Vascular inflammation imaging with 18F-FDG PET/CT: when to image?

We prospectively investigated the ideal imaging time to measure vascular uptake after injection of (18)F-FDG. A total of 17 patients with atherosclerotic abdominal aortic aneurysm underwent dynamic abdominal PET/CT using 2-min frames between 45 and 53, 57 and 65, 115 and 123, and 175 and 183 min after injection of (18)F-FDG. For each period of dynamic imaging, vessel wall and lumen uptake were measured using the maximum standardized uptake value (SUV(max)) and target-to-background ratio (TBR). No significant difference in TBR across all time points (repeated measures ANOVA, P = 0.206) was observed, despite a significant difference in aortic wall and lumen uptake with time (repeated measures ANOVA, P = 0.02 and P < 0.001, respectively). There was no significant difference between aortic wall uptake at 60 min (SUV(max), 2.15 +/- 0.11 SE) and 180 min (SUV(max), 1.99 +/- 0.18 SE) (paired t test, P = 0.367). There was a significant difference in lumen uptake at 60 min (SUV(max), 2.4 +/- 0.11 SE) and 180 min (SUV(max), 1.7 +/- 0.1 SE) (paired t test, P = 0.001). There was no significant difference in TBR between 60 min (0.91 +/- 0.03) and 180 min (1.01 +/- 0.06 SE) (paired t test, P = 0.131). With increasing delayed imaging, there was increasing variability (SE) in the SUV(max) for the aortic wall and TBRs. There was no significant advantage in imaging at 3 h over 1 h after (18)F-FDG injection.