A STUDY OF THERMAL LASER ABLATION OF BIOLOGICAL TISSUES

Abstract

In this thesis we have studied the thermal laser-tissue ablation process theoretically and experimentally. We have chosen an existing one­ dimensional mixed initial-boundary value model, which describes light penetration, heat and water diffusion, carbonization and subsurface explosive vaporization for the case of absorbing media. We have modified this model by:

1- introducing the radial component in the analysis; 2- taking into account the effect of light scattering; 3- taking into account the effect of heat generation due to the exothermic reactions during carbonization; and 4- incorporate the damage rate model (Arrhenius rate model) to estimate the extent of thermal damage. The value of our modification in this new model has been discussed. We have also studied the process of laser ablation of biological tissues experimentally using 980 nm, 18 watts Diode laser, focusing our study on the Sclera tissue and collecting some experimental data regarding the temperature distribution and the depth of ablation. These experimental data were compared with the results of both the old existing and the newly developed models. The causes of discrepancy and the suggestion for further improvement are presented. The model has then been used to study numerically; the effect of laser parameters on scleral ablation (the optimum parameters for this process as suggested by the model are presented); and the role of optical properties of tissues and its temperature dependence in laser irradiation of tissues. Suggestion for further improvement of the model are presented.