Investigating low-dose image quality in whole-body pediatric 18F-FDG scans using TOF-PET/MRI.

In this study we investigate the diagnostic performance of whole-body F18-FDG imaging using a simultaneous PET/MRI scanner with Time-of-Flight (TOF) capability for low-dose clinical imaging of pediatric patients. In addition to clinically acquired image data using a dosing regimen of 3.7 MBq/kg, images from simulated low-dose regimens (1.9 MBq/kg - 0.41 MBq/kg) were evaluated using several metrics: standardized uptake value (SUV) quantitation, qualitative image quality and lesion detectability. Methods: Low-dose images were generated by truncating the list-mode PET data. A total of 60 image volumes were analyzed, generated from 12 patient scans. Changes in PET quantitation for low-dose images were assessed using ROI analysis of healthy tissue and suspected lesions. Three pediatric radiologists reviewed the image volumes blinded to the dose level. Qualitative image quality was assessed based on Likert scoring. Radiologists were also asked to identify suspected lesions within the liver for PET-only and fused PET/MR images. The lesion detectability was measured using a receiver operator characteristic study and quantified using a free response receiving operator characteristic (FROC) methodology to assess changes in performance for low-dose images. Results: Our analysis of ROI quantitation shows that SUV values remain stable down to 1/3 dose (1.2 MBq/kg). Likert scoring of fused PET/MRI images showed no noticeable trend with dose level, however scores of PET-only images were lower for low-dose scans, with a 12% reduction for 1/3 dose images compared to full-dose. There was minimal change in lesion total lesion count for different does levels, however all three readers had an increase in false-negatives for 1/3 dose images compared to full-dose. Using the FROC methodology to quantify human observer lesion detection performance, no significant differences were observed for the three dosing levels when using the averaged reader data (all p values \u003e 0.103). The FROC performance for fused PET/MR images was higher for all readers compared to PET alone. Conclusion: Reductions to the lowest recommended pediatric dosing regimens are possible when using PET/MR. Data suggests that administered dose can be decreased to 2.6 MBq/kg, a 30% reduction in PET activity leading to a corresponding reduction in absorbed dose.