Comparative study of multilayers used in monochromators for synchrotron‐based coherent hard X‐ray imaging

A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B₄C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X‐ray micro‐imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer monochromators, these results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal‐based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron‐based micro‐radiography and ‐tomography.     

Advanced phase‐contrast imaging using a grating interferometer

Phase‐sensitive X‐ray imaging methods can provide substantially increased contrast over conventional absorption‐based imaging, and therefore new and otherwise inaccessible information. Differential phase‐contrast (DPC) imaging, which uses a grating interferometer and a phase‐stepping technique, has been integrated into TOMCAT, a beamline dedicated to tomographic microscopy and coherent radiology experiments at the Swiss Light Source. Developments have been made focusing on the fast acquisition and post‐processing of data to enable a high‐throughput of samples, with obvious advantages, also through increasing the efficiency of the detecting system, of helping to reduce radiation dose imparted to the sample. A novel aquarium design allows a vertical rotation axis below the sample with measurements performed in aqueous environment. Optimization of the data acquisition procedure enables a full phase volume (1024 × 1024 pixels × 1000 projections × 9 phase steps, i.e. 9000 projections in total) to be acquired in 20 min (with a pixel size of 7.4 µm), and the subsequent post‐processing has been integrated into the beamline pipeline for sinogram generation. Local DPC tomography allows one to focus with higher magnification on a particular region of interest of a sample without the presence of local tomography reconstruction artifacts. Furthermore, `widefield' imaging is shown for DPC scans for the first time, enabling the field of view of the imaging system to be doubled for samples that are larger than the magnification allows. A case study is illustrated focusing on the visualization of soft tissue features, and particularly the substantia nigra of a rat brain. Darkfield images, based on local X‐ray scattering, can also be extracted from a grating‐based DPC scan: an example of the advantages of darkfield contrast is shown and the potential of darkfield X‐ray tomography is discussed.     

Hard X‐ray phase‐contrast tomography of non‐homogeneous specimens: grating interferometry versus propagation‐based imaging

X‐ray phase‐contrast imaging is an effective approach to drastically increase the contrast and sensitivity of microtomographic techniques. Numerous approaches to depict the real part of the complex‐valued refractive index of a specimen are nowadays available. A comparative study using experimental data from grating‐based interferometry and propagation‐based phase contrast combined with single‐distance phase retrieval applied to a non‐homogeneous sample is presented (acquired at beamline ID19‐ESRF). It is shown that grating‐based interferometry can handle density gradients in a superior manner. The study underlines the complementarity of the two techniques for practical applications.     

In vivo high‐resolution synchrotron radiation imaging of collagen‐induced arthritis in a rodent model

In vivo microstructures of the affected feet of collagen‐induced arthritic (CIA) mice were examined using a high‐resolution synchrotron radiation (SR) X‐ray refraction technique with a polychromatic beam issued from a bending magnet. The CIA models were obtained from six‐week‐old DBA/1J mice that were immunized with bovine type II collagen and grouped as grades 0–3 according to a clinical scoring for the severity of arthritis. An X‐ray shadow of a specimen was converted into a visual image on the surface of a CdWO₄ scintillator that was magnified using a microscopic objective lens before being captured with a digital charge‐coupled‐device camera. Various changes in the joint microstructure, including cartilage destruction, periosteal born formation, articular bone thinning and erosion, marrow invasion by pannus progression, and widening joint space, were clearly identified at each level of arthritis severity with an equivalent pixel size of 2.7 µm. These high‐resolution features of destruction in the CIA models have not previously been available from any other conventional imaging modalities except histological light microscopy. However, thickening of the synovial membrane was not resolved in composite images by the SR refraction imaging method. In conclusion, in vivo SR X‐ray microscopic imaging may have potential as a diagnostic tool in small animals that does not require a histochemical preparation stage in examining microstructural changes in joints affected with arthritis. The findings from the SR images are comparable with standard histopathology findings.     

A novel imaging tool for hepatic portal system using phase contrast technique with hydrogen peroxide‐generated O2 gas

The objective of this study was to investigate the potential of hydrogen peroxide‐generated oxygen gas‐based phase contrast imaging (PCI) for visualizing mouse hepatic portal veins. The O₂ gas was made from the reaction between H₂O₂ and catalase. The gas production was imaged by PCI in real time. The H₂O₂ was injected into the enteric cavity of the lower sigmoid colon to produce O₂ in the submucosal venous plexus. The generated O₂ gas could be finally drained into hepatic portal veins. Absorption contrast imaging (ACI) and PCI of O₂‐filled portal veins were performed and compared. PCI offers high resolution and real‐time visualization of the O₂ gas production. Compared with O₂‐based ACI, O₂‐based PCI significantly enhanced the revealing of the portal vein in vivo. It is concluded that O₂‐based PCI is a novel and promising imaging modality for future studies of portal venous disorders in mice models.     

In vivo physiological saline‐infused hepatic vessel imaging using a two‐crystal‐interferometer‐based phase‐contrast X‐ray technique

Using a two‐crystal‐interferometer‐based phase‐contrast X‐ray imaging system, the portal vein, capillary vessel area and hepatic vein of live rats were revealed sequentially by injecting physiological saline via the portal vein. Vessels greater than 0.06 mm in diameter were clearly shown with low levels of X‐rays (552 µGy). This suggests that in vivo vessel imaging of small animals can be performed as conventional angiography without the side effects of the presently used iodine contrast agents.     

A novel multi‐detection technique for three‐dimensional reciprocal‐space mapping in grazing‐incidence X‐ray diffraction

A new scattering technique in grazing‐incidence X‐ray diffraction geometry is described which enables three‐dimensional mapping of reciprocal space by a single rocking scan of the sample. This is achieved by using a two‐dimensional detector. The new set‐up is discussed in terms of angular resolution and dynamic range of scattered intensity. As an example the diffuse scattering from a strained multilayer of self‐assembled (In,Ga)As quantum dots grown on GaAs substrate is presented.