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

International Journal of Hyperthermia 2012; 28:1-12.

Abstract

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

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

Results: A bipolar four-electrode system with templates adjusting the inter-electrode distance was successfully developed forex vivo experiments. A complete and reliable coagulation zone of a 322-cm block was obtained most efficiently with aninter-electrode distance of 2 cm in 5.120.71 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 reliableand predictable ablation zone in ex vivo liver. The FEM analysis correctly simulated and explained the findings in ex vivoliver. The experimental set-up may serve as a platform to gain more insight and to optimise the application of RFA by meansof four or more simple needle electrodes.