Comparison of Gadoxetic Acid–enhanced MR Imaging versus Four-phase Multi–detector Row Computed Tomography in Assessing Tumor Regression after Radiofrequency Ablation in Subjects with Hepatocellular Carcinomas

Purpose To assess the diagnostic value of gadoxetic acid–enhanced magnetic resonance (MR) imaging in follow-up of patients with hepatocellular carcinomas (HCCs) who were treated with radiofrequency (RF) ablation and to compare it with that of four-phase multi–detector row computed tomography (CT). Materials and Methods From July 2007 to May 2008, 36 patients (43 HCCs) were enrolled who were treated with RF ablation (tumor size, 20–47 mm; mean, 24.5 mm) and underwent gadoxetic acid–enhanced MR imaging and four-phase (precontrast, arterial, portal venous, and equilibrium) multidetector CT for follow-up. Two radiologists independently reviewed these images, and conspicuity of tumor margins and detection of residual or recurrent tumor were assessed on a five-point scale with receiver operating characteristic (ROC) curve analysis. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were evaluated. Results The mean conspicuity value of tumor margins was significantly higher on MR imaging than on multidetector CT ( P P P = .015), as were sensitivity, specificity, PPV, NPV, and accuracy of detection rate (mean, 100%, 96.2%, 82.4%, 100%, and 96.7%, respectively, vs 41.7%, 56.8%, 13.5%, 85.7%, and 54.7% for multidetector CT). The interobserver agreement rate for MR imaging was higher (0.919) than for multidetector CT (0.672; P Conclusions Diagnostic accuracy, conspicuity of tumor margins, and detection rate of residual or recurrent tumor were found to be better with gadoxetic acid–enhanced MR imaging than with four-phase multidetector CT.