1. A method of reducing image artifacts in a tomographic image of an imaged object, such artifacts resulting from simultaneous multiple slice acquisitions of projection data, comprising the steps of: (a) acquiring a set of projection data at a plurality of angles about an axis through the image object, the projection data measuring attenuation along first rays passing through the imaged object perpendicular to the axis, and second rays passing through the imaged object but not perpendicular to the axis, wherein the set of projection data transformed into frequency space has zones of missing frequency space data as a result of the non-perpendicular angle of the second rays; (b) reconstructing the projection data to produce a three-dimensional tomographic image data set having pixels of varying density; (c) separating the three-dimensional tomographic image data set into a mid-range density image data set including pixels having density values within a predetermined range, and an extreme-range density image data set including pixels having density values outside of the predetermined range; (d) spatially filtering the mid-range density image data set to reduce the value of its spatial frequency in frequency zones corresponding to the zones of missing frequency space data of the projection set with a filter that changes as a function of the location of the pixel value along said axis; and (e) combining the filtered mid-range density image data set and the extreme-range density image data set to create a tomographic image.