No description available.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Tatyana Polenova, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has a high sensitivity (71- 100%) for detecting breast cancers. DCE-MRI is approximately twice as sensitive as mammography for patients who are genetically predisposed to breast cancer, who have an elevated lifetime risk (up to 85%) of contracting the disease, and who require rigorous screening. However, current methods of DCE-MRI often have difficulty distinguishing malignant from benign tumours, resulting in low positive predictive values (on average, PPV = 45%). The research in this thesis is motivated by the need for improvement in the ability of MRI to differentiate breast lesions. It is believed that the differentiation of malignant from benign lesions can be improved by acquiring images of high spatial resolution for visualizing morphological features of tumours and those of high temporal resolution for characterizing contrast-kinetic curves. However, simultaneously achieving high spatial and temporal resolution is limited by the inherent trade-off between speed and quality in MRI, requiring one to choose a particular balance of spatial and temporal resolution. In this thesis, novel techniques are presented that reduce the need to choose a spatiotemporal resolution before the scan. Flexible methods are presented that allow images to be retrospectively reconstructed with different balances of spatial and temporal resolution from the same dataset. Flexibility is achieved through radial sampling of k-space data, with 3D radial directions based on Multidimensional Golden Means (MGM) and Halton sequences. Radial sampling also allows constrained image reconstruction techniques such as Compressed Sensing and Prior-Image Constrained Compressed Sensing to be incorporated for reducing undersampling artifacts in high-temporalresolution images. This thesis demonstrates in 2D how such reconstruction algorithms are influenced by acquisition schemes and shows how reconstruction algorithms work in synergy with flexible radial sampling to provide improvements in the quality of breast MR images. The flexibility to choose any spatiotemporal resolution combined with better image quality in fast images could potentially improve the characterization of breast lesions screened by MRI.

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has a high sensitivity (71- 100%) for detecting breast cancers. DCE-MRI is approximately twice as sensitive as mammography for patients who are genetically predisposed to breast cancer, who have an elevated lifetime risk (up to 85%) of contracting the disease, and who require rigorous screening. However, current methods of DCE-MRI often have difficulty distinguishing malignant from benign tumours, resulting in low positive predictive values (on average, PPV = 45%). The research in this thesis is motivated by the need for improvement in the ability of MRI to differentiate breast lesions. It is believed that the differentiation of malignant from benign lesions can be improved by acquiring images of high spatial resolution for visualizing morphological features of tumours and those of high temporal resolution for characterizing contrast-kinetic curves. However, simultaneously achieving high spatial and temporal resolution is limited by the inherent trade-off between speed and quality in MRI, requiring one to choose a particular balance of spatial and temporal resolution. In this thesis, novel techniques are presented that reduce the need to choose a spatiotemporal resolution before the scan. Flexible methods are presented that allow images to be retrospectively reconstructed with different balances of spatial and temporal resolution from the same dataset. Flexibility is achieved through radial sampling of k-space data, with 3D radial directions based on Multidimensional Golden Means (MGM) and Halton sequences. Radial sampling also allows constrained image reconstruction techniques such as Compressed Sensing and Prior-Image Constrained Compressed Sensing to be incorporated for reducing undersampling artifacts in high-temporalresolution images. This thesis demonstrates in 2D how such reconstruction algorithms are influenced by acquisition schemes and shows how reconstruction algorithms work in synergy with flexible radial sampling to provide improvements in the quality of breast MR images. The flexibility to choose any spatiotemporal resolution combined with better image quality in fast images could potentially improve the characterization of breast lesions screened by MRI.

This dissertation reports a study of three kinds of liquid crystals using modern solid state NMR techniques: chiral rod-like liquid crystals, bent-core mesogens and disc-like liquid crystals. The properties and structures of liquid crystals are first introduced in Chapter 1. To understand the principles of different NMR phenomena, quantum mechanical theory is adopted to study different nuclear spin interactions and NMR techniques in Chapter 2. In the next part of this dissertation (Chapter 3-6), deuterium NMR methods are used to investigate the dynamics and structures of some liquid crystal phases. This is first done using the spin relaxation study. The parameters obtained from the model simulation can describe the molecular motion and internal dynamics in the fast motion region. Secondly, we investigate the dynamic process of discotic mesophases and unwound smectic C* phase using the line shape simulation study. 2D deuterium NMR exchange experiments are then performed to study the jump process in TGBA* phase and SmC* phase. The above investigation has demonstrated some powerful NMR methods for the dynamic study of liquid crystals. The third part of the dissertation (Chapter 7-9) is concerned with C-13 NMR techniques. After we introduce the quantum theory of different pulse sequences, theoretical models are presented to fit observations such as chemical shifts and dipolar splittings. Moreover high resolution liquid C-13 NMR experiments are introduced to study some bent-core molecules. They are useful to assist the carbon peak assignments of these molecules. The structure and ordering information of liquid crystals can be determined in their mesophases. Finally, a brief summary of the dissertation is given in the last chapter. / October 2007

The purpose of our study was to determine the incidence, causes, and reversibility of leukoencephalopathies demonstrating confluent areas of restricted diffusion on magnetic resonant imaging (DWI+LE). We hypothesized DWI+LE would have a low incidence, and be primarily caused by toxic exposures. We performed a logic sentence based search of the Yale-New Haven MRI database to select for reports indicating restricted diffusion within the cerebral white matter. We examined patients neuroimaging studies and medical record. We identified a total of 35 cases of DWI+LE, which resulted in an overall incidence of 0.2% over the five-year period queried. The medical conditions associated with DWI+LE were as follows: toxic exposure (7), hypoxia with concurrent trauma (7), hypoxia with concurrent toxic exposure (4), hypoxia with concurrent metabolic derangements (4), seizure with concurrent metabolic derangements (2), metabolic derangements (2), antiepileptic therapy (2), hypoxia (1), trauma (1), and unknown (5). The most favorable outcomes were seen in patients with intrathecal methotrexate toxicity, while patients with hypoxia without a lucid interval fared worst. We concluded that DWI+ LE are rare, their etiology diverse, and its reversibility dependant upon the type and severity of the insult.

Thesis (M.S. in chemical engineering)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 21, 2010). "Department of Chemical Engineering." Includes bibliographical references (p. 28-31).

Thesis (Ph. D.)--University of Missouri--Rolla, 1993. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed January 25, 2010) Includes bibliographical references (p. 150-155).

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 129-135).