3-Tissue Compartment Model, K1/k2, Vs

This 3-tissue compartment model separates free tracer C₁(t) and non-specifically bound tracer C₃(t) in the non-displaceable compartment. K₁ and k₂ describe the exchange between arterial plasma and tissue, k₃ and k₄ between free and specifically bound tracer C₂(t) in tissue, and k₅ and k₆ between free and non-specifically bound tracer.

Differential Equation of the Mass Balance

with input curve C_p(t).

Operational Model Curve

with the concentration C_B(t) of tracer in whole blood, and the blood volume fraction v_B.

Parameter Fitting using Distribution Volumes

This variant of the 3-Tissue Compartment Model uses three distribution volumes as fitting parameters: the distribution volume of free tracer (K1/k2), of non-specifically bound tracer Vns (= (K₁*k₅)/(k₂*k₆)), and specifically bound tracer Vs (=(K₁*k₃)/(k₂*k₄)) instead of k₂, k₄ and k₆.