The whole brain T1w/T2w ratio technique enables in vivo quantitative myelin mapping using clinically acquired MRI sequences, which is potentially useful when investigating developmental myelination trajectories. Post-mortem infant myelin-staining studies provide useful references. This study characterizes myelination trajectories of 27 subcortical brain regions in typically developing 4.5 months to 1 year-old children using the T1w/T2w ratio technique and compared the patterns with those demonstrated by an autopsy infant myelin-staining study. Similar myelination trajectory patterns were observed in the structures that commenced myelination before birth. This highlights the T1w/T2w ratio as potential myelin imaging biomarker for these structures during this period.