Aortic aneurysm. Coloured MRA (magnetic resonance angiography) scan of the abdominal arteries (red) of a patient with high blood pressure. At centre, the aorta is bulging, a condition known as an aneurysm. If left untreated, the blood vessel can rupture. Risk factors for aneurysm include smoking, high blood pressure, infection and atherosclerosis (hardening of the arteries). Improved scanning techniques mean that aneurysms are increasingly detected before they cause any symptoms. MRA is a type of magnetic resonance imaging (MRI) which highlights blood vessels without the need to inject a tracer or dye into the patient.