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Kuhl Y, Mueller F, Naunheim S, Bovelett M, Lambertus J, Schug D, Weissler B, Gegenmantel E, Gebhardt P, Schulz V. A finely segmented semi-monolithic detector tailored for high-resolution PET. Med Phys 2024; 51:3421-3436. [PMID: 38214395 DOI: 10.1002/mp.16928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 12/20/2023] [Accepted: 12/20/2023] [Indexed: 01/13/2024] Open
Abstract
BACKGROUND Preclinical research and organ-dedicated applications use and require high (spatial-)resolution positron emission tomography (PET) detectors to visualize small structures (early) and understand biological processes at a finer level of detail. Researchers seeking to improve detector and image spatial resolution have explored various detector designs. Current commercial high-resolution systems often employ finely pixelated or monolithic scintillators, each with its limitations. PURPOSE We present a semi-monolithic detector, tailored for high-resolution PET applications with a spatial resolution in the range of 1 mm or better, merging concepts of monolithic and pixelated crystals. The detector features LYSO slabs measuring (24 × 10 × 1) mm3, coupled to a 12 × 12 readout channel photosensor with 4 mm pitch. The slabs are grouped in two arrays of 44 slabs each to achieve a higher optical photon density despite the fine segmentation. METHODS We employ a fan beam collimator for fast calibration to train machine-learning-based positioning models for all three dimensions, including slab identification and depth-of-interaction (DOI), utilizing gradient tree boosting (GTB). The data for all dimensions was acquired in less than 2 h. Energy calculation was based on a position-dependent energy calibration. Using an analytical timing calibration, time skews were corrected for coincidence timing resolution (CTR) estimation. RESULTS Leveraging machine-learning-based calibration in all three dimensions, we achieved high detector spatial resolution: down to 1.18 mm full width at half maximum (FWHM) detector spatial resolution and 0.75 mm mean absolute error (MAE) in the planar-monolithic direction, and 2.14 mm FWHM and 1.03 mm MAE for DOI at an energy window of (435-585) keV. Correct slab interaction identification in planar-segmented direction exceeded 80%, alongside an energy resolution of 12.7% and a CTR of 450 ps FWHM. CONCLUSIONS The introduced finely segmented, high-resolution slab detector demonstrates appealing performance characteristics suitable for high-resolution PET applications. The current benchtop-based detector calibration routine allows these detectors to be used in PET systems.
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Affiliation(s)
- Yannick Kuhl
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Florian Mueller
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Stephan Naunheim
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Matthias Bovelett
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Janko Lambertus
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - David Schug
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
- Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany
| | - Bjoern Weissler
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
- Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany
| | | | - Pierre Gebhardt
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Volkmar Schulz
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
- Hyperion Hybrid Imaging Systems GmbH, Aachen, Germany
- Physics Institute III B, RWTH Aachen University, Aachen, Germany
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2
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Saaidi R, Rodríguez-Villafuerte M, Alva-Sánchez H, Martínez-Dávalos A. Crystal scatter effects in a large-area dual-panel Positron Emission Mammography system. PLoS One 2024; 19:e0297829. [PMID: 38427663 PMCID: PMC10906883 DOI: 10.1371/journal.pone.0297829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 01/11/2024] [Indexed: 03/03/2024] Open
Abstract
Positron Emission Mammography (PEM) is a valuable molecular imaging technique for breast studies using pharmaceuticals labeled with positron emitters and dual-panel detectors. PEM scanners normally use large scintillation crystals coupled to sensitive photodetectors. Multiple interactions of the 511 keV annihilation photons in the crystals can result in event mispositioning leading to a negative impact in radiopharmaceutical uptake quantification. In this work, we report the study of crystal scatter effects of a large-area dual-panel PEM system designed with either monolithic or pixelated lutetium yttrium orthosilicate (LYSO) crystals using the Monte Carlo simulation platform GATE. The results show that only a relatively small fraction of coincidences (~20%) arise from events where both coincidence photons undergo single interactions (mostly through photoelectric absorption) in the crystals. Most of the coincidences are events where at least one of the annihilation photons undergoes a chain of Compton scatterings: approximately 79% end up in photoelectric absorption while the rest (<1%) escape the detector. Mean positioning errors, calculated as the distance between first hit and energy weighted (assigned) positions of interaction, were 1.70 mm and 1.92 mm for the monolithic and pixelated crystals, respectively. Reconstructed spatial resolution quantification with a miniDerenzo phantom and a list mode iterative reconstruction algorithm shows that, for both crystal types, 2 mm diameter hot rods were resolved, indicating a relatively small effect in spatial resolution. A drastic reduction in peak-to-valley ratios for the same hot-rod diameters was observed, up to a factor of 14 for the monolithic crystals and 7.5 for the pixelated ones.
