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Taguchi K, Schaart DR, Goorden MC, Hsieh SS. Imaging performance of a LaBr 3:Ce scintillation detector for photon counting x-ray computed tomography: Simulation study. Med Phys 2024. [PMID: 39361516 DOI: 10.1002/mp.17436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Revised: 09/11/2024] [Accepted: 09/12/2024] [Indexed: 10/05/2024] Open
Abstract
BACKGROUND Photon counting detectors (PCDs) for x-ray computed tomography (CT) are the future of CT imaging. At present, semiconductor-based PCDs such as cadmium telluride (CdTe), cadmium zinc telluride, and silicon have been either used or investigated for clinical PCD CT. Unfortunately, all of them have the same major challenges, namely high cost and limited spectral signal-to-noise ratio (SNR). Recent studies showed that some high-quality scintillators, such as lanthanum bromide doped with cerium (LaBr3:Ce), are less expensive and almost as fast as CdTe. PURPOSE The objective of this study is to assess the performance of a LaBr3:Ce PCD for clinical x-ray CT. METHODS We performed Monte Carlo simulations and compared the performance of 3 mm thick LaBr3:Ce and 2 mm thick CdTe for PCD CT with x-rays at 120 kVp and 20-1000 mA. The two PCDs were operated with either a threshold-subtract (TS) counting scheme or a direct energy binning (DB) counting scheme. The performance was assessed in terms of the accuracy of registered spectra, counting capability, and count-rate-dependent spectral imaging-task performance, for conventional CT imaging, water-bone material decomposition, and K-edge imaging with tungsten as the K-edge material. The performance for these imaging-tasks was quantified by nCRLB, that is, the Cramér-Rao lower bound on the variance of basis line-integral estimation, normalized by the corresponding value of CdTe at 20 mA. RESULTS The spectrum recorded by CdTe was distorted significantly due to charge sharing, whereas the spectra recorded by LaBr3:Ce better matched the incident spectrum. The dead time, estimated by fitting a paralyzable detector model to the count-rate curves, was 20.7, 15.0, 37.2, and 13.0 ns for CdTe with TS, CdTe with DB, LaBr3:Ce with TS, and LaBr3:Ce with DB, respectively. Conventional CT imaging showed an adverse effect of reduced geometrical efficiency due to optical reflectors in LaBr3:Ce PCD. The nCRLBs (a lower value indicates a better SNR) for CdTe with TS, CdTe with DB, LaBr3:Ce with TS, LaBr3:Ce with DB, and the ideal PCD, were 1.00 ± 0.01, 1.00 ± 0.01, 1.18 ± 0.02, 1.18 ± 0.02, and 0.79 ± 0.01, respectively, at 20 mA. The nCRLBs for water-bone material decomposition, in the same order, were 1.00 ± 0.02, 1.00 ± 0.02, 0.85 ± 0.02, 0.85 ± 0.02, and 0.24 ± 0.02, respectively, at 20 mA; and 0.98 ± 0.02, 0.98 ± 0.02, 1.09 ± 0.02, 0.83 ± 0.02, and 0.24 ± 0.02, respectively, at 1000 mA. Finally, the nCRLBs for K-edge imaging, the most demanding task among the five, were 1.00 ± 0.02, 1.00 ± 0.02, 0.55 ± 0.02, 0.55 ± 0.02, and 0.13 ± 0.02, respectively, at 20 mA; and 2.45 ± 0.02, 2.29 ± 0.02, 3.12 ± 0.02, 2.11 ± 0.02, and 0.13 ± 0.02, respectively, at 1,000 mA. CONCLUSION The Monte Carlo simulations showed that, compared to CdTe with either TS or DB, LaBr3:Ce with DB provided more accurate spectra, comparable or better counting capability, and superior spectral imaging-task performances, that is, water-bone material decomposition and K-edge imaging. CdTe had a better performance than LaBr3:Ce for the conventional CT imaging task due to its higher geometrical efficiency. LaBr3:Ce PCD with DB scheme may be an excellent alternative option for CdTe PCD.
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Affiliation(s)
- Katsuyuki Taguchi
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Dennis R Schaart
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Marlies C Goorden
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Scott S Hsieh
- Department of Radiology, May Clinic, Rochester, Minnesota, USA
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Yoshida E, Yamaya T. PET detectors with depth-of-interaction and time-of-flight capabilities. Radiol Phys Technol 2024; 17:596-609. [PMID: 38888821 DOI: 10.1007/s12194-024-00821-x] [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: 05/07/2024] [Revised: 06/09/2024] [Accepted: 06/09/2024] [Indexed: 06/20/2024]
Abstract
In positron emission tomography (PET), measurements of depth-of-interaction (DOI) information and time-of-flight (TOF) information are important. DOI information reduces the parallax error, and TOF information reduces noise by measuring the arrival time difference of the annihilation photons. Historically, these have been studied independently, and there has been less implementation of both DOI and TOF capabilities because previous DOI detectors did not have good TOF resolution. However, recent improvements in PET detector performance have resulted in commercial PET scanners achieving a coincidence resolving time of around 200 ps, which result in an effect even for small objects. This means that TOF information can now be utilized even for a brain PET scanner, which also requires DOI information. Therefore, various methods have been proposed to obtain better DOI and TOF information. In addition, the cost of PET detectors is also an important factor to consider, since several hundred detectors are used per PET scanner. In this paper, we review the latest DOI-TOF detectors including the history of detector development. When put into practical use, these DOI-TOF detectors are expected to contribute to the improvement of imaging performance in brain PET scanners.
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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.
| | - Taiga Yamaya
- National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba, 263-8555, Japan
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Pullano SA, Oliva G, Titirsha T, Shuvo MMH, Islam SK, Laganà F, La Gatta A, Fiorillo AS. Design of an Electronic Interface for Single-Photon Avalanche Diodes. SENSORS (BASEL, SWITZERLAND) 2024; 24:5568. [PMID: 39275479 PMCID: PMC11398220 DOI: 10.3390/s24175568] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2024] [Revised: 08/26/2024] [Accepted: 08/27/2024] [Indexed: 09/16/2024]
Abstract
Single-photon avalanche diodes (SPADs) belong to a family of avalanche photodiodes (APDs) with single-photon detection capability that operate above the breakdown voltage (i.e., Geiger mode). Design and technology constraints, such as dark current, photon detection probability, and power dissipation, impose inherent device limitations on avalanche photodiodes. Moreover, after the detection of a photon, SPADs require dead time for avalanche quenching and recharge before they can detect another photon. The reduction in dead time results in higher efficiency for photon detection in high-frequency applications. In this work, an electronic interface, based on the pole-zero compensation technique for reducing dead time, was investigated. A nanosecond pulse generator was designed and fabricated to generate pulses of comparable voltage to an avalanche transistor. The quenching time constant (τq) is not affected by the compensation capacitance variation, while an increase of about 30% in the τq is related to the properties of the specific op-amp used in the design. Conversely, the recovery time was observed to be strongly influenced by the compensation capacitance. Reductions in the recovery time, from 927.3 ns down to 57.6 ns and 9.8 ns, were observed when varying the compensation capacitance in the range of 5-0.1 pF. The experimental results from an SPAD combined with an electronic interface based on an avalanche transistor are in strong accordance, providing similar output pulses to those of an illuminated SPAD.
