Imaging
Doppler Ultrasound
A Doppler ultrasound uses sound waves to show how blood is flowing through your veins and arteries — commonly used to look for a deep vein thrombosis (DVT) or narrowed leg arteries.
Quick answer
Doppler Ultrasound: what it is and what the results mean
A Doppler (duplex) ultrasound combines standard ultrasound imaging with Doppler measurement of blood flow. It shows both the structure of a blood vessel and the direction and speed of blood moving through it.
- Why it is done: It is used to check for blood clots such as DVT in the legs, to assess varicose veins, to look for narrowed or blocked arteries causing leg pain (peripheral arterial disease), and to check blood flow to organs or a transplant.
- Understanding results: The scan shows whether blood is flowing normally, whether there is a clot, and whether vessels are narrowed or leaking backwards (reflux).
What it is
A Doppler (duplex) ultrasound combines standard ultrasound imaging with Doppler measurement of blood flow. It shows both the structure of a blood vessel and the direction and speed of blood moving through it.
Why it is done
It is used to check for blood clots such as DVT in the legs, to assess varicose veins, to look for narrowed or blocked arteries causing leg pain (peripheral arterial disease), and to check blood flow to organs or a transplant.
What to expect
You lie or sit with the area exposed. A sonographer applies gel and moves a probe over the skin, sometimes gently squeezing the limb to see how blood flows. It is painless and usually takes 20–45 minutes.
Understanding the results
The scan shows whether blood is flowing normally, whether there is a clot, and whether vessels are narrowed or leaking backwards (reflux). Results guide treatment such as blood thinners, compression or referral for vein procedures.
Good to know
Risks and limitations
Ultrasound is safe with no radiation. Very small or deep clots and heavily swollen limbs can be harder to assess, so a scan is sometimes repeated or combined with a D-dimer blood test.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Doppler Ultrasound: frequently asked questions
Can a Doppler scan definitely rule out a DVT?
A good-quality leg vein scan is very reliable, but if the first scan is normal and clinical suspicion remains high, it is sometimes repeated after about a week alongside a D-dimer blood test.
Do I need to prepare for a Doppler ultrasound?
Usually no special preparation is needed for leg scans. For some abdominal artery scans you may be asked to avoid eating beforehand — you will be told in advance.
Related tests
Other imaging investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Radiologists / relevant professional body
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