4. Magnetic resonance imaging (MRI) MRI is done at baseline, 2 and 4 years of follow-up, using the same MRI scanner. We will evaluate the potential benefits of new MRI protocols for prediction of future AD. MRI will also be used to study the pathogenesis of AD. These new approaches include: 3D-MP RAGE, T2* GRE, DTI/DTT, ASL and MRS.