1. A method of tomographic image reconstruction comprising: reconstructing a first image volume from an incomplete projection dataset; reconstructing a second image volume from a projection dataset; taking the difference of the first image volume and the second image volume to produce a difference volume; projecting the difference volume over a set of view angles in a parallel three-dimensional geometry to produce a respective set of parallel views; applying shift-variant filtration to the set of parallel views to remove frequencies that are represented in at least the incomplete projection dataset to produce a set of filtered parallel views; backprojecting the filtered parallel views to produce a filtered difference volume; and adding the filtered difference volume to the first image volume to produce a final image volume.