As noted earlier, brain MR imaging was performed in all subjects as a result of their participation in the CHS. The standardized CHS brain MR imaging acquisition protocol has been previously described.34 Magnetic resonance imaging was performed on either a 1.5-T scanner (General Electric, Milwaukee, Wis) (n=248) or a 0.35-T scanner (Toshiba) (n=82) at 1 of 2 CHS field centers (Pittsburgh and Hagerstown, respectively). Head position was oriented in the scanner and was stabilized during the scanning procedure by the use of Velcro straps and foam head supports. To establish slice orientation, the first scanning sequence consisted of a T1-weighted sagittal series (repetition time [TR], 500 milliseconds; echo time [TE], 20 milliseconds; thickness, 5 mm; gap, 0 mm; and matrix, 128×256) centered at the midline to define the anterior commissure–posterior commissure (AC/PC) line. Then a second series of proton-density (TR, 3000 milliseconds; TE, 30 milliseconds; flow compensated) and T2-weighted (TR, 3000 milliseconds; TE, 100 milliseconds; flow compensated) images was obtained (thickness, 5 mm; gap, 0 mm; matrix, 256×192; number of excitations, one-half [1 on the 0.35-T scanner]), oriented parallel to the AC/PC line, and extending from the vertex to the skull base. A third series consisting of T1-weighted (TR, 500 milliseconds; TE, 20 milliseconds) axial images was then obtained (thickness, 5 mm; gap, 0 mm; matrix, 256×192; number of excitations, 1), oriented parallel to the AC/PC line, and extending from vertex to skull base. Images were stored on 9-track magnetic tape.