Numerical Analysis And Experimental Research On Laser Induced Thermal Effect In Bio-tissues

This dissertation is devoted to provide full parameters prediction method of laser induced bio-tissue thermal effect by combining numerical analysis and experimental means. This research is in the interest of exploring bio-heat transfer theory in the laser medicine and enhancing the security and validity of laser application.At first laser heat source term expression was modified in the heat conduction equation from analyzing the light distribution and thermal transferring in the bio-tissue, and multilayer model was presented. Solution conditions of heat transfer equation were summarized entirely, which include tissue optical properties, tissue thermal properties, blood perfusion rate, boundary conditions and initial conditions. Laser characteristics are also important parameters adapt to choosing and controlling. Then the bio-heat transfer equation was solved numerically. The compute area was divided reasonably to two dimensions in the axial symmetry cylinder coordinate. The Finite Element Method(FEM) realized by Matlab software is used to solve the bio-heat transfer nonlinear Partial Differential Equation(PDE). The tissue temperature distribution was calculated and can display in three dimensions dynamically. The temperature response of several typical thermal laser applications were simulated, such as the typical scatter dominating Nd:YAG laser coagulating the liver in the Laser Interstitial Thermotherapy (LITT), Nd:YAG laser irradiating the in vivo murine skin, typical absorption dominating CO2 laser irradiating in vitro porcine tissue, CO2 laser irradiating in vivo murine skin and the three layers model of HeNe laser irradiating in vivo human skin. The temperature of space distribution and time behavior on different conditions can be shown clearly from the simulation results. The influence of light source, perfusion and multilayer to the calculation results was analysed. And the temperature dynamical balance phenomena of in vivo tissue under low power and long time laser irradiation was discussed. Finally, in order to validate the veracity of theory model and calculation an experiment system which can be used in noninvasive or minimally invasive temperature measuring in laser medicine was constructed. This system used miniature thermocouple and infrared radiation thermometer to monitor the inner and surface temperature synchronously. Such a system is suitable to high precision, large range, minute point and rapid response temperature measuring. Several group experiments were designed in the clinic application range by changing the laser parameters(laser power, continue/pulse, irradiate time). Temperature of Two typical thermal effect laser, CO2 and Nd:YAG laser, irradiating several tissue, in vitro porcine liver, fat, muscle and in vivo murine skin were measured on line. The temperature experiments of pulse CO2 and Nd:YAG laser irradiating in vivo murine skin were done at the first time. The temperature changing rule before, during and after laser irradiating were recorded, some main influencing factors were summarized and analysed. The results proved the prediction and experiments have well coherence. The modified model is more reasonable. This method can be applied in several thermal laser application prediction and can obtain permanent life with the development of noninvasive measurement techniques of tissue properties.This work has been supported by Tianjin Natural Science Funds(Research on real time monitoring and prediction technique of Laser-Tissue Thermal Damage, No. 023602611).