Dynamic MRI of swallowing: real-time volumetric imaging at 12 frames per second at 3 T

Objective

Dysphagia or difficulty in swallowing is a potentially hazardous clinical problem that needs regular monitoring. Real-time 2D MRI of swallowing is a promising radiation-free alternative to the current clinical standard: videofluoroscopy. However, aspiration may be missed if it occurs outside this single imaged slice. We therefore aimed to image swallowing in 3D real time at 12 frames per second (fps).

Materials and methods

At 3 T, three 3D real-time MRI acquisition approaches were compared to the 2D acquisition: an aligned stack-of-stars (SOS), and a rotated SOS with a golden-angle increment and with a tiny golden-angle increment. The optimal 3D acquisition was determined by computer simulations and phantom scans. Subsequently, five healthy volunteers were scanned and swallowing parameters were measured.

Results

Although the rotated SOS approaches resulted in better image quality in simulations, in practice, the aligned SOS performed best due to the limited number of slices. The four swallowing phases could be distinguished in 3D real-time MRI, even though the spatial blurring was stronger than in 2D. The swallowing parameters were similar between 2 and 3D.

Conclusion

At a spatial resolution of 2-by-2-by-6 mm with seven slices, swallowing can be imaged in 3D real time at a frame rate of 12 fps.

     

Cytotoxicity and cellular uptake of tri-block copolymer nanoparticles with different size and surface characteristics

Particulate matter (PM) pollution is responsible for hundreds of thousands of deaths worldwide, the majority due to cardiovascular disease (CVD). While many potential pathophysiological mechanisms have been proposed, there is not yet a consensus as to which are most important in causing pollution-related morbidity/mortality. Nor is there consensus regarding which specific types of PM are most likely to affect public health in this regard. One toxicological mechanism linking exposure to airborne PM with CVD outcomes is oxidative stress, a contributor to the development of CVD risk factors including atherosclerosis. Recent work suggests that accelerated shortening of telomeres and, thus, early senescence of cells may be an important pathway by which oxidative stress may accelerate biological aging and the resultant development of age-related morbidity. This pathway may explain a significant proportion of PM-related adverse health outcomes, since shortened telomeres accelerate the progression of many diseases. There is limited but consistent evidence that vehicular emissions produce oxidative stress in humans. Given that oxidative stress is associated with accelerated erosion of telomeres, and that shortened telomeres are linked with acceleration of biological ageing and greater incidence of various age-related pathology, including CVD, it is hypothesized that associations noted between certain pollution types and sources and oxidative stress may reflect a mechanism by which these pollutants result in CVD-related morbidity and mortality, namely accelerated aging via enhanced erosion of telomeres. This paper reviews the literature providing links among oxidative stress, accelerated erosion of telomeres, CVD, and specific sources and types of air pollutants. If certain PM species/sources might be responsible for adverse health outcomes via the proposed mechanism, perhaps the pathway to reducing mortality/morbidity from PM would become clearer. Not only would pollution reduction imperatives be more focused, but interventions which could reduce oxidative stress would become all the more important.     

A V-Nitrogenase Variant Containing a Citrate-Substituted Cofactor

Nitrogenases catalyze the ambient reduction of N₂ and CO at its cofactor site. Herein we present a biochemical and spectroscopic characterization of an Azotobacter vinelandii V nitrogenase variant expressing a citrate-substituted cofactor. Designated VnfDGK^Cit, the catalytic component of this V nitrogenase variant has an αβ₂(δ) subunit composition and carries an 8Fe P* cluster and a citrate-substituted V cluster analogue in the αβ dimer, as well as a 4Fe cluster in the “orphaned” β-subunit. Interestingly, when normalized based on the amount of cofactor, VnfDGK^Cit shows a shift of N₂ reduction from H₂ evolution toward NH₃ formation and an opposite shift of CO reduction from hydrocarbon formation toward H₂ evolution. These observations point to a role of the organic ligand in proton delivery during catalysis and imply the use of different reaction sites/mechanisms by nitrogenase for different substrate reductions. Moreover, the increased NH₃/H₂ ratio upon citrate substitution suggests the possibility to modify the organic ligand for improved ammonia synthesis in the future.     

Mechanism of Change in Cognitive-Behavioral Treatment of Panic Disorder: Evidence for the Fear of Fear Mediational Hypothesis.

