Vision-Based Augmented Reality System for Middle Ear Surgery: Evaluation in Operating Room Environment.

Hypothesis: Augmented reality (AR) solely based on image features is achievable in operating room conditions and its precision is compatible with otological surgery.

Background: The objective of this work was to evaluate the performance of a vision-based AR system for middle ear surgery in the operating room conditions.

Methods: Nine adult patients undergoing ossicular procedures were included in this prospective study. AR was obtained by combining real-time video from the operating microscope with the virtual image obtained from the preoperative computed tomography (CT)-scan. Initial registration between the video and the virtual CT image was achieved using manual selection of six points on the tympanic sulcus. Patient-microscope movements during the procedure were tracked using image-feature matching algorithm. The microscope was randomly moved at an approximated speed of 5 mm/s in the three axes of space and rotation for 180 seconds. The accuracy of the system was assessed by calculating the distance between each fiducial point selected on the video image and its corresponding point on the scanner.

Results: AR could be obtained for at least 3 minutes in seven out of nine patients. The overlay fiducial and target registration errors were 0.38 ± 0.23 mm (n = 7) and 0.36 ± 0.15 mm (n = 5) respectively, with a drift error of 1.2 ± 0.5 μm/s. The system was stable throughout the procedure and achieved a refresh rate of 12 fps. Moderate bleeding and introduction of surgical instruments did not compromise the performance of the system.

Conclusion: The AR system yielded sub-millimetric accuracy and remained stable throughout the experimental study despite patient-microscope movements and field of view obtrusions.