Selection of measurement frequencies for optimal extraction of tissue impedance model parameters

The results are presented of a study performed to determine the measurement frequencies that provide optimal extraction of tissue impedance model para meters from in vivo measured electrical impedance spectra. Measurement freq uency sets that are logarithmic and quasi-linear, and frequency sets that p roduce angularly equidistant points on the Nyquist loci are used to test th e parametric fitting algorithm that calculates R-0, R-infinity, alpha and t au tissue parameters from complex impedance spectra. Simulated data, calcul ated in the presence of less than or equal to 5% measurement noise, and in vivo experiments indicate that the quality of the fitted parameters depends upon the selection of measurement frequencies. The results show that, if m easurements are performed with a system that has a realistic measurement ba ndwidth, then, for the best estimation of: R-0, the measurement frequencies should include the decade from 100 Hz-1kHz; R-infinity, the algorithm shou ld not include frequencies under 1 kHz; alpha and tau, the measurement freq uencies should be equidistantly spaced on the Nyquist locus.