MRI scans were obtained using a Siemens Sonata 1.5 Tesla scanner (Siemens, AG, Erlangen, Germany). Head positioning was standardized using canthomeatal landmarks. Anatomical images were acquired using a 3D MP-RAGE sequence (repetition time, 24 msec; echo time, 2.96 msec; 45° flip angle; 256 × 192 matrix; field of view, 30 cm; 2 excitations, slice thickness 1.2 mm; 124 contiguous slices encoded for sagittal slice reconstruction with voxel dimensions of 1.17 mm × 1.17 mm × 1.2 mm).
We corrected large-scale variations in image intensity using a validated algorithm developed at the Montreal Neurological Institute (Sled et al., 1998 (link)). We removed extracerebral tissues using an automated tool for extracting the brain (Shattuck and Leahy, 2002 (link)). Connecting dura was then removed manually on each slice in the sagittal view and checked in the orthogonal views. The brainstem was transected at the pontomedullary junction. We measured whole brain volume (WBV) for use as a covariate to control for global scaling effects in statistical analyses of conventional volumes. This measure included not only gray and white matter but also cerebrospinal fluid within the ventricles and cortical sulci to ensure the exclusion of any possible confound of age-related effects of tissue atrophy with this general measure of body scaling (Skullerud, 1985 (link)).
We corrected large-scale variations in image intensity using a validated algorithm developed at the Montreal Neurological Institute (Sled et al., 1998 (link)). We removed extracerebral tissues using an automated tool for extracting the brain (Shattuck and Leahy, 2002 (link)). Connecting dura was then removed manually on each slice in the sagittal view and checked in the orthogonal views. The brainstem was transected at the pontomedullary junction. We measured whole brain volume (WBV) for use as a covariate to control for global scaling effects in statistical analyses of conventional volumes. This measure included not only gray and white matter but also cerebrospinal fluid within the ventricles and cortical sulci to ensure the exclusion of any possible confound of age-related effects of tissue atrophy with this general measure of body scaling (Skullerud, 1985 (link)).
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