Comparative in vitro study of contact- and image-based rigid registration for computer-aided surgery

We present an in vitro study of rigid registration methods for computer-aided surgery. The goals of the study were to obtain accuracy measures empirically under optimal laboratory conditions, and to identify the weak links in the registration chain. Specifically, we investigated two common registration methods (contact-based registration and image-based landmark registration) and established a framework for comparing the accuracy of both methods. The phantoms, protocols, and algorithms for tool tip calibration, contact-based registration with an optical tracker, fluoroscopic X-ray camera calibration, and fluoroscopic X-ray image-based landmark registration are described. Average accuracies of 0.5 mm (1.5 mm maximum) and 2.75 mm (3.4 mm maximum) were found for contact-based and image-based landmark registration, respectively. Based on these findings, the camera calibration was identified as being the main source of error in image-based landmark registration. Protocol improvements and algorithmic refinements to improve the accuracy of image-based landmark registration are proposed.