High-accuracy 3D image-based registration of endoscopic video to C-arm cone-beam CT for image-guided skull base surgery

Registration of endoscopic video to preoperative CT facilitates high-precision surgery of the head, neck, and skull-base. Conventional video-CT registration is limited by the accuracy of the tracker and does not use the underlying video or CT image data. A new image-based video registration method has been developed to overcome the limitations of conventional tracker-based registration. This method adds to a navigation system based on intraoperative C-arm conebeam CT (CBCT) that reflects anatomical change, in turn providing high-accuracy registration of video to the surgical scene. The resulting registration enables visualization of the CBCT and planning data within the endoscopic video. The system incorporates a mobile C-arm for high-performance CBCT, integrated with an optical tracking system, video endoscopy, deformable registration of preoperative CT with intraoperative CBCT, and 3D visualization. As in the tracker-based approach, in the image-based video-CBCT registration the endoscope is localized using an optical tracking system that provides a quick initialization followed by a direct 3D image-based registration of the video to the CBCT. In this way, the system achieves video-CBCT registration that is both fast and accurate. Application in skull-base surgery demonstrates overlay of critical structures (e.g., carotid arteries and optic nerves) and surgical target volumes with submm accuracy. Phantom and cadaver experiments show consistent improvement in target registration error (TRE) in video overlay over conventional tracker-based registration – e.g., 0.92 mm versus 1.82 mm for image-based and trackerbased registration, respectively. The proposed method represents a two-fold advance–first, through registration of video to up-to-date intraoperative CBCT (overcoming limitations associated with navigation with respect to preoperative CT), and second, through direct 3D image-based video-CBCT registration, which together provide more confident visualization of target and normal tissues within up-to-date images and improved targeting precision.