Identifying micro-anatomical compartments of mammalian optic nerve based on NMR T2-relaxation analysis

We analyzed the differences in NMR transverse-relaxation (T₂) times for various nervous tissues. The unique characteristic of transverse relaxation in different micro-anatomical structures of nerve allows us to establish a relationship between the components of the T₂-spectrum and the micro-anatomical compartments of the nerve. Three different T₂ components have been identified in the frog and rat sciatic and rat optic nerves. Paramagnetic agents were used to demonstrate that optic nerve exhibits three different T₂-relaxation time components. For the frog and rat sciatic nerves, the short-lived component with a T₂ time of 10-20 ms is assumed to be a signal coming from myelin. The intermediate-lived component with a T₂ time of 80-100 ms is believed to originate from the interaxonal water and the long-lived component with a T₂ time of 240-260 ms is thought to be a signal originating from the axoplasm. For frog and rat sciatic nerves an accurate relationship between the components of the T₂ spectrum and the compartments of the micro-anatomical structures of the nerve has been established. However, for the rat optic nerve this relationship has not yet been identified.