Comparison of the effects of in-vivo thermal ablation of pig liver by microwave and radiofrequency coagulation

Microwave and radiofrequency coagulation is frequently used for the treatment of hepatic tumors. However, differences between these types of therapy have not been clearly demonstrated so far. We performed both types of thermal ablative treatment on pig liver, and compared the size and shape of the coagulated areas produced. The effects of combining both treatments and interrupting hepatic blood flow were also evaluated. The liver of an anesthetized pig was thermally coagulated, with or without interruption of hepatic blood flow, using a needle electrode at 40 W for 150 s with 2450-MHz microwaves and/or with a 460-kHz radiofrequency current. The diameters of the coagulated areas in the liver were 20 ± 3 mm (mean ± SD; n = 4) after microwave coagulation and 28 ± 3 mm following radiofrequency coagulation when blood flow was not interrupted, whereas they were 31 ± 2 mm and 37 ± 3 mm, respectively, when blood flow was interrupted. When these treatments were combined sequentially, the diameters of the lesions were 43 ± 3 mm and 29 ± 2 mm with and without blood flow interruption, respectively. The ellipticity of the coagulated area, as measured by the largest-to-smallest ratio of its diameters, was 2.3 ± 0.4 after microwave coagulation and 1.1 ± 0.1 following radiofrequency coagulation. We conclude that radiofrequency coagulation produces a larger and more spherical coagulated area in the liver (P < 0.01) than does microwave coagulation. The lesion becomes larger (P < 0.05) with both treatments when hepatic blood flow is interrupted during the treatment. The sequential combination of these treatments produces a much larger lesion (P < 0.05) than that produced by either treatment alone.