A 2D/3D US/CT-guided system for percutaneous focal liver thermal ablation

Image-guided percutaneous thermal ablations are promising techniques for the treatment of focal liver tumors. Conventionally, 2D ultrasound (US)-guidance is used extensively to assist liver tumor treatment. Recently, 3D US imaging has attracted much attention as its provided volumetric information can better help physicians interpret and localize liver structures. However, 3D US imaging still has the same limitation as conventional 2D US imaging in visualizing ultrasonically invisible cases. To address this issue, the current mainstream solution is to provide real-time 2D US-CT/MRI registered images by leveraging external tracking systems, such as electromagnetic (EM) or optical approaches. Due to their inevitable constraints, such as the presence of ferromagnetic structures in the case of EM tracking systems, or the line-of-sight limitation for optical systems, whether these solutions can be readily applied to the clinic has been under investigation. In this paper, we aim to investigate the feasibility of a 3D US-based ablation paradigm using our developed 2D/3D US/CT-guided liver ablation system. To achieve this goal and provide accurate guidance for ablation procedures, we proposed a local-and-global calibration method to track our mechatronic guidance arm. We also used a fiducial-based registration method to align 3D US with diagnostic CT images and implemented the re-slicing function to display the CT image corresponding to the US transducer's pose. Results demonstrated the feasibility of our system to visualize the complementary information from multiple image modalities in real time. Our calibration method can provide accurate tracking with an unsigned error of 1.6 mm +/- 0.4 mm. This work is a step towards providing a system to guide the liver ablation procedure, including cases with ultrasonically invisible or poorly visible tumors.