1. A method for operating a computed tomography apparatus wherein volume data for a volume region of an examination subject are registered, comprising the steps of: (a) producing an x-ray shadowgram of a region of an examination subject containing the volume region; (b) mixing a plurality of markings for identifying reconstruction regions in said volume region for which image data are to be reconstructed from said volume data; (c) allocating at least one reconstruction parameter to each of said reconstruction regions; and (d) reconstructing image data for each of said reconstruction regions employing the at least one reconstruction parameter allocated to the respective reconstruction region.