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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
341

Solution Studies of ⁶Li Enriched Organolithium Compounds Using New NMR Techniques

Ellington, Donald H. (Donald Howard) 05 1900 (has links)
With the values of 6Li T1 measured and the literature values of J(13C-6Li) for these compounds, three new 13C NMR techniques are developed for the analysis of organolithium compounds. Modifications to the spectrometer are discussed, as well as calibrations of the 6Li decoupler channel needed to set up these new experiments. The theoretical development of each technique is presented, as well as data from their verification, using organolithium compounds of known structure. Once qualified, the new experimental techniques are used to analyze a series of alkyllithium / lithium alkoxide mixed aggregates in solution, where structures and values of J(13C-6Li) may not be known. The combination of Ti relaxation measurements and 13C{1H, 6Li} triple resonance techniques serves as a means of determining the structure of organolithium aggregates in solution.
342

Status epilepticus in the elderly: Prognostic implications of rhythmic and periodic patterns in electroencephalography and hyperintensities on diffusion-weighted imaging / 高齢者のてんかん重積状態:脳波上の律動性および周期性パターンと拡散強調画像における高信号の予後的意義

Yoshimura, Hajime 25 September 2017 (has links)
京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13125号 / 論医博第2134号 / 新制||医||1024(附属図書館) / (主査)教授 宮本 享, 教授 村井 俊哉, 教授 井上 治久 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM
343

Magnetic Resonance Fingerprinting

MA, DAN 03 June 2015 (has links)
No description available.
344

Development of semi-automated steady state exogenous contrast cerebral blood volume mapping

Provenzano, Frank Anthony January 2016 (has links)
Functional magnetic resonance imaging (fMRI) as it exists, in its many forms and vari- ants, has revolutionized the fields of neurology and psychology by revealing functional differences non-invasively. Although blood oxygenation level dependent (BOLD) fMRI is used interchangeably with fMRI, it measures one single difference in a phys- iological measurement using a set sequence. As such, there are other established changes in the brain that relate to blood movement and capacity that can also be measured using MRI. One measure, exogenous steady state cerebral blood volume, uses a bolus routine contrast agent administered intravenously alongside a pair of high resolution ‘structural-like’ MRI images to provide detailed information within small cortical and subcortical structures. In this thesis I design a semi-automated algorithm to generate maps of steady state exogenous cerebral blood volume magnetic resonance imaging datasets. To do this I developed an algorithm and tested it on existing MRI scanning protocols. A series of automated pre-processing steps are developed and tested, including automated scan flagging for artifacts and requisite vascular segmentation. Then, a methodology is developed to create cerebral blood volume (CBV) region of interest (ROI) masks that can then be applied on an existing database to test known CBV dysfunction in a group of patients at high risk for psychosis. Finally, we develop an experiment to see if template based cerebral blood alterations co-registered with class segmentation maps have any positive predictive value in determining disease state in a well characterized cohort of five age-matched groups in an Alzheimer’s disease neuroimaging study.
345

Diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging

Frost, Stephen Robert January 2012 (has links)
Diffusion-weighted (DW) magnetic resonance imaging is an important neuroimaging technique that has successful applications in diagnosis of ischemic stroke and methods based on diffusion tensor imaging (DTI). Tensor measures have been used for detecting changes in tissue microstructure and for non-invasively tracing white matter connections in vivo. The most common image acquistion strategy is to use a DW single-shot echo-planar imaging (ss-EPI) pulse sequence, which is attractive due to its robustness to motion artefacts and high imaging speed. However, this sequence has limited achievable spatial resolution and suffers from geometric distortion and blurring artefacts. Readout-segmented echo-planar imaging (rs-EPI) is a DW sequence that is capable of acquiring high-resolution images by segmenting the acquisition of k- space into multiple shots. The fast, short readouts reduce distortion and blurring and the problem of artefacts due to motion-induced phase changes between shots can be overcome with navigator techniques. The rs-EPI sequence has two main shortcomings. (i) The method is slow to produce image volumes, which is limiting for clinical scans due to patient welfare and prevents us from acquiring very many directions in DTI. (ii) The sequence (like other diffusion techniques) is far from the optimum repetition time (TR) for acquiring data with the highest possible signal-to-noise ratio (SNR) in a given time. The work in this thesis seeks to address both of these important issues using a range of approaches. In Chapter 4 a partial Fourier extension is presented, which addresses point (i) by reducing the number of readout segments acquired and estimating the missing data. This allows reductions in scan time by approximately 40% and the reliability of the images is demonstrated in comparisons with the original images. The application of a simultaneous multi-slice scheme to rs-EPI, to address points (i) and (ii), is described in Chapter 5. Using the slice-accelerated rs-EPI sequence, tractography data were compared to ss-EPI data and high-resolution trace-weighted data were acquired in clinically relevant scan times. Finally, a 3D multi-slab extension that addresses point (i) is presented in Chapter 6. A 3D sequence could also allow higher resolution in the slice direction than 2D multi-slice methods, which are limited by the difficulties in exciting thin, accurate slices. A 3D version of rs-EPI was simulated and implemented and a k-space acquisition synchronised to the cardiac cycle showed substantial improvements in image artefacts compared to a conventional k-space acquisition.
346

