Phase contrast and time-of-flight magnetic resonance angiography of the intracerebral arteries at 1.5, 3 and 7 T

Purpose

Time-of-flight (ToF) and phase contrast (PC) magnetic resonance angiographies (MRAs) are noninvasive applications to depict the cerebral arteries. Both approaches can image the cerebral vasculature without the administration of intravenous contrast. Therefore, it is used in routine clinical evaluation of cerebrovascular diseases, e.g., aneurysm and arteriovenous malformations. However, subtle microvascular disease usually cannot be resolved with standard, clinical-field-strength MRA. The purpose of this study was to compare the ability of ToF and PC MRA to visualize the cerebral arteries at increasing field strengths.

Materials and Methods

The Institutional Review Board-approved study included eight healthy volunteers (age: 36±10 years; three female, five male). All subjects provided written informed consent. ToF and PC MRAs were obtained at 1.5, 3 and 7 T. Signal intensities of the large, primary vessels of the Circle of Willis were measured, and signal-to-noise ratios were calculated. Visualization of smaller first- and second-order branch arteries of the Circle of Willis was also evaluated.

Results

The results show that both ToF and PC MRAs allow the depiction of the large primary vessels of the Circle of Willis at all field strengths. Ultrahigh field (7 T) provides only small increases in the signal-to-noise ratio in these primary vessels due to the smaller voxel size acquired. However, ultrahigh-field MRA provides better visualization of the first- and second-order branch arteries with both ToF and PC approaches. Therefore, ultrahigh-field MRA may become an important tool in future neuroradiology research and clinical care.     

New Interior-Point Algorithm for Symmetric Optimization Based on a Positive-Asymptotic Barrier Function

Abstract

We define a new interior-point method (IPM), which is suitable for solving symmetric optimization (SO) problems. The proposed algorithm is based on a new search direction. In order to obtain this direction, we apply the method of algebraically equivalent transformation on the centering equation of the central path. We prove that the associated barrier cannot be derived from a usual kernel function. Therefore, we introduce a new notion, namely the concept of the positive-asymptotic kernel function. We conclude that this algorithm solves the problem in polynomial time and has the same complexity as the best known IPMs for SO.     

Determination of particle size in multiphase blends by different methods

Different methods for characterizing the morphology of multiphase blends were applied to a blend of thermoplastic polyurethane with 20 wt% polypropylene as the dispersed phase. Optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and light scattering were compared. The microscopy methods were evaluated with respect to their suitability for quantitative image analysis for determination of the particle size distribution. Comparison of the particle size distributions revealed that the dependence of the measured particle size on the method of preparation and technique was not very pronounced. The main difference resulted from cutting the particles outside their maximum diameter. The measured particle sizes determined with methods that analyze the whole particles, such as SEM on separated particles and laser light scattering, are larger than those measured on cut specimens. The factor 4/π valid in monodisperse systems for the ratio between the real particle size and that measured on sections was found also to be applicable to this polydisperse blend system. Although light micros-copy requires the least preparation efforts, it is a reliable method for this blend system.     

Phosgenite,Pb2CO3Cl2 – a novel SRS‐active crystal

Lead carbonate chloride, Pb₂CO₃Cl₂, known as mineral phosgenite, is introduced as a novel SRS‐active carbonate crystal with tetragonal symmetry. Under picosecond one‐micron laser pumping Raman‐induced χ⁽³⁾‐nonlinear generation in the near‐IR is observed. All recorded high‐order Stokes and anti‐Stokes sidebands are identified and attributed to two SRS‐promoting vibration modes with ω_SRS1 ≈ 1062 cm^–1 and ω_SRS2 ≈ 86 cm^–1.

