| Magnetic resonance imaging (MRI) is the only medical imaging modality to measure the diffusion process non-invasively, and has the ability to diagnose otherwise undetectable changes such as damage to brain axonal fibers and cerebral infarcts. The majority of diffusion MRI applies 2D Diffusion-Weighted Spin-Echo Echo Planar Imaging (DW SE EPI) due to its unparalleled acquisition speed and its immunity to motion artifacts. This current standard, however, has two well-known problems in distortion and thickness resolution. The goal of the dissertation is to solve limitations of DW SE EPI while keeping the data acquisition time within a reasonable range and to reduce the motion artifacts.;Once the TORQ is developed, DW extension of the TORQ is performed using DW half Fourier single shot echo (HASTE) sequence. When tested with a water phantom, the images reconstructed from DW TORQ show no signs of distortions. Also DW TORQ results in the true 3D diffusion MRI images with isotropic resolution of sub-2mm3. Although the DW TORQ cannot match the speed of the D W-EPI sequence, it has a potential to be reasonably fast when time-reduction techniques are applied. In conclusion, the DW TORQ has been successfully implemented on the clinical 3T MRI scanner, and with further development, the DW TORQ will be a viable alternative to the conventional 2D DW MRI.;As a solution, non-EPI 3D diffusion MRI method using the three dimensional overlapped "rod" acquisition (TORQ), a 3D extension of the PROPELLER, is proposed. The TORQ is a novel k-space sampling strategy based on the rotating "rod" elements with oversampled spherical cores for the bulk motion corrections. Also the TORQ has a potential of reducing scantime with k-space undersampling and other strategies. In this dissertation, the Turbo Spin Echo (TSE) based TORQ is developed. The TORQ is first developed from the k-space "rod" trajectory model, and then implemented to Siemens 3T Trio scanner. The "rod" data are then reconstructed with MATLAB. The TORQ is tested with a water phantom, and it has comparable image quality with its 3D TSE counterpart. Also the effectiveness of k-space undersampling as a scantime reduction strategy is verified. |
