Quantitative technique for bio-electrical spectroscopy

Bio-electrical impedance measurements have been widely used for the study of body tissues. Apart from recordings of biophysical signals (respiration, perfusion, cardiac output, red cell settling, etc.) measurements of specific resistivity of a tissue provide information about its pathological state. Mapping electrical parameters will give more detailed information. The interpretation of recorded data and the design of equipment, both require a preliminary knowledge of the values encountered under normal and pathological conditions. The purpose of the technique described here is to determine the complex resistivity of breast tissue samples in vitro at frequencies between 0.5 kHz and 1 MHz. The equipment is described and the calibration procedure explained. A calculation of the final error interval is given. Characteristic spectra of modulus and phase angle recorded in normal and pathological breast tissue are shown. The technique can however be used for other body tissues, typical applications being fundamental tissue studies and a determination of the most suitable frequencies for use with impedance measuring devices. In clinical practice it could contribute to the determination of intra- and extracellular volume, the monitoring of transplanted organs and the examination of surgically treated tumours, and to any technique based on tissue characterization.