7t scanner

Nine healthy volunteers (three women and six men; age = 28 ± 8 years) were recruited for measurements of metabolite concentrations and relaxation times in the frontal cortex. Two of the volunteers were scanned twice. No data were excluded and all collected data were used in the analysis. All volunteers gave informed consent in accordance with procedures approved by our local institutional review board. Experiments were performed on a Siemens 7 T scanner equipped with a 32-channel receiver head coil. T₁-weighted magnetization prepared rapid gradient echo (MPRAGE) images were acquired with TR = 3 s, TE = 3.9 ms, matrix = 256 × 256 × 256, and resolution = 1 × 1 × 1 mm³ to position the MRS voxel and perform tissue segmentation. For each subject, MRS data were collected from two 2 × 2 × 2 cm³ voxels in the frontal cortex. One voxel was placed in the grey matter (GM) dominant region of prefrontal cortex (PFC) and medial pregenual anterior cingulate cortex (pgACC), both of which have been implicated in several brain disorders (23 (link),24 (link)). The other voxel was placed in the white matter (WM) dominant right frontal cortex. B₀ field inhomogeneities were minimized by first- and second-order shimming, achieving mean water linewidth of 11.1 Hz and 13.4 Hz for the voxels in the GM and WM regions, respectively. MRS data acquisition for each voxel lasted < 10 min.

A Siemens 7T scanner equipped with a 32-channel head coil was used in Experiment 2. Functional scans were obtained using a gradient-echo EPI sequence (54 slices, TR/TE = 2000/25ms, slice thickness = 2mm, FOV = 192 mm, flip angle = 50°, image matrix: 96×96, 343 volumes) covering the whole brain. An additional high-resolution anatomical scan was acquired in each participant (MPRAGE; TR/TE/TI=3000/3.88/1500ms, FA = 6°, FOV = 256×256mm, 192 sagittal slices, slice thickness/gap = 1.00/0.50 mm, in-plane resolution = 1×1mm). The stimuli were presented via a video projector (resolution 1024×768 pixel, 60 Hz) that projected from the head-end of the scanner onto a screen. Participants viewed the projection through mirror glasses. The data for subject 6 were acquired in two sessions; those for the other subjects were acquire in a single session.

Imaging data were collected on a Siemens 7T scanner with a Siemens 32-channel surface coil. Each scan session began with a high resolution T1-weighted Magnetization Prepared Rapid Gradient Echo (MPRAGE) sequence (TE = 3.88 msec; TR = 3000 msec; flip angle = 6°; matrix size = 256 X 256; voxel size = 1 mm × 1 mm x 1 mm; 192 axial slices). The functional images were acquired with a single-shot interleaved gradient-recalled echo planar imaging sequence, with slices positioned to cover all of the occipital and temporal lobes (TE = 27 msec; TR = 2000 msec; flip angle = 70°; matrix size = 126 × 126; voxel size = 1.6 mm × 1.6 mm x 1.6 mm; 43 oblique axial slices, no acceleration was used). Supplementary Figure S3B shows the fMRI scan slice coverage overlaid on a representative human brain.