In the case that MR scans on the 1.5T/3T and 4T MR scanners cannot be coordinated on the same visit day at the McLean Brain Imaging center due to scheduling conflicts, the subject will be offered the opportunity to return to McLean to have the remaining scan on a separate day. Subjects will still be offered $50 for completion of each scan. Also, in the case that the data collected during MR imaging is not usable (due to technical problems with the scanner, excessive noise in the measurement, etc.), the subject may be contacted and offered a repeat MRS scan on a separate date. Subjects will be compensated an additional $100 for completion of such a repeat MRS scan.