The accuracy of image guidance in spinal surgery can be compromised by intervertebral motion between preoperativesupine CT images and intraoperative prone positioning. Patient registration and image updating approaches have beendeveloped to register CT images with intraoperative spine and compensate for posture and alignment changes. We havedeveloped a hand-held stereovision (HHS) system to acquire intraoperative profiles of the exposed spine and facilitateimage registration and surgical navigation during open spinal surgery. First, we calibrated the stereo parameters using acheckerboard pattern, and the mean reprojection error was 0.33 pixel using 42 image pairs. Second, we attached anactive tracker to the HHS device to track its location using a commercial navigation system. We performed spatialcalibration to find the transformation between camera space and tracker space, and the error was 0.73 ± 0.39 mm.Finally, we evaluated the accuracy of the HHS using an ex-vivo porcine specimen. We used a tracked stylus to acquirelocations of landmarks such as spinous and transverse processes, and calculated the distances between these points andthe reconstructed stereovision surface. The resulting accuracy was 0.91 ± 0.58 mm, with an overall computationalefficiency of ～ 5s for each image pair. Compared to our previous microscope-based stereovision system, the accuracyand efficiency of HHS are similar while HHS is more practical and functional, and would be more broadly applicable inspine procedures.
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