (4): 599-?
Magnetic resonance (MR) imaging is an effective and noninvasive modality for evaluating hepatobiliary pathologic conditions. This article provides an up-to-date review of anatomy, indications, and imaging goals and protocols, including patient preparation, pulse sequences, and contrast agents used in pediatric MR hepatobiliary imaging. This article also highlights some of the common MR features of pediatric liver pathologic conditions, including tumors, congenital biliary ductal plate malformations, trauma, fibrosis, and infection.
View details for DOI 10.1016/j.rcl.2013.03.005
View details for Web of Science ID 000322847100004
View details for PubMedID 23830788
Venous and arterial flow quantification are equally accurate and precise with parallel imaging compressed sensing 4D phase contrast MRI
JOURNAL OF MAGNETIC RESONANCE IMAGING
2013; 37 (6): 1419-1426
To evaluate the precision and accuracy of parallel-imaging compressed-sensing 4D phase contrast (PICS-4DPC) magnetic resonance imaging (MRI) venous flow quantification in children with patients referred for cardiac MRI at our children's hospital.With Institutional Review Board (IRB) approval and Health Insurance Portability and Accountability Act (HIPAA) compliance, 22 consecutive patients without shunts underwent 4DPC as part of clinical cardiac MRI examinations. Flow measurements were obtained in the superior and inferior vena cava, ascending and descending aorta, and the pulmonary trunk. Conservation of flow to the upper, lower, and whole body was used as an internal physiologic control. The arterial and venous flow rates at each location were compared with paired t-tests and F-tests to assess relative accuracy and precision.Arterial and venous flow measurements were strongly correlated with the upper (ρ = 0.89), lower (ρ = 0.96), and whole body (ρ = 0.97); net aortic and pulmonary trunk flow rates were also tightly correlated (ρ = 0.97). There was no significant difference in the value or precision of arterial and venous flow measurements in upper, lower, or whole body, although there was a trend toward improved precision with lower velocity-encoding settings.With PICS-4DPC MRI, the accuracy and precision of venous flow quantification are comparable to that of arterial flow quantification at velocity-encodings appropriate for arterial vessels. J. Magn. Reson. Imaging 2013;37:1419-1426. © 2012 Wiley Periodicals, Inc.
View details for DOI 10.1002/jmri.23936
View details for Web of Science ID 000319420000016
View details for PubMedID 23172846
An investigational study to evaluate sildenafil for the treatment of lymphatic malformations
NATURE PUBLISHING GROUP. 2013: S175-S175
View details for Web of Science ID 000317698901320
Abdominal MR Imaging in Children: Motion Compensation, Sequence Optimization, and Protocol Organization
2013; 33 (3): 703-719
Familiarity with basic sequence properties and their trade-offs is necessary for radiologists performing abdominal magnetic resonance (MR) imaging. Acquiring diagnostic-quality MR images in the pediatric abdomen is challenging due to motion, inability to breath hold, varying patient size, and artifacts. Motion-compensation techniques (eg, respiratory gating, signal averaging, suppression of signal from moving tissue, swapping phase- and frequency-encoding directions, use of faster sequences with breath holding, parallel imaging, and radial k-space filling) can improve image quality. Each of these techniques is more suitable for use with certain sequences and acquisition planes and in specific situations and age groups. Different T1- and T2-weighted sequences work better in different age groups and with differing acquisition planes and have specific advantages and disadvantages. Dynamic imaging should be performed differently in younger children than in older children. In younger children, the sequence and the timing of dynamic phases need to be adjusted. Different sequences work better in smaller children and in older children because of differing breath-holding ability, breathing patterns, field of view, and use of sedation. Hence, specific protocols should be maintained for younger children and older children. Combining longer-higher-resolution sequences and faster-lower-resolution sequences helps acquire diagnostic-quality images in a reasonable time.
View details for DOI 10.1148/rg.333125027
View details for Web of Science ID 000319111700009
View details for PubMedID 23674770
Coil compression for accelerated imaging with Cartesian sampling
MAGNETIC RESONANCE IN MEDICINE
2013; 69 (2): 571-582
MRI using receiver arrays with many coil elements can provide high signal-to-noise ratio and increase parallel imaging acceleration. At the same time, the growing number of elements results in larger datasets and more computation in the reconstruction. This is of particular concern in 3D acquisitions and in iterative reconstructions. Coil compression algorithms are effective in mitigating this problem by compressing data from many channels into fewer virtual coils. In Cartesian sampling there often are fully sampled k-space dimensions. In this work, a new coil compression technique for Cartesian sampling is presented that exploits the spatially varying coil sensitivities in these nonsubsampled dimensions for better compression and computation reduction. Instead of directly compressing in k-space, coil compression is performed separately for each spatial location along the fully sampled directions, followed by an additional alignment process that guarantees the smoothness of the virtual coil sensitivities. This important step provides compatibility with autocalibrating parallel imaging techniques. Its performance is not susceptible to artifacts caused by a tight imaging field-of-view. High quality compression of in vivo 3D data from a 32 channel pediatric coil into six virtual coils is demonstrated.
View details for DOI 10.1002/mrm.24267
View details for Web of Science ID 000314059500031
View details for PubMedID 22488589
IMPROVED VISUALIZATION AND QUANTIFICATION OF 4D FLOW MRI DATA USING DIVERGENCE-FREE WAVELET DENOISING
2013 IEEE 10TH INTERNATIONAL SYMPOSIUM ON BIOMEDICAL IMAGING (ISBI)
View details for Web of Science ID 000326900100297
Nonrigid motion correction in 3D using autofocusing withlocalized linear translations
MAGNETIC RESONANCE IN MEDICINE
2012; 68 (6): 1785-1797
MR scans are sensitive to motion effects due to the scan duration. To properly suppress artifacts from nonrigid body motion, complex models with elements such as translation, rotation, shear, and scaling have been incorporated into the reconstruction pipeline. However, these techniques are computationally intensive and difficult to implement for online reconstruction. On a sufficiently small spatial scale, the different types of motion can be well approximated as simple linear translations. This formulation allows for a practical autofocusing algorithm that locally minimizes a given motion metric--more specifically, the proposed localized gradient-entropy metric. To reduce the vast search space for an optimal solution, possible motion paths are limited to the motion measured from multichannel navigator data. The novel navigation strategy is based on the so-called "Butterfly" navigators, which are modifications of the spin-warp sequence that provides intrinsic translational motion information with negligible overhead. With a 32-channel abdominal coil, sufficient number of motion measurements were found to approximate possible linear motion paths for every image voxel. The correction scheme was applied to free-breathing abdominal patient studies. In these scans, a reduction in artifacts from complex, nonrigid motion was observed.
