Development of a Liver Respiratory Motion Simulator to Investigate Magnetic Tracking for Abdominal Interventions

摘要

We have designed and constructed a liver respiratory motion simulator as a first step in demonstrating the feasibility of using a new magnetic tracking system to follow the movement of internal organs. The simulator consists of a dummy torso, a synthetic liver, a linear motion platform, a graphical user interface for image overlay, and a magnetic tracking system along with magnetically tracked instruments. While optical tracking systems are commonly used in commercial image-guided surgery systems for the brain and spine, they are limited to procedures in which a line of sight can be maintained between the tracking system and the instruments which are being tracked. Magnetic tracking systems have been proposed for image-guided surgery applications, but most currently available magnetically tracked sensors are too small to be embedded in the body. The magnetic tracking system employed here, the AURORA? from Northern Digital, can use sensors as small as 0.9 mm in diameter by 8 mm in length. This makes it possible to embed these sensors in catheters and thin needles. The catheters can then be wedged in a vein in an internal organ of interest so that tracking the position of the catheter gives a good estimate of the position of the internal organ. Alternatively, a needle with an embedded sensor could be placed near the area of interest. To demonstrate this concept, our liver respiratory motion simulator includes a synthetic liver mounted on a one degree of freedom linear motion platform. The linear motion platform is computer controlled, allowing arbitrary respiratory motion cycles to be simulated. The liver includes veins so that a catheter can be placed inside it. A graphical user interface (GUI) has been developed based on the VTK (Visualization Toolkit) graphics package. The GUI allows the user to view a set of axial CT slices of the liver and track the moving liver in real-time, as well as display an image overlay of a magnetically tracked probe. This type of GUI could be used in future studies such as biopsy of internal organs while compensating for respiratory motion. This paper describes the simulator components and presents our concept for using magnetic tracking to assist the physician in targeting internal organs, including the tracking of respiratory motion. We believe this will be a first step in extending image-guided surgery from the current stage of tracking of rigid objects such as the skull and vertebral bodies to the tracking of internal organs and compensation for respiration.