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Affiliation(s)
- Salvatore A Pullano
- Department of Health Sciences, "Magna Graecia" University, 88100 Catanzaro, Italy
- Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO 65211, USA
| | - Giuseppe Oliva
- Department of Health Sciences, "Magna Graecia" University, 88100 Catanzaro, Italy
| | - Twisha Titirsha
- Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO 65211, USA
| | - Md Maruf Hossain Shuvo
- Department of Electrical and Computer Engineering, University of Texas at El Paso, El Paso, TX 79968, USA
| | - Syed Kamrul Islam
- Department of Electrical Engineering and Computer Science, University of Missouri, Columbia, MO 65211, USA
| | - Filippo Laganà
- Department of Health Sciences, "Magna Graecia" University, 88100 Catanzaro, Italy
| | - Antonio La Gatta
- Department of Health Sciences, "Magna Graecia" University, 88100 Catanzaro, Italy
| | - Antonino S Fiorillo
- Department of Health Sciences, "Magna Graecia" University, 88100 Catanzaro, Italy
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Villa I, Monguzzi A, Lorenzi R, Orfano M, Babin V, Hájek F, Kuldová K, Kučerková R, Beitlerová A, Mattei I, Buresova H, Pjatkan R, Čuba V, Prouzová Procházková L, Nikl M. On the Origin of the Light Yield Enhancement in Polymeric Composite Scintillators Loaded with Dense Nanoparticles. NANO LETTERS 2024; 24:8248-8256. [PMID: 38949190 DOI: 10.1021/acs.nanolett.4c00681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Fast emitting polymeric scintillators are requested in advanced applications where high speed detectors with a large signal-to-noise ratio are needed. However, their low density implies a weak stopping power of high energy radiation and thus a limited light output and sensitivity. To enhance their performance, polymeric scintillators can be loaded with dense nanoparticles (NPs). We investigate the properties of a series of polymeric scintillators by means of photoluminescence and scintillation spectroscopy, comparing standard scintillators with a composite system loaded with dense hafnium dioxide (HfO2) NPs. The nanocomposite shows a scintillation yield enhancement of +100% with an unchanged time response. We provide for the first time an interpretation of this effect, pointing out the local effect of NPs in the generation of emissive states upon interaction with ionizing radiation. The obtained results indicate that coupling fast conjugated emitters with optically inert dense NPs could lead to surpassing the actual limits of pure polymeric scintillators.
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Affiliation(s)
- Irene Villa
- Dipartimento di Scienza Dei Materiali, Università Degli Studi Milano-Bicocca, 20125 Milano, Italy
| | - Angelo Monguzzi
- Dipartimento di Scienza Dei Materiali, Università Degli Studi Milano-Bicocca, 20125 Milano, Italy
- NANOMIB, Center for Biomedical Nanomedicine, University of Milano-Bicocca, P.zza Ateneo Nuovo 1, 20126 Milan, Italy
| | - Roberto Lorenzi
- Dipartimento di Scienza Dei Materiali, Università Degli Studi Milano-Bicocca, 20125 Milano, Italy
| | - Matteo Orfano
- Dipartimento di Scienza Dei Materiali, Università Degli Studi Milano-Bicocca, 20125 Milano, Italy
| | - Vladimir Babin
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
| | - František Hájek
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
| | - Karla Kuldová
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
| | - Romana Kučerková
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
| | - Alena Beitlerová
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
| | - Ilaria Mattei
- INFN Sezione di Milano, via G. Celoria 16, 20133 Milan, Italy
| | - Hana Buresova
- NUVIA a.s., Trojanova 117, 278 01 Kralupy nad Vltavou, Czech Republic
| | - Radek Pjatkan
- NUVIA a.s., Trojanova 117, 278 01 Kralupy nad Vltavou, Czech Republic
| | - Václav Čuba
- Faculty of Nuclear Sciences and Physical Engineering CTU in Prague, 115 19 Praha, Czech Republic
| | - Lenka Prouzová Procházková
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
- Faculty of Nuclear Sciences and Physical Engineering CTU in Prague, 115 19 Praha, Czech Republic
| | - Martin Nikl
- FZU-Institute of Physics of the Czech Academy of Sciences, Cukrovarnická 10/112, 16 200 Prague, Czech Republic
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Yoshida E, Obata F, Yamaya T. Optical crosstalk of protective cover on MPPC array for TOF PET detector. Phys Med Biol 2024; 69:125012. [PMID: 38815615 DOI: 10.1088/1361-6560/ad5268] [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: 03/18/2024] [Accepted: 05/30/2024] [Indexed: 06/01/2024]
Abstract
Objective. Time-of-flight (TOF) is an important factor that directly affects the image quality of PET systems, and various attempts have been made to improve the coincidence resolving time (CRT) of PET detectors. For independent readout detectors, the timing is acquired for each silicon photomultiplier (SiPM), so they are less sensitive to diffused scintillation light, resulting in a better CRT. Further improvement can be expected if the light can be focused on a single SiPM. However, existing SiPM arrays have a thin protective cover on the SiPM and the gap between the SiPMs is filled with either air or the protective cover, so the light must diffuse through the cover. In this work, we investigated optical crosstalk in the protective cover to improve the CRT.Approach. We used 3.1 × 3.1 × 20 mm3fast LGSO crystals and 3 mm square 8 × 8 multi pixel photon counter (MPPC) arrays. Pitch of the MPPCs was 3.2 mm and thickness of the protective cover on them was 150μm. To reduce diffusion of scintillation light in the protective cover, the part of the inactive areas on the MPPC array were optically separated using reflective material. Specifically, 50, 100, 150, and 350μm deep grid-shaped slits were made along the inactive area of the MPPCs and they were filled with BaSO4powder as the reflective material.Main results. Coincidence counts were measured with a pair of TOF detectors, and the CRT was shorter with a deeper slit depth. The CRT before improvement was 235 ps, and using the cover having the 350μm deep slits filled with reflective material lowered the CRT to 211 ps.Significance. Up to 10% of the scintillation light was diffused to other MPPCs by the protective cover, and the CRT was degraded by 10% due to optical crosstalk of the cover. The proposed method promises to improve the CRT of the TOF detector.
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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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Ye W, Yong Z, Go M, Kowal D, Maddalena F, Tjahjana L, Wang H, Arramel A, Dujardin C, Birowosuto MD, Wong LJ. The Nanoplasmonic Purcell Effect in Ultrafast and High-Light-Yield Perovskite Scintillators. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2309410. [PMID: 38235521 DOI: 10.1002/adma.202309410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 01/14/2024] [Indexed: 01/19/2024]
Abstract
The development of X-ray scintillators with ultrahigh light yields and ultrafast response times is a long sought-after goal. In this work, a fundamental mechanism that pushes the frontiers of ultrafast X-ray scintillator performance is theoretically predicted and experimentally demonstrated: the use of nanoscale-confined surface plasmon polariton modes to tailor the scintillator response time via the Purcell effect. By incorporating nanoplasmonic materials in scintillator devices, this work predicts over tenfold enhancement in decay rate and 38% reduction in time resolution even with only a simple planar design. The nanoplasmonic Purcell effect is experimentally demonstrated using perovskite scintillators, enhancing the light yield by over 120% to 88 ± 11 ph/keV, and the decay rate by over 60% to 2.0 ± 0.2 ns for the average decay time, and 0.7 ± 0.1 ns for the ultrafast decay component, in good agreement with the predictions of our theoretical framework. Proof-of-concept X-ray imaging experiments are performed using nanoplasmonic scintillators, demonstrating 182% enhancement in the modulation transfer function at four line pairs per millimeter spatial frequency. This work highlights the enormous potential of nanoplasmonics in optimizing ultrafast scintillator devices for applications including time-of-flight X-ray imaging and photon-counting computed tomography.
