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Colour-flow duplex scan

Please note the information provided is intended to support patients and is not a substitute for medical advice and treatment. We strongly recommend consultation with your doctor or health care professional, before using any information obtained from articles of this website.

What is duplex ultrasound scanning?

Duplex ultrasound scanning (or colour-flow duplex ultrasonography) combines two kinds of information: (i) the conventional imaging of a vessel and (ii) the Doppler blood flow characteristics in the vessel. It shows how blood flows in the vessel and allows measurement of the speed of the flow. The diameter of the vessel and the degree of narrowing can be estimated.

Conventional ultrasound uses ultrasound waves (sound waves that the human ear cannot hear). A computer converts the ultrasound waves into two-dimensional, black-and-white moving images, called B-mode imaging.

Doppler ultrasound measures how ultrasound waves reflect on moving objects (in this case the red blood cells) and sends the information to the computer, which produces colour images to show whether the blood flow in the vessels is affected by problems in them.

In duplex scanning, the “double” information (structure of the vessel and flow in it) is used together.

Your physician may recommend this test to help assess certain conditions that affect blood vessels, such as

The test may be performed in a clinic, a medical office or a hospital by a physician or a vascular ultrasound technologist (trained in this type of investigation), and is pain-free. Its duration depends upon the number and the location of vessels (arteries, veins) to be examined.


Before the investigation

No special preparation is required in most cases of duplex ultrasonography not involving the abdomen. However, for imaging of vessels in the abdomen, you may be asked to fast overnight before the test, in order to reduce bowel gas which is not permeable by the ultrasound waves.


What does it involve?

Initially, you will be asked to sit or lie on the table in a certain position.

Then, over the area to be examined, a special gel will be spread, to allow better transmission of ultrasound waves. The examiner presses the probe against the skin and moves it back and forth. This may cause mild discomfort but no pain. As the probe moves, it sends information which appears as an image on a video screen.

During the test, you may hear a rythmical whooshing sound which represents the blood flow in the vessel examined.


What can I expect after the investigation?

There are no special instructions and you may resume all of your normal activities.


Last modified 22/02/2014