A study of composite electrode-tissue impedance

Electrical impedance tomography has been used in the medical environment for many years. Recently it has been used for brain function imaging. This type of technology uses a large number of electrodes on the scalp, examples in the literature ranging from 8 to 64. In this paper, the composite impedance of the electrode in contact with tissue is investigated. An experimental method has been developed to enable the use of a commercial impedance analyzer in compliance with medical safety standards. The magnitude and long-term stability of the composite impedance of the electrode-tissue system is found to be greatly dependent on the type of electrodes used.