 The investigators use multimodel MRI to evaluate the extent of blood-brain barrier and white matter fiber tracts destruction , iron deposition and cerebral blood flow of associated regions in multiple sclerosis and neuromyelitis optica spectrum disorders using contrast-enhanced magnetic resonance imaging , quantitative susceptibility mapping, diffusion tension imaging, and arterial spin labeling with post labeling delay of 2.0 seconds. Transfer constant volume , magnetic susceptibility, cerebral blood flow and fractional anisotropyFA value were measured in lesion and normal appearing white matter. 