What is the best time to evaluate treatment response after radiofrequency ablation of hepatocellular carcinoma using contrast-enhanced sonography?

Purpose: To observe the visibility and changes in the echogenicity of ablated tumor and ablated nontumor areas after radiofrequency ablation (RFA) over time using gray-scale sonography, and, consequently, to decide on the best timing for contrast-enhanced sonography to evaluate the response of hepatocellular carcinoma to RFA. Materials and Methods: Thirty-eight patients with 48 hepatocellular carcinoma nodules underwent RFA. Consecutive gray-scale sonographic observations were made 10 min before RFA and at five points within 4 days after RFA. Two hepatologists blindly reviewed the sonographic images to assess the identifiability of the boundary of the ablated nodules and to semiquantitatively score the echogenicity of the ablated tumor and ablated nontumor regions in 15 hypoechoic nodules with detectable boundaries within 4 days after RFA. Results: The detection rates of the boundaries of ablated tumors were 56.5, 65.2, 54.3, 43.5, and 39.1% at 3-6 h and 15-22 h and on the 3rd, 4th, and 5th days after RFA. There was a significant difference between the detection rate for ablated tumors at 15-22 h and that on the 3rd and 4th days. The difference in echogenicity between ablated tumor and ablated nontumor tissue reached a maximum at 15-22 h after RFA. Conclusion: Ablated tumor can be clearly identified within the ablated area in 65.2% of cases using gray-scale sonography at 15-22 h after RFA. The day following RFA is most appropriate and practical for the performance of contrast-enhanced sonography to evaluate the therapeutic response, including a safety margin.