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.