A main challenge in x-ray µCT with laboratory radiation derives from the broad spectral content, which in contrast to monochromatic synchrotron radiation gives rise to reconstruction artifacts and ...impedes quantitative reconstruction. Due to the low spectral brightness of these sources, monochromatization is unfavorable and parallel recording of a broad bandpath is practically indispensable. While conventional CT sums up all spectral components into a single detector value, spectral CT discriminates the data in several spectral bins. Here we show that a new generation of charge integrating and interpolating pixel detectors is ideally suited to implement spectral CT with a resolution in the range of 10 µm. We find that the information contained in several photon energy bins largely facilitates automated classification of materials, as demonstrated for of a mouse cochlea. Bones, soft tissues, background and metal implant materials are discriminated automatically. Importantly, this includes taking a better account of phase contrast effects, based on tailoring reconstruction parameters to specific energy bins.
The propagation of hard X‐ray synchrotron beams in waveguides with guiding layer diameters in the 9–35 nm thickness range has been studied. The planar waveguide structures consist of an optimized ...two‐component cladding. The presented fabrication method is suitable for short and leak‐proof waveguide slices with lengths (along the optical axis) in the sub‐500 µm range, adapted for optimized transmission at photon energies of 11.5–18 keV. A detailed comparison between finite‐difference simulations of waveguide optics and the experimental results is presented, concerning transmission, divergence of the waveguide exit beam, as well as the angular acceptance. In a second step, two crossed waveguides have been used to create a quasi‐point source for propagation‐based X‐ray imaging at the new nano‐focus endstation of the P10 coherence beamline at Petra III. By inverting the measured Fraunhofer diffraction pattern by an iterative error‐reduction algorithm, a two‐dimensional focus of 10 nm × 10 nm is obtained. Finally, holographic imaging of a lithographic test structure based on this optical system is demonstrated.
We have investigated the structure of lipid bilayers containing varied molar ratios of different lipids and the antimicrobial peptides magainin and alamethicin. For this structural study, we have ...used x-ray reflectivity on highly aligned solid-supported multilamellar lipid membranes. The reflectivity curves have been analyzed by semi-kinematical reflectivity theory modeling the bilayer density profile
ρ(
z). Model simulations of the reflectivity curves cover a large range of vertical momentum transfer
q
z, and yield excellent agreement between data and theory. The structural changes observed as a function of the molar peptide/lipid concentration
P/
L are discussed in a comparative way.
Coherent x-ray diffractive microscopy enables full reconstruction of the complex transmission function of an isolated object to diffraction-limited resolution without relying on any optical elements ...between the sample and detector. In combination with ptychography, also specimens of unlimited lateral extension can be imaged. Here we report on an application of ptychographic coherent diffractive imaging (PCDI) in the soft x-ray regime, more precisely in the so-called water window of photon energies where the high scattering contrast between carbon and oxygen is well-suited to image biological samples. In particular, we have reconstructed the complex sample transmission function of a fossil diatom at a photon energy of 517 eV. In imaging a lithographically fabricated test sample a resolution on the order of 50 nm (half-period length) has been achieved. Along with this proof-of-principle for PCDI at soft x-ray wavelengths, we discuss the experimental and technical challenges which can occur especially for soft x-ray PCDI.
In this work, we propose a novel computed tomography (CT) approach for three-dimensional (3D) object reconstruction, based on a generalized tomographic geometry with two-dimensional angular sampling ...(two angular degrees of freedom). The reconstruction is based on the 3D Radon transform and is compatible with anisotropic beam conditions. This allows isotropic 3D imaging with a source, which can be extended along one direction for increased flux, while high resolution is achieved by a small source size only in the orthogonal direction. This novel scheme for analytical CT is demonstrated by numerical simulations and proof-of-concept experiments. In this way high resolution and coherence along a single direction determines the reconstruction quality of the entire 3D data set, opening up, for example, new opportunities to achieve nanoscale resolution and/or phase contrast with low brilliance sources such as laboratory x-ray or neutron sources.
Cationic lipid–DNA (CL-DNA) complexes comprise a promising new class of synthetic nonviral gene delivery systems. When positively charged, they attach to the anionic cell surface and transfer DNA ...into the cell cytoplasm. We report a comprehensive x-ray diffraction study of the lamellar CL-DNA self-assemblies as a function of lipid composition and lipid/DNA ratio, aimed at elucidating the interactions determining their structure, charge, and thermodynamic stability. The driving force for the formation of charge-neutral complexes is the release of DNA and lipid counterions. Negatively charged complexes have a higher DNA packing density than isoelectric complexes, whereas positively charged ones have a lower packing density. This indicates that the overcharging of the complex away from its isoelectric point is caused by changes of the bulk structure with absorption of excess DNA or cationic lipid. The degree of overcharging is dependent on the membrane charge density, which is controlled by the ratio of neutral to cationic lipid in the bilayers. Importantly, overcharged complexes are observed to move toward their isoelectric charge-neutral point at higher concentration of salt co-ions, with positively overcharged complexes expelling cationic lipid and negatively overcharged complexes expelling DNA. Our observations should apply universally to the formation and structure of self-assemblies between oppositely charged macromolecules.
This paper presents an investigation of the reconstructibility of coherent X‐ray diffractive imaging diffraction patterns for a class of binary random `bitmap' objects. Combining analytical results ...and numerical simulations, the critical fluence per bitmap pixel is determined, for arbitrary contrast values (absorption level and phase shift), both for the optical near‐ and far‐field. This work extends previous investigations based on information theory, enabling a comparison of the amount of information carried by single photons in different diffraction regimes. The experimental results show an order‐of‐magnitude agreement.
The critical photon fluence for reconstructing objects from noisy diffraction patterns is computed by a maximum‐likelihood estimator, for the optical near‐ and far‐field regimes, of random binary bitmap images as a function of contrast value.
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