X-ray computed tomography (CT) has replaced X-ray projection techniques. CT provides images of brain cross sections in “digital” quality. In CT, an X-ray tube and detectors mounted on the opposite side in relation to the object move in a circle, with the object under study being in the center. During the movement of the tube, detectors sequentially record a plurality of projection data—ray sums—from different directions. Each ray sum includes the result of X-ray attenuation from each element of the object—a voxel—through which an X-ray beam passes from the tube to the detector.