Effect of Alemtuzumab on Microglial Activation Positron Emission Tomography (PET) in Multiple Sclerosis

Specific Aims The specific aims of the study are: * Primary Objective: To assess the effect of alemtuzumab on microglial activation in MS patients. The hypothesis is that alemtuzumab reduces microglial activation in MS, which may mediate its effect on reducing conversion of RRMS patients to SPMS, and its effects on cognition, including cognitive fatigue. * Secondary Objective: To determine the time course of effect of alemtuzumab on microglial activation. The hypothesis is that alemtuzumab reduces microglial activation at 6 months after initiation of treatment and this effect persists and is accentuated at 18 years, i.e. after administration of the second course