The initial examination is Doppler US of the carotid arteries. This provides data concerning the amount and location of carotid atherosclerosis and allows an estimate of degree of stenosis. The Doppler part of the evaluation allows hemodynamics to be assessed in detail, unlike other modalities. Generally speaking, if stenosis >80% with or without symptoms or stenosis <80% with symptoms is present, surgical or stent intervention is considered. The next examination is typically magnetic resonance angiography (MRA) of the great vessels of the head and neck, since portions of the carotid arteries are not well seen by US and the circle of Willis can be assessed. If the carotid US and MRA are in agreement this is considered an adequate presurgical evaluation. If the MRA and US aren't in agreement then angiography of the carotid arteries is indicated for final presurgical evaluation. In cases where the patient isn't a surgical candidate or disease doesn't yet warrant intervention carotid US can be performed approximately every 6-12 months to monitor disease stability or progression.