Impact of number of channels on RF shimming at 3T

Object

At high-field strengths (≥3T) inhomogeneity of the radio frequency (RF) field and RF power deposition become increasingly problematic. Parallel Transmission (PTx)—the use of segmented transmission arrays with independently driven elements—affords the ability to combat both of these issues. There are a variety of existing designs for PTx coils, ranging from systems with two channels to systems with eight or more. In this work, we have investigated the impact of the number of independent channels on the achievable results for both homogeneity improvement and power reduction in vivo.

Materials and methods

A 3T Philips Achieva MRI system fitted with an 8-channel PTx body coil was driven so as to emulate configurations with 1, 2 4 and 8 independent channels. RF shimming was used in two different anatomies in order to assess improvements in RF homogeneity.

Results

Significant homogeneity improvements were observed when increasing from 1 to 2, 2 to 4, and 4 to 8 channel configurations. Reductions in RF power requirements and local SAR were predicted for increasing numbers of channels.

Conclusion

Increasing the number of RF transmit channels adds extra degrees of freedom which can be used to benefit homogeneity improvement or power reduction for body imaging at 3T.     

Role of Operating Process Parameters on Stability Performance of Green Emulsion Liquid Membrane Based on Rice Bran Oil

Theoretical Foundations of Chemical Engineering - The current research work elucidates an experimental study on the stability performance of a green emulsion liquid membrane (GELM). A GELM based on...     

3-Hydroxypicolinic Acid as an Effective Matrix for Sophorolipid Structural Elucidation Using Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry

Determination of the distribution of sophorolipid (SL) congeners controls their self-assembly structures and therefore their employment as glycolipid biosurfactants in cosmetics, environmental remediation, and personal care applications. The compatibility of 3-hydroxypicolinic acid (HPA) as a matrix for compositional analysis of SL using palm olein as carbon energy source by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) analysis under positive and negative ion modes is studied in this work. Examination in positive ion mode revealed ions that were not detected in negative ion mode. Molecular ions produced using HPA matrix were lactonic Glc-Glc-1′,4″-C18:1, anionic Glc-Glc-1′-C18:1, lactonic monoacetate of Glc-Glc-1′,4″-C18:1, and anionic monoacetate Glc-Glc-1′-C18:1 and the anionic diacetate of Glc-Glc-1′-C18:1. We also detected Glc-Glc-1′-C18:0, GlcOAc-Glc-1′-C18:0, GlcOAc-GlcOAc-1′,4″-C18:0, and GlcOAc—GlcOAc-1′-C18:0 which are congeners of SL with stearic acid moieties. 3-HPA has been established to be the superior matrix for elucidation of structures for SL using MALDI-TOF MS.     

Development of value-added polyethylene grades with extended service lifetime: Weathering resistant flame retarded materials for outdoor applications

The current article deals with the development of different novel, tailor-made polyolefin formulations exhibiting both low flammability and high weathering resistance, so as to provide value-added polyethylene grades with extended service lifetime. Two low-density (LDPE) and one linear low-density (LLDPE) polyethylene grades were modified via melt compounding with an additive system comprising: (a) a nitrogen-phosphorous intumescent system for flame retardance and (b) a hindered amine light stabilizer and a benzophenone-type UV absorber for UV/heat stabilization, at a total loading of 30–35 wt%. The target was to reach V0 classification in UL94V flammability tests, while to a large extent maintaining the mechanical properties, such as, tensile and impact strength of the investigated polymers, thus ensuring that the additives do not interfere significantly with the material quality. Subsequently, the compounds were subjected to separate artificial UV and heat aging at 100°C for 1500 h; the formulations showed good flame retardance, even after prolonged artificial weathering, but there was an observable, although acceptable, decrease in the mechanical properties. Nevertheless, all the results show that the developed polyethylene compounds are very promising for outdoor applications, such as, irrigation piping and profiles, where long-term weathering stability is important, and where flame retardance is important for safety during storage.     

Agile practices and performance: Examining the role of psychological empowerment

This study draws on the literature on psychological empowerment to conceptualize agile practices as a source of intrinsic motivation that enables the agile teams to deliver innovative outcomes. Then, drawing on the resource based view of innovative projects, the innovative behaviour of agile teams is cast as a project capability that affects project performance. To test this original conceptualization, data was collected to find support for the hypothesized relationships between agile practices, psychological empowerment, innovative behaviour and project performance. The statistical results showed that the agile practices of team autonomy and agile communication contributed to psychological empowerment that led to the innovative behaviour of agile teams. The innovative behaviour also affected project performance. The empirical validation of agile practices as a source of empowerment and motivation for agile teams is a new finding in the literature which has strong implications for both the theory and practice.     

Effect of Organic Additives on the Phase Separation Phenomenon of Amphiphilic Drug Solutions

The effect of various organic additives, viz. sugars, ureas, alcohols, hydrotropes and bile salts on the clouding (phase separation) phenomenon of the amphiphilic antidepressant drug amitriptyline hydrochloride was investigated in the present study. All sugars lowered the cloud point (CP) due to their water structure-making property. Urea and alkylureas were found to lower the CP. In contrast, thioureas increased the CP slightly, but the presence of methyl group(s) had a similar effect in alkylureas. Short chain alcohols affected the CP insignificantly while higher ones decreased it, and medium chain alcohols showed peak behavior. Addition of hydrotropes and bile salts increased the CP at lower concentrations, while a decrease was observed at higher concentrations (like the medium chain alcohols). In addition, thermodynamic parameters were also evaluated but only for those additives which formed mixed micelles with the drug.     

Low-Cost Magnetic Fe3O4/Chitosan Nanocomposites for Adsorptive Removal of Carcinogenic Diazo Dye

Theoretical Foundations of Chemical Engineering - The eco-friendly adsorptive removal of Congo red (CR) from aqueous medium using Fe3O4/chitosan nanocomposites was investigated. The nanocomposites...     

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl₃ and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs.     

Locality-aware process placement for parallel and distributed simulation in cloud data centers

The Journal of Supercomputing - Cloud is a multi-tenant paradigm providing resources as a service. With its easily available computing infrastructure, researchers are adopting cloud for...