Scan and reconstruction of helical cone-beam industrial CT for big workpiece

In 3D cone-beam Industrial Computed Tomography (ICT), in addition to the case which the inspected workpiece is longer than the detector, it is common that the diameter of the detected workpiece is bigger than the width of the detector. The helical trajectory can solve the problem of long object scan, not the problem of big object scan. In this paper, a scan mode and reconstruction method is discussed, which trajectory is translation and dually helical. It does not only inspect the large and long object but also has fewer redundant projections. Firstly, the gantry is horizontally translated before scan, one part of the detected workpiece can be covered by ray-beam, and projections of the first spiral scan are acquired. Then, the gantry is horizontally translated along opposite direction before the second scan, another part of the detected workpiece can be covered by ray-beam, and projections of the second helical locus are acquired. The 3D image is reconstructed according to modified helical FDK algorithm. When reconstructing, projections don’t need to be rebinned. The scan mode presented by this paper is easily implemented and efficiency is also high. The results of computer simulation validate the FOV(Field Of View) radius via this method can be improved to about two times compared with the traditionally helical cone-beam CT.