Creation of radiofrequency lesions in a porcine model: Correlation with sonography, CT, and histopathology

OBJECTIVE. We studied the correlation between sonographic and CT appearance s of radiofrequency thermal lesions created in porcine liver and histopatho logic findings to evaluate the accuracy of these techniques in revealing th e extent of tissue necrosis. MATERIALS AND METHODS. We used sonographic guidance and a 2.0-cm-diameter, eight-prong retractable radiofrequency electrode to view 12 hepatic lesions that were created in five pigs. Biphasic helical CT was performed 12-48 hr after ablation. The animals were sacrificed immediately after CT, and thei r livers were histopathologically examined. The maximum lesion size in the long and short axes as measured on CT and sonography was then correlated wi th the histopathologically determined lesion size. RESULTS. On sonography, lesions changed rapidly within 5 min after the term ination of ablation. An early echogenic cloud became peripherally hypoechoi c with a variable thin echogenic rim. Early (0-2 min after ablation) sonogr ams led to an underestimation of true lesion sizes on histopathology (r = 0 .3-0.49; p < 0.05). Delayed (2-5 min after ablation) sonograms also led to an underestimation of true lesion size (r = 0.5-0.62, p < 0.05); however, l esions were larger and better demarcated. Biphasic contrast-enhanced helica l CT revealed avascular lesions surrounded by hyperemic rims that closely c orrelated with true pathologic lesion size (r = 0.93-0.95; p 0.05). Lesions with hyperemic rims that were measured on CT led to overestimations of tru e lesion size. CONCLUSION. Sonography led to underestimations of the true size of ablated lesions within the first 5 min after creation: however, delayed images prov ided better results, The avascular lesion measured on contrast-enhanced hel ical CT closely correlated with the size of ablated tissue; therefore, cont rast-enhanced CT is preferred for serially monitoring the effect of radiofr equency ablation.