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 20 of 60 for “"Contrast Imaging"”.
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X-ray phase contrast imaging of preclinical atherosclerosis
… biochemical profile, followed by angiographic imaging. However, patients with subclinical atherosclerotic disease can also be at high risk for ACS. In fact, nearly half of the patients suffer from sudden cardiac death without any prior indication of atherosclerotic disease. For these patients, …
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High Contrast Imaging: Exoplanet and Low Stellar Mass Populations
… of a re-analysis of archival Spitzer IRAC direct imaging sur- veys encompassing 121 nearby stars. While the small size of Spitzer provides a lower resolution than 8 m class AO-assisted ground-based telescopes, which have been used for constraining the frequency of 0.5 − 13 MJ planets at …
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Compact tomographic X-ray phase-contrast imaging of breast cancer
Non-invasive imaging plays an important role throughout the clinical diagnosis and management process of breast cancer. Unfortunately, existing imaging methods lack the combination of spatial resolution and soft-tissue contrast necessary to visualize pathological changes in the breast. X-ray …
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Adaptive Wavefront Estimation Algorithms for High-Contrast Imaging of Exoplanets
The direct imaging of exoplanets orbiting stars outside our solar system remains one of the crucial tools we have available to answer whether there exists life beyond Earth. The light from an Earth-like exoplanet is approximately ten orders of magnitude dimmer than its host star and hence the …
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Capabilities and limitations of Phase Contrast Imaging techniques with X-rays and neutrons
Phase Contrast Imaging (PCI) was studied with the goal of understanding its relevance and its requirements. Current literature does not provide insight on the effect of a relaxation in coherence requirements on the PCI capabilities of an imaging system. This problem is all the more important since …
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An experimental study of turbulence by phase-contrast imaging in the DIII-D takamak
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997.
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Phase contrast imaging measurements and modeling of short wavelength turbulence in the DIII-D tokamak
The DIII-D phase contrast imaging (PCI) diagnostic has been upgraded and used to measure turbulence in the outer plasma region (0.7 < r/a < 1). These upgrades extended its operational range to high frequencies (10 kHz - 10 MHz), short wavelength (2 - 30 cm-1), and improved the signal-to-noise ratio …
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A study of reversed shear Alfvén eigenmodes in Alcator C-Mod with phase contrast imaging
… spatial structures of RSAEs measured by phase contrast imaging, and interpreted with a synthetic diagnostic using numerical results from the ideal MHD code NOVA, provides constraints on the evolution of qmi,. Additional observations including mode coupling, mode tunneling, and minimum frequency …
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A Novel Method to Assess Pulse Wave Velocity using Single Velocity Encoding in Phase Contrast Imaging
… wave velocity (PWV) using conventional phase contrast magnetic resonance imaging (PC-MRI) is recognized as a standard technique to assess arterial stiffness by measuring the arrival times of blood velocity waveforms. Conventional PC-MRI requires the acquisition of two sets of complex images …
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A combined phase contrast imaging and heterodyne interferometer system for multiscale fluctuation measurements on DIII-D
… interferometer to the pre-existing phase contrast imaging (PCI) system, both of which measure line-integrated electron-density fluctuations. The port-space footprint is minimized by using a single 10.6 pm CO2 laser and a single beampath. With temporal bandwidths in excess of 1 MHz, the PCI …
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Studies of ICRF mode conversion with phase contrast imaging and full-wave simulations in Alcator C-Mod
… codes be validated against experiment. The phase contrast imaging (PCI) technique has been used on Alcator C-Mod to measure directly the rf waves. The measurements were compared to predictions of full-wave simulations using a synthetic diagnostic method. The measured mode converted wave intensity …
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Developing a Microbubble-based Contrast Agent for X-ray Phase Contrast Imaging to Detect Neovasculature in Breast Cancer
X-ray phase contrast imaging (XPC) generates contrast from refraction and scattering of X-rays, unlike absorption in conventional radiology. This technique greatly improves the sharpness of boundaries and reveals micro-structured tissues that are not easily detected by conventional absorption-based …
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Turbulence and transport studies with phase contrast imaging in the Alcator C-Mod tokamak and comparisons with gyrokinetic simulations
An upgraded phase contrast imaging (PCI) diagnostic is used to study turbulence and transport in Alcator C-Mod. The upgraded PCI system is capable of measuring density fluctuations with high temporal (2 kHz-5 MHz) and wavenumber (0.5-55 cm-1) resolution. An upgrade of the system has enabled PCI to …
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Ray-based Physical Optics for the Design of Astronomical Observatories
… to image faint stellar companions at high contrast using specialized pupil-plane and image-plane masks. When imaging Earth-like exoplanets at small angular separations, coronagraphs are limited by telescope stability and polarization aberrations. The state of the art handles the diffraction …
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Ultracold Fermi gas with repulsive interactions
… in-trap density distributions monitored by phase contrast imaging. For interaction parameters kFa > 0.25 fast decay of the gas prevents the observation of equilibrium profiles. For smaller interaction parameters, the results are adequately described by first-order perturbation theory. A novel …
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Investigation of alternative jet fuels in gas turbine combustion systems using x-ray radiography
… conventional jet fuel. In this work, x-ray phase-contrast imaging is performed at 90,517 Hz on a combusting fuel spray in a realistic gas turbine combustor, allowing characterization of breakup process of fuel into ligaments and then individual droplets as it leaves a nozzle. This imaging is …
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Simulation and testing of wavefront reconstruction algorithms for the deformable mirror (DeMi) cubesat
… host stars by a factor of 10₁₀, meaning high-contrast imaging is required to see them. Coronagraphs are typically used to block the starlight to achieve high contrast, but atmospheric, thermal, and mechanical aberrations can cause spurious speckles of starlight to contaminate the image. Use of …
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Two-Color interferometry as a fluctuation diagnostic on Alcator C-Mod
… and low-kR wavenumber response of phase-contrast imaging, to aid in gyrokinetic transport model validation research. Agreement between the two diagnostics is demonstrated for broadband fluctuations and the low-kR component of the quasi-coherent mode, improving confidence in the …
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