A multi-spectral X-ray detector comprising: - a first X-ray detector configured to receive incident X-ray radiation; - a structured spectral filter configured to receive intermediate X-ray radiation propagating out of the first X-ray detector; and - a second X-ray detector axially aligned with the first X-ray detector and the structured spectral filter, and configured to receive filtered intermediate X-ray radiation propagating out of the structured spectral filter; wherein the first X-ray detector comprises a contiguous plurality of pixels forming a superpixel (SP 1 , SP 2 , SP 3 , SP 4 ); wherein the second X-ray detector comprises a first plurality of pixels (P 11 , P 21 , P 31 , P 41 ) and a second plurality of pixels (P 12 , P 22 , P 32 , P 42 ), each aligned to receive a portion of the filtered intermediate X-ray radiation having passed through the superpixel; wherein the structured spectral filter comprises a filter structure aligned with pixels of the superpixel, and comprising a first region aligned with the first plurality of pixels of the second X-ray detector, and a second region aligned with the second plurality of pixels of the second X-ray detector, wherein the first region is configured to alter the spectrum of the intermediate X-ray radiation incident on the first plurality of pixels of the second X-ray detector to form the filtered intermediate X-ray radiation; and wherein the contiguous plurality of pixels forming the superpixel of the first X-ray detector are in alignment with at least the first and the second pluralities of pixels of the second X-ray detector, so as to provide, when the multi-spectral X-ray detector is in use, at least three X-ray spectra per superpixel (SP 1 , SP 2 , SP 3 , SP 4 ). - a first X-ray detector configured to receive incident X-ray radiation; - a structured spectral filter configured to receive intermediate X-ray radiation propagating out of the first X-ray detector; and - a second X-ray detector axially aligned with the first X-ray detector and the structured spectral filter, and configured to receive filtered intermediate X-ray radiation propagating out of the structured spectral filter; wherein the first X-ray detector comprises a contiguous plurality of pixels forming a superpixel (SP 1 , SP 2 , SP 3 , SP 4 ); wherein the second X-ray detector comprises a first plurality of pixels (P 11 , P 21 , P 31 , P 41 ) and a second plurality of pixels (P 12 , P 22 , P 32 , P 42 ), each aligned to receive a portion of the filtered intermediate X-ray radiation having passed through the superpixel; wherein the structured spectral filter comprises a filter structure aligned with pixels of the superpixel, and comprising a first region aligned with the first plurality of pixels of the second X-ray detector, and a second region aligned with the second plurality of pixels of the second X-ray detector, wherein the first region is configured to alter the spectrum of the intermediate X-ray radiation incident on the first plurality of pixels of the second X-ray detector to form the filtered intermediate X-ray radiation; and wherein the contiguous plurality of pixels forming the superpixel of the first X-ray detector are in alignment with at least the first and the second pluralities of pixels of the second X-ray detector, so as to provide, when the multi-spectral X-ray detector is in use, at least three X-ray spectra per superpixel (SP 1 , SP 2 , SP 3 , SP 4 ). <EOS>