Assessing and Improving Quantitative Magnetic Resonance Imaging Metrics in Human Subjects

* INCLUSION CRITERIA: In order to be eligible to participate in this study, an individual must meet all of the following criteria: * Stated willingness to comply with all study procedures and availability for the duration of the study * Male or female, aged 18 years of age and older * In good general health as evidenced by medical history * Ability of subject to understand and the willingness to sign a written informed consent document. * Must have had a neurological physical exam as prescribed by NINDS policy. At the time of writing, this is required at least once every 2 years, and record of the exam should be in the medical record. This exam must be done prior to having MRI # 1. If deemed adequate by the Investigators, reports of examination by clinicians who are not Investigators on this study may be used. In addition, subjects must complete the most-recent version of the NMR safety screening form or NIH Radiology and IS MRI safety questionnaire when required at each visit. EXCLUSION CRITERIA: An individual who meets any of the following criteria will be excluded from participation in this study: * Has any metal implant or objects of unknown identity or composition, or if it s known to be non-compatible with MRI, such as pacemakers, medication pumps, aneurysm clips, metallic prosthesis (such as heart valves or cochlear implants), certain orthopedic implants (pins and rods), shrapnel, or small metal fragments in the eye; * Has claustrophobia to a degree that would preclude lying comfortably in the scanner for the duration of the examination; * Cannot lie comfortably for up to 120 minutes; * Has hearing problems which would make it difficult to tolerate scanner noise; * Subjects with tattoos or permanent eye liner; liner; will not be excluded, however, tattoos carry a small risk of heating and burns. Therefore, each tattoo will be considered on a case by case basis, taking into account the age of the tattoo and the location of the tattoo on the subject s body. * Has medical health problems such as pulmonary or airway disease, heart failure, coronary artery disease, which would require physiological monitoring during the scan; * History of any medical condition that could result in an emergency medical situation while undergoing the MRI scan; * For \>7T: Has a ferromagnetic dental crown or a bridge. * Non-English speakers are excluded as it is important that volunteers understand the complex instructions required to undergo an MRI procedure, and there is no direct benefit to participants. * Pregnant women: * a) If a woman is pregnant at the time of enrollment, we will popstpone enrollment until she is no longer pregnant. * Participants will not remain on the study should they have a positive pregnancy test at a study visit.