Optical coordinate tracking system using afocal optics for image-guided surgery

Image-guided surgery using medical robots supports surgeons by providing critical real-time feedback information, such as surgical instrument tracking, patient-specific models, and the use of surgery robots. An image-guided surgery system based on afocal optics was developed to overcome the problems associated with conventional optical tracking systems.

An optical tracking system was developed that utilizes afocal optics. Instead of using geometrically specified marker spheres as tracking targets, the proposed system uses a marker with a lens and a micro-engraved data-coded pattern. A position and orientation-tracking algorithm was developed to utilize the observed afocal images of the marker patterns. The marker used in this tracking system can be manufactured in a smaller size than traditional optical tracker markers, and the accuracy of the proposed tracking system has significant potential for improvement due to its focused and highly magnified image. The system was tested in vitro on an optical bench with position and orientation measurement experiments using a commercial optical tracker, Polaris Vicra (NDI Corp.) for comparison.

The afocal optical system provided accuracy in position and orientation that was equal or better than a commercial optical tracker system, and provided a high degree of consistency during in vitro testing. The position error was 21μ m, and the orientation error was 0.093°.

An afocal optical tracker is feasible and potentially advantageous for surgical navigation, as it is expected to have fewer occlusions and provide greater efficiency for coordinate matching and tracking of patient-specific models, surgical instruments, and surgery robots. This promising new system requires in vivo testing.