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Browsing by Subject "Spatiotemporal"

Now showing 1 - 2 of 2
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    Challenges of field inhomogeneities and a method for compensation
    (2011-11) Styczynski Snyder, Angela Lynn
    MRI of the body at 7 T has become possible only very recently. High fields bring the advantages of increased signal to noise ratio, resolution gains, faster image acquisition through better parallel imaging, improved and novel types of contrast, and greater spectral dispersion. There are many obstacles to be faced in the advancement to 7 T including field inhomogeneities, transmit inhomogeneities, and increased RF-absorption risk. Inhomogeneous B1+ is possibly the most significant obstacle currently facing 7 T body imaging in consistently producing clinical-quality images. In this work, the first demonstrations of MR imaging and spectroscopy (MRS) of the liver at 7 T are presented and evaluated with special attention given to parallel imaging. Also presented here is the first demonstration of imaging of the uterus at 7 T with particular emphasis on contrast between uterine layers. A comparison was done between 3 T and 7 T, and relaxation rates were mapped including higher rotating frame relaxations.SWIRLY (spatiotemporal-encoding with incremental refocusing along a trajectory) is a novel pulse sequence that employs a frequency and amplitude modulated excitation pulse in the presence of sinusoidal gradients to move a region of resonance through space along a spiral trajectory. The signal can be sequentially refocused and acquired in an entirely spatiotemporal manner such that no Fourier Transform is needed for reconstruction. Because each resonance region can be treated entirely independently, this sequence has incredible potential for addressing problems that are inherently spatial in nature, such as B1+ and B0 inhomogeneities.
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    A geospatial analysis of West Nile virus in the Twin Cities metropolitan area of Minnesota.
    (2009-07) Ghosh, Debarchana
    The West Nile virus (WNV) is an infectious disease transmitted to humans and other mammals by mosquitoes that acquire the virus by feeding on WNV-infected birds. Since its initial occurrence in New York in 1999, the virus has spread rapidly west and south, causing seasonal epidemics and illness among thousands of birds, animals, and humans. Yet, we only have a rudimentary understanding of how the mosquito-borne virus operates in complex avian-human-environmental systems. The virus first reached Minnesota in 2002 and resulted in several hotspots by 2003. The year 2007 saw one of the severest incidences of WNV in Minnesota. For my dissertation research, I have developed novel approaches to understand the spread and dynamics of the virus by using key environmental, built environment, and anthropogenic risk factors that determine why, when, and where WNV strikes in the Twin Cities Metropolitan area (TCMA). The first study demonstrates the use of a novel spatiotemporal approach to identify exposure areas. The method retrospectively delineates transmission cycles as exposure areas in their entirety, involving dead birds, mosquito pools, and human cases. Given the strong spatial clustering of WNV infections in the urban areas of TCMA, the next study explores how urban landscape features contributed to the viral activities. This investigation contributed to the broader research question in the field of health geography, of how the heterogeneous urban landscape affects human health and disease patterns. The remaining studies focus on the building and interpreting a nonlinear model which captures the complex relationships between the disease incidences and the hypothesized risk factors. The goal of these studies is to identify risk factor(s) whose management would result in effective disease prevention and containment. This dissertation has applied contributions to the vector control policies. The findings from the studies can answer two fundamental questions to eliminate larva and adult mosquitoes capable of carrying WNV. First, when is the optimal time to apply insecticides and pesticides? Second, where (area) should we target spraying of pesticides? This will lead to efficient allocation of resources and allow a balance between mosquito eradication and environmental conservation efforts with respect to insecticide usage.