Cholesterol of myelin is the determinant of gray‐white contrast in MRI of brain

The relative brightness of adult white matter in T 1 ‐weighted MRI arises from myelin, but the mechanisms responsible remain to be clarified. Koenig et al. [Magn. Reson. Med. 14 , 482 (1990)] conjectured that the cholesterol of myelin (∼ 30% of its lipid) was responsible. We present 1/ T 1 and magnetization transfer contrast imaging data [Wolff and Balaban, Magn. Reson. Med. 10 , 135 (1989)] on a model system— 50% lipid—50% water by weight, with the lipid one‐half phosphatidyl cholinc (PC) and one‐half cholesterol—and a control in which the lipid is all PC. The differences between the model and control samples mimic the myelin contribution to white matter in both experiments. © 1991 Academic Press, Inc.