Dielectric properties of rat liver in vivo: a noninvasive approach using an open-ended coaxial probe at audio/radio frequencies

To characterize the passive electrical properties of liver cells in vivo, we measured the frequency dependence of relative permittivity and conductivity for rat liver lobes in situ by means of a noninvasive surface probe coupled with a fast impedance analyzer, covering the frequency range 10²–10⁸ Hz. Securing a stable contact, mechanical as well as electrochemical, between the probe and tissue surface both wetted with physiological saline, made it possible to collect a highly reproducible set of data even from lobes undergoing respiratory movement in situ. The data obtained traced a broad dielectric dispersion curve over the range 10³–10⁸ Hz, suggestive of the involvement of widely distributed relaxation times. As its theoretical analyses based on cell membrane models are made in a companion paper [V. Raicu, T. Saibara, H. Enzan, A. Irimajiri, Dielectric properties of rat liver in vivo: analysis by modeling hepatocytes in the tissue architecture, Bioelectrochem. Bioenerg. 47 (1998) 333–342.], this report describes experimental conditions required for reliable measurements on a well-defined superficial region of viable liver lobes. The most important factors among these are the tissue surface condition such as `wet' or `dry' and the effective penetration depth of field lines defined by the probe's geometric characteristics.