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Affiliation(s)
- Wenzheng Ye
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Zhihua Yong
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Michael Go
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Dominik Kowal
- Łukasiewicz Research Network-PORT Polish Center for Technology Development, Stabłowicka 147, 54-066, Wrocław, Poland
| | - Francesco Maddalena
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Liliana Tjahjana
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Hong Wang
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
| | - Arramel Arramel
- Nano Center Indonesia, Jalan Raya PUSPIPTEK, South Tangerang, Banten, 15314, Indonesia
| | - Christophe Dujardin
- Universite Claude Bernard Lyon 1, Institut Lumière Matière, UMR 5306 CNRS, Villeurbanne, F-69622, France
- Institut Universitaire de France, 1 Rue Descartes, Paris, Île-de-France, 75005, Paris, France
| | - Muhammad Danang Birowosuto
- Łukasiewicz Research Network-PORT Polish Center for Technology Development, Stabłowicka 147, 54-066, Wrocław, Poland
| | - Liang Jie Wong
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore
- CINTRA (CNRS-International-NTU-THALES Research Alliance), IRL 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6, Singapore, 637553, Singapore
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Carr Delgado H, Moradifar P, Chinn G, Levin CS, Dionne JA. Toward "super-scintillation" with nanomaterials and nanophotonics. NANOPHOTONICS 2024; 13:1953-1962. [PMID: 38745841 PMCID: PMC11090085 DOI: 10.1515/nanoph-2023-0946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2023] [Accepted: 03/18/2024] [Indexed: 05/16/2024]
Abstract
Following the discovery of X-rays, scintillators are commonly used as high-energy radiation sensors in diagnostic medical imaging, high-energy physics, astrophysics, environmental radiation monitoring, and security inspections. Conventional scintillators face intrinsic limitations including a low extraction efficiency of scintillated light and a low emission rate, leading to efficiencies that are less than 10 % for commercial scintillators. Overcoming these limitations will require new materials including scintillating nanomaterials ("nanoscintillators"), as well as new photonic approaches that increase the efficiency of the scintillation process, increase the emission rate of materials, and control the directivity of the scintillated light. In this perspective, we describe emerging nanoscintillating materials and three nanophotonic platforms: (i) plasmonic nanoresonators, (ii) photonic crystals, and (iii) high-Q metasurfaces that could enable high performance scintillators. We further discuss how a combination of nanoscintillators and photonic structures can yield a "super scintillator" enabling ultimate spatio-temporal resolution while enabling a significant boost in the extracted scintillation emission.
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Affiliation(s)
- Hamish Carr Delgado
- Department of Materials Science and Engineering, Stanford University, Stanford, CA94305, USA
| | - Parivash Moradifar
- Department of Materials Science and Engineering, Stanford University, Stanford, CA94305, USA
| | - Garry Chinn
- Department of Radiology, Stanford University, Stanford, CA, 94305, USA
| | - Craig S. Levin
- Department of Radiology, Stanford University, Stanford, CA, 94305, USA
| | - Jennifer A. Dionne
- Department of Materials Science and Engineering, Stanford University, Stanford, CA94305, USA
- Department of Radiology, Stanford University, Stanford, CA, 94305, USA
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Chen M, Gerges M, Raynor WY, Park PSU, Nguyen E, Chan DH, Gholamrezanezhad A. State of the Art Imaging of Osteoporosis. Semin Nucl Med 2024; 54:415-426. [PMID: 38087745 DOI: 10.1053/j.semnuclmed.2023.10.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 10/24/2023] [Accepted: 10/24/2023] [Indexed: 05/18/2024]
Abstract
Osteoporosis is a common disease, particularly prevalent in geriatric populations, which causes significant worldwide morbidity due to increased bone fragility and fracture risk. Currently, the gold-standard modality for diagnosis and evaluation of osteoporosis progression and treatment relies on dual-energy x-ray absorptiometry (DXA), which measures bone mineral density (BMD) and calculates a score based upon standard deviation of measured BMD from the mean. However, other imaging modalities can also be used to evaluate osteoporosis. Here, we review historical as well as current research into development of new imaging modalities that can provide more nuanced or opportunistic analyses of bone quality, turnover, and density that can be helpful in triaging severity and determining treatment success in osteoporosis. We discuss the use of opportunistic computed tomography (CT) scans, as well as the use of quantitative CT to help determine fracture risk and perform more detailed bone quality analysis than would be allowed by DXA . Within magnetic resonance imaging (MRI), new developments include the use of advanced MRI techniques such as quantitative susceptibility mapping (QSM), magnetic resonance spectroscopy, and chemical shift encoding-based water-fat MRI (CSE-MRI) to enable clinicians improved assessment of nonmineralized bone compartments as well as a way to longitudinally assess bone quality without the repeated exposure to ionizing radiation. Within ultrasound, development of quantitative ultrasound shows promise particularly in future low-cost, broadly available screening tools. We focus primarily on historical and recent developments within radiotracer use as applicable to osteoporosis, particularly in the use of hybrid methods such as NaF-PET/CT, wherein patients with osteoporosis show reduced uptake of radiotracers such as NaF. Use of radiotracers may provide clinicians with even earlier detection windows for osteoporosis than would traditional biomarkers. Given the metabolic nature of this disease, current investigation into the role molecular imaging can play in the prediction of this disease as well as in replacing invasive diagnostic procedures shows particular promise.
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Affiliation(s)
- Michelle Chen
- Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA
| | - Maria Gerges
- Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA; Charles E. Schmidt College of Medicine, Florida Atlantic University, Boca Raton, FL
| | - William Y Raynor
- Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA; Department of Radiology, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ
| | - Peter Sang Uk Park
- Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA; Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA
| | - Edward Nguyen
- Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA
| | - David H Chan
- Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA
| | - Ali Gholamrezanezhad
- Department of Radiology, Keck School of Medicine, University of Southern California, Los Angeles, CA.
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El Ouaridi A, Ait Elcadi Z, Mkimel M, Bougteb M, El Baydaoui R. The detection instrumentation and geometric design of clinical PET scanner: towards better performance and broader clinical applications. Biomed Phys Eng Express 2024; 10:032002. [PMID: 38412520 DOI: 10.1088/2057-1976/ad2d61] [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: 11/03/2023] [Accepted: 02/27/2024] [Indexed: 02/29/2024]
Abstract
Positron emission tomography (PET) is a powerful medical imaging modality used in nuclear medicine to diagnose and monitor various clinical diseases in patients. It is more sensitive and produces a highly quantitative mapping of the three-dimensional biodistribution of positron-emitting radiotracers inside the human body. The underlying technology is constantly evolving, and recent advances in detection instrumentation and PET scanner design have significantly improved the medical diagnosis capabilities of this imaging modality, making it more efficient and opening the way to broader, innovative, and promising clinical applications. Some significant achievements related to detection instrumentation include introducing new scintillators and photodetectors as well as developing innovative detector designs and coupling configurations. Other advances in scanner design include moving towards a cylindrical geometry, 3D acquisition mode, and the trend towards a wider axial field of view and a shorter diameter. Further research on PET camera instrumentation and design will be required to advance this technology by improving its performance and extending its clinical applications while optimising radiation dose, image acquisition time, and manufacturing cost. This article comprehensively reviews the various parameters of detection instrumentation and PET system design. Firstly, an overview of the historical innovation of the PET system has been presented, focusing on instrumental technology. Secondly, we have characterised the main performance parameters of current clinical PET and detailed recent instrumental innovations and trends that affect these performances and clinical practice. Finally, prospects for this medical imaging modality are presented and discussed. This overview of the PET system's instrumental parameters enables us to draw solid conclusions on achieving the best possible performance for the different needs of different clinical applications.
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Affiliation(s)
- Abdallah El Ouaridi
- Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Health Sciences and Technologies, Settat, Morocco
| | - Zakaria Ait Elcadi
- Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Health Sciences and Technologies, Settat, Morocco
- Electrical and Computer Engineering, Texas A&M University at Qatar, Doha, 23874, Qatar
| | - Mounir Mkimel
- Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Health Sciences and Technologies, Settat, Morocco
| | - Mustapha Bougteb
- Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Health Sciences and Technologies, Settat, Morocco
| | - Redouane El Baydaoui
- Hassan First University of Settat, High Institute of Health Sciences, Laboratory of Health Sciences and Technologies, Settat, Morocco
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Krishnamoorthy S, Surti S. Advances in Breast PET Instrumentation. PET Clin 2024; 19:37-47. [PMID: 37949606 DOI: 10.1016/j.cpet.2023.09.001] [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] [Indexed: 11/12/2023]
Abstract
Dedicated breast PET scanners currently have a spatial resolution in the 1.5 to 2 mm range, and the ability to provide tomographic images and quantitative data. They are also commercially available from a few vendors. A review of past and recent advances in the development and performance of dedicated breast PET scanners is summarized.
