Dynamic organ modeling for minimally-invasive cardiac surgery

While most currently available minimally invasive robotically assisted cardiac surgical systems do not employ 3D image guidance, such support can be generated using pre operative images such as CT. Previously we demonstrated a virtual model of the thorax with simulated surgical instruments, and a pulsating virtual model of the coronary arteries. In this paper we report the overlay of optical endoscopic images of a beating heart phantom with CT-based dynamic volumetric images of the phantom. Spatial matching is obtained through optical tracking of the endoscope and of the phantom, while time synchronization of the display of the model utilizes ECG gating. The spatial accuracy between the optical and virtual images varies from about 0.8 mm to –2.6 mm, while the time discrepancy depends on the frame-rate at which the virtual model is refreshed, and is typically 50-100 ms. Although the CT-based dynamic images are sufficient for animation of the model, artefacts associated with the image registration prevent seamless animation. Instead, to reconstruct the various phases of heart pulsation, we used a high-quality semi-static image of the diastolic phase of the phantom, and warped it to match the CT-based images corresponding to other phases of the heart pulsation.