1,730,979 research outputs found
Development of in vivo Human Brain DTI-MRE
No full textMagnetic resonance elastography (MRE) and diffusion tensor imaging (DTI) are widely-used non-invasive MRI techniques that can characterize the mechanical and diffusive behaviors of biological tissue under various pathological conditions. Both MRE and DTI can provide potential biomarkers (stiffness and diffusivity) for neurological disorders, such as Alzheimer’s disease, amyotrophic lateral sclerosis, meningioma, traumatic brain injury and neuroinflammation. Besides applications in the diagnosis of neurological diseases, DTI and MRE can assess changes occurring in the brain during aging (atrophy, softening, demyelination). Such changes in the microstructural environment combine imaging with changes in tissue diffusion and stiffness that DTI and MRE measure in a complimentary manner by encoding vibration in the phase of the MRI signal while simultaneously modulating diffusion in the signal magnitude.
Both techniques require specialized magnetic field gradients that are applied in three-dimensional space. Thus, simultaneous acquisitions of DTI and MRE can be achieved by inducing mechanical vibration and by choosing a motion encoding gradient (MEG) that is sensitive to both diffusion and vibration. The benefits of acquiring DTI and MRE together include obtaining multiple parameters without increasing scan time and requiring no co-registration between diffusive and mechanical property maps. Previous studies using a mouse brain demonstrated the feasibility of simultaneous acquisition of DTI and MRE. However, further improvement of the accuracy in property maps requires minimizing the interference between diffusion and vibration encoding (specific aim 1). Additionally, we propose simultaneous acquisition of DTI and multi-frequency MRE (mMRE), to increase the effective image resolution for brain stiffness (specific aim 2). Overall, both aims improve the sensitivity and specificity of DTI and MRE by more efficient diffusion and vibration encoding, and by minimization of signal loss.
This dissertation seeks to develop and optimize the new dual-imaging tool that enables concurrent acquisitions of DTI and MRE (DTI-MRE) in the human brain. The development and optimization of the dual-imaging technique was conducted by simulating different MEG waveforms and by finding the optimal experimental parameters that minimize the signal loss due to intravoxel phase dispersion on the magnitude images. In order to test the simulation results, two sets of parameters, with different signal loss on the magnitude images were selected and tested on five healthy volunteers. Simultaneous acquisition of DTI and mMRE was performed at vibration frequencies of 40 Hz and 50 Hz with the same diffusion encoding on nineteen healthy volunteers. A correlation analysis was carried out on both voxel-wise values and ROI-wise averaged values between novel and conventional techniques.
The ROI-wise correlation between multi-frequency DTI-MRE and conventional acquisitions was high on separate property maps, while taking account of the repeatability of each method. The multi-frequency DTI-MRE produced higher voxel-wise correlation of mechanical property maps than mono-frequency DTI-MRE, while maintained good correlation (greater than 0.75) of diffusive property maps. Furthermore, multifrequency DTI-MRE and 3D-multifrequency-MRE have close interindividual mean values of stiffness maps with acceptable error margin, in the meantime, the multifrequency DTI-MRE and conventional DTI measurements have nearly identical mean values of fractional anisotropy and mean diffusivity. In conclusion, multifrequency DTI-MRE saves imaging time and improves the diagnostic accuracy of DTI and MRE
Dynamic analysis of magnetorheological elastomer configured sandwich structures
No full textThe work presented in this thesis is concerned with the investigation of the dynamic behaviour of magnetorheological elastomers (MREs) and smart sandwich structures. An extensive review, covering existing smart materials and their applications, has highlighted that smart materials and structures can be applied to large scale structures. Comprehensive experimental tests have been carried out in order to gain knowledge and data on the dynamic shear properties and behaviour of stiffness change of MRE and MRE cored adaptive sandwich beam structures depending on magnetic fields. Dynamic shear property tests with different curing stages have been enhanced to obtain various properties. The new developed forced vibration test rig enabled forced vibration tests of MRE embedded sandwich beam with various aspects such as different magnetic field strength, various oscillations of force amplitudes, boundary conditions and damping effects under localised magnetic fields to be made. In parallel to these experimental investigations, a new theoretical model was developed by combining the magnetisation effects on iron particles in terms of the curing times. In addition, a new macro scale modelling approach for rubber like materials (nonlinear behaving materials) was made by adopting FEA analysis to obtain the optimum volume of pores and size of iron particles to enhance the performance of MREs. A higher order sandwich beam theory is extended to include damping properties of MRE. It has been demonstrated that a higher order sandwich beam theory appears to be the most versatile and accurate modelling method for a sandwich beam with an MRE core material. The results from higher order theory have been combined with a power flow analysis for the smart floating sandwich raft vibration isolation system. Finally, an experimental study was performed to illustrate the control capabilities of MRE adaptive vibration absorber for a propeller shaft in real time. From this research work, a better understanding of the dynamic behaviour of MRE embedded sandwich beam has been acquired
MRE-11 and COM-1 promote RAD-51 accumulation in <i>app-1</i> mutant germ lines.
