Bipolar radiofrequency ablation with four electrodes: ex vivo liver experiments and finite element method analysis. Influence of inter-electrode distance on coagulation size and geometry.

Purpose: The aim of this study was to develop an electrode system with simple needle electrodes which would allow a reliable and predictable ablation zone with radiofrequency ablation (RFA).

Materials And Methods: In the first step, four parallel electrodes (active length 3 cm, diameter 1.8 mm) were inserted in ex vivo bovine liver. A power of 50 W was applied between two pairs of electrodes for 10 min or until current shut-off due to impedance rise. In the second step, the influence of changing inter-electrode distance on coagulation size and geometry was measured. In the third step, a finite element method (FEM) analysis of the experiment was performed to better understand the experimental findings.

Results: A bipolar four-electrode system with templates adjusting the inter-electrode distance was successfully developed for ex vivo experiments. A complete and reliable coagulation zone of a 3 × 2 × 2-cm block was obtained most efficiently with an inter-electrode distance of 2 cm in 5.12 ± 0.71 min. Above 2 cm, coagulation was incomplete due to a too low electric field, as demonstrated by the FEM analysis.

Conclusions: The optimal inter-electrode distance of the present bipolar four-electrode system was 2 cm, allowing a reliable and predictable ablation zone in ex vivo liver. The FEM analysis correctly simulated and explained the findings in ex vivo liver. The experimental set-up may serve as a platform to gain more insight and to optimise the application of RFA by means of four or more simple needle electrodes.