Projection-angle-dependent distortion correction in high-speed image-intensifier-based x-ray computed tomography

Abstract

Geometric distortion is inevitable in facilities using x-ray image intensifiers. When the induced distortion pattern varies over time, each recorded frame should be corrected accordingly, which is the case in conventional C-arm imaging, for example. This demonstrates the need for reliable and easy-to-use, projection-angle-dependent correction methods. In the present work, we demonstrate such a dynamic approach, based on digital image correlation (DIC). We validate the method in a set-up for high-speed x-ray tomography, where the variable distortion is induced by an inhomogeneous distribution of ferromagnetic components in the sample rotation stage. By comparing the ideal positions of metal beads in a rectilinear pattern and their positions in the corrected radiographs of that pattern, we deduced the minimum number of frames required to estimate the varying distortion behavior during a full revolution of the stage. Next, this method was validated in a geometry calibration algorithm for a tomographic set-up, as well as in a tomographic reconstruction. Before the application of any distortion correction, the recorded images suffer from, on average, a mean and maximum distortion of 11.12 pixels (1.56 mm) and 42.79 pixels (6.10 mm), respectively. From our experiments, we conclude that three projections, sampled with a 120° interval, are sufficient to correct any frame recorded under an intermediate angle, with mean and maximum residual errors respectively below 0.48 pixels (0.068 mm) and 1.68 pixels (0.240 mm) while using a 14” image intensifier covering a 292 mm × 292 mm field of view. These results imply a decrease of the mean and maximum distortion errors of at least 96%, regardless of the projection angle. Next, the results showed improved accuracy in the system’s geometry calibration, which resulted in a reduced blurring of edges and better contrast, as well as shape preservation in the tomographic reconstruction. This demonstrates that the new method is accurate and reliable and, due to the common availability of DIC software, it is very accessible and easy to use.

Geometry Calibration of a Modular Stereo Cone-Beam X-ray CT System

“…The X-ray image intensifiers in the 3D YMOX system cause two major geometric distortions, namely pincushion and sigmoidal distortion [ 30 ]. The pincushion distortion is the result of the incident X-ray to be detected on a curved input phosphor, while the latter is due to the magnetic interaction of the produced photo-electrons inside the image intensifier.…”

“…The pincushion distortion is the result of the incident X-ray to be detected on a curved input phosphor, while the latter is due to the magnetic interaction of the produced photo-electrons inside the image intensifier. The projection-dependent distortion correction described in [ 30 ] was applied to correct for these distortions. Flatfield and log correction were applied to the acquired radiographs to compensate for the different responses in the detectors.…”

Methodological Advances in Studying Postnatal Locomotor Development

“…Metal bead markers, 0.5 mm standard soldering balls made out of a lead-tin alloy (Sn 63 P b 37 ), were glued to the extracted bone to simulate the typical XROMM necessity of marked bones and facilitate landmark tracking on videos. Biplanar x-ray video recordings were performed on the University of Antwerp's 3D2YMOX system (Nguyen et al, 2021;Sanctorum et al, 2020), with two experimental settings. In one setting, the femur hung on a long, thin nylon string pendulum (appearing on camera to be "flying").…”

Assessment of perceptual quality measures for multi-exposure radiography and tomography

“…As the set-up is highly modular, the geometry of the set-up was calibrated using a phantom-based method 8,9 . Prior to geometry calibration and reconstruction, the geometric distortion in the projections induced by the Xray image intensifier was corrected using a method based on digital image correlation 10,11 .…”