X-ray phase-contrast microscopy and microtomography

Optics Express (Impact Factor: 3.49). 10/2003; 11(19):2289-302. DOI: 10.1364/OE.11.002289
Source: PubMed

ABSTRACT In-line phase contrast enables weakly absorbing specimens to be imaged successfully with x-rays, and greatly enhances the visibility of fine scale structure in more strongly absorbing specimens. This type of phase contrast requires a spatially coherent beam, a condition that can be met by a microfocus x-ray source. We have developed an x-ray microscope, based on such a source, which is capable of high resolution phase-contrast imaging and tomography. Phase retrieval enables quantitative information to be recovered from phase-contrast microscope images of homogeneous samples of known composition and density, and improves the quality of tomographic reconstructions.

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Available from: Sheridan Clare Mayo, Aug 18, 2014
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    • "In contrast, at the middle of the cortical bone in the turbulent zone, lacunae orientations were irregular, and the parallel arrangement of canaliculi was no longer apparent in the anterior-posterior plane. In this study, the defocused image in Fig. 3(b) was reconstructed without phase retrieval [21]. We relied instead on the fact that most fine canalicular structures were effectively visualized by the defocus contrast method, even if canaliculus diameter is equivalent to or even less than the system spatial resolution. "
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    ABSTRACT: The three-dimensional network of lacunae and canaliculi that regulates metabolism in bone contains osteocytes and their dendritic processes. We constructed a synchrotron radiation X-ray microscope for sequential tomography of mouse tibia first by using a Talbot interferometer to detect the degree of bone mineralization and then by using absorption contrast under a slightly defocused setting to enhance outline contrast thereby visualizing structures of the osteocyte lacuno-canalicular network. The resultant pair of tomograms was precisely aligned with each other, allowing evaluation of mineral density in the vicinity of each osteocyte lacuna and canaliculus over the entire thickness of the cortical bone. Thus, multiscan microscopic X-ray tomography is a powerful tool for analyzing bone mineralization in relation to the lacuno-canalicular network at the submicron resolution level.
    Biomedical Optics Express 06/2013; 4(6):917-23. DOI:10.1364/BOE.4.000917 · 3.65 Impact Factor
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    • "Using the same geometry, but a scanning electron microscope beam as the electron gun, one can generate X-rays of up to 30 kV from a very small spot, with very low fluxes and long acquisition times. A resolution of 50 nm has been demonstrated with this arrangement, with phase contrast effects (see Section 2.3) playing a prominent role [51]. One way to improve the SNR at high resolution is to use helical scanning, in which the object is vertically translated while being rotated, so moving through a spiral path. "
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    ABSTRACT: We report here on recent developments and advances in pore-scale X-ray tomographic imaging of subsurface porous media. Our particular focus is on immiscible multi-phase fluid flow, i.e., the displacement of one immiscible fluid by another inside a porous material, which is of central importance to many natural and engineered processes. Multiphase flow and displacement can pose a rather difficult problem, both because the underlying physics is complex, and also because standard laboratory investigation reveals little about the mechanisms that control micro-scale processes. X-ray microtomographic imaging is a non-destructive technique for quantifying these processes in three dimensions within individual pores, and as we report here, with rapidly increasing spatial and temporal resolution.
    Advances in Water Resources 03/2013; 51(01, 2013). DOI:10.1016/j.advwatres.2012.07.018 · 3.42 Impact Factor
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    • "The average helium porosity of the Donnybrook sandstone measured by the automatic porosity/permeability system AP-608 is 15% and permeability is around 9 millidarcies. The micro-CT images are obtained with a resolution of 2 μm on an X-ray microscope which has an advantage of giving a high phase-contrast useful for highlighting high-spatial frequency features at grain boundaries in these samples (Mayo et al. 2003). First a cube of 400×400×400 voxels is cropped from the centre of the microtomogram and segmented using the methods described below, into a solid phase and a pore space. "
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    ABSTRACT: Up‐scaling the elastic properties of digitized rock volumes as obtained from X‐ray computer tomography (CT) imaging via computer simulations has the potential to assist and complement laboratory measurements. This computational up‐scaling approach remains a challenging task as the overall elastic properties are not only dependent on the elastic properties of individual grains but also on the hardly resolvable pore spaces between adjacent grains such as micro‐cracks. We develop a digitized rock image and elastic up‐scaling workflow based on general‐purpose and widely available software packages. Particular attention is paid to CT image processing including filtering, smoothing and segmentation. A strategy for optimal meshing for subsequent finite‐element modelling is also proposed. We apply this workflow to the micro‐tomographic image of a well‐consolidated, feldspatic sandstone sample and determine the up‐scaled bulk and shear moduli. These effective elastic moduli are compared to the moduli inferred from laboratory ultrasound measurements at variable effective stresses (0–70 MPa). We observe that the numerically up‐scaled elastic moduli correspond to the moduli at a certain effective stress level (50 MPa), beyond which the effective‐stress dependency follows a linear trend. This indicates that the computational up‐scaling approach yields moduli as if all compliant (soft) porosity was absent, i.e., microcracks are closed. To confirm this hypothesis, we estimate the amount of soft porosity on the basis of the double‐porosity theory (Shapiro, 2003) and find that at 50 MPa the soft porosity is indeed practically zero. We conclude that our computational elastic up‐scaling approach yields physically consistent effective moduli even if some geometrical features are below CT resolution. To account for these sub‐resolution features either theoretical or additional computational approaches can be used.
    Geophysical Prospecting 01/2012; 61(2). DOI:10.1111/j.1365-2478.2012.01082.x · 1.47 Impact Factor
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