Peripheral artery disease (PAD) is a disease of the arteries that occurs outside the heart or brain. In PAD, the arteries become narrowed or blocked. It is usually caused by atherosclerosis or plaque buildup. It often affects the arteries in the legs. Common methods for evaluating peripheral artery disease include vascular ultrasound, Doppler ultrasound, catheter angiography, computed tomography angiography (CTA), and magnetic resonance angiography (MRA).