Browsing by Subject "magnetic resonance imaging"

Now showing 1 - 4 of 4
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    Experimental Techniques and Image Reconstruction for Magnetic Resonance Imaging with Inhomogeneous Fields
    (2019-08) Mullen, Michael
    Magnetic resonance imaging is quite sensitive to experimental imperfections, necessitating extremely expensive electrical infrastructure and design requirements to permit high-quality experiments to be performed. By relaxing the sensitivity to imperfection, the entire system can be made less expensive and more accessible by shrinking the magnet generating the polarizing field. Decreasing the magnet size relative to the bore increases the polarizing field inhomogeneity. Moreover, current progress in MRI at ultra-high field (greater than or equal to 7T) is pushing the limits of conventional MRI methods, as field inhomogeneity increases with field strength. Hence, while many of the methods herein were developed with a small magnet in mind, they also apply at ultra-high field. The appeal of ultra-high field is increased detection sensitivity such that ever-smaller structures may be imaged in animals and humans. The primary goal of this work is to extend the current ability of magnetic resonance imaging to tolerate a large degree of spatial variation in both the transmit and polarizing fields involved. A novel method of decreasing radiofrequency pulse duration for multidimensional pulses is presented, rendering them more robust to field inhomogeneity. Furthermore, this method is leveraged to accelerate data acquisition. A new imaging sequence for quantitative determination of transverse relaxation rates is presented, which tolerates large variations in both the transmit and polarizing magnetic fields, as is often found when imaging with iron-oxide nanoparticles and/or at ultrahigh field. Finally, a computationally efficient approach for spatiotemporally-encoded image reconstruction is presented, which is inherently robust to field inhomogeneity.
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    Morphological and functional properties of the conducting human airways investigated by in vivo CT and in vitro MRI
    (2017-10-26) Van de Moortele, Tristan; Wendt, Christine H.; Coletti, Filippo
    The accurate representation of the human airway anatomy is crucial for understanding and modeling the structure-function relationship in both healthy and diseased lungs. The present knowledge in this area is based on morphometric studies of excised lung casts, partially complemented by in vivo studies in which computed tomography (CT) was used on a small number of subjects. In the present study, we analyze CT scans of a cohort of healthy subjects and obtain comprehensive morphometric information down to the seventh generation of bronchial branching, including airway diameter, length, branching angle, and rotation angle. While some of the geometrical parameters (such as the child-to-parent branch diameter ratio) are found to be in line with accepted values, for others (such as the branch length-to-diameter ratio) our findings challenge the common assumptions. We also evaluate several metrics of self-similarity, including the fractal dimension of the airway tree. Additionally, we use phase-contrast magnetic resonance imaging (MRI) to obtain the volumetric flow field in the 3D printed airway model of one of the subjects during steady inhalation. This is used to relate structural and functional parameters and, in particular, to close the power-law relationship between branch flow rate and diameter. The diameter exponent is found to be significantly lower than in the usually assumed Poiseuille regime, which we attribute to the strong secondary (i.e. transverse) velocity component. The strength of the secondary velocity with respect to the axial component exceeds the levels found in idealized airway models, and persists within the first seven generations.
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    Noninvasive Assessment of Neurochemical Biomarkers in Humans with Amyotrophic Lateral Sclerosis: Correlates of Clinical Heterogeneity
    (2018-06) Cheong, Ian
    Noninvasive neuroimaging techniques can provide objective measures of disease status that are critical for the development of neurological disease therapies. They can also unlock important information on pathologic changes in the brain in vivo. Proton magnetic resonance spectroscopy is a powerful tool for investigating abnormalities in the brain’s neurochemistry. This thesis work validates and applies a highly optimized version of this technique to study the devastating neuromuscular disease amyotrophic lateral sclerosis (ALS). Specific objectives focus on the identification of disease markers that can aid therapeutic development in ALS.
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    A Patient’s Guide to Magnetic Resonance Imaging (MRI)
    (2008-09-02) Johnson, Joshua B
    A guide of patient information about magnetic resonance imaging (MRI) including what to expect during the test, reasons for not being able to have an MRI, and how MRI works. You may be getting an MRI for a variety of reasons. For the definitive diagnosis of a stress injury, MRI in the best imaging test.