Finite-element modeling of needle electrodes in tissue from the perspective of frequent model computation

Abstract

Information about electric field distribution in tissue is very important for effective electropermeabilization. In heterogeneous tissues with complex geometry, finite-element (FE) models provide one of alternative sources of such information. In the present study, modeling of needle electrode geometry in the FE model was investigated in order to determine the most appropriate geometry by considering the need for frequent FE model computation present in electroporation models. The 8-faceted needle electrode geometry proposed--determined on a model with a single needle electrode pair by means of criteria function--consisted of the weighted sum of relative difference between measured and computed total current, the relative difference in CPU time spent on solving model, and the relative difference in cross section surface of electrodes. Such electrode geometry was further evaluated on physical models with needle arrays by comparison of computed total current and measured current. The agreement between modeled and measured current was good (within 9% of measurement), except in cases with very thin gel. For voltage above 50 V, a linear relationship between current and voltage was observed in measurements. But at lower voltages, a nonlinear behavior was detected resulting from side (electrochemical) effects at electrode-gel interface. This effect was incorporated in the model by introducing a 50-V shift which reduced the difference between the model and the measurement to less than 3%. As long as material properties and geometry are well described by FE model, current-based validation can be used for a rough model validation. That is a routine assay compared with imaging of electric field, which is otherwise employed for model validation. Additionally, current estimated by model, can be preset as maximum in electroporator in order to protect tissue against damage.

Numerical Modeling and Optimization of Electric Field Distribution in Subcutaneous Tumor Treated With Electrochemotherapy Using Needle Electrodes

“…Four needle electrode pairs caused the Table IV. least healthy tissue damage; however, they required more current and more healthy tissue to be reversibly electropermeabilized ( Fig. 7(b), Table IV), confirming previous results of our group-more electrodes mean a more invasive procedure, higher needed current, and lower needed voltage to obtain the same target tissue coverage [11], [26]. The 2 × 2 hexagonal needle electrode array caused the least volume of healthy tissue to be reversibly electropermeabilized and more to be irreversibly electropermeabilized (Fig.…”

“…However, only after the experimental validation of a numerical model was performed by comparing the numerical calculations to histological examinations of electropermeabilized tissue did numerical modeling gain ground in ECT research [11]. Different geometries of needle electrodes have been since then compared by [14], [26], and [27]; however, none of these included optimization and only Sel et al [28] used a 3-D model. In our study, three needle electrode pairs, four needle electrode pairs, and 2 × 2 hexagonal needle electrode array all gave similar results, whereas the 3 × 3 hexagonal needle electrode array was significantly worse than the others.…”

Safety and Feasibility of Irreversible Electroporation (IRE) in Patients with Locally Advanced Pancreatic Cancer: Results of a Prospective Study

“…It has been clearly demonstrated that the effectiveness of LEDC is highly associated with the distribution of the electric field in the tissue (with the contributing variables including voltage, distance between the electrodes and depth of electrodes insertion) required to reach the optimal electrode configuration and tumor coverage [3,10,36,38,39,40,41]. Irreversible electroporation aims to completely extirpate the tumor or, at least, to dramatically modify the neoplastic microenvironment without damaging the surrounding tissues or vessels.…”

Optimization of electrode position and electric pulse amplitude in electrochemotherapy

“…14,15,19,[24][25][26] We examined the adequacy for ECT of needle electrode array geometries by calculating the values of total electric current through the model (must be as low as possible to avoid nerve stimulation 27 and not exceed the capacities of the electric pulse generator 28 ) and volumes of reversibly and irreversibly electroporated tumor tissue and healthy tissue. Three-needle electrode pairs were best for the spherical and the realistic tumor geometry; they required the lowest total electric current and caused only a small volume of healthy tissue to be irreversibly electroporated (healthy tissue damage) (Figure 4).…”