Methods of information extraction from impedance spectra of biological tissue, in particular skin and oral mucosa - a critical review and suggestions for the future

Although classical models of tissues, such as those based upon the Cole-equation, usually give an adequate fit to the measured data, the parameter sensitivity if often very low, and interpretation of the model is difficult in the context of multi-layered structures as skin and mucosa. Four indices have been found to extract most of the information in the relevant part of the complex electrical impedance spectrum for skin and oral mucosa. Each index can be used to quantify tissue reactions, and patterns of the set of indices facilitates classification of some types of reactions or diseases. No lumped or distributed parameter model is assumed. Tolerance tables of index baseline data facilitates evaluation of tissue conditions also when all skin or oral mucosa are involved, but contra-lateral or ipsi-lateral reference sites are strongly recommended when possible, or a site could be followed in time before and after exposure to a test substance in an experimental situation. (C) 1998 Elsevier Science S.A. All rights reserved.