Speaking of CT scan ,it is common to have different pictures when CT scans are taken on 2 different machines. The reason being there is no one standard for calibration of these machines among manufacturers. Not to get too deep in the boring world of photons , beams and wavelengths, standard calibration insures that all machines operate under the same conditions and provide the same result. Our health care system is great but most of the time and due to competition, the left hand does not know what the right hand is doing.