Harbecke, Dual-energy in industrial CT - How simple math can reveal structures hidden by artefacts, in Proceedings of the 6th International Conference on Image Formation in X-Ray Computed Tomography, 2020, pp. Riddle, Inversion of fan-beam scans in radio astronomy, Astron. Mahnken, Image fusion in dual energy computed tomography, Invest. Macovski, Energy-selective reconstructions in x-ray computerised tomography, Phys. This paper presents this filtered method and, for the first time, provides a theoretical basis for demonstrating the effectiveness of the filter-based methodology.ġ. However, to date, no mathematical basis for its impressive performance has been found. Experiments reveal that this new method is remarkably effective at reducing BHAs in the presence of high-attenuation materials, and it has already been applied to several industrial CT problems. Very recently, a new BHA-reduction method that uses a beam-hardening filter placed in front of an X-ray beam was developed independently by the first author and Butzer et al. Here, the linear assumption is violated by nonlinear characteristics depending on the polychromatic nature of the X-ray beam combined with the energy-dependent variations in the attenuation coefficients of highly attenuating materials. The presence of highly attenuating materials produces BHAs in CT images because of violating the mathematical CT model assumption of the projection data (i.e., that the data is a linear transform of an image). © 2020 American Association of Physicists in Medicine.One of the most challenging issues in computed tomography (CT) is the reduction of beam-hardening artifacts (BHAs). Talbot-Lau beam hardening grating interferometry image quality phase contrast ring artifacts. The method depends on calibrations that can be performed on any system and does not require detailed knowledge of the x-ray spectrum, detector energy response, grating attenuation properties and imperfections, or the geometry and composition of the imaged object.

The described method, which was developed to remove artifacts in absorption, phase, and normalized visibility micro-CT images due to beam hardening in the system gratings and imaged object, reduced the MSE by up to 96%. When the water calibration coefficients were applied to the lung sample, ring artifacts most prominent in the absorption contrast were eliminated. These improvements were due to the removal of ring artifacts for all contrasts and reduced cupping in absorption and phase images and reduced capping in visibility images. The silicon sample created severe artifacts in all contrasts, but following correction, MSE was reduced by 94% in absorption, 96% in phase, and 90% in visibility images. The water sample's absorption CT image was most impacted by spectral artifacts, but following correction to decrease ring artifacts, an 80% reduction in MSE and 57% reduction in standard deviation was observed. Finally, the model developed using the water sample was applied to a fixated murine lung sample to demonstrate robustness for similar materials. Spectral artifacts such as cupping and ring artifacts were quantified using mean squared error (MSE) from the beam-hardening-free target image and standard deviation within a reconstructed image of the sample. The method's feasibility was demonstrated using a tabletop Talbot-Lau grating interferometer micro-computed tomography (CT) system using CT acquisitions of a water sample and a silicon sample, representing low and high atomic number materials. To account for the multicontrast nature of grating interferometry, this approach was extended to each contrast to obtain three sets of correction coefficients, which were determined empirically from a calibration scan. The proposed two-variable polynomial expansion strategy was inspired by work performed to address beam hardening from a primary modulator.

The purpose of this work was to develop and validate a correction strategy for grating-based x-ray imaging that accounts for beam hardening generated from both the imaged object and the gratings. Consequently, the different energy dependencies of absorption, phase, and visibility contrasts impose challenges that so far have limited the achievable image quality. As a result, grating inhomogeneities due to manufacturing imperfections can cause spectral nonuniformity artifacts when used with polychromatic sources. However, these sources introduce beam hardening effects not only from the samples but also from the gratings. Talbot-Lau grating interferometry enables the use of polychromatic x-ray sources, extending the range of potential applications amenable to phase contrast imaging.

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