The main arteries (carotid) in your neck supply 80% of the brain's blood supply. Almost 70% of all strokes are related to blood flow problems in areas outside of the skull. As a result of atherosclerosis, cholesterol deposits or plaque may accumulate in the inner layer of the artery wall narrowing the blood vessel which may affect blood flow. The composition of the plaque may cause the formation of small blood clots or parts of the plaque may break off and the debris may lodge and settle in smaller arteries within the brain. Both situations may result in a cerebrovascular accident or stroke. Ultrasound is used to visualise the carotid arteries, assess them for the presence of blood clots or plaque and determine its composition. By measuring the velocity of the blood ultrasound can determine whether or not the narrowing is significant. If surgery is required to "clean-out the carotid artery ultrasound is used to assess the outcome and follow-up patients' progress.