1.5 t signa advantage system

MRI scans were acquired as described previously (Parsey et al., 2006 (link)). Briefly, a sagittal scout localizer scan was performed on a GE 1.5 T Signa Advantage system, followed by a transaxial T1 weighted sequence (1.5 mm slice thickness) in a coronal plane orthogonal to the AC-PC plane, over the whole brain. Scan parameters of the 3-dimensional Spoiled Gradient Recalled Acquisition in the Steady State (SPGR) sequence were as follows: TR 34 msec, TE 5 msec, flip angle 45°, no gap, 124 slices, field of view 22 × 16 cm, 256 × 192 matrix, reformatted to 256 × 256 (yielding a voxel size 1.5 mm × 0.9 mm × 0.9 mm), time of acquisition 11 min.
Coronal MRI images were cropped to remove non-brain material, utilizing the Exbrain v.2 utility (Lemieux et al., 2003 (link)). In some cases, the Brain Extraction Tool (BET) v1.2 of the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) (Smith, 2002 (link)) was used, followed by manual removal of any imaged non-brain matter.

PET scans were acquired using a second-generation High Resolution Research Tomograph scanner (HRRT, Siemens Healthcare, Knoxville, TN), an LSO-based, dedicated brain PET scanner with 2.5 mm resolution. The 90 min list mode data were binned into 30 frames (four 15 s, four 30 s, three 1 min, two 2 min, five 4 min, and twelve 5 min frames). The data were then reconstructed using the iterative ordered subset expectation maximization (OS-EM) algorithm (with 6 iterations and 16 subsets), with correction for radioactive decay, dead time, attenuation, scatter and randoms (Rahmim et al. 2004 (link)). The attenuation maps were generated from 6 min transmission scans performed with a ¹³⁷Cs point source prior to the emission scans. The reconstructed image space consisted of cubic voxels, each 1.22 mm³ in size, and spanning dimensions of 31 cm×31 cm (transaxially) and 25 cm (axially).
All subjects also underwent brain magnetic resonance imaging (MRI) to facilitate anatomical delineation of regions of interest (ROIs) on brain PET images after PET-MRI co-registration (detailed below). MRI T1-weighted images were obtained on either a 1.5 T Signa Advantage system (GE Medical Systems, Waukesha, WI) as previously described (Endres et al. 2009 ) or on a Phillips Achieva 3 T scanner (Andover, MA) with a 32-channel head coil to obtain a 1×1× 1 mm 3D MP-RAGE sequence.