1. An apparatus for generating a motion map, the apparatus comprising: a radiation source; a radiation sensitive detector which detects radiation emitted by the source that has traversed an examination region; and a reconstructor and an image processor; wherein the radiation source and the radiation sensitive detector are used to acquire projection data at a plurality of angular positions relative to an object disposed in the examination region; wherein the reconstructor is used to generate a reference image from the projection data; wherein reference projection data is obtained from a forward projection of the reference image; wherein differences between the acquired projection data and the reference projection data are computed to determine line integral differences; and wherein the image processor uses the line integral differences to generate a motion map indicative of the regions of a corresponding image reconstructed from the projection data that are affected by motion.