A model with vascular binding has been developed by Rizzo et al.  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 Cvasc 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 Cp(t).
Operational Model Curve
with the concentration CB(t) of tracer in whole blood, and the blood volume fraction vB.
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.