CT versus sonography for monitoring radiofrequency ablation in a porcine liver

OBJECTIVE. The objective of this study was to compare CT and sonography for monitoring radiofrequency (RF) lesions in porcine livers. SUBJECTS AND METHODS. RF lesions (n = 12) were created in three pig livers by applying 13 min of current to a multielectrode RF probe with a target te mperature of 95 degrees C. Helical unenhanced CT and corresponding axial so nography were performed before ablation, at 2 min, 8 min, and immediately a fter ablation. Contrast-enhanced CT was performed after ablation. CT scans and sonograms were evaluated by blinded observers for conspicuity of the RF lesion, edge detection (visibility of liver-lesion interface), and artifac ts. Hounsfield units were recorded at every time interval, and radiologic-p athologic correlation fur lesion size and configuration was performed. RESULTS. Mean size of RF lesions was 3.03 +/- 0.9 cm, On CT, RF lesions had consistently lower attenuation values than surrounding liver (22.2 H lower than liver at 8 min, p < 0.0001). Echogenicity was variable with sonograph y (hypoechoic = 59%, hyperechoic = 25%, isoechoic = 16%). Unenhanced CT sig nificantly improved conspicuity, edge detection of RF lesions, and decrease d artifacts compared with sonography (p < 0.05). Contrast-enhanced CT impro ved RF lesion detection. border discrimination. and artifacts compared with sonography (p < 0.05). Unenhanced CT had the best correlation to pathologi c size (r = 0.74), followed by contrast-enhanced CT (r = 0.72) and sonograp hy (r = 0.56). Contrast-enhanced CT bust correlated with lesion shape, but slightly overestimated size because of areas of ischemia peripheral to the RF lesion. CONCLUSION. In this animal model, unenhanced CT was an effective way to mon itor RF ablation compared with sonography because of increased lesion discr imination, reproducible decreased attenuation during ablation, and improved correlation to pathologic size.