This 3-tissue compartment model separates free tracer C_{1}(t) and non-specifically bound tracer C_{3}(t) in the non-displaceable compartment. K_{1} and k_{2} describe the exchange between arterial plasma and tissue, k_{3} and k_{4} between free and specifically bound tracer C_{2}(t) in tissue, and k_{5} and k_{6} 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** (= (K_{1}*k_{5})/(k_{2}*k_{6})), and specifically bound tracer **Vs** (=(K_{1}*k_{3})/(k_{2}*k_{4})) instead of k_{2}, k_{4} and k_{6}.