Magnetic resonance imaging (MRI) angiography is a non-invasive imaging test that uses a strong magnetic field, radio waves and a computer to create 2-D or 3-D images of carotid arteries. A contrast dye is used to better visualize the blood vessels. The scan helps diagnose carotid stenosis (due to build-up of plaques), blood clots, carotid dissection/tears, brain injury from trauma, and predict the risk of future heart attacks and stroke.