Real-Time Contrast-Enhanced Ultrasonography-CT/MRI Fusion Guidance for Percutaneous Radiofrequency Ablation of Inconspicuous, Small Liver Tumors

Percutaneous radiofrequency ablation (RFA) has been widely implemented as a curative treatment for liver malignancies. The overall survival post-RFA is comparable to that of surgical outcomes for small hepatocellular carcinomas (HCCs) (≤ 3 cm). US guidance for RFA is common in Asia because the real-time capability of US allows precise electrode placement. However, precisely targeting small liver malignancies with poor sonographic conspicuity in US-guided RFA is often challenging. To solve this problem, CEUS or real-time fusion imaging (FI) of US and CT/MRI have been used. Both approaches have been reported to improve the confidence for tumor localization in RFA for small HCCs with poor B-mode US visibility. However, when an index tumor is entirely invisible on B-mode US, neither method is ideal, especially for multiple-electrode RFA, due to inherent registration errors on FI or insonation-induced bubble destruction on CEUS with SonoVue. Therefore, there is a clinical need to compensate for the inherent registration errors of US-CT/MRI FI for inconspicuous tumors on both US and US-CT/MRI FI.

Recent studies reported that after adding CEUS using Sonazoid (GE Healthcare, Waukesha, WI, USA) or SonoVue to FI, 83.3% to 90% of target liver cancers that were initially difficult to visualize on FI became conspicuous, allowing them to be directly targeted for RFA. However, these studies had limitations, including a retrospective study design, a small sample size (< 30 inconspicuous tumors), or a short-term follow-up (< 1 year). Furthermore, no prospective study has explored the value of CEUS-CT/MRI FI, using both SonoVue and Sonazoid as contrast agents, for localizing index tumors and guiding RFA procedures in patients with inconspicuous tumors on B-mode US and reported its therapeutic impact on local tumor control.

Therefore, the present study investigated whether CEUS-CT/MRI FI improved the visibility of small (≤ 3 cm) primary and secondary liver tumors that were invisible or difficult to visualize on B-mode US for percutaneous RFA.