The purpose of this project is to assess the utility of a new magnetic resonance technique called magnetic resonance elastography (MRE) in the non-invasive diagnosis of normal pressure hydrocephalus. The investigators hypothesize that MRE produces a unique imaging signature for hydrocephalus that distinguishes the disease from the normal (non-hydrocephalic) but atrophied brain, a distinction not possible with conventional MR imaging studies that are presently available.