Courtesy of Intermountain Medical Imaging, Boise, Idaho.

Figure 1 shows an angiogram (a type of X-ray) of a normal neck artery (carotid artery) with smooth walls. Figure 2 shows a narrowed carotid artery with ulcerated plaque (the surface of the plaque is irregular and broken) that is the source of clots. If clots travel to the brain and block blood flow, they can cause a TIA or stroke.