The Role of CEUS in Radiofrequency Ablation of HCC

Abstract

The treatment efficiency of local thermal ablation therapy (including through percutaneous, laparoscopic or intraoperative approaches) on hepatic malignant tumors, both HCC and liver metastases, has been emphasized and affirmed. Unenhanced US is commonly used to guide ablation it is easy to use and widely available‍. However, CEUS can provide more important information and plays a more significant role in ablation therapy. 1. Choose indications according to number and size of lesions: Number and size are of crucial importance to define the eligibility of the patient for treatment. CEUS is sensitive to detect small lesions which are invisible on unenhanced US or CT, even satellite lesions of 3-5mm, providing evidence for choosing indication. Usage of CEUS to choose indications can reduce recurrence rate and prolong survival time [Chen, JUM 2007]. 2. Measurement of tumor size: CEUS can accurately show the dimensions of tumors. The assessment of size must include the perilesional hypervascular halo or area which must be included in the treatment volume. unenhanced US cannot detect all the lesions visualized by CECT or CEMRI, real-time CT/MRI–US fusion imaging helps define the location, characteristics, and the size of the sonographically undetectable lesions. 3. Definition of tumor margins: CEUS can depict the infiltrating margin and the invasiveness of tumors better than unenhanced US [Chen, CR 2007]. Precise depiction of the tumor margins by CEUS allows better definition of its relationships with surrounding structures, such as the intestines, diaphragm and gallbladder, thus helping develop appropriate treatment strategies and reducing the risks of complications[Chen, JVIR 2006; Chen, JUM 2007]. This is especially important for subcapsular and exophytic tumors. 4. Assessment of degree of enhancement and homogeneity of vascularity and presence of necrosis to direct ablation therapy: For liver metastases, in substance phase CEUS can be more sensitive to display small washout lesions invisible on CECT or CEMRI, which should be positively treated by ablation. In addition, CEUS can accurately guide electrode placement. 5. Identification of blockage of tumor feeding vessels: when these are detected with CEUS, the region where they enter the tumor should be ablated first because a larger treatment volume can be achieved once the main blood supply has been blocked. Subsequently, a secondary CEUS evaluates the effect of blocking tumor feeding vessels to guide ablation, which can increase the effective inactivation rate [Hou, WJG 2009]. 6. Early diagnosis of bleeding: CEUS can precisely show whether there’s active bleeding in liver, judge the degree of liver damage and origin of vessel damage, direct clinical therapy or guide puncture ablation coagulation therapy and evaluate hemostatic effect. At the end of ablation, once liquid collection detected in the front of liver, CEUS should be performed to monitor and evaluate bleeding. 7. The location of residual recurrence for ablation therapy: U US can’t easily identify recurrent residual area shown on CT/MR. CEUS can sensitively show activity area and guide puncture, which can efficiently improve the second ablation treatment effect of residual recurrent tumors. [Minami Y, AJR 2004] With the development of ablation technique and improvement of its efficiency, the cases of big hepatocarcinoma, liver metastases and residual recurrent tumors after ablation clinically requiring ablation treatment have increased. In light of local ablation therapy challenges, the application value of CEUS has been increasingly valued clinically. In the course of ablation treatment, each patient needs one contrast agent(such as Sonovue), which can be used several times. The common dosage is 2ml-1ml-1ml-1ml or 2.4ml-1ml-1.5ml. Its effectiveness, practicability and economic efficiency demonstrate that CEUS has played an irreplaceable role in improving the ablation treatment efficiency of liver tumors.