  Purpose: Trans-oral robotic surgery (TORS) using the da Vinci surgical robot
is a new minimally-invasive surgery method to treat oropharyngeal tumors, but
it is a challenging operation. Augmented reality (AR) based on intra-operative
ultrasound (US) has the potential to enhance the visualization of the anatomy
and cancerous tumors to provide additional tools for decision-making in
surgery. Methods: We propose and carry out preliminary evaluations of a
US-guided AR system for TORS, with the transducer placed on the neck for a
transcervical view. Firstly, we perform a novel MRI-transcervical 3D US
registration study. Secondly, we develop a US-robot calibration method with an
optical tracker and an AR system to display the anatomy mesh model in the
real-time endoscope images inside the surgeon console. Results: Our AR system
reaches a mean projection error of 26.81 and 27.85 pixels for the projection
from the US to stereo cameras in a water bath experiment. The average target
registration error for MRI to 3D US is 8.90 mm for the 3D US transducer and
5.85 mm for freehand 3D US, and the average distance between the vessel
centerlines is 2.32 mm. Conclusion: We demonstrate the first proof-of-concept
transcervical US-guided AR system for TORS and the feasibility of
trans-cervical 3D US-MRI registration. Our results show that trans-cervical 3D
US is a promising technique for TORS image guidance.
