Quantitative measurement of regional porcine hepatic blood flow by [O-15]H2O and[O-15]CO positron emission tomography (PET)

Background: Due to the dual blood supply of the liver, to date no satisfact ory method has been available for the quantitative in vivo measurement of h epatic hemodynamics. This study was undertaken to evaluate [O-15]H2O PET in the analysis of liver hemodynamics. In principle, the freely diffusible tr acer [O-15]H2O allows the determination of the arterial and portal venous b lood flow. [O-15]CO allows the determination of the localization of larger vessels within the field of view. Methods: Liver blood flow was investigated in 7 anaesthetized pigs. To inve stigate the reliability of [O-15]H2O PET measurements over a wide now range , segmental arterial flow reductions were induced by occlusions of several branches of the hepatic artery. After bolus injection of [O-15]H2O, liver b lood flow was measured by a 10-min. dynamic PET scan, followed by a 10-min. [O-15]CO PET scan in 4 experiments. Kinetic parameters for arterial and po rtal venous blood flow were estimated from tissue, arterial and portal veno us blood activity curves using an extended one tissue compartment model to account for the dual blood supply. The resulting flow estimates were then c ompared with microspheres reference blood flow measurements obtained from m ultiple liver tissue samples. Results: A highly significant positive correlation between regional arteria l blood flow measurements using PET and microspheres was found (r(2) = 0,80 ; p < 0,001). As long as the shape of the portal venous blood activity curv e was different from the tissue response curve, portal venous blood flow co uld be predicted from [O-15]H2O PET with high accuracy (r(2) = 0,77; p < 0, 001). The portal vein was easily identified in [O-15]CO PET images, which a llowed to define regions of interest within the portal vein in order to obt ain the portal input function non-invasively. Repeated [O-15]H2O PET scans in 3 experiments revealed a highly significant correlation between measurem ents of f(a) and f(p) (f(a): r(2) = 0,95; f(p): r(2) = 0,79; p < 0,001). Conclusion: The arterial liver blood now can be estimated precisely with [O -15]H2O PET. [O-15]H2O PET can address portal venous blood flow, as long as the shape of the portal venous blood activity curve differs from the tissu e response curve (which can easily be checked). Additional [O-15]CO PET eli minates the need to catheterize the portal vein for portal venous blood flo w estimation, which is a precondition for clinical applications of the meth od in transplantation dysfunctions, liver cirrhosis and malignancies.