  Robot-assisted surgery is rapidly developing in the medical field, and the
integration of augmented reality shows the potential of improving the surgeons'
operation performance by providing more visual information. In this paper, we
proposed a markerless augmented reality framework to enhance safety by avoiding
intra-operative bleeding which is a high risk caused by the collision between
the surgical instruments and the blood vessel. Advanced stereo reconstruction
and segmentation networks are compared to find out the best combination to
reconstruct the intra-operative blood vessel in the 3D space for the
registration of the pre-operative model, and the minimum distance detection
between the instruments and the blood vessel is implemented. A robot-assisted
lymphadenectomy is simulated on the da Vinci Research Kit in a dry lab, and ten
human subjects performed this operation to explore the usability of the
proposed framework. The result shows that the augmented reality framework can
help the users to avoid the dangerous collision between the instruments and the
blood vessel while not introducing an extra load. It provides a flexible
framework that integrates augmented reality into the medical robot platform to
enhance safety during the operation.
