[A tetrapolar circuit method using magnetic field for biological resistivity measurement]

A local impedance and its change were measured using a tetrapolar circuit combined with magnetic eddy current generator. By this method, current distribution can be restricted to a desired part, so as to eliminate errors due to uncertainty of the resistance between the electrode and the skin. The resistivity of a substance in a biological model measured by this method was nearly equal to that of the substance separated from the model. Sensitivity and localization were assessed in the other model composed of a piece of metal plate in a saline pool. The detection sensitivity was validated theoretically. The localization of the impedance pulsatile waveforms, measured at the proximal part of the forearm, was consistent with that of the arteries at this part. These results suggest that this method using eddy current should expand the application area of bio-impedance measurements.