An X ray imaging system comprises an X ray tube (6) a ceiling suspension (2) for the X ray tube a detector trolley (12) with an X ray detector (10) mounted thereon an active sensor matrix (24) an optical indication unit (20) and a control unit (26). The active sensor matrix (24) is fixedly mounted on the ceiling suspension (2) the optical indication unit (20) is fixedly mounted to the detector trolley (12) and is adapted for emitting an optical indication (22) onto the active sensor matrix (24). The control unit (26) is connected to the active sensor matrix (24) and is adapted for acquiring the position of the optical indication (22) on the active sensor matrix (24) and to create control signals for aligning the detector trolley position and the ceiling suspension position relative to each other such that the optical indication is present on a predetermined spot on the active sensor matrix. This eliminates the need of a mechanically fixed arm carrying a detector unit at a fixed spatial relationship to an X ray arm as the detector and the X ray tube are be linked by a position following process.