View details for DOI 10.1002/mrm.24189
View details for Web of Science ID 000311398600012
View details for PubMedID 22307933
Evaluation of Valvular Insufficiency and Shunts with Parallel-imaging Compressed-sensing 4D Phase-contrast MR Imaging with Stereoscopic 3D Velocity-fusion Volume-rendered Visualization
2012; 265 (1): 87-95
To assess the potential of compressed-sensing parallel-imaging four-dimensional (4D) phase-contrast magnetic resonance (MR) imaging and specialized imaging software in the evaluation of valvular insufficiency and intracardiac shunts in patients with congenital heart disease.Institutional review board approval was obtained for this HIPAA-compliant study. Thirty-four consecutive retrospectively identified patients in whom a compressed-sensing parallel-imaging 4D phase-contrast sequence was performed as part of routine clinical cardiac MR imaging between March 2010 and August 2011 and who had undergone echocardiography were included. Multiplanar, volume-rendered, and stereoscopic three-dimensional velocity-fusion visualization algorithms were developed and implemented in Java and OpenGL. Two radiologists independently reviewed 4D phase-contrast studies for each of 34 patients (mean age, 6 years; age range, 10 months to 21 years) and tabulated visible shunts and valvular regurgitation. These results were compared with color Doppler echocardiographic and cardiac MR imaging reports, which were generated without 4D phase-contrast visualization. Cohen ? statistics were computed to assess interobserver agreement and agreement with echocardiographic results.The 4D phase-contrast acquisitions were performed, on average, in less than 10 minutes. Among 123 valves seen in 34 4D phase-contrast studies, 29 regurgitant valves were identified, with good agreement between observers (k=0.85). There was also good agreement with the presence of at least mild regurgitation at echocardiography (observer 1, ?=0.76; observer 2, ?=0.77) with high sensitivity (observer 1, 75%; observer 2, 82%) and specificity (observer 1, 97%; observer 2, 95%) relative to the reference standard. Eight intracardiac shunts were identified, four of which were not visible with conventional cardiac MR imaging but were detected with echocardiography. No intracardiac shunts were found with echocardiography alone.With velocity-fusion visualization, the compressed-sensing parallel-imaging 4D phase-contrast sequence can augment conventional cardiac MR imaging by improving sensitivity for and depiction of hemodynamically significant shunts and valvular regurgitation.
View details for DOI 10.1148/radiol.12120055
View details for Web of Science ID 000309517600011
View details for PubMedID 22923717
DIfferential subsampling with cartesian ordering (DISCO): A high spatio-temporal resolution dixon imaging sequence for multiphasic contrast enhanced abdominal imaging
JOURNAL OF MAGNETIC RESONANCE IMAGING
2012; 35 (6): 1484-1492
To develop and evaluate a multiphasic contrast-enhanced MRI method called DIfferential Sub-sampling with Cartesian Ordering (DISCO) for abdominal imaging.A three-dimensional, variable density pseudo-random k-space segmentation scheme was developed and combined with a Dixon-based fat-water separation algorithm to generate high temporal resolution images with robust fat suppression and without compromise in spatial resolution or coverage. With institutional review board approval and informed consent, 11 consecutive patients referred for abdominal MRI at 3 Tesla (T) were imaged with both DISCO and a routine clinical three-dimensional SPGR-Dixon (LAVA FLEX) sequence. All images were graded by two radiologists using quality of fat suppression, severity of artifacts, and overall image quality as scoring criteria. For assessment of arterial phase capture efficiency, the number of temporal phases with angiographic phase and hepatic arterial phase was recorded.There were no significant differences in quality of fat suppression, artifact severity or overall image quality between DISCO and LAVA FLEX images (P > 0.05, Wilcoxon signed rank test). The angiographic and arterial phases were captured in all 11 patients scanned using the DISCO acquisition (mean number of phases were two and three, respectively).DISCO effectively captures the fast dynamics of abdominal pathology such as hyperenhancing hepatic lesions with a high spatio-temporal resolution. Typically, 1.1 × 1.5 × 3 mm spatial resolution over 60 slices was achieved with a temporal resolution of 4-5 s.
View details for DOI 10.1002/jmri.23602
View details for Web of Science ID 000304035100028
View details for PubMedID 22334505
Fast l(1)-SPIRiT Compressed Sensing Parallel Imaging MRI: Scalable Parallel Implementation and Clinically Feasible Runtime
IEEE TRANSACTIONS ON MEDICAL IMAGING
2012; 31 (6): 1250-1262
We present l?-SPIRiT, a simple algorithm for auto calibrating parallel imaging (acPI) and compressed sensing (CS) that permits an efficient implementation with clinically-feasible runtimes. We propose a CS objective function that minimizes cross-channel joint sparsity in the wavelet domain. Our reconstruction minimizes this objective via iterative soft-thresholding, and integrates naturally with iterative self-consistent parallel imaging (SPIRiT). Like many iterative magnetic resonance imaging reconstructions, l?-SPIRiT's image quality comes at a high computational cost. Excessively long runtimes are a barrier to the clinical use of any reconstruction approach, and thus we discuss our approach to efficiently parallelizing l?-SPIRiT and to achieving clinically-feasible runtimes. We present parallelizations of l?-SPIRiT for both multi-GPU systems and multi-core CPUs, and discuss the software optimization and parallelization decisions made in our implementation. The performance of these alternatives depends on the processor architecture, the size of the image matrix, and the number of parallel imaging channels. Fundamentally, achieving fast runtime requires the correct trade-off between cache usage and parallelization overheads. We demonstrate image quality via a case from our clinical experimentation, using a custom 3DFT spoiled gradient echo (SPGR) sequence with up to 8× acceleration via Poisson-disc undersampling in the two phase-encoded directions.
View details for DOI 10.1109/TMI.2012.2188039
View details for Web of Science ID 000304911300008
View details for PubMedID 22345529
- Images in clinical medicine. Splenic spirals. New England journal of medicine 2012; 366 (22): 2111-?