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Affiliation(s)
- Rahal Saaidi
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
| | | | - Héctor Alva-Sánchez
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
| | - Arnulfo Martínez-Dávalos
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
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3
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Petersen E, LaBella A, Li Y, Wang Z, Goldan AH. Resolving inter-crystal scatter in a light-sharing depth-encoding PET detector. Phys Med Biol 2024; 69:035024. [PMID: 38169459 DOI: 10.1088/1361-6560/ad19f1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Accepted: 01/02/2024] [Indexed: 01/05/2024]
Abstract
Objective.Inter-crystal scattering (ICS) in light-sharing positron emission tomography (PET) detectors leads to ambiguity in positioning the initial interaction, which significantly degrades the contrast, quantitative accuracy, and spatial resolution of the resulting image. Here, we attempt to resolve the positioning ambiguity of ICS in a light-sharing depth-encoding detector by exploiting the confined, deterministic light-sharing enabled by the segmented light guide unique to Prism-PET.Approach.We first considered a test case of ICS between two adjacent crystals using an analytical and a neural network approach. The analytical approach used a Bayesian estimation framework constructed from a scatter absorption model-the prior-and a detector response model-the likelihood. A simple neural network was generated for the same scenario, to provide mutual validation for the findings. Finally, we generalized the solution to three-dimensional event positioning that handles all events in the photopeak using a convolutional neural network with unique architecture that separately predicts the identity and depth-of-interaction (DOI) of the crystal containing the first interaction.Main results.The analytical Bayesian method generated an estimation error of 20.5 keV in energy and 3.1 mm in DOI. Further analysis showed that the detector response model was sufficiently robust to achieve adequate performance via maximum likelihood estimation (MLE), without prior information. We then found convergent results using a simple neural network. In the generalized solution using a convolutional neural network, we found crystal identification accuracy of 83% and DOI estimation error of 3.0 mm across all events. Applying this positioning algorithm to simulated data, we demonstrated significant improvements in image quality over the baseline, centroid-based positioning approach, attaining 38.9% improvement in intrinsic spatial resolution and enhanced clarity in hot spots of diameters 0.8 to 2.5 mm.Significance.The accuracy of our findings exceeds those of previous reports in the literature. The Prism-PET light guide, mediating confined and deterministic light-sharing, plays a key role in ICS recovery, as its mathematical embodiment-the detector response model-was the essential driver of accuracy in our results.
