Figure 3.

Estimation of gyrification. The traditional gyrification index can be calculated as the ratio between the outer and inner contour of the cortex in coronal slices (upper row). This allows to approximate the global degree of gyrification or convolution. More recently developed gyrification measures extend this idea to 3D, e.g. by replacing the ratio of outer and inner contours by the ratio of outer and inner surface area (which allows the local estimation of gyrification, bottom row), or by using other measures of contour, shape or curvature.