Eight channel phase array head coil

Participants were imaged in a 3 T General Electric Excite MR system with an eight-channel phase-array head coil (General Electric Medical Systems, USA). A scout scan ensured good head placement and whole-brain coverage. High angular resolution diffusion images (Frank, 2001 (link)) were collected along 61 non-collinear directions determined by the electrostatic repulsion model which minimizes bias in measurements by sampling with approximately uniform distribution on a sphere (Jones et al. 1999 (link)), in addition to a reference image with no diffusion weighting (b=0). The diffusion encoding scheme consisted of a single-shot dual spin echo excitation optimized for minimum echo time (TE) and reduction of eddy current artifacts (Reese et al. 2003 (link)). The following sequence parameters were applied: TE=93 ms, repetition time (TR)=10900 ms, field of view=240 mm, matrix=128×128, 34 contiguous slices, 3 mm slice thickness, b-value=1500s/mm², one average. Two field maps were collected for un-warping to correct for signal loss and geometric distortion due to B0 field inhomogeneities (Jezzard & Balaban, 1995 (link); Andersson & Skare, 2002 (link)). Total scan time including field maps was 16 min 2 s.

High-resolution anatomical and functional images were collected at the University of California at San Diego Center for Functional MRI on a 3-Tesla CXK4 short bore Excite-2 MR system (General Electric, Milwaukee, WI) with an eight-channel phase-array head coil. Participants were positioned on the scanner table, and the head was stabilized within the head coil using foam cushions to help minimize movement (NoMoCo, La Jolla, CA). Scan sessions involved a 10-s scout scan to assure good head placement and slice selection covering the whole brain followed by a high-resolution T1-weighted sequence using a sagittally acquired spoiled gradient recalled sequence (field of view = 24 cm, 256 × 256 × 192 matrix, 0.94 × 0.94 1 mm voxels, 176 slices, repetition time = 20 ms, echo time = 4.8 ms; flip angle 12°, acquisition time = 7:26 min).

Magnetic resonance imaging (MRI) was obtained from all participants at the baseline year (age 12–14 years) and at follow-ups; the present analyses focus on imaging from the baseline time point only. All scans were acquired on a single 3.0 T CXK4 short bore Excite-2 magnetic resonance system (General Electric, Milwaukee, WI) with an eight-channel phase array head coil at the UCSD Center for Functional MRI. Subjects were instructed to remain motionless while a high-resolution T1-weight anatomical spoil gradient recall (SPGR) scan was obtained (TE/TR = min full, field of view = 24 cm, resolution = 1 mm³, 170 continuous slices). For the present analyses, structural MRIs were acquired on a single occasion at baseline. Cortical thickness, area, and volume estimates were obtained in the same manner as previously published by our laboratory (Jacobus et al. 2014 (link), 2015 (link)). FreeSurfer (version 5.1, surfer.nmr.mgh.harvard.edu) was used for cortical surface reconstruction and to obtain cortical thickness estimates (Fischl et al. 1999 (link); Dale et al. 1999 (link)). The cross-sectioning process, cortical thickness calculation, and parcellation procedure have previously been described in detail (Jacobus et al. 2015 (link)). The Desikan-Killiany atlas was used for generating parcellation units.