Content area
Full text
Brain Imaging and Behavior (2012) 6:426436 DOI 10.1007/s11682-012-9155-6
Local susceptibility causes diffusion alterationsin patients with Alzheimers disease and mild cognitive impairment
Geon-Ho Jahng & Songfan Xu
Published online: 14 March 2012# Springer Science+Business Media, LLC 2012
Abstract Recent studies with positron emission tomography (PET) using the Pittsburgh compound B (PIB) found widespread amyloid plaque depositions in patients with Alzheimers disease (AD) and mild cognitive impairment (MCI) and even in cognitively normal (CN) subjects. The aim of this study was to investigate whether the local susceptibility gradients in brain tissue alter regional diffusion measurements using MRI in patients with AD and MCI. Two diffusion tensor (DT)-MRI data sets were acquired with alternating polarities of the external diffusion-sensitizing gradients. Three subject groups were included: 15 patients with AD, 18 patients with MCI and 16 CN. Maps of mean diffusivity (MD) and fractional anisotropy (FA) were computed separately for positive (p) and negative(n) polarities (pMD and nMD, pFA and nFA). Voxel-wise paired t-tests were performed between pMD versus nMD or between pFA versus nFA maps, separately for each subject group. We also investigated regions-of-interest (ROIs) in the brain. Based on the pair-wise comparisons, we found significant differences between pMD and nMD in all three groups. Results of ROI-based analyses showed that the non-linear behaviors of the ROI data sets were shown for all three groups. In conclusion, significant differences of MD maps between the two polarities of diffusion-
sensitizing gradients were found, suggesting that the intrinsic background gradients may alter MD signals in specific regions. It can be important to take into account the effects of local gradient alterations during diffusion measurements in patients with AD, MCI and elderly controls.
Keywords Local susceptibility gradients . Diffusion tensor imaging . Two polarities of diffusion gradients . Alzheimers disease . Mild cognitive impairment
Introduction
Previous findings of diffusion tensor (DT)-MRI in patients with Alzheimers disease (AD) and mild cognitive impairment (MCI) showed that diffusion isotropy was increased and diffusion anisotropy was decreased against cognitively normal (CN) subjects in specific regions of the brain (Duan et al. 2006; Medina et al. 2006; Naggara et al. 2006; Rose et al. 2008; Stahl et al. 2007; Zhang et al. 2007). Increased mean diffusivity (MD) and decreased fractional anisotropy (FA) in the brains of...