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Affiliation(s)
- Srilalan Krishnamoorthy
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA.
| | - Suleman Surti
- Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA
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11
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Nuyts J, Defrise M, Morel C, Lecoq P. The SNR of time-of-flight positron emission tomography data for joint reconstruction of the activity and attenuation images. Phys Med Biol 2023; 69:10.1088/1361-6560/ad078c. [PMID: 37890469 PMCID: PMC10811362 DOI: 10.1088/1361-6560/ad078c] [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: 08/01/2023] [Accepted: 10/27/2023] [Indexed: 10/29/2023]
Abstract
Objective.Measurement of the time-of-flight (TOF) difference of each coincident pair of photons increases the effective sensitivity of positron emission tomography (PET). Many authors have analyzed the benefit of TOF for quantification and hot spot detection in the reconstructed activity images. However, TOF not only improves the effective sensitivity, it also enables the joint reconstruction of the tracer concentration and attenuation images. This can be used to correct for errors in CT- or MR-derived attenuation maps, or to apply attenuation correction without the help of a second modality. This paper presents an analysis of the effect of TOF on the variance of the jointly reconstructed attenuation and (attenuation corrected) tracer concentration images.Approach.The analysis is performed for PET systems that have a distribution of possibly non-Gaussian TOF-kernels, and includes the conventional Gaussian TOF-kernel as a special case. Non-Gaussian TOF-kernels are often observed in novel detector designs, which make use of two (or more) different mechanisms to convert the incoming 511 keV photon to optical photons. The analytical result is validated with a simple 2D simulation.Main results.We show that if two different TOF-kernels are equivalent for image reconstruction with known attenuation, then they are also equivalent for joint reconstruction of the activity and the attenuation images. The variance increase in the activity, caused by also jointly reconstructing the attenuation image, vanishes when the TOF-resolution approaches perfection.Significance.These results are of interest for PET detector development and for the development of stand-alone PET systems.
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Affiliation(s)
- Johan Nuyts
- KU Leuven, University of Leuven, Department of Imaging and Pathology, Nuclear Medicine & Molecular imaging; Medical Imaging Research Center (MIRC), B-3000, Leuven, Belgium
| | - Michel Defrise
- Department of Nuclear Medicine, Vrije Universiteit Brussel, B-1090, Brussels, Belgium
| | | | - Paul Lecoq
- Polytechnic University of Valencia, Spain
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12
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Nadig V, Hornisch M, Oehm J, Herweg K, Schulz V, Gundacker S. 16-channel SiPM high-frequency readout with time-over-threshold discrimination for ultrafast time-of-flight applications. EJNMMI Phys 2023; 10:76. [PMID: 38044383 PMCID: PMC10694125 DOI: 10.1186/s40658-023-00594-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 11/20/2023] [Indexed: 12/05/2023] Open
Abstract
BACKGROUND Over the past five years, ultrafast high-frequency (HF) readout concepts have advanced the timing performance of silicon photomultipliers (SiPMs). The shown impact in time-of-flight (TOF) techniques can further push the limits in light detection and ranging (LiDAR), time-of-flight positron-emission tomography (TOF-PET), time-of-flight computed tomography (TOF-CT) or high-energy physics (HEP). However, upscaling these electronics to a system-applicable, multi-channel readout, has remained a challenging task, posed by the use of discrete components and a high power consumption. To this day, there are no means to exploit the high TOF resolution of these electronics on system scale or to measure the actual timing performance limits of a full detector block. METHODS In this work, we present a 16-channel HF readout board, including leading-edge discrimination and a linearized time-over-threshold (TOT) method, which is fully compatible with a high-precision time-to-digital converters (TDCs), such as the picoTDC developed at CERN. The discrete implementation allows ideal adaptation of this readout to a broad range of detection tasks. As a first step, the functionality of the circuit has been tested using the TOFPET2 ASIC as back-end electronics to emulate the TDC, also in view of its properties as a highly scalable data acquisition solution. RESULTS The produced board is able to mitigate influences of baseline shifts in the TOFPET2 front end, which has been shown in experiments with a pulsed laser, increasing the achievable intrinsic coincidence timing resolution (CTR) of the TOFPET2 readout electronics from 70 ps (FWHM) to 62 ps (FWHM). Single-channel coincidence experiments including a [Formula: see text]-source, 2[Formula: see text]2[Formula: see text]3 mm[Formula: see text] LYSO:Ce,Ca crystals and Broadcom NUV-MT SiPMs resulted in a CTR of 118 ps (FWHM). For a 4[Formula: see text]4 matrix of 3.88[Formula: see text]3.88[Formula: see text]19 mm[Formula: see text] LYSO:Ce,Ca crystals one-to-one coupled to a 4[Formula: see text]4 array of Broadcom NUV-MT SiPMs, an average CTR of 223 ps (FWHM) was obtained. CONCLUSION The implemented 16-channel HF electronics are fully functionall and have a negligible influence on the timing performance of the back-end electronics used, here the TOFPET2 ASIC. The ongoing integration of the picoTDC with the 16-channel HF board is expected to further set the path toward sub-100 ps TOF-PET and sub-30ps TOF resolution for single-photon detection.
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Affiliation(s)
- Vanessa Nadig
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany
| | - Matthias Hornisch
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany
| | - Jakob Oehm
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany
| | - Katrin Herweg
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany
| | - Volkmar Schulz
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany
- Hyperion Hybrid Imaging Systems GmbH, Pauwelsstraße 19, 52074, Aachen, Germany
- III. Physikalisches Institut B, RWTH Aachen University, Otto-Blumenthal-Straße, 52074, Aachen, Germany
- Fraunhofer Institute for Digital Medicine MEVIS, Forckenbeckstraße 55, 52074, Aachen, Germany
| | - Stefan Gundacker
- Department of Physics of Molecular Imaging Systems, Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstraße 55, 52074, Aachen, Germany.
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Acconcia G, Ceccarelli F, Gulinatti A, Rech I. Timing measurements with silicon single photon avalanche diodes: principles and perspectives [Invited]. OPTICS EXPRESS 2023; 31:33963-33999. [PMID: 37859164 DOI: 10.1364/oe.491400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 09/10/2023] [Indexed: 10/21/2023]
Abstract
Picosecond timing of single photons has laid the foundation of a great variety of applications, from life sciences to quantum communication, thanks to the combination of ultimate sensitivity with a bandwidth that cannot be reached by analog recording techniques. Nowadays, more and more applications could still be enabled or advanced by progress in the available instrumentation, resulting in a steadily increasing research interest in this field. In this scenario, single-photon avalanche diodes (SPADs) have gained a key position, thanks to the remarkable precision they are able to provide, along with other key advantages like ruggedness, compactness, large signal amplitude, and room temperature operation, which neatly distinguish them from other solutions like superconducting nanowire single-photon detectors and silicon photomultipliers. With this work, we aim at filling a gap in the literature by providing a thorough discussion of the main design rules and tradeoffs for silicon SPADs and the electronics employed along them to achieve high timing precision. In the end, we conclude with our outlook on the future by summarizing new routes that could benefit from present and prospective timing features of silicon SPADs.
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Loignon-Houle F, Toussaint M, Bertrand É, Lemyre FC, Lecomte R. Timing Estimation and Limits in TOF-PET Detectors Producing Prompt Photons. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2023; 7:692-703. [PMID: 38156329 PMCID: PMC10751813 DOI: 10.1109/trpms.2023.3279455] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2023]
Abstract
The production of prompt photons providing high photon time densities is a promising avenue to reach ultrahigh coincidence time resolution (CTR) in time-of-flight PET. Detectors producing prompt photons are receiving high interest experimentally, ignited by past exploratory theoretical studies that have anchored some guiding principles. Here, we aim to consolidate and extend the foundations for the analytical modeling of prompt generating detectors. We extend the current models to a larger range of prompt emission kinetics where more stringent requirements on the prompt photon yield rapidly emerge as a limiting factor. Lower bound and estimator evaluations are investigated with different underlying models, notably by merging or keeping separate the prompt and scintillation photon populations. We further show the potential benefits of knowing the proportion of prompt photons within a detection set to improve the CTR by mitigating the detrimental effect of population (prompt vs scintillation) mixing. Taking into account the fluctuations on the average number of detected prompt photons in the model reveals a limited influence when prompt photons are accompanied by fast scintillation (e.g., LSO:Ce:Ca) but a more significant effect when accompanied by slower scintillation (e.g., BGO). Establishing performance characteristics and limitations of prompt generating detectors is paramount to gauging and targeting the best possible timing capabilities they can offer.
