Bio


Georg is a visiting instructor in the lab of Fernando Boada at RSL since 2022 focussing mainly on medical image reconstruction.

He obtained in Master in Nuclear Physics from TU Dresden in Germany in 2011. His master thesis project "Analysis and Simulation of Photon Scattering and Neutron Capture
Gamma Spectra" was performed at Helmholtz-Zentrum Dresden-Rossendorf in the lab of Dr. Andreas Wagner.

In 2015, Georg completed his PhD with summa cum laude in the lab of Prof. Jörg van den Hoff at Helmholtz-Zentrum Dresden-Rossendorf / TU Dresden
where he focussed on "Evaluation and Improvement of MR-based Attenuation Correction for PET/MR".

From 2015 to 2022, Georg worked as a postdoctoral fellow in the lab of Prof. Johan Nuyts at KU Leuven, Belgium, where he mostly worked on image reconstruction problems in PET/MR and PET/CT imaging.

In the lab of Fernando Boada at RSL, Georg's research focuses on improving the reconstruction of sodium MR images.

Academic Appointments


  • Visiting Instructor/Lecturer, Radiology

Professional Education


  • PhD, TU Dresden, Germany, Medical Imaging (2015)
  • MSc, TU Dresden, Germany, Physics (2011)

All Publications


  • Fast and memory-efficient reconstruction of sparse Poisson data in listmode with non-smooth priors with application to time-of-flight PET PHYSICS IN MEDICINE AND BIOLOGY Schramm, G., Holler, M. 2022; 67 (15)

    Abstract

    Objective.Complete time of flight (TOF) sinograms of state-of-the-art TOF PET scanners have a large memory footprint. Currently, they contain ∼4 · 109data bins which amount to ∼17 GB in 32 bit floating point precision. Moreover, their size will continue to increase with advances in the achievable detector TOF resolution and increases in the axial field of view. Using iterative algorithms to reconstruct such enormous TOF sinograms becomes increasingly challenging due to the memory requirements and the computation time needed to evaluate the forward model for every data bin. This is especially true for more advanced optimization algorithms such as the stochastic primal-dual hybrid gradient (SPDHG) algorithm which allows for the use of non-smooth priors for regularization using subsets with guaranteed convergence. SPDHG requires the storage of additional sinograms in memory, which severely limits its application to data sets from state-of-the-art TOF PET systems using conventional computing hardware.Approach.Motivated by the generally sparse nature of the TOF sinograms, we propose and analyze a new listmode (LM) extension of the SPDHG algorithm for image reconstruction of sparse data following a Poisson distribution. The new algorithm is evaluated based on realistic 2D and 3D simulationsn, and a real data set acquired on a state-of-the-art TOF PET/CT system. The performance of the newly proposed LM SPDHG algorithm is compared against the conventional sinogram SPDHG and the listmode EM-TV algorithm.Main results.We show that the speed of convergence of the proposed LM-SPDHG is equivalent the original SPDHG operating on binned data (TOF sinograms). However, we find that for a TOF PET system with 400 ps TOF resolution and 25 cm axial FOV, the proposed LM-SPDHG reduces the required memory from approximately 56 to 0.7 GB for a short dynamic frame with 107prompt coincidences and to 12.4 GB for a long static acquisition with 5·108prompt coincidences.Significance.In contrast to SPDHG, the reduced memory requirements of LM-SPDHG enables a pure GPU implementation on state-of-the-art GPUs-avoiding memory transfers between host and GPU-which will substantially accelerate reconstruction times. This in turn will allow the application of LM-SPDHG in routine clinical practice where short reconstruction times are crucial.

    View details for DOI 10.1088/1361-6560/ac71f1

    View details for Web of Science ID 000830794000001

    View details for PubMedID 35594853

  • Rigid motion tracking using moments of inertia in TOF-PET brain studies PHYSICS IN MEDICINE AND BIOLOGY Rezaei, A., Spangler-Bickell, M., Schramm, G., Van Laere, K., Nuyts, J., Defrise, M. 2021; 66 (18)

    Abstract

    A data-driven method is proposed for rigid motion estimation directly from time-of-flight (TOF)-positron emission tomography (PET) emission data. Rigid motion parameters (translations and rotations) are estimated from the first and second moments of the emission data masked in a spherical volume. The accuracy of the method is analyzed on 3D analytical simulations of the PET-SORTEO brain phantom, and subsequently tested on18F-FDG as well as11C-PIB brain datasets acquired on a TOF-PET/CT scanner. The estimated inertia-based motion is later compared to rigid motion parameters obtained by directly registering the short frame backprojections. We find that the method provides sub mm/degree accuracies for the estimated rigid motion parameters for counts corresponding to typical 0.5 s, 1 s, and 2 s18F-FDG brain scans, with the current TOF resolutions clinically available. The method provides robust motion estimation for different types of patient motion, most notably for a continuous patient motion case where conventional frame-based approaches which rely on little to no intra-frame motion of short time intervals could fail. The method relies on the detection of stable eigenvectors for accurate motion estimation, and a monitoring of this condition can reveal time-frames where the motion estimation is less accurate, such as in dynamic PET studies.

    View details for DOI 10.1088/1361-6560/ac2268

    View details for Web of Science ID 000695278700001

    View details for PubMedID 34464941

  • Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES Schaart, D. R., Schramm, G., Nuyts, J., Surti, S. 2021; 5 (5): 598-618

    Abstract

    The first time-of-flight positron emission tomography (TOF-PET) scanners were developed as early as in the 1980s. However, the poor light output and low detection efficiency of TOF-capable detectors available at the time limited any gain in image quality achieved with these TOF-PET scanners over the traditional non-TOF PET scanners. The discovery of LSO and other Lu-based scintillators revived interest in TOF-PET and led to the development of a second generation of scanners with high sensitivity and spatial resolution in the mid-2000s. The introduction of the silicon photomultiplier (SiPM) has recently yielded a third generation of TOF-PET systems with unprecedented imaging performance. Parallel to these instrumentation developments, much progress has been made in the development of image reconstruction algorithms that better utilize the additional information provided by TOF. Overall, the benefits range from a reduction in image variance (SNR increase), through allowing joint estimation of activity and attenuation, to better reconstructing data from limited angle systems. In this work, we review these developments, focusing on three broad areas: 1) timing theory and factors affecting the time resolution of a TOF-PET system; 2) utilization of TOF information for improved image reconstruction; and 3) quantification of the benefits of TOF compared to non-TOF PET. Finally, we offer a brief outlook on the TOF-PET developments anticipated in the short and longer term. Throughout this work, we aim to maintain a clinically driven perspective, treating TOF as one of multiple (and sometimes competitive) factors that can aid in the optimization of PET imaging performance.

    View details for DOI 10.1109/TRPMS.2021.3084539

    View details for Web of Science ID 000692207700004

    View details for PubMedID 34553105

    View details for PubMedCentralID PMC8454900

  • 2-D Feasibility Study of Joint Reconstruction of Attenuation and Activity in Limited Angle TOF-PET IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES Vergara, M., Rezaei, A., Schramm, G., Rodriguez-Alvarez, M., Baviera, J., Nuyts, J. 2021; 5 (5): 712-722

    Abstract

    Several research groups are studying organ-dedicated limited angle positron emission tomography (PET) systems to optimize performance-cost ratio, sensitivity, access to the patient and/or flexibility. Often open systems are considered, typically consisting of two detector panels of various sizes. Such systems provide incomplete sampling due to limited angular coverage and/or truncation, which leads to artefacts in the reconstructed activity images. In addition, these organ-dedicated PET systems are usually stand-alone systems, and as a result, no attenuation information can be obtained from anatomical images acquired in the same imaging session. It has been shown that the use of time-of-flight information reduces incomplete data artefacts and enables the joint estimation of the activity and the attenuation factors. In this work, we explore with simple 2D simulations the performance and stability of a joint reconstruction algorithm, for imaging with a limited angle PET system. The reconstruction is based on the so-called MLACF (Maximum Likelihood Attenuation Correction Factors) algorithm and uses linear attenuation coefficients in a known-tissue-class region to obtain absolute quantification. Different panel sizes and different time-of-flight (TOF) resolutions are considered. The noise propagation is compared to that of MLEM reconstruction with exact attenuation correction (AC) for the same PET system. The results show that with good TOF resolution, images of good visual quality can be obtained. If also a good scatter correction can be implemented, quantitative PET imaging will be possible. Further research, in particular on scatter correction, is required.

    View details for DOI 10.1109/TRPMS.2021.3079462

    View details for Web of Science ID 000692207700016

    View details for PubMedID 34541435

    View details for PubMedCentralID PMC8445242

  • Approximating anatomically-guided PET reconstruction in image space using a convolutional neural network NEUROIMAGE Schramm, G., Rigie, D., Vahle, T., Rezaei, A., Van Laere, K., Shepherd, T., Nuyts, J., Boada, F. 2021; 224: 117399

    Abstract

    In the last two decades, it has been shown that anatomically-guided PET reconstruction can lead to improved bias-noise characteristics in brain PET imaging. However, despite promising results in simulations and first studies, anatomically-guided PET reconstructions are not yet available for use in routine clinical because of several reasons. In light of this, we investigate whether the improvements of anatomically-guided PET reconstruction methods can be achieved entirely in the image domain with a convolutional neural network (CNN). An entirely image-based CNN post-reconstruction approach has the advantage that no access to PET raw data is needed and, moreover, that the prediction times of trained CNNs are extremely fast on state of the art GPUs which will substantially facilitate the evaluation, fine-tuning and application of anatomically-guided PET reconstruction in real-world clinical settings. In this work, we demonstrate that anatomically-guided PET reconstruction using the asymmetric Bowsher prior can be well-approximated by a purely shift-invariant convolutional neural network in image space allowing the generation of anatomically-guided PET images in almost real-time. We show that by applying dedicated data augmentation techniques in the training phase, in which 16 [18F]FDG and 10 [18F]PE2I data sets were used, lead to a CNN that is robust against the used PET tracer, the noise level of the input PET images and the input MRI contrast. A detailed analysis of our CNN in 36 [18F]FDG, 18 [18F]PE2I, and 7 [18F]FET test data sets demonstrates that the image quality of our trained CNN is very close to the one of the target reconstructions in terms of regional mean recovery and regional structural similarity.

    View details for DOI 10.1016/j.neuroimage.2020.117399

    View details for Web of Science ID 000600796800022

    View details for PubMedID 32971267

    View details for PubMedCentralID PMC7812485

  • Use of Multimodal Imaging and Clinical Biomarkers in Presymptomatic Carriers of C9orf72 Repeat Expansion JAMA NEUROLOGY De Vocht, J., Blommaert, J., Devrome, M., Radwan, A., Van Weehaeghe, D., De Schaepdryver, M., Ceccarini, J., Rezaei, A., Schramm, G., van Aalst, J., Chio, A., Pagani, M., Stam, D., Van Esch, H., Lamaire, N., Verhaegen, M., Mertens, N., Poesen, K., van den Berg, L. H., van Es, M. A., Vandenberghe, R., Vandenbulcke, M., Van den Stock, J., Koole, M., Dupont, P., Van Laere, K., Van Damme, P. 2020; 77 (8): 1008-1017

    Abstract

    During a time with the potential for novel treatment strategies, early detection of disease manifestations at an individual level in presymptomatic carriers of a hexanucleotide repeat expansion in the C9orf72 gene (preSxC9) is becoming increasingly relevant.To evaluate changes in glucose metabolism before symptom onset of amyotrophic lateral sclerosis or frontotemporal dementia in preSxC9 using simultaneous fluorine 18-labeled fluorodeoxyglucose ([18F]FDG positron emission tomographic (PET) and magnetic resonance imaging as well as the mutation's association with clinical and fluid biomarkers.A prospective, case-control study enrolled 46 participants from November 30, 2015, until December 11, 2018. The study was conducted at the neuromuscular reference center of the University Hospitals Leuven, Leuven, Belgium.Neuroimaging data were spatially normalized and analyzed at the voxel level at a height threshold of P < .001, cluster-level familywise error-corrected threshold of P < .05, and statistical significance was set at P < .05 for the volume-of-interest level analysis, using Benjamini-Hochberg correction for multiple correction. W-score maps were computed using the individuals serving as controls as a reference to quantify the degree of [18F]FDG PET abnormality. The threshold for abnormality on the W-score maps was designated as an absolute W-score greater than or equal to 1.96. Neurofilament levels and performance on cognitive and neurologic examinations were determined. All hypothesis tests were 1-sided.Of the 42 included participants, there were 17 with the preSxC9 mutation (12 women [71%]; mean [SD] age, 51 [9] years) and 25 healthy controls (12 women [48%]; mean [SD] age, 47 [10] years). Compared with control participants, significant clusters of relative hypometabolism were found in frontotemporal regions, basal ganglia, and thalami of preSxC9 participants and relative hypermetabolism in the peri-Rolandic region, superior frontal gyrus, and precuneus cortex. W-score frequency maps revealed reduced glucose metabolism with local maxima in the insular cortices, central opercular cortex, and thalami in up to 82% of preSxC9 participants and increased glucose metabolism in the precentral gyrus and precuneus cortex in up to 71% of preSxC9 participants. Other findings in the preSxC9 group were upper motor neuron involvement in 10 participants (59%), cognitive abnormalities in 5 participants (29%), and elevated neurofilament levels in 3 of 16 individuals (19%) who underwent lumbar puncture.The results suggest that [18F]FDG PET can identify glucose metabolic changes in preSxC9 at an individual level, preceding significantly elevated neurofilament levels and onset of symptoms.

