<qa>  What is the MRI study optional?3. to assess the effect of Memantine in clinical course new relapses, relapse rate, patients free of relapses, disability EDSS, MSFC, MSSS and MRI parameters active lesions: new T2 lesions, change in T2 lesion load, new gadolinium enhancing lesions and global and regional atrophy in the response to Memantine. MRI study is optional. 