Angioplasty of the carotid artery. Coloured angiogram of a section through the neck of a 47-year-old patient, showing a catheter (light line) with a stent (orange, centre-left) being implanted into the internal carotid artery to treat stenosis (narrowing). Stents are wire mesh tubes that are used to provide support to passageways within the body. They are guided into position using a catheter. Once the stent is in position, a balloon is inflated inside it in order to expand it. The balloon is then deflated and the catheter removed, leaving the stent in place. This procedure is known as balloon angioplasty. The most common cause of arterial narrowing is atherosclerosis, the deposition of fatty plaques of atheroma (yellow) on the inner wall of an artery.