1. An apparatus for extending the effective field of view (FOV) of a computer tomography (CT) scanner, comprising: a storage medium that stores an image mask and stores acquired CT projection transmission data of said CT scanner to be used in calculating image reconstruction data; and a processor that performs a direct inversion data calculation using said CT projection transmission data defined by said image mask to obtain image reconstruction data for a reconstructed CT image, wherein the calculation uses the image mask and image center as one boundary; and wherein the reconstructed CT image includes areas outside the image mask and outside the CT scanner FOV.