Automatic positioning of surgical instruments in minimally invasive robotic surgery through vision-based motion analysis

Robotic surgery has experienced a rapid progress in a diversity of interventions, especially in minimally invasive surgery (MIS). In this type of interventions the patient body is accessed by inserting especial instruments through small incisions. As these instruments are manipulated by robotic assistants, passive wrists are incorporated for free compliance with the port of entry. With this wrist configuration it is only possible to locate accurately an instrument tip if its port of entry or fulcrum point is known. A vision oriented method is proposed in this paper to estimate the position of this external point of incision. It is based on motion analysis in a sequence of images where geometric properties of projected features and 3D transformations of the instrument are related. In this work we show that it is possible to accurately estimate the position and orientation of this 3D point, as well as the orientation of the instrument with respect to the laparoscopic camera applying determined movements through the robotic assistant.