The invention relates to a control module for controlling an x-ray system (140) during the acquisition of step images for phase imaging. The control module comprises a step image quantity providing unit (111) for providing a step image quantity, a detector dose providing unit (112) for providing a target detector dose, an applied detector dose determination unit (113) for determining an applied detector dose absorbed by a part of the detector (144) during the acquisition of a step image, and a step image acquisition control unit (114) for controlling the x-ray imaging system (140) during the acquisition of each step image based on the applied detector dose, the target detector dose and the step image quantity. The control module allows to control the x-ray imaging system such that the target detector dose is not exceeded while at the same time ensuring a sufficient quality of the step images.
