Comparison of Microwave Ablation and Multipolar Radiofrequency Ablation In Vivo Using Two Internally Cooled Probes

OBJECTIVE: The objective of our study was to compare the effectiveness of microwave ablation (MWA) and multipolar radiofrequency ablation (RFA) in vivo using two internally cooled probes. MATERIALS AND METHODS: MWA (n=24) was performed by simultaneous application of double internally cooled-shaft antennae. Three power settings (60, 70, and 80 W) were used. Multipolar RFA (n=16) was also performed by simultaneously using two internally cooled bipolar applicators (lengths: 3-cm T30 and 4-cm T40) at 60 and 80 W. Probe spacing was 2 cm. Each power setting was applied for eight ablations with a 10-minute duration for each. The cooled-shaft probes were inserted approximately 7 cm into the liver parenchyma of seven adult Wuzhishan pigs under ultrasound guidance, and ablations were performed in various segments of porcine liver. The long-axis diameter (Dl), short-axis diameter (Ds) and the ratio Ds/Dl for each ablation was measured. Temperature curves at 0, 2, and 3 cm from the middle of the two probes and the time to reach 60°C at 0 cm from the parallel central line between the two probes were recorded. RESULTS: The long-axis diameter and short-axis diameter for all the power settings of MWA were significantly larger than that of both kinds of multipolar RFA (p<0.05). The rates of temperature rise to 60°C at 0 cm from the parallel central line between the two probes for all MWA power settings were significantly faster compared with RFA. CONCLUSION: MWA, by the simultaneous application of double antennae, can generate a larger ablation zone, in vivo, compared with multipolar RFA.