ABC of Vascular Disease

Duplex Doppler Ultrasound

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1. What is a duplex scan?
A duplex ultrasound scan is a quick, simple, painless, non-invasive method of looking at arteries and veins and measuring their size and the flow of blood through them.  Duplex ultrasound scans are usually done as outpatient tests.

2. How does a duplex scanner work?
The duplex ultrasound scanner consists of a probe which emits very short pulses of very high frequency sound, much higher than the ear can hear.  The probe is applied to the skin using a special lubricating jelly to make a good contact, and by pointing the probe in different directions, the structures under the skin down a depth of several inches can be scanned.  The pulses of sound are bounced back from the structures, like echoes in cave, and picked up by the same probe.  These echoes are analysed and used to build a picture of the structures in the path of the ultrasound beam.  If the structure is moving then the echo comes back at a slightly different frequency (called the Doppler effect) and this frequency shift 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 gray image and the speed as a colour image; hence the alternative name colour flow Doppler imaging.

3. What is a duplex scan used for?
A duplex scan is a very useful method for looking at arteries and veins deep within the body.  A duplex scan is very useful in both arterial and venous disease and avoids the need for x-rays in many patients.

4. How long will I wait for a duplex scan?
In many cases a duplex scan can be done in the outpatient clinic when you see your vascular surgeon (one stop clinics).  The scan is normally done by someone specially trained to perform the scan and interpret the images and the result is available immediately to assist your specialist in making an accurate diagnosis and deciding the best course of treatment.  In many cases no other tests need to be done.

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S.R.Dodds 2006

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