Abstract
The present study aimed to optimize the injected dose of 18F-FDG in whole-body PET/CT scans and assess its effect on noise-equivalent count rate (NECR) and visual image quality (IQ). Methods: Patients scheduled to undergo 18F-FDG PET/CT were prospectively recruited in the study from January to December 2019, regardless of the indication or underlying disease. Patients were divided into 4 groups and injected with different amounts of 18F-FDG radioactivity per kilogram of body weight (1.85, 3.7, 5.5, and 7.4 MBq/kg). All patients underwent 18F-FDG PET/CT studies, and NECRlocal was calculated by noting the trues rate, total prompts, and randoms rate for each bed position. Whole-body NECRglobal was calculated as the average NECR for all bed positions. IQ was qualitatively assessed for each bed position (IQlocal) and for whole-body PET (IQglobal) by 2 readers using 5-point scores based on prevalence of noise, contrast, and lesion detectability. NECR and IQ were compared among all 4 activity groups. Patients were also subdivided into 4 body-mass-index groups (group I, 15–20 kg/m2; group II, 20.1–25 kg/m2; group III, 25.1–30 kg/m2; and group IV, 30.1–35 kg/m2) for comparison. A P value of less than 0.05 was considered significant. Results: In total, 109 patients underwent 18F-FDG PET/CT studies after injection of different amounts of 18F-FDG radioactivity and a mean uptake time of 62.32 min. The mean NECRglobal and IQglobal for each group were significantly different from other groups (P < 0.05), with NECR and IQ being higher in high-activity groups than in low-activity groups. The overall IQ was acceptable in all patients, even in the lowest-activity group (1.84 MBq/kg). The mean NECRglobal and IQglobal were significantly different in all 4 body-mass-index groups (P < 0.05), except between groups II and III (P > 0.05). NECRlocal and IQlocal correlated moderately (r = 0.64). Conclusion: Optimization of injected 18F-FDG radioactivity from 7.4 MBq/kg (200 μCi/kg) to 1.85 MBq/kg (50 μCi/kg) resulted in acceptable IQ, despite a reduction in NECR.
Footnotes
↵* Contributed equally to this work.
Published online Sep. 4, 2020.
This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.
SNMMI members
Login to the site using your SNMMI member credentials
Individuals
Login as an individual user