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Affiliation(s)
- Francis Loignon-Houle
- Sherbrooke Molecular Imaging Center of CRCHUS and with the Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada, currently with Instituto de Instrumentación para Imagen Molecular, Centro Mixto CSIC-Universitat Politècnica de València, 46022 Valencia, Spain
| | - Maxime Toussaint
- Sherbrooke Molecular Imaging Center of CRCHUS and with the Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Émilie Bertrand
- CRCHUS and with the Department of Mathematics, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Félix Camirand Lemyre
- CRCHUS and with the Department of Mathematics, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Roger Lecomte
- Sherbrooke Molecular Imaging Center of CRCHUS and with the Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada, and also with IR&T Inc., Sherbrooke, QC, Canada
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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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16
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Kiyokawa M, Kang HG, Yamaya T. Tracking the same fast-LGSO crystals by changing surface treatments for better coincidence timing resolution in PET. Biomed Phys Eng Express 2023; 9. [PMID: 36689772 DOI: 10.1088/2057-1976/acb552] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 01/23/2023] [Indexed: 01/24/2023]
Abstract
Achieving fast coincidence timing resolution (CTR) is an important issue in clinical time-of-flight positron emission tomography (TOF-PET) to improve the reconstructed image quality. One of the major factors affecting the CTR is the crystal surface treatment, which is often parameterized as surface roughness. However, previous studies on the crystal surface treatment optimization had two limitations of crystal-by-crystal variation and worse CTR over 200 ps. Here, we report the effects of the crystal surface treatment on the performance of a 20 mm long fast-LGSO crystal based TOF detector by tracking the same crystals in the sub-180 ps CTR regime. The light collection efficiency (LCE), energy resolution (ER) and CTR of the TOF detector were evaluated with six different crystal surface treatments of chemically polished (C.P), C.P half side roughened (1/2S) treatment, and then the C.P one side roughened (1S) treatment, mechanically polished (M.P) treatment, M.P 1/2S treatment, and M.P 1S treatment. The four lateral surfaces of each crystal were wrapped by using enhanced specular reflector film while the top surface was covered by using Teflon tape. The bottom surface of the crystal was optically coupled to a silicon photomultiplier. The timing and energy signals were extracted by using a custom-made high-frequency readout circuit, and then digitized by using a waveform digitizer. All the experimental conditions were same except the crystal surface treatment. Among the six different crystal surface treatments, the M.P 1S would be the optimal crystal surface treatment which balanced enhancements in the CTR (165 ± 3 ps) and ER (10.5 ± 0.5%). Unlike the M.P 1S, the C.P 1S did not enhance the CTR and ER. Hence, the C.P without roughening would be the second-best optimal crystal surface treatment which balanced the CTR (169 ± 3 ps) and ER (10.5 ± 0.5%).
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Affiliation(s)
- Miho Kiyokawa
- National Institutes for Quantum Science and Technology, 4-9-1, Anagawa, Inage-ku, Chiba, Japan.,Department of Medical Engineering, Chiba University, 1-33, Yayoicho, Inage-ku, Chiba, 263-8522, Japan
| | - Han Gyu Kang
- National Institutes for Quantum Science and Technology, 4-9-1, Anagawa, Inage-ku, Chiba, Japan
| | - Taiga Yamaya
- National Institutes for Quantum Science and Technology, 4-9-1, Anagawa, Inage-ku, Chiba, Japan.,Center for Frontier Medical Engineering, Chiba University, 1-33, Yayoicho, Inage-ku, Chiba, 263-8522, Japan
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17
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Mehranian A, Wollenweber SD, Walker MD, Bradley KM, Fielding PA, Huellner M, Kotasidis F, Su KH, Johnsen R, Jansen FP, McGowan DR. Deep learning-based time-of-flight (ToF) image enhancement of non-ToF PET scans. Eur J Nucl Med Mol Imaging 2022; 49:3740-3749. [PMID: 35507059 PMCID: PMC9399038 DOI: 10.1007/s00259-022-05824-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 04/26/2022] [Indexed: 12/02/2022]
Abstract
PURPOSE To improve the quantitative accuracy and diagnostic confidence of PET images reconstructed without time-of-flight (ToF) using deep learning models trained for ToF image enhancement (DL-ToF). METHODS A total of 273 [18F]-FDG PET scans were used, including data from 6 centres equipped with GE Discovery MI ToF scanners. PET data were reconstructed using the block-sequential-regularised-expectation-maximisation (BSREM) algorithm with and without ToF. The images were then split into training (n = 208), validation (n = 15), and testing (n = 50) sets. Three DL-ToF models were trained to transform non-ToF BSREM images to their target ToF images with different levels of DL-ToF strength (low, medium, high). The models were objectively evaluated using the testing set based on standardised uptake value (SUV) in 139 identified lesions, and in normal regions of liver and lungs. Three radiologists subjectively rated the models using testing sets based on lesion detectability, diagnostic confidence, and image noise/quality. RESULTS The non-ToF, DL-ToF low, medium, and high methods resulted in - 28 ± 18, - 28 ± 19, - 8 ± 22, and 1.7 ± 24% differences (mean; SD) in the SUVmax for the lesions in testing set, compared to ToF-BSREM image. In background lung VOIs, the SUVmean differences were 7 ± 15, 0.6 ± 12, 1 ± 13, and 1 ± 11% respectively. In normal liver, SUVmean differences were 4 ± 5, 0.7 ± 4, 0.8 ± 4, and 0.1 ± 4%. Visual inspection showed that our DL-ToF improved feature sharpness and convergence towards ToF reconstruction. Blinded clinical readings of testing sets for diagnostic confidence (scale 0-5) showed that non-ToF, DL-ToF low, medium, and high, and ToF images scored 3.0, 3.0, 4.1, 3.8, and 3.5 respectively. For this set of images, DL-ToF medium therefore scored highest for diagnostic confidence. CONCLUSION Deep learning-based image enhancement models may provide converged ToF-equivalent image quality without ToF reconstruction. In clinical scoring DL-ToF-enhanced non-ToF images (medium and high) on average scored as high as, or higher than, ToF images. The model is generalisable and hence, could be applied to non-ToF images from BGO-based PET/CT scanners.
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Affiliation(s)
| | | | - Matthew D Walker
- Department of Medical Physics and Clinical Engineering, Oxford University Hospitals NHS FT, Oxford, UK
| | - Kevin M Bradley
- Wales Research and Diagnostic PET Imaging Centre, University Hospital of Wales, Cardiff, UK
| | | | | | | | | | | | | | - Daniel R McGowan
- Department of Medical Physics and Clinical Engineering, Oxford University Hospitals NHS FT, Oxford, UK.
- Department of Oncology, University of Oxford, Oxford, UK.
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18
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Park H, Yi M, Lee JS. Silicon photomultiplier signal readout and multiplexing techniques for positron emission tomography: a review. Biomed Eng Lett 2022; 12:263-283. [PMID: 35892029 PMCID: PMC9308856 DOI: 10.1007/s13534-022-00234-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 05/21/2022] [Accepted: 05/30/2022] [Indexed: 12/03/2022] Open
Abstract
In recent years, silicon photomultiplier (SiPM) is replacing the photomultiplier tube (PMT) in positron emission tomography (PET) systems due to its superior properties, such as fast single-photon timing response, small gap between adjacent photosensitive pixels in the array, and insensitivity to magnetic fields. One of the technical challenges when developing SiPM-based PET systems or other position-sensitive radiation detectors is the large number of output channels coming from the SiPM array. Therefore, various signal multiplexing methods have been proposed to reduce the number of output channels and the load on the subsequent data acquisition (DAQ) system. However, the large PN-junction capacitance and quenching resistance of the SiPM yield undesirable resistance-capacitance delay when multiple SiPMs are combined, which subsequently causes the accumulation of dark counts and signal fluctuation of SiPMs. Therefore, without proper SiPM signal handling and processing, the SiPMs may yield worse timing characteristics than the PMTs. This article reviews the evolution of signal readout and multiplexing methods for the SiPM. In this review, we focus primarily on analog electronics for SiPM signal multiplexing, which allows for the reduction of DAQ channels required for the SiPM-based position-sensitive detectors used in PET and other radiation detector systems. Although the applications of most technologies described in the article are not limited to PET systems, the review highlights efforts to improve the physical performance (e.g. spatial, energy, and timing resolutions) of PET detectors and systems.
