The invention relates to a photon counting x-ray radiation detection system. The system (31) comprises an x-ray radiation device (2) for providing polychromatic x-ray radiation (4) for traversing an examination zone (5) during a detection period of a scan. A photon counting detection device (6) comprising detection elements (3) detects the x-ray radiation after having traversed the examination zone and measures for each detection element photon counts in one or more energy bins during the detection period. A correction unit (12) estimates for each detection element an amount of a build up charge present in the detection element and corrects the measured photon counts for the detection element based on the estimated amount of the build up charge. This allows the corruption of the photon count rates caused by the build up charges to be compensated and to improve the determination of the photon counts.