Abstract
X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X-rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients. Here we review the use of phase-contrast imaging and tomography for a wide variety of materials science characterization problems using both synchrotron and laboratory sources and further demonstrate the particular benefits of phase contrast in the laboratory setting with a series of case studies.
Highlights
The origins of X-ray tomographic methods sit firmly in the medical sphere with the development of computerized tomography (CT) by Hounsfield and Ambrose in the early 70s [1,2]
They will be visible where they can be resolved by the imaging system, which will depend on the magnification, source size and detector resolution
In the 17 years since it was first demonstrated with hard X-rays, in-line phase-contrast imaging and tomography has demonstrated its worth in a wide variety of applications in materials science
Summary
The origins of X-ray tomographic methods sit firmly in the medical sphere with the development of computerized tomography (CT) by Hounsfield and Ambrose in the early 70s [1,2]. The simplest X-ray phase-contrast method, and the one which is the main focus of this paper, follows in the footsteps of Gabor’s development of in-line holography for improving the resolution of electron microscopy [40] This technique, better known as in-line phase-contrast, makes use of the Fresnel diffraction of X-rays to enhance the visibility of edges and boundaries within an object and was first observed in the holographic imaging regime using soft X-rays from a synchrotron source [41]. The advantages of laboratory sources for in-line phase-contrast imaging are; Stability, possibility of large magnification and the ability to use comparatively low spatial resolution detectors (such as Imaging Plates or flat panel detectors) and the possibility to use energy-resolving detectors to do multi-spectral imaging The latter are not so readily applied at synchrotron sources due to the much high intensities involved. It will illustrate the capability of the technique with a series of case studies demonstrating the application of lab-based in-line phase-contrast methods to a variety of materials applications
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