Absorption Contrast Imaging Research Articles

Propagation phase-contrast micro-computed tomography allows laboratory-based three-dimensional imaging of articular cartilage down to the cellular level

High-resolution non-invasive three-dimensional (3D) imaging of chondrocytes in articular cartilage remains elusive. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) permits imaging cells within articular cartilage. Bovine osteochondral plugs were prepared four ways: in phosphate-buffered saline (PBS) or 70% ethanol (EtOH), both with or without phosphotungstic acid (PTA) staining. Specimens were imaged with micro-CT following two protocols: 1) absorption contrast (AC) imaging 2) propagation phase-contrast (PPC) imaging. All samples were scanned in liquid. The contrast to noise ratio (C/N) of cellular features quantified scan quality and were statistically analysed. Cellular features resolved by micro-CT were validated by standard histology. The highest quality images were obtained using propagation phase-contrast imaging and PTA-staining in 70% EtOH. Cellular features were also visualised when stained in PBS and unstained in EtOH. Under all conditions PPC resulted in greater contrast than AC (p<0.0001 to p=0.038). Simultaneous imaging of cartilage and subchondral bone did not impede image quality. Corresponding features were located in both histology and micro-CT and followed the same distribution with similar density and roundness values. Three-dimensional visualisation and quantification of the chondrocyte population within articular cartilage can be achieved across a field of view of several millimetres using laboratory-based micro-CT. The ability to map chondrocytes in 3D opens possibilities for research in fields from skeletal development through to medical device design and treatment of cartilage degeneration.

Visualization of ultraviolet absorption distribution beyond the diffraction limit of light by electron-beam excitation-assisted optical microscope.

We demonstrated that the high spatial resolution absorption contrast imaging of the crystal of vitamin B9 has absorption at ultraviolet wavelengths. The absorption wavelength matches with the wavelength of the emission of the fluorescent thin film of an electron-beam excitation-assisted (EXA) optical microscope. The fine crystal structure was imaged beyond the optical diffraction limit. The image contrast corresponded with the thickness of the crystal. The illumination light is absorbed with the vitamin B9 crystal and the intensity of the transmitted light depends on the thickness of the vitamin B9 crystal. The EXA optical microscope is useful for analysis of growth of a crystal, bioimaging and so on.

On the Deformation of Dendrites During Directional Solidification of a Nickel-Based Superalloy

Synchrotron X-ray imaging has been used to examine in situ the deformation of dendrites that takes place during the solidification of a nickel-based superalloy. By combining absorption and diffraction contrast imaging, deformation events could be classified by their localization and permanence. In particular, a deformation mechanism arising from thermal contraction in a temperature gradient was elucidated through digital image correlation. It was concluded that this mechanism may explain the small misorientations typically observed in single crystal castings.

X-ray characterization of the micromechanical response ahead of a propagating small fatigue crack in a Ni-based superalloy

The small fatigue crack (SFC) growth regime in polycrystalline alloys is complex due to the heterogeneity in the local micromechanical fields, which result in high variability in crack propagation directions and growth rates. In this study, we employ a suite of techniques, based on high-energy synchrotron-based X-ray experiments that allow us to track a nucleated crack, propagating through the bulk of a Ni-based superalloy specimen during cyclic loading. Absorption contrast tomography is used to resolve the intricate 3D crack morphology and spatial position of the crack front. Initial near-field high-energy X-ray diffraction microscopy (HEDM) is used for high-resolution characterization of the grain structure, elucidating grain orientations, shapes, and boundaries. Cyclic loading is periodically interrupted to conduct far-field HEDM to determine the centroid position, average orientation, and average lattice strain tensor for each grain within the volume of interest. Reciprocal space analysis is used to further examine the deformation state of grains that plasticize in the vicinity of the crack. Analysis of the local micromechanical state in the grains ahead of the crack front is used to rationalize the advancing small crack path and growth rate. Specifically, the most active slip system in a grain, determined by the maximum resolved shear stress, aligns with the crack growth direction; and the degree of microplasticity ahead of the crack tip helps to identify directions for potential occurrences of crack arrest or propagation. The findings suggest that both the slip system level stresses and microplasticity events within grains are necessary to get a complete description of the SFC progression. Further, this detailed dataset, produced by a suite of X-ray characterization techniques, can provide the necessary validation, at the appropriate length-scale, for SFC models.

