Figure 1. Illustration of a dual-input single-compartment model. C_a(t), C_p(t) and C_L(t) represent the concentrations of the contrast agent (CA) at time t in the hepatic artery or aorta, the portal vein, and the liver region of interest, respectively. K_1a, K_1p and k₂ are the rate constants for the exchanges of CA from the hepatic artery or aorta to the liver, from the portal vein to the liver, and from the liver to plasma, respectively.