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Saaidi R, Rodríguez-Villafuerte M, Alva-Sánchez H, Martínez-Dávalos A. Crystal scatter effects in a large-area dual-panel Positron Emission Mammography system. PLoS One 2024; 19:e0297829. [PMID: 38427663 PMCID: PMC10906883 DOI: 10.1371/journal.pone.0297829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 01/11/2024] [Indexed: 03/03/2024] Open
Abstract
Positron Emission Mammography (PEM) is a valuable molecular imaging technique for breast studies using pharmaceuticals labeled with positron emitters and dual-panel detectors. PEM scanners normally use large scintillation crystals coupled to sensitive photodetectors. Multiple interactions of the 511 keV annihilation photons in the crystals can result in event mispositioning leading to a negative impact in radiopharmaceutical uptake quantification. In this work, we report the study of crystal scatter effects of a large-area dual-panel PEM system designed with either monolithic or pixelated lutetium yttrium orthosilicate (LYSO) crystals using the Monte Carlo simulation platform GATE. The results show that only a relatively small fraction of coincidences (~20%) arise from events where both coincidence photons undergo single interactions (mostly through photoelectric absorption) in the crystals. Most of the coincidences are events where at least one of the annihilation photons undergoes a chain of Compton scatterings: approximately 79% end up in photoelectric absorption while the rest (<1%) escape the detector. Mean positioning errors, calculated as the distance between first hit and energy weighted (assigned) positions of interaction, were 1.70 mm and 1.92 mm for the monolithic and pixelated crystals, respectively. Reconstructed spatial resolution quantification with a miniDerenzo phantom and a list mode iterative reconstruction algorithm shows that, for both crystal types, 2 mm diameter hot rods were resolved, indicating a relatively small effect in spatial resolution. A drastic reduction in peak-to-valley ratios for the same hot-rod diameters was observed, up to a factor of 14 for the monolithic crystals and 7.5 for the pixelated ones.
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Affiliation(s)
- Rahal Saaidi
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
| | | | - Héctor Alva-Sánchez
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
| | - Arnulfo Martínez-Dávalos
- Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán, Mexico City, Mexico
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Guberman D, Paoletti R, Rugliancich A, Wunderlich C, Passeri A. Large-Area SiPM Pixels (LASiPs): A cost-effective solution towards compact large SPECT cameras. Phys Med 2021; 82:171-184. [PMID: 33640837 DOI: 10.1016/j.ejmp.2021.01.066] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 12/11/2020] [Accepted: 01/13/2021] [Indexed: 11/30/2022] Open
Abstract
Single Photon Emission Computed Tomography (SPECT) scanners based on photomultiplier tubes (PMTs) are still largely employed in the clinical environment. A standard camera for full-body SPECT employs ~50-100 PMTs of 4-8 cm diameter and is shielded by a thick layer of lead, becoming a heavy and bulky system that can weight a few hundred kilograms. The volume, weight and cost of a camera can be significantly reduced if the PMTs are replaced by silicon photomultipliers (SiPMs). The main obstacle to use SiPMs in full-body SPECT is the limited size of their sensitive area. A few thousand channels would be needed to fill a camera if using the largest commercially-available SiPMs of 6 × 6 mm2. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6 × 6 mm2 SiPM. We built a proof-of-concept micro-camera consisting of a 40 × 40 × 8 mm3 NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of 15×15 mm2, where we were able to reconstruct images of a 99mTc capillary with an intrinsic spatial resolution of ~2 mm and an energy resolution of ~11.6% at 140 keV. We used these measurements to validate Geant4 simulations of the system. This can be extended to simulate a larger camera with more and larger pixels, which could be used to optimize the implementation of LASiPs in large SPECT cameras. We provide some guidelines towards this implementation.
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Affiliation(s)
- D Guberman
- Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Pisa, I-56126 Pisa, Italy; Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Universitá di Siena, I-53100 Siena, Italy.
| | - R Paoletti
- Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Pisa, I-56126 Pisa, Italy; Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Universitá di Siena, I-53100 Siena, Italy
| | - A Rugliancich
- Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Pisa, I-56126 Pisa, Italy
| | - C Wunderlich
- Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Pisa, I-56126 Pisa, Italy; Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Universitá di Siena, I-53100 Siena, Italy
| | - A Passeri
- Dipartimento di Scienze Biomediche Sperimentali e Cliniche (SBSC), Universitá di Firenze, I-50134 Florence, Italy
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Lara-Camacho VM, Hernández-Acevedo EM, Alva-Sánchez H, Murrieta-Rodríguez T, Martínez-Dávalos A, Moranchel M, Rodríguez-Villafuerte M. Experimental validation of the ANTS2 code for modelling optical photon transport in monolithic LYSO crystals. Phys Med 2021; 81:215-226. [PMID: 33482439 DOI: 10.1016/j.ejmp.2020.12.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 12/11/2020] [Accepted: 12/31/2020] [Indexed: 11/16/2022] Open
Abstract
In this work the scintillation energy spectra originating from the background radioactivity from polished monolithic lutetium yttrium oxyorthosilicate coupled to position-sensitive silicon photomultipliers (SiPM) was studied using the open source Monte Carlo simulation package ANTS2. Two crystal sizes, fully and partially covering the photosensor area, three surface crystal wrappings (black, specular or diffuse) and the full signal formation process in the photosensor were considered. The simulation results were validated with experimental data acquired under the same geometric and detector operating conditions. In all cases ANTS2 simulated spectra have very good agreement with experimental results, reproducing the expected shape, with correct onset and end at 88 and 1190 keV, respectively, as well as sharp edges at the reference energies of 88, 88 + 202, 88 + 307 and 88 + 202 + 307 keV. The normalized root-mean square error between simulated and measured spectra varied between 4.3% and 10.4%.
