High-resolution Diffusion MRI of Targeted Regions PDF Download

Author: Emine Ülkü Sarıtaş
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 131

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Book Description
Diffusion magnetic resonance imaging (MRI) is an MRI method that provides information about random microscopic motion of water molecules in biological tissues. In addition to offering a higher sensitivity for the diagnosis of white matter diseases such as stroke and multiple sclerosis, and producing connectivity maps of the brain, it is a promising prognostic tool in the assessment and treatment response monitoring of cancer in the body. While high in-plane resolution is desirable for all diffusion MRI applications, it is particularly essential for imaging of small structures. Unfortunately, the performance of diffusion MRI techniques is often hindered by a variety of factors including susceptibility variations, field inhomogeneities and bulk physiologic motion. This thesis presents a reduced field-of-view (FOV) single-shot echo-planar imaging (ss-EPI) method to address these problems and enable high-resolution diffusion MRI of targeted regions. The proposed method utilizes a two-dimensional (2D) echo-planar radio-frequency (RF) excitation pulse to achieve a sharp reduced-FOV profile, while still allowing contiguous multi-slice imaging and suppressing the fat signal. Extensive clinical evaluation of the technique demonstrated that sub-mm diffusion-weighted imaging (DWI) on human spinal cords is feasible with minimal artifacts. High-resolution fiber tractography of the spinal cord successfully visualized the connectivity between the cord and the medulla oblongata, delineating internal structures such as gray/white matter. In vivo DWI of the larynx, breast and prostate validated the effectiveness of this technique in providing detailed depiction of the morphology outside the central nervous system. When the exponential diffusion attenuation is combined with high spatial resolution, DWI may suffer from poor signal-to-noise ratio (SNR). The last part of this thesis presents an optimization strategy for the DWI parameters as a function of the imaging SNR. Specifically, the optimum b-value is shown to be a monotonically increasing function of the imaging SNR, with a convergence asymptote identical to the previously proposed values in literature. The effects of T2 relaxation are also incorporated for a more accurate optimization. In vitro and in vivo experiments demonstrated reduced error in ADC estimations and improved SNR in the diffusion-weighted images with the proposed technique.