Inside-Out Instrument Tracking for Surgical Navigation in Augmented Reality

Surgical navigation requires tracking of instruments with respect to the patient. Conventionally, tracking is done with stationary cameras, and the navigation information is displayed on a stationary display. In contrast, an augmented reality (AR) headset can superimpose surgical navigation information directly in the surgeon's view. However, AR needs to track the headset, the instruments and the patient, often by relying on stationary infrastructure. We show that 6DOF tracking can be obtained without any stationary, external system by purely utilizing the on-board stereo cameras of a HoloLens 2 to track the same retro-reflective marker spheres used by current optical navigation systems. Our implementation is based on two tracking pipelines complementing each other, one using conventional stereo vision techniques, the other relying on a single-constraint-at-a-time extended Kalman filter. In a technical evaluation of our tracking approach, we show that clinically relevant accuracy of 1.70 mm/1.11° and real-time performance is achievable. We further describe an example application of our system for untethered end-to-end surgical navigation.