High-resolution Phase-contrast X-ray Research Articles

X-ray Zernike apodized photon sieves for phase-contrast microscopy

We present a kind of diffractive lens Zernike apodized photon sieves (ZAPS) whose structure is based on the combination of two concepts: apodized photon sieves and Zernike phase-contrast. Combined with the synchrotron light source, the ZAPS can be used as an objective for high-resolution phase-contrast X-ray microscopy in physical and life sciences. The ZAPS is a single optic unit that integrates the appropriate /2 radians phase shift through selective zone placement shifts in an apodized photon sieve. The focusing properties of the ZAPS can be easily controlled by apodizing its pupil function. An apodized photon sieve with Gaussian pupil is fabricated by lithographic technique and shows that the side-lobes are significantly suppressed at the expense of slightly widening the width of the main lobe.

Zernike apodized photon sieves for high-resolution phase-contrast x-ray microscopy

We present a type of diffractive lens, Zernike apodized photon sieves (ZAPS), used as the objective for high spatial resolution and high phase-contrast imaging of weakly absorbing materials in x rays. The structure of ZAPS is based on the combination of two concepts: apodized photon sieves and Zernike phase contrast. The ZAPS is a single optic that integrates the appropriate ±π/2 rad phase shift through selective zone placement shifts in an apodized photon sieve. Analysis of the focusing properties of the apodized photon sieve in terms of point-spread function show that the sidelobes have been significantly suppressed at the expense of slightly widening the width of the main lobe. In combination with synchrotron light sources, ZAPS offers new opportunities for high-resolution phase-contrast x-ray microscopy in the physical and life sciences.

Phase-contrast X-ray imaging of breast

When an X-ray wave traverses an object, its amplitude and phase change, resulting in attenuation, interference, and refraction, and in phase-contrast X-ray imaging (PCI) these are converted to intensity changes. The relative change of the X-ray phase per unit path length is even orders of magnitude larger than that of the X-ray amplitude, so that the image contrast based on variation of the X-ray phase is potentially much stronger than the contrast based on X-ray amplitude (absorption contrast). An important medical application of PCI methods is soft-tissue imaging, where the absorption contrast is inherently weak. It is shown by in vitro examples that signs of malignant human breast tumor are enhanced in PCI images. Owing to the strong contrast, the radiation dose can be greatly reduced, so that a high-resolution phase-contrast X-ray tomography of the breast is possible with about 1 mGy mean glandular dose. Scattered radiation carries essential information on the atomic and molecular structure of the object, and particularly small-angle X-ray scattering can be used to trace cancer. The imaging methods developed at the synchrotron radiation facilities will become available in the clinical environment with the ongoing development of compact radiation sources, which produce intense X-ray beams of sufficient coherence. Several developments that are under way are described here.

High-throughput, high-resolution X-ray phase contrast tomographic microscopy for visualisation of soft tissue

The use of conventional absorption based X-ray microtomography can become limited for samples showing only very weak absorption contrast. However, a wide range of samples studied in biology and materials science can produce significant phase shifts of the X-ray beam, and thus the use of the phase signal can provide substantially increased contrast and therefore new and otherwise inaccessible information. The application of two approaches for high-throughput, high-resolution X-ray phase contrast tomography, both available on the TOMCAT beamline of the SLS, is illustrated. Differential Phase Contrast (DPC) imaging uses a grating interferometer and a phase-stepping technique. It has been integrated into the beamline environment on TOMCAT in terms of the fast acquisition and reconstruction of data and the availability to scan samples within an aqueous environment. The second phase contrast approach is a modified transfer of intensity approach that can yield the 3D distribution of the phase (refractive index) of a weakly absorbing object from a single tomographic dataset. These methods are being used for the evaluation of cell integrity in 3D, with the specific aim of following and analyzing progressive cell degeneration to increase knowledge of the mechanistic events of neurodegenerative disorders such as Parkinson's disease.

High-resolution differential phase contrast imaging using a magnifying projection geometry with a microfocus x-ray source

Differential x-ray phase contrast imaging using a grating interferometer was combined with a magnifying cone beam geometry using a conventional microfocus x-ray tube. This brings the advantages of a magnifying cone beam setup, namely, a high spatial resolution in the micron range and the possibility of using an efficient, low resolution detector, into differential phase contrast imaging. The authors present methodical investigations which show how the primary measurement signal depends on the magnification factor. As an illustration of the potential of this quantitative imaging technique, a high-resolution x-ray phase contrast tomography of an insect is presented.

Nature of laminations and mineralization in rhinoceros enamel using histology and X-ray synchrotron microtomography: Potential implications for palaeoenvironmental isotopic studies

Incremental features of rhinoceros molar enamel were studied quantitatively on histological slices. The different kinds of incremental features of enamel were related to one another and counted to determine the rate and duration of crown formation and to clarify the status of the laminations. The mineralization and the microstructure of the enamel were examined in a rhinoceros molar germ using X-ray synchrotron microtomography respectively using absorption and phase contrast mode at different levels of resolution, from 45.71 μm for the largest scale up to 0.28 μm for the finest one. The different microtomographic data were combined to obtain a multiscale integrated overview of the microstructure and mineralization in order to understand better the relationship between these two aspects. Additional human and herbivorous mammal teeth were examined qualitatively using histological sectioning to obtain a better understanding of laminations in mammal tooth enamel. Laminations, regularly spaced features parallel to the Retzius lines, represent regular isochrons of enamel deposition. This study shows that laminations and cross-striations are equivalent daily features in enamel of rhinoceros, humans, and probably of middle sized and large herbivorous mammals in general. Laminations are shown to be three-dimensional alignments of cross-striations. In addition to the fact that cross-striations are visible only in prismatic enamel, observation of histological slices, and high resolution phase contrast X-ray synchrotron microtomography demonstrate three main parameters influencing the dominant aspect of daily features in rhinoceros and human enamel: the angle between prisms and Retzius lines, the enamel deposition rate and the thickness of the histological slices. Given their daily nature, laminations can be used to determine the crown formation time of middle sized and big herbivorous mammals. Quantitative study of the enamel mineralization in the rhinoceros germ fragment using X-ray synchrotron microtomography suggests that the innermost 20 μm of the enamel near the enamel–dentin junction are highly mineralised (77–90% of the final enamel mineralization) during, or just after the deposition of the corresponding enamel matrix. Integrated microtomographic study shows that this area corresponds to the thin aprismatic enamel layer at the EDJ level plus a thin layer of radial enamel directly adjacent. It appears that, in some parts of the enamel, there may be a considerable time lag between matrix deposition and full maturation, which could have important implications for geochemical studies. This study reinforces the previously suggested hypothesis that isotopic measurements derived from the innermost enamel may represent the period most closely related to matrix secretion. By using information derived from incremental features (laminations and Retzius lines) and restricting the isotopic measurements to the innermost part of the enamel, precise temporal calibration of isotopic signals should be possible, and the complication of time averaging due to enamel maturation could be avoided or strongly reduced.

High Resolution Phase Contrast X-ray Imaging of Cosmic Dust Captured in Aerogel

High Resolution Phase Contrast X-ray Imaging of Cosmic Dust Captured in Aerogel