1. An X-ray computed tomography (CT) system comprising: a support structure including a gantry mounted to rotate about a vertical axis of rotation during scanning; a first assembly including an X-ray source mounted on the gantry to rotate therewith for generating a cone X-ray beam, wherein the X-ray source is mounted to move a focal spot through a plurality of planes perpendicular to the axis of rotation during scanning; a second assembly including a planar X-ray detector mounted on the gantry to rotate therewith wherein the detector is spaced from the source on the gantry for enabling a human or other animal body part to be interposed therebetween so as to generate output data comprising a plurality of two-dimensional electronic representations of an area of the detector on which an X-ray beam impinges during scanning; and a data processor for processing the output data to obtain a CT image of the body part.