Dual-Energy Computed Tomography to Assess Tumor Response to Hepatic Radiofrequency Ablation Potential Diagnostic Value of Virtual Noncontrast Images and Iodine Maps

Purpose: To determine the value of dual-energy (DE) scanning with virtual noncontrast (VNC) images and iodine maps in the evaluation of therapeutic response to radiofrequency ablation (RFA) for hepatic tumors. Materials and Methods: A total of 75 patients with hepatic tumors and who underwent DE computed tomography (CT) after RFA, were enrolled in this study. Our DE CT protocol included precontrast, arterial, and portal phase scans. VNC images and iodine maps were created from 80 to 140 kVp images during the arterial and portal phases. VNC images were then compared with true, noncontrast (TNC) images, and iodine maps were compared with linearly blended images, both qualitatively and quantitatively. For the former comparison, image quality and acceptability of the VNC images as a replacement for TNC images were both rated. The CT numbers of the hepatic parenchyma, ablation zone, and image noise were measured. For the latter comparison, lesion conspicuity of the ablation zone and the additional benefit of integrating the iodine map into the routine protocol, were assessed. Contrast-to-noise ratios (CNR) of the ablation zone-to-liver and aorta-to-liver as well as the CT number differences between the center and the periphery of the ablation zone were calculated. Results: The image quality of the VNC images was rated as good (mean grading score, 1.88) and the level of acceptance was 90% (68/75). The mean CT numbers of the hepatic parenchyma and ablation zone did not differ significantly between the TNC and the VNC images (P > 0.05). The lesion conspicuity of the ablation zone was rated as excellent or good in 97% of the iodine map (73/75), and the additional benefits of the iodine maps were positively rated as better to the same (mean 1.5). The CNR of the aorta-to-liver parenchyma was significantly higher on the iodine map (P = 0.002), and the CT number differences between the center and the periphery of the ablation zone were significantly lower on the iodine map (P < 0.001). Conclusion: With DE CT scanning, VNC images can be an alternative to TNC images for evaluating the ablation zone after RFA in patients who had no a previous transcatheter arterial chemoembolization history. The iodine map improves the conspicuity of the ablation zone more than linearly blended images because of its excellent internal homogeneity and sharp ablative margin. Higher lesion-to-liver CNR on an iodine map than on standard images can be helpful for detecting residual tumors.