Fast and accurate calibration of an X-ray imager to an electromagnetic tracking system for interventional cardiac procedures

Cardiovascular disease affects millions of Americans each year. Interventional guidance systems are being developed as treatment options for some of the more delicate procedures, including targeted stem cell therapy. As advanced systems for such types of interventional guidance are being developed, electromagnetic (EM) tracking is coming in demand to perform navigation. To use this EM tracking technology, a calibration is necessary to register the tracker to the imaging system. In this paper we investigate the calibration of an Xray imaging system to EM tracking. Two specially designed calibration phantoms have been designed for this purpose, each having a rigidly attached EM sensor. From a clinical usability point-of-view, we propose to divide this calibration problem into two steps: i) an initial calibration of the EM sensor to the phantom design using an EM tracked needle to trace out grooves in the phantom surface and ii) segmentation from Xray images and 3D reconstruction of beads embedded in the phantom in a known geometric pattern. Combining these two steps yields an X-ray-to-EM calibration accuracy of less than 1 mm when overlaying an EM tracked needle on X-ray images.