• Jeong Min Lee, Joon Koo Han, Seung Hong Choi, Se Hyung Kim, Jae Young Lee, Kyung Sook Shin, Chang Jin Han, and Byung Ihn Choi.
• Department of Radiology and the Institute of Radiation Medicine, Seoul National University College of Medicine, 28 Yongon-dong, Chongno-gu, Seoul 110-744, South Korea.
• AJR Am J Roentgenol. 2005 Mar 1; 184 (3): 897-905.

ObjectiveWe sought to determine whether hypertonic-saline (HS)-augmented bipolar radiofrequency ablation has advantages over monopolar radiofrequency ablation for creating larger areas of coagulation necrosis in the kidney.Materials And MethodsUsing a 200-W generator and bipolar perfused-cooled electrodes or a monopolar cooled-tip electrode, we performed 14 radiofrequency ablations in explanted bovine kidneys. Radiofrequency was applied in standard monopolar (n = 7) or bipolar (n = 7) modes at 100 W for 10 min. In the bipolar mode, the perfused-cooled electrodes were placed at interelectrode distances of 3 cm, and a 6% sodium chloride solution was instilled into tissue at a rate of 2 mL/min through the electrodes. For in vivo experiments, either monopolar (n = 7) or HS-augmented bipolar (n = 7) radiofrequency ablation was performed in the lower pole of canine kidneys. Three days after the procedure, contrast-enhanced CT scans were obtained to evaluate the volumes of the ablation regions, and the kidneys were harvested for gross measurements. Technical parameters such as changes in impedance and current during radiofrequency ablation and dimensions of the thermal ablation zones were compared between the two groups.ResultsIn ex vivo and in vivo experiments, the frequency of the pulsed radiofrequency application caused by rises in impedance was higher in the monopolar mode than in the bipolar mode during the application of radiofrequency energy. The in vivo study showed that the bipolar radiofrequency ablation allowed larger mean current flows than the monopolar radiofrequency ablation (i.e., mean +/- SD, 1,654 +/- 144 mA vs 967 +/- 597 mA) (p < 0.05). Ex vivo studies revealed that the volumes of bipolar radiofrequency-induced ablation regions were substantially larger than those of monopolar radiofrequency-induced ablation regions (26.1 +/- 10.5 cm(3) vs 10.2 +/- 4.2 cm(3)). In vivo studies showed bipolar radiofrequency ablation achieved larger coagulation necrosis than monopolar radiofrequency (3.2 +/- 0.3 cm vs 2.4 +/-0.4 cm) (p < 0.05). This was confirmed by the measured volume of nonenhancing area on contrast-enhanced CT (20.4 +/- 6.4 cm(3) vs 13.5 +/- 6.0 cm(3)).ConclusionHS-augmented bipolar radiofrequency ablation using perfused-cooled electrodes shows better performance in creating coagulation necrosis than monopolar radiofrequency ablation in the kidney of an animal model.

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