Numerical analysis of contrast agent concentration in a tissue homogeneity model using computational fluid dynamics.

Using computational fluid dynamics (CFD), we demonstrated a method for numerical analysis of the transcapillary exchange of contrast agent (CA) in a tissue homogeneity (TH) model consisting of the intravascular space (IVS) and extravascular space (EVS). To validate the CFD method, we compared the time-dependent concentrations of CA in the IVS (C(i)(t)) and the EVS (C(e)(t)) obtained by it with analytical solutions to the TH model using the Laplace transform for a simulated arterial input function. When the diffusion of CA in the capillary was taken into account in the CFD method, there was a good agreement between its results and those of the analytical solutions. As illustrative examples, we presented C(i)(t) and C(e)(t) calculated by the CFD method for various permeability-surface area products (PS), velocities, blood flows, ratios of the volume of the EVS to that of the IVS and lengths of the capillary. We also studied the effect of diffusion and the case when the PS changed depending on the axial position along the capillary. We concluded that the CFD method presented here will be useful for analysis of CA in the TH model, and it will contribute to a better understanding of the transcapillary exchange of CA.