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A low-cost PET detector module with dual-ended readout based on sparse SiPM arrangement. (#264)
M. Seo1, H. Park1, S. Lee1, G. B. Ko2, J. S. Lee1, 2
1 Seoul National University, Department of Biomedical Sciences, Seoul, Republic of Korea
The positron emission tomography (PET) detector using dual-ended readout scheme based on silicon photomultiplier (SiPM) provides depth-of-interaction (DOI) information, which is useful for improving signal-to-noise ratio and spatial resolution uniformity of PET systems. However, PET detectors using the dual-ended readout requires twice the number of SiPMs compared to conventional single-ended readout PET detectors, increasing complexity and cost. Therefore, we propose a novel sparse SiPM arrangement for dual-ended readout with a smaller number of SiPM channels compared to conventional dual-ended readout detectors. In this study, we measured the performance of the proposed detector developed using LSO crystals, including DOI, energy, and timing resolutions. The DOI resolution measured using side-on irradiation was 2.6 mm and the energy resolution was 17% FWHM, on average. By applying DOI correction, 594 ps FWHM timing resolution was achieved. Therefore, we can expect that the proposed sparse PET detector will allow accurate DOI measurement at a reasonable cost in PET studies.
Keywords: positron emission tomography (PET), silicon photomultiplier (SiPM), low-cost, sparse, dual-ended signal readout
Development and Evaluation of a Compact High-Resolution Animal PET Dedicated for Preclinical Onboard PET/CT Image-Guided Radiotherapy (#1039)
X. Cheng1, D. Yang1, K. Hu1, Y. Shao1
1 University of Texas Southwestern Medical Center, Department of Radiation Oncology, Dallas, Texas, United States of America
We report the development and evaluation of a compact high-resolution animal PET dedicated for preclinical PET/CT image-guided radiotherapy. It consists of 12 detectors configured in a dodecagon; each panel has a 30x30 array of 1x1x20 mm3 LYSO scintillators with each end of the scintillator array optically connected to Silicon Photomultiplier (SiPM) arrays for depth-of-interaction (DOI) measurement. The imaging field-of-view (FOV) size is 8.0 cm in diameter and 3.5 cm axially, with a 1.8% sensitivity at the center FOV under a 350-650 keV energy threshold. The gantry of PET has 33 cm outer diameter, 11 cm axial length, 11 cm animal port, and 6.5 kg weight. The energy, DOI, and coincidence timing resolutions of the system are around 22.1%, 3.1 mm, and 1.92 ns, respectively. The spatial resolution was measured ~1.1 mm uniformly over 6 cm diameter within FOV. All rods of 1.0 mm diameter can be clearly resolved from the image of the ultra-micro hot-rods phantom reconstructed with an OSEM algorithm based open source code. Overall, this compact and lightweight PET dedicated for integrating with an animal irradiator has demonstrated its designed capability and performance that will lead to providing onboard functional/biological/molecular image to guide the preclinical RT research.
This study is supported in part by grants from National Institute of Health (1R01EB019438, 1R01EB019438-04S, 1R01CA218402) and a career development grant from the Department of Radiation Oncology, University of Texas Southwestern Medical Center.
Keywords: PET, pre-clincial, DOI, FPGA, radiaotherapy
Addressing Light Distribution Truncation and 3D Impact Positioning in PET: Edgeless Approach (#852)
M. Freire1, G. Cañizares1, A. Gonzalez-Montoro1, S. S. Berr2, M. B. Williams2, A. J. Gonzalez1
1 Institute for Instrumentation in Molecular Imaging (i3M), Valencia, Spain
Improving spatial resolution and sensitivity drive the instrumentation research in small animal Positron Emission Tomography (PET) imaging. Moreover, including accurate photon Depth of Interaction (DOI) information plays an important role in small aperture scanners, since it is essential for obtaining homogeneous spatial resolution across the Field of View (FOV).
