[BIC-announce] PhD defense

[Ives LEVESQUE]

PhD Defense - Ives Levesque, (Supervisor: Bruce Pike)
Tuesday, August 25th 2009, 14:00
R.E. Bell Conference Room (room 103), Rutherford Physics Building

Title:
Quantitative magnetic resonance imaging of magnetization transfer and T2 
relaxation in human white matter pathology

Abstract:
The primary aim of this thesis is the reconciliation of two seemingly disparate 
quantitative magnetic resonance imaging (MRI) techniques proposed to 
characterize human brain white matter (WM) in health and disease. Quantitative 
magnetization transfer imaging (QMTI) and multi-component analysis of T2 
relaxation (QT2) both attempt to quantify myelin content in vivo, but are based 
on fundamentally different models of WM. QMTI probes the macromolecular 
component of tissue using a two-pool model of magnetization transfer, while QT2 
isolates the water signal from distinct micro-anatomical compartments. The 
specific objectives were to determine the interrelationship between 
measurements made with both techniques in the context of potential pathological 
changes associated with multiple sclerosis (MS), and to apply both to track WM 
changes in the acute phase of MS lesions. First, simulations were used to 
evaluate the theoretical sensitivity of each technique to the 
characteristics of a model of WM that incorporates four pools of 
magnetization, based on published in vitro measurements. Next, the 
experimental reproducibility of each technique was investigated, and the 
impact of certain basic variations in the data acquisition and analysis 
procedures was evaluated. In the final stage, both methods were applied 
longitudinally in vivo to assess the dynamic changes that occur in acute, 
contrast-enhancing lesions of MS. The theoretical results illustrate the 
sensitivity and limitations of QMTI and QT2 to specific pathology-inspired 
modi#cations of WM, and shed new light on the potential speci#city of 
often-neglected QMTI parameters. The reproducibility of both techniques is 
acceptable for use in repeated clinical measurements, and QMTI has lower 
variability overall. The importance of corrections for magnetic field 
inhomogeneity in QMTI is demonstrated, and a simple optimization of the 
QMTI data acquisition is introduced. Both techniques were sensitive to 
active disease pathology in the longitudinal study of MS patients. 
Overall, this thesis demonstrates the complementary nature and usefulness 
of QMTI and QT2 in the characterization of the natural disease course of a 
degenerative disease of the human central nervous system. With further 
refinement, these techniques could play an important role in the study of 
other diseases, and have the potential to serve as outcome measures in 
clinical trials.




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Ives R. Levesque, MSc			  McGill University
NeuroImaging Lab, MNI		    3801 University, WB-325
ives at bic.mni.mcgill.ca			   Montreal, Quebec
Tel: (514) 398-8547			     Canada H3A 2B4
 	       www.bic.mni.mcgill.ca/users/ives
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