Background and purpose: Magnetic resonance spectroscopy (MRS) allows the measurement of a number of brain tissue metabolites in vivo, including N-acetylaspartate (NAA), a putative marker of neuronal integrity. Unlike single voxel MRS, magnetic resonance spectroscopic imaging (MRSI) enables quantification of these metabolites simultaneously from multiple anatomically localized voxels. Both single voxel MRS and MRSI allow the absolute quantification of these metabolites and, when combined with tissue segmentation, can give accurate metabolite concentrations even in the presence of partial volume effects from nearby cerebrospinal fluid.
Methods: Using MRSI with cubic voxels with a nominal volume of 1.0 cm(3), we tested the hypothesis that concentrations of NAA in the basal ganglia in multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) would show differences compared to Parkinson's disease (IPD). NAA values (in mM) from MRSI voxels centred to the putamen, pallidum and thalamus were obtained from 11 patients with IPD, 11 with MSA-P, six with MSA-C, 13 with PSP and 18 controls. The mean concentrations of NAA and its bulk grey and white matter values were also estimated over the whole brain slab.
Results: N-acetylaspartate concentrations in the pallidum, putamen and lentiform nucleus were significantly lower in patients with MSA-P and PSP compared to IPD and controls. The putaminal values were also significantly reduced in PSP compared to MSA-P. There were no significant differences between groups in the thalamus and over the whole brain slab.
Conclusion: Our findings support the notion that MRSI can potentially quantify basal ganglia cellular pathology in MSA and PSP.