1. A method for producing a computed tomography (CT) image comprising the steps of: (a) scanning a subject, having a region exhibiting a periodic motion, with a conical x-ray beam emanating from a focus and detecting said beam, after attenuation by said subject, with a matrix-like detector array while moving said focus along a spiral path around said subject relative to a system axis, said detector array generating output data dependent on radiation from said x-ray beam that is incident thereon; (b) dividing said output data, for a segment of said spiral path having a length adequate for reconstructing a CT image, into a plurality of datasets respectively for a plurality of sub-segments of said segment, each of said sub-segments having a length shorter than said length adequate for reconstructing a CT image; (c) for each of said sub-segments, reconstructing a plurality of segment images having a plane inclined relative to said system axis from the dataset for that sub-segment; (d) obtaining a signal representing a time curve of said periodic motion during said scanning; (e) allocating a z-position on said system axis and a time position with respect to said periodic motion to the respective segment images; (f) selecting segment images within a range of z-positions and a range of time positions so that the respective sub-segments of the selected segment images comprise a total length adequate for reconstruction of a CT image; and (g) at least indirectly combining the selected segment images to form a resulting CT image with respect to a target image plane.