MRI Measurements of T2-Relaxation in a Rat Optic Nerve

Detailed Transverse relaxation time (T2) MRI imaging studies of a rat optic nerve model were performed in order to elucidate the effect of axonal regeneration in an optic nerve after traumatic injury. After rats were subjected to left optic nerve crush, a Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence was used to acquire T2 relaxation decay curves from both the crushed left optic nerve (LOP) and the control right optic nerve (ROP) one week and one month after injury. The LOP and ROP T2 relaxation decay curves were best fit to biexponential functions, which were tentatively assigned to myelin associated water protons and water within or between axonal compartments. The fast T2 relaxation time and the fractional size in LOP one week after injury were significantly less than in ROP, indicating a reduction in myelin associated water and a change in its motional state. One month after injury, no significant differences in the fractional sizes and relaxation times in LOP and ROP were observed, consistent with nerve regeneration and repair of the crush injury. key words: biexponential,T2 relaxation, optic nerve.