ESTIMATING NAA IN CORTICAL GRAY-MATTER WITH APPLICATIONS FOR MEASURING CHANGES DUE TO AGING

N-acetylaspartic acid (NAA), a prominent peak in the proton spectrum, is an amino acid thought to be present almost exclusively in neurons a nd their dendritic and axonal extensions, While H-1 MRS studies are sh owing promise in identifying NAA deficits in different patient groups, unwanted lipid signal from subcutaneous fat surrounding the skull, an d necessarily large voxels have limited investigators' ability to asse ss NAA in cortical gray matter. Here we report a technique developed t o derive estimates of NAA signal from cortical gray matter. This appro ach uses an inversion recovery imaging pulse sequence with a long TE t o suppress lipid signal from the scalp and information from concurrent ly obtained structural MR images to determine the CSF, white and gray matter composition of each spectroscopic voxel, A regression analysis is then used to estimate what NAA levels would be in ''pure'' white an d gray matter voxels, This technique has been applied to demonstrate r educed NAA gray/white levels in the brains of five healthy older compa red with five healthy younger women.