    View details for DOI 10.1001/jamaneurol.2020.1087

    View details for Web of Science ID 000562851800014

    View details for PubMedID 32421156

    View details for PubMedCentralID PMC7417970

  • Long-term Ashtanga yoga practice decreases medial temporal and brainstem glucose metabolism in relation to years of experience EJNMMI RESEARCH van Aalst, J., Ceccarini, J., Schramm, G., Van Weehaeghe, D., Rezaei, A., Demyttenaere, K., Sunaert, S., Van Laere, K. 2020; 10 (1): 50

    Abstract

    Yoga is increasingly popular worldwide with several physical and mental benefits, but the underlying neurobiology remains unclear. Whereas many studies have focused on pure meditational aspects, the triad of yoga includes meditation, postures, and breathing. We conducted a cross-sectional study comparing experienced yoga practitioners to yoga-naive healthy subjects using a multiparametric 2 × 2 design with simultaneous positron emission tomography/magnetic resonance (PET/MR) imaging.18F-FDG PET, morphometric and diffusion tensor imaging, resting state fMRI, and MR spectroscopy were acquired in 10 experienced (4.8 ± 2.3 years of regular yoga experience) yoga practitioners and 15 matched controls in rest and after a single practice (yoga practice and physical exercise, respectively).In rest, decreased regional glucose metabolism in the medial temporal cortex, striatum, and brainstem was observed in yoga practitioners compared to controls (p < 0.0001), with a significant inverse correlation of resting parahippocampal and brainstem metabolism with years of regular yoga practice (ρ < - 0.63, p < 0.05). A single yoga practice resulted in significant hypermetabolism in the cerebellum (p < 0.0001). None of the MR measures differed, both at rest and after intervention.Experienced yoga practitioners show regional long-term decreases in glucose metabolism related to years of practice. To elucidate a potential causality, a prospective longitudinal study in yoga-naive individuals is warranted.

    View details for DOI 10.1186/s13550-020-00636-y

    View details for Web of Science ID 000536491800001

    View details for PubMedID 32410000

    View details for PubMedCentralID PMC7225240

  • Whole liver segmentation based on deep learning and manual adjustment for clinical use in SIRT EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING Tang, X., Jafargholi Rangraz, E., Coudyzer, W., Bertels, J., Robben, D., Schramm, G., Deckers, W., Maleux, G., Baete, K., Verslype, C., Gooding, M. J., Deroose, C. M., Nuyts, J. 2020; 47 (12): 2742-2752

    Abstract

    In selective internal radiation therapy (SIRT), an accurate total liver segmentation is required for activity prescription and absorbed dose calculation. Our goal was to investigate the feasibility of using automatic liver segmentation based on a convolutional neural network (CNN) for CT imaging in SIRT, and the ability of CNN to reduce inter-observer variability of the segmentation.A multi-scale CNN was modified for liver segmentation for SIRT patients. The CNN model was trained with 139 datasets from three liver segmentation challenges and 12 SIRT patient datasets from our hospital. Validation was performed on 13 SIRT datasets and 12 challenge datasets. The model was tested on 40 SIRT datasets. One expert manually delineated the livers and adjusted the liver segmentations from CNN for 40 test SIRT datasets. Another expert performed the same tasks for 20 datasets randomly selected from the 40 SIRT datasets. The CNN segmentations were compared with the manual and adjusted segmentations from the experts. The difference between the manual segmentations was compared with the difference between the adjusted segmentations to investigate the inter-observer variability. Segmentation difference was evaluated through dice similarity coefficient (DSC), volume ratio (RV), mean surface distance (MSD), and Hausdorff distance (HD).The CNN segmentation achieved a median DSC of 0.94 with the manual segmentation and of 0.98 with the manually corrected CNN segmentation, respectively. The DSC between the adjusted segmentations is 0.98, which is 0.04 higher than the DSC between the manual segmentations.The CNN model achieved good liver segmentations on CT images of good image quality, with relatively normal liver shapes and low tumor burden. 87.5% of the 40 CNN segmentations only needed slight adjustments for clinical use. However, the trained model failed on SIRT data with low dose or contrast, lesions with large density difference from their surroundings, and abnormal liver position and shape. The abovementioned scenarios were not adequately represented in the training data. Despite this limitation, the current CNN is already a useful clinical tool which improves inter-observer agreement and therefore contributes to the standardization of the dosimetry. A further improvement is expected when the CNN will be trained with more data from SIRT patients.

    View details for DOI 10.1007/s00259-020-04800-3

    View details for Web of Science ID 000527462500001

    View details for PubMedID 32314026

  • Combined brain and spinal FDG PET allows differentiation between ALS and ALS mimics EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING Van Weehaeghe, D., Devrome, M., Schramm, G., De Vocht, J., Deckers, W., Baete, K., Van Damme, P., Koole, M., Van Laere, K. 2020; 47 (11): 2681-2690

    Abstract

    Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder with on average a 1-year delay between symptom onset and diagnosis. Studies have demonstrated the value of [18F]-FDG PET as a sensitive diagnostic biomarker, but the discriminatory potential to differentiate ALS from patients with symptoms mimicking ALS has not been investigated. We investigated the combination of brain and spine [18F]-FDG PET-CT for differential diagnosis between ALS and ALS mimics in a real-life clinical diagnostic setting.Patients with a suspected diagnosis of ALS (n = 98; 64.8 ± 11 years; 61 M) underwent brain and spine [18F]-FDG PET-CT scans. In 62 patients, ALS diagnosis was confirmed (67.8 ± 10 years; 35 M) after longitudinal follow-up (average 18.1 ± 8.4 months). In 23 patients, another disease was diagnosed (ALS mimics, 60.9 ± 12.9 years; 17 M) and 13 had a variant motor neuron disease, primary lateral sclerosis (PLS; n = 4; 53.6 ± 2.5 years; 2 M) and progressive muscular atrophy (PMA; n = 9; 58.4 ± 7.3 years; 7 M). Spine metabolism was determined after manual and automated segmentation. VOI- and voxel-based comparisons were performed. Moreover, a support vector machine (SVM) approach was applied to investigate the discriminative power of regional brain metabolism, spine metabolism and the combination of both.Brain metabolism was very similar between ALS mimics and ALS, whereas cervical and thoracic spine metabolism was significantly different (in standardised uptake values; cervical: ALS 2.1 ± 0.5, ALS mimics 1.9 ± 0.4; thoracic: ALS 1.8 ± 0.3, ALS mimics 1.5 ± 0.3). As both brain and spine metabolisms were very similar between ALS mimics and PLS/PMA, groups were pooled for accuracy analyses. Mean discrimination accuracy was 65.4%, 80.0% and 81.5%, using only brain metabolism, using spine metabolism and using both, respectively.The combination of brain and spine FDG PET-CT with SVM classification is useful as discriminative biomarker between ALS and ALS mimics in a real-life clinical setting.

    View details for DOI 10.1007/s00259-020-04786-y

    View details for Web of Science ID 000527462500002

    View details for PubMedID 32314027

  • Limited Angle Tomography reconstruction for non-standard MBI system by means of parallel-hole and pinhole optics Poma, G. E., Garibaldi, F., Giuliani, F., Insero, T., Lucentini, M., Marcucci, A., Musico, P., Nuyts, J., Santavenere, F., Schramm, G., Sutera, C., Cisbani, E. IOP PUBLISHING LTD. 2020
  • Estimation of Crystal Timing Properties and Efficiencies for the Improvement of (Joint) Maximum-Likelihood Reconstructions in TOF-PET IEEE TRANSACTIONS ON MEDICAL IMAGING Rezaei, A., Schramm, G., Van Laere, K., Nuyts, J. 2020; 39 (4): 952-963

    Abstract

    With increasing improvements in the time of flight (TOF) resolution of positron emission tomography (PET) scanners, an accurate model of the TOF measurements is becoming increasingly important. This work considers two parameters of the TOF kernel; the relative positioning of the timing data-bins and the timing resolution along each line of response (LOR). Similar to an existing data-driven method, we assume that any shifts of data-bins along lines of response can be modelled as differences between crystal timing offsets. Inspired by this, timing resolutions of all LORs are modelled as the hypotenuse of timing resolutions of the crystal-pairs in coincidence. Furthermore, in order to mitigate the influence of potential inaccuracies of detector-pair sensitivities on crystal timing resolutions, relative LOR sensitivities are modelled as the product of efficiency factors for the two crystals in coincidence. We validate estimating maps of crystal timing offsets, timing resolutions and efficiencies from the emission data using noisy simulations of a brain phantom. Results are shown for phantom and patient data scanned on clinically available TOF-PET scanners. We find that the estimation of crystal timing resolutions is more sensitive to the data statistics than the estimation of crystal timing offsets. As a result, estimation of crystal timing properties could either be limited to high count emission data, or be obtained utilizing additional regularizations on the estimates. Using a more accurate model of the TOF acquisition, improvements are observed in standard activity reconstructions as well as joint reconstructions of activity and attenuation.

    View details for DOI 10.1109/TMI.2019.2938028

    View details for Web of Science ID 000525265800013

    View details for PubMedID 31478844

    View details for PubMedCentralID PMC7212322

  • Benefits of Using a Spatially-Variant Penalty Strength With Anatomical Priors in PET Reconstruction IEEE TRANSACTIONS ON MEDICAL IMAGING Tsai, Y., Schramm, G., Ahn, S., Bousse, A., Arridge, S., Nuyts, J., Hutton, B. F., Stearns, C. W., Thielemans, K. 2020; 39 (1): 11-22

    Abstract

    In this study, we explore the use of a spatially-variant penalty strength in penalized image reconstruction using anatomical priors to reduce the dependence of lesion contrast on surrounding activity and lesion location. This work builds on a previous method to make the local perturbation response (LPR) approximately spatially invariant. While the dependence of lesion contrast on the local properties introduced by the anatomical penalty is intentional, the method aims to reduce the influence from surroundings lying along the lines of response (LORs) but not in the penalty neighborhood structure. The method is evaluated using simulated data, assuming that the anatomical information is absent or well-aligned with the corresponding activity images. Since the parallel level sets (PLS) penalty is convex and has shown promising results in the literature, it is chosen as the representative anatomical penalty and incorporated into the previously proposed preconditioned algorithm (L-BFGS-B-PC) for achieving good image quality and fast convergence rate. A 2D disc phantom with a feature at the center and a 3D XCAT thorax phantom with lesions inserted in different slices are used to study how surrounding activity and lesion location affect the visual appearance and quantitative consistency. A bias and noise analysis is also performed with the 2D disc phantom. The consistency of the algorithm convergence rate with respect to different data noise and background levels is also investigated using the XCAT phantom. Finally, an example of reconstruction for a patient dataset with inserted pseudo lesions is used as a demonstration in a clinical context. We show that applying the spatially-variant penalization with PLS can reduce the dependence of the lesion contrast on the surrounding activity and lesion location. It does not affect the bias and noise trade-off curves for matched local resolution. Moreover, when using the proposed penalization, significant improvement in algorithm convergence rate and convergence consistency is observed.

