Carotid duplex ultrasound uses a technique called Doppler ultrasound to measure blood flow through the carotid arteries inside the neck, which supply blood to the brain. A device called a transducer is passed lightly over your neck, directing high-frequency sound waves (ultrasound) into the carotid arteries. The sound waves are reflected back at frequencies that correspond to the velocity of blood flow, and are converted into audible sounds and graphic recordings.

Duplex scanning combines Doppler ultrasound with real-time ultrasound imaging of the carotid arteries, allowing calculation of the percent of narrowing in the vessels. Images are displayed on a viewing monitor and may also be recorded on film or video for later examination.

Purpose of the Carotid Duplex Ultrasound

  • To assess blood flow in the carotid arteries and detect any blockages, such as blood clots or atherosclerosis (narrowing due to the buildup of plaques)
  • To locate a blood clot (hematoma) in the carotid arteries that may slow and eventually stop blood flow
  • To detect a split between layers of the carotid artery wall (dissection) that may lead to obstruction of blood flow or a weakening of the wall of the artery
  • To evaluate the condition of the carotid artery after surgery to restore normal blood flow
  • To check the position of a metal stent placed to maintain blood flow in the carotid artery

Who Performs Carotid Duplex Ultrasound

  • A sonographer (ultrasound technologist) or radiologist

Special Concerns about Carotid Duplex Ultrasound

  • None

Before the Carotid Duplex Ultrasound

  • No special preparation is necessary.
  • Wear loose clothing, especially at the neck. Do not to wear turtlenecks or silk shirts (because of the gel that will be used).

What You Experience during Carotid Duplex Ultrasound

  • You will lie on your back on an examination table, and your head will be supported to inhibit movement.
  • A water-soluble gel is applied to the skin on your neck to enhance sound wave transmission.
  • The examiner then moves the transducer back and forth over one side of your neck to obtain different views of the carotid artery. The other side of your neck is then checked in the same way.
  • Once clear images of the carotid artery are obtained, they are recorded on film or video for later analysis.
  • The test takes about 15 to 30 minutes.

Risks and Complications of Carotid Duplex Ultrasound

  • Ultrasound is painless, noninvasive, and involves no exposure to radiation. There are no associated risks.

After the Carotid Duplex Ultrasound

  • The examiner removes the conductive gel from your skin.
  • You may resume your normal activities.

Carotid Duplex Ultrasound Results

  • A physician reviews the recorded images and other test data for evidence of abnormalities. High blood flow velocity indicates narrowing of the carotid arteries.
  • If the carotid arteries are blocked, appropriate therapy will be initiated to reduce your risk of stroke.
  • In some cases—especially if surgery to remove carotid blockages is contemplated—additional diagnostic tests, such as arteriography, may be ordered to determine the exact location and extent of the occlusive plaques.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at

Published: 04 Jan 2012

Last Modified: 13 Jan 2015