Non-destructive three-dimensional crystallographic orientation analysis of olivine using laboratory diffraction contrast tomography

AbstractX-ray laboratory diffraction contrast tomography (LabDCT) produces three-dimensional (3D) maps of crystallographic orientation. The non-destructive nature of the technique affords the key benefit of full 3D context of these, and other, in situ measurements. This study is the first to apply the technique to any material other than a metal or silicon. We report the first 3D measurements of the crystallographic orientation of olivine, which also makes this study the first to apply LabDCT to (1) a non-metallic, non-cubic system and (2) geological material. First, we scanned fragments of olivine set in resin alongside glass microbeads using LabDCT and absorption contrast tomography (ACT). Then we reconstructed these data assuming an orthorhombic crystal system. We show that: (1) the regions within the sample that index well according to the orthorhombic system correspond to olivine fragments in the ACT image; (2) crystalline regions not corresponding to olivine are not indexed assuming the same lattice parameters; and (3) the diffraction data discriminates crystalline from non-crystalline materials as expected. Finally, we demonstrate that the method resolves sub-degree orientation differences between distinct regions within individual olivine fragments. We conclude that DCT can be applied to the study of rocks and other crystalline materials, and offers advantages over conventional techniques. We also note that LabDCT may offer a solution to the crystallographic measurement of substances that would otherwise be difficult to measure due to challenges in obtaining a perfect sample polish. Future developments to accommodate larger experimental volumes and additional crystallographic systems within a sample promises to expand the applicability and impact of DCT.

Statistics and Reproducibility of Grain Morphologies and Crystallographic Orientations Mapped by Laboratory Diffraction Contrast Tomography

Laboratory diffraction contrast tomography (LabDCT) enables a user to reconstruct 3D grain maps of polycrystalline materials non-destructively. For each grain, the morphology and crystallographic orientation, as well as derived properties such as grain boundary properties can be determined. Through two application examples this paper demonstrates the capabilities and potential of the current LabDCT implementation. Firstly, for well-annealed grain structures the reproducibility of LabDCT for more than 95% of the grains was found to be 5 μm on grain center-of-mass positions and 0.02° on orientations, while 90% of the grain boundary locations are determined with an accuracy better than 4 μm. The second example highlights the available statistics on thousands of grains, as well as the complementarity between LabDCT and absorption contrast tomography, readily available due to the integration of LabDCT on a commercial X-ray microscope

Photoacoustic lymphangiography.

Photoacoustic lymphangiography, which is based on photoacoustic technology, is an optical imaging that visualizes the distribution of light absorbing tissue components like hemoglobin or melanin, as well as optical absorption contrast imaging agents like indocyanine green (ICG) in the lymphatic channels, with high spatial resolution. In this report, we introduce the three-dimensional (3D) images of human lymphatic vessels obtained with photoacoustic lymphangiography. We used the 3D photoacoustic visualization system (PAI-05). Some healthy subjects and lymphedema patients were recruited. To image the lymphatic structures of the limbs ICG was administered subcutaneously as in fluorescence lymphangiography. Photoacoustic images were acquired by irradiating the tissue using a laser at wavelengths of near-infrared region. On the same occasion, fluorescence images were also recorded. The lymphatic vessels up to the diameter of 0.2 mm could be observed three-dimensionally with the venules around them. In the patient-group, dermal backflow patterns were often observed as dense interconnecting 3D structures of lymphatic vessels. Collecting vessels passing below the dermis were also observed, which were not observed by fluorescence lymphography. Photoacoustic lymphangiography provided the detailed observation of each lymphatic vessel, leading to deeper understanding of 3D structures and physiological state of the vessel.

Hard and soft X-ray imaging to resolve human ovarian cortical structures.

