1. A method of operating a CT device, by means of which volume data pertaining to a volume region of a test object can be recorded, comprising the following method steps: a) recording volume data pertaining to a volume region of a test object and creating and displaying an X-ray shadow image of the volume region from the volume data recorded, b) inserting at least one marking into the X-ray shadow image for identifying a reconstruction region, with respect to which image data is to be reconstructed from volume data, c) reconstructing and displaying a slice of the start and/or end of the reconstruction region from the volume data recorded, and then d) reconstructing image data pertaining to each reconstruction region.