Identification of Superficial White Matter Abnormalities in Alzheimer's Disease and Mild Cognitive Impairment Using Diffusion Tensor Imaging

Abstract

Background: Diffusion tensor imaging (DTI) estimates the microstructural alterations of the brain, as a magnetic resonance imaging (MRI)-based neuroimaging technique. Prior DTI studies reported decreased structural integrity of the superficial white matter (SWM) in the brain diseases.

Objective: This study aimed to determine the diffusion characteristics of SWM in Alzheimer's disease (AD) and mild cognitive impairment (MCI) using tractography and region of interest (ROI) approaches.

Methods: The diffusion MRI data were downloaded from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database on 24 patients with AD, 24 with MCI, and 24 normal control (NC) subjects. DTI processing was performed using DSI Studio software. First, for ROI-based analysis, The superficial white matter was divided into right and left frontal, parietal, temporal, insula, limbic and occipital regions by the Talairach Atlas, Then, for tractography-based analysis, the tractography of each of these regions was performed with 100000 seeds. Finally, the average diffusion values were extracted from voxels within the ROIs and tracts.

Results: Both tractography and ROI analyses showed a significant difference in radial, axial and mean diffusivity values between the three groups (p < 0.05) across most of the SWM. Furthermore, The Mini-Mental State Examination was significantly correlated with radial, axial, and mean diffusivity values in parietal and temporal lobes SWM in the AD group (p < 0.05).

Conclusion: DTI provided information indicating microstructural changes in the SWM of patients with AD and MCI. Therefore, assessment of the SWM using DTI may be helpful for the clinical diagnosis of patients with AD and MCI.

Keywords: Alzheimer’s disease; diffusion tensor imaging; mild cognitive impairment; superficial white matter; tractography.

Fig.1

Three-plane view of whole brain Superficial White Matter Mask which was obtained from the similar study [18, 21] in Montreal Neurological Institute space.

Fig.2

Overview of the division of the SWM of the brain into the frontal (pink), insula (green), limbic (yellow), parietal (blue), temporal (orange), occipital (Purple) lobes. a) 3D sagittal view b) 3D Axial View.

Fig.3

Example of SWM fibers pathways which generated by tractography of total SWM regions in standard MNI-ICBM152 template. Fibers pathways were recognized automatically according to an atlas-based tractography segmentation. (After performing the tractography of SWM regions, regions have been removed to better fibers pathways appear.)