title: 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.
abstract: OBJECTIVE
  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).
  
  
  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.
authors.affiliation: Theragnostic Laboratory, Department of Imaging and Pathology, Biomedical Sciences Group, KU Leuven, Belgium.
authors.forename: Stefaan
authors.initials: S
authors.lastname: Mulier
authors.forename: Yansheng
authors.initials: Y
authors.lastname: Jiang
authors.forename: Chong
authors.initials: C
authors.lastname: Wang
authors.forename: Jacques
authors.initials: J
authors.lastname: Jamart
authors.forename: Guy
authors.initials: G
authors.lastname: Marchal
authors.forename: Luc
authors.initials: L
authors.lastname: Michel
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Ni
mesh_terms: D000818:Animals; D002417:Cattle; D004564:Electrocoagulation / Q000295:instrumentation* / Q000379:methods; D004566:Electrodes; D020342:Finite Element Analysis; D008099:Liver / Q000601:surgery