MRI data were acquired on a 3 T Philips Achieva XT MRI scanner (Amsterdam, the Netherlands) using a 32‐channel dStream head coil across four sessions. Single‐shot, 2D gradient echo‐planar images (EPI) were acquired in 33 slices oriented perpendicular to the floor of the fourth ventricle and to the longitudinal extent of the LC (Keren, Lozar, Harris, Morgan, & Eckert, 2009 (link)): 2 × 2 mm in‐plane resolution, 3 mm slice thickness (no gaps), FOV 192 × 192 × 99 mm. TR = 2 s; echo time [TE] = 27.62 ms; flip angle = 76.1°; SENSE acceleration factor = 3.0; bandwidth = 2,213 Hz/pixel. A structural T1‐weighted scan was acquired for anatomical co‐registration (voxel size: 1 × 1 × 1 mm3, TR = 8.13 ms, TE = 3.7 ms, flip angle = 8°). A B0‐field map was acquired for unwarping (voxel size: 2 × 2 × 2 mm3, TR = 10.85 ms, TE = 3.03, flip angle = 8°). Slices were acquired sequentially in the ascending (foot to head) direction.
We chose anisotropic voxels and the above orientation of the imaging volume for EPI to optimize spatial sampling for the LC (for details, see de Gee et al., 2017 (link)). The LC is an elongated structure with small diameter (a few millimeters) and comparably large longitudinal extent (~15 mm) along the floor of the fourth ventricle (Betts et al., 2019 (link)). The rationale was that the LC was the smallest brainstem nucleus to be assessed here.
We chose anisotropic voxels and the above orientation of the imaging volume for EPI to optimize spatial sampling for the LC (for details, see de Gee et al., 2017 (link)). The LC is an elongated structure with small diameter (a few millimeters) and comparably large longitudinal extent (~15 mm) along the floor of the fourth ventricle (Betts et al., 2019 (link)). The rationale was that the LC was the smallest brainstem nucleus to be assessed here.
