Abstract: There is provided an X-ray imaging system having an X-ray source, an X-ray detector and a collimator assembly in the X-ray path between the X-ray source and the X-ray detector. The X-ray detector comprises a plurality of detector modules arranged side-by-side and adapted to be oriented towards the X-ray source, the detector modules being arranged side-by-side along a direction substantially orthogonal to the direction of incoming X-rays. The collimator assembly is based on a plurality of spaced collimator plates arranged side-by-side in a direction coinciding with the direction of the detector modules. The collimator assembly further comprises a physically stabilizing lateral support structure arranged in a lateral plane extending in a direction substantially orthogonal to the direction of incoming X-rays.