False-colour angiogram of the human legs, showing stenoses (obstructions) in both femoral arteries caused by the accumulation of fatty, atheroma plaques. The femoral arteries appear as large purple channels running down the inside of both legs. Angiograms are X-ray images that are taken following the injection of a radio-opaque contrast medium into the arteries under investigation via a catheter. Both femoral arteries are partially obstructed in several places - the narrowed areas represent obstructions to blood flow.