3t discovery 750 scanner

Images were acquired using a 3T Discovery 750 scanner from General Electric. Functional T2*-weighted images were obtained as a single-shot gradient echoplanar imaging sequence used for BOLD contrast imaging (repetition time: 2000 ms, acquiring 37 slices; echo time: 30 ms; flip angle: 80°; field of view: 25 × 25 cm; 96 × 96 voxels zero-filled to 128 × 128 voxels; and 3.9-mm slice thickness). Ten dummy scans were automatically collected and discarded prior to image acquisition to eliminate signals arising from progressive saturation. Anatomical T1-weighted images were obtained with a Fast SPGR sequence (repetition time: 8.2 ms; echo time: 3.2 ms; 25 × 25 cm field of view; 512 × 512 voxels; 1-mm slice thickness). After acquisition, the DICOM images were converted to NIfTI format.

Scanning was performed exclusively on 3 T MRIs across five imaging centers as follows: Siemens Verio (Pittsburgh, PA), Siemens Trio (Charleston, SC and Salt Lake City, UT), Siemens Skyra (San Francisco, CA), and a GE 3 T Discovery 750 scanner (Palo Alto, CA). All Siemens sites used a 12-channel head coil with the exception of San Francisco which used a 32-channel head coil, and the GE site used an 8-channel head coil. High-resolution structural MRI (T1) of approximately 1mm³ in-plane resolution was collected using the protocols from the Alzheimer’s Disease Neuroimaging Initiative (http://adni.loni.ucla.edu). The echoplanar fMRI pulse sequences were adapted from the functional biomedical informatics research network (fBIRN; Brown et al., 2011 ; Greve et al., 2011 ). Functional MRI scans were collected in an axial plane using an echoplanar sequence (TR 2 s, TE 30 ms, 77-degree flip angle, image resolution 3.44 × 3.44 × 3.5 mm, 30 4-mm slices) of eight minutes duration (240 repetitions). Seven participants completed six-minute runs (180 repetitions) prior to the decision to lengthen the sequence to improve data robustness. Before commencing data collection an fBIRN (Keator et al., 2016 ) phantom and a traveling subject were scanned and cross site image quality was evaluated by our lead MR physicist.