Parameter estimation of lumped element circuit for tissue impedance

Equivalent circuits representing tissue impedances in the beta dispersion region are dealt with. The circuits composed of lumped elements (resistance and capacitance) are used because of easiness and usefulness for corresponding circuit elements to tissue structures, especially from a viewpoint of tissue diagnoses. Higher order circuits with four to six elements are considered in addition to a conventional three elements circuit, to represent higher frequency impedances as well as low frequency ones. A modified Levenberg Marquardt's algorithm is applied for estimating parameter values of the equivalent circuits from given impedance data. It was found from computer simulations that the algorithm can estimate the parameter values with high precision, even for the data including noise. The higher order equivalent circuits and the parameter estimation will be useful for medical diagnoses on the tissue.