STUDY OF THE FLUID DISTRIBUTION BY MULTI-FREQUENCY IMPEDANCE CT

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1. We have tried to estimate the intra- and extra-cellular fluid distribution in the specified tissue from the frequency characteristics of tissue impedance in a β dispersion region. In order to extract the information of the specified tissue from the impedance measured on the body surface, we designed and produced the multi-frequency impedance CT.2. There is a important problem we must solve before applying the multi-frequency impedance CT. The relation between the intra- and extra-cellular fluid distribution and the electrical impedance of the specific tissue is not quantitatively understood yet. In order to collaborate the relation, we made the following three experiments.(1) Changing the NaCl concentration in plasma controlled the size of erythrocytes. We experimentally measured the impedance change of the flowing blood, hematcrit and the size of erythrocytes. And discussed the relation theoretically. From the results, it is found that the resistance of tissue at low frequency is related to the extra-cellular fluid volume and that at high frequency the extra- and intra-cellular fluid volume. And the intra-cellular resistance changes in proportion to the change of intracellular fluid volume but the change rate of the extra-cellular resistance is less than that of the extra-cellular fluid volume. The change rate of the extra-cellular fluid depends upon the cell size and arrangement. Under these fundamental results,(2) we estimated the shift fluid volume in the intra- and extra-cellular by the change of the leg impedance during HD, HDF and ECUM hemodialysis. The change of leg impedance provides us the information about the condition of the intra- and extra-cellular fluid distribution change.(3) When the tissue temperature rises up during hyperthermia therapy, the tissue impedance decreases and the blood volume and flow in the tissue increase. We could estimate the blood volume change by the multi-frequency impedance method.