DTI measures in crossing-fibre areas: Increased diffusion anisotropy reveals early white matter alteration in MCI and mild Alzheimer's disease

►Mode of anisotropy detects the only differences between MCI and healthy elderly ►Increase of anisotropy (mode, FA) is found in crossing-fibre regions in MCI and AD. ►Increase of anisotropy is due to selective degeneration of secondary fibre (SLF). ►Tractography shows the selective degeneration of secondary fibre in crossing fibres.