49 ablations were performed on 15 pigs under general anesthesia using 15G monopolar CO2-cooled RF applicators, 17G monopolar water-cooled RF applicators and 15G internally CO2-cooled microwave devices. The power of the MW device was 45 W, the current of the gas-cooled RF device was 1200-1600 mA. At the water-cooled RF probe, maximum power of 200 W was set. Ablation time was 15 min. The short and long axes of the ablation zone were measured. Histological analyses and NADH-staining were performed. The diameters and the ablation volumes were compared using an analysis of variance.
No spots of untreated tissue were observed close to the cooled needle track in any of the ablation zones. The largest short axis diameter was 3.4 ¡À 0.5 cm achieved with the gas-cooled monopolar applicator. With the water-cooled applicators, short axis diameter was significantly smaller, reaching 2.5 ¡À 0.4 cm. Gas-cooled MW probes achieved 2.9 ¡À 1.0 cm. The largest ablation volume was 31.5 ¡À 12 ml (gas-cooled RF), and the smallest was 12.7 ¡À 4 ml (water-cooled RF). Short/long axis ratio was largest for gas-cooled RF probes with 0.73 ¡À 0.08 versus 0.64 ¡À 0.04 for the water-cooled probes and 0.49 ¡À 0.25 for the microwave applicator.
Gas-cooled RF applicators may have a higher potential for effective destruction of liver lesions than comparable water-cooled RF systems, and may be an alternative to standard RF and MW ablation devices.