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 theore tically using a finite element method with a modulating laser heat sou rce to simulate feedback controlled laser delivery with a constant sur face temperature. The effects of uncertainty in scattering and absorpt ion 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 c arbonization, the constant surface temperature scenario provided a bet ter overall control over the coagulation process. In particular, predi ction of coagulative damage in a constant temperature scenario was les s sensitive to uncertainties in optical properties and their dynamic c hanges during the course of coagulation. Also, subsurface overheating under surface convective conditions could be compensated for under con stant temperature irradiation by lowering the surface temperature.