Abstract
Over the recent years X-ray differential phase-contrast imaging was developed for the hard X-ray regime as produced from laboratory X-ray sources. The technique uses a grating-based Talbot-Lau interferometer and was shown to yield image contrast gain, which makes it very interesting to the fields of medical imaging and non-destructive testing, respectively. In addition to X-ray attenuation contrast, the differential phase-contrast and dark-field images provide different structural information about a specimen. For the dark-field even at length scales much smaller than the spatial resolution of the imaging system. Physical interpretation of the dark-field information as present in radiographic and tomographic (CT) images requires a detailed look onto the geometric orientation between specimen and the setup. During phase-stepping the drop in intensity modulation, due to local scattering effects within the specimen is reproduced in the dark-field signal. This signal shows strong dependencies on micro-porosity and micro-fibers if these are numerous enough in the object. Since a grating-interferometer using a common unidirectional line grating is sensitive to X-ray scattering in one plane only, the dark-field image is influenced by the fiber orientations with respect to the grating bars, which can be exploited to obtain anisotropic structural information. With this contribution, we attempt to extend existing models for 2D projections to 3D data by analyzing dark-field contrast tomography of anisotropically structured materials such as carbon fiber reinforced carbon (CFRC).
Highlights
The X-ray Talbot-Lau interferometer has become an important tool over the past decade for its ability to record differential phase-contrast (DPC) images by using spatially incoherent laboratory X-ray sources in combination with line gratings which encode the differential phase of the wave field and of the object transmission function [1, 2]
The information, which today is retrieved from DPC images is threefold and is extracted in the form of three separate images: (a) The attenuation signal which corresponds to the line integrals of the material’s linear absorption coefficient; (b) The differential phase-contrast which can be integrated to an image of the phase gradient, which is the refractive index or electron density gradient; (c) The visibility or so-called scattering or dark-field contrast (DFC), that is linked to the integrated scattering power of the investigated specimen
In order to illustrate the potential of such measurements we present a DFC tomography of a carbon fiber reinforced carbon (CFRC) sample
Summary
The X-ray Talbot-Lau interferometer has become an important tool over the past decade for its ability to record differential phase-contrast (DPC) images by using spatially incoherent laboratory X-ray sources in combination with line gratings which encode the differential phase of the wave field and of the object transmission function [1, 2] This relatively new method has to be considered a complementary technique to inline phase-contrast imaging which is used to numerically retrieve the phase-map from Fresnel-propagated radiographs [3]. It corresponds to ultra-small-angle X-ray scattering [8,9] and predominantly does not relate to ab-
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