Characterization of Conductivity Changes During High-Frequency Irreversible Electroporation for Treatment Planning.

For irreversible-electroporation (IRE)-based therapies, the underlying electric field distribution in the target tissue is influenced by the electroporation-induced conductivity changes and is important for predicting the treatment zone. OBJECTIVE: In this study, we characterized the liver tissue conductivity changes during high-frequency irreversible electroporation (H-FIRE) treatments of widths 5 and 10 µs and proposed a method for predicting the ablation zones. METHODS: To achieve this, we created a finite-element model of the tissue treated with H-FIRE and IRE pulses based on experiments conducted in an in-vivo rabbit liver study. We performed a parametric sweep on a Heaviside function that captured the tissue conductivity versus electric field behavior to yield a model current close to the experimental current during the first burst/pulse. A temperature module was added to account for the current increase in subsequent bursts/pulses. The evolution of the electric field at the end of the treatment was overlaid on the experimental ablation zones determined from hematoxylin and eosin staining to find the field thresholds of ablation. RESULTS: Dynamic conductivity curves that provided a statistically significant relation between the model and experimental results were determined for H-FIRE. In addition, the field thresholds of ablation were obtained for the tested H-FIRE parameters. CONCLUSION: The proposed numerical model can simulate the electroporation process during H-FIRE. SIGNIFICANCE: The treatment planning method developed in this study can be translated to H-FIRE treatments of different widths and for different tissue types.

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

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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. SIGNIFICANCE: 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.