To improve both spatial resolution and sensitivity, we already constructed an edgeless PET system based on a single scintillator annulus with DOI capabilities. Our Zero prototype was based on a single LYSO piece with inner cylindrical face but ten outer planar facets to allow for easy photodetector coupling. We present here, an upgraded version based on a single LYSO piece with both inner and outer cylindrical faces.
Monte Carlo simulations have been performed using both nuclear and optical tracking. An improvement on the light distribution profiles collected by this novel approach without faceted sides was observed. A spatial resolution of 0.5 mm and a sensitivity of 12% were obtained at the system center of the Field of View.
Keywords: Monolithic detectors, Edgeless PET, Simulations
PET imaging performance of a dedicated breast PET-DBT (BPET-DBT) scanner (#695)
S. Krishnamoorthy1, E. Morales2, W. J. Ashmanskas2, M. E. Werner1, T. Vent3, A. D. Maidment1, J. S. Karp1, 2, S. Surti1
1 University of Pennsylvania, Radiology, Philadelphia, Pennsylvania, United States of America
Our group at the University of Pennsylvania has designed and built a dedicated high spatial resolution time-of-flight (TOF)-capable breast PET (BPET) scanner integrated with a digital breast tomosynthesis (DBT) unit in a common gantry to provide co-registered PET-DBT images. The BPET scanner is comprised of two detector heads, with each head composed of a 4x2 array of PET detectors built using 1.5x1.5x15 mm3 LYSO crystals. The PET detector head separation is set to 9 cm, providing a PET FOV of 20x9x10 cm3. In comparison with conventional dual-headed PET scanners, TOF information will help in alleviating limited-angle image artifacts and improve lesion quantification. This dedicated scanner will thus provide the ability to more accurately measure radiotracer uptake in smaller lesions that are prevalent in breast cancer. A custom data acquisition system performs fast signal waveform sampling at 4 Gsps with minimal deadtime. Initial system measurements show good crystal discrimination, CTR of ~400 ps, and 16% energy resolution. This paper describes the full system design architecture and presents the imaging performance of the dedicated breast PET scanner. In particular, results from reconstructed spatial resolution, sensitivity, count-rate performance, and detailed phantom measurements will be presented as well as a possible clinical study.
The work was supported by National Institutes of Health R01CA196528, R01CA113941, R01EB028764 & R21CA239177, Komen Foundation (IIR13264610), and Burroughs Wellcome Foundation (IRSA 1016451) grants.
Keywords: PET, TOF-PET, breast-PET, PET-DBT, dedicated organ PET
Sampling uEXPLORER Total-body PET Data to Mimic Altered Scanner Geometries (#1129)
R. Bayerlein2, E. Berg3, E. K. Leung2, 3, B. A. Spencer2, E. M. Revilla3, N. Omidvari3, Y. G. Abdelhafez2, E. J. Li3, X. Zhang3, S. R. Cherry2, R. D. Badawi2, 3
1 University of California Davis, Department of Radiology, Sacramento, California, United States of America
The uEXPLORER total-body PET scanner is the first clinically operating PET system that can capture the entire human subject in the axial field-of-view (AFOV) and permits total-body imaging. Aside from benefits related to image signal-to-noise ratio, fast dynamic imaging, or dose reduction that are available with total-body imaging, the complete total-body PET list-mode dataset allows investigations into alternative scanner designs (e.g., axial gaps or sparse detector configurations), error analysis with defective detector modules, and optimization of clinical multi-bed imaging protocols with conventional short-AFOV PET systems. Here we explore these possibilities and describe the methodology using uEXPLORER list-mode data. A software tool was developed to modify the crystal efficiency map used in normalization, and to sample the list-mode data accordingly. First, we tested the methodology by rejecting all coincidences outside of a 24-cm AFOV region to mimic a single bed position of a conventional PET system. Data was collected and reconstructed from a scan of a 15-cm diameter × 210-cm length cylinder source. The coefficients of variation obtained within cylindrical volumes-of-interest (VOIs) placed inside the phantom were consistent between the subsampled data and the complete total-body images compared to theoretical expectations.
