US-US Overlay Fusion Imaging in the Evaluation of Treatment Response After RFA

Abstract

Recent advancements in technology permit two-dimensional (2D) multiplanar reconstruction images of CT or MRI to display in the same plane as US images in real time. It was reported that fusion imaging–guided RFA was useful in the treatment of hepatic malignancies that were inconspicuous on B-mode US. Moreover, the application of fusion imaging allows display of the tumor before and during/after ablation on the same US images side by side, and the imaging overlays can show the tumor image before ablation within an ablated hyperechoic zone in real time. Therefore, the image overlay of US–US fusion imaging can visualize the ablative margin three dimensionally according to the US probe action. We have developed US–US overlay fusion imaging in RFA for hepatocellular carcinoma. US–US fusion imaging has 3 clinical applications in RFA therapy. The first is the real-time monitoring of RFA lesion formation. Clinicians can employ B-mode US to observe the bubble-related hyperechoic region and preliminarily evaluate the ablation zones comparing the pre-ablation image of the tumor using US–US fusion imaging. The second application is related to decision making about additional ablation. We could confirm any lesion with a poor ablative margin during the session, and then extend the necrotic area by additional ablation. The third is visualization of the safety margin on US. Although the endpoint of conventional RFA cannot be based on objective evidence with US, US–US fusion imaging offers an evidence-based quality improvement in RFA therapy. In conclusion, US–US fusion imaging could show tumor images before ablation and the ablative area on US in real time. The image overlay of US–US fusion could visualize the ablative margin of RFA on US. Therefore, US–US fusion imaging can contribute to RFA therapy with a safety margin, that is, the so-called precise RFA.