No-Touch Radiofrequency Ablation: A Comparison of Switching Bipolar and Switching Monopolar Ablation in Ex Vivo Bovine Liver

Abstract

Objective: To evaluate the feasibility, efficiency, and safety of no-touch switching bipolar (SB) and switching monopolar (SM) radiofrequency ablation (RFA) using ex vivo bovine livers.

Materials and methods: A pork loin cube was inserted as a tumor mimicker in the bovine liver block; RFA was performed using the no-touch technique in the SM (group A1; 10 minutes, n = 10, group A2; 15 minutes, n = 10) and SB (group B; 10 minutes, n = 10) modes. The groups were compared based on the creation of confluent necrosis with sufficient safety margins, the dimensions, and distance between the electrode and ablation zone margin (DEM). To evaluate safety, small bowel loops were placed above the liver surface and 30 additional ablations were performed in the same groups.

Results: Confluent necroses with sufficient safety margins were created in all specimens. SM RFA created significantly larger volumes of ablation compared to SB RFA (all p < 0.001). The DEM of group B was significantly lower than those of groups A1 and A2 (all p < 0.001). Although thermal injury to the small bowel was noted in 90%, 100%, and 30% of the cases in groups A1, A2, and B, respectively, full depth injury was noted only in 60% of group A2 cases.

Conclusion: The no-touch RFA technique is feasible in both the SB and SM modes; however, SB RFA appears to be more advantageous compared to SM RFA in the creation of an ablation zone while avoiding the unnecessary creation of an adjacent parenchymal ablation zone or adjacent small bowel injuries.

Keywords: Bovine; Hepatocellular carcinoma; Minimally invasive; No-touch technique; Preclinical; Radiofrequency ablation.

Fig. 1. Ex vivo study to evaluate adjacent bowel injury during RFA.

Photograph shows segment of small bowel wall neighboring upper surface of liver block that was dipped into 30 × 20 × 20-cm³ saline-filled acrylic bath at room temperature. Note that one of Octopus electrodes is inserted into bovine liver 14 mm below liver upper surface, and thermocouple is placed between small bowel wall and liver surface for real time temperature measurement.

Fig. 2. Diagram showing typical patterns of switching monopolar and switching bipolar modes.

In switching bipolar mode, pair of electrodes is activated.

Fig. 3. Comparison of radio frequency ablation (RFA)-induced coagulation.

Transverse cut surfaces of ablated specimens in groups A1, A2, and B, respectively. Black bars indicate distance between outer margin of ablation zone and electrode.

Fig. 4. Comparison of adjacent small bowel thermal injury during RFA in groups A2 and B.

A, B. Vertical cut surface of ablated specimens and adjacent small bowel in group A2. Note that ablated area extended to liver surface and there is color change of small bowel wall by thermal injury (arrow). C, D. Vertical cut surfaces of ablated specimens and adjacent small bowel in group B. Note that liver surface was not ablated and adjacent small bowel showed no thermal injury.