Diffusion abnormality in posterior cingulate fiber tracts in Alzheimer's disease: tract-specific analysis

Purpose. The aim of this study was to determine diffusion abnormalities in the posterior cingulate fiber tracts (PCFTs) in patients with Alzheimer's disease (AD) by diffusion tensor tractography (DTT). Materials and methods. We studied 23 AD patients and 18 age-matched normal controls who underwent magnetic resonance imaging using diffusion tensor imaging (DTI). DTT of PCFTs was generated from DTI. Mean diffusivity (MD) and fractional anisotropy (FA) were measured in co-registered voxels along with DTT of PCFTs. Student's t-test was used to compare results between the AD patients and normal controls. Results. The MD in PCFTs was significantly higher in AD patients than in normal controls (P = 0.019). The FA in PCFTs was significantly lower in AD patients than in normal controls (P = 0.007). Conclusion. The abnormal MD increase and FA decrease, which is considered to indicate a net loss of barriers that restrict water molecular motion and tissue anisotropy of white matter, is consistent with neuropathological data that demonstrate partial loss of myelin, axons, and oligodendrial cells in white matter of AD brains. Our results suggest that MD and FA reflect progression of AD-related histopathological changes in the PCFTs and may represent a useful biological index for monitoring AD.