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Mapping Adolescent Brain Change 71Figure 3-8 Cortical thickness maps: A, original T1-weighted image for one representativesubject; B, tissue segmented image; C, gray matter thickness image where thicknessis progressively coded in mm from inner to outer layers of cortex using the 3-D EikonalFire equation. Note the images were resampled to a voxel size of 0.33 mm cubed, so thethickness measures are at a submillimeter level of precision, according to the color bar onthe right (mm). Figures A through C are sliced at the same level in all three image volumesfrom the same subject. Shown in D is an in vivo average cortical thickness map createdfrom our 45 subjects at their first scan. The brain surface is color coded according to thecolor bar, where thickness is shown in mm. Our average thickness map can be comparedto an adapted version of the 1929 cortical thickness map of von Economo (1929; E). Colorcoding has been applied over his original stippling pattern, respecting the boundaries ofhis original work, to highlight the similarities between the two maps. See color insert.(Sowell et al., 2004a.)71