Inversion-recovery-prepared dixon bSSFP: Initial clinical experience with a novel pulse sequence for renal MRA within a breathhold
JOURNAL OF MAGNETIC RESONANCE IMAGING
2012; 35 (4): 875-881
To evaluate the capability of a new breathhold non-contrast-enhanced MRA method (Non-contrast Outer Radial Inner Square k-space Scheme, NORISKS) to visualize renal arteries by comparing the method with a routine clinical but significantly longer non-contrast-enhanced (non-CE) MRA technique.Eighteen subjects referred for abdominal MRI were examined with NORISKS and a routine non-contrast-enhanced MRA technique. Two versions of NORISKS were evaluated: with and without ECG gating. The images were then scored independently and in blinded manner by two radiologists on 5-point scales for visualization of the proximal and distal renal arteries and quality of fat suppression.No statistically significant difference was detected between NORISKS and routine clinical non-CE MRA in all categories except for visualization of the distal renal arteries where ungated NORISKS performed poorer than the routine non-CE MRA (P < 10(-4) ).We have demonstrated a promising non-CE MRA method for acquiring renal angiograms within a breathhold without any compromise in spatial resolution or coverage. ECG-gated NORISKS is able to acquire renal angiograms that are comparable to a routine clinical non-CE MRA method (Inhance IFIR, GE Healthcare), which requires approximately seven times the scan time of NORISKS.
View details for DOI 10.1002/jmri.23503
View details for Web of Science ID 000301712400015
View details for PubMedID 22095672
Rapid Pediatric Cardiac Assessment of Flow and Ventricular Volume With Compressed Sensing Parallel Imaging Volumetric Cine Phase-Contrast MRI
AMERICAN JOURNAL OF ROENTGENOLOGY
2012; 198 (3): W250-W259
The quantification of cardiac flow and ventricular volumes is an essential goal of many congenital heart MRI examinations, often requiring acquisition of multiple 2D phase-contrast and bright-blood cine steady-state free precession (SSFP) planes. Scan acquisition, however, is lengthy and highly reliant on an imager who is well-versed in structural heart disease. Although it can also be lengthy, 3D time-resolved (4D) phase-contrast MRI yields global flow patterns and is simpler to perform. We therefore sought to accelerate 4D phase contrast and to determine whether equivalent flow and volume measurements could be extracted.Four-dimensional phase contrast was modified for higher acceleration with compressed sensing. Custom software was developed to process 4D phase-contrast images. We studied 29 patients referred for congenital cardiac MRI who underwent a routine clinical protocol, including cine short-axis stack SSFP and 2D phase contrast, followed by contrast-enhanced 4D phase contrast. To compare quantitative measurements, Bland-Altman analysis, paired Student t tests, and F tests were used.Ventricular end-diastolic, end-systolic, and stroke volumes obtained from 4D phase contrast and SSFP were well correlated (? = 0.91-0.95; r(2) = 0.83-0.90), with no statistically significant difference. Ejection fractions were well correlated in a subpopulation that underwent higher-resolution compressed-sensing 4D phase contrast (? = 0.88; r(2) = 0.77). Four-dimensional phase contrast and 2D phase contrast flow rates were also well correlated (? = 0.90; r(2) = 0.82). Excluding ventricles with valvular insufficiency, cardiac outputs derived from outlet valve flow and stroke volumes were more consistent by 4D phase contrast than by 2D phase contrast and SSFP.Combined parallel imaging and compressed sensing can be applied to 4D phase contrast. With custom software, flow and ventricular volumes may be extracted with comparable accuracy to SSFP and 2D phase contrast. Furthermore, cardiac outputs were more consistent by 4D phase contrast.
View details for DOI 10.2214/AJR.11.6969
View details for Web of Science ID 000301069000006
View details for PubMedID 22358022
Rapid MR venography in children using a blood pool contrast agent and multi-station fat-water-separated volumetric imaging
2012; 42 (2): 242-248
A rapid, reliable radiation-free method of pediatric body venography might complement US by evaluating veins in the abdomen and pelvis and by providing a global depiction of venous anatomy. We describe a MR venography technique utilizing gadofosveset, a blood pool contrast agent, in children. The technique allows high-spatial-resolution imaging of the veins from the diaphragm to the knees in less than 15 min of total exam time.
View details for DOI 10.1007/s00247-011-2254-5
View details for Web of Science ID 000301664100015
View details for PubMedID 21989981
- Sildenafil for Severe Lymphatic Malformations NEW ENGLAND JOURNAL OF MEDICINE 2012; 366 (4): 384-386
Estimation of liver T*2 in transfusion-related iron overload in patients with weighted least squares T*2 IDEAL
MAGNETIC RESONANCE IN MEDICINE
2012; 67 (1): 183-190
MRI imaging of hepatic iron overload can be achieved by estimating T(2) values using multiple-echo sequences. The purpose of this work is to develop and clinically evaluate a weighted least squares algorithm based on T(2) Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation (IDEAL) technique for volumetric estimation of hepatic T(2) in the setting of iron overload. The weighted least squares T(2) IDEAL technique improves T(2) estimation by automatically decreasing the impact of later, noise-dominated echoes. The technique was evaluated in 37 patients with iron overload. Each patient underwent (i) a standard 2D multiple-echo gradient echo sequence for T(2) assessment with nonlinear exponential fitting, and (ii) a 3D T(2) IDEAL technique, with and without a weighted least squares fit. Regression and Bland-Altman analysis demonstrated strong correlation between conventional 2D and T(2) IDEAL estimation. In cases of severe iron overload, T(2) IDEAL without weighted least squares reconstruction resulted in a relative overestimation of T(2) compared with weighted least squares.
View details for DOI 10.1002/mrm.22986
View details for Web of Science ID 000298482800021
View details for PubMedID 21574184
Combined respiratory and cardiac triggering improves blood pool contrast-enhanced pediatric cardiovascular MRI
2011; 41 (12): 1536-1544
Contrast-enhanced cardiac MRA suffers from cardiac motion artifacts and often requires a breath-hold.This work develops and evaluates a blood pool contrast-enhanced combined respiratory- and ECG-triggered MRA method.An SPGR sequence was modified to enable combined cardiac and respiratory triggering on a 1.5-T scanner. Twenty-three consecutive children referred for pediatric heart disease receiving gadofosveset were recruited in HIPAA-compliant fashion with IRB approval and informed consent. Children underwent standard non-triggered contrast-enhanced MRA with or without suspended respiration. Additionally, a free-breathing-triggered MRA was acquired. Triggered and non-triggered studies were presented in blinded random order independently to two radiologists twice. Anatomical structure delineation was graded for each triggered and non-triggered acquisition and the visual quality on triggered MRA was compared directly to that on non-triggered MRA.Triggered images received higher scores from each radiologist for all anatomical structures on each of the two reading sessions (Wilcoxon rank sum test, P?0.05). In direct comparison, triggered images were preferred over non-triggered images for delineating cardiac structures, with most comparisons reaching statistical significance (binomial test, P?0.05).Combined cardiac and respiratory triggering, enabled by a blood pool contrast agent, improves delineation of most anatomical structures in pediatric cardiovascular MRA.
