Evaluating the effects of detector angular misalignments on simulated computed tomography data

• Volumetric coordinate errors (dx, dy, dz) were evaluated in the presence of detector angular misalignments by simulation and systematic behaviours were observed.
• Radiographic errors, i.e. pixel coordinate errors in the radiographic intensity image, due to angular misalignments of the detector are modelled.
• The radiographic error model is applied to re-bin the simulated radiographs in the presence of detector misalignments. Volumetric errors are reduced when the volumes are reconstructed with the re-binned radiographs.
• Reduction of volumetric errors validate the efficacy of the radiographic error model, which can be used to develop a geometrical error model for CT measurements.

The quality of dimensional measurements made by industrial X-ray computed tomography (CT) depends on a variety of influence factors in the measurement process. In this paper, the effects of angular misalignments of a flat-panel detector are investigated. First, a forward projection model is applied to evaluate distortions of the radiographic pixel coordinates assigned to X-ray intensities due to various detector rotation angles. Distortion maps are presented for a set of representative detector rotations and the sensitivity of image distortions to each rotation is discussed. It is shown from a simulation study that detector angular misalignments result in systematic errors of the reconstructed volume. The distortion model is inversely applied to generate correction maps that are used to correct the simulated radiographs from a misaligned detector. A new volume is reconstructed from the corrected radiographs and the new deviations are compared to the uncorrected results. The reduction of observed volumetric errors after radiographic correction validates the efficacy of the radiographic distortion model. Additionally, the output of this study can contribute to the development of a geometrical error model for volumetric measurements made by CT.