A study on imaging of thermal properties of the skin

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The aim of this study is to develop a non-contact imaging system of emissivity and thermal inertia of the skin. In this study, results as follows have been achieved. The system consists of a thermal camera and a hood covering the object surface in which the temperature of its inside is controlled so as to realize a step change of the surface radiation. The emissivity can be estimated from the apparent change of radiation, and the thermal inertia can be estimated from the slope of increasing object surface temperature. The estimations can be performed at each pixel so that images of emissivity and thermal inertia of skin can be obtained. Observed emissivities were consistent with other measurement data including that of ours using high precision spot radiometer. Thermal inertia values were also consistent with other reports. Parallel relation between thermal inertia and blood flow of the skin was also observed. As an application of this method, the change in thermal inertia before and after arterial occlusion was studied, and we found that non-uniform thermal inertia image was observed together with a reactive hyperemia. This fact suggests that blood flow distribution just after an arterial occlusion is non-uniform. While the system could be used for such physiological studies, improvements of the measurement system were attempted so as to apply in clinical diagnosis. A modified system was proposed in that a radiation source with a mechanical shutter placed distant from the object is used instead of the hood. A preliminary study showed that the method is quite promising. Relating to this measurement principle and configuration of the system, a patent was applied.