    View details for DOI 10.1109/TMI.2019.2913889

    View details for Web of Science ID 000506577100002

    View details for PubMedID 31144629

  • Quantitative PET in the 2020s: A Roadmap. Physics in medicine and biology Meikle, S. R., Sossi, V. n., Roncali, E. n., Cherry, S. R., Banati, R. n., Mankoff, D. A., Jones, T. n., James, M. L., Sutcliffe, J. n., Ouyang, J. n., Petibon, Y. n., Ma, C. n., El Fakhri, G. n., Surti, S. n., Karp, J. S., Badawi, R. D., Yamaya, T. n., Akamatsu, G. n., Schramm, G. n., Rezaei, A. n., Nuyts, J. n., Fulton, R. R., Kyme, A. Z., Lois, C. n., Sari, H. n., Price, J. n., Boellaard, R. n., Jeraj, R. n., Bailey, D. L., Eslick, E. M., Willowson, K. P., Dutta, J. n. 2020

    Abstract

    Positron emission tomography (PET) plays an increasingly important role in research and clinical applications, catalysed by remarkable technical advances and a growing appreciation of the need for reliable, sensitive biomarkers of human function in health and disease. Over the last 30 years a large amount of the physics and engineering effort in PET has been motivated by the dominant clinical application during that period, oncology. This has led to important developments such as PET/CT, whole-body PET, 3D PET, accelerated statistical image reconstruction, and time-of-flight PET. Despite impressive improvements in image quality as a result of these advances, the emphasis on static, semi-quantitative "hot spot" imaging for oncologic applications has meant that the capability of PET for quantifying biologically relevant parameters based on tracer kinetics has not been fully exploited. More recent advances, such as PET/MR and total body PET, have opened up the ability to address a vast range of new research questions from which a future expansion of applications and radiotracers appears highly likely. Many of these new applications and tracers will, at least initially, require quantitative analyses that more fully exploit the exquisite sensitivity of PET and the tracer principle on which it is based. It is also expected that they will require more sophisticated quantitative analysis methods than those that are currently available. At the same time, artificial intelligence is revolutionizing data analysis and impacting the relationship between the statistical quality of the acquired data and the information we can extract from the data. In this roadmap, leaders of the key sub-disciplines of the field identify the challenges and opportunities to be addressed over the next 10 years that will enable PET to realise its full quantitative potential, initially in research laboratories and, ultimately, in clinical practice.

    View details for DOI 10.1088/1361-6560/abd4f7

    View details for PubMedID 33339012

  • Low septal to lateral wall F-18-FDG ratio is highly associated with mechanical dyssynchrony in non-ischemic CRT candidates EJNMMI RESEARCH Degtiarova, G., Claus, P., Duchenne, J., Cvijic, M., Schramm, G., Nuyts, J., Voigt, J., Gheysens, O. 2019; 9 (1): 105

    Abstract

    In order to better understand the concept of mechanical dyssynchrony, a promising hallmark of cardiac resynchronization therapy (CRT) response, we investigated its effect on regional myocardial metabolism and myocardial blood flow (MBF) in non-ischemic CRT candidates.Thirty consecutive non-ischemic CRT eligible patients underwent static 18F-FDG and resting dynamic 13N-NH3 PET/CT. 18F-FDG uptake and MBF for septal and lateral wall were analysed and septal-to-lateral wall ratios (SLR) were calculated. Based on the presence of mechanical dyssynchrony (septal flash and/or apical rocking) on echocardiography, patients were divided into 2 groups, with (n = 23) and without (n = 7) mechanical dyssynchrony. Patients with mechanical dyssynchrony had significantly lower 18F-FDG SUVmean in the septum compared with the lateral wall (5.58 ± 2.65 vs 11.19 ± 4.10, p < 0.0001), while patients without mechanical dyssynchrony had a more homogeneous 18F-FDG distribution (7.33 ± 2.88 vs 8.31 ± 2.50, respectively, p = 0.30). Similarly, MBF was significantly different between the septal and lateral wall in the dyssynchrony group (0.57 ± 0.11 ml/g/min vs 0.92 ± 0.23 ml/g/min, respectively, p < 0.0001), whereas no difference was observed in the non-dyssynchrony group (0.61 ± 0.23 ml/g/min vs 0.77 ± 0.21 ml/g/min, respectively, p = 0.16). 18F-FDG SLR, but not MBF SLR, was associated with the presence of mechanical dyssynchrony and showed a significant inverse correlation with volumetric reverse remodeling after CRT (r = - 0.62, p = 0.001).Non-ischemic heart failure patients with mechanical dyssynchrony demonstrate heterogeneous regional metabolism and MBF compared with patients without dyssynchrony. However, only 18F-FDG SLR appeared to be highly associated with the presence of mechanical dyssynchrony.Clinicaltrials, NCT02537782. Registered 2 September 2015.

    View details for DOI 10.1186/s13550-019-0575-9

    View details for Web of Science ID 000513870000001

    View details for PubMedID 31820130

    View details for PubMedCentralID PMC6901655

  • Regional Accuracy of ZTE-Based Attenuation Correction in Static [F-18]FDG and Dynamic [F-18]PE2I Brain PET/MR FRONTIERS IN PHYSICS Schramm, G., Koole, M., Willekens, S. A., Rezaei, A., Van Weehaeghe, D., Delso, G., Peeters, R., Mertens, N., Nuyts, J., Van Laere, K. 2019; 7
  • A Quantitative Evaluation of Joint Activity and Attenuation Reconstruction in TOF PET/MR Brain Imaging JOURNAL OF NUCLEAR MEDICINE Rezaei, A., Schramm, G., Willekens, S. A., Delso, G., Van Laere, K., Nuyts, J. 2019; 60 (11): 1649-1655

    Abstract

    Time-of-flight (TOF) PET data provide an effective means for attenuation correction (AC) when no (or incomplete or inaccurate) attenuation information is available. Since MR scanners provide little information on photon attenuation of different tissue types, AC in hybrid PET/MR scanners has always been challenging. In this contribution, we aim at validating the activity reconstructions of the maximum-likelihood ordered-subsets activity and attenuation (OSAA) reconstruction algorithm on a patient brain data set. We present a quantitative comparison of joint reconstructions with the current clinical gold standard-ordered-subsets expectation maximization-using CT-based AC in PET/CT, as well as the current state of the art in PET/MR, that is, zero time echo (ZTE)-based AC. Methods: The TOF PET emission data were initially used in a preprocessing stage to estimate crystal maps of efficiencies, timing offsets, and timing resolutions. Applying these additional corrections during reconstructions, OSAA, ZTE-based, and the vendor-provided atlas-based AC techniques were analyzed and compared with CT-based AC. In our initial study, we used the CT-based estimate of the expected scatter and later used the ZTE-based and OSAA attenuation estimates to compute the expected scatter contribution of the data during reconstructions. In all reconstructions, a maximum-likelihood scaling of the single-scatter simulation estimate to the emission data was used for scatter correction. The reconstruction results were analyzed in the 86 segmented regions of interest of the Hammers atlas. Results: Our quantitative analysis showed that, in practice, a tracer activity difference of +0.5% (±2.1%) and +0.1% (±2.3%) could be expected for the state-of-the-art ZTE-based and OSAA AC methods, respectively, in PET/MR compared with the clinical gold standard in PET/CT. Conclusion: Joint activity and attenuation estimation methods can provide an effective solution to the challenging AC problem for brain studies in hybrid TOF PET/MR scanners. With an accurate TOF-based (timing offsets and timing resolutions) calibration, and similar to the results of the state-of-the-art method in PET/MR, regional errors of joint TOF PET reconstructions are within a few percentage points.

    View details for DOI 10.2967/jnumed.118.220871

    View details for Web of Science ID 000493975400030

    View details for PubMedID 30979823

    View details for PubMedCentralID PMC6836858

  • Impact of left bundle branch block on myocardial perfusion and metabolism: A positron emission tomography study JOURNAL OF NUCLEAR CARDIOLOGY Degtiarova, G., Claus, P., Duchenne, J., Schramm, G., Nuyts, J., Verberne, H. J., Voigt, J., Gheysens, O. 2021; 28 (4): 1730-1739

    Abstract

    Better understanding of pathophysiological changes, induced by left bundle branch block (LBBB), may improve patient selection for cardiac resynchronization therapy (CRT). Therefore, we assessed the effect of LBBB on regional glucose metabolism, 13N-NH3-derived absolute and semiquantitative myocardial blood flow (MBF), and their relation in non-ischemic CRT candidates.Twenty-five consecutive non-ischemic patients with LBBB underwent 18F-FDG and resting dynamic 13N-NH3 PET/CT prior to CRT implantation. Regional 18F-FDG uptake, absolute MBF, and late 13N-NH3 uptake were analyzed and corresponding septal-to-lateral wall ratios (SLR) were calculated. Segmental analysis was performed to evaluate "reverse mismatch," "mismatch," and "match" patterns, based on late 13N-NH3/18F-FDG uptake ratios.A significantly lower 18F-FDG uptake was observed in the septum compared to the lateral wall (SLR 0.53 ± 0.17). A similar pattern was observed for MBF (SLR 0.68 ± 0.18), whereas late 13N-NH3 uptake showed a homogeneous distribution (SLR 0.96 ± 0.13). 13N-NH3/18F-FDG "mismatch" and "reverse mismatch" segments were predominantly present in the lateral (52%) and septal wall (61%), respectively.Non-ischemic CRT candidates with LBBB demonstrate lower glucose uptake and absolute MBF in the septum compared to the lateral wall. However, late static 13N-NH3 uptake showed a homogenous distribution, reflecting a composite measure of altered regional MBF and metabolism, induced by LBBB.

    View details for DOI 10.1007/s12350-019-01900-y

    View details for Web of Science ID 000488918900001

    View details for PubMedID 31578659

  • Preliminary Results of Whole Liver Segmentation with Deep Learning for SIRT Tang, X., Rangraz, E., Coudyzer, W., Bertels, J., Robben, D., Schramm, G., Deckers, W., Deroose, C. M., Baete, K., Gooding, M. J., Nuyts, J. SPRINGER. 2019: S763
  • Estimation of the spatial resolution of [F-18]-FDG brain PET(MR) scans using phantom measurements and human scan data Marques da Silva, A., Schramm, G., van Aalst, J., Mertens, N., Van Laere, K., Koole, M. SPRINGER. 2019: S789
  • Low septal to lateral wall F-18-FDG ratio is a marker of mechanical dyssynchrony in non-ischemic CRT candidates Degtiarova, G., Claus, P., Duchenne, J., Cvijic, M., Verberne, H. J., Schramm, G., Nuyts, J., Voigt, J., Gheysens, O. SPRINGER. 2019: S101
  • Systematic inaccuracies in the timing offset calibration may lead to large reconstructed transaxial asymmetries in the GE SIGNA PET/MR MP24 Schramm, G., Rezaei, A., van Aalst, J., Van Weehaeghe, D., Koole, M., Nuyts, J., Van Laere, K. SPRINGER. 2019: S60-S61
  • Impact of MR -guided P1-44T Reconstruction on Seizure Foci Localization th FDG PET Shepherd, T., Schramm, G., Vahle, T., Rigie, D., Friedman, K., Zan, E., Ghesani, M., Nuyts, J., Boada, F. SOC NUCLEAR MEDICINE INC. 2019
  • Interobserver variability of image-derived arterial blood SUV in whole-body FDG PET EJNMMI RESEARCH Hofheinz, F., Maus, J., Zschaeck, S., Rogasch, J., Schramm, G., Oehme, L., Apostolova, I., Kotzerke, J., van den Hoff, J. 2019; 9: 23

