ABC of Vascular Disease
Duplex Doppler Ultrasound
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
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.