Porous media based bio-heat transfer analysis on counter-current artery vein tissue phantoms: Applications in photo thermal therapy

The present work deals with the determination of transient variation of temperature distributions inside laser irradiated biological tissue phantoms consisting of an artery-vein counter current arrangement. An optical inhomogeneity that is absorbing in nature and embedded inside an otherwise homogenous medium has been employed to model the abnormal cells. The surrounding tissue region has been modeled as a porous medium consisting of solid and fluid matrices. Separate energy equations for solid and fluid matrices of the porous tissue regions have been solved as part of the bio-heat transfer model. A short pulse laser has been employed to irradiate the phantom. A numerical model coupling the Discrete Ordinates Method (DOM) for solving the transient form of Radiative Transport Equation (RTE) with that of the porous media based bio-heat transfer model has been developed and benchmarked. The convective cooling effects of blood flow through a single blood vessel as well as counter current blood vessels under local thermal non-equilibrium (LTNE) conditions have been investigated. Thermal response of the porous tissue phantom with respect to the changes in the Reynolds number (Re = 1 and 10) and for varying porosity levels has been presented. The effect of blood vessel diameter on the resultant temperature distribution within the body of the laser irradiated tissue phantom has been studied. Results have been presented in the form of temporal variations of temperature distributions, local variations in the heat transfer rates (Nusselt numbers) along the spatial dimensions of various interfaces present in the physical domain. Finally, the influence of the position of the embedded inhomogeneity with respect to the point of laser irradiation on the temperature rise at the location of the inhomogeneity has been investigated. The study reveals a strong dependence of the maximum possible temperature rise on the relative position of the embedded abnormal cells for a given set of laser parameters.