    Abstract

    Today, the standardized uptake value (SUV) is essentially the only means for quantitative evaluation of static [18F-]fluorodeoxyglucose (FDG) positron emission tomography (PET) investigations. However, the SUV approach has several well-known shortcomings which adversely affect the reliability of the SUV as a surrogate of the metabolic rate of glucose consumption. The standard uptake ratio (SUR), i.e., the uptake time-corrected ratio of tumor SUV to image-derived arterial blood SUV, has been shown in the first clinical studies to overcome most of these shortcomings, to decrease test-retest variability, and to increase the prognostic value in comparison to SUV. However, it is unclear, to what extent the SUR approach is vulnerable to observer variability of the additionally required blood SUV (BSUV) determination. The goal of the present work was the investigation of the interobserver variability of image-derived BSUV.FDG PET/CT scans from 83 patients (72 male, 11 female) with non-small cell lung cancer (N = 46) or head and neck cancer (N = 37) were included. BSUV was determined by 8 individuals, each applying a dedicated delineation tool for the BSUV determination in the aorta. Two of the observers applied two further tools. Altogether, five different delineation tools were used. With each used tool, delineation was performed for the whole patient group, resulting in 12 distinct observations per patient. Intersubject variability of BSUV determination was assessed using the fractional deviations for the individual patients from the patient group average and was quantified as standard deviation (SD is), 95% confidence interval, and range. Interobserver variability of BSUV determination was assessed using the fractional deviations of the individual observers from the observer-average for the considered patient and quantified as standard deviations (SD p, SD d) or root mean square (RMS), 95% confidence interval, and range in each patient, each observer, and the pooled data respectively.Interobserver variability in the pooled data amounts to RMS = 2.8% and is much smaller than the intersubject variability of BSUV (SD is= 16%). Averaged over the whole patient group, deviations of individual observers from the observer average are very small and fall in the range [ - 0.96, 1.05]%. However, interobserver variability partly differs distinctly for different patients, covering a range of [0.7, 7.4]% in the investigated patient group.The present investigation demonstrates that the image-based manual determination of BSUV in the aorta is sufficiently reproducible across different observers and delineation tools which is a prerequisite for accurate SUR determination. This finding is in line with the already demonstrated superior prognostic value of SUR in comparison to SUV in the first clinical studies.

    View details for DOI 10.1186/s13550-019-0486-9

    View details for Web of Science ID 000460560600001

    View details for PubMedID 30830508

    View details for PubMedCentralID PMC6399366

  • Maximum Likelihood Estimation of the Geometric Sensitivities in PET Rezaei, A., Deller, T., Wangerin, K., Schramm, G., Jansen, F., Van Laere, K., Nuyts, J., IEEE IEEE. 2019
  • 4D CBCT reconstruction with TV regularization on a dynamic software phantom Heylen, R., Schramm, G., Suetens, P., Nuyts, J., IEEE IEEE. 2019
  • Metal artifact correction strategies in MRI-based attenuation correction in PET/MRI. BJR open Schramm, G., Ladefoged, C. N. 2019; 1 (1): 20190033

    Abstract

    In hybrid positron emission tomography (PET) and MRI systems, attenuation correction for PET image reconstruction is commonly based on processing of dedicated MR images. The image quality of the latter is strongly affected by metallic objects inside the body, such as e.g. dental implants, endoprostheses, or surgical clips which all lead to substantial artifacts that propagate into MRI-based attenuation images. In this work, we review publications about metal artifact correction strategies in MRI-based attenuation correction in PET/MRI. Moreover, we also give an overview about publications investigating the impact of MRI-based attenuation correction metal artifacts on the reconstructed PET image quality and quantification.

    View details for DOI 10.1259/bjro.20190033

    View details for PubMedID 33178954

  • Image Quality Evaluation of SiPM-Based and Standard PMT-based Time-Of-Flight Systems for Yttrium-90 PET/CT imaging Caribe, P., Schramm, G., D'Asseler, Y., Bertin, H., Koole, M., Vandenberghe, S. SPRINGER. 2018: S712-S713
  • Evaluation of Parallel Level Sets and Bowsher's Method as Segmentation- Free Anatomical Priors for Time-of-Flight PET Reconstruction IEEE TRANSACTIONS ON MEDICAL IMAGING Schramm, G., Holler, M., Rezaei, A., Vunckx, K., Knoll, F., Bredies, K., Boada, F., Nuyts, J. 2018; 37 (2): 590-603

    Abstract

    In this article, we evaluate Parallel Level Sets (PLS) and Bowsher's method as segmentation-free anatomical priors for regularized brain positron emission tomography (PET) reconstruction. We derive the proximity operators for two PLS priors and use the EM-TV algorithm in combination with the first order primal-dual algorithm by Chambolle and Pock to solve the non-smooth optimization problem for PET reconstruction with PLS regularization. In addition, we compare the performance of two PLS versions against the symmetric and asymmetric Bowsher priors with quadratic and relative difference penalty function. For this aim, we first evaluate reconstructions of 30 noise realizations of simulated PET data derived from a real hybrid positron emission tomography/magnetic resonance imaging (PET/MR) acquisition in terms of regional bias and noise. Second, we evaluate reconstructions of a real brain PET/MR data set acquired on a GE Signa time-of-flight PET/MR in a similar way. The reconstructions of simulated and real 3D PET/MR data show that all priors were superior to post-smoothed maximum likelihood expectation maximization with ordered subsets (OSEM) in terms of bias-noise characteristics in different regions of interest where the PET uptake follows anatomical boundaries. Our implementation of the asymmetric Bowsher prior showed slightly superior performance compared with the two versions of PLS and the symmetric Bowsher prior. At very high regularization weights, all investigated anatomical priors suffer from the transfer of non-shared gradients.

    View details for DOI 10.1109/TMI.2017.2767940

    View details for Web of Science ID 000424467000024

    View details for PubMedID 29408787

    View details for PubMedCentralID PMC5821901

  • Low-dose PET/MRI of patients with non-lesional epilepsy Cal-Gonzalez, J., Schramm, G., Vunckx, K., Rausch, I., Sundar, L., Nuyts, J., Iraub-Weidinger, I., Beyer, I. SPRINGER. 2017: S611-S612
  • Validation of ZTE head attenuation correction in the GE SIGNA PET/MR initial results Schramm, G., Rezaei, A., Willekens, S., Van Weehaeghe, D., Mertens, N., Koole, M., Nuyts, J., Van Laere, K. SOC NUCLEAR MEDICINE INC. 2017
  • FDG PET/MR in initial staging of sarcoma: Initial experience and comparison with conventional imaging CLINICAL IMAGING Platzek, I., Beuthien-Baumann, B., Schramm, G., Maus, J., Laniado, M., Kotzerke, J., van den Hoff, J., Schuler, M. 2017; 42: 126-132

    Abstract

    To assess the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with 18F-fluordeoxyglucose (FDG) for initial staging of sarcoma.Twenty-nine patients with sarcoma were included in this study. Weighted kappa (κ) was used to assess the agreement between PET/MR and conventional imaging (CT and MR). The accuracy of PET/MR and conventional imaging for distant metastases was compared using receiver operating characteristic (ROC) analysis.T and M stage were identical for PET/MR and conventional modalities in all patients (κ=1). N stage was identical for 28/29 patients (κ=0.65).FDG PET/MR shows excellent agreement with the currently preferred imaging methods (CT and MR) in initial staging of sarcoma.

    View details for DOI 10.1016/j.clinimag.2016.11.016

    View details for Web of Science ID 000394732700020

    View details for PubMedID 27951459

  • Data driven time alignment for TOF-PET Rezaei, A., Schramm, G., Van Laere, K., Nuyts, J., IEEE IEEE. 2017
  • Spatially-variant Strength for Anatomical Priors in PET Reconstruction Tsai, Y., Schramm, G., Nuyts, J., Ahn, S., Stearns, C. W., Bousse, A., Arridge, S., Thielemans, K., IEEE IEEE. 2017
  • Validation of atlas-based head attenuation correction in the GE SIGNA PET/MR - initial results Schramm, G., Rezaei, A., Willekens, S., Peeters, R., Koole, M., Nuyts, J., van Laere, K. SPRINGER. 2016: S508
  • Synthesis and Kinetic Characterisation of Water-Soluble Fluorogenic Acyl Donors for Transglutaminase 2 (vol 17, pg 1263, 2016) CHEMBIOCHEM Wodtke, R., Schramm, G., Pietzsch, J., Pietsch, M., Loeser, R. 2016; 17 (17): 1674

    View details for DOI 10.1002/cbic.201600423

    View details for Web of Science ID 000383695600016

    View details for PubMedID 27592853

  • Synthesis and Kinetic Characterisation of Water-Soluble Fluorogenic Acyl Donors for Transglutaminase 2 CHEMBIOCHEM Wodtke, R., Schramm, G., Pietzsch, J., Pietsch, M., Loeser, R. 2016; 17 (13): 1263-1281

    Abstract

    Small glutamate-containing peptides bearing coumarin derivatives as fluorescent leaving groups attached to the γ-carboxylic acid group of the Glu residue were synthesised and investigated with regard to their potential to act as substrates for transglutaminase 2 (TGase 2). Their synthesis was accomplished by an efficient solid-phase approach. The excellent water solubility of the compounds enabled their extensive kinetic characterisation in the context of TGase 2-catalysed hydrolysis and aminolysis. The influence of the coumarin skeleton's substitution pattern on the kinetic properties was studied. Derivatives containing 7-hydroxy-4-methylcoumarin (HMC) revealed properties superior to those of their 7-hydroxycoumarin counterparts; analogous amides are not accepted as substrates. Z-Glu(HMC)-Gly-OH, which exhibited the best substrate properties out of the investigated derivatives, was selected for representative kinetic characterisation of acyl acceptor substrates and irreversible inhibitors.

    View details for DOI 10.1002/cbic.201600048

    View details for Web of Science ID 000379826400014

    View details for PubMedID 27124709

  • NEMA PET performance measurements of the GE SIGNA integrated TOF PET/MR Schramm, G., Vunckx, K., D'Hoe, E., Vandenberghe, S., Verhaeghe, J., Van Laere, K., Nuyts, J., Koole, M. SOC NUCLEAR MEDICINE INC. 2016
  • Role of electric and magnetic dipole strength functions in the Cd-114(gamma,gamma ') and Cd-113(n,gamma.) reactions PHYSICAL REVIEW C Massarczyk, R., Schramm, G., Belgya, T., Schwengner, R., Beyer, R., Bemmerer, D., Elekes, Z., Grosse, E., Hannaske, R., Junghans, A. R., Kis, Z., Koegler, T., Lorenz, C., Schmidt, K., Szentmiklosi, L., Wagner, A., Weil, J. L. 2016; 93 (1)
  • PET Reconstruction with Non-smooth Gradient-based Priors Schramm, G., Holler, M., Koesters, T., Boada, F., Knoll, F., Bredies, K., Nuyts, J., IEEE IEEE. 2016
  • Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis Hannaske, R., Bemmerer, D., Beyer, R., Birgersson, E., Ferrari, A., Grosse, E., Junghans, A. R., Kempe, M., Koegler, T., Kosev, K., Marta, M., Massarczyk, R., Matic, A., Schilling, K. D., Schramm, G., Schwengner, R., Wagner, A., Yakorev, D., IOP IOP PUBLISHING LTD. 2016
  • Early and late effects of radiochemotherapy on cerebral blood flow in glioblastoma patients measured with non-invasive perfusion MRI RADIOTHERAPY AND ONCOLOGY Petr, J., Platzek, I., Seidlitz, A., Mutsaerts, H. M., Hofheinz, F., Schramm, G., Maus, J., Beuthien-Baumann, B., Krause, M., van den Hoff, J. 2016; 118 (1): 24-28

    Abstract

    To provide a systematic measure of changes of brain perfusion in healthy tissue following a fractionated radiotherapy of brain tumors.Perfusion was assessed before and after radiochemotherapy using arterial spin labeling in a group of 24 patients (mean age 54.3 ± 14.1 years) with glioblastoma multiforme. Mean relative perfusion change in gray matter in the hemisphere contralateral to the tumor was obtained for the whole hemisphere and also for six regions created by thresholding the individual dose maps at 10 Gy steps.A significant decrease of perfusion of -9.8 ± 20.9% (p=0.032) compared to the pre-treatment baseline was observed 3 months after the end of radiotherapy. The decrease was more pronounced for high-dose regions above 50 Gy (-16.8 ± 21.0%, p=0.0014) than for low-dose regions below 10 Gy (-2.3 ± 20.0%, p=0.54). No further significant decrease compared to the post-treatment baseline was observed 6 months (-0.4 ± 18.4%, p=0.94) and 9 months (2.0 ± 15.4%, p=0.74) after the end of radiotherapy.Perfusion decreased significantly during the course of radiochemotherapy. The decrease was higher in regions receiving a higher dose of radiation. This suggests that the perfusion decrease is at least partly caused by radiotherapy. Our results suggest that the detrimental effects of radiochemotherapy on perfusion occur early rather than later.

