A noninvasive imaging modality that combines ultrasound imaging of vessels with Doppler assessment of blood flow. An arterial duplex scan can be used to identify the site and severity of arterial occlusion in peripheral arterial disease as well as to diagnose aneurysms. Venous duplex scan is the test of choice to identify the patency of deep veins (e.g., in suspected DVT) and to identify venous reflux and the site of incompetent valves in chronic venous insufficiency.