The present invention relates to light guiding in an X-ray detector. In order to provide a focussing of a scintillator, an X-ray detector (30) is provided comprising a scintillator arrangement (32) in a first layer (34), an optical guide arrangement (36) in a second layer (38), and a light-sensitive sensor arrangement (40) in a third layer (42). The second layer is provided between the first and the third layer. The scintillator arrangement comprises a structured scintillator with a plurality of scintillator elements (44) arranged as trenches separated from each other by wall elements (46) in a grating structure; wherein the trenches are configured to receive X-ray radiation from one side and wherein the trenches are configured to emit visible light on a second side. The trenches are arranged focused on a common point in which an X-ray source is arrangeable. The light-sensitive sensor arrangement comprises a plurality of sensor elements (48) that detect light generated by the scintillator elements. The optical guide arrangement comprises a light guiding plate (10), the light guiding plate comprising a plurality of light guide elements (12) arranged extending between a first surface (14) of the light guiding plate and an opposite second surface (16) of the light guiding plate. The first surface is configured for entry (18) of light generated by the scintillator to be arranged on top of the light guiding plate; and wherein the second surface is configured for exit (20) of the light towards the light-sensitive sensor arrangement being arranged adjacent the light guiding plate. The light guide elements are configured to guide light from the first surface to the second surface. Further, the first surface and the second surface are provided at least partly inclined relative to each other.