Abstract: A system for measuring the charge distribution on a photoreceptor plate which has been exposed to X-ray radiations to form an image of an object thereon is disclosed. The system comprises a transparent sensor electrode adapted to be positioned over the photoreceptor plate, means for scanning a pulsed laser beam through the transparent sensor electrode to discharge the photoreceptor surface charge pixel-by-pixel and so induce a corresponding voltage on the sensor electrode to be read by a suitable read-out device, such sensor electrode being of sufficient width so as to achieve good capacitive coupling with the region around the area to be discharged by the laser, and means for moving the sensor electrode or the photoreceptor plate step by step or continuously transversely of the laser scanning direction for reading out the image impressed on the photoreceptor surface.