    View details for DOI 10.1016/j.radonc.2015.12.017

    View details for Web of Science ID 000371551100004

    View details for PubMedID 26747756

  • Correction of quantification errors in pelvic and spinal lesions caused by ignoring higher photon attenuation of bone in [F-18]NaF PET/MR MEDICAL PHYSICS Schramm, G., Maus, J., Hofheinz, F., Petr, J., Lougovski, A., Beuthien-Baumann, B., Oehme, L., Platzek, I., van den Hoff, J. 2015; 42 (11): 6468-6476

    Abstract

    MR-based attenuation correction (MRAC) in routine clinical whole-body positron emission tomography and magnetic resonance imaging (PET/MRI) is based on tissue type segmentation. Due to lack of MR signal in cortical bone and the varying signal of spongeous bone, standard whole-body segmentation-based MRAC ignores the higher attenuation of bone compared to the one of soft tissue (MRACnobone). The authors aim to quantify and reduce the bias introduced by MRACnobone in the standard uptake value (SUV) of spinal and pelvic lesions in 20 PET/MRI examinations with [18F]NaF.The authors reconstructed 20 PET/MR [18F]NaF patient data sets acquired with a Philips Ingenuity TF PET/MRI. The PET raw data were reconstructed with two different attenuation images. First, the authors used the vendor-provided MRAC algorithm that ignores the higher attenuation of bone to reconstruct PETnobone. Second, the authors used a threshold-based algorithm developed in their group to automatically segment bone structures in the [18F]NaF PET images. Subsequently, an attenuation coefficient of 0.11 cm(-1) was assigned to the segmented bone regions in the MRI-based attenuation image (MRACbone) which was used to reconstruct PETbone. The automatic bone segmentation algorithm was validated in six PET/CT [18F]NaF examinations. Relative SUVmean and SUVmax differences between PETbone and PETnobone of 8 pelvic and 41 spinal lesions, and of other regions such as lung, liver, and bladder, were calculated. By varying the assigned bone attenuation coefficient from 0.11 to 0.13 cm(-1), the authors investigated its influence on the reconstructed SUVs of the lesions.The comparison of [18F]NaF-based and CT-based bone segmentation in the six PET/CT patients showed a Dice similarity of 0.7 with a true positive rate of 0.72 and a false discovery rate of 0.33. The [18F]NaF-based bone segmentation worked well in the pelvis and spine. However, it showed artifacts in the skull and in the extremities. The analysis of the 20 [18F]NaF PET/MRI examinations revealed relative SUVmax differences between PETnobone and PETbone of (-8.8%±2.7%, p=0.01) and (-8.1%±1.9%, p=2.4×10(-8)) in pelvic and spinal lesions, respectively. A maximum SUVmax underestimation of -13.7% was found in lesion in the third cervical spine. The averaged SUVmean differences in volumes of interests in lung, liver, and bladder were below 3%. The average SUVmax differences in pelvic and spinal lesions increased from -9% to -18% and -8% to -17%, respectively, when increasing the assigned bone attenuation coefficient from 0.11 to 0.13 cm(-1).The developed automatic [18F]NaF PET-based bone segmentation allows to include higher bone attenuation in whole-body MRAC and thus improves quantification accuracy for pelvic and spinal lesions in [18F]NaF PET/MRI examinations. In nonbone structures (e.g., lung, liver, and bladder), MRACnobone yields clinically acceptable accuracy.

    View details for DOI 10.1118/1.4932367

    View details for Web of Science ID 000364402100032

    View details for PubMedID 26520736

  • The influence of ignoring higher bone attenuation on pelvic and spinal lesions in [18F]NaF PET/MRI examinations. Schramm, G., Oehme, L., Maus, J., Hofheinz, F., Petr, J., Lougovski, A., Beuthien-Baumann, B., van den Hoff, J. SPRINGER. 2015: S151
  • Evaluation of in vivo quantification accuracy of the Ingenuity-TF PET/MR MEDICAL PHYSICS Maus, J., Schramm, G., Hofheinz, F., Oehme, L., Lougovski, A., Petr, J., Platzek, I., Beuthien-Baumann, B., Steinbach, J., Kotzerke, J., van den Hoff, J. 2015; 42 (10): 5773-5781

    Abstract

    The quantitative accuracy of standardized uptake values (SUVs) and tracer kinetic uptake parameters in patient investigations strongly depends on accurate determination of regional activity concentrations in positron emission tomography (PET) data. This determination rests on the assumption that the given scanner calibration is valid in vivo. In a previous study, we introduced a method to test this assumption. This method allows to identify discrepancies in quantitative accuracy in vivo by comparison of activity concentrations of urine samples measured in a well-counter with activity concentrations extracted from PET images of the bladder. In the present study, we have applied this method to the Philips Ingenuity-TF PET/MR since at the present stage, absolute quantitative accuracy of combined PET/MR systems is still under investigation.Twenty one clinical whole-body F18-FDG scans were included in this study. The bladder region was imaged as the last bed position and urine samples were collected afterward. PET images were reconstructed including MR-based attenuation correction with and without truncation compensation and 3D regions-of-interest (ROIs) of the bladder were delineated by three observers. To exclude partial volume effects, ROIs were concentrically shrunk by 8-10 mm. Then, activity concentrations were determined in the PET images for the bladder and for the urine by measuring the samples in a calibrated well-counter. In addition, linearity measurements of SUV vs singles rate and measurements of the stability of the coincidence rate of "true" events of the PET/MR system were performed over a period of 4 months.The measured in vivo activity concentrations were significantly lower in PET/MR than in the well-counter with a ratio of the former to the latter of 0.756 ± 0.060 (mean ± std. dev.), a range of 0.604-0.858, and a P value of 3.9 ⋅ 10(-14). While the stability measurements of the coincidence rate of "true" events showed no relevant deviation over time, the linearity scans revealed a systematic error of 8%-11% (avg. 9%) for the range of singles rates present in the bladder scans. After correcting for this systematic bias caused by shortcomings of the manufacturers calibration procedure, the PET to well-counter ratio increased to 0.832 ± 0.064 (0.668 -0.941), P = 1.1 ⋅ 10(-10). After compensating for truncation of the upper extremities in the MR-based attenuation maps, the ratio further improved to 0.871 ± 0.069 (0.693-0.992), P = 3.9 ⋅ 10(-8).Our results show that the Philips PET/MR underestimates activity concentrations in the bladder by 17%, which is 7 percentage points (pp.) larger than in the previously investigated PET and PET/CT systems. We attribute this increased underestimation to remaining limitations of the MR-based attenuation correction. Our results suggest that only a 2 pp. larger underestimation of activity concentrations compared to PET/CT can be observed if compensation of attenuation truncation of the upper extremities is applied. Thus, quantification accuracy of the Philips Ingenuity-TF PET/MR can be considered acceptable for clinical purposes given the ±10% error margin in the EANM guidelines. The comparison of PET images from the bladder region with urine samples has proven a useful method. It might be interesting for evaluation and comparison of the in vivo quantitative accuracy of PET, PET/CT, and especially PET/MR systems from different manufacturers or in multicenter trials.

    View details for DOI 10.1118/1.4929936

    View details for Web of Science ID 000362570100020

    View details for PubMedID 26429251

  • Evaluation of the influence of truncation artifacts using in-vivo based quantification accuracy methods in combined PET/MRI Maus, J., Schramm, G., Hofheinz, F., Oehme, L., Lougovski, A., Petr, J., Platzek, I., Beuthien-Baumann, B., Steinbach, J., Kotzerke, J., van den Hoff, J. SPRINGER. 2015: S18-S19
  • On the relation between Kaiser-Bessel blob and tube of response based modelling of the system matrix in iterative PET image reconstruction PHYSICS IN MEDICINE AND BIOLOGY Lougovski, A., Hofheinz, F., Maus, J., Schramm, G., van den Hoff, J. 2015; 60 (10): 4209-4224

    Abstract

    We investigate the question of how the blob approach is related to tube of response based modelling of the system matrix. In our model, the tube of response (TOR) is approximated as a cylinder with constant density (TOR-CD) and the cubic voxels are replaced by spheres. Here we investigate a modification of the TOR model that makes it effectively equivalent to the blob model, which models the intersection of lines of response (LORs) with radially variant basis functions ('blobs') replacing the cubic voxels. Implications of the achieved equivalence regarding the necessity of final resampling in blob-based reconstructions are considered. We extended TOR-CD to a variable density tube model (TOR-VD) that yields a weighting function (defining all system matrix elements) which is essentially identical to that of the blob model. The variable density of TOR-VD was modelled by a Gaussian and a Kaiser-Bessel function, respectively. The free parameters of both model functions were determined by fitting the corresponding weighting function to the weighting function of the blob model. TOR-CD and the best-fitting TOR-VD were compared to the blob model with a final resampling step (BLOB-RS) and without resampling (BLOB-NRS) in phantom studies. For three different contrast ratios and two different voxel sizes, resolution noise curves were generated. TOR-VD and BLOB-NRS lead to nearly identical images for all investigated contrast ratios and voxel sizes. Both models showed strong Gibbs artefacts at 4 mm voxel size, while at 2 mm voxel size there were no Gibbs artefacts visible. The spatial resolution was similar to the resolution with TOR-CD in all cases. The resampling step removed most of the Gibbs artefacts and reduced the noise level but also degraded the spatial resolution substantially. We conclude that the blob model can be considered just as a special case of a TOR-based reconstruction. The latter approach provides a more natural description of the detection process and allows for modifications that are not readily representable within the blob framework.