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Affiliation(s)
- Eric Petersen
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY, United States of America
- Department of Radiology, Weill Cornell Medical College, Cornell University, New York, NY, United States of America
| | - Andy LaBella
- Department of Radiology, Stony Brook University, Stony Brook, NY, United States of America
| | - Yixin Li
- Department of Radiology, Weill Cornell Medical College, Cornell University, New York, NY, United States of America
- Department of Electrical and Computer Engineering, Stony Brook University, Stony Brook, NY, United States of America
| | - Zipai Wang
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY, United States of America
- Department of Radiology, Weill Cornell Medical College, Cornell University, New York, NY, United States of America
| | - Amir H Goldan
- Department of Radiology, Weill Cornell Medical College, Cornell University, New York, NY, United States of America
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4
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Yoshida E, Obata F, Yamaya T. Calibration method of crosshair light sharing PET detector with TOF and DOI capabilities. Biomed Phys Eng Express 2023; 9:055031. [PMID: 37586333 DOI: 10.1088/2057-1976/acf0c7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Accepted: 08/16/2023] [Indexed: 08/18/2023]
Abstract
Objective. A crosshair light sharing (CLS) PET detector as a TOF-DOI PET detector with high spatial resolution has been developed. To extend that work, a detector calibration method was developed to achieve both higher coincidence resolving time (CRT) and DOI resolution.Approach. The CLS PET detector uses a three-layer reflective material in a two-dimensional crystal array to form a loop structure within a pair of crystals, enabling a CRT of about 300 ps and acquisition of DOI from multi-pixel photon counter (MPPC) output ratios. The crystals were 1.45 × 1.45 × 15 mm3fast LGSO, and the crystal array was optically coupled to an MPPC array. It is important to reduce as many inter-crystal scattering (ICS) events as possible in advance for the accurate detector calibration. DOI information is also expected to improve the CRT because it can estimate the time delay due to the detection depth of crystals.Main results. Using crystal identification and light collection rate of the highest MPPC output reduces the number of ICS events, and CRT is improved by 26%. In addition, CRT is further improved by 13% with a linear correction of time delay as a function of energy. The DOI is ideally estimated from the output ratio of only the MPPC pairs optically coupled to the interacted crystals, which is highly accurate, but the error is large due to light leakage in actual use. The previous method, which also utilizes light leakage to calculate the output ratio, is less accurate, but the error can be reduced. Using the average of the two methods, it is possible to improve the DOI resolution by 12% while maintaining the smaller error.Significance. By applying the developed calibration method, the CLS PET detector achieves the CRT of 251 ps and the DOI resolution of 3.3 mm.
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Affiliation(s)
- Eiji Yoshida
- National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
| | - Fujino Obata
- National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
| | - Taiga Yamaya
- National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
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5
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Cao X, Labella A, Zeng X, Zhao W, Goldan AH. Depth of Interaction and Coincidence Time Resolution Characterization of Ultrahigh Resolution Time-of-Flight Prism-PET Modules. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2022. [DOI: 10.1109/trpms.2021.3110902] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Xinjie Cao
- Department of Eletrical and Computer Engineering, Stony Brook University, Stony Brook, NY, USA
| | - Andy Labella
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY, USA
| | - Xinjie Zeng
- Department of Eletrical and Computer Engineering, Stony Brook University, Stony Brook, NY, USA
| | - Wei Zhao
- Department of Radiology, Stony Brook University, Stony Brook, NY, USA
| | - Amir H. Goldan
- Department of Radiology, Stony Brook University, Stony Brook, NY, USA
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6
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Kang HG, Tashima H, Nishikido F, Akamatsu G, Wakizaka H, Higuchi M, Yamaya T. Initial results of a mouse brain PET insert with a staggered 3-layer DOI detector. Phys Med Biol 2021; 66. [PMID: 34666328 DOI: 10.1088/1361-6560/ac311c] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 10/19/2021] [Indexed: 11/11/2022]
Abstract
Objective.Small animal positron emission tomography (PET) requires a submillimeter resolution for better quantification of radiopharmaceuticals. On the other hand, depth-of-interaction (DOI) information is essential to preserve the spatial resolution while maintaining the sensitivity. Recently, we developed a staggered 3-layer DOI detector with 1 mm crystal pitch and 15 mm total crystal thickness, but we did not demonstrate the imaging performance of the DOI detector with full ring geometry. In this study we present initial imaging results obtained for a mouse brain PET prototype developed with the staggered 3-layer DOI detector.Approach.The prototype had 53 mm inner diameter and 11 mm axial field-of-view. The PET scanner consisted of 16 DOI detectors each of which had a staggered 3-layer LYSO crystal array (4/4/7 mm) coupled to a 4 × 4 silicon photomultiplier array. The physical performance was evaluated in terms of the NEMA NU 4 2008 protocol.Main Results.The measured spatial resolutions at the center and 15 mm radial offset were 0.67 mm and 1.56 mm for filtered-back-projection, respectively. The peak absolute sensitivity of 0.74% was obtained with an energy window of 400-600 keV. The resolution phantom imaging results show the clear identification of a submillimetric rod pattern with the ordered-subset expectation maximization algorithm. The inter-crystal scatter rejection using a narrow energy window could enhance the resolvability of a 0.75 mm rod significantly.Significance.In an animal imaging experiment, the detailed mouse brain structures such as cortex and thalamus were clearly identified with high contrast. In conclusion, we successfully developed the mouse brain PET insert prototype with a staggered 3-layer DOI detector.
