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What is a duplex scan?
A duplex scan is a noninvasive procedure using ultrasound to assess the blood flow of the body's arteries and veins.
The term “duplex” refers to the fact that two modes of ultrasound are used: Doppler and B-mode. The B-mode transducer (like a microphone) obtains an image of the carotid artery being studied. The Doppler probe within the transducer evaluates the speed and direction of blood flow in the vessel.
A transducer sends out ultrasonic sound waves at a frequency too high to be heard. When the transducer is placed on certain locations and angles, the ultrasonic sound waves move through the skin and other body tissues to the blood vessels, where the waves echo off the blood cells.
The transducer picks up the reflected waves and sends them to an amplifier, which makes the ultrasonic sound waves audible. Absence or faintness of these sounds may indicate an obstruction to the blood flow.
There is no radiation used and generally no discomfort from the application of the ultrasound transducer to the skin.
How is the procedure done?
You will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan. If you are asked to remove clothing, you will be given a gown to wear.
You will lie on an examination table and a clear gel will be placed on the skin at various locations on the carotid arteries.
The Doppler transducer will be pressed against the skin and moved around over the area of the artery being studied. When blood flow is detected, you may hear a “whoosh, whoosh” sound. The probe will be moved around to compare blood flow in different areas of the artery.
Once the procedure has been completed, the gel will be wiped off.
Are there special preparations before the procedure?
Generally, no prior preparation, such as fasting or sedation, is required.
Your physician may give you specific instructions about smoking and consuming caffeine. You may be asked to refrain from smoking for at least two hours before the test, as smoking causes blood vessels to constrict. You may also be asked to refrain from consuming caffeine in any form for about two hours prior to the test.
If your abdominal vessels will be examined, you may be asked to fast before the procedure.
Excerpt from Duplex Scan, St. Luke's Medical Center advertorial.