Use of diffusion tensor imaging for evaluating changes in the microstructural integrity of white matter over 3 years in patients with amnesic-type mild cognitive impairment converting to Alzheimer's disease

Abstract

Background and purpose: Patients with amnestic mild cognitive impairment (aMCI) are at risk of developing Alzheimer's disease (AD). It is therefore important to identify biomarkers of conversion to AD. This study examined whether the integrity of white matter can predict this conversion.

Methods: Magnetic resonance imaging (MRI), diffusion tensor imaging (DTI) and neuropsychological features of aMCI subjects (n = 41) were compared with normal controls (n = 20) for 12-36 months.

Results: Compared to controls, 22 aMCI subjects had lower fractional anisotropy (FA) values in the cingulate fasciculus (CF) at baseline, and 19 of those converted to AD during follow-up. Only two of the other 19 aMCI patients converted to AD. Compared to baseline, AD converters showed lower FA values in the anterior frontal lobe, temporal lobe, hippocampus, inferior fronto-occipital fascicles, corpus callosum genu and CF, and higher apparent diffusion coefficient values in the temporal lobe and hippocampus.

Conclusions: Those aMCI subjects with lower than normal FA values in the CF were more likely to convert to AD. The connectivity of the hippocampus and cingulate bundles may be affected in the early stage of AD. Impairment of white matter and fiber bundles was more severe at the AD stage than the aMCI stage.

Keywords: Alzheimer's disease; apparent diffusion coefficient; diffusion tensor imaging; fractional anisotropy; mild cognitive impairment.