Reducing scan time using time-of-flight protocol in clinical [18F]FDG-PET/CT imaging: A feasibility study

This study evaluates scan time reduction using time-of-flight (TOF) PET, when quantitative parameters including volumetric measures are considered.

32 patients were included in the study. The reconstruction parameters for TOF were 2 iterations, 18 and 24 subsets, and for non-TOF was 3 iterations and 18 subsets. A post smoothing filter with FWHM of 5.4 mm and 6.4 mm were used for TOF and 6.4 mm for non-TOF. TOF reconstruction was performed with 2, 2.5 and 3 min/bed position, and 3 min/bed position scan time was applied in non-TOF. Quantitative parameters such as coefficient of variation (COV), signal-to-noise ratio (SNR), lesion-to-background ratio (LBR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) were utilized. Standard uptake value (SUV) was also measured. Different segmentation thresholds were studied.

Improvement in SNR for TOF relative to non-TOF was observed when utilizing 18 subsets, 5.4 mm filter size with 3 min scan time/bed position (P-value<0.0001), and for 18 subsets, 6.4 mm filter size when 2.5- and 3-min scan time/bed positions was applied (P-value≤0.02). Scan time reduction did not illustrate significant variation for the SUVs and lesion size. In all TOF protocols for both TLG and MTV, the measured values decreased with increasing segmentation thresholds, as expected, with significantly more impact for higher thresholds (70%, 75%). Meanwhile, higher values were observed for higher post smoothing filter in each specified threshold. With increasing of the threshold, ΔTLG was increased with more impact for higher post smoothing filter. ΔMTV were -10.10±11.09 (-1.35±8.59) and 0.68±17.51 (12.42±18.90) in 2 min/bed position with 5.4 (6.4 mm post smoothing filter) for threshold of 45% and 75% respectively.

Scan time reduction from 3 to 2 min can be obtained with TOF in comparison with non-TOF, especially when higher segmentation threshold values with higher subset number (24) and 6.4 mm filters are utilized.