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A precise augmented reality combining video and 3D CT-scan data can be applied to otoendoscopy without the use of conventional neuronavigation tracking thanks to computer vision algorithms.

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Transtympanic procedures aim at accessing the middle ear structures through a puncture in the tympanic membrane. They require visualization of middle ear structures behind the eardrum. Up to now, this is provided by an oto endoscope. This work focused on implementing a real-time augmented reality based system for robotic-assisted transtympanic surgery. A preoperative computed tomography scan is combined with the surgical video of the tympanic membrane in order to visualize the ossciles and labyrinthine windows which are concealed behind the opaque tympanic membrane. The study was conducted on 5 artificial and 4 cadaveric temporal bones. Initially, a homography framework based on fiducials (6 stainless steel markers on the periphery of the tympanic membrane) was used to register a 3D reconstructed computed tomography image to the video images. Micro/endoscope movements were then tracked using Speeded-Up Robust Features. Simultaneously, a micro-surgical instrument (needle) in the frame was identified and tracked using a Kalman filter. Its 3D pose was also computed using a 3-collinear-point framework. An average initial registration accuracy of 0.21 mm was achieved with a slow propagation error during the 2-minute tracking. Similarly, a mean surgical instrument tip 3D pose estimation error of 0.33 mm was observed. This system is a crucial first step towards keyhole surgical approach to middle and inner ears.