Exploring the feasibility of a 40-minute uptake time for long axial field of view [18F]FDG PET/CT tumour scan: an evidence-based single-center study.

Purpose
The EANM/SNMMI guidelines recommend an uptake time of 60 min for 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) in oncology imaging, with an acceptable range of 55 to 75 min. Over time, positron emission tomography (PET) technology has advanced significantly in terms of signal collection efficiency. This study aims to explore the feasibility of PET acquisition after a 40-minute uptake period following [18F]FDG administration in patients with tumours.Methods
Forty-three oncological patients who underwent 60-min total-body dynamic [18F]FDG PET scan were retrospectively included as the exploration cohort. The raw data was reconstructed into 55 image frames to calculate and compare the lesion-to-background ratios (LBRs) of different image frames (GD57-60 served as the reference). The data from 40 to 52 min and 57-60 min were then reconstructed into static PET images (G40 - 43, G43 - 46, G46 - 49, G49 - 52, and G57 - 60). The differences in image quality (subjective image score, standardized uptake value [SUV], signal-to-noise ratio [SNR], and LBRs) and lesion-detection rate (histopathology served as reference) among groups were evaluated. In the validation cohort, 46 oncological patients who underwent a 20-min total-body PET/CT scan at 40 min after [18F]FDG injection were prospectively enrolled. The raw data were reconstructed using the same protocols with dynamic scan and briefly called: G40 - 43', G43 - 46', G46 - 49', G49 - 52', and G57 - 60', and the image quality and lesion detection rate among groups were assessed.Results
The activity curves reveal that the average LBRs gradually increased with time, with no significant difference between GD45-48 and GD57-60 (all p ≥ 0.27). The static PET image quality in both cohorts was as good as the 57-min uptake imaging. In the exploration cohort, the SNRs of G57 - 60 were not better than the other groups. For all lesions, SUVmax, lesion-to-liver ratio (LLR), lesion-to-muscle ratio (LMR), and lesion-to-normal tissue ratio (LNR) showed no statistically significant differences between G49 - 52 and G57 - 60 (all p ≥ 0.06), with the exception of lesion-to-blood pool ratio (LBPR) (p < 0.05). The lesion-detection rate was 85.7% (48/56; 95% CI: 0.74-0.94) in all groups. In the validation cohort, G40 - 43' and G57 - 60' shared comparable background SNRs and the same lesion detection rate (94.0%, 63/67; 95% CI: 0.85-0.98).Conclusion
Reducing the uptake time from 60 min to 40 min after [18F]FDG injection in oncology patients can still yield PET images with sufficient quality and lesion detectability to meet clinical requirements in total body PET/CT. Shortening the uptake time raised the efficiency of the uptake room, increased patient throughput, and enhanced patient comfort, without changing the scan protocol or compromising imaging quality.