What Is a Duplex Ultrasound? Vascular Surgeon Explains

Duplex ultrasound combines an image of a blood vessel with information about the blood flowing through it. Ultrasound provides the picture; Doppler assesses movement and flow. Together, they help us investigate problems affecting arteries and veins.

In this video, I explain why a duplex scan is frequently used for varicose veins, leg swelling, blocked arteries and possible blood clots. Understanding what the test measures can make a scan appointment less unfamiliar and help you understand the next steps in your care.

What does the ultrasound part show?

Ultrasound uses high-frequency sound waves. A probe sends these waves into the body and receives the echoes that return from tissues. The machine converts those echoes into an image.

For a vascular scan, this helps show the vessel and the structures around it. The person performing the scan can examine a particular area and take measurements relevant to the clinical question.

What does Doppler add?

Doppler uses changes in reflected sound waves to assess moving blood. It provides information about the direction and speed of flow, which can be displayed as colours or waveforms and sometimes heard as a sound.

This matters because a vessel’s appearance is only part of the story. I also need to understand whether blood is passing through effectively, whether flow is altered by narrowing, or whether it is moving backwards through a vein. Duplex brings the image and flow assessment together.

Which circulation problems can a duplex scan investigate?

• Varicose veins and venous reflux: identifying backward flow and mapping affected veins when assessing venous symptoms.

• Possible blood clots: examining the deep veins when deep vein thrombosis (DVT) is suspected.

• Narrowed or blocked arteries: assessing blood flow in people with symptoms that may relate to peripheral arterial disease.

• Treatment planning or follow-up: providing information that may guide a procedure or help assess circulation afterwards.

The scan is tailored to the reason for referral. An examination for venous reflux is not identical to an arterial scan or a scan for suspected DVT. Explaining your symptoms clearly helps ensure the assessment answers the relevant question.

What happens during the scan?

Usually, gel is applied to the skin and a handheld probe is moved over the area being examined. You may be asked to change position so the vessels can be assessed properly. The area needs to be accessible, so comfortable clothing can be helpful.

A standard external duplex scan is non-invasive and does not use ionising radiation. You may hear the machine’s blood-flow sounds during the examination. Let the sonographer know if an area is painful or if you have difficulty standing or changing position.

Preparation and appointment length depend on the vessels being examined. Follow the instructions supplied by the clinic rather than assuming every ultrasound appointment has the same requirements.

Does a scan result tell the whole story?

No single investigation replaces a clinical assessment. I interpret the findings alongside your symptoms, examination and medical history. Sometimes duplex provides the information needed; sometimes further tests or another form of imaging are appropriate.

Useful questions to ask include: What was the scan looking for? What did it show? Does the finding explain my symptoms? What should happen next? The aim is to connect the result to a clear care plan, rather than leave you with an unfamiliar technical term.

Duplex ultrasound assessment in Singapore

As I explain in the video, our practice has its own vascular laboratory and a dedicated vascular sonographer who focuses on vascular scans. For advice about an assessment, contact Andrew Choong Vascular Surgery at Mount Elizabeth Novena Specialist Centre, #09-22, 38 Irrawaddy Road, Singapore 329563.

New one-sided painful leg swelling needs urgent assessment; do not wait for a routine scan appointment. Sudden breathlessness, chest pain or collapse requires emergency care. Call 995 in Singapore for a life-threatening emergency.

This article provides general education and does not replace an individual medical assessment.