CEUS in hepatic tumor: Evaluation for RFA efficacy

Abstract

The importance of assessing tumor response during or after treatment with a novel therapy has long been recognized. Several standardized approaches have been proposed and utilized to evaluate tumor response after systemic and/or loco-regional therapy (LRT). Among the LRT modalities, RFA is one of the most widely accepted methods for treating malignant hepatic tumors. Conventional cross-sectional imaging techniques, such as CT and MRI, have traditionally been used primarily to assess tumor response to RFA, however, ultrasound (US) is the most convenient imaging technique during or after treatment. The utility of microbubble contrast agents (MBCA) greatly enhances the ability of US to delineate lesions or structures and therefore provide more information in diagnosis. Imaging technique providing adequate information pre- and during RFA treatment of liver is crucial to achieve optimal therapeutic outcomes. Studies have shown that CEUS with second-generation USCA as a pre-treatment imaging may increase the target lesion conspicuity and enhance the treatment efficacy. In patients with FLL such as HCC and liver metastases not clearly demarcated on conventional US, complete tumor necrosis could be achieved by using a single session of RFA in 94% with US guidance. While complete tumor necrosis rate as high as 98.2% could be achieved in the CEUS-guided group. The tumor size and number are the most important factors related to the complete ablation and tumor recurrence after RFA. With CEUS guidance and monitoring, an RFA procedure can be done optimally. We herein review the methodologies for measuring tumor response and survival, among patients treated with RFA for primary and secondary hepatic malignancies. The learning objectives of this review include spectrum of US/ CEUS techniques and findings during and after RFA of hepatic tumors.