The invention relates to a detection apparatus comprising a filter (20) for filtering a conical radiation beam (4) such that at least a first region (22) and a second region (23) of the radiation beam are generated having different energy spectra, wherein the first region of the radiation beam illuminates a first detector area (25) on a detection surface (21) of a detector, thereby generating a first set of detection values, and the second region of the radiation beam illuminates a second detector area (26) on the detection surface, thereby generating a second set of detection values. For example, by using the filter the detection apparatus can be used as dual-energy computed tomography apparatus, wherein, for instance, a standard computed tomography apparatus can be transformed to a dual-energy computed tomography apparatus by adding the filter to the standard computed tomography apparatus, preferentially without modifying the radiation source and the detector.
