Brain Diffusion Changes in Patients Diagnosed with Alzheimer's Disease

Alzheimer's disease is the most common neurodegenerative disease that features mainly memory impairment. The results of several pathologic and radiologic studies suggest that the brain damage in Alzheimer's disease extends well beyond the medial temporal lobes. The recent development of diffusion magnetic resonance imaging allows for measuring the diffusion of water molecules in the brain. The apparent diffusion coefficient represents the diffusion intensity. Molecules inside the neuronal axon have a low probability of crossing the myelin membrane, and thus brain diffusion is usually anisotropic. Diffusion tensor imaging enables measurements of diffusion in multiple directions and the fractional anisotropy in each direction to be calculated for each voxel. These new methods allow researchers to construct brain maps of fiber directions to examine the connectivity of different regions in the brain. Here we review changes in diffusion properties in the brain, such as the apparent diffusion coefficient and fractional anisotropy, observed in patients with Alzheimer's disease.