Magnetic resonance imaging (MRI) is an imaging technique that utilizes strong magnetic fields and radio waves to generate images of tissues in the body. MRI generates high resolution images of brain structure. In healthy aging and Alzheimer’s disease, MRI is used to measure changes in regional brain volume and cortical thickness over time. These measurements allow us to draw inferences about how the brain ages, and particularly to understand how a variety of factors including Aβ and tau may lead to neurodegeneration. Structural brain measures are very closely related to cognitive ability as well. Other types of MRI scans can be used to measure white matter tracts which contain fibers that represent neuron interconnections.