Comparison of 18F-FDG kinetics between oral uptake and venous injection

Objectives FDG-PET has been widely applied in oncology. Usually, FDG is administrated intravenously. However, venous access is not always available. Oral administration is thus an alternative consideration. This study was designated to investigate kinetics of FDG after oral uptake to optimize imaging protocol.

Methods 4 volunteers were enrolled. FDG was injected intravenously in one subject as a venous group (VG). In another three subjects, FDG was administrated orally, with 500 ml water, as an oral group (OG). Dosage of FDG was same for both groups, 0.1 mCu/kg. After administration of FDG, static scanning was acquired at 5, 20, 35, 50 and 70 min. Regions of interest (ROI) was drawn on mouth, esophagus, stomach, small intestine, colon, brain, lung, left ventricular cavity, left ventricular myocardium, liver and kidney. Mean activities in ROIs were taken in time series as a tissue-active curve. Image analysis was performed using Carimas (Turku PET Centre of Finland). Based on tissue-active curves from each organ, time reaching 90% of maximum was defined as maximal uptake time (MUT) for OG.

Results In VG, uptake of FDG in different organs was very fast, after 5-10 min, activity in brain, liver, lung and kidney reaches the plateau, except myocardium continued to take FDG. In OG, FDG was seen clearly to go dynamically through mouth, esophagus, stomach, small intestine and colon. After 5 min, radio activity starts to appear in liver, lung, kidney, heart and brain. MUT was 30, 43, 50 and 65 min for liver, lung, kidney and brain, respectively. Note that activity was still going up in brain at end of observation, implying that uptake of FDG in brain tissue does not reach maximum after 70 min.

Conclusions Oral FPG uptake is an alternative way for patients with difficult venous access. PET images should be acquired at around 60 min after oral FDG administration. For brain, a longer interval (>70min) is required.