A method for measuring the energy spectrum of coincidence events in positron emission tomography

Goertzen, Andrew L.; Stout, David; Thompson, Christopher J.

doi:10.1088/0031-9155/55/2/013

Cited by 8 publications

(6 citation statements)

References 12 publications

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“…The response of the photodetector and electronics is also not included, and the energy resolution was accounted for through the convolution of the predicted energy spectra with a variable Gaussian kernel that reflects the measured energy resolution. For the Monte Carlo simulations using GATE, our results are in good agreement with those reported in [22,24].…”

Section: Analytical Model Vs Experiments and Simulationssupporting

confidence: 88%

“…For energy calibration purposes, the 202 and 307 keV gamma rays, from the isomeric transitions of the 176 Hf excited states, were used. Additionally, a sealed 22 Na source was used to obtain a third calibration point (511 keV). Finally, all experimental energy spectra were normalized to have an area under the curve equal to unity to allow an easy comparison with the analytical and simulation results.…”

Section: Methodsmentioning

confidence: 99%

“…In singles mode, this intrinsic energy spectrum has been previously reported [17][18][19][20][21]. In 2010, Goertzen et al [22] developed a method for estimating the energy spectrum of coincidence events in a PET system and compared it with measurements and Monte Carlo simulations using GATE (Geant4 Application for Tomographic Emission) [23]. A more detailed model of 176 Lu in GATE was further reported by McIntosh et al [24].…”

Section: Introductionmentioning

confidence: 91%

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Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Enriquez-Mier-y-Teran¹,

Ortega-Galindo²,

Murrieta-Rodríguez³

et al. 2020

EJNMMI Phys

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Background: Lutetium oxyorthosilicate or lutetium yttrium oxyorthosilicate (LYSO) scintillation crystals used in most current PET scanner detectors contain 176 Lu, which decays by beta emission to excited states of 176 Hf 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 176 Lu 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 176 Lu 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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Section: Analytical Model Vs Experiments and Simulationssupporting

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

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Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Enriquez-Mier-y-Teran¹,

Ortega-Galindo²,

Murrieta-Rodríguez³

et al. 2020

EJNMMI Phys

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“…Hence, this intrinsic radioactivity can produce up to 1 million counts per second as detected by the entire scanner, with a total random coincidence rate of 1,600 cps in a 350-to 650-keV acceptance window, and falsely contributes a true coincidence rate of approximately 600 cps in an LSO scanner (21,22). The intrinsic rate can be reduced from 940 cps in a 250-to 750-keV energy window to less than 2 cps in a 400-to 750-keV window as demonstrated in an LSO-based smallanimal PET scanner (23). The D-690 scanner has set the lower threshold to 425 keV, and the significantly reduced reported intrinsic rate of about 1 cps (10) can be considered negligible in clinical settings but not at low counting rates such as in lesions with low 18 F-FDG avidity.…”

Section: Discussionmentioning

confidence: 99%

Determining the Minimal Required Radioactivity of ¹⁸F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study

Chen

Ménard

Cheng

2016

J. Nucl. Med. Technol.

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In pursuit of as-low-as-reasonably-achievable (ALARA) doses, this study investigated the minimal required radioactivity and corresponding imaging time for reliable semiquantification in PET/CT imaging. Methods: Using a phantom containing spheres of various diameters (3.4, 2.1, 1.5, 1.2, and 1.0 cm) filled with a fixed 18 F-FDG concentration of 165 kBq/mL and a background concentration of 23.3 kBq/mL, we performed PET/CT at multiple time points over 20 h of radioactive decay. The images were acquired for 10 min at a single bed position for each of 10 half-lives of decay using 3-dimensional list mode and were reconstructed into 1-, 2-, 3-, 4-, 5-, and 10-min acquisitions per bed position using an ordered-subsets expectation maximum algorithm with 24 subsets and 2 iterations and a gaussian 2-mm filter. SUV max and SUV avg were measured for each sphere. Results: The minimal required activity (±10%) for precise SUV max semiquantification in the spheres was 1.8 kBq/mL for an acquisition of 10 min, 3.7 kBq/mL for 3-5 min, 7.9 kBq/mL for 2 min, and 17.4 kBq/mL for 1 min. The minimal required activity concentration-acquisition time product per bed position was 10-15 kBq/mL⋅min for reproducible SUV measurements within the spheres without overestimation. Using the total radioactivity and counting rate from the entire phantom, we found that the minimal required total activity-time product was 17 MBq⋅min and the minimal required counting rate-time product was 100 kcps⋅min. Conclusion: Our phantom study determined a threshold for minimal radioactivity and acquisition time for precise semiquantification in 18 F-FDG PET imaging that can serve as a guide in pursuit of achieving ALARA doses.Key Words: PET; phantom; dosimetry; dose reduction; acquisition time; standard uptake value J Nucl Med Technol 2016; 44:26-30 DOI: 10.2967/jnmt.115.165258 There is a growing trend to minimize ionizing radiation exposure, particularly from diagnostic medical imaging involving x-rays and internal radiation from administration of radionuclides. Recent evidence from a retrospective largecohort study of over 178,600 U.K. residents who were exposed to radiation from CT scans in childhood found that a cumulative dose of more than 30 mGy to red bone marrow from as few as 5-10 head CT scans in children younger than 15 y carried a relative risk of 3.18 for leukemia as compared with a cumulative dose of less than 5 mGy. For brain cancer, a cumulative dose of 50-74 mGy to brain from as few as 2-3 head CT scans carried a relative risk of 2.82, as compared with those receiving a cumulative dose of less than 5 mGy (1). In a study of 680,000 Australians exposed to CT scans in childhood and adolescence, Mathews et al. found an incidence rate ratio of 1.24 for all cancers, with an observed dose-response relation of 0.16 per additional CT scan using an estimated average effective radiation dose of 4.5 mSv per scan (2).18 F-FDG PET/CT has been widely used for oncologic and cardiac imaging, with radiation exposure being derived from the injected dose of radiot...

