Finite element analysis of temperature controlled coagulation in laser irradiated tissue.

The Theoretical study of thermal damage processes in laser irradiated tissue provides further insight into the design of optimal coagulation procedures. Controlled laser coagulation of tissue was studied theoretically using a finite element method with a modulating laser heat source to simulate feedback controlled laser delivery with a constant surface temperature. The effects of uncertainty in scattering and absorption properties of the tissue, thermal denaturation induced changes in optical properties, and surface convection were analyzed. Compared to a single pulse CW irradiation in which a doctor would presumably stop CW laser delivery after noticing some effect such as vaporization or carbonization, the constant surface temperature scenario provided a better overall control over the coagulation process. In particular, prediction of coagulative damage in a constant temperature scenario was less sensitive to uncertainties in optical properties and their dynamic changes during the course of coagulation. Also, subsurface overheating under surface convective conditions could be compensated for under constant temperature irradiation by lowering the surface temperature.