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Cosmi V, Wang B, Goorden MC, Beekman FJ. NaI gamma camera performance for high energies: Effects of crystal thickness, photomultiplier tube geometry and light guide thickness. Med Phys 2024; 51:4696-4708. [PMID: 38569052 DOI: 10.1002/mp.17043] [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: 06/28/2023] [Revised: 12/18/2023] [Accepted: 03/12/2024] [Indexed: 04/05/2024] Open
Abstract
BACKGROUND Gamma camera imaging, including single photon emission computed tomography (SPECT), is crucial for research, diagnostics, and radionuclide therapy. Gamma cameras are predominantly based on arrays of photon multipliers tubes (PMTs) that read out NaI(Tl) scintillation crystals. In this way, standard gamma cameras can localize ɣ-rays with energies typically ranging from 30 to 360 keV. In the last decade, there has been an increasing interest towards gamma imaging outside this conventional clinical energy range, for example, for theragnostic applications and preclinical multi-isotope positron emission tomography (PET) and PET-SPECT. However, standard gamma cameras are typically equipped with 9.5 mm thick NaI(Tl) crystals which can result in limited sensitivity for these higher energies. PURPOSE Here we investigate to what extent thicker scintillators can improve the photopeak sensitivity for higher energy isotopes while attempting to maintain spatial resolution. METHODS Using Monte Carlo simulations, we analyzed multiple PMT-based configurations of gamma detectors with monolithic NaI (Tl) crystals of 20 and 40 mm thickness. Optimized light guide thickness together with 2-inch round, 3-inch round, 60 × 60 mm2 square, and 76 × 76 mm2 square PMTs were tested. For each setup, we assessed photopeak sensitivity, energy resolution, spatial, and depth-of-interaction (DoI) resolution for conventional (140 keV) and high (511 keV) energy ɣ using a maximum-likelihood algorithm. These metrics were compared to those of a "standard" 9.5 mm-thick crystal detector with 3-inch round PMTs. RESULTS Estimated photopeak sensitivities for 511 keV were 27% and 53% for 20 and 40 mm thick scintillators, which is respectively, 2.2 and 4.4 times higher than for 9.5 mm thickness. In most cases, energy resolution benefits from using square PMTs instead of round ones, regardless of their size. Lateral and DoI spatial resolution are best for smaller PMTs (2-inch round and 60 × 60 mm2 square) which outperform the more cost-effective larger PMT setups (3-inch round and 76 × 76 mm2 square), while PMT layout and shape have negligible (< 10%) effect on resolution. Best spatial resolution was obtained with 60 × 60 mm2 PMTs; for 140 keV, lateral resolution was 3.5 mm irrespective of scintillator thickness, improving to 2.8 and 2.9 mm for 511 keV with 20 and 40 mm thick crystals, respectively. Using the 3-inch round PMTs, lateral resolutions of 4.5 and 3.9 mm for 140 keV and of 3.5 and 3.7 mm for 511 keV were obtained with 20 and 40 mm thick crystals respectively, indicating a moderate performance degradation compared to the 3.5 and 2.9 mm resolution obtained by the standard detector for 140 and 511 keV. Additionally, DoI resolution for 511 keV was 7.0 and 5.6 mm with 20 and 40 mm crystals using 60 × 60 mm2 square PMTs, while with 3-inch round PMTs 12.1 and 5.9 mm were obtained. CONCLUSION Depending on PMT size and shape, the use of thicker scintillator crystals can substantially improve detector sensitivity at high gamma energies, while spatial resolution is slightly improved or mildly degraded compared to standard crystals.
