Radiofrequency Ablation by a 21-Gauge Internally Cooled Electrode: Ex Vivo and In Vivo Evaluation by Rat Liver

Purpose To evaluate the coagulative performance of a 21-gauge (G) internally cooled radiofrequency (RF) electrode using ex vivo and in vivo rat liver. Materials and Methods We developed a prototype of 21-G internally cooled monopolar RF electrode with 5.0 mm active tip length. The ablative zone size created by this electrode was evaluated in ex vivo and in vivo rat liver. Five RF powers (3 W, 5 W, 7 W, 9 W, and 11 W) were applied with and without circulation of chilled water within the electrode. The ablation zone sizes were compared. Histopathological evaluation of the ablation zone was also performed at 24 h and at 7 days after RF ablation. Results From ex vivo experiments, the ablation volume was found to increase significantly when RF energy was applied with the chilled water circulation. Results of in vivo experiments demonstrate that the ablation volume reached its maximum value when RF power of 7 W was applied (532.3 ± 110.3 mm 3 ). Histopathological examination showed delineated coagulation necrosis at 24 h after RF ablation, which clarified the ablation zone border. Fibrotic change was also observed at 7 days after RF ablation. Conclusion RF ablation using a 21-gauge electrode produced coagulation necrosis in the rat liver. The ablation volume became maximum when RF power of 7 W was applied with chilled water circulation.