View details for DOI 10.1007/s00247-011-2196-y
View details for Web of Science ID 000297621800005
View details for PubMedID 21786125
Functional hepatobiliary MR imaging in children
2011; 41 (10): 1250-1258
Clinical application efforts for the hepatocyte-specific MRI contrast agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) have mainly been directed toward detection and characterization of various hepatic masses in the adult population.Here we report our initial experience with Gd-EOB-DTPA for evaluating congenital and acquired hepatobiliary pathologies in the pediatric population.Twenty-one consecutive children receiving Gd-EOB-DTPA for functional hepatobiliary evaluation at our institution were retrospectively identified with IRB approval. The use of Gd-EOB-DTPA was classified in each case as definite, potential, or no clinical utility, focusing on the clinical value gained beyond traditional noncontrast fluid-sensitive MR cholangiopancreatography (FS-MRCP) and other imaging modalities.Definite added value of Gd-EOB-DTPA was found in 12 patients, with potential value in 4 patients, and no value in 5 patients. Benefit was seen in cases of iatrogenic and non-iatrogenic biliary strictures, perihepatic fluid collections for biliary leak, hepatobiliary dysfunction in the absence of hyperbilirubinemia, and in the functional exclusion of cystic duct occlusion that can be seen in acute cholecystitis.This is the first reported series of children with Gd-EOB-DTPA and this early work suggests potential pediatric applications.
View details for DOI 10.1007/s00247-011-2086-3
View details for Web of Science ID 000294690500005
View details for PubMedID 21553038
Point/counterpoint: dose-related issues in cardiac CT imaging.
2011; 41: 528-533
This manuscript reviews some of the more controversial dose-related issues in cardiac CT imaging. Discussion covers the relative merits of cardiac CT versus MR, advantages and concerns regarding gated versus nongated cardiac CT and advantages and concerns regarding the use of breast shields in girls undergoing cardiac CT imaging.
View details for DOI 10.1007/s00247-011-2153-9
View details for PubMedID 21847735
Advances in pediatric body MRI.
2011; 41: 549-554
MRI offers an alternative to CT, and thus is central to an ALARA strategy. However, long exam times, limited magnet availability, and motion artifacts are barriers to expanded use of MRI. This article reviews developments in pediatric body MRI that might reduce these barriers: high field systems, acceleration, navigation and newer contrast agents.
View details for DOI 10.1007/s00247-011-2103-6
View details for PubMedID 21847737
Active gastrointestinal hemorrhage identification by blood pool contrast-enhanced magnetic resonance angiography
2011; 41 (9): 1198-1200
Localization of the source of gastrointestinal hemorrhage can be challenging. Currently, this is often accomplished with tagged red blood cell scintigraphy, with attendant ionizing radiation and relatively poor spatial resolution. We describe an analogous method of detecting acute gastrointestinal hemorrhage by enhanced MRI with blood pool contrast agent. Briefly, following precontrast fat-suppressed volumetric T1-weighted image acquisition, single-dose gadofosveset trisodium, a blood pool agent, is administered. Then serial post-T1-weighted images are obtained. This technique is a novel method for evaluating gastrointestinal hemorrhage.
View details for DOI 10.1007/s00247-011-2139-7
View details for Web of Science ID 000293979800013
View details for PubMedID 21594539
Volumetric fat-water separated T2-weighted MRI
2011; 41 (7): 875-883
Pediatric body MRI exams often cover multiple body parts, making the development of broadly applicable protocols and obtaining uniform fat suppression a challenge. Volumetric T2 imaging with Dixon-type fat-water separation might address this challenge, but it is a lengthy process.We develop and evaluate a faster two-echo approach to volumetric T2 imaging with fat-water separation.A volumetric spin-echo sequence was modified to include a second shifted echo so two image sets are acquired. A region-growing reconstruction approach was developed to decompose separate water and fat images. Twenty-six children were recruited with IRB approval and informed consent. Fat-suppression quality was graded by two pediatric radiologists and compared against conventional fat-suppressed fast spin-echo T2-W images. Additionally, the value of in- and opposed-phase images was evaluated.Fat suppression on volumetric images had high quality in 96% of cases (95% confidence interval of 80-100%) and were preferred over or considered equivalent to conventional two-dimensional fat-suppressed FSE T2 imaging in 96% of cases (95% confidence interval of 78-100%). In- and opposed-phase images had definite value in 12% of cases.Volumetric fat-water separated T2-weighted MRI is feasible and is likely to yield improved fat suppression over conventional fat-suppressed T2-weighted imaging.
View details for DOI 10.1007/s00247-010-1963-5
View details for Web of Science ID 000292167300011
View details for PubMedID 21243349
Improved cardiovascular flow quantification with time-resolved volumetric phase-contrast MRI
2011; 41 (6): 711-720
Cardiovascular flow is commonly assessed with two-dimensional, phase-contrast MRI (2-D PC-MRI). However, scan prescription and acquisition over multiple planes is lengthy, often requires direct physician oversight and has inconsistent results. Time-resolved volumetric PC-MRI (4-D flow) may address these limitations.We assess the degree of agreement and internal consistency between 2-D and 4-D flow quantification in our clinical population.Software enabling flow calculation from 4-D flow was developed in Java. With IRB approval and HIPAA compliance, 18 consecutive patients without shunts were identified who underwent both (1) conventional 2-D PC-MRI of the aorta and main pulmonary artery and (2) 4-D flow imaging. Aortic and pulmonary flow rates were assessed with both techniques.Both methods showed general agreement in flow rates (?: 0.87-0.90). Systemic and pulmonary arterial flow rates were well-correlated (?: 4-D 0.98-0.99, 2-D 0.93), but more closely matched with 4-D (P < 0.05, Brown-Forsythe). Pulmonary flow rates were lower than systemic rates for 2-D (P < 0.05, two-sample t-test). In a sub-analysis of patients without pulmonary or aortic regurgitation, 2-D showed improved correlation of flow rates while 4-D phase-contrast remained tightly correlated (?: 4-D 0.99-1.00, 2-D 0.99).4-D PC-MRI demonstrates greater consistency than conventional 2-D PC-MRI for flow quantification.
