The choice of injected dose of 18 F -FDG and acquisition time is important in obtaining consistently high-quality PET images. The aim of this study was to determine the optimal acquisition protocols based on patient weight for 3-dimensional lutetium oxyorthosilicate PET/CT. Methods: This study was a retrospective analysis of 76 patients ranging from 29 to101 kg who were injected with 228-395.2 MBq of 18 F -FDG for PET imaging. The study population was divided into 4 weight-based groups: less than 45 kg (group 1), 45-59 kg (group 2), 60-74 kg (group 3), and 75 kg or more (group 4). We measured the true coincidence rate, random coincidence rate, noise-equivalent counting rate (NECR), and random fraction and evaluated image quality by the coefficient of variance (COV) in the largest liver slices. Results: The true coincidence rate, random coincidence rate, and NECR significantly increased with increasing injected dose per kilogram (r = 0.91, 0.83, and 0.90; all P < 0.01). NECR maximized at10.11 MB/kg in underweight patients. The true coincidence rate differed significantly among the 4 groups, except for group 3 versus group 4 (P < 0.01). The ratio of the true coincidence rate for group 2 to groups 3 and 4 was 1.4 and 1.6, respectively. The average random fraction for all 4 groups was approximately 35%.The COV of the 4 groups differed for all pairs (P< 0.01). The COVs in overweight patients were larger than those in underweight patients, and image quality in overweight patients was poor. Conclusion: We modified acquisition protocols for 18 F -FDG PET/CT according to the characteristics of a 3-dimensional lutetium orthosilicate PET scanner
We determined that the optimal reconstruction parameter for OSEM(RRSCAC) was 90 update numbers with 6.6 mm FWHM of the Gaussian filter. Our results suggested that the optimal reconstruction parameters have a potential to improve the performance and the image quality of (123)I-FP-CIT SPECT in comparison with the FBP reconstruction.
We developed a custom-designed phantom for bone single photon emission computed tomography (SPECT)specific radioactivity distribution and linear attenuation coefficient. The aim of this study was to evaluate the accuracy of the phantom. The lumbar phantom consisted of the trunk of a body phantom (background) containing a cylinder (vertebral body), a sphere (tumor), and a T-shaped container (processus). The vertebral body, tumor, and processus phantoms contained a K2HPO4 solution of bone equivalent density and 50, 300 and 50 kBq/mL of 99m Tc, respectively. The body phantom contained 8 kBq/mL of 99m Tc solution. SPECT images were acquired using lowenergy high-resolution collimation, a 128×128 matrix and 120 projections over 360°with a dwell time of 15 sec/view×4 times. Thereafter, CT images were acquired at 130 kV and 70 ref mAs using adaptive dose modulation. The SPECT data were reconstructed with ordered subset expectation maximization with three-dimensional, scatter, and CT-based attenuation correction. Count ratio, linear attenuation coefficient (LAC), and full-width at halfmaximum (FWHM) were measured. Count ratios between the background, the vertebral body, and the tumor in SPECT images were 463.
We have demonstrated that a high-resolution image reconstruction algorithm for brain F-FDG-PET is promising without the use of a GF because of high true coincidence counts and that combined with PSF and TOF is optimal for obtaining a better SNR of the image.
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