Bipolar Radiofrequency ablation: Is the shape of the coagulation volume different in comparison to monopolar RF‐ablation using variable active tip lengths?

We investigated the differences between bipolar and monopolar radiofrequency (RF)-ablation devices regarding the shape and volume of the induced coagulation zone. RF-ablations were performed in freshly excised porcine liver. For bipolar RF-ablation needle electrodes with 9, 20 and 30 mm active tip lengths were used. Each electrode was used ten times in accordance with the vendor's recommended ablation protocol. For monopolar RF-ablation a needle electrode was also used. Active tip length was modified by removing parts of the insulation resulting in tips lengths of 9, 20 and 30 mm. The lesion shape and volume were calculated and compared. In general, lesion size increased with increasing active tip length. At 9 mm tip length lesion volumes were significantly larger using the monopolar RF-system (0.598+/-0.094 cm(3) vs. 0.139+/-0.028 cm(3)). At 20 and 30 mm tip length bipolar RF-ablation created significantly larger areas of necrosis (20 mm: 3.498+/-0.605 cm(3) vs. 2.569+/-0,620 cm(3), 30 mm: 7.441+/-906 cm(3) vs. 3.317+/-0.737 cm(3)). Using the probes with 9 mm, active length areas of necrosis induced by the monopolar system are more spherical, whereas with 20 and 30 mm active tip length the bipolar system creates more spherical lesions. The proper combination of RF-system and electrode length allows to individually adapt the shape and volume of the generated coagulation necrosis to the target lesion.