The effect of methodology and tracer identity on a non-invasive index of liver blood flow.
There are a number of clinical conditions in which quantification of the relative flow in the arterial and portal vessels supplying the liver may be of diagnostic use. The hepatic perfusion index has been proposed as a non-invasive indicator of relative blood flows. The technique involves analysis of first-pass time-activity curves over the liver and kidney with the calculations of an index which is derived from the slopes of the hepatic curve before and after the renal peak. In previously published studies, the methodology adopted has been variable, both in the analysis and in tracer identity. This study examines the effect of both physical and physiological variables on the index. The results indicate that in addition to relative arterial and portal flows, the index is dependent on bolus quality, the length of time over which the slopes are averaged, transit times through the liver and splenic and mesenteric circulations, and the degree of tracer extraction. Furthermore, the data suggest that values in the currently considered abnormal range may be poor indicators of relative arterial and portal venous flows.