In a polychromatic spectrum, lower energy X-ray photons are attenuated more significantly. These algorithms are based on Lambert–Beer’s law which implies a linear relationship between X-ray attenuation and specimen thickness and is strictly valid only for monochromatic X-rays. Furthermore, gradients of decreasing grey values towards the center of otherwise homogeneous objects can appear (cupping artefacts).īoth streak and cupping artefacts are caused by the polychromatic X-ray spectrum which is not thoroughly considered in standard filtered backprojection (FBP) reconstruction algorithms. Polychromatic beam hardening also plays an important role for metal artefacts which appear as bright and dark streaks between high-density objects (streak artifacts). The polychromatic nature of X-ray anodes in laboratory XCT devices causes well known beam hardening artifacts, which deteriorate the reconstructed XCT image data. However, XCT encounters some limitations when high-density materials such as metals are included in the specimen, particularly in close proximity to materials of lower density. The possibility of an in-depth investigation of multi-material specimens is equally important in medical and industrial applications. In the past decades, X-ray microcomputed tomography (XCT) was established as an invaluable method for the three-dimensional characterization of components and materials. This work demonstrates the potential of PCI-XCT for the reduction of metal artifacts and presents the first quantitative comparison to established AC-XCT methods. However, hardware pre-filtering leads to worse CNR and artifacts close to the surface of metal inserts could not be removed sufficiently by the MAR algorithm. Results showed that streak artifacts are significantly reduced in PCI-XCT and only matched by AC-XCT in combination with hardware pre-filtering of the X-ray beam and post-processing by a MAR algorithm. Artifacts and image quality were evaluated by a streak index which provides a quantitative metric for the assessment of streak artifacts and contrast-to-noise ratio (CNR). MethodsĪ polymer specimen including four Ti6Al4V inserts was investigated by PCI- and AC-XCT with different pre-filter settings and metal artifact reduction (MAR) algorithm. In the course of this work, this absence in literature is addressed by a quantitative comparison of PCI-XCT to attenuation contrast XCT (AC-XCT). Although phase contrast imaging XCT (PCI-XCT) is known to be less prone to metal artifacts caused by beam hardening, so far only little effort was made for its comparison to other, more established methods. Metal artifacts arising around high-density components are a widely known problem in X-ray computed tomography (XCT) for both medical and industrial applications.
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