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Affiliation(s)
- Haewook Park
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080 South Korea
- Department of Nuclear Medicine, Seoul National University College of Medicine, 101, Daehak-ro, Jongno-gu, Seoul, 03080 South Korea
| | - Minseok Yi
- Department of Nuclear Medicine, Seoul National University College of Medicine, 101, Daehak-ro, Jongno-gu, Seoul, 03080 South Korea
- Interdisciplinary Program in Bioengineering, Seoul National University College of Engineering, Seoul, 03080 South Korea
- Integrated Major in Innovative Medical Science, Seoul National University College of Engineering, Seoul, 03080 South Korea
| | - Jae Sung Lee
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul, 03080 South Korea
- Department of Nuclear Medicine, Seoul National University College of Medicine, 101, Daehak-ro, Jongno-gu, Seoul, 03080 South Korea
- Interdisciplinary Program in Bioengineering, Seoul National University College of Engineering, Seoul, 03080 South Korea
- Integrated Major in Innovative Medical Science, Seoul National University College of Engineering, Seoul, 03080 South Korea
- Brightonix Imaging Inc, Seoul, 04782 South Korea
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Pagano F, Kratochwil N, Salomoni M, Pizzichemi M, Paganoni M, Auffray E. Advances in heterostructured scintillators: toward a new generation of detectors for TOF-PET. Phys Med Biol 2022; 67. [PMID: 35609611 DOI: 10.1088/1361-6560/ac72ee] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 05/24/2022] [Indexed: 11/12/2022]
Abstract
Objective.Time-of-flight-positron emission tomography would highly benefit from a coincidence time resolution (CTR) below 100 ps: improvement in image quality and patient workflow, and reduction of delivered dose are among them. This achievement proved to be quite challenging, and many approaches have been proposed and are being investigated for this scope. One of the most recent consists in combining different materials with complementary properties (e.g. high stopping power for 511 keVγ-ray and fast timing) in a so-calledheterostructure,metascintillatorormetapixel. By exploiting a mechanism of energy sharing between the two materials, it is possible to obtain a fraction of fast events which significantly improves the overall time resolution of the system.Approach.In this work, we present the progress on this innovative technology. After a simulation study using the Geant4 toolkit, aimed at understanding the optimal configuration in terms of energy sharing, we assembled four heterostructures with alternating plates of BGO and EJ232 plastic scintillator. We fabricated heterostructures of two different sizes (3 × 3 × 3 mm3and 3 × 3 × 15 mm3), each made up of plates with two different thicknesses of plastic plates. We compared the timing of these pixels with a standard bulk BGO crystal and a structure made of only BGO plates (layeredBGO).Main results.CTR values of 239 ± 12 ps and 197 ± 10 ps FWHM were obtained for the 15 mm long heterostructures with 100µm and 200µm thick EJ232 plates (both with 100µm thick BGO plates), compared to 271 ± 14 ps and 303 ± 15 ps CTR for bulk and layered BGO, respectively.Significance.Significant improvements in timing compared to standard bulk BGO were obtained for all the configurations tested. Moreover, for the long pixels, depth of interaction (DOI) collimated measurements were also performed, allowing to validate a simple model describing light transport inside the heterostructure.
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Affiliation(s)
- Fiammetta Pagano
- CERN, Esplanade de Particules 1, 1211 Meyrin (Geneva), Switzerland.,University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, I-20126 Milan, Italy
| | - Nicolaus Kratochwil
- CERN, Esplanade de Particules 1, 1211 Meyrin (Geneva), Switzerland.,University of Vienna, Universitaetsring 1, A-1010 Vienna, Austria
| | - Matteo Salomoni
- CERN, Esplanade de Particules 1, 1211 Meyrin (Geneva), Switzerland
| | - Marco Pizzichemi
- CERN, Esplanade de Particules 1, 1211 Meyrin (Geneva), Switzerland.,University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, I-20126 Milan, Italy
| | - Marco Paganoni
- CERN, Esplanade de Particules 1, 1211 Meyrin (Geneva), Switzerland.,University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, I-20126 Milan, Italy
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Liu Z, Niu M, Kuang Z, Ren N, Wu S, Cong L, Wang X, Sang Z, Williams C, Yang Y. High resolution detectors for whole-body PET scanners by using dual-ended readout. EJNMMI Phys 2022; 9:29. [PMID: 35445890 PMCID: PMC9023628 DOI: 10.1186/s40658-022-00460-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 04/08/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Most current whole-body positron emission tomography (PET) scanners use detectors with high timing resolution to measure the time-of-flight of two 511 keV photons, improving the signal-to-noise ratio of PET images. However, almost all current whole-body PET scanners use detectors without depth-encoding capability; therefore, their spatial resolution can be affected by the parallax effect. METHODS In this work, four depth-encoding detectors consisting of LYSO arrays with crystals of 2.98 × 2.98 × 20 mm3, 2.98 × 2.98 × 30 mm3, 1.95 × 1.95 × 20 mm3, and 1.95 × 1.95 × 30 mm3, respectively, were read at both ends, with 6 × 6 mm2 silicon photomultiplier (SiPM) pixels in a 4 × 4 array being used. The timing signals of the detectors were processed individually using an ultrafast NINO application-specific integrated circuit (ASIC) to obtain good timing resolution. The 16 energy signals of the SiPM array were read using a row and column summing circuit to obtain four position-encoding energy signals. RESULTS The four PET detectors provided good flood histograms in which all crystals could be clearly resolved, the crystal energy resolutions measured being 10.2, 12.1, 11.4 and 11.7% full width at half maximum (FWHM), at an average crystal depth of interaction (DOI) resolution of 3.5, 3.9, 2.7, and 3.0 mm, respectively. The depth dependence of the timing of each SiPM was measured and corrected, the timing of the two SiPMs being used as the timing of the dual-ended readout detector. The four detectors provided coincidence time resolutions of 180, 214, 239, and 263 ps, respectively. CONCLUSIONS The timing resolution of the dual-ended readout PET detector was approximately 20% better than that of the single-ended readout detector using the same LYSO array, SiPM array, and readout electronics. The detectors developed in this work used long crystals with small cross-sections and provided good flood histograms, DOI, energy, and timing resolutions, suggesting that they could be used to develop whole-body PET scanners with high sensitivity, uniform high spatial resolution, and high timing resolution.
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Affiliation(s)
- Zheng Liu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Ming Niu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Zhonghua Kuang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Ning Ren
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - San Wu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Longhan Cong
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Xiaohui Wang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Ziru Sang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Crispin Williams
- European Centre for Nuclear Research (CERN), Geneva, Switzerland
| | - Yongfeng Yang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
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21
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Onishi Y, Hashimoto F, Ote K, Ota R. Unbiased TOF estimation using leading-edge discriminator and convolutional neural network trained by single-source-position waveforms. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac508f] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 01/31/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Objective. Convolutional neural networks (CNNs) are a strong tool for improving the coincidence time resolution (CTR) of time-of-flight (TOF) positron emission tomography detectors. However, several signal waveforms from multiple source positions are required for CNN training. Furthermore, there is concern that TOF estimation is biased near the edge of the training space, despite the reduced estimation variance (i.e. timing uncertainty). Approach. We propose a simple method for unbiased TOF estimation by combining a conventional leading-edge discriminator (LED) and a CNN that can be trained with waveforms collected from one source position. The proposed method estimates and corrects the time difference error calculated by the LED rather than the absolute time difference. This model can eliminate the TOF estimation bias, as the combination with the LED converts the distribution of the label data from discrete values at each position into a continuous symmetric distribution. Main results. Evaluation results using signal waveforms collected from scintillation detectors show that the proposed method can correctly estimate all source positions without bias from a single source position. Moreover, the proposed method improves the CTR of the conventional LED. Significance. We believe that the improved CTR will not only increase the signal-to-noise ratio but will also contribute significantly to a part of the direct positron emission imaging.
