Optical-Thermal Response Research Of Skin Tissue

With the development of laser medicine, the distribution of laser propaga-tion in the biology tissue and the interaction between laser and tissue have become very important research topics. A new subject called 'tissue optics' has thus been motivated. Since the seminal work of R. R Anderson and J. A Parrish on 'selective photothermolysis effect' in 1980s, the laser techniques have been widely applied to skin hairdressing and treatment. However, the theory research, especially on how to set the light irradiation exposal dose, has been far behind the clinic applications. In practice, the light irradiation exposal dose is set blindly and tentatively in a sense which usually leads to the problems of security and validity.To solve the problem above, this dissertation aims to find the principal of optical-thermal interaction of biology tissues and thus to give some rules to set the light irradiation exposal dose and exposal parameters (pulse width, pulse interval, etc.) by using experimental design and numerical analysis methods.In the dissertation, the basic theory work, including the interaction be- tween the light and biology tissues, the light propagation and the heat trans-mission in tissues, are introduced firstly.Next, according to the characteristic that skin absorbs light induced ther-mal effect, Monte Carlo method is adopted to simulate and analyze the light distribution in the skin under different optical parameters.Then, a finite-element method (FEM) is employed to simulate the skin's optical-thermal response, focusing on the analysis of selection about light ir-radiation exposal dose and exposal parameters. An evaluation functionδis thus established to evaluate the loss of heat. Based onδ, the selection of pulse width and pulse interval is studied. These results are helpful to guide the selection of exposure parameters, such as pulse width and pulse interval, etc. In addition, the model of intense pulsed light (IPL) is put forward for the first time and is analyzed using FEM.The experimental study includes two aspects. Firstly, the spectrum char-acteristic experiment of skin tissue is studied. The porcine skin is chosen to be the sample for its similar characteristic with human skin, tissue-simulating phantoms (intralipid, india ink) as well. Their spectrums are analyzed and then the different spectrum characteristic between scattering particle and ab-sorbing particle is achieved. Using blood's spectrum, which contain these two kinds of particle, validate this verdict. Secondly, the optical-thermal response experiment of skin is studied. A new kind of two dimensional movable accu-rately thermocouple temperature measuring system which is fit for soft biol-ogy tissue is designed. This system's probe possesses high position accuracy (10um), moves easily in two dimensions. Using this system, the temperature experiments of laserCO2 , Nd:YAG and IPL irradiating porcine skin are meas-ured on line. The comparison has been made between prediction by FEM in chapter five and the experiments. The result reveals the better consistency between them. Also, the results'rationality of numerical simulation has been proved and can be used to guide the clinic application.This work is supported by National Natural Science Funds (No. 60678054).