Estimating NAA in cortical gray matter with applications for measuring changes due to aging

Area of Science:

• Neuroimaging
• Biochemistry
• Gerontology

Background:

• N-acetylaspartic acid (NAA) is a key neuronal marker detected via proton magnetic resonance spectroscopy (1H MRS).
• Assessing NAA in cortical gray matter is challenging due to lipid artifacts and large voxel sizes in conventional 1H MRS.
• Previous studies show potential for NAA deficits in various patient groups, but localized gray matter analysis is limited.

Purpose of the Study:

• To develop and validate a novel technique for estimating NAA signal specifically within cortical gray matter.
• To overcome limitations of lipid suppression and voxel composition in standard 1H MRS for gray matter analysis.
• To investigate age-related differences in gray matter NAA levels.

Main Methods:

• Utilized an inversion recovery imaging pulse sequence with a long echo time (TE) to suppress subcutaneous lipid signals.
• Integrated concurrently acquired structural MRI data to determine the cerebrospinal fluid (CSF), white matter, and gray matter composition of each spectroscopic voxel.
• Employed regression analysis to estimate NAA levels in pure white and gray matter voxels.

Main Results:

• Successfully derived estimates of NAA signal from cortical gray matter.
• Demonstrated reduced NAA gray/white matter ratios in healthy older women compared to healthy younger women.
• The technique effectively suppressed lipid signals from the scalp.

Conclusions:

• The developed technique enables accurate NAA quantification in cortical gray matter.
• Findings suggest potential age-related decline in gray matter NAA levels.
• This method enhances the utility of 1H MRS for studying neurochemistry in aging and neurological conditions.