A Reconstruction Method Through Projection Data Conversion under the Displaced Detector Scanning for Industrial Cone-beam CT

In the application of industrial cone-beam computed tomography (CBCT), the displaced detector scanning mode can significantly enlarge the field of view (FOV) of the CT system. However, when this mode is applied to inspect a large object, the connecting line between the X-ray focus and the center-of-rotation projection may not be perpendicular to the real flat-panel detector, which makes most of the existing reconstruction methods impractical. The purpose of this article is to explain the work done in developing an image reconstruction method under the displaced detector scanning mode. We first establish a virtual detector to make the connecting line be perpendicular to the virtual detector, and the real projection data are then converted into the virtual detector. The geometrical parameters of the real CT system are converted into the CT system with the virtual detector, in which the virtual detector and the twist angles of the reconstructed images are effectively corrected by adjusting angles of the projection sequence. Based on the corrected projection data and the converted geometry parameters, the cross sections of the object are accurately reconstructed through the FDK reconstruction algorithm combined with the Wang weighting function. Computer simulation results and CBCT experiment results demonstrate that the image artifacts and the twist angles of the reconstructed images are well corrected. Through this method, the FOV of the CT system is enlarged by 78% without changing the original geometric layout of the system, which is significant for engineering applications.