     

Direct binding assay for the detection of type IV allosteric inhibitors of Abl

Abelson (Abl) tyrosine kinase is an important cellular enzyme that is rendered constitutively active in the breakpoint cluster region (BCR)-Abl fusion protein, contributing to several forms of leukemia. Although inhibiting BCR-Abl activity with imatinib shows great clinical success, many patients acquire secondary mutations that result in resistance to imatinib. Second-generation inhibitors such as dasatinib and nilotinib can overcome the majority of these mutations but fail to treat patients with an especially prevalent T315I mutation at the gatekeeper position of the kinase domain. However, a combination of nilotinib with an allosteric type IV inhibitor was recently shown to overcome this clinically relevant point mutation. In this study, we present the development of a direct binding assay that enables the straightforward detection of allosteric inhibitors which bind within the myristate pocket of Abl. The assay is amenable to high-throughput screening and exclusively detects the binding of ligands to this unique allosteric site.     

Revision of iron(III)–citrate speciation in aqueous solution. Voltammetric and spectrophotometric studies

A detailed study of iron (III)–citrate speciation in aqueous solution (θ = 25 °C, I_c = 0.7 mol L⁻¹) was carried out by voltammetric and UV–vis spectrophotometric measurements and the obtained data were used for reconciled characterization of iron (III)–citrate complexes. Four different redox processes were registered in the voltammograms: at 0.1 V (pH = 5.5) which corresponded to the reduction of iron(III)–monocitrate species (Fe:cit = 1:1), at about −0.1 V (pH = 5.5) that was related to the reduction of FeL₂⁵⁻, FeL₂H⁴⁻ and FeL₂H₂³⁻ complexes, at −0.28 V (pH = 5.5) which corresponded to the reduction of polynuclear iron(III)–citrate complex(es), and at −0.4 V (pH = 7.5) which was probably a consequence of Fe(cit)₂(OH)_x species reduction. Reversible redox process at −0.1 V allowed for the determination of iron(III)–citrate species and their stability constants by analyzing E_p vs. pH and E_p vs. [L⁴⁻] dependence. The UV–vis spectra recorded at varied pH revealed four different spectrally active species: FeLH (log β = 25.69), FeL₂H₂³⁻ (log β = 48.06), FeL₂H⁴⁻ (log β = 44.60), and FeL₂⁵⁻ (log β = 38.85). The stability constants obtained by spectrophotometry were in agreement with those determined electrochemically. The UV–vis spectra recorded at various citrate concentrations (pH = 2.0) supported the results of spectrophotometric–potentiometric titration.     

Macroporous silicon chips for laterally resolved, multi-parametric analysis of epithelial barrier function

This study describes a novel assay to visualize the macromolecular permeability of epithelial and endothelial cell layers with subcellular lateral resolution. Defects within the cell layer and details about the permeation route of the migrating solute are revealed. The assay is based on silicon chips with densely packed, highly ordered, dead-ended pores of μm-diameters on one side. The cells under study are grown on the porous side of the chip such that the pores in the growth surface serve as an array of femtolitre-sized cuvettes in which the permeating probe accumulates at the site of permeation. The pattern of pore filling reveals the permeability characteristics of the cell layer with a lateral resolution in the μm range. Coating of the chip surface with a thin layer of gold allows for impedance analysis of the adherent cells in order to measure their tightness for inorganic ions at the same time. The new assay provides an unprecedented look on epithelial and endothelial barrier function.     

A microchamber array for single cell isolation and analysis of intracellular biomolecules

We present a microfluidic device that enables the determination of intracellular biomolecules in multiple single cells. The cells are individually trapped and isolated in a microchamber array. Since the microchambers can be opened and closed reversibly, the cells can be exposed to different solutions sequentially, e.g. for incubation, washing steps, labelling and finally, for lysis. The tightly sealed microchambers enable the retention and analysis of cell lysate derived from single cells. The performance of the device is demonstrated by monitoring the levels of the cofactors NADPH and NADH both in healthy mammalian cells and in cells exposed to oxidative stress. The platform was also used to determine the toxic impact of the alkaloid camptothecin on the intracellular enzyme glucose-6-phosphate dehydrogenase levels. In general, the device is applicable for the analysis of cell auto-stimulation and the detection of intracellular metabolite concentration or expression levels of proteins.