9 microns spheres underestimated blood flows in all regions studied : by 13-19 percent in the cerebral cortex , midbrain , brain stem and cerebellum , by 34-42 percent in the cortical white matter , corpus callosum and cervical cord , and by 64-81 percent in pituitary gland and choroid plexus .
C0025462
midbrain
C0006121
brain stem