T1-weighted and T2-weighted MRI acquisition protocols (Glasser and Van Essen 2011; Glasser et al. 2013; Glasser et al. 2014) lays the foundation for repurposing existing MRI data to estimate the temporal order of normal regional cortical development throughout adolescence to maturity (Casey et al. 2000; Stiles and Jernigan 2010). The repurposing is possible as the lipids composing about 70% of myelin are a dominant source of T1-weighted and T2-weighted MRI contrasts in brain tissue (Leuze et al. 2017). A postmortem study (Miller et al. 2012) has shown that the age-dependent slope of this unitless metric is specific to individual regions.
