Non-invasive measurement of thermal conductivity and thermal diffusivity of Rat liver

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Thermophysical properties of biological materials are usually measured by using a thermal probe that is inserted into living tissues. Since a pool of blood and other fluids lay form around the probe because of mechanical trauma and it will significantly alter the result, a non-invasive technique is preferable for living tissues. The objective of this research was to develop a new technique to measure the thermal conductivity and the thermal diffusivity of biological materials, and to apply it to the rat liver.The temperature history of the specimen surface that was heated by a C0_2 laser was measured by an infrared thermometer. Both the thermal conductivity and the thermal diffusivity were determined from comparison of measured data with theoretical analysis of transient heat conduction for the same situation. One of the important points in the present technique was to exclude the effect of convection and radiation heat transfer on the temperature history.An acrylic resin block was chosen to check the validity of the present technique, and it was confirmed that the measured data agreed well with reference values. Then the present technique was applied to a rat liver. A SD rat was abdominally operated under anesthesia and the thermophysical properties of liver were measured in vivo. Appropriate data were obtained for a given value of absorption coefficient for the C0_2 laser, but the measured data depended largely on the absorption coefficient. Although more study is therefore needed to solve this problem, it was confirmed that the present technique was useful to clarify the effect of blood flow on the thermophysical properties.