2-Tissue Compartment Model with Vascular Binding

A model with vascular binding has been developed by Rizzo et al. [1] for the analysis of [11C]-PBR28 uptake in the human brain. In addition to the compartments in the standard 2-tissue compartment model, a compartment C_vasc was introduced which represents slow binding of the tracer to the endothelium of the vasculature. This variant allows for reversible endothelial binding. Additionally, K₁/k₂ was introduced as a fit parameter, allowing to reduce the number of fit parameters via regional parameter coupling.

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

The model includes the 6 fitable parameters vB, K1, K1/k2, k3, k4, Kb1 and kb2. Usually, vB is fixed at a physiologic value of 3-5%. Where possible, the default initial parameter values are the ones which were used for PBR28.