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Sodium MRI optimization for the human head with application to acute stroke Open Access


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Type of item
Degree grantor
University of Alberta
Author or creator
Stobbe, Robert
Supervisor and department
Koles, Zoltan (Electrical and Computer Engineering)
Beaulieu, Christian (Biomedical Engineering)
Examining committee member and department
Thompson, Richard (Biomedical Engineering)
Allen, Peter (Biomedical Engineering)
Wasylishen, Roderick (Chemistry)
Bartha, Robert (Diagnostic Radiology and Nuclear Medicine)
Wilman, Alan (Biomedical Engineering)
Medical Sciences - Biomedical Engineering and Electrical and Computer Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
25 years after the first sodium images of the human brain were created, sodium MRI remains on the periphery of MR research, despite intimate sodium involvement in cellular metabolism and implicated abnormal concentrations in numerous disorders. The difficulties of sodium MRI include not only tissue concentration, ~1750x less than proton, but also rapid biexponential signal decay. The purpose of this work was to optimize human brain sodium MRI and facilitate a study of sodium increase following onset of acute human stroke, with potential ‘timing’ application for those patients who present with unknown time-of-onset, as effective treatment is currently bound by a 4.5 hour time-window. Optimization begins with radial ‘center-out’ k-space acquisition, which minimizes echo time (TE) and signal loss, and in particular concerns the twisted projection imaging (TPI) technique, which has not found wide use. This thesis first considers a new application of TPI, i.e. k-space filtering by sampling density design to minimize detrimental ringing artifact associated with cerebral spinal fluid. Image noise correlation is addressed next, and a method for measuring volumes of statistical noise independence presented, as this correlation together with signal-to-noise ratio (SNR) defines the confidence of signal-averaging measurements. Radial acquisition is then considered with respect to a new imaging metric, i.e. the minimum object volume that can be precisely (with respect to noise) and accurately (with respect to image intensity modulation with object volume) quantified. It is suggested that TPI is a highly beneficial radial acquisition technique when implemented with ‘long’ readout duration (countering common thought), reduced SNR (i.e. small voxel volumes), and in particular small TPI parameter p. Sequence optimization for bulk-tissue sodium analysis demonstrates a large SNR/voxel-volume advantage for TPI implementation in a steady-state approach, even though excitation pulse length and TE must be increased to mitigate power deposition. Finally, an inversion-recovery based fluid-nulling method that facilitates sodium environment separation based on rapid relaxation during soft inversion pulses is presented, with possible application for intracellular weighted imaging. On ‘high quality’ sodium images a clear trend of lesion intensity increase with time-after-onset is demonstrated for the first time in acute stroke patients, as expected from animal models.
License granted by Rob Stobbe ( on 2010-03-26T17:27:22Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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