The Effect of Partial Electrical Insulation of the Tip and Active Needle Length of Monopolar Irreversible Electroporation Electrodes on the Electric Field Line Pattern and Temperature Gradient to Improve Treatment Control

SIMPLE SUMMARY: To control and reduce the impact of thermal effects on critical structures in the vicinity of irreversible electroporation (IRE) electrodes, the effect of partial electrical insulation of the original monopolar IRE electrodes (tip and/or part of the active needle length (ANL)) was investigated and visualized. Electric field lines strongly fanned out and showed the highest density near the electrode tip. Without any additional insulation, the highest change in temperature gradient was visualized near the electrode tip, indicating a risk for thermal effects. A combination of ANL and tip insulation reduced the area where current and heat release can occur, leading to an increase in temperature (gradient) at the uninsulated ANL. Electrically insulating the electrode tip could offer an improvement in treatment control, predictability where current pathways are formed. Further research on the tip insulation method and clinical applicability will prove this innovation’s future. ABSTRACT: Unintentional local temperature effects can occur during irreversible electroporation (IRE) treatment, especially near the electrodes, and most frequently near the tip. Partial electrical insulation of the IRE electrodes could possibly control these temperature effects. This study investigated and visualized the effect of partial electrical insulation applied to the IRE electrodes on the electric field line pattern and temperature gradient. Six designs of (partial) electrical insulation of the electrode tip and/or active needle length (ANL) of the original monopolar 19G IRE electrodes were investigated. A semolina in castor oil model was used to visualize the electric field line pattern in a high-voltage static electric field. An optical method to visualize a change in temperature gradient (color Schlieren) was used to image the temperature development in a polyacrylamide gel. Computational models were used to support the experimental findings. Around the electrode tip, the highest electric field line density and temperature gradient were present. The more insulation was applied to the electrodes, the higher the resistance. Tip and ANL insulation together reduced the active area of and around the electrodes, resulting in a visually enlarged area that showed a change in temperature gradient. Electrically insulating the electrode tip together with an adjustment in IRE parameter settings could potentially reduce the uncontrollable influence of the tip and may improve the predictability of the current pathway development.