Imaging the ultrasmall-angle x-ray scattering distribution with grating interferometry.

X-ray imaging with grating interferometry has previously been regarded as a technique providing information only in direct space. It delivers absorption, phase, and dark-field contrast, which can be viewed as parameters of the underlying but unresolved scattering distribution. Here, we present a method that provides the ultrasmall-angle x-ray scattering distribution and, thus, allows simultaneous access to direct and reciprocal space information.

Crystallization and preliminary X-ray diffraction studies of Drosophila melanogaster Gαo-subunit of heterotrimeric G protein in complex with the RGS domain of CG5036.

Regulator of G-protein signalling (RGS) proteins negatively regulate heterotrimeric G-protein signalling through their conserved RGS domains. RGS domains act as GTPase-activating proteins, accelerating the GTP hydrolysis rate of the activated form of Gα-subunits. Although omnipresent in eukaryotes, RGS proteins have not been adequately analysed in non-mammalian organisms. The Drosophila melanogaster Gαo-subunit and the RGS domain of its interacting partner CG5036 have been overproduced and purified; the crystallization of the complex of the two proteins using PEG 4000 as a crystallizing agent and preliminary X-ray crystallographic analysis are reported. Diffraction data were collected to 2.0 Å resolution using a synchrotron-radiation source.

Crystallization and preliminary X-ray analysis of monalysin, a novel β-pore-forming toxin from the entomopathogen Pseudomonas entomophila.

Monalysin was recently described as a novel pore-forming toxin (PFT) secreted by the Drosophila pathogen Pseudomonas entomophila. Recombinant monalysin is multimeric in solution, whereas PFTs are supposed to be monomeric until target membrane association. Monalysin crystals were obtained by the hanging-drop vapour-diffusion method using PEG 8000 as precipitant. Preliminary X-ray diffraction analysis revealed that monalysin crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 162.4, b = 146.2, c = 144.4 Å, β = 122.8°, and diffracted to 2.85 Å resolution using synchrotron radiation. Patterson self-rotation analysis and Matthews coefficient calculation indicate that the asymmetric unit contains nine copies of monalysin. Heavy-atom derivative data were collected and a Ta6Br14 cluster derivative data set confirmed the presence of ninefold noncrystallographic symmetry.

Body composition by X-ray absorptiometry and bioelectrical impedance in chronic respiratory insufficiency patients.

Nutrition assessment is important during chronic respiratory insufficiency to evaluate the level of malnutrition or obesity and should include body composition measurements. The appreciation of fat-free and fat reserves in patients with chronic respiratory insufficiency can aid in designing an adapted nutritional support, e.g., nutritional support in malnutrition and food restriction in obesity. The purpose of the present study was to cross-validate fat-free and fat mass obtained by various bioelectric impedance (BIA) formulas with the fat-free and fat mass measured by dual-energy X-ray absorptiometry (DXA) and determine the formulas that are best suited to predict the fat-free and fat mass for a group of patients with severe chronic respiratory insufficiency. Seventy-five patients (15 women and 60 men) with chronic obstructive and restrictive respiratory insufficiency aged 45-86 y were included in this study. Body composition was calculated according to 13 different BIA formulas for women and 12 for men and compared with DXA. Because of the variability, calculated as 2 standard deviations, of +/- 5.0 kg fat-free mass for women and +/- 6.4 kg for men for the best predictive formula, the use of the various existing BIA formulas was considered not clinically relevant. Therefore disease-specific formulas for patients with chronic respiratory insufficiency should be developed to improve the prediction of fat-free and fat mass by BIA in these patients.

Direct mapping of 19F in 19FDG-6P in brain tissue at subcellular resolution using soft X-ray fluorescence

Low energy x-ray fluorescence (LEXRF) detection was optimized for imaging cerebral glucose metabolism by mapping the fluorine LEXRF signal of 19 F in 19 FDG, trapped as intracellular 19 F-deoxyglucose-6-phosphate ( 19 FDG-6P) at 1μm spatial resolution from 3μm thick brain slices. 19 FDG metabolism was evaluated in brain structures closely resembling the general cerebral cytoarchitecture following formalin fixation of brain slices and their inclusion in an epon matrix. 2-dimensional distribution maps of 19 FDG-6P were placed in a cytoarchitectural and morphological context by simultaneous LEXRF mapping of N and O, and scanning transmission x-ray (STXM) imaging. A disproportionately high uptake and metabolism of glucose was found in neuropil relative to intracellular domains of the cell body of hypothalamic neurons, showing directly that neurons, like glial cells, also metabolize glucose. As 19 F-deoxyglucose-6P is structurally identical to 18 F-deoxyglucose-6P, LEXRF of subcellular 19 F provides a link to in vivo 18 FDG PET, forming a novel basis for understanding the physiological mechanisms underlying the 18 FDG PET image, and the contribution of neurons and glia to the PET signal.

Reproducibility of Vertebral Fracture Assessment Readings From Dual-energy X-ray Absorptiometry in Both a Population-based and Clinical Cohort: Cohen's and Uniform Kappa.

Vertebral fracture assessments (VFAs) using dual-energy X-ray absorptiometry increase vertebral fracture detection in clinical practice and are highly reproducible. Measures of reproducibility are dependent on the frequency and distribution of the event. The aim of this study was to compare 2 reproducibility measures, reliability and agreement, in VFA readings in both a population-based and a clinical cohort. We measured agreement and reliability by uniform kappa and Cohen's kappa for vertebral reading and fracture identification: 360 VFAs from a population-based cohort and 85 from a clinical cohort. In the population-based cohort, 12% of vertebrae were unreadable. Vertebral fracture prevalence ranged from 3% to 4%. Inter-reader and intrareader reliability with Cohen's kappa was fair to good (0.35-0.71 and 0.36-0.74, respectively), with good inter-reader and intrareader agreement by uniform kappa (0.74-0.98 and 0.76-0.99, respectively). In the clinical cohort, 15% of vertebrae were unreadable, and vertebral fracture prevalence ranged from 7.6% to 8.1%. Inter-reader reliability was moderate to good (0.43-0.71), and the agreement was good (0.68-0.91). In clinical situations, the levels of reproducibility measured by the 2 kappa statistics are concordant, so that either could be used to measure agreement and reliability. However, if events are rare, as in a population-based cohort, we recommend evaluating reproducibility using the uniform kappa, as Cohen's kappa may be less accurate.