Magnetization transfer imaging of the spinal cord and the optic nerve in patients with multiple sclerosis

Magnetization transfer (MT) imaging has been successfully applied to patien ts with multiple sclerosis (MS), showing lesion heterogeneity, subtle chang es in the normal-appearing white matter, and a better correlation with disa bility, in comparison with conventional magnetic resonance imaging. MT imag ing is a fairly simple technique, which allows a quantitative analysis with high spatial resolution to delicate structures like the optic nerve and sp inal cord. In the spinal cord, MT imaging can be applied as a contrast augm entation technique. Using the MT ratio (MTR), two studies have reported a m ild, but significant, reduction in MT ratio in the cervical spinal cord, co mpared with healthy controls. In one study, clinical disability correlated independently of cord atrophy with MTR, which may relate to preliminary fin dings of a correlation between axonal loss and MTR in the spinal cord. In t he optic nerve, two studies reported strongly decreased MTR in affected ner ves, even in the absence of lesions on conventional imaging; unaffected ner ves showed values similar to white matter in the brain. In one study, MTR w as significantly correlated with electrophysiological parameters, but not w ith vision. In conclusion, MT imaging provides a quantifiable parameter tha t can be applied with high spatial resolution to delicate structures, such as the spinal cord and the optic nerve. Further work is needed to correlate MTR measurements with pathology and, most importantly, with the functional status. Such relationships being established, a quantitative technique suc h as MTR could be useful in monitoring disease progression in MS.