Comparison between different thickness umbrella-shaped expandable radiofrequency electrodes (SuperSlim and CoAccess): Experimental and clinical study

Abstract

The purpose of the present study was to compare the size and configuration of the ablation zones created by SuperSlim and CoAccess electrodes, using various ablation algorithms in ex vivo bovine liver and in clinical cases. In the experimental study, we ablated explanted bovine liver using 2 types of electrodes and 4 ablation algorithms (combinations of incremental power supply, stepwise expansion and additional low-power ablation) and evaluated the ablation area and time. In the clinical study, we compared the ablation volume and the shape of the ablation zone between both electrodes in 23 hepatocellular carcinoma (HCC) cases with the best algorithm (incremental power supply, stepwise expansion and additional low-power ablation) as derived from the experimental study. In the experimental study, the ablation area and time by the CoAccess electrode were significantly greater compared to those by the SuperSlim electrode for the single-step (algorithm 1, p=0.0209 and 0.0325, respectively) and stepwise expansion algorithms (algorithm 2, p=0.0002 and <0.0001, respectively; algorithm 3, p= 0.006 and 0.0407, respectively). However, differences were not significant for the additional low-power ablation algorithm. In the clinical study, the ablation volume and time in the CoAccess group were significantly larger and longer, respectively, compared to those in the SuperSlim group (p=0.0242 and 0.009, respectively). Round ablation zones were acquired in 91.7% of the CoAccess group, while irregular ablation zones were obtained in 45.5% of the SuperSlim group (p=0.0428). In conclusion, the CoAccess electrode achieves larger and more uniform ablation zones compared with the SuperSlim electrode, though it requires longer ablation times in experimental and clinical studies.

Figure 1.

Image of the radiofrequency (RF) electrodes used in the present study (LeVeen Electrode System). (a) Array (3 cm) SuperSlim electrode. (b) The array (3 cm) CoAccess electrode system consists of a CoAccess electrode (top) and coaxial insulated needle (bottom). (c) Magnified view of the diamond-cut tip of the coaxial insulated needle.

Figure 2.

(a) Diagram showing the system for ablating ex vivo bovine liver. A block of bovine liver is placed on a copper plate with grounding pads, and the electrode needle is positioned in the liver from the upper side under sonographic guidance. We measured the ablation time and area for each algorithm. (b) Cut surface of the ablated liver, cut along the puncture line of the radiofrequency (RF) electrode. The ablation area was measured using Image J software.

Figure 3.

CT images of representative clinical cases treated by CoAccess and by SuperSlim electrodes. (a) Female (75 years old) with a 2.2-cm hepatocellular carcinoma (HCC) in liver segment II, treated using a 3-cm CoAccess electrode. Arterial phase of dynamic CT reveals a round-shaped ablation zone (arrow). (b) Male (76 years old) with a 2-cm HCC in liver segment VII, treated using a 3-cm SuperSlim electrode. Arterial phase of dynamic CT reveals the irregular outline of the ablation zone (arrow).