Keywords: Total-body PET, Positron Emission Tomography
Monte Carlo Simulations of Flux Rates with the NeuroEXPLORER Design Geometry based on Total-body Human Imaging Data (#469)
T. Li1, E. K. Leung1, T. Toyonaga3, T. Feng4, J. Hoye3, Z. Xie1, C. - C. Liu1, E. Morris3, R. D. Badawi1, 2, J. Qi1, A. Hillmer3
1 University of California, Davis, Department of Biomedical Engineering, Davis, California, United States of America
The NeuroEXPLORER (NX) dedicated brain PET/CT scanner is under development, featuring high spatial resolution and high sensitivity. One unique strength of PET is its ability to provide absolute quantification of radiotracer distribution. Accurate quantification is especially important for brain imaging using dynamic PET protocols. A limiting factor in accurate quantification is the detector deadtime, which results in nonlinear response at high photon flux (singles) rates. Correction for the deadtime effect is difficult when the radiotracer distribution is non-uniform and is changing rapidly over time, which occurs after a bolus injection. In this study, we performed GATE simulations to characterize expected singles rates for the NX detectors in realistic imaging situations. We built a Monte Carlo model of the NX scanner using GATE and used existing [EKSL2] [TL3] PET/CT images of three radiotracers (18F-FDG, 18F-SynVesT-1, and 11C-MRB) to examine the singles rates at various time points after bolus injection. Simulation results showed that the peak singles rate reached 5.7kps/mCi for a 6.6×6.6 mm2 detector unit and occurred when most of the radioactivity was concentrated inside the lungs shortly after bolus injection. The flux rates became much lower after the radiotracer was distributed throughout the body. These simulation results provided important information for guiding detector design for accurate PET quantification.
Keywords: Monte Carlo simulation, PET, flux rates
Design Considerations for Neuro-PET (#959)
R. L. Harrison1, S. Ahn2, W. Hunter1, S. Dolinsky2, P. E. Kinahan1, R. S. Miyaoka1
1 University of Washington, Radiology, Seattle, Washington, United States of America
For the BRAIN-Initiative we are developing a BRAIN-Initiative Next Generation (BING) Positron Emission Tomograph based on slat detectors. In this study we use simulation to understand the effects of detector design choices on image quality. We investigate the trade-offs as we vary slat thickness, time-of-flight (TOF), and depth-of-interaction (DOI) resolution using contrast-to-noise-ratio (CNR) as an image quality metric. Using an elliptical phantom with multiple 1 mm and 2 mm spherical lesions at different radial positions, we simulate a cylindrical LYSO-based tomograph and varied the effective slat thickness (1 mm or 2 mm thick), TOF resolution (100 ps, 200 ps, or no time-of-flight), and DOI resolution (5 or 9 DOI bins over 15 mm crystal depth). We reconstruct simulated data with OSEM and compute contrast-to-noise ratios. We find 9 DOI tomographs outperform 5 DOI tomographs even if the 5 DOI tomographs have better TOF. Tomographs with 1 mm slats outperform those with 2 mm slats, particularly for small spheres.
This work was supported in part by NIH R01 EB026964-01.
