Evaluation of a numerical simulation for multibipolar radiofrequency ablation

The aim of this study was to assess the accuracy of a custom-developed numerical simulation of hepatic multibipolar radiofrequency ablation (mbRFA) under standardized conditions, accounting for temperature-dependent changes in tissue properties, dehydration and coagulation. The model was specifically assessed for its ability to predict vascular cooling effects induced by large vessels using an established ex vivo porcine liver model. A GPU-accelerated finite-difference time-domain (FDTD) simulation coupling the quasi-static Maxwell and Pennes' bioheat equations was implemented to model mbRFA.

Ex vivo mbRFA were performed using three internally cooled bipolar applicators. A saline-perfused glass tube was employed to simulate a standardized blood flow and positioned at five predefined distances from the ablation center in 2.5 mm increments. Simulated and experimental ablations were compared using area-, surface- and classification-based metrics on a standardized two-dimensional (2D) cross section to evaluate the model's predictive accuracy.

The numerical simulation reliably predicted the ablation shape for mbRFA while effectively accounting for vascular cooling effects. Conformity between simulated and real ablation areas was 96% across all experimental settings. The average similarity between the ex vivo ablations and the simulation were 0.92 (Dice coefficient) and 0.85 (Jaccard coefficient), respectively. Compared to the reference area, the simulation overestimated the ablation zone by 4% (false-positive regions) and underestimated it by 10% (false-negative regions).

Overall, the numerical model demonstrated good spatial agreement with the experimental ablations, confirming its suitability for quantitative prediction of ablation geometry.