Essential to the analysis was the harmonization of two large data sets collected in 912 healthy, young male and female participants in the NCANDA and HCP studies. Both the NCANDA and the HCP studies used very similar gradient-echo MPRAGE sequence for acquiring T1-weighted MRIs, which yielded excellent gray and white matter contrasts. Furthermore, data coordination involved use of the same processing steps and normalization of the myelin content across the data sets, which corrected for residual biases and made the mean of the normalized myelin content over the entire cortex similar across subjects. This approach for MRI processing substantially reduced variances in the estimate of myelin content (see Appendix A.4), thereby improving sensitivity to reveal selective differences in regional developmental patterns of myelin content. The processing did not, however, normalize the variance across the two data sets, which was much larger for the HCP data set (see Figure 4), and most likely caused by their discrepancy in T2-weighted MRI acquisition. Critically, the cross-sectional results reported herein were verified with respect to the young adults on the original MRIs provided by
