Two-stage registration for real-time deformable compensation using an electromagnetic tracking device.

Electromagnetic tracking systems have the potential to track instruments inside the body because they are not limited by the line of sight constraints that characterize optical tracking systems. To integrate an electromagnetic tracking device into a surgical navigation system, accurate registration is required. We present a two-stage registration mechanism designed to be more accurate than the widely used global fiducial-based registration method. The first stage uses a hybrid Iterative Closest Point (ICP) registration method and the Simulated Annealing (SA) optimization algorithm, to increase the initial registration accuracy. The second stage exploits multiple implanted tracking needles that are used to calculate the affine transform based on the initial transform information, and thereby to compensate for the deformation in real time. Phantom and swine studies have demonstrated the utility of this technique.