To reduce quality losses in edge areas of an X-ray image, caused by temperature fluctuations, an X-ray detector (1) is arranged with a scintillator (2) for converting X radiation into light and with an active matrix (3) of pixel readout elements, arranged behind it in the direction of X radiation, in such a manner that the active matrix (3) is shielded in an optically opaque manner with respect to the scintillator (2) in at least one edge area (6) of the cross-over area of the scintillator (2) and the active matrix (3); in particular, the optically opaque shielding is suitable for forming a dark reference zone (5) when the scintillator (2) is present.