Fig. 1: Workflow of SyMRI data processing.

This figure illustrates two main processing streams: whole-brain volumetric analysis (left panel) and subcortical myelin content extraction (right panel). For volumetric analysis, raw SyMRI data were processed using Synthetic MR software to automatically segment brain tissues and compute structural volumes, including gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), brain parenchymal volume (BPV), and intracranial volume (ICV), along with relevant volumetric ratios. For subcortical analysis, 3D T1-weighted anatomical images were rigidly registered to the T1 mapping and then normalized to Montreal Neurological Institute (MNI) space using Advanced Normalization Tools (ANTs). The PD25 subcortical atlas was subsequently transformed from MNI space back to each participant’s native space and aligned with the corresponding MyC maps. Manual inspection was performed to ensure accurate anatomical correspondence. Myelin content (MyC) values were then extracted from 16 subcortical nuclei, including the substantia nigra (SN), red nucleus (RN), caudate nucleus, putamen, internal and external globus pallidus (GPi and GPe), subthalamic nucleus (STN), and thalamus.