It is a non-invasive imaging technique that uses a strong magnetic field, radio waves and a computer to create 2-D or 3-D images of the blood vessels in the lower limb. Your doctor may advise this test to look at the stenosis (narrowing of a blood vessel), aneurysm (ballooning of a blood vessel), vasospasm (spasm of a blood vessel), blood clots, blockage, tumours and bleeding. A contrast agent is used to better visualize the vessels.