CORRECTION FOR RING-LIKE IMAGE ARTEFACTS

A computer tomography device is provided with a reconstruction unit (1) for deriving brightness values of an image from density values. An image processing system (2) for deriving corrected brightness values from the brightness values of the image is arranged to calculate the variation of brightness values of the image in the radial direction and in the tangential direction. The image processing system is also arranged to calculate the deviation between the variation in the radial direction and the variation in the tangential direction and to derive corrected brightness values from brightness values of the image and the deviation.