Keywords: Positron emission tomography, simulation
Prism-PET Brain Scanner for High Resolution andHigh Sensitivity Imaging of Monoaminergic Nuclei: A GATE Simulation Study (#1002)
A. LaBella1, A. Biegon1, X. Cao2, N. Clayton1, Z. Wang3, E. Petersen3, X. Zeng2, G. A. Ulaner4, 5, W. Zhao1, A. H. Goldan1
1 Stony Brook University, Department of Radiology, Stony Brook, New York, United States of America
High spatial resolution and sensitivity are necessary for accurate quantitative in vivo molecular neuroimaging, particularly for small brain structures. Positron emission tomography (PET) is an attractive candidate to bring quantitative molecular imaging into standard clinical care due to its high target specificity based on the radiopharmaceutical being imaged. However, commercially available PET scanners suffer from relatively poor spatial resolution compared to other clinical imaging modalities, such as MRI and CT, due to the use of large detector elements and lack of depth-encoding capabilities on the readout side, thus limiting their ability to accurately quantify radiotracer uptake in brain regions and nuclei smaller than 3-5 mm in diameter. In this work, we introduce a practical, cost-effective high resolution brain PET scanner that uses our novel Prism-PET detector module configuration to achieve unprecedented PET spatial performance using high resolution depth of interaction (DOI) readout to enable accurate radiotracer uptake quantification in small brain nuclei. We use GATE to accurately simulate the performance of our proposed Prism-PET brain scanner when imaging radiotracers for 5-HT1A receptors, which are abundant in the dorsal raphe nucleus (DRN), and norepinephrine transporters, which are highly concentrated in the bilateral locus coeruleus (LC). We compare our scanner's performance to that of a current state-of-the-art clinical time-of-flight (TOF) PET scanner, the Siemens Biograph Vision. Our brain-dedicated Prism-PET scanner enables accurate quantification of radiotracer uptake in the RN and LC, with a 20-fold and 3-fold improvement in quantifying uptake in the DRN and bilateral LC, respectively, compared to the Biograph Vision. Based on our simulation results, our proposed high resolution, high sensitivity Prism-PET brain scanner is a clinically viable candidate for quantitative molecular human neuroimaging.
Keywords: PET, Neuroimaging, Prism-PET, DOI, GATE
Design of the NeuroEXPLORER, a next-generation ultra-high performance human brain PET imager (#386)
R. E. Carson1, R. D. Badawi2, E. Berg2, S. R. Cherry2, J. Du2, T. Feng3, K. Fontaine1, P. Gravel1, A. Hillmer1, P. Honhar1, J. Hoye1, L. Hu3, T. Jones2, E. Leung2, T. Li2, C. Liu1, Y. Lu1, S. Majewski2, E. D. Morris1, T. Mulnix1, J. Schmall3, A. Selfridge3, T. Toyonaga1, J. Qi2, H. Li3
1 Yale University, Department of Radiology and Biomedical Imaging / Yale PET Center, New Haven, Connecticut, United States of America
PET human brain imaging has evolved dramatically, with specific radiotracers and imaging paradigms to measure numerous brain targets and to assess neurotransmitter and receptor dynamics. However, state-of-the-art for dedicated brain PET has not progressed since the HRRT, so there is a compelling need to build next generation human brain PET systems. This is the goal of the NeuroEXPLORER (NX) project. Based on experience with >4500 human brain PET studies at Yale and with the total-body uEXPLORER system at UC Davis, our NX design goals are: 1) Ultra-high sensitivity, to be achieved with a long axial field-of-view (aFOV) plus excellent time-of-flight (TOF); 2) Exceptional image resolution through small detectors, depth of interaction (DOI) readout, and corrections for inter-crystal scatter; 3) Continuous head motion tracking and correction. The NX design is a cylinder with diameter and aFOV of ~50 cm. The system consists of 5 complete detector rings, with an additional incomplete 6th ring to accommodate shoulders to place the brain in the aFOV center. LYSO crystals (20-mm deep) have an in-plane dimension of 1.5 mm, leading to a resolution of 1.6-1.8 mm. To reduce parallax error, a novel single-end DOI design was developed with < 4 mm FWHM. The projected TOF resolution is < 250 ps. Combined with the long aFOV, we project that the NX will have > 10-fold higher effective sensitivity than the HRRT for the brain, with an even greater advantage for the carotids. Head motion tracking is performed with a real-time stereovision system. Optimization of reconstruction and quantification is performed with high-resolution brain simulations and novel phantom configurations. Ultimately, human imaging paradigms will demonstrate the effectiveness of the NX: 1) showing the dramatic sensitivity increase compared to the HRRT, 2) leveraging high sensitivity to reliably measure uptake in small nuclei, and 3) opening new frontiers of imaging neurotransmitter dynamics.
