Simulation of tissue heating by a short light pulse

Abstract

We have stated and analytically solved heat transfer equations for a multi-component biological tissue iluminated by a temporal delta-pulse at different heat exchange mechanisms between blood vessels and its surroundings of basic tissue and between the tissue as a whole and its ambient external medium. The contribution of each mechanism to temperature fields inside the tissue is studied in detail. Empirical constants of the mechanisms are estimated from rather strict and general viewpoints of thermal physics. Specific numerical values of the constants are given for air or water as the environment. The starting HTEs were substantially simplified by evaluating optical and thermal physical parameters of tissues to show that the tissue can be regarded as optically and thermally uniform with localized light absorption or additional heat sources in blood vessels. The thermal fuction of a human organism is approximated to include the boundary contact of a tissue with an ambient medium having a temperature other than that of the tissue. The applicability limits of the used 1D HTEs are discussed and substantiated for the estimations. Sample results illustrating temporal and spatial temperature distributions for convective and thermal conduction surface losses to the environment are given. It is shown, in particular, that the lower the volume content of blood vessels in tissue, the higher the temperature of the vessels and their tissue surroudings immediately after irradiation. The opposite situation occurs in a fraction of a millisecond after the irradiation, i.e. the tissue temperature increases with the volume content of the vessels.