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Diffusion-weighted magnetic resonance imaging with high gradient fields.

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Call No.	QC762 .D55 1996
Author	Ding, Shujun
Title	Diffusion-weighted magnetic resonance imaging with high gradient fields.
Date	1996
Abstract	Diffusion-weighted magnetic resonance imaging (MRI) provides unique contrast reflecting the translational motion of water in its microscopic environment. This imaging modality has been shown to highlight infarcted regions within minutes after an ischemic insult. However, diffusion imaging is technically difficult to implement and the mechanisms that produce contrast are not well understood. In this dissertation, two fast pulse sequences have been developed for diffusion imaging utilizing high magnetic gradient fields: one is based on the steady-state free precession scheme and the other uses multiple spin-echoes. Both sequences reduce scan times compared with conventional techniques and overcome some problems inherent in existing fast sequences. These new sequences were theoretically analyzed and assessed in phantom experiments and in in vivo experiments. To understand the contrast mechanisms of diffusion-weighted MRI at the cellular level, a two-compartment exchange model has been developed and an analytical expression derived for the apparent diffusion coefficient (ADC). The model predicts that the ADC measured by MRI at long diffusion times is not a constant as the magnitude of the applied gradient is varied over a large range. At low gradient strengths the system is in the fast exchange regime and the ADC can be approximated as a weighted average of the characteristic diffusion coefficients of the extracellular and intracellular compartments. Experiments were performed in red blood cell suspensions to verify the model. The theory and experiments were in reasonable agreement. It is further suggested that the ADC may be used as a marker for the noninvasive determination of extracellular volume. Potential application of the model for the measurement of oxygen tension in tumors is investigated.
Description	1 online resource (xii, 184 leaves) : illustrations
Format	application/pdf
Subject	Magnetic resonance imaging. ; Nuclear magnetic resonance.
College	Dartmouth College -- Department of Physics and Astronomy.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D)--Dartmouth College.
Copyright	In Copyright. This material is protected by copyright and/or related rights. You are free to use this material in any way that is permitted by copyright law that applies to your use. For other uses, you need to obtain permission from the rights-holder(s). http://rightsstatements.org/page/InC/1.0/
DOI	https://doi.org/10.1349/ddlp.2705

Title	ding1996 1
Full Text	DIFFUSION-WEIGHTED MAGNETIC RESONANCE IMAGING WITH HIGH GRADIENT FIELDS A Thesis Submitted to the Faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Department of Physics and Astronomy by Shujun Ding Dartmouth College Hanover, New Hampshire May, 1996

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