New tetrapolar circuit method using magnetic field for measurement of local impedance change in biological substances

A tetrapolar circuit and method using a magnetic field is proposed for measuring the local electric impedance change in living tissue. On the basis of this method, the authors designed an apparatus that can detect impedance changes in two closely situated parts of living tissue, simultaneously and independently. Using this apparatus, they showed the effectiveness of the proposed method by an in vitro experiment and by an in vivo measurement of pulsatile waveforms in the forearm arteries. The detection sensitivity for a local impedance change was confirmed to be higher than that of the conventional tetrapolar method. Pulsatile impedance waveforms measured in the radial and the ulnar parts of the forearm were consistent with those estimated from the anatomical structure.