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Affiliation(s)
- Valerio Cosmi
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands
| | - Beien Wang
- 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
| | - Freek J Beekman
- Department of Radiation Science and Technology, Delft University of Technology, Delft, The Netherlands
- Free Bee International, Gouda, The Netherlands
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DrAdda I, Morahan AJ, Carminati M, Erlandsson K, Ljungberg M, Hutton BF, Fiorini C. A Statistical DOI Estimation Algorithm for a SiPM-Based Clinical SPECT Insert. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2022. [DOI: 10.1109/trpms.2022.3140411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Ozsahin I, Chen L, Könik A, King MA, Beekman FJ, Mok GSP. The clinical utilities of multi-pinhole single photon emission computed tomography. Quant Imaging Med Surg 2020; 10:2006-2029. [PMID: 33014732 PMCID: PMC7495312 DOI: 10.21037/qims-19-1036] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Accepted: 07/30/2020] [Indexed: 11/06/2022]
Abstract
Single photon emission computed tomography (SPECT) is an important imaging modality for various applications in nuclear medicine. The use of multi-pinhole (MPH) collimators can provide superior resolution-sensitivity trade-off when imaging small field-of-view compared to conventional parallel-hole and fan-beam collimators. Besides the very successful application in small animal imaging, there has been a resurgence of the use of MPH collimators for clinical cardiac and brain studies, as well as other small field-of-view applications. This article reviews the basic principles of MPH collimators and introduces currently available and proposed clinical MPH SPECT systems.
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Affiliation(s)
- Ilker Ozsahin
- Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Macau, China
- Department of Biomedical Engineering, Faculty of Engineering, Near East University, Nicosia/TRNC, Mersin-10, Turkey
- DESAM Institute, Near East University, Nicosia/TRNC, Mersin-10, Turkey
| | - Ling Chen
- Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Macau, China
| | - Arda Könik
- Department of Imaging, Dana Farber Cancer Institute, Boston, MA, USA
| | - Michael A. King
- Department of Radiology, University of Massachusetts Medical School, Worcester, MA, USA
| | - Freek J. Beekman
- Section of Biomedical Imaging, Department of Radiation Science and Technology, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands
- MILabs B.V, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, The Netherlands
| | - Greta S. P. Mok
- Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Macau, China
- Center for Cognitive and Brain Sciences, Institute of Collaborative Innovation, University of Macau, Macau, China
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El Bitar Z, Pino F, Candela C, Ros D, Pavía J, Rannou FR, Ruibal A, Aguiar P. The performance of a hybrid analytical-Monte Carlo system response matrix in pinhole SPECT reconstruction. Phys Med Biol 2014; 59:7573-85. [DOI: 10.1088/0031-9155/59/24/7573] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Characterisation of a high resolution small field of view portable gamma camera. Phys Med 2014; 30:331-9. [DOI: 10.1016/j.ejmp.2013.10.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 09/27/2013] [Accepted: 10/21/2013] [Indexed: 11/22/2022] Open
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Heemskerk JWT, Kreuger R, Goorden MC, Korevaar MAN, Salvador S, Seeley ZM, Cherepy NJ, van der Kolk E, Payne SA, Dorenbos P, Beekman FJ. Experimental comparison of high-density scintillators for EMCCD-based gamma ray imaging. Phys Med Biol 2012; 57:4545-54. [PMID: 22722678 DOI: 10.1088/0031-9155/57/14/4545] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Dey J. Improvement of Performance of Cardiac SPECT Camera Using Curved Detectors With Pinholes. IEEE TRANSACTIONS ON NUCLEAR SCIENCE 2012; 59:334-347. [PMID: 32952207 PMCID: PMC7495883 DOI: 10.1109/tns.2011.2182660] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
SPECT is primarily used in the clinic for cardiac myocardial perfusion imaging. However, for SPECT, sensitivity is impaired due to the need for collimation. System resolution FWHM is poor as well (~ 1 cm). In this work the resolution of a curved detector was theoretically derived. The advantage of a curved detector over a flat detector with pinhole collimation was demonstrated for cardiac applications using theoretical derivations as well as a ray-tracing voxel-based forward projector. For the flat detector using parameters close to what was expected for the new multi-pinhole GE Discovery system, it is shown that using a paraboloid detector one may obtain a better system resolution (about 29% better on the average), keeping same pinhole opening. Alternately, sensitivity gains of as much as 2.25 may be obtained, for similar resolutions as a flat detector by just using a different pinhole with higher hole-diameter.
