A low-cost geometry calibration procedure for a modular cone-beam X-ray CT system

Nguyen, Van; Beenhouwer, Jan De; Sanctorum, Joaquim G.; Wassenbergh, Sam Van; Bazrafkan, Shabab; Dirckx, Joris J.J.; Sijbers, Jan

doi:10.1080/10589759.2020.1774580

Cited by 14 publications

(7 citation statements)

References 21 publications

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“…Calibration datasets were acquired with the stereo cone-beam system and the technique presented in [ 18 ] was followed to extract the centers of the markers from the radiographs. Calibration methods based on markers make use of the markers’ positions on the detector to estimate the geometry parameters.…”

Section: Methodsmentioning

confidence: 99%

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

et al. 2021

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Compared to single source systems, stereo X-ray CT systems allow acquiring projection data within a reduced amount of time, for an extended field-of-view, or for dual X-ray energies. To exploit the benefit of a dual X-ray system, its acquisition geometry needs to be calibrated. Unfortunately, in modular stereo X-ray CT setups , geometry misalignment occurs each time the setup is changed, which calls for an efficient calibration procedure. Although many studies have been dealing with geometry calibration of an X-ray CT system, little research targets the calibration of a dual cone-beam X-ray CT system. In this work, we present a phantom-based calibration procedure to accurately estimate the geometry of a stereo cone-beam X-ray CT system. With simulated as well as real experiments, it is shown that the calibration procedure can be used to accurately estimate the geometry of a modular stereo X-ray CT system thereby reducing the misalignment artifacts in the reconstruction volumes.

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Section: Methodsmentioning

confidence: 99%

“…In previous work [ 18 ], we presented a LEGO phantom-based calibration technique for a single cone-beam X-ray system. However, the angle between the two systems was not taken into account, it is necessary to have a comprehensive calibration procedure that estimates the relative position of the two cone-beam X-ray CT systems.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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“…After each manipulation of the geometry, it is indispensable to record a dataset to calibrate the geometry of the set-up. For geometry calibration, a method developed by Nguyen et al is used (Nguyen et al 2020(Nguyen et al , 2021. The amount of detector shift can be extracted from the calibration results, which will be used to calculate the resulting effective FOV.…”

Section: Lego Phantommentioning

confidence: 99%

Extended imaging volume in cone-beam x-ray tomography using the weighted simultaneous iterative reconstruction technique

Sanctorum¹,

Wassenbergh²,

Nguyen³

et al. 2021

Phys. Med. Biol.

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An issue in computerized X-ray tomography is the limited size of available detectors relative to objects of interest. A solution was provided in the past two decades by positioning the detector in a lateral offset position, increasing the effective field of view (FOV) and thus the diameter of the reconstructed volume. However, this introduced artifacts in the obtained reconstructions, caused by projection truncation and data redundancy. These issues can be addressed by incorporating an additional data weighting step in the reconstruction algorithms, known as redundancy weighting. In this work, we present an implementation of redundancy weighting in the widely-used Simultaneous Iterative Reconstruction Technique (SIRT), yielding the W-SIRT method. The new technique is validated using geometric phantoms and a rabbit specimen, by performing both simulation studies as well as physical experiments. The experiments are carried out in a highly flexible stereoscopic X-ray system equipped with X-ray image intensifiers (XRIIs). The simulations showed that higher values of CNR could be obtained using the W-SIRT approach as compared to a weighted implementation of SART. The convergence rate of the W-SIRT was accelerated by including a relaxation parameter in the W-SIRT algorithm, creating the aW-SIRT algorithm. This allowed to obtain the same results as the W-SIRT algorithm, but at half the number of iterations, yielding a much shorter computation time. The aW-SIRT algorithm has proven to perform well for both large as well as small regions of overlap, outperforming the pre-convolutional Feldkamp-David-Kress (FDK) algorithm for small overlap regions (or large detector offsets). The experiments confirmed the results of the simulations. Using the aW-SIRT algorithm, the effective FOV was increased by >75%, only limited by experimental constraints. Although an XRII is used in this work, the method readily applies to flat-panel detectors as well.

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“…Therefore, to obtain good tomographic reconstructions, the geometry of the set-up needs to be calibrated accurately prior to the reconstruction algorithm. In this work, an algorithm developed by Nguyen et al [15] , which uses a low-cost phantom consisting of LEGO® bricks and five steel beads (strategically inserted in some of the bricks), is used to calibrate the set-up. In the algorithm, the trajectories of the five beads throughout the projection series are extracted.…”

Section: C) System Calibration and Tomographic Reconstructionsmentioning

confidence: 99%

“…The dataset contained 450 projections (angular interval of 0.8°), guaranteeing a difference in angle space between the dataset used to estimate the dynamic distortion and the calibration dataset. Since approximately 100 images are enough for calibration purposes [15] , every fourth projection image was extracting from the dataset, to obtain a smaller set of 113 projections. From this smaller dataset, we created three different corrected sets: one dataset which was not corrected for distortion, another one on which the static correction was applied, and the last set which was corrected using the dynamic method.…”

Section: E) Effect Of Dynamic Distortion Correction On Calibration An...mentioning

confidence: 99%

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

Sanctorum¹,

Wassenbergh²,

Nguyen³

et al. 2020

Meas. Sci. Technol.

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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.

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A low-cost geometry calibration procedure for a modular cone-beam X-ray CT system

Cited by 14 publications

References 21 publications

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

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

Extended imaging volume in cone-beam x-ray tomography using the weighted simultaneous iterative reconstruction technique

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

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