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Radiofrequency versus Microwave Ablation in a Hepatic Porcine Model¹

¹ From the Departments of Surgery (A.S.W., D.M.M.), Radiology (L.A.S., F.T.L.), and Pathology (T.F.W.), University of Wisconsin, 600 Highland Ave, Madison, WI 53792-3252. Received August 11, 2003; revision requested October 28; final revision received August 4, 2004; accepted September 2. Address correspondence to F.T.L. (e-mail: ftlee{at}wisc.edu).

PURPOSE: To compare microwave (MW) and radiofrequency (RF) ablation in a hepatic porcine model.

MATERIALS AND METHODS: Institutional animal research committee approval was obtained. Nineteen pigs were divided into groups based on time of sacrifice (group A, immediate; group B, 2 days; group C, 28 days; group D, 28 days). Groups A, B, and C each underwent a combination of RF and MW ablation. Group D underwent either four MW or four RF ablations. Ablation was performed with a prototype MW device (915 Mhz, 40 W, 10 minutes) and a commercial RF system (150 W, 10 minutes, 3-cm deployment). Computed tomography (CT) was performed in groups B and C at 2 days and in group C at 28 days. Group D underwent serial laboratory testing. Specimens were serially sectioned, and short-axis diameter and length of each were measured. The percentage deflection caused by local blood vessels (heat-sink effect) was also measured in group A. Likelihood ratio tests and unpaired t tests were used for statistical analyses as appropriate.

RESULTS: MW ablation zones were longer at days 0, 2, and 28 (P < .05), but short-axis diameter was not different from that with RF ablation at any time point (P > .05). Local blood vessels caused 3.5% ± 5.3 (standard deviation) deflection at MW ablation compared with 26.2% ± 27.9 at RF ablation (P < .05). MW and RF ablation zones were indistinguishable at CT or pathologic evaluation. Laboratory test results were similar between RF ablation–only animals and MW ablation–only animals, with the exception of a slightly higher alkaline phosphatase levels at day 2 in RF ablation–only animals (P < .02).

CONCLUSION: MW and RF ablation zones are similar in pathologic appearance and imaging characteristics. Increased length with MW ablation is likely caused by the length of the radiating segment of the antenna. MW ablation may be less affected by the heat-sink effect that is thought to contribute to local recurrence after RF ablation.

© RSNA, 2005

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