A method is provided for determining, in a fourth-generation computed tomography (CT) scanner, a positional offset of a center of a ring of fixed energy-discriminating detectors with respect to an iso-center of a third-generation X-ray source/detector system. The method includes obtaining a plurality of offset images, each offset image being obtained from a scan executed with the ring of fixed energy-discriminating detectors positioned in a known offset location with respect to the iso-center performing a current scan executed with the ring positioned in an unknown offset location with respect to the iso-center, to obtain a current image calculating, for each offset image, a corresponding error value between the offset image and the current image and determining the positional offset of the center of the ring to be an offset location corresponding to an offset image having the smallest error value.
