1. A CT scanner comprising: at least one source of X-rays within an x-ray spectra; a detector array comprising a plurality of detectors; and an X-ray filter mask arrangement disposed between the at least one source of X-rays and detector array so as to modify the spectra of the X-rays transmitted from the at least one source through the filter mask arrangement to at least some of the detectors so that the X-ray spectra detected by at least one set of detectors is different from the X-ray spectra detected by at least one other set of detectors; wherein the CT scanner has X, Y and Z-axes, wherein the X and Y-axes define a scanning plane, and the Z-axis defines the axis of rotation of the at least one source of X-rays and detector array, and the CT scanner further comprises a processor arrangement configured so as to process signals from the detectors to generate interpolated data so that the set of interpolated data representing interpolated values is provided in accordance with a four point Lagrange interpolation along the X-axis.