NONLINEAR FINITE-ELEMENT ANALYSIS OF THE ROLE OF DYNAMIC CHANGES IN BLOOD PERFUSION AND OPTICAL-PROPERTIES IN LASER COAGULATION OF TISSUE

A nonlinear finite-element program was developed to simulate the dynam ic evolution of coagulation in tissue considering temperature and dama ge dependence of both the optical properties and blood perfusion rate, These dynamic parameters were derived based on the Arrhenius rate pro cess formulation of thermal damage and kinetics of vasodilation. Using this nonlinear model, we found that the region of increased blood flo w that formed at the periphery of the coagulation region significantly reduces the heat penetration, Moreover, increased scattering in the n ear-surface region prevents light penetration into the deeper region, Therefore, if the dynamic parameters are ignored, a relatively signifi cant overestimation of the temperature rise occurs in a deeper area re sulting in an overestimation in predicted depth of coagulation, Mathem atical modeling techniques that simulate laser coagulation may not pro vide reliable information unless they take into account these dynamic parameters.