An imaging system comprising a radiation source and radiation thereby； a detector having an input surface； a monitor configured to display images detected by the detector； a Graphical User Interface (GUI) for determining at least one Region of Interest (ROI) on a displayed image； and a collimator comprising means for modulating intensity of the radiation according to the at least one ROI； wherein the GUI comprises means for displaying detected images and means for determining shape and location of the at least one ROI.
