Magnetic resonance spectroscopy (MRS) is a brain scanning technique that allows measurement of brain lactic acid. When performed in conjunction with conventional MRI scanning, the relationship of lactate accumulation to stroke expansion can be established. SELESTIAL is a randomised, placebo-controlled trial of insulin infusions of 24 or 72 hours (h) duration in acute stroke patients with hyperglycaemia, to establish whether insulin prevents lactate accumulation over the initial 72h after stroke, how this relates to stroke evolution, and the effect of treatment on stroke size and clinical outcomes at 1 week.