Selection of optimal acquisition duration or injected activity for pediatric FDG-PET/CT

Objectives Pediatric FDG dosing and acquisition durations are generally based on coarse extrapolation from adult guidelines. This study seeks to determine if shorter acquisition durations or a lower FDG injected activity can be used for pediatric FDG-PET/CT exams while maintaining diagnostic utility. Reduction of overall scan time potentially reduces motion artifacts, improves patient comfort and decreases length of sedation. Alternatively, decreased FDG dose minimizes radiation risk.

Methods Wholebody FDG-PET/CT scans were performed on 14 patients (13-109kg, aged 1-23 years) with a weight-based injected activity (0.144mCi/kg), fixed acquisition durations (3 min/FOV if < 22kg, 5 min/FOV if >22kg), and list-mode acquisition. For each patient, the list-mode data were truncated to form multiple data sets with shorter acquisition durations down to a minimum of 1 min/FOV (i.e. 1, 2, 3, 4, and 5min/FOV data were formed from single 5min/FOV acquisition). 56 image volumes were generated, randomized, and reviewed blindly with corresponding CT image volumes by 5 radiologists. Both overall adequacy and lesion detection accuracy/confidence by body region were evaluated.

Results All exams with maximum acquisition duration (n=14) were graded as adequate and were used as the standard for detection accuracy. For patients <22kg, the average threshold of time for an adequate exam was 2.0+-1.0min/FOV. For patients >22kg, the threshold was 1.5+-0.7min/FOV. Lesion detection accuracy/confidence was not degraded from 5 down to 1 min/FOV for abdominal lesions, but chest lesion detection became less accurate when imaging acquisition was reduced more than 30%.

Conclusions Evaluation of image volumes generated from shorter acquisition durations suggests that imaging times can be reduced by 30% without a loss of diagnostic utility in pediatric PET/CT. Using decreased acquisition times as a surrogate for FDG dose, FDG dose can be reduced by approximately 30% following the proposed protocols