View details for DOI 10.1007/s00247-010-1932-z
View details for Web of Science ID 000290544500005
View details for PubMedID 21221566
An Approach to Pediatric Liver MRI
AMERICAN JOURNAL OF ROENTGENOLOGY
2011; 196 (5): W519-W526
This article illustrates an approach to MRI for hepatobiliary imaging in children. The indications, patient preparation, protocols, pulse sequences, and contrast agents will be highlighted.Significant advances in hepatobiliary MRI have allowed reliable, high quality imaging in a pediatric population.
View details for DOI 10.2214/AJR.10.6076
View details for Web of Science ID 000289769000004
View details for PubMedID 21512040
PRACTICAL PARALLEL IMAGING COMPRESSED SENSING MRI: SUMMARY OF TWO YEARS OF EXPERIENCE IN ACCELERATING BODY MRI OF PEDIATRIC PATIENTS.
2011 8TH IEEE INTERNATIONAL SYMPOSIUM ON BIOMEDICAL IMAGING: FROM NANO TO MACRO
View details for Web of Science ID 000298849400238
Adrenal and renal corticomedullary junction iron deposition in red cell aplasia
2010; 40 (12): 1955-1957
Iron deposition can occur in the kidneys as a result of hemolysis or extensive iron overload from transfusions. With T2* MRI, renal iron deposition can be visualized. In this report, renal corticomedullary junction iron deposition is noted using T2* MRI in a boy with red cell aplasia. The renal corticomedullary junction iron deposition is an indication of the severity of his iron overload. This is an unusual finding and brings clinical attention to the boy's renal function for further evaluation.
View details for DOI 10.1007/s00247-010-1824-2
View details for Web of Science ID 000284375300013
View details for PubMedID 20852855
A method of rapid robust respiratory synchronization for MRI
2010; 40 (10): 1690-1692
Respiratory motion degrades MRI exams. Adequate detection of respiratory motion with pneumatic respiratory belts in small children is challenging and time-consuming.
View details for DOI 10.1007/s00247-010-1755-y
View details for Web of Science ID 000281907100014
View details for PubMedID 20567966
Respiratory Navigated Free Breathing 3D Spoiled Gradient-Recalled Echo Sequence for Contrast-Enhanced Examination of the Liver: Diagnostic Utility and Comparison With Free Breathing and Breath-Hold Conventional Examinations
AMERICAN JOURNAL OF ROENTGENOLOGY
2010; 195 (3): 687-691
The purpose of our study was to evaluate image quality in a 3D spoiled gradient-recalled echo (SPGR) sequence that was modified to incorporate respiratory navigation to limit the deleterious effects of respiratory motion and to compare it with conventional scanning during breath-holding and free breathing.Respiratory navigation of 3D SPGR sequences is technically feasible, and image quality is modestly improved over free breathing acquisitions using conventional 3D SPGR sequences. This may represent a promising imaging alternative for patients who cannot hold their breath.
View details for DOI 10.2214/AJR.09.3892
View details for Web of Science ID 000281180500022
View details for PubMedID 20729447
Improved Pediatric MR Imaging with Compressed Sensing
2010; 256 (2): 607-616
To develop a method that combines parallel imaging and compressed sensing to enable faster and/or higher spatial resolution magnetic resonance (MR) imaging and show its feasibility in a pediatric clinical setting.Institutional review board approval was obtained for this HIPAA-compliant study, and informed consent or assent was given by subjects. A pseudorandom k-space undersampling pattern was incorporated into a three-dimensional (3D) gradient-echo sequence; aliasing then has an incoherent noiselike pattern rather than the usual coherent fold-over wrapping pattern. This k-space-sampling pattern was combined with a compressed sensing nonlinear reconstruction method that exploits the assumption of sparsity of medical images to permit reconstruction from undersampled k-space data and remove the noiselike aliasing. Thirty-four patients (15 female and 19 male patients; mean age, 8.1 years; range, 0-17 years) referred for cardiovascular, abdominal, and knee MR imaging were scanned with this 3D gradient-echo sequence at high acceleration factors. Obtained k-space data were reconstructed with both a traditional parallel imaging algorithm and the nonlinear method. Both sets of images were rated for image quality, radiologist preference, and delineation of specific structures by two radiologists. Wilcoxon and symmetry tests were performed to test the hypothesis that there was no significant difference in ratings for image quality, preference, and delineation of specific structures.Compressed sensing images were preferred more often, had significantly higher image quality ratings, and greater delineation of anatomic structures (P < .001) than did images obtained with the traditional parallel reconstruction method.A combination of parallel imaging and compressed sensing is feasible in a clinical setting and may provide higher resolution and/or faster imaging, addressing the challenge of delineating anatomic structures in pediatric MR imaging.
View details for DOI 10.1148/radiol.10091218
View details for Web of Science ID 000280272100032
View details for PubMedID 20529991
T-2 relaxation times of C-13 metabolites in a rat hepatocellular carcinoma model measured in vivo using C-13-MRS of hyperpolarized [1-C-13]pyruvate
NMR IN BIOMEDICINE
2010; 23 (4): 414-423
A single-voxel Carr-Purcell-Meibloom-Gill sequence was developed to measure localized T(2) relaxation times of (13)C-labeled metabolites in vivo for the first time. Following hyperpolarized [1-(13)C]pyruvate injections, pyruvate and its metabolic products, alanine and lactate, were observed in the liver of five rats with hepatocellular carcinoma and five healthy control rats. The T(2) relaxation times of alanine and lactate were both significantly longer in HCC tumors than in normal livers (p?0.002). The HCC tumors also showed significantly higher alanine signal relative to the total (13)C signal than normal livers (p?0.006). The intra- and inter-subject variations of the alanine T(2) relaxation time were 11% and 13%, respectively. The intra- and inter-subject variations of the lactate T(2) relaxation time were 6% and 7%, respectively. The intra-subject variability of alanine to total carbon ratio was 16% and the inter-subject variability 28%. The intra-subject variability of lactate to total carbon ratio was 14% and the inter-subject variability 20%. The study results show that the signal level and relaxivity of [1-(13)C]alanine may be promising biomarkers for HCC tumors. Its diagnostic values in HCC staging and treatment monitoring are yet to be explored.
