Acute ischemic stroke represents the vast majority of strokes. The priority in mitigating the impact is getting to hospital quickly. Once at the hospital we use medical imaging to determine the type of stroke and type of treatment. Medical imaging provides many measurements of brain tissue for the assessment of stroke. These measurements provide insight about tissue that we can save with treatment. As well as the amount of tissue that could die without treatment. Currently we determine the outer boundary of the tissue-at-risk by measuring cerebral blood flow.