The invention refers to a system for providing a spectral image using a conventional CT system. The system comprises a data providing unit (11) for providing first projection data and second projection data, wherein the first and second projection data have been acquired using different acquisition spectra, wherein the first projection data has been acquired during a scout scan and the second projection data has been acquired during a diagnostic scan, or wherein the first and second projection data have been acquired by a first and second part of the detector, respectively. The first and second part of the detector acquire projection data with different acquisition spectra. A spectral image generation unit (12) generates a spectral image based on the projection data. With this system a spectral image can be provided using a conventional CT system with a decreased acquisition time.