Keywords: NeuroEXPLORER, Sensitivity, Resolution, Brain, PET
NiftyPET: Fast Quantitative Image Reconstruction For a New Brain PET Camera CareMiBrain (#1147)
C. Morera-Ballester1, 2, S. Jiménez-Serrano1, S. Beschwitz3, F. Schmidt3, P. J. Markiewicz4
1 Oncovision, Valencia, Spain
AcknowledgmentCareMiBrain is funded by the European Union Horizon 2020 research and Innovation Programme, under grant number 713323.
Keywords: Brain PET, reconstruction, qunatification
Implementation and image quality benefit of a hybrid-space PET point spread function (#314)
T. W. Deller1, S. Ahn2, F. P. Jansen1, G. Schramm3, K. A. Wangerin1, M. G. Spangler-Bickell1, C. W. Stearns1, M. M. Khalighi4
1 GE Healthcare, Waukesha, Wisconsin, United States of America
Detector response modeling during reconstruction of PET data improves image resolution. Such modeling is typically performed either in sinogram (projection) domain, or in image domain. This work proposes a hybrid approach, with a portion of the point spread function (PSF) modeling in each domain. The approach includes a spatially varying radial smoothing of the sinogram data (or broadened line of response if performing list mode reconstruction), combined with a spatially invariant image smoothing. The image-based smoothing component mitigates high-frequency artifacts that can emerge from the projectors when small pixel sizes are used with low levels of post-smoothing; this benefit is important for many high-resolution PET imaging approaches. Unlike fully-image-based PSF approaches, this method integrates well with motion-corrected list-mode reconstruction by applying the appropriate PSF kernel for each LOR, even when its position is adjusted for motion. The hybrid approach opens the way to isotope-dependent positron range imaging, by allowing the use of different image-based kernels for isotopes with different positron range, while preserving the same projection-based kernel (which is a function of detector design only). The effectiveness of the method is demonstrated with a brain 18F-FDG dataset and spatial resolution point sources.
Keywords: High-resolution imaging, PET, point spread function, spatial resolution
Impact of a Penalized Likelihood Reconstruction (Q.Clear) on PET Texture Radiomic Features with a Custom Heterogeneity Phantom Study (#986)
M. A. Lewis1, S. L. Bowen1
1 UT Southwestern Medical Center, Radiology, Dallas, Texas, United States of America
Background: Texture radiomic features quantify heterogeneity of PET radiotracer uptake. A penalized likelihood reconstruction method, Q.Clear, is available on commercial PET-CT systems. However, the impact of Q.Clear on texture features as a function of image heterogeneity is not well characterized.
Objective: To evaluate the influence of Q.Clear and penalty factor (β) strength on PET texture features measured from an anthropomorphic phantom containing a range of image textures and activity concentration ratios.
Methods: A custom insert for the NEMA IEC body phantom was fabricated to hold six 50 ml centrifuge tubes. Two sets of three centrifuge tubes were filled with 1) 90%, 60%, and 30% activity-absorbing zeolites by mass, well-mixed with polyethylene beads of similar size, and 2) 18F-FDG solutions of 6:1 and 3:1, relative to background. The combination resulted in image textures and contrasts ranging from comparatively heterogenous to uniform, and matched to a 3:1 background contrast ratio, respectively. The phantom was scanned for 2 min. with a time-of-flight (ToF) capable GE Discovery MI PET-CT and images reconstructed with Q.Clear for β values ranging from 50 to 500. Texture features were computed with pyradiomics and assessed with a coefficient of variation (CoV) analysis.
