In the exemplary embodiments a layer is to be scanned which is generally parallel to the longitudinal axis of the patient support. For example, a radiation source and a radiation receiver may be rotated in an arc about a rotational axis which lies perpendicular to the longitudinal axis of the patient support to scan a layer area in such a way that the scanned layer within the exposure subject is traversed exclusively along beam paths each of which is crossed along its entire length in the subject by a multitude of other beam paths.