Laboratory and synchrotron X-ray tomography are powerful tools for non-invasive studies of biological samples at micrometric resolution. In particular, the development of phase contrast imaging is enabling the visualization of sample details with a small range of attenuation coefficients, thus allowing in-depth analyses of anatomical and histological structures. Reproductive medicine is starting to profit from these techniques, mainly applied to animal models. This study reports the first imaging of human ovarian tissue where the samples consisted of surgically obtained millimetre fragments, properly fixed, stained with osmium tetroxide and included in epoxydic resin. Samples were imaged by the use of propagation phase contrast synchrotron radiation micro-computed tomography (microCT), obtained at the SYRMEP beamline of Elettra light source (Trieste, Italy), and X-ray absorption microCT at the Theoretical Biology MicroCT Imaging Laboratory in Vienna, Austria. The reconstructed microCT images were compared with the soft X-ray absorption and phase contrast images acquired at the TwinMic beamline of Elettra in order to help with the identification of structures. The resulting images allow the regions of the cortex and medulla of the ovary to be distinguished, identifying early-stage follicles and visualizing the distribution of blood vessels. The study opens to further application of micro-resolved 3D imaging to improve the understanding of human ovary's structure and support diagnostics as well as advances in reproductive technologies.

Ring artifact suppression in X-ray computed tomography using a simple, pixel-wise response correction.

We present a pixel-specific, measurement-driven correction that effectively reduces errors in detector response that give rise to the ring artifacts commonly seen in X-ray computed tomography (CT) scans. This correction is easy to implement, suppresses CT artifacts significantly, and is effective enough for use with both absorption and phase contrast imaging. It can be used as a standalone correction or in conjunction with existing ring artifact removal algorithms to further improve image quality. We validate this method using two X-ray CT data sets acquired using monochromatic sources, showing post-correction signal-to-noise increases of up to 55%, and we define an image quality metric to use specifically for the assessment of ring artifact suppression.

Simultaneous three‐dimensional elemental mapping of Hollandite and Pyrochlore material phases in ceramic waste form materials

AbstractDifferential X‐ray absorption contrast tomography was performed on model ceramic composite systems to image the 3D spatial distributions of Ga and Nd containing phases. The model material systems were fabricated such that they contained two constituent phases. Ga–doped Ba hollandite (Ba1.33Ga2.66Ti5.34O16), and pyrochlore (Nd2Ti2O7) which are under consideration as nuclear waste immobilization matrices. Two complementary techniques have been used to characterize the 3D distribution of phases. The analysis suggests that the 3D spatial distributions of hollandite and pyrochlore can be readily identified through the distributions Ga and Nd, respectively. These results represent a critical development towards characterizing the complex microstructure inherent to practical materials such as multiphase ceramic composite waste forms. Moreover, these methods can be applied to elucidate microstructural features that fundamentally determine the performance and properties of complex systems, which is central to the design of durable waste forms as well as many other real materials such fuel cells, batteries, ultra‐high temperature ceramics.

Fast X-ray Differential Phase Contrast Imaging with One Exposure and without Movements

Grating interferometry X-ray differential phase contrast imaging (GI-XDPCI) has provided enhanced imaging contrast and attracted more and more interests. Currently the low imaging efficiency and increased dose remain to be the bottlenecks in the engineering applications of GI-XDPCI. Different from the widely-used X-ray absorption contrast imaging (XACI) found in hospitals and factories, GI-XDPCI involves a grating stepping procedure that is time-consuming and leads to a significantly increased X-ray exposure time. In this paper, we report a fast GI-XDPCI method without movements by designing a new absorption grating. There is no grating stepping in this approach, and all components remain stationary during the imaging. Three kinds of imaging contrasts are provided with greatly reduced time. This work is comprised of a numerical study of the method and its verification using a sub-set of the dataset measured with a standard GI-XDPCI system at the beam line BL13W1 of the Shanghai Synchrotron Radiation Facility (SSRF). These results have validated the presented method.

