a method and imaging system for operating imaging computed tomography using a radiation source and a plurality of detectors to generate an image of an object . the method includes : defining a desired image characteristics ; and performing calculations to determine the pattern of fluence to be applied by the radiation source , to generate said desired image quality or characteristics . then , the 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 comprise at least one of desired levels of contrast - to - noise ratio and signal - to - noise ratio , and may 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 .