Results: The variation in β from 50-200 resulted in CoV exceeding 10% for six of the eleven texture features considered. For these six features CoV was an average of 14% greater for images reconstructed with β values in a 50-200 relative to a 250-500 range. The impact of β on texture features was strongly dependent on the image texture in some instances. For example, Gray Level Size Zone Matrix low-level zone emphasis resulted in a CoV of 26% and 16% for the 90% zeolite (6:1 activity ratio) and 30% zeolite (6:1 activity ratio) ROIs, respectively.
Conclusions: Both the β value and texture features should be carefully selected when using Q.Clear and quantitative texture analysis.
Keywords: penalized likelihood, texture features, pet
Challenges in optimization of a stationary tomographic Molecular Breast Imaging system (#1021)
K. Erlandsson1, A. Wirth2, K. Thielemans1, I. Baistow2, A. Cherlin2, B. F. Hutton1
1 University College London, Institute of Nuclear Medicine, London, United Kingdom
A prototype Molecular Breast Imaging (MBI) system is currently under development, motivated by the need of a practical low-dose system for use in patients with dense breast tissue, where conventional mammography is limited. The system is based on dual opposing CZT detector arrays and multi-pinhole collimators which allow for multiplexing in the projection data. We have performed optimisation of various design parameters based on either contrast-to-noise ratio (CNR) in the reconstructed images or area-under-the-localisation-receiver-operating-characteristics curve (LROC-AUC) obtained using the scan statistic model. The optimisations were based on simulated data, and the parameters investigated were pinhole size and opening angle, pinhole separation and collimator-to-detector separation. The two optimisation approaches resulted in similar design parameters, allowing for reconstruction of tomographic images with high CNR and lesion detectability, which can lead to a reduced dose or scan time as compared to planar MBI.
AcknowledgmentThe Institute of Nuclear Medicine is supported by the NIHR University College London Hospitals Biomedical Research Centre. Kromek are supported by an Innovate UK grant (104296).
Keywords: CNR, CZT, LROC, multi-pinhole collimator, multiplexing
First Demonstration of Rat Total-Body PET Imaging with 4-Layer DOI Information (#201)
H. G. Kang1, H. Wakizaka1, E. Yoshida1, H. Tashima1, M. Higuchi1, T. Yamaya1
1 National Institutes for Quantum and Radiological Science and Technology (QST), Department of Advanced Nuclear Medicine Science, Chiba, Japan
Preclinical positron emission tomography (PET) has been playing an important role for new drug development. The quantification accuracy of radiopharmaceuticals inside living small animals (e.g. mouse or rat) is mainly determined by the sensitivity which can be increased by using a thick crystal and long axial FOV. However, the thick crystal and long axial FOV can cause significant parallax errors for small animal PET scanners. Therefore, last year, we developed a total-body small animal PET (TBSAP) with a 4-layer depth-of-interaction (DOI) detector to achieve high sensitivity (16.7%) while minimizing the parallax error. In this study, we present the initial in vivo imaging results of the TBSAP with various radiotracers. The TBSAP has the 155 mm ring diameter and 315.6 mm axial FOV. The TBSAP consists of 6 rings each of which has 10 DOI detectors. Each DOI detector has a 4-layer GSOZ crystal array which results in a 30 mm total thickness and 2.9 mm crystal pitch. Whole-body rat imaging was performed for 15 min without any bed motion. The PET images were reconstructed by using OSEM algorithm and shown by maximum intensity projection (MIP). The in vivo imaging results show a clear bone structure (NaF) and glucose metabolism of the rat brain (FDG). In conclusion, the whole-body rat images can be obtained without any bed motion with the TBSAP. In the future, we plan to use the TBSAP for ultralow activity imaging applications such as in vivo single cell tracking and in-beam small animal PET imaging using micro carbon ion beams.
Keywords: Total-body PET, DOI, Small animal PET