Cervical vertebrae tracking in video-fluoroscopy using the normalized gradient field

For patients with neck problems valuable functional and diagnostic information can be obtained from a fluoroscopy video of a flexion-extension movement of the cervical spine. In most cases physicians have to manually extract the vertebrae, making the analysis of these video sequences tedious and time consuming. In this paper we propose an automatic fast and precise method for tracking cervical vertebrae. Our method relies only on a rough selection of template areas of each vertebra in a single frame of the video sequence. Compared to existing automated methods, no contours need to be extracted and no vertebra segmentation is required. Tracking is done with a normalized gradient field, using only the gradient orientations as features. Experimental results show that the algorithm is robust and able to track the vertebrae accurately even if they are partially occluded or if a disc prosthesis is present.