Evaluation of Usability on Mobile Detector X-ray Absorption, scattering, and Phased Image Phantom

Existing X-ray medical imaging acquired the image data of X-ray absorption difference using the difference in density of the subject tissue. X-ray scattering and phase contrast imaging technology is a technology that dramatically increases boundary information between homogeneous materials of similar density using scattering and phase contrast information. To acquire and evaluate absorption, scattering, and phase contrast images, using the phantom made of polyethylene, on a round rod with a diameter of 3×1cm, a hole with a diameter of 0.5cm was drilled on 5 round rods, and the medical phantom was produced by sealing with sodium chloride, neon, calcium, phosphorus, and selenium powder. At a distance of 40cm from the focus, the distribution of absorbed doses have shown 1, 277 ± 0.31μGy in the center area. The measurement dose in the anode side direction was 110.1 ± 0.35μGy and the cathode side direction was 117.7 ± 0.77μGy. It has shown dose inequality that depends on the geometry of the target. It has shown similar tendency in 60cm and 80cm Compared with absorption images in graphite materials, it was confirmed that scattering and phase contrast images were showing relatively high image information. These results are expected to be utilized as an important basic data for reducing medical exposure dose and acquiring, evaluating and utilizing X-ray absorption, scattering and phase contrast images.

Abstract ID: 368 Imaging radiologico a contrasto di fase e a conteggio fotonico

An introduction to novel imaging modalities, which take advantage of energy and phase characteristics of X-ray quanta will be here provided. X-ray detection in medical imaging typically involves an integration of the spectrum of X-rays exiting a patient, weighted by the detector’s energy response. This procedure yields information related to the average energy of the spectrum exiting the patient, which for many clinical applications is sufficient. The spectral imaging methods allow instead the form, or shape, of the X-ray distribution exiting the patient to be measured [1]. In particular, energy-sensitive photon-counting detectors allow for further improvements of the diagnostic information by optimising the signal-to-noise ratio, anatomical background subtraction or quantitative analysis of object constituents [2]. Phase-contrast imaging has had an undeniable impact in the field of X-ray imaging during the last decades, and one of the main advantages lies in the fact that the phase shifting effects are related to characteristic properties of materials that are different from the ones involved in conventional X-ray imaging (i.e. the well-known absorption-contrast imaging) [3]. The mechanism that allows one to produce and to detect images according to this physical phenomenon will be here discussed, together with a review of main phase-contrast imaging techniques. Finally, the potential of both phase-contrast and spectral imaging in diagnostic radiology will be presented by means of specific applications.

Structural Evolution of Highly Active Multicomponent Catalysts for Selective Propylene Oxidation

Multicomponent Bi-Mo-Fe-Co oxide catalysts prepared via flame spray pyrolysis were tested for selective propylene oxidation, showing high conversion (&gt;70%) and selectivity (&gt;85%) for acrolein and acrylic acid at temperatures of 330 °C. During extended time-on-stream tests (5–7 days), the catalysts retained high activity while undergoing diverse structural changes. This was evident on: (a) the atomic scale, using powder X-ray diffraction, Raman spectroscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy; and (b) the microscopic scale, using synchrotron X-ray nanotomography, including full-field holotomography, scanning X-ray fluorescence, and absorption contrast imaging. On the atomic scale, sintering, coke formation, growth, and transformation of active and spectator components were observed. On the microscopic scale, the catalyst life cycle was studied at various stages through noninvasive imaging of a ~50-µm grain with 100-nm resolution. Variation of catalyst synthesis parameters led to the formation of notably different structural compositions after reaction. Mobile bismuth species formed agglomerates of several hundred nanometres and segregated within the catalyst interior. This appeared to facilitate the formation of different active phases and induce selectivity for acrolein and acrylic acid. The combined multiscale approach here is generally applicable for deconvolution of complex catalyst systems. This is an important step to bridge model two-component catalysts with more relevant but complex multicomponent catalysts.

Advancement of X-ray radiography using microfocus X-ray source in conjunction with amplitude grating and SOI pixel detector, SOPHIAS.

We show how to improve microfocus X-ray radiography by using the SOPHIAS silicon-on-insulator pixel detector in conjunction with an amplitude grating. Single-exposure multi-energy absorption and differential phase contrast imaging was performed using the single amplitude grating method. The sensitivity in differential phase contrast imaging in a two-pixel-pitch setup was enhanced by 39% in comparison with the previously reported method [Rev. Sci. Instrum. 81, 113702 (2010).] by analyzing charge-sharing effects. Small-angle-scattering imaging was also possible in the two-pixel-pitch setup by counting the number of X-ray photons passing the pixel boundaries.

