Cerebral Metabolism in Patients with Cognitive Disorders: a Combined Magnetic Resonance Spectroscopy and Positron Emission Tomography Study

Objectives. Magnetic resonance spectroscopy (MRS) allows the contents of many metabolites in living tissues to be assessed. There is a good number of studies analyzing MRS data in Alzheimer’s disease (AD), though their results are contradictory. In this regard, there is value in comparing MRS data with fluorodeoxyglucose (FDG) positron emission tomography (PET) results, which assess the functional state of nervous tissue. The present study provides a comparison of MRI scan data in AD and moderate cognitive impairment (MCI) with the characteristics of cerebral glucose metabolism assessed from FDG-PET data. Materials and methods. Multivoxel proton MRS of the supraventricular region was carried out in patients with AD (n = 16) and MCI (n = 14). The following metabolite ratios were determined: NAA/Cr, Cho/Cr, and NAA/Cho (NAA is N-acetylaspartate, Cr is creatine, and Cho is choline). Patients underwent neurological investigation, assessment of cognitive status, and PET scans with FDG. Results. Patients with AD showed decreases in NAA/Cr and Cho/Cr in the white matter of the medial cortex of the supraventricular areas of both hemispheres. The MCI group showed a decrease in the NAA/Cr ratio in only one area of the white matter of the left hemisphere, adjacent to the parietal cortex. Positive correlations were found between NAA/Cr and Cho/Cr with measures of cognitive status and with the rate of glucose metabolism measured from PET data in the frontal, parietal, and temporal areas and the cingulate cortex. Conclusions. The decrease in the NAA/Cr ratio in the supraventricular white matter and the medial cortex in AD and the correlation of this parameter with cognitive test results and cerebral glucose metabolism constitute evidence that it may have diagnostic value, reflecting the severity of cognitive impairments. Assessment of the NAA/Cr ratio should be carried out with consideration of the fact that dementia alters the concentrations of both metabolites (NAA and Cr).