Harmonized T1-Weighted MRI Acquisition Protocols

MRI acquisition was performed in every centre to acquire T₁-weighted images. The Montreal cohort underwent T₁-weighted imaging with a 3 T Siemens TIM Trio scanner with a 12-channel head coil, magnetization-prepared rapid acquisition gradient echo (MPRAGE) sequence with the following parameters: repetition time (TR): 2300 ms, echo time (TE): 2.91 ms, flip angle: 9°, and voxel size: 1 mm³ isotropic. The Paris cohort underwent T₁-weighted imaging with a 3 T Siemens TIM Trio scanner with a 12-channel head coil, MPRAGE sequence: TR: 2300 ms, TE: 4.18 ms, inversion time (TI): 900 ms, flip angle: 9°, and voxel size: 1 mm³ isotropic; or a 3 T PRISMA Fit scanner with a 64-channel head coil, MP2RAGE sequence: TR: 5000 ms, TE: 2.98 ms, TI: 700 and 2500 ms, flip angle: 4° and 5°, GRAPPA: 3, and voxel size: 1 mm³ isotropic. The Sydney cohort was imaged with a GE Discovery MR750 3 T scanner with an 8-channel head coil, BRAVO sequence: TR: 5800 ms, TE: 2.6 ms, flip angle: 12°, and voxel size: 1 mm³ isotropic. The Aarhus cohort was imaged with a 3 T Siemens MAGNETOM Skyra scanner with a 32-channel head coil, MPRAGE sequence: TR: 2420 ms, TE: 3.7 ms, TI: 960 ms, flip angle: 9°, and voxel size: 1 mm³ isotropic. The T₁-weighted images from the Parkinson’s Progression Markers Initiative cohort are described elsewhere.^{24 (link)}