(Invited) Understanding Fuel Cell Catalyst Layer Morphology and Its Transport Properties Via Advanced Diagnostics, Imaging and Modeling

Optimizing activity and morphology of the cathode catalyst layer is one of the major challenges to overcome cost and durability of polymer electrolyte fuel cells (PEFCs). The PEFC performance is primarily determined by the losses in the catalyst layer. These are kinetic and mass-transport overpotentials associated with the sluggish oxygen reduction reaction (ORR), transport of oxygen and water flooding at high current densities. A combination of characterization, modeling and multi-modal imaging techniques is used to understand morphology and to decouple the transport processes that limit electrocatalsyt utilization and mass transport within the catalyst layer. Hydrogen pump technique is used to measure ionic conductivity of the catalyst layers without Pt. The technique is a modified version of that previously reported [1], where a pseudo-catalyst layer is fabricated with an ionomer and carbon. The interlayer thickness is varied to plot the catalyst layer ionic resistance as a function of the layers thickness (Figure 1). The slope of the curve produces an inverse of ionic conductivity, whereas the intercept with y-axis is due to membrane and contact resistances. We varied the inter-layer thickness (three to four thicknesses), ratio of ionomer to carbon (I/C) content and the type of ionomer within the carbon black support (Vulcan XC-72). We observed an increase in ionic conductivity with increase in I/C ratio, and also PFIA ionomer at low RH showed higher conductivity compared to PFSA ionomer for the same I/C ratios. Increased ionic conductivity of PFIA ionomer explained some of the improvements in the polarization behavior of the PEFC with PFIA-containing ionomer. Hydrogen pump “DC” method is also compared to the electrochemical impedance spectroscopy (EIS) method to explain some of the differences observed in literature with DC vs AC methods [2]. To probe local ionomer interaction with the electrocatalyst a CO-displacement experiment [3] is performed on the catalyst layers with varied ionomers, I/C ratios and carbon supports. A combined rotating disc electrode (RDE) and membrane electrode assembly (MEA) studies are performed. Electrochemical studies for ionic conductivity measurements are compared to direct imaging of ionomer distribution in the catalyst layers using nano X-ray computed tomography (CT) and spectroscopy. Current methods to image ionomer rely on staining it with heavy Cesium ions to enhance the absorption contrast imaging. However, distinguishing between the Cs- stained ionomer and Pt is challenging because of similar X-ray attenuation coefficients. We use X-ray absorption near edge spectroscopy (XANES) to image samples at Cs and Pt K-edges, enabling distinction between these two phases. Figure 1 shows images above and below Pt L3-edge, as well as volume-rendered representation of Pt and ionomer-phases. Ionomer tortuosity values obtained with imaging and hydrogen pump technique show good agreement. Lastly, direct imaging of water formation within the catalyst layer is still challenging due to either resolution, ambient environment or field of view limitations of the imaging techniques. Over the last two years we have been developing operando nano X-ray computed tomography PEFC hardware to enable imaging with 30-60 nm resolution and 80 um field of view. Challenges of X-ray beam damage to membrane at low energies were solved by using synchrotron beamline ID 16B at ESRF with higher X-ray energy (17.5 keV) and Kirkpatrick-Baez optics. We observed no beam damage to the MEAs at these operating conditions. Complementary continuum and pore-network model bridging was conducted to explain water distributions in catalyst layers. Acknowledgement: This material is based upon work supported by the Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), under Award Number DE-EE0007270

Visualizing the 3D cytoarchitecture of the human cochlea in an intact temporal bone using synchrotron radiation phase contrast imaging.

