CONTACTLESS IMPEDANCE MEASUREMENT BY MAGNETIC INDUCTION - A POSSIBLE METHOD FOR INVESTIGATION OF BRAIN IMPEDANCE

Using a primary coil that induces eddy currents in a volume conductor, and a pair of secondary coils configured to form a differential trans former, it is possible to measure the conductivity of a volume conduct or by the magnetic fields of the induced eddy currents. This method is especially favourable for measuring impedance of the brain, as the lo w conductance of the surrounding skull interferes only very slightly w ith the measuring process. In a simulation experiment a life-size skul l model was filled with NaCl solutions of different concentrations in each half, so as to model the impedances of a normal and an oedematous hemisphere. The impedance differences could be clearly detected by a coil system of 25 mm diameter.