Modeling the thermal response of porcine cartilage to laser irradiation

During laser irradiation of biological tissue, a number of physical processes take place that determine temperature elevation and thermal damage rates. Some of those important to laser-tissue interaction are: 1) propagation of light in scattering media; 2) transformation of laser light into photochemical, acoustic, or thermal energy; 3) tissue-tissue and tissue-environment heat and mass transfer; 4) and the occurrence of low-energy phase transformations responsible for structural alterations. The aim of this study was to formulate a finite-element model (FEM) able to predict the temperature distribution in a slab of porcine nasal cartilage during laser irradiation. The FEM incorporates heat diffusion, light propagation in tissue, and water evaporation from the surfaces of the slab. Numerical results were compared to experimental temperature distributions where surface and internal temperatures were measured while heating cartilage using a pulsed Nd: YAG laser (λ = 1.32 μm). Rectangular specimens, 1-4-mm thick, were secured perpendicular to the laser beam and irradiated for 1-15 s using different laser-beam powers (1-10 W)