The gold standard method for visualizing the pathologies underlying human sensorineural hearing loss has remained post-mortem histology for over 125 years, despite awareness that histological preparation induces severe artifacts in biological tissue. Historically, the transition from post-mortem assessment to non-invasive clinical biomedical imaging in living humans has revolutionized diagnosis and treatment of disease; however, innovation in non-invasive techniques for cellular-level intracochlear imaging in humans has been difficult due to the cochlea's small size, complex 3D configuration, fragility, and deep encasement within bone. Here we investigate the ability of synchrotron radiation-facilitated X-ray absorption and phase contrast imaging to enable visualization of sensory cells and nerve fibers in the cochlea's sensory epithelium in situ in 3D intact, non-decalcified, unstained human temporal bones. Our findings show that this imaging technique resolves the bone-encased sensory epithelium's cytoarchitecture with unprecedented levels of cellular detail for an intact, unstained specimen, and is capable of distinguishing between healthy and damaged epithelium. All analyses were performed using commercially available software that quickly reconstructs and facilitates 3D manipulation of massive data sets. Results suggest that synchrotron radiation phase contrast imaging has the future potential to replace histology as a gold standard for evaluating intracochlear structural integrity in human specimens, and motivate further optimization for translation to the clinic.

Feasibility evaluation of a neutron grating interferometer with an analyzer grating based on a structured scintillator.

We introduce an analyzer grating based on a structured scintillator fabricated by a gadolinium oxysulfide powder filling method for a symmetric Talbot-Lau neutron grating interferometer. This is an alternative way to analyze the Talbot self-image of a grating interferometer without using an absorption grating to block neutrons. Since the structured scintillator analyzer grating itself generates the signal for neutron detection, we do not need an additional scintillator screen as an absorption analyzer grating. We have developed and tested an analyzer grating based on a structured scintillator in our symmetric Talbot-Lau neutron grating interferometer to produce high fidelity absorption, differential phase, and dark-field contrast images. The acquired images have been compared to results of a grating interferometer utilizing a typical absorption analyzer grating with two commercial scintillation screens. The analyzer grating based on the structured scintillator enhances interference fringe visibility and shows a great potential for economical fabrication, compact system design, and so on. We report the performance of the analyzer grating based on a structured scintillator and evaluate its feasibility for the neutron grating interferometer.

Microbubbles containing gadolinium as contrast agents for both phase contrast and magnetic resonance imaging.

Portal vein imaging is an important method for investigating portal venous disorders. However, the diagnostic requirements are not usually satisfied when using single imaging techniques. Diagnostic accuracy can be improved by combining different imaging techniques. Contrast agents that can be used for combined imaging modalities are needed. In this study, the feasibility of using microbubbles containing gadolinium (MCG) as contrast agents for both phase contrast imaging (PCI) and magnetic resonance imaging (MRI) are investigated. MCG were made by encapsulating sulfur hexafluoride (SF6) gas with gadolinium and lyophilized powder. Absorption contrast imaging (ACI) and PCI of MCG were performed and compared in vitro. MCG were injected into the main portal trunk of living rats. PCI and MRI were performed at 2 min and 10 min after MCG injection, respectively. PCI exploited the differences in the refractive index and visibly showed the MCG, which were not detectable by ACI. PCI could facilitate clear revelation of the MCG-infused portal veins. The diameter of the portal veins could be determined by the largest MCG in the same portal vein. The minimum diameter of clearly detected portal veins was about 300 µm by MRI. These results indicate that MCG could enhance both PCI and MRI for imaging portal veins. The detection sensitivity of PCI and MRI could compensate for each other when using MCG contrast agents for animals.

Implementation of a double-grating interferometer for phase-contrast computed tomography in a conventional system nanotom® m.

Visualizing the internal architecture of large soft tissue specimens within the laboratory environment in a label-free manner is challenging, as the conventional absorption-contrast tomography yields a poor contrast. In this communication, we present the integration of an X-ray double-grating interferometer (XDGI) into an advanced, commercially available micro computed tomography system nanotom® m with a transmission X-ray source and a micrometer-sized focal spot. The performance of the interferometer is demonstrated by comparing the registered three-dimensional images of a human knee joint sample in phase- and conventional absorption-contrast modes. XDGI provides enough contrast (1.094 ± 0.152) to identify the cartilage layer, which is not recognized in the conventional mode (0.287 ± 0.003). Consequently, the two modes are complementary, as the present XDGI set-up only reaches a spatial resolution of (73 ± 6) μm, whereas the true micrometer resolution in the absorption-contrast mode has been proven. By providing complimentary information, XDGI is especially a supportive quantitative method for imaging soft tissues and visualizing weak X-ray absorbing species in the direct neighborhood of stronger absorbing components at the microscopic level.