Evaluation of the posterior cingulate region with FDG-PET and advanced MR techniques in patients with amnestic mild cognitive impairment: comparison of the methods.

BACKGROUND: The posterior cingulate region is an area of the earliest pathological changes in amnestic mild cognitive impairment (aMCI). The utility of FDG-PET imaging in dementia is already well established.

OBJECTIVES: The aim of the study was to compare FDG-PET with advanced MR measurements: MR spectroscopy (MRS), perfusion weighted imaging (PWI), and diffusion tensor imaging (DTI) within the posterior cingulate region in patients with aMCI.

METHODS: Fifty-five patients diagnosed with aMCI (66.5 y) and 20 age-matched controls (69 y) underwent MR examination including MRS, PWI, and DTI followed by FDG-PET scanning. Values of MRS metabolite ratios (NAA/Cr, Cho/Cr, mI/Cr), PWI cerebral blood volume (rCBV), and DTI fractional anisotropy (FA) were compared to the FDG-PET rates of glucose metabolism.

RESULTS: Compared to controls, aMCI patients showed significant (p < 0.05) glucose hypometabolism, and lower rCBV and FA values. FDG-PET results correlated significantly with rCBV values. Compared to FDG-PET, PWI showed similar and DTI greater accuracy in distinguishing aMCI from controls. According to FDG-PET findings, two groups of aMCI patients were established: those with lower (PET-positive) and normal (PET-negative) glucose uptake. PET-positive aMCI subjects showed normal MRS findings, lower rCBV and FA values, while PET-negative patients revealed normal MRS and PWI results but significantly lower FA values.

CONCLUSIONS: Advanced MR techniques such as PWI and particularly DTI may be regarded as competitive techniques to FDG-PET. DTI was the only method to show alterations in aMCI patients with normal FDG-PET, PWI, and MRS findings. DTI seems to be a very sensitive biomarker of early degeneration in aMCI.