Study of temperature distribution in light--tissue interaction using the FEM

Abstract

In this paper, the numerical modeling of interaction between light sources and living biological tissue is studied. One of the most important results of physical interactions of light with biological tissue are thermal changes, which are a consequence of absorption of light. The severity of the effects is dependent upon several factors, including exposure duration, wavelength of the beam, beam energy, tissue type, and the area that is exposed to the beam. The temperature response of tissue irradiation is governed by the extensively used Pennes bioheat equation in a 3-dimensional space. The Pennes equation is solved initially for a single-layer human skin model, thanks to which temperature distribution can be predicted using different laser light radiation burns at steady state. Furthermore, a multilayer model is used to investigate the effects of the energy of the beam and exposure duration. The numerical solutions are obtained by the finite element method (FEM), in which the geometry studied is divided into a finite element mesh. This method gives a better description of the geometry with a smaller number of nodes when compared with the finite difference time domain (FDTD) method. Using the FDTD method, which may require spatial step ranges to achieve convergence, makes the computational simulation time increase dramatically. On the contrary, less memory space and disk space with shorter run times make the FEM more advantageous than other numerical solution techniques and that is why this method has been chosen for this study. Temperature contours and penetration depths are plotted in 3-dimensional spaces. In this work it is demonstrated that by adjusting the exposure duration, wavelength of the beam, energy of the beam, and the area and type of tissue, temperature effects of light on tissue can be altered.