The thermal response of laser irradiated tissue

The extent of thermal destruction of tissue by visible and near-infrared lasers is governed by heat deposition in the tissue, heat transfer, and temperature-dependent rate reactions. Often the thermal response has been analyzed by linear models with constant coefficients that presume exponential absorption of the laser irradiation with depth. However, for weakly absorbing tissues, light scattering dominates the optical properties. These properties may be altered by thermal damage of the tissue. Also, thermal properties for tissue vary with temperature and water content. Typical therapeutic laser irradiations vaporize water in the tissue causing sharp increases in temperature beyond 100°C, and continued irradiation causes ablation of the tissue. Models for all these events are discussed.