Motion Correction Strategies for Interventional Angiography Images: A Comparative Approach

Digital subtraction angiography (DSA) is an important tool in interventional procedures and enables the surgeon to visualize the blood vessels in the projection X-ray images. Due to the motion of patient as well as motion of internal tissues constituting the background anatomy of the patient, the difference images may contain motion artifacts. The artifacts due to motion may be severe enough to make the visualization useless or erroneous and the images need to be motion compensated. Image registration is used for motion correction of DSA images such that the background mask image is placed in coordinates of the blood vessel enhanced image. The background structures are aligned as a result of image registration and are therefore removed from the subtraction image. There exist a large number of image registration techniques depending upon the application and the available information. In this paper, we compare two intensity based image registration techniques for motion correction of DSA images using signal-to-noise ratio as the evaluation metric. The methods discussed are: inverse consistent linear elastic image registration using b-splines and modified demons method, using a hierarchical strategy that focuses on region of intensity differences, like HAMMER. Both methods derive the driving function from image intensities, but impose different kind of constraints.