To obtain functional information 110 energising a first set of x-ray emitters of the panel over a first period of time and directing the x-rays at the first object; using the detector to detect the x-rays 35 after passing through the first object; processing the detected x-rays to create a first set of images to obtain tomosynthesis data 100; energising a second set of x-ray emitters of the panel over a second period of time and directing the x-rays at the first object; using the detector to detect the x-rays after passing through the first object; processing the detected x-rays to create a second set of images to obtain tomosynthesis data, wherein the number of emitters used in the second period of time is less than used in the first period of time; and comparing at least some images from each set of images to provide functional information.