Characterization of Nonlinearity and Dispersion in Tissue Impedance During High-Frequency Electroporation

The use of high-voltage, high-frequency bipolar pulses (HFBPs) is an emerging electroporation-based therapy for the treatment of solid tumors. In this study, we quantify the extent of nonlinearity and dispersion during the HFBP treatment.

We utilize flat-plate electrodes to capture the impedance of the porcine liver tissue during the delivery of a burst of HFBPs of widths 1 and 2  $\mu$s at different pulse amplitudes. Next, we fit the impedance data to a frequency-dependent parallel RC network to determine the conductivity and permittivity of the tissue as a function of frequency, for different applied electric fields. Finally, we present a simple model to approximate the field distribution in the tissue using the conductivity function at a frequency that could minimize the errors due to approximation with a nondispersive model.

The conductivity/permittivity of the tissue was plotted as a function of frequency for different electric fields. It was found that the extent of dispersion reduces with higher applied electric field magnitudes.

This is the first study to quantify dispersion and nonlinearity in the tissue during the HFBP treatment. The data have been used to predict the field distribution in a numerical model of the liver tissue utilizing two needle electrodes.

The data and technique developed in this study to monitor the electrical properties of tissue during treatment can be used to generate treatment-planning models for future high-frequency electroporation therapies as well as provide insights regarding treatment effect.