Study On The Temperature Distribution In Skin Tissue Induced By Laser Based On Thermal Pain Stimulation

Pain has important research value in basic research and clinical application.And the pain evoked potentials is used to researching pain frequently.LEPs(Laser evoked potentials)is one of the most competitive techniques in the field of pain evoked potential technology.Since the appearance of LEPs,because of its unique advantages,such as objective and accurate diagnosis results and shorter measurement time,it has been favored by most experts and scholars.In order to selecting the reasonable laser dose objectively and accurately can achieve the best pain effect while avoiding the damage of normal tissue,the mechanism of pain induced by LEPs has become the main focus of the study.So,the effect of tissue photo thermal had been become the focus by most scholars.And the method of establishing tissue temperature distribution model was used to study,and have made breakthrough research results.However,most of the research results are only applicable to mid far infrared lasers,and few achievements have been made on the mechanism of near infrared laser induced pain.Compared with mid and far infrared laser,using near infrared laser for pain stimulation,not only can reduce the risk of damage to the skin surface,but also can directly activate the nociceptive receptor to ensure the accuracy of the pain signal.Therefore,it is urgent to establish a simple and accurate model of tissue temperature distribution induced by laser irradiation,which is used to guide the experimental study and clinical application of near infrared laser in pain stimulation.In order to solve the above problems,in this study,980nm pulsed laser,which has been successfully applied to LEPs research,had been taken as a breakthrough.The photo thermal effect had been studied which near infrared laser in biological tissue,and establish the corresponding model.And a corresponding model had been established to solve the problem of lacking theoretical model in the study of laser stimulated pain.At first,in this study,according to the form of interaction between 980nm laser and biological tissue,three layers skin model was optimized.And a five-layer finite element model(FEM-5)was constructed,which includes the stratum corneum layer,epiderrmis layer,upper dermis layer,blood layer,and lower dermis layer.At the same time,the biological heat conduction equation of Pennes was confirmed as the theoretical foundation of establishing the model.The approximate solution of the equation is solved by the finite element analysis method.Secondly,according to the radiative transfer equation describing the light distribution in skin tissue,the diffuse scattering equation was used to solve the approximate solution about flux density in skin tissue.According to the change of luminous process laser heat source formation and tissue density,while considering the scattering effect,the general expressions of the source term could be gotten.Then,according to the structure of the skin model,the laser heat source and the Pennes biological heat conduction equation are optimized carefully.According to the actual situation,the boundary condition and initial condition of the equation were determined.MATLAB software was used to simulate the model results.Finally,the accuracy of the model was verified by in vitro and in vivo experiments.The results of experiments had been shown that the model can determine the laser dose objectively and accurately,so as to achieve a safe and effective stimulation of pain,and avoid unnecessary damage.Then the temperature distribution model had been established which induced by 980nm pulsed laser in skin tissue.