Duplex Ultrasound

Basic Facts

  • Ultrasound is a painless, noninvasive, radiation-free diagnostic test that uses high-frequency sound waves to make images of body tissues.
  • Duplex ultrasound allows doctors to measure the speed of blood flow and to see images of the blood vessels. Physicians use duplex ultrasound to diagnose and examine diseases that affect the blood vessels, as well as to plan for surgical and minimally invasive therapies.
  • Duplex ultrasound uses high-frequency sound waves to produce images that differentiate between the body’s soft tissues and its fluid-filled structures. Duplex ultrasound can also detect motion, such as the movement of blood cells.
  • A physician can use ultrasound to evaluate the veins and arteries in a person’s neck, arms, abdomen, and legs. The test also allows the physician to watch blood as it flows through blood vessels.
  • Ultrasound uses sound waves higher than human hearing can detect. A device called a transducer that connects to a computer and control panel emits ultrasound waves are directed through the skin and into the body. When the sound waves hit body structures such as blood vessels they echo off of the structures and then travel back toward the transducer. A computer analyzes the echoes, the time it takes them to travel, and their distance from the transducer and produces a two-dimensional, real-time image of the shape and structure of blood vessels.
  • Duplex ultrasound combines standard ultrasound technology and Doppler ultrasound, which uses short-bursts of ultrasonic waves to produce images of the direction and speed of the flow of blood. Duplex ultrasound allows physicians to measure the velocity of blood flow and to see images of the structure of the blood vessel through which the blood is flowing.


The physician will provide any special instructions regarding medications, as appropriate. There are usually no restrictions on food or liquid before the duplex ultrasound is performed. Before the test is administered, the patient may be asked to change into a hospital gown.


There are no known risks associated with the test.


Most duplex ultrasound tests are performed in an ultrasound lab, which is usually at a physician’s office or a hospital.

The ultrasound technician will request that the patient lay quietly during the test to help ensure that the images are clear. He or she will then apply a special gel directly on the skin above the area to be examined to increase sound wave conduction and reception. The technician will then press the transducer against the person’s skin and may move the transducer back and forth to get clear images of the underlying blood vessels and structures.

People who undergo a duplex ultrasound may hear a “whooshing” sound timed with their heartbeat. This is an echocardiogram machine’s translation of the sound of blood in motion.

The procedure typically lasts for 30 minutes, but the duration varies depending on the structure being examined.


Following a duplex ultrasound scan, patients can resume normal activities.

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Medical Review Date: August 13, 2009 / Copyright © 2012 NorthPoint Domain, Inc. All rights reserved. This material cannot be reproduced in digital or printed form without the express consent of NorthPoint Domain, Inc. Unauthorized copying or distribution of NorthPoint Domain’s Content is an infringement of the copyright holder’s rights.