Disclosed are procedures for converting x-ray cone beam data (line integrals through an object) to Radon data (planar integrals) for 3D CT image reconstruction by inverse Radon transformation. The radial derivative of each planar integral is determined by integrating to determine weighted line integrals along each of a pair of lines on a normalized detector plane, which lines are defined as intersections with the normalized detector plane of a corresponding pair of integration planes sharing a rotation axis and rotated with respect to each other by a rotation angle delta beta , and then dividing the difference between the weighted line integrals by the rotation angle delta beta . The procedure can be employed to convert the cone beam data to values representing planar integrals on any arbitrary set of planes in Radon space, such as a set of coaxial vertical planes. <IMAGE>
