Fig. 2

Segmentation of the cerebellum on MR images. The cerebellum was defined as the area lateral to the line connecting the anterior lobe of the cerebellum (I segment) and cerebellar flocculus (X segment) (a). Using DICOM data from cranial MRI T1 sagittal sections, the cerebellum was traced freehand on each cerebellum MRI sagittal section slice (b). Then, on the central slice, the fourth ventricle and surrounding cerebellar tissue were selected, and the cerebellum was automatically extracted. The cerebellar volume was determined by linear interpolation from the automatically extracted cerebellar tissue area and slice thickness. The anteroposterior diameter of the cranium (the distance between two points, A and P, at which the skull and the anterior commissure-posterior commissure line intersect) was used for the cerebellar volume correction (c). The posterior cranial fossa volume was determined by five anatomical landmarks (A: the upper tentorial end, B: infundibular recess, C: basilar impression, D: posterior pole of the hard palate, E: internal occipital protuberance) and used for additional cerebellar volume correction (d)