View details for DOI 10.1002/nbm.1481
View details for Web of Science ID 000277525800011
View details for PubMedID 20175135
State-of-the-Art in Pediatric Body and Musculoskeletal Magnetic Resonance Imaging
SEMINARS IN ULTRASOUND CT AND MRI
2010; 31 (2): 86-99
Pediatric body and musculoskeletal MRI has seen tremendous advances over the past few years. These advances have enabled high-quality imaging in even the smallest children and expanded the range of clinical problems amenable to MRI. In this review, we highlight some advances: transition to 3 Tesla, parallel imaging, motion compensation, and new contrast agents. Given the increasing saliency of concerns regarding ionizing radiation from computed tomography, these advances could not be more welcome.
View details for DOI 10.1053/j.sult.2010.01.005
View details for Web of Science ID 000276295500004
View details for PubMedID 20304318
MRI of the liver-how to do it
2010; 40 (4): 431-437
This article details indications, patient preparation, pulse sequences/protocols, and contrast agents for pediatric hepatobiliary MRI. When performed well, MRI provides superior diagnostic information relative to CT for evaluation of hepatic tumors, liver transplants, and biliary disease.
View details for DOI 10.1007/s00247-009-1522-0
View details for Web of Science ID 000275555900008
View details for PubMedID 20225098
Navigated abdominal T1-W MRI permits free-breathing image acquisition with less motion artifact
2010; 40 (3): 340-344
T1-W imaging of the pediatric abdomen is often limited by respiratory motion artifacts. Although navigation has been commonly employed for coronary MRA and T2-W imaging, navigation for T1-W imaging is less developed. Thus, we incorporated a navigator pulse into a fat-suppressed T1-W SPGR sequence such that steady-state contrast was not disrupted. Ten children were scanned after gadolinium administration three times in immediate succession: breath-hold with no navigation, free-breathing with navigation, and free-breathing without navigation. Motion artifacts were scored for each sequence by two radiologists,showing fewer motion artifacts with navigation compared to free-breathing and greater motion artifacts than with breath-holding. This work demonstrates the feasibility and potential utility of navigation for pediatric abdominal T1-W imaging.
View details for DOI 10.1007/s00247-009-1502-4
View details for Web of Science ID 000274386700008
View details for PubMedID 20066407
Magnetic resonance imaging for uterine and vaginal anomalies
CURRENT OPINION IN OBSTETRICS & GYNECOLOGY
2009; 21 (5): 379-389
Pediatric pelvic MRI has had dramatic advances in the past few years. This review documents studies demonstrating the accuracy of MRI for the evaluation of uterine and vaginal anomalies and discusses the salient changes to MRI methods that are particularly applicable to evaluating the pediatric patient with these developmental anomalies.MRI has high accuracy for evaluation of uterine and vaginal anomalies. Significant advances, such as volumetric imaging, increased resolution, decreased motion artifacts, and shorter examination time, have increased the access and utility of MRI for pediatric patients.MRI techniques have evolved markedly in the past several years, providing a robust method of evaluating uterine and vaginal anomalies in the pediatric patient.
View details for DOI 10.1097/GCO.0b013e3283307c3e
View details for Web of Science ID 000270062100003
View details for PubMedID 19623067
Appendiceal hyperemia and/or distention is not always appendicitis: appendicitis mimicry in the pediatric population
2009; 33 (5): 402-405
Appendicitis is the most common surgical cause of acute abdominal pain in the pediatric population. Several conditions can mimic the clinical presentation of appendicitis, leaving imaging as an essential modality to uncover the etiology, yet under certain circumstances, it can be misleading. Here, we present three cases where findings on multidetector computerized tomography scans supported the diagnosis of appendicitis, yet an alternate cause was found. These cases highlight a particular pitfall of satisfaction of search.
View details for DOI 10.1016/j.clinimag.2009.01.010
View details for Web of Science ID 000269764400014
View details for PubMedID 19712824
MR Voiding Cystography for Evaluation of Vesicoureteral Reflux
AMERICAN JOURNAL OF ROENTGENOLOGY
2009; 192 (5): W206-W211
The purpose of our study is to present a real-time interactive continuous fluoroscopy MRI technique for vesicoureteral reflux (VUR) diagnosis.MR voiding cystography with a real-time interactive MR fluoroscopic technique on an open MRI magnet is feasible for the evaluation of VUR in children.
View details for DOI 10.2214/AJR.08.1251
View details for Web of Science ID 000265387300045
View details for PubMedID 19380524
Advances in Pediatric MR Imaging
MAGNETIC RESONANCE IMAGING CLINICS OF NORTH AMERICA
2008; 16 (3): 385-?
This article describes the considerable technical achievements that have been made in MR imaging in the evaluation of pediatric patients. The latest techniques in improving signal intensity, resolution, and speed are discussed. The multitude of new options for pediatric MR imaging are illustrated, including higher field strength imaging, multi-channel coil technology coupled with parallel imaging, and new pulse sequence designs. Several future directions in the field of pediatric body and musculoskeletal imaging also are highlighted.
View details for DOI 10.1016/j.mric.2008.04.008
View details for Web of Science ID 000264835900002
View details for PubMedID 18585595
Balanced SSFP imaging of the musculoskeletal system
JOURNAL OF MAGNETIC RESONANCE IMAGING
2007; 25 (2): 270-278
Magnetic resonance imaging (MRI), with its unique ability to image and characterize soft tissue noninvasively, has emerged as one of the most accurate imaging methods available to diagnose bone and joint pathology. Currently, most evaluation of musculoskeletal pathology is done with two-dimensional acquisition techniques such as fast spin echo (FSE) imaging. The development of three-dimensional fast imaging methods based on balanced steady-state free precession (SSFP) shows great promise to improve MRI of the musculoskeletal system. These methods may allow acquisition of fluid sensitive isotropic data that can be reformatted into arbitrary planes for improved detection and visualization of pathology. Sensitivity to fluid and fat suppression are important issues in these techniques to improve delineation of cartilage contours, for detection of marrow edema and derangement of other joint structures.
