Transverse Relaxation Times of Major Brain Metabolites in Gulf War Illness
Chang, Audrey Jennifer
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Because many neurodegenerative diseases, like Gulf War Illness (GWI), are unidentifiable on conventional MRI or other imaging modalities in their early stages, diagnosis and treatment must wait until the disease has progressed to a more debilitating and obvious phase. The first aim of this thesis was to develop a reliable protocol to investigate the more subtle changes in metabolite concentrations and T2 relaxation times in GWI. This protocol generated reproducible MRS results, with small inter- and intrasubject variability, on normal controls in the basal ganglia region using single voxel spectroscopy. The second aim of this thesis was to compare T2 values of major brain metabolites in the basal ganglia in Gulf War Syndromes 1-3 and age-matched control veterans. Significant differences were found between Syndrome 2 and controls for NAA and Cr in left basal ganglia and for Cho in right basal ganglia. Finally, measured T2 values were also used to correct concentrations of brain metabolites to investigate relaxation effects on concentration results. At low TE values (TE=30 ms in this study) T2 relaxation measurements were found to have a small effect (approximately 10%) on concentration data. At larger TE values (TE=270 ms in this study) T2 relaxation measurements have a greater impact on concentration results. This finding reinforces the concentration data as evidence of neurophysical damage underlying cognitive difficulties experienced by Gulf War Illness patients, instead of T2 time effects creating false differences in concentration or metabolite signal ratios. / By establishing a dependable and efficient method of acquisition, T2 relaxation measurements can be incorporated into future MRS protocols, ensuring metabolite concentration measurements can be accurately corrected, especially for acquisitions with long TE, instead of using a static quantity, and moving the analysis of single voxel spectroscopy towards true absolute quantitation values. Also, this method, confirmed here to be reliable on existing equipment, can be expanded for use in other disease models which are similarly difficult to detect in conventional MRI.