Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 19 of 19 for “"Flip angle"”.
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Multiphoton Parallel Transmit MRI for Flip Angle Mitigation Without SAR Concerns
… a standard birdcage volume coil suffers from a flip angle inhomogeneity problem. For example, in 7 T brain MRI, such an excitation has a flip angle as much as three-fold higher in the center of the head than near the periphery. This is due to a wave interference effect, whereby the wavelength of …
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Mitigating Inhomogeneity in High-Field MRI Excitations: Arbitrary Waveform Optimization and Multiphoton Parallel Transmission (MP-pTx)
… volume coil results in a spatially varying flip angle across the body, which renders images difficult to clinically interpret. This arises from the complex interactions of electromagnetic fields from current-carrying elements surrounding the imaging region. Parallel transmission (pTx) …
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Temperature mapping of particles during aseptic processing via magnetic resonance imaging
… aseptic processing were studied. A variable flip angle gradient echo sequence was initially tested. With this sequence T1 maps were obtained from two images acquired in sequence with a total imaging time of approximately 25 seconds. With a T1 vs temperature calibration, temperature …
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Design algorithms for parallel transmission in magnetic resonance imaging
… methods that extend to non-linear large-flip-angle excitation, as well as a new algorithm for simultaneous spectral and spatial excitation critical to quantification of low-SNR brain metabolites in MR spectroscopic imaging. For testing and validation, these methods were implemented on a …
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Inherent insensitivity to RF inhomogeneity in FLASH imaging
… an interesting observation that the fast low-angle shot (FLASH) sequence, which is often used for anatomic imaging and morphometric studies, can be insensitive to RF inhomogeneity when the same coil is used for both transmission and reception and a proper nominal flip angle is employed. …
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Artifact reduction in cardiac MRI in patients with varying heart rate
… of the artifacts through dynamic adaptation of flip angle and inversion time is proposed. The artifact reduction method was tested on the simulation and was found to reduce some artifacts, while enhancing others. If proved to work in practice, this method could contribute to improving image …
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Three-dimensional T1 quantification techniques for assessment of cartilage quality using dGEMRIC
… of B1 inhomogeneities and slab profile flip angle variations in the 3D-LL data. From in vivo and phantom measurements the methods were shown to be reliable, with T1 results that agreed very well to gold standard two-dimensional inversion recovery (2D-IR). A 3D variable flip angle …
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Coil performance evaluation based on electrodynamics : tools for hardware design and validation in magnetic resonance imaging
… smallest RF energy deposition for a target flip angle distribution, and we calculated the corresponding ideal current patterns. Knowledge of these optimal current patterns will serve as an important guide for future high-field coil designs.
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Zero Quantum Nuclear Magnetic Resonance experiments utilizing a toroid cell and coil
… factors 1) B1 homogeneity, 2) B₀ homogeneity, 3) flip angle dependence, and 4) sensitivity. Finally, the two probes will be contrasted using spectral analysis in the spin-spin mapping of a simple molecule (nâ butanol) and a complex molecular system (taxol).
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Encapsulated Contrast Agent Markers For Mri-Based Post-Implant Dosimetry
… effect of varying MRI scan parameters such as flip angle, number of excitations, bandwidth, field of view, slice thickness, and encoding steps, on the Sirius MRI markers' signal and contrast, as well as image noise, artifact and scan time. On patients implanted with Sirius MRI markers, I …
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Magnetic resonance spectroscopic imaging using parallel transmission at 7T
… are proposed and demonstrated to yield excellent flip angle mitigation of the brain metabolites, and also enable improved suppression of the undesired water and lipid signals. A major obstacle to the deployment of 7T pTx applications for clinical imaging is the monitoring and management of local …
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Parallel radiofrequency transmission for 3 Tesla and 7 Tesla magnetic resonance imaging
… technique is developed for slice selective high flip angle imaging which is clinically the most common imaging technique. Next, the performance of the developed technique in reducing SAR and the image contrast non-uniformity is demonstrated through simulations and in phantom experiments for 7T …
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Quantification of Fat Content and Fatty Acid Composition Using Magnetic Resonance Imaging
… precision may be increased using a higher flip angle if a pure fat reference is used for quantification, without compromising quantification accuracy. (Papers I and II) Water/Fat Imaging has become an appreciated technique for abdominal applications in which breath-hold is necessary for …
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Executive functioning in methamphetamine psychosis
… TR=2530ms; graded TE=1.53, 3.21, 4.89, 6.57ms; flip angle=7°; FOV=256mm; slice thickness=1mm; 160 slices; and acquisition duration of 10.49 min. Cortical thickness was assessed employing a surface-based cortical reconstruction and automatic labelling tool in the FreeSurfer software package. …
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The analysis of dynamic contrast-enhanced magnetic resonance imaging data: treatment effects, sampling rates and repeatability
… for variations in the saturation pulse flip-angle. The effect of contrast agent signal non-linearity was investigated using an additional CT study which provided a sample of vascular input functions (VIFs) for comparison with those measured by MR. VIFs from each modality showed a similar …
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Tracking of Transplanted Mesenchymal Stem Cells Labeled with Fluorescent Magnetic Nanoparticle in Liver Cirrhosis Rat Model with 3T MRI
… ; matrix, 256 x 256; field of view, 60 x 60 mm ; flip angle , 30°) sequences were performed before injection and at 3 hours, 5 hours, 1 day and 7 days after injection. A rat was sacrificed at 3 hours, 1 day and 7 days after stem cell injection for the evaluation of degree of liver fibrosis and …
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Imaging The Vasculature With Susceptibility Weighted Imaging: Applications And Analysis
… smaller than approximately 500 µm. The role of flip angle, echo time, image subtraction, and resolution were examined to increase contrast and make much smaller arteries in the 100-200 µm range visible. While hints of these vessels appear, calculations based on current optimized signal levels …
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Slice-selective parallel transmit magnetic resonance imaging at 7T
… cost) in 93% of cases. BOGAT pulses improved flip angle homogeneity and EPI image quality in volunteers. Complementing the BOGAT pulse designs, in Chapter 6, a scanner software Sequence Building Block (SBB) was developed to streamline spokes pTx pulse implementation on Siemens Terra scanners. …
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Validation of first pass magnetic resonance myocardial perfusion imaging using fractional flow reserve
… sequence (TI 90ms, TE 0.99ms, TR 173ms, Flip Angle 8 degrees, Matrix 80 x 128). Thereafter long and short axis slices were acquired for the detection of LGE (turboFLASH). Maximal hyperaemia was achieved using intravenous adenosine (140µg/kg/min). The first pass bolus contained 0.1mmol/kg …