The invention relates to a combined imaging detector (110) for the detection of x-ray and gamma quanta. The combined imaging detector (110) is adapted for simultaneous detection of gamma and x-ray quanta. The combined imaging detector (110) includes an x-ray anti-scatter grid (111), a layer of x-ray scintillator elements (112), a first photodetector array (113), a layer of gamma scintillator elements (114), and a second photodetector array (115) that are arranged in a stacked configuration along a radiation-receiving direction (116). The x-ray anti-scatter grid (111) comprises a plurality of septa (117A, B, C) that define a plurality of apertures (118) which are configured to collimate both x-ray quanta and gamma quanta received from the radiation receiving direction (116) such that received gamma quanta are collimated only by the x-ray anti-scatter grid (111). The use of the x-ray anti-scatter grid as a collimator for received gamma quanta results in a significantly lighter combined imaging detector.