Affiliations: Department of Neurological Sciences, Rush University
Medical Center, Chicago, IL, USA
Note: [] Corresponding author: G.T. Stebbins, Rush University Medical
Center, 1725 W Harrison, Suite 755, Chicago, IL 60612, USA. E-mail:
gstebbin@rush.edu
Abstract: Structural magnetic resonance imaging (MRI) studies of Alzheimer's
disease and mild cognitive impairment (MCI) have focused on the hippocampus and
entorhinal cortex; gray matter structures in the medial temporal lobe. Few
studies have investigated the integrity of white matter in patients with AD or
MCI. Diffusion tensor imaging (DTI) is a MRI technique that allows for the
interrogation of the microstructural integrity of white matter. Based on
increases in translational diffusion (mean diffusivity: MD) and decreases
directional diffusion (fractional anisotropy: FA) damage to white matter can be
assessed. Studies have identified regions of increased MD and decreased FA in
patients with AD and MCI in all lobes of the brain, as well as medial temporal
lobe structures including the hippocampus, entorhinal cortex and
parahippocampal white matter. The pattern of white matter integrity disruption
tends to follow an anterior to posterior gradient with greater damage noted in
posterior regions in AD and MCI. Recent studies have exploited inter-voxel
directional similarities to develop models of white matter pathways, and have
used these models to assess the integrity of inter-cerebral connections.
Particular focus has been applied to the parahippocampal white matter
(including the perforant path) and the posterior cingulum. Although many
studies have found DTI indicators of impaired white matter in AD and MCI, other
studies have failed to detect any differences in MD or FA between the groups,
demonstrating the need for large replicative studies. DTI is an evolving
technique and advances in its application ought to provide new insights into AD
and MCI.
Keywords: Dementia, fractional anisotropy, mean diffusivity, perforant path, tractography, entorhinal cortex, magnetic resonance imaging, hippocampus, memory, medial temporal lobe
