Ultrasound image-guided mapping of endoscopic views on a 3D placenta model: A tracker-less approach

This work presents a framework for mapping of free-hand endoscopic views onto 3D anatomical model constructed from ultrasound images without the use of external trackers. It is non-disruptive in terms of existing surgical workflow as surgeons do not need to accommodate operational constraints associated with the use of additionally installed motion sensors or tracking systems. A passive fiducial marker is attached to the tip of the endoscope to create a geometric eccentricity that encodes the position and orientation of the camera. The relative position between the endoscope and the anatomical model under the ultrasound image reference frame is used to establish a texture map that overlays endoscopic views onto the surface of the model. This addresses operational challenges including the limited field-of-view (FOV) and the lack of 3D perspective associated with minimally invasive procedure. Experimental results show that average tool position and orientation errors are 1.32 mm and 1.6^o respectively. The R.M.S. error of the overall image mapping obtained based on comparison of dimension of landmarks is 3.30 mm with standard deviation of 2.14 mm. The feasibility of the framework is also demonstrated through implementations on a phantom model.