No full textQuantification of RAD-51 foci in germ lines of indicated genotypes, graphs display the regions along the germ line (X axis) and the percentage of nuclei with a given number of RAD-51 foci (Y axis) as indicated in color key. Note that removing MRE-11 or COM-1 from app-1 mutants causes a reduction in the number of RAD-51 observed in meiotic nuclei compared to app-1 single and app-1; spo-11 double mutants (see Fig 1D). Number of nuclei analysed per genotype and zone: mre-11 (211, 178, 245, 226, 241, 175, 98), app-1(tm1715); mre-11 (101, 199, 193, 170, 171, 146, 103), com-1 (125, 150, 183, 177, 122, 126, 63), and app-1(tm1715); com-1 (167, 177, 121, 125, 153, 150, 95). See S1 Table for underlaying numerical data of graphs.</p
sj-docx-1-mre-10.1177_14707853211030482 – Supplemental material for Does sustainable consumption make consumers happy?
No full textSupplemental material, sj-docx-1-mre-10.1177_14707853211030482 for Does sustainable consumption make consumers happy? by Encarnación Ramos-Hidalgo, Rosalia Diaz-Carrion and Carlos Rodríguez-Rad in International Journal of Market Research</p
sj-pdf-1-mre-10.1177_14707853211068008 – Supplemental Material for Impact of question topics and filter question formats on web survey breakoffs
No full textSupplemental Material, sj-pdf-1-mre-10.1177_14707853211068008 for Impact of question topics and filter question formats on web survey breakoffs by Zeming Chen, Alexandru Cernat, Natalie Shlomo and Stephanie Eckman in International Journal of Market Research</p
sj-docx-1-mre-10.1177_14707853221095002 – Supplemental material for How are e-retailer brands related to the manufacturer brands they offer?
No full textSupplemental material, sj-docx-1-mre-10.1177_14707853221095002 for How are e-retailer brands related to the manufacturer brands they offer? by Richard Huaman-Ramirez and Jean-Fran�ois Toti in International Journal of Market Research</p
sj-pdf-1-mre-10.1177_14707853211052177 – Supplemental Material for Using examples to increase recall in self-administered questionnaires
No full textSupplemental Material, sj-pdf-1-mre-10.1177_14707853211052177 for Using examples to increase recall in self-administered questionnaires by Joan M Phillips Sever in International Journal of Market Research</p
sj-pdf-1-mre-10.1177_14707853211050916 – Supplemental Material for A Meta-Analysis of How Country-Level Factors Affect Web Survey Response Rates
No full textSupplemental Material, sj-pdf-1-mre-10.1177_14707853211050916 for A Meta-Analysis of How Country-Level Factors Affect Web Survey Response Rates by Jessica Daikeler, Henning Silber and Michael Bošnjak in International Journal of Market Research</p
MRE Forecast (math projection)
No full textMRE Forecast Fields: Year: 1 to 11, considering 10 years between the first and the last measurement. Project: P1 to P10 Estimated: All projects of same size, 100 hours. Real: Hipotetical real effort Deviation: Real - Estimated Error: Absolute Deviation MRE: Absolute of (Real-Estimated)/Estimated Avg. Estimated: Average of Estimated StdDev. Error: Standard Deviation of MRE Margin of Error: Avg. Estimated + StdDev. Error
On the equivalence of blind equalizers based on MRE and subspace intersections
No full textTwo classes of algorithms recently proposed for the blind equalization of multiple channels driven by a single source are the Mutually Referenced Equalizers (MRE) method by Gesbert et al., and the Subspace Intersection (SSI) method by van der Veen et al. Although these methods seem at first sight unrelated, we show here that a variant of the SSI method and a particular member in the class of MRE methods provide mathematically identical solutions
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