Many fields, from aerospace engineering to cultural heritage, can benefit from x-ray micro computed tomography (micro-CT). However, access to x-ray imaging tools remains limited for non-expert users. The UK’s National X-Ray Computed Tomography facility (NXCT) therefore aims to provide access and expert support to academia and industry. As part of the NXCT, at UCL we have developed a unique user facility with multi-scale and multi-contrast x-ray micro-CT capabilities. Our custom system has an x-ray generator with Molybdenum and Copper targets, which can be changed to adapt the energy to the needs of an imaging experiment. The x-rays are emitted on both sides of the source allowing for two imaging stations: one at mm-sized field-of-view (FOV) with resolutions of around 1μm, the “high-resolution station”; and one at cm-sized FOV with resolutions of around 10μm, the “large FOV station”. The high-resolution station is fitted with a custom mirror which gives a monochromatic beam at 17.5keV (for Mo) and 8keV (for Cu). Both stations can be operated with phase-contrast methods such as free-space propagation or beam tracking. Access to this new imaging facility, dedicated to academic and industrial users, is supported through free-at-the-point-of-access and paid schemes.
A rotating-anode x-ray source and custom-built sCMOS-based detector have been integrated into a lab-based micro-CT system to demonstrate full CT acquisition in as little as 132ms. This has been used to examine the expansion of a polymer foam in 4D, with a temporal resolution of 2Hz. The system is easily adapted to carry out fast phase-sensitive multi-contrast CT with sub-10s CT acquisition times. This is made possible through the beam-tracking technique, which is capable of multi-contrast CT using only a single shot per projection angle, while also being compatible with incoherent sources. This paves the way to dynamic, phase-sensitive, multi-contrast micro-CT in the laboratory.
X-ray dark-field imaging is used to visualize the ultra-small angle x-ray scattering signal that originates from sub-resolution density fluctuations within the sample microstructure. Dark-field tomography using the edge-illumination x-ray imaging system is presented as a tool for measuring this scattering signal in a sample in three dimensions. Its applicability to different fields is shown through example images of a multi-material phantom, a tissue-engineered esophagus, a pouch cell battery and a short-fiber reinforced composite material. The multichannel contrast available in edge-illumination helps with material identification, with high contrast at boundaries enhancing dark-field reconstructions.
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