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22
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Shibuya K, Saito H, Tashima H, Yamaya T. Using inverse Laplace transform in positronium lifetime imaging. Phys Med Biol 2022; 67. [PMID: 35008076 DOI: 10.1088/1361-6560/ac499b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 01/10/2022] [Indexed: 11/11/2022]
Abstract
Positronium (Ps) lifetime imaging is gaining attention to bring out additional biomedical information from positron emission tomography (PET). The lifetime of Psin vivocan change depending on the physical and chemical environments related to some diseases. Due to the limited sensitivity, Ps lifetime imaging may require merging some voxels for statistical accuracy. This paper presents a method for separating the lifetime components in the voxel to avoid information loss due to averaging. The mathematics for this separation is the inverse Laplace transform (ILT), and the authors examined an iterative numerical ILT algorithm using Tikhonov regularization, namely CONTIN, to discriminate a small lifetime difference due to oxygen saturation. The separability makes it possible to merge voxels without missing critical information on whether they contain abnormally long or short lifetime components. The authors conclude that ILT can compensate for the weaknesses of Ps lifetime imaging and extract the maximum amount of information.
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Affiliation(s)
- Kengo Shibuya
- Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan.,Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan
| | - Haruo Saito
- Institute of Physics, Graduate School of Arts and Sciences, University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan
| | - Hideaki Tashima
- Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan
| | - Taiga Yamaya
- Institute for Quantum Medical Science, National Institutes for Quantum Science and Technology, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan
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23
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Windows-Yule CRK, Herald MT, Nicuşan AL, Wiggins CS, Pratx G, Manger S, Odo AE, Leadbeater T, Pellico J, de Rosales RTM, Renaud A, Govender I, Carasik LB, Ruggles AE, Kokalova-Wheldon T, Seville JPK, Parker DJ. Recent advances in positron emission particle tracking: a comparative review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2022; 85:016101. [PMID: 34814127 DOI: 10.1088/1361-6633/ac3c4c] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 11/23/2021] [Indexed: 06/13/2023]
Abstract
Positron emission particle tracking (PEPT) is a technique which allows the high-resolution, three-dimensional imaging of particulate and multiphase systems, including systems which are large, dense, and/or optically opaque, and thus difficult to study using other methodologies. In this work, we bring together researchers from the world's foremost PEPT facilities not only to give a balanced and detailed overview and review of the technique but, for the first time, provide a rigorous, direct, quantitative assessment of the relative strengths and weaknesses of all contemporary PEPT methodologies. We provide detailed explanations of the methodologies explored, including also interactive code examples allowing the reader to actively explore, edit and apply the algorithms discussed. The suite of benchmarking tests performed and described within the document is made available in an open-source repository for future researchers.
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Affiliation(s)
- C R K Windows-Yule
- School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - M T Herald
- School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - A L Nicuşan
- School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - C S Wiggins
- Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, 401 West Main Street, Box 843015, Richmond, Virginia 23284, United States of America
- Department of Physics and Astronomy, University of Tennessee, Knoxville, 1408 Circle Drive, Knoxville, TN 37996, United States of America
| | - G Pratx
- Department of Radiation Oncology, Division of Medical Physics, Stanford University School of Medicine, Stanford University, Stanford, CA, United States of America
- Molecular Imaging Program at Stanford (MIPS), School of Medicine, Stanford University, Stanford, CA, United States of America
| | - S Manger
- School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - A E Odo
- Department of Physics, Federal University Oye-Ekiti, Nigeria
- Department of Physics, University of Cape Town, Rondebosch 7701, South Africa
| | - T Leadbeater
- Department of Physics, University of Cape Town, Rondebosch 7701, South Africa
| | - J Pellico
- School of Biomedical Engineering & Imaging Sciences, King's College London, St. Thomas' Hospital, London SE1 7EH, United Kingdom
| | - R T M de Rosales
- School of Biomedical Engineering & Imaging Sciences, King's College London, St. Thomas' Hospital, London SE1 7EH, United Kingdom
| | - A Renaud
- School of Mathematics, The University of Edinburgh, Old College, South Bridge, Edinburgh EH8 9YL, United Kingdom
| | - I Govender
- Mintek, P/Bag X3015, Ranburg, Gauteng 2121, South Africa
- Centre for Minerals Research, University of Cape Town, P/Bag Rondebosch 7701, South Africa
- School of Engineering, University of KwaZulu Natal, Glenwood 4041, South Africa
| | - L B Carasik
- Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, 401 West Main Street, Box 843015, Richmond, Virginia 23284, United States of America
| | - A E Ruggles
- Department of Nuclear Engineering, University of Tennessee, Knoxville, 1412 Circle Drive, Knoxville, TN 37996, United States of America
| | - Tz Kokalova-Wheldon
- School of Physics and Astronomy, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - J P K Seville
- School of Chemical Engineering, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
| | - D J Parker
- School of Physics and Astronomy, The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
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24
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Kwon SI, Ota R, Berg E, Hashimoto F, Nakajima K, Ogawa I, Tamagawa Y, Omura T, Hasegawa T, Cherry SR. Ultrafast timing enables reconstruction-free positron emission imaging. NATURE PHOTONICS 2021; 15:914-918. [PMID: 35663419 PMCID: PMC9165659 DOI: 10.1038/s41566-021-00871-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 08/04/2021] [Indexed: 05/07/2023]
Abstract
X-ray and gamma-ray photons are widely used for imaging but require a mathematical reconstruction step, known as tomography, to produce cross-sectional images from the measured data. Theoretically, the back-to-back annihilation photons produced by positron-electron annihilation can be directly localized in three-dimensional space using time-of-flight information without tomographic reconstruction. However, this has not yet been demonstrated due to the insufficient timing performance of available radiation detectors. Here, we develop techniques based on detecting prompt Cerenkov photons, which when combined with a convolutional neural network for timing estimation resulted in an average timing precision of 32 picoseconds, corresponding to a spatial precision of 4.8 mm. We show this is sufficient to produce cross-sectional images of a positron-emitting radionuclide directly from the detected coincident annihilation photons, without using any tomographic reconstruction algorithm. The reconstruction-free imaging demonstrated here directly localizes positron emission, and frees the design of an imaging system from the geometric and sampling constraints that normally present for tomographic reconstruction.
