Influence of scan time point and volume of intravenous contrast administration on blood-pool and liver SUVmax and SUVmean in [18F] FDG PET/CT

Summary Aim: To investigate the influence of scan time point and volume of intravenous contrast material in 18F-FDG PET/CT on maximum and mean standardized uptake values (SUVmax/mean) in bloodpool and liver. Methods: In 120 patients scheduled for routine whole-body 18F-FDG PET/CT the maximum and mean standardized uptake values (SUVmax/SUVmean) in the liver and blood pool were measured after varying scan time-point (delay 0 s-140 s post injectionem) and volume of contrast material (CM; 0 ml, 80 ml, 100 ml of 300 mg/ml of Iodine). Six groups of 20 patients were investigated: (1) without intravenous CM, (2-5) injection of 100 ml CM with a delay of 80 s (2), 100 s (3), 120 s (4), 140 s (5), and 80 ml CM and a delay of 100 s (6). SUVmax, SUVmean, maximum Hounsfield units (HUmax) and average Hounsfield units (HUav) were calculated with the use of manually drawn regions of interests (ROIs) over the aortic arch and healthy liver tissue. Results: SUVmax in bloodpool was significantly higher in group 3, 4 and 6 compared to group 1. Groups 2 and 5 also showed higher mean values of SUVmax, but the difference was not significant. SUVmean in bloodpool was also higher in groups 2, 3, 4, 5 and 6 compared to group 1, but the differences were only statistically significant in group 3. Both SUVmax and SUVmean in healthy liver tissue did not show significant differences when compared to the non contrast-enhanced control group. Conclusion: SUVmax and to a lesser extent SUVmean measured in CM enhanced FDG PET/CT in blood pool could be significantly altered in high contrast CT examinations. This should be kept in mind in PET/CT protocols and evaluation relying on SUVmax and SUVmean, for example when used in the assessment of therapy response, especially in highly vascularized tumor lesions.