Sensitivity of Four-electrode Focused Impedance Measurement (FIM) system for objects with different conductivity

Abstract

This work presents the results of an empirical study of the sensitivity of a four-electrode FIM
technique developed by us earlier, for objects of different conductivity. FIM has potential for the
characterization of biological tissue in physiological study and diagnosis. Experimental
measurements were performed on a 2D phantom made up of saline with a focused square zone at the
centre. Three cylindrical objects of different conductivities (an insulator, a conductor, and a piece of
potato offering an intermediate conductivity) were used for the sensitivity measurements. Adjacent
square zones had sensitivities of about 22% of that at the center for the insulator, about 13% for the
conductor and about 10% for potato, showing a better focusing in the last case. The outer locations
had negligible sensitivities. Inverse (negative) sensitivity, which is unavoidable in tetrapolar
impedance measurements, was small and negligible in all the cases. Degree of perturbation of
equipotential lines has been suggested to be the cause of the above differences in focusing, less
perturbation giving rise to better focusing, which would apply for most biological objects to be
studied using FIM.