    View details for DOI 10.1088/0031-9155/60/10/4209

    View details for Web of Science ID 000355203100023

    View details for PubMedID 25955699

  • Quantitative accuracy of attenuation correction in the Philips Ingenuity TF whole-body PET/MR system: a direct comparison with transmission-based attenuation correction MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Schramm, G., Langner, J., Hofheinz, F., Petr, J., Beuthien-Baumann, B., Platzek, I., Steinbach, J., Kotzerke, J., van den Hoff, J. 2015; 28 (1): 101
  • Improving the Quantification Accuracy of a PET/CT-Scanner with Pixelated Large Area Detector Nemer, U., Maus, J., Schramm, G., Meyer, P. T., Hennig, J., Mix, M., IEEE IEEE. 2015
  • Combined study of the gamma-ray strength function of Cd-114 with (n,gamma) and (gamma,gamma ') reactions Belgya, T., Massarzyk, R., Szentmiklosi, L., Schramm, G., Schwengner, R., Junghans, A. R., Wagner, A., Grosse, E., Schwengner, R., Zuber, K. E D P SCIENCES. 2015
  • Investigation of dipole strength up to the neutron separation energy at gamma ELBE Massarczyk, R., Schwengner, R., Bemmerer, D., Beyer, R., Hannaske, R., Junghans, A. R., Kempe, M., Koegler, T., Schramm, G., Wagner, A., Schwengner, R., Zuber, K. E D P SCIENCES. 2015
  • Quantitative assessment of the asphericity of pretherapeutic FDG uptake as an independent predictor of outcome in NSCLC BMC CANCER Apostolova, I., Rogasch, J., Buchert, R., Wertzel, H., Achenbach, H., Schreiber, J., Riedel, S., Furth, C., Lougovski, A., Schramm, G., Hofheinz, F., Amthauer, H., Steffen, I. G. 2014; 14: 896

    Abstract

    The aim of the present study was to evaluate the predictive value of a novel quantitative measure for the spatial heterogeneity of FDG uptake, the asphericity (ASP) in patients with non-small cell lung cancer (NSCLC).FDG-PET/CT had been performed in 60 patients (15 women, 45 men; median age, 65.5 years) with newly diagnosed NSCLC prior to therapy. The FDG-PET image of the primary tumor was segmented using the ROVER 3D segmentation tool based on thresholding at the volume-reproducing intensity threshold after subtraction of local background. ASP was defined as the relative deviation of the tumor's shape from a sphere. Univariate and multivariate Cox regression as well as Kaplan-Meier (KM) analysis and log-rank test with respect to overall (OAS) and progression-free survival (PFS) were performed for clinical variables, SUVmax/mean, metabolically active tumor volume (MTV), total lesion glycolysis (TLG), ASP and "solidity", another measure of shape irregularity.ASP, solidity and "primary surgical treatment" were significant independent predictors of PFS in multivariate Cox regression with binarized parameters (HR, 3.66; p<0.001, HR, 2.11; p=0.05 and HR, 2.09; p=0.05), ASP and "primary surgical treatment" of OAS (HR, 3.19; p=0.02 and HR, 3.78; p=0.01, respectively). None of the other semi-quantitative PET parameters showed significant predictive value with respect to OAS or PFS. Kaplan-Meier analysis revealed a probability of 2-year PFS of 52% in patients with low ASP compared to 12% in patients with high ASP (p<0.001). Furthermore, it showed a higher OAS rate in the case of low versus high ASP (1-year-OAS, 91% vs. 67%: p=0.02).The novel parameter asphericity of pretherapeutic FDG uptake seems to provide better prognostic value for PFS and OAS in NCSLC compared to SUV, metabolic tumor volume, total lesion glycolysis and solidity.

    View details for DOI 10.1186/1471-2407-14-896

    View details for Web of Science ID 000346102700001

    View details for PubMedID 25444154

    View details for PubMedCentralID PMC4265451

  • Modeling Magnetization Transfer Effects of Q2TIPS Bolus Saturation in Multi-TI Pulsed Arterial Spin Labeling MAGNETIC RESONANCE IN MEDICINE Petr, J., Schramm, G., Hofheinz, F., Langner, J., van den Hoff, J. 2014; 72 (4): 1007-1014

    Abstract

    To estimate the relaxation time changes during Q2TIPS bolus saturation caused by magnetization transfer effects and to propose and evaluate an extended model for perfusion quantification which takes this into account.Three multi inversion-time pulsed arterial spin labeling sequences with different bolus saturation duration were acquired for five healthy volunteers. Magnetization transfer exchange rates in tissue and blood were obtained from control image saturation recovery. Cerebral blood flow (CBF) obtained using the extended model and the standard model was compared.A decrease of obtained CBF of 6% (10%) was observed in grey matter when the duration of bolus saturation increased from 600 to 900 ms (1200 ms). This decrease was reduced to 1.6% (2.8%) when the extended quantification model was used. Compared with the extended model, the standard model underestimated CBF in grey matter by 9.7, 15.0, and 18.7% for saturation durations 600, 900, and 1200 ms, respectively. Results for simulated single inversion-time data showed 5-16% CBF underestimation depending on blood arrival time and bolus saturation duration.Magnetization transfer effects caused by bolus saturation pulses should not be ignored when performing quantification as they can cause appreciable underestimation of the CBF.

    View details for DOI 10.1002/mrm.25011

    View details for Web of Science ID 000342342300012

    View details for PubMedID 24194169

  • FDG PET/MR for the Assessment of Lymph Node Involvement in Lymphoma: Initial Results and Role of Diffusion-Weighted MR ACADEMIC RADIOLOGY Platzek, I., Beuthien-Baumann, B., Ordemann, R., Maus, J., Schramm, G., Kitzler, H. H., Laniado, M., Kotzerke, J., van den Hoff, J. 2014; 21 (10): 1314-1319

    Abstract

    The purpose of this study was to evaluate the sensitivity and specificity of positron emission tomography/magnetic resonance imaging (PET/MR) with 18F-fluorodeoxyglucose (FDG) for nodal involvement in malignant lymphoma.Twenty-seven patients with malignant lymphoma (16 men and 11 women; mean age, 45 years) were included in this retrospective study. The patients underwent FDG PET/MR after intravenous injection of FDG (176-357 MBq FDG, 282 MBq on average). Follow-up imaging and histology served as the standard of reference.One-hundred and twenty-seven (18.1%) of 702 lymph node stations were rated as having lymphoma involvement based on the standard of reference. One-hundred and twenty-four (17.7%) of 702 lymph node stations were rated as positive by FDG PET/MR. The sensitivity and specificity of FDG PET/MR for lymph node station involvement were 93.8% and 99.4%.FDG PET/MR is feasible for lymphoma staging and has a high sensitivity and specificity for nodal involvement in lymphoma. Comparison with PET/CT is necessary to determine whether FDG PET/MR can replace PET/CT for lymphoma staging.

    View details for DOI 10.1016/j.acra.2014.05.019

    View details for Web of Science ID 000341799400013

    View details for PubMedID 25086953

  • FDG PET/MR for lymph node staging in head and neck cancer EUROPEAN JOURNAL OF RADIOLOGY Platzek, I., Beuthien-Baumann, B., Schneider, M., Gudziol, V., Kitzler, H. H., Maus, J., Schramm, G., Popp, M., Laniado, M., Kotzerke, J., van den Hoff, J. 2014; 83 (7): 1163-1168

    Abstract

    To assess the diagnostic value of PET/MR (positron emission tomography/magnetic resonance imaging) with FDG (18F-fluorodeoxyglucose) for lymph node staging in head and neck cancer.This prospective study was approved by the local ethics committee; all patients signed informed consent. Thirty-eight patients with squamous cell carcinoma of the head and neck region underwent a PET scan on a conventional scanner and a subsequent PET/MR on a whole-body hybrid system after a single intravenous injection of FDG. The accuracy of PET, MR and PET/MR for lymph node metastases were compared using receiver operating characteristic (ROC) analysis. Histology served as the reference standard.Metastatic disease was confirmed in 16 (42.1%) of 38 patients and 38 (9.7%) of 391 dissected lymph node levels. There were no significant differences between PET/MR, MR and PET and MR (p>0.05) regarding accuracy for cervical metastatic disease. Based on lymph node levels, sensitivity and specificity for metastatic involvement were 65.8% and 97.2% for MR, 86.8% and 97.0% for PET and 89.5% and 95.2% for PET/MR.In head and neck cancer, FDG PET/MR does not significantly improve accuracy for cervical lymph node metastases in comparison to MR or PET.

    View details for DOI 10.1016/j.ejrad.2014.03.023

    View details for Web of Science ID 000338927000022

    View details for PubMedID 24746792

  • Evaluation and automatic correction of metal-implant-induced artifacts in MR-based attenuation correction in whole-body PET/MR imaging PHYSICS IN MEDICINE AND BIOLOGY Schramm, G., Maus, J., Hofheinz, F., Petr, J., Lougovski, A., Beuthien-Baumann, B., Platzek, I., van den Hoff, J. 2014; 59 (11): 2713-2726

    Abstract

    The aim of this paper is to describe a new automatic method for compensation of metal-implant-induced segmentation errors in MR-based attenuation maps (MRMaps) and to evaluate the quantitative influence of those artifacts on the reconstructed PET activity concentration. The developed method uses a PET-based delineation of the patient contour to compensate metal-implant-caused signal voids in the MR scan that is segmented for PET attenuation correction. PET emission data of 13 patients with metal implants examined in a Philips Ingenuity PET/MR were reconstructed with the vendor-provided method for attenuation correction (MRMap(orig), PET(orig)) and additionally with a method for attenuation correction (MRMap(cor), PET(cor)) developed by our group. MRMaps produced by both methods were visually inspected for segmentation errors. The segmentation errors in MRMap(orig) were classified into four classes (L1 and L2 artifacts inside the lung and B1 and B2 artifacts inside the remaining body depending on the assigned attenuation coefficients). The average relative SUV differences (ε(rel)(av)) between PET(orig) and PET(cor) of all regions showing wrong attenuation coefficients in MRMap(orig) were calculated. Additionally, relative SUV(mean) differences (ε(rel)) of tracer accumulations in hot focal structures inside or in the vicinity of these regions were evaluated. MRMap(orig) showed erroneous attenuation coefficients inside the regions affected by metal artifacts and inside the patients' lung in all 13 cases. In MRMap(cor), all regions with metal artifacts, except for the sternum, were filled with the soft-tissue attenuation coefficient and the lung was correctly segmented in all patients. MRMap(cor) only showed small residual segmentation errors in eight patients. ε(rel)(av) (mean ± standard deviation) were: (-56 ± 3)% for B1, (-43 ± 4)% for B2, (21 ± 18)% for L1, (120 ± 47)% for L2 regions. ε(rel) (mean ± standard deviation) of hot focal structures were: (-52 ± 12)% in B1, (-45 ± 13)% in B2, (19 ± 19)% in L1, (51 ± 31)% in L2 regions. Consequently, metal-implant-induced artifacts severely disturb MR-based attenuation correction and SUV quantification in PET/MR. The developed algorithm is able to compensate for these artifacts and improves SUV quantification accuracy distinctly.

    View details for DOI 10.1088/0031-9155/59/11/2713

    View details for Web of Science ID 000336459000011

    View details for PubMedID 24800752

  • Correction of scan time dependence of standard uptake values in oncological PET EJNMMI RESEARCH van den Hoff, J., Lougovski, A., Schramm, G., Maus, J., Oehme, L., Petr, J., Beuthien-Baumann, B., Kotzerke, J., Hofheinz, F. 2014; 4: 1-14

    Abstract

    Standard uptake values (SUV) as well as tumor-to-blood standard uptake ratios (SUR) measured with [ 18F-]fluorodeoxyglucose (FDG) PET are time dependent. This poses a serious problem for reliable quantification since variability of scan start time relative to the time of injection is a persistent issue in clinical oncological Positron emission tomography (PET). In this work, we present a method for scan time correction of, both, SUR and SUV.Assuming irreversible FDG kinetics, SUR is linearly correlated to Km (the metabolic rate of FDG), where the slope only depends on the shape of the arterial input function (AIF) and on scan time. Considering the approximately invariant shape of the AIF, this slope (the 'Patlak time') is an investigation independent function of scan time. This fact can be used to map SUR and SUV values from different investigations to a common time point for quantitative comparison. Additionally, it turns out that modelling the invariant AIF shape by an inverse power law is possible which further simplifies the correction procedure. The procedure was evaluated in 15 fully dynamic investigations of liver metastases from colorectal cancer and 10 dual time point (DTP) measurements. From each dynamic study, three 'static scans' at T=20,35,and 55 min post injection (p.i.) were created, where the last scan defined the reference time point to which the uptake values measured in the other two were corrected. The corrected uptake values were then compared to those actually measured at the reference time. For the DTP studies, the first scan (acquired at (78.1 ± 15.9) min p.i.) served as the reference, and the uptake values from the second scan (acquired (39.2 ± 9.9) min later) were corrected accordingly and compared to the reference.For the dynamic data, the observed difference between uncorrected values and values at reference time was (-52±4.5)% at T=20 min and (-31±3.7)% at T=35 min for SUR and (-30±6.6)% at T=20 min and (-16±4)% at T=35 min for SUV. After correction, the difference was reduced to (-2.9±6.6)% at T=20 min and (-2.7±5)% at T=35 min for SUR and (1.9% ± 6.2)% at T=20 min and (1.7 ± 3.3)% at T=35 min for SUV. For the DTP studies, the observed differences of SUR and SUV between late and early scans were (48 ± 11)% and (24 ± 8.4)%, respectively. After correction, these differences were reduced to (2.6 ± 6.9)% and (-2.4±7.3)%, respectively.If FDG kinetics is irreversible in the targeted tissue, correction of SUV and SUR for scan time variability is possible with good accuracy. The correction distinctly improves comparability of lesion uptake values measured at different times post injection.

