A comparative study of the different N-acetylaspartate measures of the medial temporal lobe in Alzheimer's disease

Objective: To investigate group differences and correlations and to determine the sensitivity and specificity of different measures of the neuronal marker N-acetylaspartate (NAA) in the medial temporal lobe of Alzheimer's Disease (AD) patients.

Methods: The metabolic ratio NAA/creatine (Cr), the absolute concentration of NAA referenced against brain tissue (BT) water and NAA multiplied with the amount of BT in the proton magnetic resonance spectroscopy (1H-MRS) voxel were assessed in patients and healthy controls with a single-voxel 1H-MRS protocol.

Results: All measures were significantly lower in AD patients compared with controls. NAA/Cr and NAA correlated weakly, and there was no correlation of NAA with the amount of BT in the voxel. The highest specificity (87%) at a sensitivity of 80% was observed for NAA multiplied with the amount of BT in the voxel. There was no correlation of the MMSE with any of the NAA parameters.

Conclusions: NAA/Cr does not reflect NAA concentration very well. NAA is not correlated with brain atrophy. The BT volume in the 1H-MRS voxel in combination with the concentration of NAA discriminates AD from healthy controls sufficiently.