Toward Individualized FDG PET/CT Protocols: Evaluating Dose–Time–Patient Size and Image Quality Relationships In Clinical Practice
Abstract
Purpose
To evaluate how patient size, injected FDG dose, and acquisition time relate to routine whole-body PET/CT image quality, and to assess whether a simple dose–time–weight index can guide individualized protocols for more consistent noise performance.
Methods
We retrospectively reviewed 130 whole-body FDG PET/CT studies from two clinical sites (Site A, n = 69; Site B, n = 61). Site A used a Siemens Biograph 40-mCT and Site B a United Imaging uMI 550. Patient-level data included height, weight, injected activity, uptake time, and acquisition time per bed position. A minimal NEC surrogate was computed as the decay-corrected injected activity at scan start multiplied by time per bed and normalized by body weight (MBq·s/kg). Liver ROIs were analyzed for SUVmean, SUVstd, SUVmax, coefficient of variation(COV), and SNR. Associations between the NEC surrogate and noise metrics were assessed.
Results
Mean patient weight was 81.2 kg (range 13.9–162.0 kg), with BMI ranging from 16 to 55kg/m². Injected activity was broadly comparable across patients, yet activity per kg varied 4.4-fold (2.35–10.27 MBq/kg). Time per bed was mostly fixed at Site A (median 91.25s/bed; IQR 91.19–91.30) but varied at Site B (90–180s/bed; median 120s/bed), yielding higher dose–time per unit body size at Site B. The NEC surrogate correlated inversely with liver COV overall (r=−0.66, p<0.001) and within Site A (r=−0.57, p<0.001) and Site B (r=−0.58, p<0.001), and correlated positively with liver SNR overall (r=0.81, p<0.001). Median liver COV was 43% lower at Site B than Site A.
Conclusion
Routine fixed-dose and fixed-time PET protocols can create substantial interpatient variability in effective dose–time per unit body size, contributing to inconsistent image noise. Dose–time–weight NEC surrogate is consistently associated with liver noise metrics and may support practical individualized adjustments of injected dose and/or acquisition time to standardize image quality while avoiding unnecessary radiation exposure.