Abstract
Purpose. 124I has a half-life of 4.2 days, which makes it suitable for imaging over several days over its uptake and washout phases. However, it has a low positron branching ratio (23%), because of prompt gamma coincidence due to high-energy γ-photons (602 to 1,691 keV), which are emitted in cascade with positrons. Methods. In this study, we investigated the optimal PET energy window for 124I PET based on image characteristics of reconstructed PET. Image characteristics such as nonuniformities, recovery coefficients (RCs), and the spillover ratios (SORs) of 124I were measured as described in NEMA NU 4-2008 standards. Results. The maximum and minimum prompt gamma coincidence fraction (PGF) were 33% and 2% in 350~800 and 400~590 keV, respectively. The difference between best and worst uniformity in the various energy windows was less than 1%. The lowest SORs of 124I were obtained at 350~750 keV in nonradioactive water compartment. Conclusion. Optimal energy window should be determined based on image characteristics. Our developed correction method would be useful for the correction of high-energy prompt gamma photon in 124I PET. In terms of the image quality of 124I PET, our findings indicate that an energy window of 350~750 keV would be optimal.
Highlights
PET is a widely used noninvasive diagnostic modality for imaging functional and biochemical phenomena in vivo
The difference between “branching ratio corrected” and “branching ratio uncorrected” sensitivities was the portion of prompt gamma coincidence fraction
When prompt gamma coincidence fraction (PGF) was compared with AC, spillover ratios (SORs) values were decreased by roughly 7.66 percentage point in air and by 12.79 percentage point in water
Summary
PET is a widely used noninvasive diagnostic modality for imaging functional and biochemical phenomena in vivo. High-energy gammas are emitted in cascade with positrons These lead to spurious coincidences and reduction of image quality [10, 11]. Because prompt gamma coincidence due to high-energy γ-photons was emitted in 124I PET, optimal PET acquisition settings. Other papers were studied count based evaluation and did not consider the prompt gamma coincidence correction [8, 10, 15] They suggest use of relatively narrow energy window in order to exclude high-energy gamma prompt photons. We assessed the image quality of reconstructed PET to determine the optimal energy window in 124I PET with various parameters on Siemens Inveon PET Image qualities such as nonuniformity, recovery coefficient, and spillover ratio were assessed according to NEMA NU 4-2008
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