Landmark-based separation of the cerebellar peduncles from the cerebellar white matter and the brainstem. On the mid-sagittal slice (slice 46/90 in this subject), perpendicular lines are drawn at a 90 degree angle to bi-commissural line at the AC and PC (arrows) and through the posterior border of the inferior colliculus (arrowhead). These lines are superimposed on all sagittal slices and the latter perpendicular line is used to differentiate the cerebellar peduncles from the brainstem. AC, anterior commissure; PC, posterior comminissure.