Non-invasive estimation of hepatic blood perfusion from H(2) (15)O PET images using tissue-derived arterial and portal input functions

The liver is perfused through the portal vein and the hepatic artery. When its perfusion is assessed using PET and 15O-labeled water (H2 15O), calculations require a dual blood input function (DIF), i.e., arterial and portal blood activity curves. The former can be generally obtained invasively, but blood withdrawal from the portal vein is not feasible in humans. The aim of the present study was to develop a new technique to estimate quantitative liver perfusion from H2 15O-PET images with a completely noninvasive approach. We studied normal pigs (n=14), in which arterial and portal blood tracer concentrations and Doppler ultrasonography flow rates were determined invasively to serve as reference measurements. Our technique consisted of using model DIF to create tissue model function, and the latter to simultaneously fit multiple liver time-activity curves from images. The parameters obtained reproduced the DIF. Simulation studies were performed to examine the magnitude of potential biases in the flow values, and to optimize the extraction of multiple tissue curves from the image. The simulation showed the error associated with assumed parameters was <10%, and the optimal number of tissue curves was between 10 and 20. The estimated DIFs were well reproduced against the measured ones. In addition, the calculated liver perfusion values were not different between the methods and showed a tight correlation (r=0.90). In conclusion, our results demonstrate DIF can be estimated directly from tissue curves obtained through H2 15O-PET imaging. This suggests the possibility to enable completely noninvasive technique to assess liver perfusion in patho-physiological studies.