A method and imaging system for operating imaging computed tomography using at least one radiation source and at least one detector to generate an image of an object. The method includes: defining desired image characteristics; and performing calculations to determine the pattern of fluence to be applied by the at least one radiation source, to generate said desired image quality or characteristics. Then, the at least one radiation source is modulated, to generate the intended pattern of fluence between the beam source and the object to be imaged. The desired image characteristics can provide at least one of: desired image quality in at least one defined region of interest; and at least one desired distribution of said image quality.