3-D image guidance for minimally invasive robotic coronary artery bypass

BACKGROUND: The introduction of a robot-assisted microsurgical system has m ade endoscopic coronary artery bypass grafting (ECABG) possible. Despite th e success of this approach, surgeons still require better visualization too ls for pre-surgical planning and intra-operative image guidance. Such visua lization tools could, for example, assist in the placement of thoracic port s to acquire optimum access to the target vessels. In this paper we discuss the essential steps toward image-guided completely endoscopic coronary byp ass surgery with robot assistance, and we present our preliminary efforts t oward the development of a three-dimensional (3-D) virtual cardiac surgical planning platform (VCSP) for ECABG. METHODS: Preoperative 3-D images of the thorax acquired with computed tomog raphy and electrocardiogram-gated magnetic resonance imaging are imported i nto VCSP. Using VCSP, a user may interactively visualize and manipulate the simulated thoracic ports in 3-D within the reconstructed thoracic region. We have also implemented a virtual endoscope to simulate the endoscopic vie w observed by the surgeon during the operation. Once the port placements fo r optimal access to the target vessels are determined, the positions of the simulated tools can be recorded and marked on the patient to specify the p ositions for port incisions. RESULTS: A static thorax phantom was used to verify the port placements obt ained from VCSP simulations. The angles and the distances between the ports , the endoscope and the markers that were placed on the surface of the phan tom were measured, and the results were compared with those obtained from s imulation. The physical measured distances and angles agreed with the simul ated results with average errors of 4 mm and 2 degrees, respectively. CONCLUSIONS: The VCSP image-guided surgical system allows a surgeon to visu alize a patient's thorax in a 3-D interactive environment for planning surg ical procedures, and to determine the optimum port placement based on preop erative 3-D images. However, during an operation, the positions and orienta tion of the heart and the coronary arteries are changed from their correspo nding locations in the preoperative images due to carbon-dioxide insufflati on, lung deflation, and dynamic motions of the beating heart. One of our fu ture goals of this project is the use of mathematical models that correct f or these changes so that our system could be applied to intra-operative ima ge guidance.