No-touch radiofrequency ablation using multiple electrodes: An in vivo comparison study of switching monopolar versus switching bipolar modes in porcine livers

Abstract

Objective: To evaluate the in vivo technical feasibility, efficiency, and safety of switching bipolar (SB) and switching monopolar (SM) radiofrequency ablation (RFA) as a no-touch ablation technique in the porcine liver.

Materials and methods: The animal care and use committee approved this animal study and 16 pigs were used in two independent experiments. In the first experiment, RFA was performed on 2-cm tumor mimickers in the liver using a no-touch technique in the SM mode (2 groups, SM1: 10 minutes, n = 10; SM2: 15 minutes, n = 10) and SB-mode (1 group, SB: 10 minutes, n = 10). The technical success with sufficient safety margins, creation of confluent necrosis, ablation size, and distance between the electrode and ablation zone margin (DEM), were compared between groups. In the second experiment, thermal injury to the adjacent anatomic organs was compared between SM-RFA (15 minutes, n = 13) and SB-RFA modes (10 minutes, n = 13).

Results: The rates of the technical success and the creation of confluent necrosis were higher in the SB group than in the SM1 groups (100% vs. 60% and 90% vs. 40%, both p < 0.05). The ablation volume in the SM2 group was significantly larger than that in the SB group (59.2±18.7 cm3 vs. 39.8±9.7 cm3, p < 0.05), and the DEM in the SM2 group was also larger than that in the SB group (1.39±0.21 cm vs. 1.07±0.10 cm, p < 0.05). In the second experiment, the incidence of thermal injury to the adjacent organs and tissues in the SB group (23.1%, 3/13) was significantly lower than that in the SM group (69.2%, 8/13) (p = 0.021).

Conclusion: SB-RFA was more advantageous for a no-touch technique for liver tumors, showing the potential of a better safety profile than SM-RFA.

Fig 1. Photograph of a prototype RFA generator and a clustered separable Octopus® electrode.

Fig 2

(a) Ultrasonograph of the agarose-based tumor-mimicker. (b) Photograph of the tumor mimicker on a sliced specimen. Ultrasonographs of an electrode inserted 1 cm apart from (c) the gallbladder and (d) liver surface. Electrodes were inserted parallel to the liver surface or gallbladder where possible.

Fig 3. Photographs showing transverse and vertical planes of the specimen.

(a, b) technical success with confluent necrosis (in the SB group). (d, e) technical failure with partial necrosis (in the SM2 group). (c) same specimen as shown in Fig 3a after TTC treatment. Arrows indicate the distance between the outer margin of the ablation zone and the electrode.

Fig 4

(a) Photograph showing the absence of stomach injury after SB-RFA. (b) Corresponding liver specimen, showing the ablation zone did not reach the liver surface abutting the stomach (arrow). (c) Photograph shows discolored thickened whitish area of the stomach suggesting thermal injury. (d) Corresponding liver specimen, showing the ablation zone reached the liver surface abutting the stomach (arrow).

Fig 5

(a) Photograph shows discolored thickened whitish area of the stomach suggesting thermal injury. (b) (c) Corresponding stomach specimen with hematoxylin and eosin staining (H&E) shows thermal injury to the mucosa. Focal mucosal necrosis is present in (b) (arrow) (x40), and myxoid degeneration of serosa, subserosa and proper muscle with dilated lymphatic channels, and fluid accumulation in subserosa are present in (c) (arrow) (x40). (d) Photograph shows the H&E stained stomach specimen without thermal injury (x12.5).

Fig 6

(a) Photograph shows the whitish area of the gall bladder suggesting thermal injury (arrow). (b) (c) Corresponding gall bladder specimen and adjacent liver parenchyma with hematoxylin and eosin staining (H&E) show thermal injury to the mucosa. Mucosal and submucosal damage are evident. Lymphatic dilatation of subserosa is noted in (b) (circle) (x12.5). The mucosal epithelium is replaced by dense fibrosis in (c) (arrow) (x100). (d) Photograph shows the H&E stained gall bladder specimen without thermal injury (x100).

Fig 7

(a) Photograph shows discolored thickened whitish area of the small bowel suggesting thermal injury. (b) (c) Corresponding small bowel specimen with hematoxylin and eosin staining (H&E) shows thermal injury to the mucosa. Mucosal ulceration was noted in (b) (arrow) (x100). Chronic active inflammation in serosa and subserosa with focal necrosis are present in (c) (arrow) (x100). (d) Photograph shows the H&E stained small bowel specimen without thermal injury (x100).