A Search for MRI diffusion coefficient standards

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Title: A Search for MRI diffusion coefficient standards
Author: Yuan, Hongmei
Abstract: Diffusion coefficients (D) can be readily measured by nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) instruments. Operators of these instruments often utilize standards with known diffusion coefficients to rapidly and conveniently test the performance of the NMR or MRI system to measure diffusion. A variety of these standards have been proposed in the scientific literature. This thesis describes a diffusion standard based on water constrained by container geometry, specifically water between tightly packed, parallel glass fiber filaments. The restricted diffusion of water in this environment gives a diffusion coefficient which is selectable by the choice of data acquisition parameters. Thus, one standard can be used to achieve multiple diffusion coefficients and replaces the need for multiple diffusion standards. Educational training was performed on a 300 MHz NMR spectrometer located at Rochester Institute of Technology (RIT). As a part of this training, pulsed magnetic field gradient strengths were calibrated and diffusion coefficients (D) measured for a series of silicone oils of different viscosities. Diffusion coefficient values for a small diameter test phantom were measured on a 600 MHz NMR spectrometer with stimulated echo pulse sequence at 25°C. A predictable behavior between the apparent diffusion coefficient and gradient separation (δ) value in the sequence was observed. Diffusion coefficient values were measured for a larger diameter phantom using a 1.5 T imager at 20°C using echo-planar imaging sequence and confirmed to follow the same D vs. δ behavior. Based on these observations, a hydrated fiber bundle can make a diffusion phantom with only water yielding the NMR signal.
Record URI: http://hdl.handle.net/1850/15279
Date: 2011-10

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