Parametric evaluation of impedance curve in radiofrequency ablation: A quantitative description of the asymmetry and dynamic variation of impedance in bovine ex vivo model

Abstract

Radiofrequency ablation (RFA) is a treatment for liver tumors with advantages over the traditional treatment of surgical resection. This procedure has the shortest recovery time in early stage tumors. The objective of this study is to parameterize the impedance curve of the RFA procedure in an ex vivo model by defining seven parameters (t1/2, tminimum, tend, Zinitial, Z1/2, Zminimum and Zend). Based on these parameters, three performance indices are defined: one to identify the magnitude of impedance curve asymmetry (δ), one Drop ratio (DR) describing the percentage of impedance decrease until the minimum impedance point is reached, and Ascent Ratio (AR) describing the magnitude of increase in impedance from the minimum impedance point to its maximum point. Fifty ablations were performed in a bovine ex vivo model to measure and evaluate the proposed parameters and performance index. The results show that the groups had an average δ of 29.02%, DR of 22.41%, and AR of 545.33% for RFA without the use of saline or deionized solutions. The saline solution and deionized water-cooled groups indicated the correlation of performance indices δ, DR, and AR with the obtained final ablation volume. Therefore, by controlling these parameters and indices, lower recurrence is achieved.

Real-time monitoring of bioelectrical impedance for minimizing tissue carbonization in microwave ablation of porcine liver

“…After stopping the ablation, both the electrical impedance magnitude and temperature rapidly decrease from their peak values. The trend in electrical impedance magnitude exhibits resemblances to findings in the literature [28][29][30] . Additionally, variations in electrical impedance magnitude and temperatures among liver tissues in each experimental group stemmed from discrepancies in the ex vivo porcine liver and the diverse placements of electrical impedance probes.…”

Short-Time Impedance Spectroscopy Using a Mode-Switching Nonsinusoidal Oscillator: Applicability to Biological Tissues and Continuous Measurement

“…Thus, the absolute value and phase of bioimpedance are used to diagnose diseases, and this process is known as bioelectric impedance vector analysis [14][15][16][17][18][19]. Impedance measurement is also used in catheter ablation for treating arrhythmia [20][21][22][23]. By measuring the local impedance at an ablation site with electrodes integrated into an ablation catheter, the cauterization of myocardial tissue can be monitored.…”

Green-Synthesized Silver Nanoparticle–Assisted Radiofrequency Ablation for Improved Thermal Treatment Distribution

“…The temperature increases recorded every 10 s over the thermal procedure demonstrate the rapid heat increase over 60 °C for 40 s and the cooling process started as the machine turns off by reaching the tissue resistance threshold. The machine turns off due to the roll-off phenomenon preventing injury of the tissue during thermal therapy [ 58 , 59 ]. Since the power dissipated during RFA is inversely proportional to the electrical impedance, as shown in Equation (1): (where P —power, I —current, and Z —impedance), when the impedance is high in the targeted region, the power is not dissipated anymore and the liquid–vapor transition begins [ 60 ].…”