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Affiliation(s)
- Han Gyu Kang
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Hideaki Tashima
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Fumihiko Nishikido
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Go Akamatsu
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Hidekazu Wakizaka
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Makoto Higuchi
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Taiga Yamaya
- National Institutes for Quantum Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan
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7
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Lee S, Lee JS. Inter-crystal scattering recovery of light-sharing PET detectors using convolutional neural networks. Phys Med Biol 2021; 66. [PMID: 34438380 DOI: 10.1088/1361-6560/ac215d] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 08/26/2021] [Indexed: 11/12/2022]
Abstract
Inter-crystal scattering (ICS) is a type of Compton scattering of photons from one crystal to adjacent crystals and causes inaccurate assignment of the annihilation photon interaction position in positron emission tomography (PET). Because ICS frequently occurs in highly light-shared PET detectors, its recovery is crucial for the spatial resolution improvement. In this study, we propose two different convolutional neural networks (CNNs) for ICS recovery, exploiting the good pattern recognition ability of CNN techniques. Using the signal distribution of a photosensor array as input, one network estimates the energy deposition in each crystal (ICS-eNet) and another network chooses the first-interacted crystal (ICS-cNet). We performed GATE Monte Carlo simulations with optical photon tracking to test PET detectors comprising different crystal arrays (8 × 8 to 21 × 21) with lengths of 20 mm and the same photosensor array (3 mm 8 × 8 array) covering an area of 25.8 × 25.8 mm2. For each detector design, we trained ICS-eNet and ICS-cNet and evaluated their respective performance. ICS-eNet accurately identified whether the events were ICS (accuracy > 90%) and selected interacted crystals (accuracy > 60%) with appropriate energy estimation performance (R2 > 0.7) in the 8 × 8, 12 × 12, and 16 × 16 arrays. ICS-cNet also exhibited satisfactory performance, which was less dependent on the crystal-to-sensor ratio, with an accuracy enhancement that exceeds 10% in selecting the first-interacted crystal and a reduction in error distances compared when no recovery was applied. Both ICS-eNet and ICS-cNet exhibited consistent performances under various optical property settings of the crystals. For spatial resolution measurements in PET rings, both networks achieved significant enhancements particularly for highly pixelated arrays. We also discuss approaches for training the networks in an actual experimental setup. This proof-of-concept study demonstrated the feasibility of CNNs for ICS recovery in various light-sharing designs to efficiently improve the spatial resolution of PET in various applications.
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Affiliation(s)
- Seungeun Lee
- Department of Nuclear Medicine, Seoul National University, Seoul, 03080, Republic of Korea.,Department of Biomedical Sciences, Seoul National University, Seoul, 03080, Republic of Korea
| | - Jae Sung Lee
- Department of Nuclear Medicine, Seoul National University, Seoul, 03080, Republic of Korea.,Brightonix Imaging Inc., Seoul, 04782, Republic of Korea
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Yoshida E, Obata F, Kamada K, Yamaya T. A Crosshair Light Sharing PET Detector With DOI and TOF Capabilities Using Four-to-One Coupling and Single-Ended Readout. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2021. [DOI: 10.1109/trpms.2020.3032466] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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9
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Wassermann C, Mueller F, Dey T, Lambertus J, Schug D, Schulz V, Miller J. High throughput software-based gradient tree boosting positioning for PET systems. Biomed Phys Eng Express 2021; 7. [PMID: 34229316 DOI: 10.1088/2057-1976/ac11c0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 07/06/2021] [Indexed: 11/12/2022]
Abstract
The supervised machine learning technique Gradient Tree Boosting (GTB) has shown good accuracy for position estimation of gamma interaction in PET crystals for bench-top experiments while its computational requirements can easily be adjusted. Transitioning to preclinical and clinical applications requires near real-time processing in the scale of full PET systems. In this work, a high throughput GTB-based singles positioning C++ implementation is proposed and a series of optimizations are evaluated regarding their effect on the achievable processing throughput. Moreover, the crucial feature and parameter selection for GTB is investigated for the segmented detectors of the Hyperion IIDPET insert with two main models and a range of GTB hyperparameters. The proposed framework achieves singles positioning throughputs of more than 9.5 GB/s for smaller models and of 240 MB/s for more complex models on a recent Intel Skylake server. Detailed throughput analysis reveals the key performance limiting factors, and an empirical throughput model is derived to guide the GTB model selection process and scanner design decisions. The throughput model allows for throughput estimations with a mean absolute error (MAE) of 175.78 MB/s.