Numerous clinical trials have demonstrated the efficacy of cognitive-behavioral treatment (CBT) for panic disorder. However, studies investigating the mechanisms responsible for improvement with CBT are lacking. The authors used regression analyses outlined by R. M. Baron and D. A. Kenny (1986) to test whether a reduction in fear of fear (FOF) underlies improvement resulting from CBT. Pre- and posttreatment measures were collected from 90 CBT-treated patients and 40 wait-list control participants. Overall, treatment accounted for 31% of the variance in symptom reduction. The potency of FOF as a mediator varied as a function of symptom facet, as full mediation was observed for the change in global disability, whereas the effects of CBT on agoraphobia, anxiety, and panic frequency were partially accounted for by reductions in FOF. Clinical implications and future research directions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

SHALES OF NORTH CAROLINA1

North Carolina contains several extensive areas of shale deposits, which are favorably located for working and which in their slightly weathered condition have been recently found to be well adapted to the manufacture of face brick, hollow blocks, sewer pipes, etc. As a result of these discoveries a number of clay working plants have been recently set in operation and others are in course of construction.     

Microwave modeling and validation in food thawing applications

Developing temperature fields in frozen cheese sauce undergoing microwave heating were simulated and measured. Two scenarios were investigated: a centric and offset placement on the rotating turntable. Numerical modeling was performed using a dedicated electromagnetic Finite Difference Time Domain (FDTD) module that was two-way coupled to the PHYSICA multiphysics package. Two meshes were used: the food material and container were meshed for the heat transfer and the microwave oven cavity and waveguide were meshed for the microwave field. Power densities obtained on the structured FDTD mesh were mapped onto the unstructured finite volume method mesh for each time-step/turntable position. On heating for each specified time-step the temperature field was mapped back onto the FDTD mesh and the electromagnetic properties were updated accordingly. Changes in thermal/electric properties associated with the phase transition were fully accounted for as well as heat losses from product to cavity. Detailed comparisons were carried out for the centric and offset placements, comparing experimental temperature profiles during microwave thawing with those obtained by numerical simulation.     

Sol‐gel derived C‐SiC composites for re‐entry structures

Composites of carbon fibers, fabrics, or their precursors as reinforcement, and sol‐gel‐derived silicon carbide as matrix, have been developed, aiming at high‐temperature stable ceramics that can be utilized for re‐entry structures. These composites are produced via the sol‐gel process, starting with a sol‐gel reaction of a mixture of silane precursors. The sol‐gel‐derived resin is cast onto the reinforcement fibers/fabrics mat (carbon or its precursors) to produce a ‘green’ composite that is being cured. The ‘green’ composite is converted into a C‐SiC composite via a gradual heat‐pressure process under inert atmosphere, during which the organic substituents on the silicon atoms undergo internal oxidative pyrolysis via the schematic reaction: (SiRO_3/2)_n → SiC + CO₂ + H₂O The composition of the resultant silicon‐oxi‐carbide is tailorable via modifying the composition of the sol‐gel reactants. The reinforcement, when made of carbon precursors, is converted into carbon during the heat‐and‐pressure processing as well. The C‐SiC composites thus derived exhibit superior thermal stability and comparable thermal conductivity, combined with good mechanical strength features and failure resistance, which render them greatly applicable for re‐entry shielding, heat‐exchange pipes, and the like.     

Tuned graft copolymers as controlled coatings for DNA microarrays

DNA microarrays have become a powerful tool for expression profiling and other genomics applications. A critical factor for their sensitivity is the interfacial coating between the chip substrate and the bound DNA. Such a coating has to embrace the divergent requirements of tightly binding the capture probe DNA during the spotting process and of minimizing the nonspecific binding of target DNA during the hybridization assay. To fulfill these conditions, most coatings require a passivation step. Here we demonstrate how the chain density of a graft copolymer with a polycationic backbone, poly(l-lysine)-graft-poly(ethylene glycol), can be tuned such that the binding capacity during capture probe deposition is maximized while the nonspecific binding during hybridization assays is kept to a minimum, thus alleviating the requirement for a separate passivation procedure. Evidence for the superior performance of such coatings in terms of signal-to-noise ratio and spot quality is presented using an evanescent field-based fluorescent sensing technique (the ZeptoREADER). The surface architecture is further characterized using optical waveguide lightmode spectroscopy and time-of-flight secondary ion mass spectrometry. Finally, in a model assay, we demonstrate that expression changes can be detected from 1 microg of total mRNA sample material with a limit of detectable differential expression of +/-1.5.     

Parameter Estimates of a Left Ventricular Model During Ejection

A network model of ventricular function consisting of a source of pressure with a series internal resistance that is coupled to a load resistance is presented. It is used as an analog of left ventricular (LV) function during the ejection phase of the cardiac cycle in order to quantitate the interaction of ventricle and load.