High-resolution morphometric brain MR data were collected using one of two imaging protocols. For subjects enrolled into the study before calendar year 2000, MRI brain scans were acquired on a 1.5-Tesla GE (General Electric Medical Systems, Milwaukee, Wisconsin) Signa MR scanner. In this earlier imaging protocol (termed ‘MR5’), three-dimensional T1-weighted images were acquired in the coronal plane using a spoiled GRASS sequence (SPGR). The parameters were: echo time (TE)=5ms, repetition time (TR)=24ms, numbers of excitations (NEX)=2, rotation angle=40 degrees, field of view (FOV)=26×19×18.6 cm, and a matrix of 256×192×124. Two-dimensional PD and T2 sequences were acquired as follows: 3.0 or 4.0 mm thick coronal slices, TR=3000ms, TE=36ms (for PD) and 96ms (for T2), NEX=1, FOV=26×26 cm, matrix=256×192. For subjects recruited in 2000 or later, we used a 1.5-Tesla Siemens Avanto scanner. In this more recent imaging protocol (termed ‘MR6’), the T1 sequence was obtained as a 3D volume in the coronal plane using a FLASH sequence with the following parameters: TE=6 ms, TR=20 ms, flip angle=30°, FOV=260×260×192 mm, matrix = 256×256×124, NEX=2, slice thickness 3 mm, ETL=5. The MR6 T2
