Proton Magnetic Resonance Imaging (MRI) is a powerful non-invasive imaging modality, which is able to accommodate multiple contrast mechanisms for studying tissue structure and function, but has severe limitations in spatial resolution. Diffusion MRI is sensitive to the microscopic motion of water molecules, which are diffusing within the tissue or flowing through the vasculature, and it can thus be used to probe cellular and microvascular microstructures in tissues exhibiting anisotropic transport properties.
There are two different stages of encoding in diffusion MRI experiment. The first refers to the classical spatial encoding needed for any MR image formation, requiring the modeling of the MR physics and the consideration of the imaging technology limitations. The second is related to the encoding of the diffusing or flowing spins displacement, requiring the mathematical modeling of water transport. The ability to quantify the tissue fiber and microvasculature architecture relies on the resolution of the spatial encoding and the ability of the underlying transport model to represent the underlying process.
The present thesis focuses on the development of acquisition procedures and model-based analysis tools for the simultaneous characterization of anisotropic tissue fiber and microvasculature architecture in vivo, and their tissue-specific implementation in two areas of particular radiological interest: the skeletal muscle in the calf and the white matter in the brain. At the MR spatial encoding level, imaging techniques are developed with focus on the spatial resolution needs which depend on the anatomy and physiology of the imaged tissue. At the transport modeling level, a generalized framework is established to account for fiber and microvascular anisotropy by treating the tissues as musculovascular and neurovascular units. The contributions of the present work at the two above levels allow the mapping of the fiber and microvasculature architecture in skeletal muscle and white matter. The thesis addresses four problems. First, in the study of skeletal muscle fiber architecture, the idea of myofiber ellipticity is presented as a novel explanation for the asymmetry of the diffusion on the transverse plane. Second, in the study of skeletal muscle fiber architecture, a new technique, labeled, Intravoxel Partially Coherent Motion (IVPCM) technique, is formulated in order to extract information about the capillary network anisotropy. Third, in the study of the white matter fiber architecture, a diffusion acquisition technique combining multi-shot diffusion imaging with a reduced-FOV approach is developed in order to increase the spatial resolution of localized white matter anatomies and the technique is implemented in the areas of the pons and the hippocampus. Fourth, in the study of the white matter microvasculature architecture, the anisotropy of the diffusion MR signal, sensitive to microcirculatory effects, is examined to characterize the architecture of the underlying capillary network.
|Advisor:||Georgiadis, John G.|
|School:||University of Illinois at Urbana-Champaign|
|School Location:||United States -- Illinois|
|Source:||DAI-B 70/02, Dissertation Abstracts International|
|Subjects:||Biomedical engineering, Medical imaging|
|Keywords:||Anisotropic tissue fiber, Capillary network, Diffusion MRI, Intravoxel partially coherent motion, MRI, Microvasculature, Skeletal muscle, White matter|
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