Dose Optimization in F-FDG PET Based on Noise-Equivalent Count Rate Measurement and Image Quality Assessment.

The present study aimed to optimize the injected dose of F-FDG in whole-body PET/CT scans and assess its effect on noise-equivalent count rate (NECR) and visual image quality (IQ). Patients scheduled to undergo F-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 F-FDG radioactivity per kilogram of body weight (1.85, 3.7, 5.5, and 7.4 MBq/kg). All patients underwent F-FDG PET/CT studies, and NECR was calculated by noting the trues rate, total prompts, and randoms rate for each bed position. Whole-body NECR was calculated as the average NECR for all bed positions. IQ was qualitatively assessed for each bed position (IQ) and for whole-body PET (IQ) 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/m; group II, 20.1-25 kg/m; group III, 25.1-30 kg/m; and group IV, 30.1-35 kg/m) for comparison. A value of less than 0.05 was considered significant. In total, 109 patients underwent F-FDG PET/CT studies after injection of different amounts of F-FDG radioactivity and a mean uptake time of 62.32 min. The mean NECR and IQ for each group were significantly different from other groups ( < 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 NECR and IQ were significantly different in all 4 body-mass-index groups ( < 0.05), except between groups II and III ( > 0.05). NECR and IQ correlated moderately ( = 0.64). Optimization of injected F-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.