View details for DOI 10.1002/jmri.20819
View details for Web of Science ID 000244133000006
View details for PubMedID 17260387
Value of delayed imaging in MDCT of the abdomen and pelvis
AMERICAN JOURNAL OF ROENTGENOLOGY
2006; 187 (1): 154-163
Our objective was to illustrate the benefits of obtaining delayed CT images.There are several clinical scenarios in which delayed CT images may improve diagnostic specificity.
View details for DOI 10.2214/AJR.05.0148
View details for Web of Science ID 000238659600027
View details for PubMedID 16794170
Articular cartilage of the knee: Evaluation with fluctuating equilibrium MR imaging - Initial experience in healthy volunteers
2006; 238 (2): 712-718
Institutional review board approval and informed consent were obtained for this HIPAA-compliant study, whose purpose was to prospectively compare three magnetic resonance (MR) imaging techniques-fluctuating equilibrium, three-dimensional (3D) spoiled gradient-recalled acquisition in the steady state (SPGR), and two-dimensional (2D) fast spin echo (SE)-for evaluating articular cartilage in the knee. The study cohort consisted of 10 healthy volunteers (four men, six women; age range, 26-42 years). Cartilage signal-to-noise ratio (SNR), SNR efficiency, cartilage-fluid contrast-to-noise ratio (CNR), CNR efficiency, image quality, cartilage visibility, and fat suppression were compared. Cartilage volume was compared for the fluctuating equilibrium and 3D SPGR techniques. Compared with 3D SPGR and 2D fast SE, fluctuating equilibrium yielded the highest cartilage SNR efficiency and cartilage-fluid CNR efficiency (P < .01 for both). Image quality was similar with all sequences. Fluctuating equilibrium imaging yielded higher cartilage visibility than did 2D fast SE imaging (P <. 01) but worse fat suppression than did 3D SPGR and 2D fast SE imaging (P < .04). Cartilage volume measurements with fluctuating equilibrium and 3D SPGR were similar. Fluctuating equilibrium MR imaging is a promising method for evaluating articular cartilage in the knee.
View details for DOI 10.1148/radiol.2381042183
View details for Web of Science ID 000234859100040
View details for PubMedID 16436826
Dual-acquisition phase-sensitive fat-water separation using balanced steady-state free precession
MAGNETIC RESONANCE IMAGING
2006; 24 (2): 113-122
Balanced steady-state free precession (SSFP) sequences use fully re-focussed gradient waveforms to achieve a high signal and useful image contrast in short scan times. Despite these strengths, the clinical feasibility of balanced SSFP is still limited both by bright fat signal and by the signal voids that result from off-resonance effects such as field or susceptibility variations. A new method, dual-acquisition phase-sensitive SSFP, combines the signals from two standard balanced SSFP acquisitions to separate fat and water while simultaneously reducing the signal voids. The acquisitions are added in quadrature and then phase corrected using a simple algorithm before fat and water can be identified simply by the sign of the signal. This method is especially useful for applications at high field, where the RF power deposition, spatial resolution requirements and gradient strength limit the minimum repetition times. Finally, dual-acquisition phase-sensitive SSFP can be combined with other magnetization preparation schemes to produce specific image contrast in addition to separating fat and water signals.
View details for DOI 10.1016/j.mri.2005.10.013
View details for Web of Science ID 000235506400002
View details for PubMedID 16455400
Controversies in protocol selection in the Imaging of articular cartilage
SEMINARS IN MUSCULOSKELETAL RADIOLOGY
2005; 9 (2): 161-172
Magnetic resonance (MR) imaging, with its unique ability to noninvasively image and characterize soft tissue, has shown promise in assessment of cartilage. The development of new, fast imaging methods with high contrast will improve the MR evaluation of cartilage morphology. In addition to morphological MR imaging methods, MR imaging contrast mechanisms under development may reveal detailed information regarding the physiology of cartilage. However, many of these methods remain to be tested in the clinical setting. Protocol selection for cartilage imaging requires understanding of the patient population and the advantages and limitations of these techniques.
View details for Web of Science ID 000230039200008
View details for PubMedID 16044384
Rapid musculoskeletal MRI with phase-sensitive steady-state free precession: Comparison with routine knee MRI
AMERICAN JOURNAL OF ROENTGENOLOGY
2005; 184 (5): 1450-1455
The aim of this work was to show the potential utility of a novel rapid 3D fat-suppressed MRI method for joint imaging.Phase-sensitive steady-state free precession provides rapid 3D joint imaging with robust fat suppression and excellent cartilage delineation.
View details for Web of Science ID 000228875300013
View details for PubMedID 15855095
Accommodation of requests for emergency US and CT: Applications of queueing theory to scheduling of urgent studies
2005; 235 (1): 244-249
The purpose of this study was to determine whether queueing theory would allow prediction of optimal number of schedule slots to be reserved for urgent computed tomography (CT) and ultrasonography (US). Institutional review board approval was obtained; informed consent was exempted. Emergency studies were modeled as a Poisson process; slots were reserved such that rate of rescheduling of routine studies to accommodate emergencies was predicted to be below a certain level. Model was tested with 3 years of emergency US and CT requests. US and CT requests showed Poisson distribution. US rescheduling was near that predicted. CT rescheduling exceeded that predicted, which reflected increasing CT use. By using more recent CT data for prediction, a more concordant rescheduling rate resulted.
View details for DOI 10.1148/radiol.2351040289
View details for Web of Science ID 000227952600036
View details for PubMedID 15716391
Analysis of multiple-acquisition SSFP
MAGNETIC RESONANCE IN MEDICINE
2004; 51 (5): 1038-1047
Refocused steady-state free precession (SSFP) is limited by its high sensitivity to local field variation, particularly at high field strengths or the long repetition times (TRs) necessary for high resolution. Several methods have been proposed to reduce SSFP banding artifact by combining multiple phase-cycled SSFP acquisitions, each differing in how individual signal magnitudes and phases are combined. These include maximum-intensity SSFP (MI-SSFP) and complex-sum SSFP (CS-SSFP). The reduction in SSFP banding is accompanied by a loss in signal-to-noise ratio (SNR) efficiency. In this work a general framework for analyzing banding artifact reduction, contrast, and SNR of any multiple-acquisition SSFP combination method is presented. A new sum-of-squares method is proposed, and a comparison is performed between each of the combination schemes. The sum-of-squares SSFP technique (SOS-SSFP) delivers both robust banding artifact reduction and higher SNR efficiency than other multiple-acquisition techniques, while preserving SSFP contrast.
