Advanced ultrasonography technologies to assess the effects of radiofrequency ablation on hepatocellular carcinoma

Abstract

Background: Radiofrequency ablation (RFA) is a curative therapy for hepatocellular carcinoma (HCC). In RFA, ultrasonography (US) is most commonly used to guide tumor puncture, while its effects are assessed using dynamic computed tomography or magnetic resonance. The differences in modalities used for RFA and assessment of its effects complicate RFA. We developed a method for assessing the effects of RFA on HCC by combining contrast-enhanced (CE) US and real-time virtual sonography with three-dimensional US data.

Patients and methods: Before RFA, we performed a sweep scan of the target HCC nodule and the surrounding hepatic parenchyma to generate three-dimensional US data. After RFA, we synchronized multi-planar reconstruction images derived from stored three-dimensional US data with real-time US images on the same US monitor and performed CEUS and real-time virtual sonography. Using a marking function, we drew a sphere marker along the target HCC nodule contour on pre-treatment US- multi-planar reconstruction images so that the automatically synchronized sphere marker represented the original HCC nodule contour on post-treatment real-time CEUS images. Ablation was considered sufficient when an avascular area with a margin of several millimeters in all directions surrounded the sphere marker on CEUS.

Results: This method was feasible and useful for assessing therapeutic effects in 13 consecutive patients with HCC who underwent RFA. In 2 patients who underwent multiple sessions of RFA, HCC-nodule portions requiring additional RFA were easily identified on US images.

Conclusions: This method using advanced US technologies will facilitate assessment of the effects of RFA on HCC.

Keywords: contrast-enhanced ultrasonography; hepatocellular carcinoma; radiofrequency ablation; real-time virtual sonography; three-dimensional ultrasonography.

FIGURE 1.

RVS synchronization using 3DUS data from a phantom model. US-MPR images from the 3D data (left) and real-time US images (right) are synchronized on the same US monitor. Furthermore, synchronized spherical markers (+, the center of the spherical marker) are displayed along the contour of a spherical structure of the phantom model on synchronized US-MPR and real-time US images. RVS = real-time virtual sonography; 3DUS = three-dimensional ultrasonography; MPR = multiplanar reconstruction

FIGURE 2.

Assessment of the effects of RFA on HCC by combination of CEUS and RVS using 3DUS data. A 57-year-old female patient had a 7-mm HCC in segment 5. Sufficient ablation was achieved in a single session of RFA. A. CEUS and RVS using 3DUS data before RFA. The Kupffer phase data set was selected for RVS. The HCC nodule is shown as a perfusion defect (arrow). The US-MPR and real-time CEUS images are synchronized. B. CEUS and RVS using 3DUS data after RFA. The US-MPR (left) and real-time CEUS (right) images are adjusted with synchronized straight markers. Each marker is drawn on the same anterior branch of the right branch of the portal vein. C. CEUS and RVS using 3DUS data after RFA. Automatically synchronized spherical markers represent the HCC contour. An avascular area surrounds the sphere marker (+, the center of the spherical marker) with a margin of several millimeters on CEUS images, suggesting sufficient ablation. D. Dynamic MR imaging. Before RFA (left), the HCC nodule is shown as a hypervascular lesion (arrow). MR image obtained after RFA (right) shows a sufficient ablation zone. CEUS = contrast-enhanced ultrasonography; HCC = hepatocellular carcinoma; MR = magnetic resonance MPR = multiplanar reconstruction; RFA = radiofrequency ablation; RVS = real-time virtual sonography; 3DUS = three-dimensional ultrasonography

FIGURE 3.

Usefulness of CEUS and RVS using 3DUS data in identifying HCC nodules requiring additional RFA. A 66-year-old female patient had a 13-mm HCC in segment 6. Because HCC was poorly visualized with conventional US, RFA was performed under CEUS guidance. After the first RFA session, dynamic MR showed a residual viable portion, but the second RFA session failed to ablate that portion. CEUS and RVS using 3DUS data clearly showed the portion requiring additional RFA. Therefore, a third RFA session was performed, which ablated the portion. A. CEUS before RFA. B. Dynamic MR imaging before RFA (left) and after the first RFA session (right). A residual viable portion is shown (arrow). C. CEUS and RVS using 3DUS data displays the portion requiring additional RFA (spherical marker). Each synchronized straight marker is drawn on the same posterior branch of the right branch of the portal vein. D. CEUS (left) and dynamic CT (right) suggest sufficient ablation. CEUS = contrast-enhanced ultrasonography; CT = computed tomography; HCC = hepatocellular carcinoma; MR = magnetic resonance; RFA = radiofrequency ablation; RVS = real-time virtual sonography; 3DUS, three-dimensional ultrasonography