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AJNR - American Journal of Neuroradiology

Published ahead of print on September 28, 2007
doi: 10.3174/ajnr.A0700

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American Journal of Neuroradiology 28:1943-1948, November-December 2007
© 2007 American Society of Neuroradiology

BRAIN

Diffusion Tensor Imaging of Normal-Appearing White Matter in Mild Cognitive Impairment and Early Alzheimer Disease: Preliminary Evidence of Axonal Degeneration in the Temporal Lobe

J. Huang^a,b, R.P. Friedland^c and A.P. Auchus^a,b

^a Department of Neurology, University of Tennessee Health Science Center, Memphis, Tenn
^b Research Services, Veterans Affairs Medical Center, Memphis, Tenn
^c Department of Neurology, Case School of Medicine, Cleveland, Ohio

Please address correspondence to Juebin Huang, MD, PhD, Department of Neurology, University of Tennessee Health Science Center, 855 Monroe Ave, Ste 415, Memphis, TN, 38163; e-mail: jhuang8{at}utmem.edu

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) is a sensitive technique for studying cerebral white matter. We used DTI to characterize microstructural white matter changes and their associations with cognitive dysfunction in Alzheimer disease (AD) and mild cognitive impairment (MCI).

MATERIALS AND METHODS: We studied elderly subjects with mild AD (n = 6), MCI (n = 11), or normal cognition (n = 8). A standardized clinical and neuropsychological evaluation was conducted on each subject. DTI images were acquired, and fractional anisotropy (FA), axial diffusivity (DA), and radial diffusivity (DR) of normal-appearing white matter (NAWM) in frontal, temporal, parietal, and occipital lobes were determined. These diffusion measurements were compared across the 3 groups, and significant differences were further examined for correlations with tests of cognitive function.

RESULTS: Compared with normal controls, AD subjects demonstrated decreased FA and increased DR in the temporal, parietal, and frontal NAWM and decreased DA in temporal NAWM. MCI subjects also showed decreased FA and decreased DA in temporal NAWM, with decreased FA and increased DR in parietal NAWM. Diffusion measurements showed no differences in occipital NAWM. Across all subjects, temporal lobe FA and DR correlated with episodic memory, frontal FA and DR correlated with executive function, and parietal DR significantly correlated with visuospatial ability.

CONCLUSIONS: We found evidence for functionally relevant microstructural changes in the NAWM of patients with AD and MCI. These changes were present in brain regions serving higher cortical functions, but not in regions serving primary functions, and are consistent with a hypothesized loss of axonal processes in the temporal lobe.

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