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Affiliation(s)
- Christian Wassermann
- High Performance Computing Group, Computational Science and Engineering Division, IT Center, RWTH Aachen University, 52074 Aachen, Germany
| | - Florian Mueller
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, 52074 Aachen, Germany
| | - Thomas Dey
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, 52074 Aachen, Germany.,Faculty 05 Electrical Engineering and Information Technology, FH Aachen University of Applied Sciences, 52074 Aachen, Germany
| | - Janko Lambertus
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, 52074 Aachen, Germany
| | - David Schug
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, 52074 Aachen, Germany.,Hyperion Hybrid Imaging Systems GmbH, 52074 Aachen, Germany
| | - Volkmar Schulz
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, 52074 Aachen, Germany.,Hyperion Hybrid Imaging Systems GmbH, 52074 Aachen, Germany.,Physics Institute III B, RWTH Aachen University, 52074 Aachen, Germany.,Fraunhofer Institute for Digital Medicine MEVIS, 52074 Aachen, Germany
| | - Julian Miller
- High Performance Computing Group, Computational Science and Engineering Division, IT Center, RWTH Aachen University, 52074 Aachen, Germany
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Zhang X, Yu H, Xie Q, Xie S, Ye B, Guo M, Zhao Z, Huang Q, Xu J, Peng Q. Design study of a PET detector with 0.5 mm crystal pitch for high-resolution preclinical imaging. Phys Med Biol 2021; 66. [PMID: 34130263 DOI: 10.1088/1361-6560/ac0b82] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 06/15/2021] [Indexed: 11/12/2022]
Abstract
Preclinical positron emission tomography (PET) is a sensitive and quantitative molecule imaging modality widely used in characterizing the biological processes and diseases in small animals. The purpose of this study is to investigate the methods to optimize a PET detector for high-resolution preclinical imaging. The PET detector proposed in this study consists of a 28 × 28 array of LYSO crystals 0.5 × 0.5 × 6.25 mm3in size, a wedged lightguide, and a 6 × 6 array of SiPMs 3 × 3 mm2in size. The simulation results showed that the most uniform flood map was achieved when the thickness of the lightguide was 2.35 mm. The quality of the flood map was significantly improved by suppressing the electronics noises using the simple threshold method with a best threshold. The peak-to-valley ratio of flood map improved 25.4% when the algorithm of ICS rejection was applied. An energy resolution (12.96% ± 1.03%) was measured on the prototype scanner constructed with 12 proposed detectors. Lastly, a prototype preclinic PET imager was constructed with 12 optimized detectors. The point source experiment was performed and an excellent spatial resolution (axial: 0.56 mm, tangential: 0.46 mm, radial: 0.42 mm) was achieved with the proposed high-performance PET detectors.
