Simulated Reduced-Count Whole-Body FDG PET: Evaluation in Children and Young Adults Imaged on a Digital PET Scanner.

Digital PET scanners with increased sensitivity may allow shorter scan acquisitions or reduced administered radiopharmaceutical activities. To evaluate in children and young adults the impact of simulated shorter acquisition times on the quality of whole-body FDG PET images obtained using a digital PET/CT system. This retrospective study included 27 children and young adults (9 males, 18 females) who underwent clinically indicated whole-body FDG PET/CT examinations on a 25-cm axial FOV PET/CT system at 90 seconds per bed position. Raw list-mode data were reprocessed to simulate acquisition times of 60, 55, 50, 45, 40, and 30 seconds/bed. Three radiologists independently reviewed reconstructed images and assigned Likert scores for lesion conspicuity, normal structure conspicuity, image quality, and image noise. A separate observer recorded SUVmax, SUVmean, and SUVSD for liver, thigh, and the most FDG-avid lesion. SUVSD/SUVmean was calculated as a surrogate of image noise. ANOVA, Friedman's test, and Dunn's test were used to compare qualitative measures (combining reader scores) and SUV measurements. Mean age was 10.8±8.3 years, mean BMI was 18.7±2.9, and mean administered FDG activity was 4.4±0.4 MBq/kg (0.12±0.01 mCi/kg). No qualitative measure showed a significant difference versus 90 seconds/bed for the 60 seconds/bed simulated acquisition (all p>.05). Significant differences (all p<.05) versus 90 seconds/bed were observed for lesion conspicuity at ≤40 seconds/bed, conspicuity of normal structures and overall image quality at ≤45 seconds/bed, and image noise at ≤55 seconds/bed. SUVmean was not significantly different from 90 seconds/bed for any site for any reduced-count simulation (all p>.05). SUVSD/SUVmean and SUVmax showed gradual increases with decreasing acquisition times and were significantly different from 90 seconds/bed only for liver at 60 seconds/bed (SUVmax: 1.00±0.00 vs 1.05±0.03, p=.02; SUVSD/SUVmean: 0.09±0.02 vs 0.11±0.02, p=.04). Favorable findings for the simulated 60 seconds/bed acquisition suggest that, in children and young adults imaged on a 25-cm FOV digital PET scanner, acquisition time or administered FDG activity may be decreased by approximately 33% from the clinical standard without significantly impacting image quality. A 25-cm axial FOV digital scanner may allow performing FDG PET/CT examinations with reduced radiation exposure or faster scan times.