Multiple Sclerosis is a chronic condition that shows changes in the way that the brain consumes sugar. It is also known that there are a number of metabolic and inflammatory sequelae following a transient ischemic attack/stroke (hereby referred to collectively as 'stroke'). This study will use a powerful new technology ('hyperpolarised magnetic resonance imaging') to detect these changes in the brains of people with multiple sclerosis and Clinically Isolated Syndrome (CIS) or following a stroke when compared to a group of healthy volunteers. It will be undertaken at the University of Oxford, and each participant will undergo up to 4 scans over the course of three years.