Usefulness of Real-Time 4D Ultrasonography during Radiofrequency Ablation in a Case of Hepatocellular Carcinoma

Geometrically variable three-dimensional ultrasound for mechanically assisted image-guided therapy of focal liver cancer tumors

PURPOSE

Image-guided focal ablation procedures are first-line therapy options in the treatment of liver cancer tumors that provide advantageous reductions in patient recovery times and complication rates relative to open surgery. However, extensive physician training is required and image guidance variabilities during freehand therapy applicator placement limit the sufficiency of ablation volumes and the overall potential of these procedures. We propose the use of three-dimensional ultrasound (3D US) to provide guidance and localization of therapy applicators, augmenting current ablation therapies without the need for specialized procedure suites. We have developed a novel scanning mechanism for geometrically variable 3D US images, a mechanical tracking system, and a needle applicator insertion workflow using a custom needle applicator guide for targeted image-guided procedures.

METHODS

A three-motor scanner was designed to use any commercially available US probe to generate accurate, consistent, and geometrically variable 3D US images. The designed scanner was mounted on a counterbalanced stabilizing and mechanical tracking system for determining the US probe orientation, which was assessed using optical tracking. Further exploiting the utility of the motorized scanner, an image-guidance workflow was developed that moved the probe to any identified target within an acquired 3D US image. The complete 3D US guidance system was used to perform mock targeted interventional procedures on a phantom by selecting a target in a 3D US image, navigating to the target, and performing needle insertion using a custom 3D-printed needle applicator guide. Registered postinsertion 3D US images and cone-beam computed tomography (CBCT) images were used to evaluate tip targeting errors when using the motors, tracking system, or mixed navigation approaches. Two 3D US image geometries were investigated to assess the accuracy of a small-footprint tilt approach and a large field-of-view hybrid approach for a total of 48 targeted needle insertions. 3D US image quality was evaluated in a healthy volunteer and compared to a commercially available matrix array US probe.

RESULTS

A mean positioning error of 1.85 ± 1.33 mm was observed when performing compound joint manipulations with the mechanical tracking system. A combined approach for navigation that incorporated the motorized movement and the in-plane tracking system corrections performed the best with a mean tip error of 3.77 ± 2.27 mm and 4.27 ± 2.47 mm based on 3D US and CBCT images, respectively. No significant differences were observed between hybrid and tilt image acquisition geometries with all mean registration errors ≤1.2 mm. 3D US volunteer images resulted in clear reconstruction of clinically relevant anatomy.

CONCLUSIONS

A mechanically tracked system with geometrically variable 3D US provides a utility that enables enhanced applicator guidance, placement verification, and improved clinical workflow during focal liver tumor ablation procedures. Evaluations of the tracking accuracy, targeting capabilities, and clinical imaging feasibility of the proposed 3D US system, provided evidence for clinical translation. This system could provide a workflow for improving applicator placement and reducing local cancer recurrence during interventional procedures treating liver cancer and has the potential to be expanded to other abdominal interventions and procedures.

Case-control study of the RFA therapeutic effect of newly developed 4D US and conventional 2D US

PURPOSE

For radiofrequency ablation (RFA) therapy of hepatocellular carcinoma (HCC), accurate positioning of the inserted needle in the index tumor seems to be an important factor affecting therapeutic effect. In a case-control study, we compared the therapeutic effect of RFA using 4D and 2D ultrasonography (US) to evaluate whether 4D US is more effective.

METHODS

Twenty subjects treated with percutaneous RFA using 4D US (4D group) and 20 subjects using conventional 2D US (2D group), who were matched for age, sex, and HCC diameter, were enrolled in this study. Aplio XG was used as the US system and PVT-375MV as the newly developed 4D US probe. The therapeutic effect of RFA was classified into four grades (A-D: "Grade A" is "absolutely curative").

RESULTS

In the 2D group, Grade A was achieved in 12 subjects (60 %). In contrast, Grade A was achieved in 19 subjects (95 %) in the 4D group. The proportion of cases in which Grade A was achieved was significantly higher in the 4D group (P < 0.01).

CONCLUSIONS

By using a 4D US device for RFA, more accurate insertion could be achieved and more effective therapy could be performed.