Quantification of [F-18]FDG uptake in the normal liver using dynamic PET: Impact and modeling of the dual hepatic blood supply

For quantification of hepatic [F-18]FDG uptake, the dual blood supply to th e liver must be considered. In contrast to the arterial input, however, the portal venous blood supply to the liver cannot be monitored directly by PE T because of the inaccessibility of the portal vein on PET scans. In this s tudy; we investigated whether the dual hepatic input can be predicted from the measurable arterial input. Moreover, we assessed the effect of differen t input models on the rate constants of the standard 3-compartment model de scribing regional uptake of FDG. Methods: Dynamic FDG PET scanning was perf ormed on 5 foxhounds. Activity concentrations in blood from the aorta and t he portal vein were measured simultaneously using external circuits. After image reconstruction, time-activity courses were determined from the aorta and the liver. The venous input was approximated by convolving the arterial input with a notional system function describing the dispersion of the art erial input on its way through the gastrointestinal tract. On the basis of these data, 5 different hepatic input models, which pertain to a single-inp ut as well as a dual-input scenario, were statistically compared with regar d to the adequacy of the model fits to liver data and to differences in the estimated rate constants. Results: Portal venous input to the liver could be approximated by convolving the arterial input function with a system fun ction. From this function, a mean transit time of 25 s was computed for FDG to pass through the gastrointestinal tract. According to the statistical a nalysis, dual-input models were superior to their single-input counterparts . However, differences in the rate constants estimated for the 5 input mode ls were in the same order as interindividual variations within the differen t model groups. For the dephosphorylation rate constant, a consistent value of 0.05 +/-0.01 min(-1) was found. Conclusion: Dual-input models proved to be superior to single-input models with respect to the adequacy of FDG mod el fits to normal liver data. However, the hepatic blood supply may be appr oximated by the arterial input function as well, especially for the evaluat ion of liver lesions mainly fed by the hepatic artery.