In-Vivo Measurement of Thermal Diffusivity of Living Subcutaneous Tissue

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In the academic year 1991, the principle of the measurement and its accuracy had been examined theoretically at first, then the thermal conductivity and diffusivity were measured for the solid materials with known thermophysical properties similar to those biological tissues and organs. From these measurements, the problems existing in the method had been clarified. In the academic year 1992, three dimensional temperature distributions in a solid were obtained numerically, then some new methods were proposed and their accuracy and applicability for the anisotropic materials were examined. Further, the measurements had been done to obtain thermal conductivity and diffusivity of the subcutaneous tissues of the brachium and the back of the hand. The main achievements of the project are concluded as follows:1. Two-dimensional symmetric heat conduction equation was solved numerically under the boundary conditions of local heating, and convection and radiation heat losses on the surface. Whe … More n the non-dimensional temperature is defined by using the average net heat flux over the heating area, an unique relation between the non-dimensional temperature and Fourier number can be obtained which is independent of these heat losses. This relation can be used to evaluate the thermal conductivity and diffusivity simultaneously.2. It is found that the present method could obtain the thermal conductivity and diffusivity of non-metal solids within an error of 10%, when the errors of heat flux and heating radius are estimated within 5% and 3%, respectively. With the help of measured results of such materials as Acryl and Chloride Vinyl plates, the reflective fraction of laser power has been estimated accurately. When the heat flux is corrected, the errors of thermal conductivity and diffusivity can be further reduced to 2-5%.3. Three-dimensional bioheat transfer equation was analyzed numerically. The effects of the anisotropic characteristic, perfusion and metabolic rate on the surface temperature distributions have been clarified.4. To improve the accuracy of measurement and to apply the method for anisotropic materials, multi-points values of the temperature-time response of the heated surface were used, and some new expanded methods have been proposed. The availability of these methods have been examined.5. The temperature-time responses of the heated surfaces of the brachium and the back of the hand have been recorded under both normal and hemostasis conditions. The effects of the perfusion and metabolic rate on thermal conductivity and diffusivity of subcutaneous tissues have now been examining based on the above new methods. Less