Contrast enhanced ultrasound: Should it play a role in immediate evaluation of liver tumors following thermal ablation?

PurposeTo compare the accuracy of immediate CEUS with results of 24-h CEUS and MDCT in early evaluation of liver tumors following thermal ablation, using the combined results of a 3 month follow-up MDCT and CEUS as a reference standard.Subjects and methodsFrom our database, we selected patients who underwent a thermal ablation immediately followed by CEUS (within 5–10 min) between February 2009 and February 2011. There were 92 patients (median age 73 years), two of whom had repeat ablation during the study period for a total of 94 tumors. Sixty tumors were treated with radiofrequency and 34 with microwave ablation. All patients underwent CEUS and CT examinations at 24 h. For patients with more than one treated tumor in the same session, the lesion imaged post-procedural and at 24-h with CEUS in all vascular phases was selected. All measurements of the necrotic zone, as an avascular zone, were performed during the portal-venous phase. Immediate post-procedural CEUS and 24 h CEUS and MDCT were blindly reviewed by two radiologists. One radiologist blindly reviewed the follow-up imaging. The mean diameters of the necrotic zone at post-procedural CEUS, and CEUS and MDCT at 24 h were compared and diagnostic accuracy to detect residual tumor calculated for each index tests compared to 3-months follow-up imaging.ResultsThe mean diameter of the necrotic zone was: 29 ± 9 mm at post-procedural CEUS, 34 ± 10 mm at 24 h CEUS and 35 ± 11 mm at 24 h MDCT. Mean diameter of the necrotic zone was significantly smaller at post-procedural CEUS compared to either CEUS or MDCT at 24 h (p < 0.001 for all).With a 95% confidence interval, the sensitivity was 25% (11–47%) for immediate CEUS, 20% (8–42%) for CEUS at 24-h, and 40% (22–61%) for CT at 24-h. Specificity was 96% (89–99%) for immediate CEUS, 97% (91–99%) for CEUS at 24-h, and 97% (91–99%) for CT at 24-h.ConclusionsDiagnostic accuracy of post-procedural CEUS in early evaluation of liver tumors following thermal ablation is comparable to both CEUS and MDCT performed at 24 h. Therefore, post-procedural CEUS can be used to detect and retreat residual viable tissue in the same ablation session.