Internally gas-cooled radiofrequency applicators as an alternative to conventional radiofrequency and microwave ablation devices: an in vivo comparison

Purpose: To test the efficacy of internally CO2-cooled radiofrequency (RF) ablation in vivo and to compare its effectiveness to a standard water-cooled RF probe and to a gas-cooled microwave (MW) device.

Method and materials: 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 45W, the current of the gas-cooled RF device was 1200-1600mA. At the water-cooled RF probe, maximum power of 200W was set. Ablation time was 15min. 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.

Results: 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±0.5cm achieved with the gas-cooled monopolar applicator. With the water-cooled applicators, short axis diameter was significantly smaller, reaching 2.5±0.4cm. Gas-cooled MW probes achieved 2.9±1.0cm. The largest ablation volume was 31.5±12ml (gas-cooled RF), and the smallest was 12.7±4ml (water-cooled RF). Short/long axis ratio was largest for gas-cooled RF probes with 0.73±0.08 versus 0.64±0.04 for the water-cooled probes and 0.49±0.25 for the microwave applicator.

Conclusion: 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.