Markerless Real-Time Target Region Tracking: Application to Frameless Sterotactic Radiosurgery

Accurate and fast registration of intra-operative 2D projection images to 3D pre-operative images is an important component of many image-guided surgical procedures. If the 2D image acquisition is repeated several times during the procedure, the registration problem can be cast instead as a 3D tracking problem. To solve the 3D problem, we propose in this paper to apply a real-time 2D region tracking algorithm to first recover the components of the transformation that are in-plane to the projections. From the 2D motion estimates of all projections, a consistent estimate of the 3D motion is derived. We compare this method to computation in 3D and a combination of both. Using clinical data with a goldstandard transformation, we show that a standard tracking algorithm is capable of accurately and robustly tracking regions in x-ray projection images, and that the use of 2D tracking greatly improves the accuracy and speed of 3D tracking.