Microscope-Rased Augmented Reality in Degenerative Spine Surgery: Initial Experience

OBJECTIVE: To establish microscope-based augmented reality (AR) support for degenerative spine surgery. METHODS: Head-up displays of operating microscopes were used to establish AR in a series of 10 patients. Segmentation of the vertebra and additional target structures, which were visualized by AR, was based on preoperative magnetic resonance and computed tomography (CT) images, that were nonrigidly fused to low-dose intraoperative CT (iCT) data. AR registration was achieved by automatic registration applying iCT and microscope calibration. RESULTS: AR support could be smoothly implemented in the surgical workflow. AR allowed to visualize the target structures reliably in the surgical field, facilitating surgical orientation. Flexible placement of the reference array enabled AR implementation for anterior, lateral, posterior median, and posterior paramedian approaches. Identification of bony and artificial landmarks allowed validating registration accuracy; the measured target registration error was 1.11 +/- 0.42 mm (mean +/- standard deviation). The effective dose for registration scanning ranged from 0.52 to 8.71 mSv, which is on average about one-third of a standard diagnostic spine scan. This depended mainly on the scan length (mean scan length cervical/thoracic/lumbar: 99/218/118 mm). Longest scan ranges were in the mid-thoracic region to ensure unambiguous vertebra assignment as prerequisite for reliable nonlinear registration (mean cervical/thoracic/lumbar effective dose: 0.52/614/2.99 mSv). CONCLUSIONS: Reliable microscope-based AR support is possible because of automatic registration based on intraoperative imaging. Application of AR in degenerative spine surgery has a big potential; it might be especially helpful in complex anatomical situations and resident education.