    View details for DOI 10.1186/2191-219X-4-18

    View details for Web of Science ID 000358043800001

    View details for PubMedID 24693879

    View details for PubMedCentralID PMC3992152

  • Nuclear Deformation and Neutron Excess as Competing Effects for Dipole Strength in the Pygmy Region PHYSICAL REVIEW LETTERS Massarczyk, R., Schwengner, R., Doenau, F., Frauendorf, S., Anders, M., Bemmerer, D., Beyer, R., Bhatia, C., Birgersson, E., Butterling, M., Elekes, Z., Ferrari, A., Gooden, M. E., Hannaske, R., Junghans, A. R., Kempe, M., Kelley, J. H., Koegler, T., Matic, A., Menzel, M. L., Mueller, S., Reinhardt, T. P., Roeder, M., Rusev, G., Schilling, K. D., Schmidt, K., Schramm, G., Tonchev, A. P., Tornow, W., Wagner, A. 2014; 112 (7): 072501

    Abstract

    The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A=124, 128, 132, and 134 in nuclear resonance fluorescence experiments using the γELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIγS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.

    View details for DOI 10.1103/PhysRevLett.112.072501

    View details for Web of Science ID 000331952500002

    View details for PubMedID 24579591

  • A volume of intersection approach for on-the-fly system matrix calculation in 3D PET image reconstruction PHYSICS IN MEDICINE AND BIOLOGY Lougovski, A., Hofheinz, F., Maus, J., Schramm, G., Will, E., van den Hoff, J. 2014; 59 (3): 561-577

    Abstract

    The aim of this study is the evaluation of on-the-fly volume of intersection computation for system's geometry modelling in 3D PET image reconstruction. For this purpose we propose a simple geometrical model in which the cubic image voxels on the given Cartesian grid are approximated with spheres and the rectangular tubes of response (ToRs) are approximated with cylinders. The model was integrated into a fully 3D list-mode PET reconstruction for performance evaluation. In our model the volume of intersection between a voxel and the ToR is only a function of the impact parameter (the distance between voxel centre to ToR axis) but is independent of the relative orientation of voxel and ToR. This substantially reduces the computational complexity of the system matrix calculation. Based on phantom measurements it was determined that adjusting the diameters of the spherical voxel size and the ToR in such a way that the actual voxel and ToR volumes are conserved leads to the best compromise between high spatial resolution, low noise, and suppression of Gibbs artefacts in the reconstructed images. Phantom as well as clinical datasets from two different PET systems (Siemens ECAT HR(+) and Philips Ingenuity-TF PET/MR) were processed using the developed and the respective vendor-provided (line of intersection related) reconstruction algorithms. A comparison of the reconstructed images demonstrated very good performance of the new approach. The evaluation showed the respective vendor-provided reconstruction algorithms to possess 34-41% lower resolution compared to the developed one while exhibiting comparable noise levels. Contrary to explicit point spread function modelling our model has a simple straight-forward implementation and it should be easy to integrate into existing reconstruction software, making it competitive to other existing resolution recovery techniques.

    View details for DOI 10.1088/0031-9155/59/3/561

    View details for Web of Science ID 000331937000005

    View details for PubMedID 24434600

  • Evaluation of PET quantification accuracy in vivo Comparison of measured FDG concentration in the bladder with urine samples NUKLEARMEDIZIN-NUCLEAR MEDICINE Maus, J., Hofheinz, F., Schramm, G., Oehme, L., Beuthien-Baumann, B., Lukas, M., Buchert, R., Steinbach, J., Kotzerke, J., van den Hoff, J. 2014; 53 (3): 67-77

    Abstract

    Quantitative positron emission tomography (PET) requires accurate scanner calibration, which is commonly performed using phantoms. It is not clear to what extent this procedure ensures quantitatively correct results in vivo, since certain conditions differ between phantom and patient scans.We, therefore, have evaluated the actual quantification accuracy in vivo of PET under clinical routine conditions.We determined the activity concentration in the bladder in patients undergoing routine [18F]FDG whole body investigations with three different PET scanners (Siemens ECAT EXACT HR+ PET: n = 21; Siemens Biograph 16 PET/CT: n = 16; Philips Gemini-TF PET/CT: n = 19). Urine samples were collected immediately after scan. Activity concentration in the samples was determined in well counters cross-calibrated against the respective scanner. The PET (bladder) to well counter (urine sample) activity concentration ratio was determined.Activity concentration in the bladder (PET) was systematically lower than in the urine samples (well counter). The patient-averaged PET to well counter ratios for the investigated scanners are (mean ± SEM): 0.881 ± 0.015 (ECAT HR+), 0.898 ± 0.024 (Biograph 16), 0.932 ± 0.024 (Gemini-TF). These values correspond to underestimates by PET of 11.9%, 10.2%, and 6.8%, respectively.The investigated PET systems consistently underestimate activity concentration in the bladder. The comparison of urine samples with PET scans of the bladder is a straightforward means for in vivo evaluation of the expectable quantification accuracy. The method might be interesting for multi-center trials, for additional quality assurance in PET and for investigation of PET/MR systems for which clear proof of sufficient quantitative accuracy in vivo is still missing.

    View details for DOI 10.3413/Nukmed-0588-13-05

    View details for Web of Science ID 000338691700001

    View details for PubMedID 24553628

  • Partial Volume Correction in Arterial Spin Labeling Using a Look-Locker Sequence MAGNETIC RESONANCE IN MEDICINE Petr, J., Schramm, G., Hofheinz, F., Langner, J., van den Hoff, J. 2013; 70 (6): 1535-1543

    Abstract

    Partial volume (PV) effects are caused by limited spatial resolution and significantly affect cerebral blood flow investigations with arterial spin labeling. Therefore, accurate PV correction (PVC) procedures are required. PVC is commonly based on PV maps obtained from segmented high-resolution T1 -weighted images. Segmentation of these images is error-prone, and it can be difficult to coregister these images accurately with the single-shot ASL images such as those created by echo-planar imaging (EPI). In this paper, an alternative method for PV map generation is proposed.The Look-Locker EPI (LL-EPI) acquisition is used for analyzing the T1 -recovery curve and for subsequent PV map generation. The new method was evaluated in five healthy volunteers (mean age 30 ± 3.7 years).By applying a linear regression method for PVC, a 12% decrease in regression error was reached with the new method.PV maps extraction from LL-EPI is a viable, possibly superior alternative to the standard approach based on segmentation of high-resolution T1 -weighted images.

    View details for DOI 10.1002/mrm.24601

    View details for Web of Science ID 000330182100006

    View details for PubMedID 23280559

  • Influence and Compensation of Truncation Artifacts in MR-Based Attenuation Correction in PET/MR IEEE TRANSACTIONS ON MEDICAL IMAGING Schramm, G., Langner, J., Hofheinz, F., Petr, J., Lougovski, A., Beuthien-Baumann, B., Platzek, I., van den Hoff, J. 2013; 32 (11): 2056-2063

    Abstract

    The goal of this article is to quantify the influence of truncation artifacts in the magnetic resonance (MR)-based attenuation map (MRMap) on reconstructed positron emission tomography (PET) image volumes and to propose a new method for minimizing this influence.PET data sets of 20 patients investigated in a Philips Ingenuity PET/MR were reconstructed with and without applying two different methods for truncation compensation (TC1 vendor-provided, TC2 newly developed). In this patient group, the extent of truncation artifacts and quality of the truncation compensation (TC) was assessed visually in the MRMaps. In three additional patients MRMaps generated by algorithm TC2 could be compared to the ground truth of transmission-based attenuation maps obtained with a Siemens ECAT HR(+) scanner. The influence of truncation on regional SUVs in lesions, other hot structures (bladder, kidney, myocardium) and the arms was assessed in suitable volume of interests (VOI).Truncation compensated MRMaps exhibited residual artifacts in the arms in 16 patients for algorithm TC1 and to a lesser extent in eight patients for algorithm TC2. Compared to the transmission-based attenuation maps algorithm TC2 slightly overestimated the size of the truncated arms by 0.3 cm in the radial direction. Without truncation compensation, VOIs located in the trunk showed an average SUVmax underestimation of less than 5.4% relative to the results obtained with TC2. Inside the patients' arms underestimations up to 46.5% were found.In the trunk, standardized uptake values (SUV) underestimations due to truncation artifacts in the MRMap are rather small. Inside the arms, severe SUV underestimations can occur. Therefore, reliable TC is mandatory and can be achieved by applying the newly developed algorithm TC2 which has yielded promising results so far. Implementation of the proposed method is straightforward and should be easily adaptable to other PET/MR systems.

    View details for DOI 10.1109/TMI.2013.2272660

    View details for Web of Science ID 000326733300009

    View details for PubMedID 24186268

  • Electromagnetic dipole strength up to the neutron separation energy from Pt-196(gamma, gamma ') and Pt-195(n, gamma) reactions PHYSICAL REVIEW C Massarczyk, R., Schramm, G., Junghans, A. R., Schwengner, R., Anders, M., Belgya, T., Beyer, R., Birgersson, E., Ferrari, A., Grosse, E., Hannaske, R., Kis, Z., Koegler, T., Kosev, K., Marta, M., Szentmiklosi, L., Wagner, A., Weil, J. L. 2013; 87 (4)
  • PET/MR for therapy response evaluation in malignant lymphoma: initial experience MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Platzek, I., Beuthien-Baumann, B., Langner, J., Popp, M., Schramm, G., Ordemann, R., Laniado, M., Kotzerke, J., van den Hoff, J. 2013; 26 (1): 49-55

    Abstract

    To evaluate the feasibility of positron emission tomography/magnetic resonance imaging (PET/MR) with (18)fluoro-2-deoxyglucose (FDG) for therapy response evaluation of malignant lymphoma.Nine patients with malignant lymphoma who underwent FDG-PET/MR before and after chemotherapy were included in this retrospective study. Average time between the two scans was 70 days. The scans were evaluated independently by two nuclear medicine physicians. The Ann Arbor classification was used to describe lymphoma stage. Furthermore, the readers also rated PET image quality using a five point scale. Weighted kappa (κ) was used to calculate interrater agreement.The initial scan showed foci of increased FDG uptake in all patients, with Ann Arbor stage varying between I and IV. In the follow-up examination, all but one patient showed complete response to chemotherapy. PET image quality was rated as very good or excellent for all scans. Interrater agreement was excellent regarding Ann Arbor stage (κ = 0.97) and good regarding image quality (κ = 0.41).PET/MR shows promising initial results for therapy response evaluation in lymphoma patients.

