Human cortical asymmetries determined with 3D MR technology

A method is described for obtaining clear 3D magnetic resonance (MR) images of the cortical surface of the brain in living human subjects. By combining volume composite and depth encoded images, we have obtained surface coordinate data that resulted in highly repeatable measurements of sulcal lengths and cortical surface areas in eight normal adult volunteers. Sulcal lengths were determined for specific parts of the Sylvian fissure, central sulcus and frontal operculum. Additionally, angles were computed between the anterior and posterior limbs of the pars triangularis and the ascending and horizontal limbs of the posterior Sylvian fissure. The cortical surface areas enclosed by these limbs were also computed. Finally, thirteen non-metric cortical features (e.g., petalias) were scored from the 3D MR images. All measurements were compared in right and left hemispheres. In addition to corroborating cortical asymmetries reported in the literature, we observed previously unrecognized directional asymmetries in the length of the anterior limb of the pars triangularis, length of the ascending limb of the posterior Sylvian fissure, and position of the lateral end of the central sulcus. We attribute the finding of three new directional asymmetries for the human cortex, as well as the high repeatability of our measurements, to the sensitivity and accuracy of the 3D MR imaging technology that has recently become available.