Thermodynamic analysis of laser irradiation of biological tissue.

A mathematical model is presented for the calculation of the 3-D time-dependent temperature distribution in a biological tissue (slab) irradiated by a laser beam of rectangular or Gaussian profile, which takes into account the different thermooptical properties of the tissue. Detailed consideration is given to the phenomenon of redistributive internal scattering, which is of noticeable magnitude in the irradiation by the argon-ion and Nd:YAG lasers commonly used for tissue coagulation in medicine. Satisfactory agreement is found with temperature measurements performed with a thermocamera, and the CO(2) and Nd:YAG lasers are compared qualitatively and quantitatively.