Multisensory integration of olfaction

Österbauer, Robert Alexander January 2007 (has links)
The primary aim of this thesis was to investigate, using functional magnetic resonance imaging (fMRI), the neurophysiological basis of multisensory integration involving smell and vision. To achieve this goal, several technical challenges had to be addressed: the attainment of sufficiently high quality fMRI images in olfactory brain regions within the orbitofrontal cortex (OFC), the construction of a stimulus delivery system adequate for rapid and controlled odour delivery in the MRI environment, and optimal strategies for delivering and perceiving liquid flavour stimuli in the scanner. In two initial fMRI experiments, strategies including sensitivity encoding and passive shimming to improve OFC image quality were explored. The results demonstrated that both methods can improve signal detection in OFC, a brain area particularly sensitive to susceptibility artefacts. In a further fMRI study, the effectiveness of two methods of delivering odorants dissolved in liquids was compared. In this study, the same set of participants was required to either swallow the liquid immediately after delivery or hold it in their mouths for a brief period of time. The results indicated that while both methods allowed detection of activity in primary olfactory and gustatory cortices, activation of the OFC was not observed when participants swallowed the liquids immediately. This was presumed to be due to the increased head motion associated with swallowing. Finally, the mechanisms underlying visual-olfactory integration were investigated using a combination of behavioural and imaging methods. An initial behavioural study revealed strong colour-odour associations for certain smells associated with fruits (e.g. lemon - yellow). In a subsequent fMRI study, volunteers were presented with a selection of the most colour-associated odours from the prior behavioural study either in isolation or in the presence of congruent and incongruent colours. Analysis of the fMRI data revealed that a highly left lateralised network of brain areas comprising of the OFC and insular showed increasingly stronger responses to odour-colour combinations of higher congruency. In a follow-up fMRI study, this same network was also found to be responsible for integrating odours, not only with colours, but also with their corresponding visual images (objects). In sum, the series of fMRI studies undertaken in this thesis argue for a fundamental role of the OFC in the integration of olfactory-visual inputs in the human brain.
347

Neural degeneration and plasticity following damage to the post-chiasmal visual pathway

Millington, Rebecca S. January 2013 (has links)
Hemianopia is a disorder where a patient loses vision in one half of their visual field, following damage to the post-chiasmal visual pathway. If the hemianopia does not spontaneously resolve within the first few months, the prognosis for recovery is poor, with very few patients recovering vision in the affected area of the visual field. The reasons for this are unclear, although it is likely that both degeneration and plasticity in the visual system have an impact on patient outcome. The goal of this research is to investigate the changes that occur in hemianopia, and how these differ for lesions at different locations in the visual pathway and with differing underlying pathologies. Patients with hemianopia arising from different causes were recruited, including 17 with a hemianopia acquired in adulthood, 9 with congenital hemianopia, and 6 patients with hemianopia due to posterior cortical atrophy (PCA). Structural, functional, and diffusion-weighted MRI data were acquired for each patient, in order to examine changes in the structural and function of the visual pathways. Analyses focused on either atrophy, or plasticity and residual function. Atrophy was assessed in acquired and congenital hemianopia by quantifying transneuronal degeneration in the optic tract, which was present in all patients with long-term lesions. Degeneration was also assessed more generally in PCA, who have substantial loss of white and grey matter in posterior brain regions. Investigation of plasticity and residual function focused on the motion processing area (MT), quantifying the level of functional activity in MT, and assessing whether subcortical pathways from the pulvinar to MT exist in hemianopia. A wide degree of variation existed between patients in the extent to which motion processing was preserved, which had no clear link to lesion location, however was related to the size of the lesion.
348

Ability and empathy : investigating the neural and behavioural substrates of manual and facial imitation in neurotypical and autistic populations

Braadbaart, Lieke January 2014 (has links)
Imitation enables social communication and is said to be deficient in people with autism. Yet little research has been done into what differentiates poor from good imitators. This project employed novel quantifiable methods of testing manual and facial imitation to determine how ability as well as empathy (which also enables social interaction) correlate with brain activation using functional Magnetic Resonance Imaging (fMRI). Manual imitation was tested (in- and outside the MRI-scanner) by asking participants to copy model drawings using a touchscreen that captured their kinematic data. Facial imitation was tested by asking people to copy composite facial expressions and blind-scoring the resulting imitation attempts. First, 28 adults were tested to establish what brain areas enable better imitation and how these relate to empathic abilities. Then, 25 young people with autism and 23 matched controls were tested to see how purported group differences in imitation related to brain activation patterns across and within groups. Results revealed that manual imitation ability correlated with increased activation in different brain areas than facial imitation ability. There was only one area of significant overlap, between facial imitation ability and empathy. Young people with autism were found to be impaired on facial imitation, empathy and some aspects of manual imitation. Nevertheless, fMRI results indicated that ability and age differences played a more important role than autism diagnosis in regulating what brain areas were activated during imitation. Only for the facial imitation task did autistic participants appear to use a different neural mechanism, but this was still mediated by ability. Overall, this methodologically innovative project shows that investigating individual differences in imitation ability, regardless of a diagnosis of autism, can shed more light on what neural mechanisms are crucial for imitation.
349

The characterization of white matter injury patterns in normal pressure hydrocephalus using magnetic resonance imaging

Keong, Nicole Chwee Har January 2014 (has links)
No description available.
350

Neuroimaging of patients with acute focal neurological symptoms : investigating new functional and structural Magnetic Resonance Imaging measures

Varsou, Ourania January 2014 (has links)
No description available.

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