Contrast-Enhanced Ultrasound Evaluation of Radiofrequency Ablation of the Kidney: Reliable Imaging of the Thermolesion

Abstract

BACKGROUND AND PURPOSE: Radiofrequency ablation (RFA) is limited by the inability to monitor progression of the thermal lesion. Contrast-enhanced ultrasonography (CEUS) imaging has considerable potential as a monitoring modality for RFA. We report our experience using CEUS to evaluate the lesion produced by RFA in a porcine model. MATERIALS AND METHODS: Five pigs underwent laparoscopic RFA twice, spaced by a 1-week interval. Post- RFA ultrasound imaging was performed transcutaneously immediately after ablation. The kidneys were assessed for a contrast void corresponding to the ablated tissue. The kidneys were then harvested and the gross RFA lesions measured to compare lesion size with that measured using CEUS. RESULTS: A clear lesion was identified at the site of each RFA application. As measured by CEUS, the acute lesions averaged 1.8 +/- 0.4, 1.7 +/- 0.4, and 1.8 +/- 0.3 cm in length, height, and width, respectively, compared with 2.0 +/- 0.5, 1.8 +/- 0.4, and 1.9 +/- 0.3 cm, respectively, by measurement in the gross specimen (P = 0.33, 0.13, and 0.44, respectively). At 1 week, the CEUS-measured dimensions of the lesions were 2.7 +/- 0.5, 2.6 +/- 0.6, and 2.6 +/- 0.6 cm, and the gross measurements of the lesion were 2.7 +/- 0.4, 2.7 +/- 0.9, and 2.6 +/- 0.4 cm (P = 0.75, 0.92, and 0.40, respectively). CONCLUSIONS: Contrast-enhanced ultrasonography appears to be an accurate modality for immediate monitoring of RFA defects. Further study is necessary to assess the clinical utility of CEUS for monitoring RFA of small renal lesions.