Hdx scanner

All participants underwent 3D volumetric ¹²⁹Xe‐MRI and ¹H‐MRI in the coronal plane at approximately functional residual capacity (FRC) + bag (for any given participant, the bag volume was titrated based on standing height and ranges from 400 ml to 1 L) or total lung capacity (TLC) with full lung coverage at 1.5 T on a HDx scanner (GE Healthcare, Milwaukee, WI, USA). A full breakdown of gas doses, titrated based on participant standing height, is included in Supplementary Table S1.

All subjects underwent 3D volumetric ³He or ¹²⁹Xe hyperpolarized gas MRI with full lung coverage at 1.5 T on a HDx scanner (GE Healthcare, Milwaukee, WI) using 3D steady-state free precession (SSFP) sequences as previously described^{22 (link)–24 (link)}. Flexible quadrature radiofrequency coils were employed for transmission and reception of MR signals at the Larmor frequencies of ³He and ¹²⁹Xe. In-plane (x–y) resolution of scans for both gases was 4 × 4mm². ¹²⁹Xe scans ranged from 16 to 34 slices with a mean of 23 slices and slice thickness of 10 mm. ³He scans ranged from 34 to 56 slices with a mean of 45 slices and slice thickness of 5 mm.

Twelve healthy subjects (aged 32 ± 6 years, 5 female) were scanned using a 3T GE HDx scanner (Milwaukee, WI, USA) equipped with an 8-channel receive head coil. An eyes-open resting state scan lasting 5.5 min was acquired using a BOLD-weighted gradient-echo echo-planar imaging sequence (TR/TE = 2000/35 ms; FOV = 22.4 cm; 35 slices, slice thickness = 4 mm; resolution = 3.5 × 3.5 × 4.0 mm³, 165 volume acquisitions). These data were collected as part of a larger study (Bright and Murphy, 2013b (link)). A whole-brain high-resolution T1-weighted structural image was acquired (resolution = 1.0 × 1.0 × 1.0 mm³), for the purpose of image registration. Cardiac pulsations were recorded using the scanner finger plethysmograph. Expired gas content was continuously monitored via a nasal cannula, and O₂ and CO₂ data were recorded (AEI Technologies, PA, USA). This study was approved by the Cardiff University School of Psychology Ethics Committee, and all volunteers gave written informed consent.

MR images were acquired using a 3T GE HDx scanner. Gradient-echo echo-planar imaging (EPI) was used to acquire 450 task-free volumes of 38 near-axial slices over a period of 15 min for each session (3 mm thickness, 0.3 mm inter-slice gap, TE = 30 ms, TR = 2000 ms, FA = 75°, in-plane resolution = 3.3 mm, matrix size = 64 × 64, field of view = 21.1 × 21.1 cm). The infusion of ketamine or saline was administered 5 min into the 15 min scan. Additionally, a high-resolution gradient-echo scan was performed resulting in 43 near-axial slices (3 mm thickness, 0.3 mm inter-slice gap, TE = 30 ms, TR = 2000 ms, FA = 90°, in-plane resolution = 3.3 mm, matrix size = 128 × 128, field of view = 24 × 24 cm).

A subset of piglets (n = 14) underwent MRI imaging at approximately PND20 (PND 20.07 ± 0.31). Piglets were sedated with propofol for intubation (0.083–0.166 mL/kg, IV) and maintained under mild anesthesia with 1.5% isoflurane during scanning. MRI scanning including T1-weighted anatomical, diffusion tensor imaging (DTI), and resting-state fMRI (rs-fMRI) were conducted at the Bioimaging Research Center at the University of Georgia utilizing a 3.0 Tesla General Electric (GE) HDx scanner and a quadrature knee coil. Piglets were monitored throughout the scan by a veterinary technician. A 3D fast spoiled gradient echo sequence (repetition time (TR) = 5.5 s, echo time (TE) = 2.1 ms, flip angle (FA) = 9°, field of view (FOV) = 12.8 × 12.8 × 6.4 cm, slice thickness = 1 mm, acquired matrix = 256 × 256 × 112) was used to acquire T1-weighted anatomical data; a spin-echo echo-planar imaging (EPI) sequence (TR = 15.5 s, TE = min-full, FOV = 12.8 × 12.8 × 6.4 cm, acquired matrix = 64 × 64 × 32, and 30 diffusion weighted images using b = 1000 s/mm²) was used for DTI acquisition; and rs-fMRI was acquired by a gradient-echo EPI sequence (TR = 3 s, TE = 30 ms, FA = 80°, FOV = 12.8 × 12.8 × 6.4 cm, acquired matrix = 96 × 96 × 32, a total volume of 300 images).

All scans were performed at the Cardiff University Brain Research Imaging Centre (CUBRIC) on a 3 T General Electric (GE) HDx scanner fitted with an 8‐channel phased array head coil. A 3D T1‐weighted, fast spoiled gradient echo (FSPGR), structural MRI scan was obtained for each participant (TE/TR = 3.0/7 .9 ms; TI = 450 ms; flip angle 20°; data matrix 256 × 192 × 176; field of view 256 × 192 × 176 mm³; acquisition time ~7 min). The FSPGR was used to aid ¹H‐MRS voxel placement during scanning, and also as part of the subsequent fMRI and ¹H‐MRS data analysis.