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Metabolite concentrations and myelin water fraction : correlations and trends within white matter measured with magnetic resonance spectroscopy and T₂ Relaxation techniques Moll, Rachel Francesca


Absolute concentrations of in vivo human brain metabolites, N-acetyl-aspartate (NAA), choline (Cho) and creatine (Cre) were measured using single voxel spectroscopy. Myelin water fractions (MWF) were measured with a 48 echo T₂ relaxation pulse sequence. NAA is a possible neuronal marker, choline may be involved in myelin lipid synthesis and MWF represents the amount of water trapped between layers of myelin. Regional distributions and trends of measurements were examined and compared to similar measurements made with magnetic resonance spectroscopic imaging (MRSI). Measurements were made in four white matter regions in normal human brain, frontal white matter (FW), occipital white matter (OW), posterior internal capsules (PIC) and the splenium of the corpus callosum (SP). In the single voxel spectroscopy study the regional distribution of MWF and absolute concentrations of NAA, Cho and Cre were consistent with previous studies. Metabolite concentrations varied significantly between white matter structures. In some cases, variation was partially attributed to the amount of white matter in the voxel. In all white matter, trends between metabolite concentrations and MWF were weakly significant for NAA and creatine. Within structures weakly significant trends were also observed and varied between structures. In the MRSI study MWF trends reproduced previous work but spectroscopy measurements, which could not be absolutely quantified, produced no significant trends between structures or any consistent results between the three volunteers. Thus it remains unclear whether myelin water fraction and metabolite concentrations such as NAA or choline should be related. The current literature provides conflicting results on both the function of NAA and the regional distribution between white and grey matter of metabolite concentrations. This study, the first to examine trends within white matter, contributes to a body of literature which aims to determine the function and importance of magnetic resonance spectroscopy visible metabolites and their possible contributions to clinical medicine.

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