Motion Tracking for Minimally Invasive Robotic Surgery

Minimally invasive surgery is a modern surgical technique in which the instruments are inserted into the patient through small incisions. An endoscopic camera provides the view to the site of surgery inside the patient. While the patient benefits from strongly reduced tissue traumatisation, the surgeon has to cope with a number of disadvantages. These drawbacks arise from the fact that, in contrast to open surgery, direct contact and view to the field of surgery are lost in minimally invasive scenarios. A sophisticated robotic system can compensate for the increased demands posed to the surgeon and provide assistance for the complicated tasks. To enable the robotic system to provide particular assistance by partly autonomous tasks e.g. by guiding the surgeon to a preoperatively planned situs or by moving the camera along the changing focus of surgery, the knowledge of intraoperative changes inside the patient becomes important. Two main types of targets can be identified in endoscopic video images, which are instruments and organs. Depending on these types different strategies for motion tracking become advantageous. Tracking of image motion from endoscopic video images can be based solely on structure information provided by the object itself or can involve artifical landmarks to aid the tracking process. In the first case, the use of natural landmarks refers to the fact that the genuine structure of the target is used to find reference positions which can be tracked. This can involve intensity or feature based tracking strategies. In the second case of artifical landmarks, markers with a special geometry or colour can be used. This enables particular tracking strategies, making use of the distinctive property of these markers. This chapter describes different motion tracking strategies used to accomplish the task of motion detection in minimally invasive surgical environments. Two example scenario are provided for which two different motion tracking strategies have been successfully implemented. Both are partly autonomous task scenarios, providing automated camera guidance for laparoscopic surgery and motion compensation of the beating heart.