Our analysis was based on estimating cortical myelin content from T1-weighted and T2-weighted MRIs taken from commonly acquired, multimodal MRI data results. This estimation is based on the observation that T1-weighted and T2-weighted MRIs show inversed MRI intensity relations for gray and white matter (Glasser and Van Essen 2011; Sigalovsky et al. 2006; Yoshiura et al. 2000), thus indicating that a ratio between T1-weighted and T2-weighted MRIs can boost the myelin contrast while reducing the noise level. The analysis is advantageous over other in vivo studies, which had limited contrasts in lightly myelinated regions due to use of a single modality (Rowley et al. 2017), included the raw myelin content in analysis that potentially affected by the residual bias (Shafee et al. 2015), or had small samples to address questions about adolescent development (Grydeland et al. 2013).
