Signa hdx 1.5t scanner

All 15 hospitals participating in this study followed the same recruitment procedure and the same MR protocols (either Siemens system or GE system). Three-dimensional high-resolution T1-weighted anatomical images were acquired by using an 8-channel phased array head coil. Scanning was performed on a 1.5 Tesla MRI system (Siemens Medical System, Erlanger, Germany) by using a T1 weighted 3D MPRAGE sequence (TR/TE = 2000/4ms, matrix = 512 × 512, 15° flip angle, slice thickness = 1mm, 192 sagittal slices), or a GE Signa HDx 1.5T scanner (Fairfield, US) by using a Spoiled Gradient Recalled Echo (SPGR) sequence (TR/TE = 2000/4 ms, matrix = 256 × 256, 15° flip angle, slice thickness = 1 mm, 146 sagittal slices). Foam padding and headphones were used to limit head motion and reduce scanning noise. The quality of each brain volume has been ensured to be in good condition and without observable brain abnormality by an experienced radiologist.

Imaging data were acquired on a single GE Signa HDx 1.5T scanner (GE Medical Systems, Milwaukee WI) equipped with an eight-channel phased array coil. Clinical imaging sequences included pre- and postcontrast T1 spin echo (TR/TE = 450/13 ms, FOV = 220 × 220 mm, matrix = 256 × 192, thickness = 3 mm), T2-fast spin echo (T2-TSE; TR/TE = 3400/95 ms, FOV = 220 × 220 mm, matrix = 256 × 192, slice thickness = 3 mm), and fluid attenuated inversion recovery (FLAIR; TR/TE/TI = 10,000/140/2200 ms, FOV = 220 × 220 mm, matrix = 256 × 192, thickness = 3 mm). Precontrast whole-brain DTI datasets were acquired using a dual spin-echo preparation period and single shot spin-echo echo planar imaging (EPI) sequence (TR/TE = 17.6/89.3 ms, FOV = 240 × 240 mm, matrix = 96 × 96, thickness = 2.5 mm, no gap, 64 slices). Diffusion gradient encoding was applied in 60 noncollinear directions with maximum b-value = 1100 s/mm² and in 10 noncollinear directions with b-value = 300 s/mm² and b-value = 0 s/mm² (80 imaging volumes total).

All MRI examinations were performed on a GE Signa HDx 1.5T scanner (GE Healthcare, Milwaukee, Wisconsin, USA). ³He was polarized to approximately 25% using a commercial spin‐exchange optical pumping polarizer (GE Healthcare, Amersham, United Kingdom). ¹²⁹Xe (comprising approximately 86% of the xenon mixture) was polarized to approximately 25% using a custom‐built spin‐exchange optical pumping polarizer 19. For study 1, a flexible transmit/receive vest coil (CMRS, Brookfield, Wisconsin, USA) tuned to the ³He Larmor frequency (48.62 MHz) was used. For study 2, a custom‐built flexible dual‐tuned transmit‐receive coil tuned to both ³He and ¹²⁹Xe Larmor frequencies (48.62 and 17.65 MHz) 23 was used, allowing a direct comparison of quantitative ventilation maps from the two nuclei without the need for position changes between scans or image registration techniques. During MBW‐I, gas flow at the mouth was recorded using a RSS 100HR pneumotachograph (Hans Rudolph, Shawnee, Kansas, USA).