Diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) are important magnetic resonance imaging (MRI) tools with significant clinical utility. However, current available spatial resolution for DWI is typically around 2mm per pixel, which is substantially lower than the submilimeter resolution of anatomical MRI. Such low spatial resolution severely limits the ability of diffusion MRI in investigating white matter structure and integrity, for example. Ultra high field strengths and emerging applications of DWI and DTI in pediatric neuroimaging, small animal neuroimaging, surgical planning and neural fiber tractography have created a strong demand for 1) higher image spatial resolution and 2) larger number of diffusion gradient directions. The overall goal of this proposal is to develop and refine advanced image formation techniques and novel diffusion analysis models. Towards this end, we propose to employ an array of novel techniques including motion navigated multi-shot sequences, parallel imaging with multiple coils, at high (3T) and ultra high magnetic field strengths (7T). Inherent advantages are that multi-shot sequences allow for improved data acquistion schemes with better SNR and reduced artifacts, which also alleviates the problem of rapid signal decay;parallel imaging provides a method for shortening the total scan time and further reducing image artifacts, while ultra high field offers stronger SNR and T2* sensitivity at the expense of potential artifacts. Although the synergy of these techniques holds great potential for high resolution DWI and DTI, many technical challenges remain.
The specific aims of this research are to meet these challenges by: 1) developing multi-shot DW sequences with efficient volumetric imaging with 3D motion navigation and;2) developing multi-shot parallel imaging acquistion techniques and fast image reconstruction algorithms that can efficiently and rapidly post-process thousands of images in a clinical setting, and finally;3) measuring higher order diffusion tensor parameters to resolve multi-modal white matter structures. These advanced techniques will not only allow better visualization and quantitation of in vivo water proton diffusion processes on the scale of a few hundred microns, but will also significantly improve the quality and speed of the image acquistions. These techniques will eventually result better diagnostic potential for diffusion-weighted images, and, ultimately, more accurate quantification of complex tissue diffusion properties.
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