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Affiliation(s)
- Xi Zhang
- School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074, Wuhan, People's Republic of China
| | - Hongsen Yu
- School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074, Wuhan, People's Republic of China
| | - Qiangqiang Xie
- School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074, Wuhan, People's Republic of China
| | - Siwei Xie
- Institute of Biomedical Engineering Shenzhen Bay Laboratory, Shenzhen, 518132, People's Republic of China
| | - Baihezi Ye
- School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074, Wuhan, People's Republic of China
| | - Minghao Guo
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, 200240, Shanghai, People's Republic of China
| | - Zhixiang Zhao
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, 200240, Shanghai, People's Republic of China
| | - Qiu Huang
- School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, 200240, Shanghai, People's Republic of China
| | - Jianfeng Xu
- School of Mechanical Science and Engineering, Huazhong University of Science and Technology, 430074, Wuhan, People's Republic of China
| | - Qiyu Peng
- Institute of Biomedical Engineering Shenzhen Bay Laboratory, Shenzhen, 518132, People's Republic of China
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11
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Kang HG, Nishikido F, Yamaya T. A staggered 3-layer DOI PET detector using BaSO4 reflector for enhanced crystal identification and inter-crystal scattering event discrimination capability. Biomed Phys Eng Express 2021; 7. [DOI: 10.1088/2057-1976/abf6a8] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 04/09/2021] [Indexed: 01/22/2023]
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12
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Prout DL, Gu Z, Shustef M, Chatziioannou AF. A digital phoswich detector using time-over-threshold for depth of interaction in PET. Phys Med Biol 2020; 65:245017. [PMID: 33202397 PMCID: PMC8382115 DOI: 10.1088/1361-6560/abcb21] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
We present the performance of a digital phoswich positron emission tomography (PET) detector, composed by layers of pixilated scintillator arrays, read out by solid state light detectors and an application specific integrated circuit (ASIC). We investigated the use of integrated charge from the scintillation pulses along with time-over-threshold (ToT) to determine the layer of interaction (DOI) in the scintillator. Simulations were performed to assess the effectiveness of the ToT measurements for separating the scintillator events and identifying cross-layer-crystal-scatter (CLCS) events. These simulations indicate that ToT and charge integration from such a detector provide sufficient information to determine the layer of interaction. To demonstrate this in practice, we used a pair of prototype LYSO/BGO detectors. One detector consisted of a 19 × 19 array of 7 mm long LYSO crystals (1.36 mm pitch) coupled to a 16 × 16 array of 8 mm long BGO crystals (1.63 mm pitch). The other detector was similar except the LYSO crystal pitch was 1.63 mm. These detectors were coupled to an 8 × 8 multi-pixel photon counter mounted on a PETsys TOFPET2 ASIC. This high performance ASIC provided digital readout of the integrated charge and ToT from these detectors. We present a method to separate the events from the two scintillator layers using the ToT, and also investigate the performance of this detector. All the crystals within the proposed detector were clearly resolved, and the peak to valley ratio was 11.8 ± 4.0 and 10.1 ± 2.9 for the LYSO and BGO flood images. The measured energy resolution was 9.9% ± 1.3% and 28.5% ± 5.0% respectively for the LYSO and BGO crystals in the phoswich layers. The timing resolution between the LYSO-LYSO, LYSO-BGO and BGO-BGO coincidences was 468 ps, 1.33 ns and 2.14 ns respectively. Results show ToT can be used to identify the crystal layer where events occurred and also identify and reject the majority of CLCS events between layers.
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Affiliation(s)
- David L Prout
- Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, CA, United States of America
- Shared first authorship
| | - Zheng Gu
- Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, CA, United States of America
- Institute of Biomedical Engineering, Shenzhen Bay Laboratory, Shenzhen, Guangdong Province, People's Republic of China
- Shared first authorship
| | - Max Shustef
- Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, CA, United States of America
| | - Arion F Chatziioannou
- Crump Institute for Molecular Imaging, David Geffen School of Medicine, University of California, Los Angeles, CA, United States of America
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13
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Park H, Lee JS. SiPM signal readout for inter-crystal scatter event identification in PET detectors. Phys Med Biol 2020; 65:205010. [PMID: 32702670 DOI: 10.1088/1361-6560/aba8b4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In positron emission tomography (PET) with pixelated detectors, a significant number of annihilation photons interact with scintillation crystals through single or multiple Compton scattering events. When these partial energy depositions occur across multiple crystal elements, we call them inter-crystal scatter (ICS) events. ICS events lead to incorrect localization of the annihilation photons, thereby degrading the PET image contrast, spatial resolution, and lesion detectability. The accurate identification of ICS events is the first essential step to improve the quality of PET images by rejecting ICS events or recovering ICS events without losing PET sensitivity. In this study, we propose a novel silicon photomultiplier (SiPM) readout method to identify ICS events in one-to-one coupled PET detectors with a reduced number of data acquisition channels. For concept verification, we assembled a PET detector that consists of a 16-channel SiPM array and 4 [Formula: see text] 4 lutetium oxyorthosilicate (LSO) array with a 3.2 mm crystal pitch. The proposed SiPM readout scheme serializes the 16 SiPM anode signals into four pulse train outputs encoded with four increasing time-delays in steps of 250 ns intervals. A Sum signal of the 16 SiPM anodes provides the timing information for time-of-flight measurement and a trigger signal for coincidence detection. A time-over-threshold (TOT) method was applied for obtaining the energy information followed by a subsequent TOT-to-energy calibration. We successfully identified the ICS events and determined their interacted positions and deposited energies by analyzing the digital pulses from the four pulse train output channels. The occurrence rate of ICS events was 10.85% for the 4 × 4 PET detector module with 3.2 mm-pitch LSO crystals. The PET detector yielded an energy resolution of 10.9 [Formula: see text] 0.6% and coincidence timing resolution of 285 [Formula: see text] 12 ps FWHM. We expect that the proposed method can be a useful solution for alleviating the readout burden of SiPM-based PET scanners with ICS event identification capability.
