Abstract: In a computer tomography apparatus having an annularly guided electron beam, has an x-ray source with an annular anode. Before the beginning of a scan event, the electron beam travels through the x-ray source concentrically relative to the annular anode until it is incident on a beam catcher at the closed end of the x-ray source. Proceeding from the end of the x-ray source at which the beam catcher is disposed, the electron beam is focused on, and scans, the annular anode. A constant focus size of the electron beam on the annular anode is thereby achieved.

Abstract: In an exemplary embodiment, a radiation-measuring arrangement comprises a radiation source which produces a fan-shaped beam of rays, and a radiation receiver which determines the radiation intensity behind the subject. The beam of rays executes a scanning movement in the layer plane for scanning a layer area which is greater than the layer area corresponding to the fan-shaped extent of the beam of rays. Furthermore, there is a rotating ring for the measuring arrangement for irradiating the radiography subject from different directions. The output signals of the radiation receiver are transformed by a measured value converter into a layer image. The measuring arrangement is mounted on a rotatable support which is pivotally mounted on the rotating ring and is swivelled by a drive element of a second rotating ring when the angular velocity of the second rotating ring differs from the angular velocity of the first rotating ring.