Evaluation of Optimal Post-Injection Timing of Hypoxic Imaging with 18F-Fluoromisonidazole-PET/CT.

PURPOSE Positron emission tomography (PET)/computed tomography (CT) using 18F-fluoromisonidazole (FMISO) has been used as an imaging tool for tumour hypoxia. However, it remains unclear whether they are useful when scanning is performed earlier, e.g. at 2-h post-injection with a high sensitivity PET scanner. This study aimed to investigate the relationship between quantitative values in 18F-fluoromisonidazole (18F-FMISO)-PET obtained at 2- and 4-h post-injection in patients with head and neck cancer. PROCEDURES We enrolled 20 patients with untreated locally advanced head and neck cancer who underwent 18F-FMISO-PET/CT scan between August 2015 and March 2018 at our institute. Image acquisition was performed 2 h and 4 h after 18F-FMISO administration using a combined PET/CT scanner. The SUVmax, SUVmean, SUVpeak, tumour-to-blood ratio (TBR), tumour-to-muscle ratio (TMR), metabolic tumour volume (MTV), and total lesion hypoxia (TLH) were measured in the region of interest of the primary tumour. We evaluated the between-image Spearman's rank correlation coefficients and percentage differences in the quantitative values. The locations of the maximum uptake pixel were identified in both scans, and the distance between them was measured. RESULTS The mean (SD) SUVmax at 2 h and 4 h was 2.2(0.7) and 2.4(0.8), respectively. The Spearman's rank correlation coefficients (ρ) and mean (SD) of the percentage differences of the measures were as follows: SUVmax (0.97; 7.0 [5.1]%), SUVmean (0.97; 5.2 [5.8]%), SUVpeak (0.94; 5.3 [4.7]%), TBR (0.96; 14.2 [9.8]%), TMR (0.96; 14.7 [8.4]%), MTV (0.98; 39.9 [41.3]%), and TLH (0.98; 40.1 [43.4]%). There were significant between-scan correlations in all quantitative values. The mean (SD) distance between the two maximum uptake pixels was 7.3 (5.3) mm. CONCLUSIONS We observed a high correlation between the quantitative values at 2 h and 4 h. When using a combined high-quality PET/CT, the total examination time for FMISO-PET can be shortened by skipping the 4-h scan.