Abstract
Purpose: Aim of our study was to evaluate the effect of stepwise reduced doses on objective and subjective image parameters and on oncologic readings in whole-body 18F-FDG-PET/MRI. Material and Methods: We retrospectively simulated the stepwise reduction of 18F-FDG doses of 19 patients (50.9 ± 11.7 y/o, Body-Mass-Index (BMI) 22.8 ± 3.2) who received a whole-body PET/MRI examination from 3 to 0.5 MBq/kgBW in intervals of 0.25. Objective imaging parameters were assessed by measuring the standardized uptake value (SUV) and coefficient of variation (CV) in different regions (aorta, liver, spleen, kidney, small bowel, lumbar vertebra, psoas muscle, urinary bladder) as well as the noise equivalent count rates (NECR) in each bed position. Subjective image quality was evaluated with a blinded reading of each simulated PET compared to the dose of 2 MBq/kgBW. Oncologic reading was performed first, according to PET response criteria in solid tumors (PERCIST) in each dose and second, by defining malignant lesions in doses of 2 MBq/kgBW and the maximum dose image (gold standard). Diagnostic confidence of each lesion was measured using a Likert scale. Results: With decreasing doses, regions in the mid abdomen showed a stronger decrease of SUVmean and NECR than regions in the upper abdomen (SUVmean: -45% and -15% on average in the small bowel and the liver, respectively). CV showed a non-linear increase, pronounced below 1.5 MBq/kgBW. Subjective image quality was stable over a range between 1.25 and 2.75 MBq/kgBW compared to 2 MBq/kgBW. However, large photopenic areas in the mid abdomen were observed in two patients. In the PERCIST reading, target lesions were above the liver threshold with a stable SUVpeak in all cases down to 2 MBq/kgBW. 86 of 90 lesions were identified correctly with a dose of 2 MBq/kgBW; Likert scores did not differ significantly. Conclusion: A reduction of doses in 18F-FDG-PET/MRI might be possible down to 2 MBq/kgBW in oncologic whole-body examinations. The image quality in the mid abdomen seems to be more affected by lower doses than in the upper abdomen and in single cases, large photopenic areas can occur. Therefore, we do not recommend reducing doses below 3 MBq/kgBW in adults at this time.
- Copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging, Inc.