Numerical Analysis And Experimental Research In Optical Thermal Response Of Bio-tissue

The transmission, distribution of optical radiation in tissue and the interaction of light with biological tissue are important basic issues in biomedical photonics research. Among a variety of effects in the interaction of light with biological tissue, the optical and thermal effect is the most important from the perspective of clinical application.At present, Monte Carlo simulation of the photons'random walk path in biological tissue has been relatively mature. Lihong Wang and S.L.Jacques's published Monte Carlo programs have been widely used in the analysis of optical transmission in tissues; the finite element method and finite difference method are generally used in thermal analysis. So far, studies have been carried out mostly on the case of laser irradiation, using fixed optical and thermal parameters to perform simulation, however, this is not fully in line with the real situation, As a matter of fact, biological tissue parameters such as optical and thermal parameters are closely related to temperature, in recent years, in addition to laser, other sort of compound light sources including the broad spectrum intense pulsed light source have been used more and more. Therefore, under the wide spectrum compound Light irradiation, the models and experimental methods for biological tissue thermal response characteristics analysis have vital practical significance.This paper combines numerical analysis and experimental methods, starts with the studying of the basic structure of biological tissue, discusses the basic mechanism of the interaction of light with biological tissue according to a variety of behaviors occurred after the interaction of light with biological tissue; On this basis, this paper analyzes the biological tissue heat conduction mechanism, describes the thermal damage phenomena and the heat transfer equation of biological tissue under light irradiation, and gives the expression of light heat items in the case of Gaussian and circular flat beam; Subsequently, using Monte Carlo method to analyze the photon number distribution and flow rate of light energy distribution inside the tissue during the interaction of light with biological tissue, applying the finite element method to solve the heat transfer equation of bovine muscle tissue containing heat source items, and then proposing a finite element method in the dynamic parameter case, calculating the optical and thermal parameters response of tissue under fixed and dynamic changes of tissue optical and thermal parameters respectively, the results are as follows: 1) if do not take the optical parameters (μaandμs) and thermal parameters (c,k andρ) changes with temperature into account, the temperature rising of bovine muscle tissue will be overestimated; 2) Compared with the thermal parameters, the dynamic optical parameters have a greater impact in the temperature response of bovine muscle tissue; 3) In the laser irradiation process, there will be an optical barrier forming near the surface of bovine muscle tissue, which may affect the photon number distribution in the surface and inside the tissue, thus affects the temperature distribution of the tissue.This paper also innovatively presents a finite element analysis and calculation model that can be used to analyze optical thermal response of biological tissues under any kind of compound light irradiation -- using monochromatic meter and optical power meter to measure the optical power of compound light source, and then applies it in numerical analysis; this paper uses a continuous xenon lamp as light source and measures its power spectrum distribution; According to the tissue optical and thermal parameters reported in the literature, this paper performs a simulation of the temperature response characteristics of porcine skin and liver, and uses self-designed two-dimensional spiral temperature measuring device in the experiment, measures the fresh porcine skin and liver temperature diversification under a continuous xenon lamp irradiation, conducts a validation of the correctness of the theoretical models. This paper is supported by the National Natural Science Foundation (No.60678054).