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Affiliation(s)
- Haewook Park
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Republic of Korea. Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul 03080, Republic of Korea
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14
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Hetzel R, Mueller F, Grahe J, Honne A, Schug D, Schulz V. Characterization and Simulation of an Adaptable Fan-Beam Collimator for Fast Calibration of Radiation Detectors for PET. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2020. [DOI: 10.1109/trpms.2020.2990651] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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15
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Ritzer C, Becker R, Buck A, Commichau V, Debus J, Djambazov L, Eleftheriou A, Fischer J, Fischer P, Ito M, Khateri P, Lustermann W, Ritzert M, Roser U, Rudin M, Sacco I, Tsoumpas C, Warnock G, Wyss M, Zagozdzinska-Bochenek A, Weber B, Dissertori G. Initial Characterization of the SAFIR Prototype PET-MR Scanner. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2020. [DOI: 10.1109/trpms.2020.2980072] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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16
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Yoshida E, Obata F, Kamada K, Yamaya T. Development of Single-Ended Readout DOI Detector With Quadrisected Crystals. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2020. [DOI: 10.1109/trpms.2020.2990788] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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17
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Xu H, Wang H, Xu F, Cheng R, Zhang B, Fang L, Xie Q, Xiao P. Neural-Network-Based Energy Calculation for Multivoltage Threshold Sampling. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2020. [DOI: 10.1109/trpms.2019.2960129] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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18
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Gu Z, Taschereau R, Vu NT, Prout DL, Lee J, Chatziioannou AF. Performance evaluation of HiPET, a high sensitivity and high resolution preclinical PET tomograph. ACTA ACUST UNITED AC 2020; 65:045009. [DOI: 10.1088/1361-6560/ab6b44] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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19
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Hsu DFC, Freese DL, Innes DR, Levin CS. Intercrystal scatter studies for a 1 mm 3 resolution clinical PET system prototype. Phys Med Biol 2019; 64:095024. [PMID: 30893659 DOI: 10.1088/1361-6560/ab115b] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Positron emission tomography (PET) systems designed with multiplexed readout do not usually have the capability to resolve individual intercrystal scatter (ICS) interactions, leading to interaction mispositioning that degrades spatial resolution and contrast. A 3D position sensitive scintillation detector capable of individual ICS readout has been designed and incorporated into a 1 mm3 resolution clinical PET system used for locoregional imaging. Incorporating ICS events increases photon sensitivity by 51.5% compared to using only photoelectric events. A Compton scatter angle error minimization algorithm is used to estimate the first ICS interaction location for accurate line-of-response pairing of coincident photons. An optimal scatter angle error threshold of 15 degrees is used to discard ICS events with a high mismatch between energy-derived and position-derived intercrystal scatter angles. Finally, positioning rather than rejecting ICS events boosts peak contrast to noise ratio by 8.1%, and allows for an equivalent dose reduction of 12% while maintaining equivalent image quality.
