The present invention is directed towards a photon counting radiation detector (10) comprising an array of pixels (13) comprising a plurality of detection pixels (131) for detecting imaging information. At least one pixel of the array of pixels (132) is shielded from receiving radiation. A dark current is determined from the shielded pixel (132) and is used to compensate for dark current in the other, non-shielded pixels (131). Embodiments are directed to integrating pixel shielding within an Anti Scatter Grid or in a mask.