A simple model to study heat transfer in two-component biological tissues under laser irradiation

An analytical approach is proposed to treat heat transfer through two-component biological tissues composing of bloodless base and blood vessels under irradiation by a pulse light beam of finite dimensions and arbitrary duration. The approach is based on the optical and thermal tissue model accounting for individual optical characteristics of the above components, heat exchange between them, and convection losses at the interface with any external medium. Under reasonable assumptions, the Green function of the equation set for bloodless tissue and blood is expressed as a product of the corresponding Green function for an infinitely wide beam by a simple radial function determined by the radial shape of the irradiating light. So for any temporal structure of the external radiation, temperature rise of the composite tissue is a single convolution-like integral from analytical functions. This enables us to study explicitly some limiting cases of the heating and cooling. The effects of critical parameters of the problem and asymptotic temperature regimes gain a physically vivid and transparent form. Sample examples of these effects are considered and discussed in the paper.