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Affiliation(s)
- D F C Hsu
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
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20
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Peng P, Judenhofer MS, Jones AQ, Cherry SR. Compton PET: A Simulation Study for a PET Module with Novel Geometry and Machine Learning for Position Decoding. Biomed Phys Eng Express 2018; 5. [PMID: 34290885 DOI: 10.1088/2057-1976/aaef03] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This paper describes a simulation study of a positron emission tomography (PET) detector module that can reconstruct the kinematics of Compton scattering within the scintillator. We used a layer structure, with which we could recover the positions and energies for the multiple interactions of a gamma ray in the different layers. Using the Compton scattering formalism, the sequence of interactions can be estimated. The true first interaction position extracted in the Compton scattering will help minimize the degradation of the reconstructed image resolution caused by intercrystal scatter events. Because of the layer structure, this module also has readily available user-defined resolution for the depth of interaction. The semi-monolithic crystals enable high light collection efficiency and an energy resolution of ~10% has been achieved in the simulation. We used machine learning to decode the gamma ray interaction locations, achieving an average spatial resolution of 0.40 mm. Our proposed detector design provides a pathway to increase the sensitivity of a system without affecting other key performance features.
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Affiliation(s)
- Peng Peng
- Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Martin S Judenhofer
- Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Adam Q Jones
- Department of Electrical and Computer Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
| | - Simon R Cherry
- Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
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21
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Hallen P, Schug D, Weissler B, Gebhardt P, Salomon A, Kiessling F, Schulz V. PET performance evaluation of the small-animal Hyperion II D PET/MRI insert based on the NEMA NU-4 standard. Biomed Phys Eng Express 2018; 4:065027. [PMID: 30675384 PMCID: PMC6329443 DOI: 10.1088/2057-1976/aae6c2] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 10/03/2018] [Accepted: 10/08/2018] [Indexed: 12/23/2022]
Abstract
The Hyperion IID PET insert is the first scanner using fully digital silicon photomultipliers for simultaneous PET/MR imaging of small animals up to rabbit size. In this work, we evaluate the PET performance based on the National Eletrical Manufacturers Association (NEMA) NU 4-2008 standard, whose standardized measurement protocols allow comparison of different small-animal PET scanners. The Hyperion IID small-animal PET/MR insert comprises three rings of 20 detector stacks with pixelated scintillator arrays with a crystal pitch of 1 mm, read out with digital silicon photomultipliers. The scanner has a large ring diameter of 209.6 mm and an axial field of view of 96.7 mm. We evaluated the spatial resolution, energy resolution, time resolution and sensitivity by scanning a 22Na point source. The count rates and scatter fractions were measured for a wide range of 18F activity inside a mouse-sized scatter phantom. We evaluated the image quality using the mouse-sized image quality phantom specified in the NEMA NU4 standard, filled with 18F. Additionally, we verified the in-vivo imaging capabilities by performing a simultaneous PET/MRI scan of a mouse injected with 18F-FDG. We processed all measurement data with an energy window of 250 keV to 625 keV and a coincidence time window of 2 ns. The filtered-backprojection reconstruction of the point source has a full width at half maximum (FWHM) of 1.7 mm near the isocenter and degrades to 2.5 mm at a radial distance of 50 mm. The scanner's average energy resolution is 12.7% (ΔE/E FWHM) and the coincidence resolution time is 609 ps. The peak absolute sensitivity is 4.0% and the true and noise-equivalent count rates reach their peak at an activity of 46 MBq with 483 kcps and 407 kcps, respectively, with a scatter fraction of 13%. The iterative reconstruction of the image quality phantom has a uniformity of 3.7%, and recovery coefficients from 0.29, 0.91 and 0.94 for rod diameters of 1 mm, 3 mm and 5 mm, respectively. After application of scatter and attenuation corrections, the air- and water-filled cold regions have spill-over ratios of 6.3% and 5.4%, respectively. The Hyperion IID PET/MR insert provides state-of-the-art PET performance while enabling simultaneous PET/MRI acquisition of small animals up to rabbit size.
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Affiliation(s)
- Patrick Hallen
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany.,
| | - David Schug
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Bjoern Weissler
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Pierre Gebhardt
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - André Salomon
- Department of Oncology Solutions, Philips Research, Eindhoven, Netherlands
| | - Fabian Kiessling
- Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany
| | - Volkmar Schulz
- Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany.,Department of Oncology Solutions, Philips Research, Eindhoven, Netherlands
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22
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Muller F, Schug D, Hallen P, Grahe J, Schulz V. Gradient Tree Boosting-Based Positioning Method for Monolithic Scintillator Crystals in Positron Emission Tomography. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2018. [DOI: 10.1109/trpms.2018.2837738] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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