Stereovision-Updated Image Guidance In Multi-Level Open Spine Surgery: Short Vs Long Exposure

In open spine surgery, the accuracy of image guidance is compromised by alignment change between supine preoperative CT images (pCT) and prone intraoperative positioning. We have developed a level-wise registration framework to compensate for the intervertebral motion by updating pCT to match with intraoperative stereovision (iSV) data of the exposed spine. In this study, we compared performance of the iSV image updating system in different lengths of exposure using retrospective data from one cadaver pig specimen. Specifically, L1 to L6 were exposed and 3 metallic mini-screws were implanted on each level as "ground truth" locations. The spine was positioned supine to acquire pCT, and then positioned prone to acquire iSV using a hand-held iSV device. One image pair of iSV was acquired from each exposed vertebra. Three exposure lengths were evaluated by selecting data from corresponding levels to compare performance: 6 levels, 4 levels, and 3 levels. Accuracy of iSV updating was assessed through point-to-point registration error (ppRE) using mini-screw locations, and the average accuracy was 1.26 +/- 0.77 mm, 1.54 +/- 0.62 mm, and 1.38 +/- 0.44 mm, for the three exposure lengths, respectively. The time cost was similar to 10-15 min and similar in all three exposure sizes. Results indicate that performance of iSV image updating was similar in different lengths of exposure, and the accuracy was within clinically acceptable range (2 mm).