Medspec system

A 4T Bruker MedSpec system with Siemens Trio console was used for acquiring MR images (Siemens, Erlangen, Germany). A 3D sagittal magnetization prepared rapid gradient echo sequence was used to acquire T1 data (TR/TE/TI = 2300/3/950 ms, 1 × 1 × 1 mm³), and a 2D axial turbo-spin echo sequence acquired T2 data (TR/TE = 8400/70 ms, 0.9 × 0.9 × 3 mm³). A dual spin echo planar imaging sequence was used to acquire 40 3-mm-thick interleaved slices (no gap) of the diffusion-weighted data (TR/TE = 6000/77 ms, 2 × 2 mm² in-plane), using six diffusion-encoding directions at b = 800 s/mm² and one at b = 0 s/mm². To reduce geometrical distortions, twofold parallel imaging acceleration was applied. Four scans were averaged after acquisition to boost signal-to-noise. Further details of data acquisition have been reported (Kuceyeski et al., 2013 (link); Zou et al., 2017 (link)).

The 4T MR data were acquired on a Bruker MedSpec system; 3D T1-weighted images were obtained with Magnetization Prepared Rapid Gradient imaging (MPR), and 3D T2-weighted images via turbo spin-echo. The 1.5T MRI data were acquired on a Siemens Vision system; MPR and T2-weighted double spin echo images were acquired. The 4T structural images were segmented into GM, WM and cerebrospinal fluid (CSF) using the Expectation Maximization Segmentation (EMS) method (32 (link)) and co-aligned with the SVS volumes of interest for determination of their tissue contribution (i.e., GM, WM, CSF) (33 (link)). The 1.5T structural images were also segmented into total brain GM, WM, and CSF via EMS. Subsequently, volumes for the four major lobes and subcortical regions were calculated and co-registered to the EMS segmentation to obtain GM, WM, and CSF fractions for the preceding regions (34 ). Finally the segmented 1.5T structural images were co-aligned with SI metabolite maps for anatomical localization (e.g., frontal WM) and determination of tissue contributions (i.e., GM, WM, CSF) in the corresponding SI voxels (23 (link), 35 (link)).

Magnetic resonance imaging (MRI) data were acquired on a 4 Tesla (4T) Bruker MedSpec system; 3D T1-weighted images were obtained with Magnetization Prepared Rapid Gradient (MPR) imaging, and 3D T2-weighted images via turbo spin-echo [see for (Durazzo et al., 2018 (link)) full MRI acquisition details]. The 4T structural images were segmented into grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF) via the Expectation Maximization Segmentation (EMS) method (Van Leemput et al., 1999 (link)) and co-aligned with the SVS volumes of interest for determination of their tissue contribution (i.e., GM, WM, CSF) (Mon et al., 2012 (link); Studholme et al., 2001 ).