Comparison of diffusion tensor imaging and proton MR spectroscopy in the posterior cingulate of patients with Alzheimer disease

Abstract

Objective To compare 1HMRS and DTI findings of Alzheimer disease (AD) patients and normal elderly controls. Methods Fifteen mild AD patients, 20 moderate to severe AD patients and 20 aging controlled normal subjects (CN) were recruited. MRS imaging and DTI were performed on a 1.5 T MRI scanner. A ROI was positioned in the posterior part of the cingulate. MRS data were processed and the metabolite ratios were estimated, including the ratios of NAA/Cr, Cho/Cr, mI/Cr. Comparing with the axial MRS location, we chose the same level to posit the ROIs on both sides of the posterior cingulated fibers on fractional anisotropy map (FA) and mean diffusivity map (MD). Mean spectroscopy data and DTI values for each groups were analysed with Mann-Whitney U non parametric test. Correlations between MRS and DTI values for AD groups were estimated using partial correlations test controlling for the age related bias. Results Compared to normal aging groups, mild AD group showed a significantly lower FA value in the left side of posterior cingulum bundle (0. 549±0. 056 vs 0. 517±0. 058,Z =2. 014,P <0. 05). Whereas, moderate to severe group versus mild AD group revealed significantly elevated MI) value and a decrease in FA value in the right side of posterior cingulate ( FA 0. 517 ± 0. 059 vs 0. 432 ± 0. 073, Z = 3. 216, P < 0. 01 ; MD (0.726±0.041) × 10-3 mm2/s vs (0.761±0.057) × 10-3 mm2/s,Z = 1.970,P <0.05) . Obvious increasing mI/Cr ratio was found in mild AD group ( 0. 61 ± 0. 07 vs 0. 68 ± 0. 12, Z = 2. 911, P < 0. 01 ). NAA/Cr ratio showed gradually decrease in AD groups. Partial correlations analysis revealed a positive correlation between ml/Cr ratio and left posterior cingulated FA value in mild AD group ( r = 0. 586, P < 0. 05) and negative correlation between NAA/Cr and MD value in the right side of posterior cingulated region ( r = - 0. 505, P < 0. 05 ). Conclusions These findings suggested that there were different regional and temporal pattern in different course of AD disease, resulting from axonal loss or gliosis. Combining MRS with DTI alternations could be a better potential indicator and could better explain the pathological changes in AD progression. Key words: Alzheimer disease; Magnetic resonance imaging; Magnetic resonance spectroscopy