View details for DOI 10.1002/mrm.20052
View details for Web of Science ID 000221239000022
View details for PubMedID 15122688
Knee cartilage volume with fluctuating equilibrium MRI
W B SAUNDERS CO LTD. 2004: S1-S1
View details for Web of Science ID 000225708200003
Fat-suppressed steady-state free precession imaging using phase detection
MAGNETIC RESONANCE IN MEDICINE
2003; 50 (1): 210-213
Fully refocused steady-state free precession (SSFP) is a rapid, efficient imaging sequence that can provide diagnostically useful image contrast. In SSFP, the signal is refocused midway between excitation pulses, much like in a spin-echo experiment. However, in SSFP, the phase of the refocused spins alternates for each resonant frequency interval equal to the reciprocal of the sequence repetition time (TR). Appropriate selection of the TR results in a 180 degrees phase difference between lipid and water signals. This phase difference can be used for fat-water separation in SSFP without any increase in scan time. The technique is shown to produce excellent non-contrast-enhanced, flow-independent angiograms of the peripheral vasculature.
View details for DOI 10.1002/mrm.10488
View details for Web of Science ID 000183961800028
View details for PubMedID 12815698
Comparison of new sequences for high-resolution cartilage imaging
MAGNETIC RESONANCE IN MEDICINE
2003; 49 (4): 700-709
The high prevalence of osteoarthritis continues to demand improved accuracy in detecting cartilage injury and monitoring its response to different treatments. MRI is the most accurate noninvasive method of diagnosing cartilage lesions. However, MR imaging of cartilage is limited by scan time, signal-to-noise ratio (SNR), and image contrast. Recently, there has been renewed interest in SNR-efficient imaging sequences for imaging cartilage, including various forms of steady-state free-precession as well as driven-equilibrium imaging. This work compares several of these sequences with existing methods, both theoretically and in normal volunteers. Results show that the new steady-state methods increase SNR-efficiency by as much as 30% and improve cartilage-synovial fluid contrast by a factor of three. Additionally, these methods markedly decrease minimum scan times, while providing 3D coverage without the characteristic blurring seen in fast spin-echo images.
View details for DOI 10.1002/mrm.10424
View details for Web of Science ID 000182007200013
View details for PubMedID 12652541
Characterization and reduction of the transient response in steady-state MR imaging
MAGNETIC RESONANCE IN MEDICINE
2001; 46 (1): 149-158
Refocused steady-state free precession (SSFP) imaging sequences have recently regained popularity as faster gradient hardware has allowed shorter repetition times, thereby reducing SSFP's sensitivity to off-resonance effects. Although these sequences offer fast scanning with good signal-to-noise efficiency, the "transient response," or time taken to reach a steady-state, can be long compared with the total imaging time, particularly when using 2D sequences. This results in lost imaging time and has made SSFP difficult to use for real-time and cardiac-gated applications. A linear-systems analysis of the steady-state and transient response for general periodic sequences is shown. The analysis is applied to refocused-SSFP sequences to generate a two-stage method of "catalyzing," or speeding up the progression to steady-state by first scaling, then directing the magnetization. This catalyzing method is compared with previous methods in simulations and experimentally. Although the second stage of the method exhibits some sensitivity to B(1) variations, our results show that the transient time can be significantly reduced, allowing imaging in a shorter total scan time. Magn Reson Med 46:149-158, 2001.
View details for Web of Science ID 000169561000019
View details for PubMedID 11443721
Linear combination steady-state free precession MRI
MAGNETIC RESONANCE IN MEDICINE
2000; 43 (1): 82-90
A new, fast, spectrally selective steady-state free precession (SSFP) imaging method is presented. Combining k-space data from SSFP sequences with certain phase schedules of radiofrequency excitation pulses permits manipulation of the spectral selectivity of the image. For example, lipid and water can be resolved. The contrast of each image depends on both T1 and T2, and the relative contribution of the two relaxation mechanisms to image contrast can be controlled by adjusting the flip angle. Several potential applications of the technique, referred to as linear combination steady-state free precession (LCSSFP), are demonstrated: fast musculoskeletal, abdominal, angiographic, and brain imaging.
View details for Web of Science ID 000084538500010
View details for PubMedID 10642734
Fluctuating equilibrium MRI
MAGNETIC RESONANCE IN MEDICINE
1999; 42 (5): 876-883
A new fast, spectrally selective imaging method called fluctuating equilibrium magnetic resonance is presented. With all gradients refocused over a repetition interval, certain phase schedules of radiofrequency excitation pulses produce an equilibrium magnetization that fluctuates from excitation to excitation, thus permitting simultaneous acquisition of several images with different contrast features. For example, lipid and water images can be rapidly acquired. The effective echo time can be adjusted using the flip angle, thus providing control over the T(2) contribution to the contrast. Several applications of the technique are presented, including fast musculoskeletal, abdominal, breast, and brain imaging, in addition to MR angiography. A technique for combining lipid and water images generated with this sequence for angiography is described and other potential applications are suggested. Magn Reson Med 42:876-883, 1999.
View details for Web of Science ID 000083447900006
View details for PubMedID 10542345
Prospective MR signal-based cardiac triggering
MAGNETIC RESONANCE IN MEDICINE
1999; 42 (1): 82-86
A cardiac motion compensation method using magnetic resonance signal-based triggering is presented. The method interlaces a triggering pulse sequence with an imaging sequence. The triggering sequence is designed to measure aortic blood velocity, from which cardiac phase can be inferred. The triggering sequence is executed repeatedly and the acquired data processed after each sequence iteration. When the desired phase of the cardiac cycle is detected, data are acquired using the imaging sequence. A signal-processing unit of a conventional scanner is used to process the triggering data in real time and issue triggering commands. Alternatively, a workstation, with a bus adaptor, can access data as they are acquired, process and display the data, and issue triggering commands. With a graphical user interface, the triggering pulse sequence and data-processing techniques can be modified instantaneously to optimize triggering. The technique is demonstrated with coronary artery imaging using both conventional two-dimensional Fourier transform scans and spiral trajectories.
View details for Web of Science ID 000081433800012
View details for PubMedID 10398953