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Affiliation(s)
- Sun Il Kwon
- Department of Biomedical Engineering, University of California; Davis, USA
| | - Ryosuke Ota
- Central Research Laboratory, Hamamatsu Photonics K.K.; Hamamatsu, Japan
| | - Eric Berg
- Department of Biomedical Engineering, University of California; Davis, USA
| | - Fumio Hashimoto
- Central Research Laboratory, Hamamatsu Photonics K.K.; Hamamatsu, Japan
| | | | - Izumi Ogawa
- Faculty of Engineering, University of Fukui; Fukui, Japan
| | | | - Tomohide Omura
- Central Research Laboratory, Hamamatsu Photonics K.K.; Hamamatsu, Japan
| | - Tomoyuki Hasegawa
- School of Allied Health Sciences, Kitasato University; Kitasato, Japan
| | - Simon R. Cherry
- Department of Biomedical Engineering, University of California; Davis, USA
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25
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Yoshida E, Obata F, Kamada K, Yoshikawa A, Yamaya T. Development of crosshair light sharing PET detector with TOF and DOI capabilities using fast LGSO scintillator. Phys Med Biol 2021; 66. [PMID: 34644694 DOI: 10.1088/1361-6560/ac2f8b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Accepted: 10/13/2021] [Indexed: 11/12/2022]
Abstract
Objective.Time-of-flight (TOF) and depth-of-interaction (DOI) are well recognized as important information to improve PET image quality. Since such information types are not correlated, many TOF-DOI detectors have been developed but there are only a few reports of high-resolution detectors (e.g. 1.5 mm resolution) for brain PET systems. Based on the DOI detector, which enables single-ended readout by optically coupling a pair of crystals and having a loop structure, we have developed the crosshair light sharing (CLS) PET detector that optically couples the four-loop structure, consisting of quadrisected crystals comparable in size to a photo-sensor, to four photo-sensors in close proximity arranged in a windmill shape. Even as a high-resolution detector, the CLS PET detector could obtain both TOF and DOI information. The coincidence resolving time (CRT) of the CLS PET detector needs to be further improved, however, for application to the brain PET system. Recently, a fast LGSO crystal was developed which has advantages in detection efficiency and CRT compared to the GFAG crystal. In this work, we developed the CLS PET detector using the fast LGSO crystal for the TOF-DOI brain PET system.Approach.The crystals were each 1.45 × 1.45 × 15 mm3and all surfaces were chemically etched. The CLS PET detector consisted of a 14 × 14 crystal array optically coupled to an 8 × 8 MPPC array.Main results.The fast LGSO array provided 10.1% energy resolution at 511 keV, 4.7 mm DOI resolution at 662 keV, and 293 ps CRT with the energy window of 440-620 keV.Significance.The developed CLS PET detector has 290% higher coincidence sensitivity, 30% better energy resolution, and 32% better time resolution compared to our previous CLS PET detector.
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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
| | - Kei Kamada
- New Industry Creation Hatchery Center, Tohoku University, Japan
| | - Akira Yoshikawa
- New Industry Creation Hatchery Center, Tohoku University, Japan.,Institute for Materials Research, Tohoku University, Japan
| | - Taiga Yamaya
- National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
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26
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Kratochwil N, Gundacker S, Auffray E. A roadmap for sole Cherenkov radiators with SiPMs in TOF-PET. Phys Med Biol 2021; 66. [PMID: 34433139 DOI: 10.1088/1361-6560/ac212a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 08/25/2021] [Indexed: 11/11/2022]
Abstract
Time of flight positron emission tomography can strongly benefit from a very accurate time estimator given by Cherenkov radiation, which is produced upon a 511 keV positron-electron annihilation gamma interaction in heavy inorganic scintillators. While time resolution in the order of 30 ps full width at half maximum (FWHM) has been reported using MCP-PMTs and black painted Cherenkov radiators, such solutions have several disadvantages, like high cost and low detection efficiency of nowadays available MCP-PMTs. On the other hand, silicon photomultipliers (SiPMs) are not limited by those obstacles and provide high photon detection efficiency with a decent time response. Timing performance of PbF2crystals of various lengths and surface conditions coupled to SiPMs was evaluated against a reference detector with an optimized test setup using high-frequency readout and novel time walk correction, with special attention on the intrinsic limits for one detected Cherenkov photon only. The average number of detected Cherenkov photons largely depends on the crystal surface state, resulting in a tradeoff between low photon time spread, thus good timing performance, and sensitivity. An intrinsic Cherenkov photon yield of 16.5 ± 3.3 was calculated for 2 × 2 × 3 mm3sized PbF2crystals upon 511 keVγ-deposition. After time walk correction based on the slew rate of the signal, assuming two identical detector arms in coincidence, and using all events, a time resolution of 215 ps FWHM (142 ps FWHM) was obtained for 2 × 2 × 20 mm3(2 × 2 × 3 mm3) sized PbF2crystals, compared to 261 ps (190 ps) without correction. Selecting on one detected photon only, a single photon coincidence time resolution of 113 ps FWHM for black painted and 166 ps for Teflon wrapped crystals was measured for 3 mm length, compared to 145 ps (black) and 263 ps (Teflon) for 20 mm length.
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Affiliation(s)
- Nicolaus Kratochwil
- CERN, Esplanade des Particules 1, 1211 Meyrin, Switzerland.,University of Vienna, Universitaetsring 1, A-1010 Vienna, Austria
| | - Stefan Gundacker
- CERN, Esplanade des Particules 1, 1211 Meyrin, Switzerland.,Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Forckenbeckstrasse 55, D-52074 Aachen, Germany
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27
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Schaart DR, Schramm G, Nuyts J, Surti S. Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2021; 5:598-618. [PMID: 34553105 PMCID: PMC8454900 DOI: 10.1109/trpms.2021.3084539] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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.
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Affiliation(s)
- Dennis R Schaart
- Section Medical Physics & Technology, Radiation Science and Technology Department, Delft University of Technology, 2629 JB Delft, The Netherlands
| | - Georg Schramm
- Department of Imaging and Pathology, Division of Nuclear Medicine, KU/UZ Leuven, 3000 Leuven, Belgium
| | - Johan Nuyts
- Department of Imaging and Pathology, Division of Nuclear Medicine, KU/UZ Leuven, 3000 Leuven, Belgium
| | - Suleman Surti
- Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104 USA
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28
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van der Sar SJ, Brunner SE, Schaart DR. Silicon photomultiplier-based scintillation detectors for photon-counting CT: A feasibility study. Med Phys 2021; 48:6324-6338. [PMID: 34169535 PMCID: PMC8596580 DOI: 10.1002/mp.14886] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 02/07/2021] [Accepted: 03/29/2021] [Indexed: 11/10/2022] Open
Abstract
PURPOSE The implementation of photon-counting detectors is widely expected to be the next breakthrough in X-ray computed tomography (CT) instrumentation. A small number of prototype scanners equipped with direct-conversion detectors based on room-temperature semiconductors, such as CdTe and CdZnTe (CZT), are currently installed at medical centers. Here, we investigate the feasibility of using silicon photomultiplier (SiPM)-based scintillation detectors in photon-counting computed tomography (PCCT) scanners, as a potential alternative to CdTe and CZT detectors. METHODS We introduce a model that allows us to compute the expected energy resolution as well as the expected pulse shape and associated rate capability of SiPM-based PCCT detectors. The model takes into account SiPM saturation and optical crosstalk, because these phenomena may substantially affect the performance of SiPM-based PCCT detectors with sub-mm pixels. We present model validation experiments using a single-pixel detector consisting of a 0.9 × 0.9 × 1.0 mm3 LuAP:Ce scintillation crystal coupled to a 1 × 1 mm2 SiPM. We subsequently use the validated model to compute the expected performance of the fast scintillators LYSO:Ce, LuAP:Ce, and LaBr3 :Ce, coupled to currently available SiPMs, as well as to a more advanced SiPM prototype with improved dynamic range, for sub-mm pixel sizes. RESULTS The model was found to be in good agreement with the validation experiments, both with respect to energy resolution and pulse shape. It shows how saturation progressively degrades the energy resolution of detectors equipped with currently available SiPMs as the pixel size decreases. Moreover, the expected pulse duration is relatively long (~200 ns) with these SiPMs. However, when LuAP:Ce and LaBr3 :Ce are coupled to the more advanced SiPM prototype, the pulse duration improves to less than 60 ns, which is in the same order of magnitude as pulses from CdTe and CZT detectors. It follows that sufficient rate capability can be achieved with pixel sizes of 400 μm or smaller. Moreover, LaBr3 :Ce detectors can provide an energy resolution of 11.5%-13.5% at 60 keV, comparable to CdTe and CZT detectors. CONCLUSIONS This work provides first evidence that it may be feasible to develop SiPM-based scintillation detectors for PCCT that can compete with CdTe and CZT detectors in terms of energy resolution and rate capability.
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Affiliation(s)
- Stefan J van der Sar
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands
| | | | - Dennis R Schaart
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands.,Holland Proton Therapy Center, Delft, The Netherlands
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