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“…Spectra were obtained from an 18 F point source for VECTor and 68 Ge line source for the Focus120 using coincidence measurements (15).…”

Section: Sensitivity Energy Resolution and Uniformitymentioning

confidence: 99%

Performance Assessment of a Preclinical PET Scanner with Pinhole Collimation by Comparison to a Coincidence-Based Small-Animal PET Scanner

et al. 2014

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PET imaging of rodents is increasingly used in preclinical research, but its utility is limited by spatial resolution and signal-to-noise ratio of the images. A recently developed preclinical PET system uses a clustered-pinhole collimator, enabling high-resolution, simultaneous imaging of PET and SPECT tracers. Pinhole collimation strongly departs from traditional electronic collimation achieved via coincidence detection in PET. We investigated the potential of such a design by direct comparison to a traditional PET scanner. Methods: Two small-animal PET scanners, 1 with electronic collimation and 1 with physical collimation using clustered pinholes, were used to acquire data from Jaszczak (hot rod) and uniform phantoms. Mouse brain imaging using 18 F-FDG PET was performed on each system and compared with quantitative ex vivo autoradiography as a gold standard. Bone imaging using 18 F-NaF allowed comparison of imaging in the mouse body. Images were visually and quantitatively compared using measures of contrast and noise. Results: Pinhole PET resolved the smallest rods (diameter, 0.85 mm) in the Jaszczak phantom, whereas the coincidence system resolved 1.1-mm-diameter rods. Contrast-to-noise ratios were better for pinhole PET when imaging small rods (,1.1 mm) for a wide range of activity levels, but this reversed for larger rods. Image uniformity on the coincidence system (,3%) was superior to that on the pinhole system (5%). The high 18 F-FDG uptake in the striatum of the mouse brain was fully resolved using the pinhole system, with contrast to nearby regions equaling that from autoradiography; a lower contrast was found using the coincidence PET system. For shortduration images (low-count), the coincidence system was superior. Conclusion: In the cases for which small regions need to be resolved in scans with reasonably high activity or reasonably long scan times, a first-generation clustered-pinhole system can provide image quality in terms of resolution, contrast, and the contrast-to-noise ratio superior to a traditional PET system. Smal l-animal PET is an increasingly important tool in biomedical research. A recent development in scanner technology has been the introduction of a focused, clustered-pinhole collimator that enables simultaneous high-spatial-resolution PET and SPECT imaging. Physical collimation of the 511-keV photons produced by positron-electron annihilation, using clustered pinholes, is a substantial change in scanner design as compared with electronic collimation via coincidence detection. Clustered pinholes can offer improved spatial resolution (1) in rodent images, despite a low fraction of single 511-keV photons being detected as compared with the fraction of detected photon pairs in traditional PET. Such scanners are likely suited to different applications. The commonly encountered sensitivity-resolution trade-off has been investigated previously: it has been known for several decades that an improvement in image quality can be achieved via a gain in spatial resolution, even if this gain...

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A method for measuring the energy spectrum of coincidence events in positron emission tomography

Cited by 8 publications

References 12 publications

Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Determining the Minimal Required Radioactivity of ¹⁸F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study

Performance Assessment of a Preclinical PET Scanner with Pinhole Collimation by Comparison to a Coincidence-Based Small-Animal PET Scanner

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A method for measuring the energy spectrum of coincidence events in positron emission tomography

Cited by 8 publications

References 12 publications

Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Coincidence energy spectra due to the intrinsic radioactivity of LYSO scintillation crystals

Determining the Minimal Required Radioactivity of 18F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study

Performance Assessment of a Preclinical PET Scanner with Pinhole Collimation by Comparison to a Coincidence-Based Small-Animal PET Scanner

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Determining the Minimal Required Radioactivity of ¹⁸F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study