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Affiliation(s)
- Víctor Manuel Lara-Camacho
- Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, Ciudad de México 01000, Mexico; Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Ciudad de México 07738, Mexico
| | | | - Héctor Alva-Sánchez
- Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, Ciudad de México 01000, Mexico
| | - Tirso Murrieta-Rodríguez
- Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, Ciudad de México 01000, Mexico
| | - Arnulfo Martínez-Dávalos
- Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, Ciudad de México 01000, Mexico
| | - Mario Moranchel
- Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Ciudad de México 07738, Mexico
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Enríquez-Mier-Y-Terán FE, Ortega-Galindo AS, Murrieta-Rodríguez T, Rodríguez-Villafuerte M, Martínez-Dávalos A, Alva-Sánchez H. Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals. EJNMMI Phys 2020; 7:21. [PMID: 32297045 PMCID: PMC7160222 DOI: 10.1186/s40658-020-00291-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 03/26/2020] [Indexed: 11/10/2022] Open
Abstract
Background Lutetium oxyorthosilicate or lutetium yttrium oxyorthosilicate (LYSO) scintillation crystals used in most current PET scanner detectors contain 176Lu, which decays by beta emission to excited states of 176Hf accompanied by the emission of prompt gamma rays or internal conversion electrons. This intrinsic radioactivity can be self-detected in singles mode as a constant background signal that has an energy spectrum whose structure has been explained previously. In this work, we studied the energy spectrum due to the intrinsic radioactivity of LYSO scintillation crystals of two opposing detectors working in coincidence mode. The investigation included experimental data, Monte Carlo simulations and an analytical model. Results The structure of the energy spectrum was completely understood and is the result of the self-detection of beta particles from 176Lu in one crystal and the detection of one or more prompt gamma rays detected in coincidence by the opposing crystal. The most probable coincidence detection involves the gamma rays of 202 and 307 keV, which result in two narrow photopeaks, superimposed on a continuous energy distribution due to the beta particle energy deposition. The relative intensities of the gamma ray peaks depend on crystal size and detector separation distance, as is explained by the analytical model and verified through the Monte Carlo simulations and experiments. Conclusions The analytical model used in this work accurately explains the general features of the coincidence energy spectrum due to the presence of 176Lu in the scintillation crystals, as observed experimentally and with Monte Carlo simulations. This work will be useful to those research studies aimed at using the intrinsic radioactivity of LYSO crystals for transmission scans and detector calibration in coincidence mode.
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Affiliation(s)
| | | | - Tirso Murrieta-Rodríguez
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico
| | | | - Arnulfo Martínez-Dávalos
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico
| | - Héctor Alva-Sánchez
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico.
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Alva-Sánchez H, Zepeda-Barrios A, Díaz-Martínez VD, Murrieta-Rodríguez T, Martínez-Dávalos A, Rodríguez-Villafuerte M. Understanding the intrinsic radioactivity energy spectrum from 176Lu in LYSO/LSO scintillation crystals. Sci Rep 2018; 8:17310. [PMID: 30470826 PMCID: PMC6251911 DOI: 10.1038/s41598-018-35684-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Accepted: 11/06/2018] [Indexed: 11/09/2022] Open
Abstract
Lutetium oxyorthosilicate (LSO) or lutetium yttrium oxyorthosilicate (LYSO) are the scintillator materials most widely used today in PET detectors due to their convenient physical properties for the detection of 511 keV annihilation photons. Natural lutetium contains 2.6% of 176Lu which decays beta to excited states of 176Hf producing a constant background signal. Although previous works have studied the background activity from LSO/LYSO, the shape of the spectrum, resulting from β-particle and γ radiation self-detection, has not been fully explained. The present work examines the contribution of the different β-particle and γ-ray interactions to provide a fuller comprehension of this background spectrum and to explain the differences observed when using crystals of different sizes. To this purpose we have shifted the continuous β-particle energy spectrum of 176Lu from zero to the corresponding energy value for all combinations of the isomeric transitions of 176Hf (γ-rays/internal conversion). The area of each shifted β-spectrum was normalized to reflect the probability of occurrence. To account for the probability of the γ-rays escaping from the crystal, Monte Carlo simulations using PENELOPE were performed in which point-like sources of monoenergetic photons were generated, inside LYSO square base prisms (all 1 cm thick) of different sizes: 1.0 cm to 5.74 cm. The analytic distributions were convolved using a varying Gaussian function to account for the measured energy resolution. The calculated spectra were compared to those obtained experimentally using monolithic crystals of the same dimensions coupled to SiPM arrays. Our results are in very good agreement with the experiment, and even explain the differences observed due to crystal size. This work may prove useful to calibrate and assess detector performance, and to measure energy resolution at different energy values.
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Affiliation(s)
- H Alva-Sánchez
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico.
| | - A Zepeda-Barrios
- Facultad de Ciencias, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - V D Díaz-Martínez
- Facultad de Ciencias, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - T Murrieta-Rodríguez
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico
| | - A Martínez-Dávalos
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico
| | - M Rodríguez-Villafuerte
- Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000, Mexico City, Mexico
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