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Affiliation(s)
- Joyoni Dey
- Department of Radiology, University of Massachusetts Medical School, Worcester, MA 01655 USA
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Abstract
The development of radiation detectors capable of delivering spatial information about gamma-ray interactions was one of the key enabling technologies for nuclear medicine imaging and, eventually, single-photon emission computed tomography (SPECT). The continuous sodium iodide scintillator crystal coupled to an array of photomultiplier tubes, almost universally referred to as the Anger Camera after its inventor, has long been the dominant SPECT detector system. Nevertheless, many alternative materials and configurations have been investigated over the years. Technological advances as well as the emerging importance of specialized applications, such as cardiac and preclinical imaging, have spurred innovation such that alternatives to the Anger Camera are now part of commercial imaging systems. Increased computing power has made it practical to apply advanced signal processing and estimation schemes to make better use of the information contained in the detector signals. In this review we discuss the key performance properties of SPECT detectors and survey developments in both scintillator and semiconductor detectors and their readouts with an eye toward some of the practical issues at least in part responsible for the continuing prevalence of the Anger Camera in the clinic.
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Affiliation(s)
- Todd E Peterson
- Institute of Imaging Science, Department of Radiology and Radiological Sciences, Department of Physics, and Program in Chemical and Physical Biology, Vanderbilt University, Nashville, TN, USA.
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Korevaar MAN, Goorden MC, Heemskerk JWT, Beekman FJ. Maximum-likelihood scintillation detection for EM-CCD based gamma cameras. Phys Med Biol 2011; 56:4785-801. [PMID: 21753231 DOI: 10.1088/0031-9155/56/15/010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Gamma cameras based on charge-coupled devices (CCDs) coupled to continuous scintillation crystals can combine a good detection efficiency with high spatial resolutions with the aid of advanced scintillation detection algorithms. A previously developed analytical multi-scale algorithm (MSA) models the depth-dependent light distribution but does not take statistics into account. Here we present and validate a novel statistical maximum-likelihood algorithm (MLA) that combines a realistic light distribution model with an experimentally validated statistical model. The MLA was tested for an electron multiplying CCD optically coupled to CsI(Tl) scintillators of different thicknesses. For (99m)Tc imaging, the spatial resolution (for perpendicular and oblique incidence), energy resolution and signal-to-background counts ratio (SBR) obtained with the MLA were compared with those of the MSA. Compared to the MSA, the MLA improves the energy resolution by more than a factor of 1.6 and the SBR is enhanced by more than a factor of 1.3. For oblique incidence (approximately 45°), the depth-of-interaction corrected spatial resolution is improved by a factor of at least 1.1, while for perpendicular incidence the MLA resolution does not consistently differ significantly from the MSA result for all tested scintillator thicknesses. For the thickest scintillator (3 mm, interaction probability 66% at 141 keV) a spatial resolution (perpendicular incidence) of 147 µm full width at half maximum (FWHM) was obtained with an energy resolution of 35.2% FWHM. These results of the MLA were achieved without prior calibration of scintillations as is needed for many statistical scintillation detection algorithms. We conclude that the MLA significantly improves the gamma camera performance compared to the MSA.
