Functional relevance and diagnostic utility of ROI-based and voxel-based diffusion-tensor imaging analyses in mild cognitive impairment

Diffusion-Tensor-Imaging (DTI) measures the translational motion of water molecules. Several studies have shown the potential of this new structural imaging technique to quantify functionally relevant alterations of white matter integrity in different neurological and psychiatric syndromes and diseases. We investigated patients with amnestic Mild Cognitive Impairment (MCI), Alzheimer's Dementia (AD) and healthy age-matched controls using DTI and hippocampus volumetry (1,2,3). ROI-based analysis: Cross-sectiolally MCI patients showed significant elevations of mean diffusivity (MD) in brain regions that are known to be early involved in AD (esp. hippocampus, temporal and parietal lobes). MMSE and delayed verbal recall performance were stronger associated with MD increases than with hippocampal volume reductions in MCI patients. Disturbances of posterior cingulate bundles correlated with delayed verbal recall performance in MCI and AD. In a 19 month follow-up assessment of MCI patients elevated MD in left hippocampal regions was a better predictor for conversion to dementia than reduced hippocampal volumes. Voxel-based analysis: MCI patients showed elevated MD values in posterior cingulate compared to controls. DTI seems to be a sensitive tool to detect functional relevant ultrastructural changes of brain tissue indicating neurodegenerative processes in MCI subjects and could be useful for predicting conversion to dementia this patient group. References: (1) Fellgiebel A et al. 2004,Dementia (2) Fellgiebel A et al. 2005, Neurobiology of Aging (3) Müller MJ et al. 2005,Neuroimage