Duplex ultrasonography (more commonly but less correctly known as duplex ultrasound) is a form of medical ultrasonography that incorporates two elements:
Grayscale ultrasound to visualize the structure or architecture of the body part. No motion or bloodflow is assessed. This is the way plaque is directly imaged in a blood vessel, with the reader typically commenting on cross-sectional narrowing (greater than 70% is typically considered worthy of treatment).
Color-doppler ultrasound to visualize the flow or movement of a structure, typically used to image blood within an artery. Blood flow velocities increase through a region of narrowing, like a finger pressing up against the end of a running garden hose. Increased velocities indicate a region of narrowing or resistance (velocities greater than 250 cm/s are typically considered worthy of treatment).
Both displays are presented on the same screen ("duplex") as overlapping images to facilitate interpretation.
Vascular ultrasonography is the main branch of radiology that uses duplex. Vascular ultrasonography, a subspeciality within ultrasonography, helps determine multiple factors within the circulatory system. It can evaluate central (abdominal) and peripheral arteries and veins; it helps determine the amount of vascular stenosis (narrowing) or occlusion (complete blockage) within an artery; it assists in ruling out aneurysmal disease; and it is the main aid to rule out thrombotic events. Duplex is an inexpensive, non-invasive way to determine pathology. Duplex evaluation is usually done prior to any invasive testing or surgical procedure. Ultrasound duplex scanning can provide additional information that may guide therapeutic decisions. The location and severity of arterial narrowings and occlusions can be identified. The vascular radiographer can map disease in lower-extremity segments with great accuracy, though duplex scanning is more time-consuming than other lower-extremity arterial studies.