.532 Nm, Continuous Process Of Laser Head Thermal Effect And Mechanism

The investigation on the thermal coagulation process and mechanism of rat brain irradiated by 532nm CW laser is performed by means of animal experiments, heat conductive modeling and numerical analysis.Experimental investigation on cerebral infarction of adult rats irradiated by 532nm CW laser(power 0.15W, spot size 2mm) is performed. There is no nervous cell at the center of the coagulation region. At the transitional zone there are partially damaged neurons. Computer image analysis technique is used to measure the area of the coagulation region.To obtain fluence distribution and heat source distribution in brain tissue irradiated by 532nm laser, simulation is carried out using Monte Carlo model. Simulation results imply light parameters such as absorption coefficient, scattering coefficient and anisotropic factor etc mainly affect distribution of fluence and heat source in the superficial layer of about 2mm in thickness.Tissue heat conductive equation is set up based on two-layered structure model. Finite difference algorithm is utilized to numerically simulate the temperature distribution in the brain tissue. Free boundary model is used to study tissue coagulation formation. The given mode of thermal coagulation comprises two stages, fast and slow. At the first stage necrosis domain grows fast. Then the necrosis domain growth becomes slower because of the competition between the heat diffusion into the surrounding undamaged tissue and the heat dissipation caused by blood perfusion. Coagulation region changes very little when prolonging irradiating time. The percentage of the coagulation region is in accord with the result of the animal experiment.The results of the thesis may offer reference to coagulate pathological brain tissue through skull and model cerebral infarction with 532nm CW laser.