Stroke is a major killer, and has a greater disability impact than any other chronic disease. Patients occupy one of the largest numbers of acute hospital bed days of any patient group (2.6 million per year), and the disease consumes between 4-6% of NHS expenditure (approx £2.8 billion) with costs projected to rise 30% by 2010 as life expectancy and survive rates increase. Treatment options are limited (clot busting drugs like rt-PA or aspirin) with less than 2% of stroke patients receiving rt-PA since it must be given within 3 hours of stroke for safety reasons, and patients must have a brain scan first to rule out brain haemorrhage. rt-PA is very effective in patients where brain damage has not fully evolved. In the first few hours after stroke, injured but potentially salvageable tissue (penumbra) can be saved by rt-PA. Penumbral tissue can be identified by magnetic resonance imaging (MRI), but current techniques underestimate penumbra size. If a rapid, more accurate MRI technique was available, more patients could be treated and recruitment into clinical trials to study new therapies, improved. This proposal describes development and validation of such a technique and provides preliminary MRI data from animal models and man.