Moving-shot versus fixed electrode techniques for radiofrequency ablation: comparison in an ex-vivo bovine liver tissue model

Abstract

Objective: To compare the ablation characteristics of the moving-shot technique (MST) and the fixed electrode technique (FET) for radiofrequency (RF) ablation in an ex-vivo bovine liver tissue model.

Materials and methods: We performed RF ablation using FET in 110 bovine liver blocks using 11 different ablation times ranging from 5 seconds to 5 minutes (10 blocks per each time duration). Ten bovine liver blocks at each ablation time of 1- or 2-minute, were ablated with MST, which treated conceptual ablation units by moving the electrode tip. We evaluated the ablation volume obtained with FET across ablation time lengths. The results of FET and MST performed with the same ablation time lengths, i.e., 1- and 2-minute ablation time were also compared.

Results: The ablation volume achieved with FET gradually increased with increasing ablation time; however, the pair-wise statistical comparison between 2 neighboring ablation time lengths was not significant after 30 seconds. MST with either 1- or 2-minute ablation time achieved larger ablation volumes (1.1 ± 0.2 mL vs. 2.7 ± 0.3 mL, p < 0.001; and 1.4 ± 0.2 mL vs. 5.6 ± 0.4 mL, p < 0.001, respectively), longer true RF times (46.7 ± 4.6 seconds vs. 60 seconds, p < 0.001; and 64.8 ± 4.6 seconds vs. 120 seconds, p < 0.001, respectively), fewer numbers of RF cut-offs (1.6 ± 0.5 vs. 0, p < 0.001; and 5.5 ± 0.5 vs. 0, p < 0.001, respectively), and greater energy deposition (2050.16 ± 209.2 J vs. 2677.76 ± 83.68 J, p < 0.001; and 2970.64 ± 376.56 J vs. 5564.72 ± 5439.2 J, p < 0.001, respectively), than FET.

Conclusion: The MST can achieve a larger ablation volume by preventing RF cut-off, compared with the FET in an ex-vivo bovine liver model.

Keywords: Fixed electrode technique; Intervention; Moving shot technique; Radiofrequency ablation; Thyroid nodule.

Fig. 1

Measurement of ablation zone. A. On longitudinal plane, we measured vertical diameter (DV) along electrode. B. On transverse plane, we measured transverse diameter (DT1) perpendicular to DV in L-plane and another transverse diameter (DT2) in T-plane.

Fig. 2

Relationship between ablation volume and time using fixed electrode technique. Ablation volume gradually increased with increasing ablation time; however, pair-wise statistical comparison between 2 neighboring ablation time lengths was not significant after 30 seconds.

Fig. 3

Graphs of radiofrequency (RF) power, current, impedance, and temperature during 2-minute ablation using fixed electrode and moving-shot techniques. A. With fixed electrode technique, power graphed over time demonstrates that first RF cut-off appears at 33 seconds (arrow) and 6 RF cut-offs times (arrows) were detected during 2-minute ablation procedure. Drops of RF current and sudden increases of impedance were detected in corresponding area. These RF cut-offs denote cooling period that serves to prevent tissue carbonization near electrode tip. Total energy deposition was 0.68 kcal. B. With moving shot technique, RF power is maintained at approximately 50 watts during entire ablation procedure (arrows). Moving electrode tip could prevent RF cut-off, and total energy deposition was 1.32 kcal.