This study aims to use [C-11]MRB PET (positron emission tomography) imaging to look at brain injury in patients with Multiple Sclerosis (MS) and healthy individuals. The overarching hypothesis is that there is decreased radioligand binding to the norepinephrine transporter in multiple sclerosis, reflecting injury to the noradrenergic system and that it plays a role in disease pathogenesis, its clinical manifestations and severity. This strategy is targeted to address an unmet need because currently available MRI techniques lack sensitivity and specificity for assessing such changes in the brains of people with MS.