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Duplex Ultrasound Scan

Note: the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital.

What is duplex ultrasound?

Duplex ultrasound is a special ultrasound technique that can assess how fast blood is flowing through a blood vessel. The test combines traditional ultrasound with Doppler ultrasound. Regular ultrasound uses sound waves that bounce off different structures of the body to create pictures. Doppler ultrasound records sound waves reflecting off moving objects, such as blood, to measure their speed and other aspects of how they flow.

A duplex ultrasound scan is a quick, simple, painless, noninvasive test. It is a way of looking at arteries and veins, measuring their size and the flow of blood through them. Duplex ultrasound scans are usually done as outpatient tests.

What is ultrasound?

Ultrasound is a high-frequency sound that you cannot hear, but it can be emitted and detected by special machines.

How does duplex ultrasound work?

Ultrasound travels freely through fluid and soft tissues. However, ultrasound is reflected back (it bounces back as ‘echoes’) when it hits a more solid (dense) surface. For example, the ultrasound will travel freely though blood in a heart chamber. But, when it hits a solid valve, a lot of the ultrasound echoes back. Another example is that when ultrasound travels though bile in a gallbladder it will echo back strongly if it hits a solid gallstone.

So, as ultrasound ‘hits’ different structures in the body of different density, it sends back echoes of varying strength.

Traditional ultrasound looks at body parts that stay in one place. Duplex ultrasound can look at moving objects. If the structure is moving then the echo comes back at a slightly different frequency (called the Doppler effect). This difference in frequency can be used to measure the speed of movement. Blood moving in an artery or vein causes small echoes and these are used to measure the speed of the blood. In most machines the structure of the object is displayed as a grey image and the speed as a colour image.

What does a duplex ultrasound scan involve?

You lie on a couch and an operator places a probe on your skin over the part of your body to be examined. The probe is a bit like a very thick blunt pen. Lubricating jelly is put on your skin so that the probe makes good contact with your body. The probe is connected by a wire to the ultrasound machine and monitor. Pulses of ultrasound are sent from the probe through the skin into your body. The ultrasound waves then echo (‘bounce back’) from the various structures in the body.

The echoes are detected by the probe and are sent down the wire to the ultrasound machine. They are displayed as a picture on the monitor. The picture is constantly updated so the scan can show movement as well as structure. The operator moves the probe around over the skin surface to get views from different angles.

The scan is painless and takes about 15-45 minutes, depending on which parts of the body are being examined. A record of the results of the test can be made as still pictures or as a video recording.

What is duplex ultrasound used for?

Duplex ultrasound is most commonly used to evaluate the blood flow in various arteries and veins in the body. The scan can help diagnose the following conditions:

  • Abdominal aneurysm (widening of the main artery in the abdomen).
  • Blockage to an artery – known as an arterial occlusion.
  • Blood clot.
  • Carotid occlusive disease (blockage to the arteries in the neck).
  • Renal (kidney) vascular disease.
  • Varicose veins.
  • Venous insufficiency (a condition where veins have a problem sending blood back to the heart).

What should I do to prepare for a duplex ultrasound?

Usually, there is no preparation needed for a duplex ultrasound. However, if you are having a scan of the abdomen (tummy) you may be asked to stop eating for a few hours before the test. Your local hospital should be able to give you more information on this.

Are there any side-effects or complications from a duplex ultrasound?

There are no side-effects with this type of ultrasound scan. Duplex ultrasound does not involve the use of radiation and is therefore a very safe test.

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