Figure 4a:

(a) Schematic diagrams show key features of single-input, dual-input, single-compartment, and dual-compartment models. Single-input model (top) assumes vascular supply to hepatic lesions is mainly from hepatic artery, although normal liver is supplied from both hepatic artery and portal vein. Dual-input model (middle) adopts physiologic status of liver which is supplied by low-pressure portal vein (75%) and supplemented by high-pressure hepatic artery (25%). Using single-compartment model (top and middle), only vascular compartment is considered. Dual-compartment model (bottom) assumes dynamic distribution of contrast agent between two compartments. Using a dual-compartment model, kinetic properties such as permeability surface area product (PS) can be quantified. (b) Behavior of normal liver can be approximated by a single-compartment model because the space of Disse (equivalent to interstitial space of other organs) communicates freely with sinusoids through fenestrae. However, in disease states such as liver cirrhosis, deposition of collagen impedes free exchange of contrast material between the two spaces, requiring use of dual-compartment model.