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Affiliation(s)
- Marc A N Korevaar
- Department of Radiation, Radionuclides and Reactors, Section of Radiation Detection and Medical Imaging, Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
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Alhassen F, Kudrolli H, Singh B, Kim S, Seo Y, Gould RG, Nagarkar VV. Depth-of-Interaction Compensation Using a Focused-Cut Scintillator for a Pinhole Gamma Camera. IEEE TRANSACTIONS ON NUCLEAR SCIENCE 2011; 58:634-638. [PMID: 21731108 PMCID: PMC3126617 DOI: 10.1109/tns.2011.2136386] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Preclinical SPECT offers a powerful means to understand the molecular pathways of drug interactions in animal models by discovering and testing new pharmaceuticals and therapies for potential clinical applications. A combination of high spatial resolution and sensitivity are required in order to map radiotracer uptake within small animals. Pinhole collimators have been investigated, as they offer high resolution by means of image magnification. One of the limitations of pinhole geometries is that increased magnification causes some rays to travel through the detection scintillator at steep angles, introducing parallax errors due to variable depth-of-interaction in scintillator material, especially towards the edges of the detector field of view. These parallax errors ultimately limit the resolution of pinhole preclinical SPECT systems, especially for higher energy isotopes that can easily penetrate through millimeters of scintillator material. A pixellated, focused-cut (FC) scintillator, with its pixels laser-cut so that they are collinear with incoming rays, can potentially compensate for these parallax errors and thus improve the system resolution. We performed the first experimental evaluation of a newly developed focused-cut scintillator. We scanned a Tc-99m source across the field of view of pinhole gamma camera with a continuous scintillator, a conventional "straight-cut" (SC) pixellated scintillator, and a focused-cut scintillator, each coupled to an electron-multiplying charge coupled device (EMCCD) detector by a fiber-optic taper, and compared the measured full-width half-maximum (FWHM) values. We show that the FWHMs of the focused-cut scintillator projections are comparable to the FWHMs of the thinner SC scintillator, indicating the effectiveness of the focused-cut scintillator in compensating parallax errors.
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Affiliation(s)
- Fares Alhassen
- UCSF Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 185 Berry St. Suite 350, San Francisco, CA 94017 USA
| | - Haris Kudrolli
- Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA 02472 USA
| | - Bipin Singh
- Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA 02472 USA
| | - Sangtaek Kim
- UCSF Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 185 Berry St. Suite 350, San Francisco, CA 94017 USA
| | - Youngho Seo
- UCSF Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 185 Berry St. Suite 350, San Francisco, CA 94017 USA
| | - Robert G. Gould
- UCSF Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 185 Berry St. Suite 350, San Francisco, CA 94017 USA
| | - Vivek V. Nagarkar
- Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA 02472 USA
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Heemskerk JWT, Korevaar MAN, Huizenga J, Kreuger R, Schaart DR, Goorden MC, Beekman FJ. An enhanced high-resolution EMCCD-based gamma camera using SiPM side detection. Phys Med Biol 2010; 55:6773-84. [PMID: 21030743 DOI: 10.1088/0031-9155/55/22/011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Electron-multiplying charge-coupled devices (EMCCDs) coupled to scintillation crystals can be used for high-resolution imaging of gamma rays in scintillation counting mode. However, the detection of false events as a result of EMCCD noise deteriorates the spatial and energy resolution of these gamma cameras and creates a detrimental background in the reconstructed image. In order to improve the performance of an EMCCD-based gamma camera with a monolithic scintillation crystal, arrays of silicon photon-multipliers (SiPMs) can be mounted on the sides of the crystal to detect escaping scintillation photons, which are otherwise neglected. This will provide a priori knowledge about the correct number and energies of gamma interactions that are to be detected in each CCD frame. This information can be used as an additional detection criterion, e.g. for the rejection of otherwise falsely detected events. The method was tested using a gamma camera based on a back-illuminated EMCCD, coupled to a 3 mm thick continuous CsI:Tl crystal. Twelve SiPMs have been mounted on the sides of the CsI:Tl crystal. When the information of the SiPMs is used to select scintillation events in the EMCCD image, the background level for (99m)Tc is reduced by a factor of 2. Furthermore, the SiPMs enable detection of (125)I scintillations. A hybrid SiPM-/EMCCD-based gamma camera thus offers great potential for applications such as in vivo imaging of gamma emitters.
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Affiliation(s)
- J W T Heemskerk
- Department of Nuclear Medicine, Image Sciences Institute, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands
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