The preparation and a novel sample environment for X-ray based imaging of freeze-dried Dictyostelium discoideum cells are presented. As a first application a fluorescence imaging experiment with a ...nanofocused hard X-ray beam has been performed. The successful preparation was verified in elemental mappings with sub-200nm resolution, which allowed for the isolation of several ionic components specific to the cell body.
We have used x-ray waveguides as highly confining optical elements for nanoscale imaging of unstained biological cells using the simple geometry of in-line holography. The well-known twin-image ...problem is effectively circumvented by a simple and fast iterative reconstruction. The algorithm which combines elements of the classical Gerchberg-Saxton scheme and the hybrid-input-output algorithm is optimized for phase-contrast samples, well-justified for imaging of cells at multi-keV photon energies. The experimental scheme allows for a quantitative phase reconstruction from a single holographic image without detailed knowledge of the complex illumination function incident on the sample, as demonstrated for freeze-dried cells of the eukaryotic amoeba Dictyostelium discoideum. The accessible resolution range is explored by simulations, indicating that resolutions on the order of 20 nm are within reach applying illumination times on the order of minutes at present synchrotron sources.
Deficits in attention and arousal play a major role in the clinical presentation of hepatic encephalopathy. Attention deficits are also the main components of minimal hepatic encephalopathy. The ...present paper summarizes some findings about attentional and memory dysfunction in hepatic encephalopathy, with reference to basic knowledge about normal attention and memory function and their cerebral representation.
Background: Early hepatic encephalopathy (HE) is characterized by deficits in motor performance, visual perception, visuo-constructive abilities and attention. Whether defective memory is a feature ...of early HE is controversial.
Aims: To analyze memory function in patients with early HE.
Methods: Memory tests were applied to cirrhotic patients with grade 0 HE, minimal HE and grade I HE (
n=45) and controls (
n=52). The battery included short and long term memory tests requiring free recall or recognition. Minimal HE was diagnosed by assessing the psychometric hepatic encephalopathy score using the PSE-Syndrom-Test and by carrying out a neurological examination. Group differences of the test results were analyzed using analysis of covariance.
Results: HE 0 patients achieved test results similar to the controls in all but two tests. Patients with early HE (minimal and grade I HE) scored lower than the controls in all tests applied. A detailed analysis of test performance showed that the patients’ deficits were in attention and visual perception, rather than memory.
Conclusions: Patients with early HE score lower than controls in memory tasks predominantly because of deficits in attention and visual perception.
Charged surfaces and ion–water interactions at an interface play a decisive role in many physico-chemical and biological processes. The classical treatment of ions at charged interfaces is the ...Poisson–Boltzmann (PB) theory. Despite severe simplifying assumptions it describes surprisingly well univalent ions not too close to the interface for low electrolyte concentrations in the mmol regime. However, it breaks down in the vicinity of the interface at higher surface charge densities. Consequently the list of decorations and modifications of the original PB equation is long aiming for a more realistic picture. One striking deficiency of the treatment on the pure electrostatic level is the prediction that ions of the same valence produce the same results, independent of their chemical nature. In contrast, experiments reveal pronounced differences between different ions. Specific ion effects can be found everywhere in chemistry and biology and there are many reports of pronounced differences in the properties of charged monolayers, micelles, vesicles, dispersions or polyelectrolyte multilayers using different identically charged counterions. The so-called “counterion effect” is usually discussed in terms of the Hofmeister series for cations or anions which are the result of a subtle balance of several competing evenly matched interactions. The complex interplay of electrostatics, dispersion forces, thermal motion, polarization, fluctuations, hydration, ion size effects and the impact of interfacial water structure makes it hard to identify a universal law. The diversity of specific ion effects is a direct consequence of this subtle interplay of forces and imposes a true challenge for the theories. The decisive information for an assessment of the theories is knowledge of the prevailing ion distribution. Hence a considerable amount of work has been applied to develop suitable model systems and to push surface characterization tools such as (resonant) X-ray reflectivity, total reflection X-ray fluorescence or X-ray standing waves to new limits. These techniques give direct information on the ions and on the interfacial architecture. A second alternative to complement these studies is infrared–visible sum frequency spectroscopy allowing to record surface vibrational spectra of the water as it is perturbed in the presence of the salts. The paper is organized in sections describing various facets of ion specific effects discussed within the network.
The routine atomic resolution structure determination of single particles is expected to have profound implications for probing structure–function relationships in systems ranging from energy-storage ...materials to biological molecules. Extremely bright ultrashort-pulse X-ray sources – X-ray free-electron lasers (XFELs) – provide X-rays that can be used to probe ensembles of nearly identical nanoscale particles. When combined with coherent diffractive imaging, these objects can be imaged; however, as the resolution of the images approaches the atomic scale, the measured data are increasingly difficult to obtain and, during an X-ray pulse, the number of photons incident on the 2D detector is much smaller than the number of pixels. This latter concern, the signal `sparsity', materially impedes the application of the method. An experimental analog using a conventional X-ray source is demonstrated and yields signal levels comparable with those expected from single biomolecules illuminated by focused XFEL pulses. The analog experiment provides an invaluable cross check on the fidelity of the reconstructed data that is not available during XFEL experiments. Using these experimental data, it is established that a sparsity of order 1.3 × 10
−3
photons per pixel per frame can be overcome, lending vital insight to the solution of the atomic resolution XFEL single-particle imaging problem by experimentally demonstrating 3D coherent diffractive imaging from photon-sparse random projections.
The propagation of hard X-ray synchrotron beams in waveguides with guiding layer diameters in the 9-35nm 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 mu m range, adapted for optimized transmission at photon energies of 11.5-18keV. 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 10nm 10nm is obtained. Finally, holographic imaging of a lithographic test structure based on this optical system is demonstrated.
Brain imaging techniques have provided substantial insight into the pathophysiology of hepatic encephalopathy (HE). Magnetic resonance imaging gave hint to the fact that there is an increased ...deposition of manganese especially in the basal ganglia. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) showed that the preference of the basal ganglia might be due to differences in regional cerebral blood flow and an additional redistribution of blood flow from the cortex to subcortical regions in cirrhotics. PET studies using ammonia as tracer showed that the cerebral metabolism of ammonia and the permeability of the blood brain barrier for ammonia is increased in cirrhotic patients compared to healthy controls. The regional ammonia supply is in accordance with the regional blood flow. In accordance with these findings fluorodesoxyglucose-PET-studies of the brain in cirrhotics showed characteristic alterations of glucose utilisation in the patients with a relative decrease of the glucose utilisation of the cingulate gyrus, the frontomedial, frontolateral, and parieto-occipital cortex, while the glucose utilisation of the basal ganglia, the hippocampus, and the cerebellum was relatively increased. These findings fit well with the clinical characteristics of early stages of HE such as deficits in attention, visuo-spatial orientation, visuo-constructive abilities, motor speed, and accuracy.
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