The goal of this case-control study is to investigate glucose brain metabolism in people with multiple sclerosis and age- and sex-matched healthy controls. The main questions it aims to answer are: * How does brain glucose metabolism in people with multiple sclerosis compare to age- and sex-matched healthy controls? * How is the brain glucose metabolism of people with multiple sclerosis associated with disease severity? Participants will come in for testing lasting approximately three hours and undergo deuterium metabolic imaging, physical function test, cognitive function test, and answer survey.