    View details for DOI 10.1007/s10334-012-0342-7

    View details for Web of Science ID 000314888300005

    View details for PubMedID 22983794

    View details for PubMedCentralID PMC3572376

  • Quantitative accuracy of attenuation correction in the Philips Ingenuity TF whole-body PET/MR system: a direct comparison with transmission-based attenuation correction MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE Schramm, G., Langner, J., Hofheinz, F., Petr, J., Beuthien-Baumann, B., Platzek, I., Steinbach, J., Kotzerke, J., van den Hoff, J. 2013; 26 (1): 115-126

    Abstract

    Evaluation of the quantitative accuracy of MR-based attenuation correction (MRAC) in the Philips Ingenuity TF whole-body PET/MR.In 13 patients, PET emission data from the PET/MR were reconstructed using two different methods for attenuation correction. In the first reconstruction, the vendor-provided standard MRAC was used. In the second reconstruction, a coregistered transmission-based attenuation map from a second immediately preceding investigation with a stand-alone Siemens ECAT EXACT HR(+) PET scanner was used (TRAC). The two attenuation maps were compared regarding occurrence of segmentation artifacts in the MRAC procedure. Standard uptake values (SUVs) of multiple VOIs (liver, cerebellum, hot focal structures at various locations in the trunk) were compared between both reconstructed data sets. Furthermore, a voxel-wise intensity correlation analysis of both data sets in the lung and trunk was performed.VOI averaged SUV differences between MRAC and TRAC were as follows (relative differences, mean ± standard deviation): (+12 ± 6) % cerebellum, (-4 ± 9) % liver, (-2 ± 11) % hot focal structures. The fitted slopes of the voxel-wise correlations in the lung and trunk were 0.87 ± 0.17 and 0.95 ± 0.10 with averaged adjusted R (2) values of 0.96 and 0.98, respectively. These figures include two instances with partially erroneous lung segmentation due to artifacts in the underlying MR images.The MR-based attenuation correction implemented on the Philips Ingenuity PET/MR provides reasonable quantitative accuracy. On average, deviations from TRAC-based results are small (on the order of 10% or below) across the trunk, but due to interindividual variability of the segmentation quality, deviations of more than 20% can occur. Future improvement of the segmentation quality would help to increase the quantitation accuracy further and to reduce the inter-subject variability.

    View details for DOI 10.1007/s10334-012-0328-5

    View details for Web of Science ID 000314888300010

    View details for PubMedID 22923020

    View details for PubMedCentralID PMC3572377

  • Dual time point based quantification of metabolic uptake rates in F-18-FDG PET EJNMMI RESEARCH van den Hoff, J., Hofheinz, F., Oehme, L., Schramm, G., Langner, J., Beuthien-Baumann, B., Steinbach, J., Kotzerke, J. 2013; 3: 16

    Abstract

    Assessment of dual time point (DTP) positron emission tomography was carried out with the aim of a quantitative determination of Km, the metabolic uptake rate of [18F]fluorodeoxyglucose as a measure of glucose consumption.Starting from the Patlak equation, it is shown that Km≈mt/ca0+V̄r/τa, where mt is the secant slope of the tissue response function between the dual time point measurements centered at t = t0. ca0=ca(t0) denotes arterial tracer concentration, V̄r is an estimate of the Patlak intercept, and τa is the time constant of the ca(t) decrease. We compared the theoretical predictions with the observed relation between Ks=mt/ca0 and Km in a group of nine patients with liver metastases of colorectal cancer for which dynamic scans were available, and Km was derived from conventional Patlak analysis. Twenty-two lesion regions of interest (ROIs) were evaluated. ca(t) was determined from a three-dimensional ROI in the aorta. Furthermore, the correlation between Km and late standard uptake value (SUV) as well as retention index was investigated. Additionally, feasibility of the approach was demonstrated in a whole-body investigation.Patlak analysis yielded a mean Vr of V̄r=0.53±0.08 ml/ml. The patient averaged τa was 99 ± 23 min. Linear regression between Patlak-derived Km and DTP-derived Ks according to Ks = b · Km + a yielded b = 0.98 ± 0.05 and a = -0.0054 ± 0.0013 ml/min/ml (r = 0.98) in full accordance with the theoretical predictions b = 1 and a≈-V̄r/τa. Ks exhibits better correlation with Km than late SUV and retention index, respectively. Ks(c)=Ks+V̄r/τa is proposed as a quantitative estimator of Km which is independent of patient weight, scan time, and scanner calibration.Quantification of Km from dual time point measurements compatible with clinical routine is feasible. The proposed approach eliminates the issues of static SUV and conventional DTP imaging regarding influence of chosen scanning times and inter-study variability of the input function. Ks and Ks(c) exhibit improved stability and better correlation with the true Km. These properties might prove especially relevant in the context of radiation treatment planning and therapy response control.

    View details for DOI 10.1186/2191-219X-3-16

    View details for Web of Science ID 000209435800016

    View details for PubMedID 23497553

    View details for PubMedCentralID PMC3717002

  • PET/MRI in head and neck cancer: initial experience EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING Platzek, I., Beuthien-Baumann, B., Schneider, M., Gudziol, V., Langner, J., Schramm, G., Laniado, M., Kotzerke, J., van den Hoff, J. 2013; 40 (1): 6-11

    Abstract

    To evaluate the feasibility of PET/MRI (positron emission tomography/magnetic resonance imaging) with FDG ((18)F-fluorodeoxyglucose) for initial staging of head and neck cancer.The study group comprised 20 patients (16 men, 4 women) aged between 52 and 81 years (median 64 years) with histologically proven squamous cell carcinoma of the head and neck region. The patients underwent a PET scan on a conventional scanner and a subsequent PET/MRI examination on a whole-body hybrid system. FDG was administered intravenously prior to the conventional PET scan (267-395 MBq FDG, 348 MBq on average). The maximum standardized uptake values (SUV(max)) of the tumour and of both cerebellar hemispheres were determined for both PET datasets. The numbers of lymph nodes with increased FDG uptake were compared between the two PET datasets.No MRI-induced artefacts where observed in the PET images. The tumour was detected by PET/MRI in 17 of the 20 patients, by PET in 16 and by MRI in 14. The PET/MRI examination yielded significantly higher SUV(max) than the conventional PET scanner for both the tumour (p < 0.0001) and the cerebellum (p = 0.0009). The number of lymph nodes with increased FDG uptake detected using the PET dataset from the PET/MRI system was significantly higher the number detected by the stand-alone PET system (64 vs. 39, p = 0.001).The current study demonstrated that PET/MRI of the whole head and neck region is feasible with a whole-body PET/MRI system without impairment of PET or MR image quality.

    View details for DOI 10.1007/s00259-012-2248-z

    View details for Web of Science ID 000312082500003

    View details for PubMedID 23053322

    View details for PubMedCentralID PMC3510405

  • EXPERIMENTS WITH NEUTRONS AND PHOTONS AT ELBE Schwengner, R., Beyer, R., Junghans, A. R., Massarczyk, R., Schramm, G., Bemmerer, D., Birgersson, E., Ferrari, A., Grosse, E., Hannaske, R., Kempe, M., Koegler, T., Matic, A., Schilling, K. D., Wagner, A., Rusev, G., Makinaga, A., Belgya, T., Kis, Z., Szentmiklosi, L., Weil, J., Becvar, F., Krticka, M., Garrett, P. E., Hadinia, B. WORLD SCIENTIFIC PUBL CO PTE LTD. 2013: 465-474
  • The PET-derived tumor-to-blood standard uptake ratio (SUR) is superior to tumor SUV as a surrogate parameter of the metabolic rate of FDG EJNMMI RESEARCH van den Hoff, J., Oehme, L., Schramm, G., Maus, J., Lougovski, A., Petr, J., Beuthien-Baumann, B., Hofheinz, F. 2013; 3: 77

    Abstract

    The standard uptake value (SUV) approach in oncological positron emission tomography has known shortcomings, all of which affect the reliability of the SUV as a surrogate of the targeted quantity, the metabolic rate of [18F]fluorodeoxyglucose (FDG), Km. Among the shortcomings are time dependence, susceptibility to errors in scanner and dose calibration, insufficient correlation between systemic distribution volume and body weight, and, consequentially, residual inter-study variability of the arterial input function (AIF) despite SUV normalization. Especially the latter turns out to be a crucial factor adversely affecting the correlation between SUV and Km and causing inter-study variations of tumor SUVs that do not reflect actual changes of the metabolic uptake rate. In this work, we propose to replace tumor SUV by the tumor-to-blood standard uptake ratio (SUR) in order to distinctly improve the linear correlation with Km.Assuming irreversible FDG kinetics, SUR can be expected to exhibit a much better linear correlation to Km than SUV. The theoretical derivation for this prediction is given and evaluated in a group of nine patients with liver metastases of colorectal cancer for which 15 fully dynamic investigations were available and Km could thus be derived from conventional Patlak analysis.For any fixed time point T at sufficiently late times post injection, the Patlak equation predicts a linear correlation between SUR and Km under the following assumptions: (1) approximate shape invariance (but arbitrary scale) of the AIF across scans/patients and (2) low variability of the apparent distribution volume Vr (the intercept of the Patlak Plot). This prediction - and validity of the underlying assumptions - has been verified in the investigated patient group. Replacing tumor SUVs by SURs does improve the linear correlation of the respective parameter with Km from r = 0.61 to r = 0.98.SUR is an easily measurable parameter that is highly correlated to Km. In this respect, it is clearly superior to SUV. Therefore, SUR should be seriously considered as a drop-in replacement for SUV-based approaches.

    View details for DOI 10.1186/2191-219X-3-77

    View details for Web of Science ID 000209435800077

    View details for PubMedID 24267032

    View details for PubMedCentralID PMC4175513

  • Electromagnetic dipole strength of Ba-136 below the neutron separation energy PHYSICAL REVIEW C Massarczyk, R., Schwengner, R., Doenau, F., Litvinova, E., Rusev, G., Beyer, R., Hannaske, R., Junghans, A. R., Kempe, M., Kelley, J. H., Koegler, T., Kosev, K., Kwan, E., Marta, M., Matic, A., Nair, C., Raut, R., Schilling, K. D., Schramm, G., Stach, D., Tonchev, A. P., Tornow, W., Trompler, E., Wagner, A., Yakorev, D. 2012; 86 (1)
  • Improved anatomic visualization of a glomus caroticum tumour within the carotic bifurcation with combined Ga-68-DOTATATE PET/MRI EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING Beuthien-Baumann, B., Platzek, I., Lauterbach, I., van den Hoff, J., Schramm, G., Zoephel, K., Laniado, M., Kotzerke, J. 2012; 39 (6): 1087-1088

    View details for DOI 10.1007/s00259-012-2097-9

    View details for Web of Science ID 000303523400022

    View details for PubMedID 22422041

  • Quantitative accuracy of MR-based attenuation correction in whole-body PET/MR Schramm, G., Langner, J., Hofheinz, F., Baumann, B., Platzek, I., Kotzerke, J., Steinbach, J., van den Hoff, J. SOC NUCLEAR MEDICINE INC. 2012
  • Dipole strength in Se-78 below the neutron separation energy from a combined analysis of Se-77(n, gamma)and Se-78(gamma, gamma ') experiments PHYSICAL REVIEW C Schramm, G., Massarczyk, R., Junghans, A. R., Belgya, T., Beyer, R., Birgersson, E., Grosse, E., Kempe, M., Kis, Z., Kosev, K., Krticka, M., Matic, A., Schilling, K. D., Schwengner, R., Szentmiklosi, L., Wagner, A., Weil, J. L. 2012; 85 (1)
  • Investigation of dipole strength at the ELBE accelerator in Dresden-Rossendorf Massarczyk, R., Schramm, G., Birgersson, E., Schwengner, R., Grosse, E., Junghans, A. R., Wagner, A., Krticka, M., Becvar, F., Kroll, J. E D P SCIENCES. 2012
  • ELECTROMAGNETIC STRENGTH IN HEAVY NUCLEI - EXPERIMENTS AND A GLOBAL FIT INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS Beyer, R., Birgersson, E., Junghans, A. R., Massarczyk, R., Schramm, G., Schwengner, R., Grosse, E. 2011; 20 (2): 431-442
  • Photon strength function deduced from photon scattering and neutron capture Massarczyk, R., Birgersson, E., Schramm, G., Schwengner, R., Belgya, T., Beyer, R., Grosse, E., Hannaske, R., Junghans, A. R., Matic, A., Szentimiklosi, L., Weil, J., Wagner, A., Granier, T., Laurent, B., Ledoux, Marmouget, J. G. E D P SCIENCES. 2010
  • Photon strength in spherical and deformed heavy nuclei Grosse, E., Junghans, A., Becvar, F., Birgersson, E., Massarczyk, R., Schramm, G., Granier, T., Laurent, B., Ledoux, Marmouget, J. G. E D P SCIENCES. 2010