Transcranial Doppler (TCD) Anterior and Posterior Circulation

What is Transcranial Doppler (TCD) Anterior and Posterior Circulation?

TCD Anterior and Posterior Circulation uses sound waves to measure blood flows in the major arteries inside your brain. It shows how fast blood is moving and how it flows through these vessels. This test can help detect narrowing of blood vessels, blockages or reduced blood flow, changes in circulation and abnormal blood flow patterns. 

Your brain receives blood through two main pathways:

• Anterior circulation – supplies the front of the brain and the eyes
• Posterior circulation – supplies the back of the brain 

Your doctor may want to assess either one or both pathways, depending on your condition.

Your doctor may recommend this test if you have symptoms or conditions such as:

• Stroke or Transient ischemic attack (TIA) 
• Headaches or migraines
• Dizziness or balance problems 
• Problems regarding vision 
• Suspected narrowing or blockage of brain arteries

How should I prepare for TCD Anterior and Posterior Circulation?

• Ensure the eyelids, temples, and back of the neck are not covered (please avoid heavy makeup, accessories, medicated patches or clothing that may block these areas)
• For Posterior circulation test: Neck braces, tudung or tracheostomy collar may need to be temporarily removed for the test duration
• Not required to fast
• Continue with your regular diet and medications 
• If you feel unwell, please inform the lab prior to the test

How is TCD Anterior and Posterior Circulation performed?

The test is done by a sonographer and takes approximately 30–45 minutes.

• The test is performed while you are lying on a bed. 
• A clear, water-soluble gel is applied to a handheld ultrasound probe to help transmit sound waves.
• The probe is placed on areas such as your closed eyelids, temples, and/or the base of your skull (back of the neck). 
• You may hear a “whooshing” sound, which represents blood flow in your arteries.
• The sonographer may ask you to perform simple movements, such as turning your head to the left or right. 
• To ensure accurate results, please avoid talking or moving during the test unless instructed.
• Once the test is complete, the gel will be cleaned off. It is not oily and can be removed using water. 
• A detailed report will be sent to your doctor within two weeks. Your doctor will discuss the findings with you at your next appointment.

Frequently Asked Questions about TCD Anterior and Posterior Circulation

Is the test safe?

• Non-invasive (no needles)
• Radiation-free
• Widely used (the modality is similar to that for pregnancy scans)
• A sonographer will be present throughout the process. If you feel unwell, please inform the sonographer.

If you have any questions or concerns, please contact your designated neurodiagnostic laboratory or healthcare team.

Are there any limitations to the test?

In some patients, the ultrasound signal cannot pass effectively through the skull at the temple area due to thicker bone (this is known as an absent temporal window). When this occurs, it may not be possible to fully assess the brain arteries, and in some cases the test cannot be done. 

This is more common in older adults and may occur more frequently in Asian women due to natural variations in skull thickness. If this occurs, your doctor will advise on the next appropriate steps. In such cases, there will be no charge for the Anterior Circulation TCD test.

Can I use Medisave to pay for this test?

This test may be claimable under:

• Flexi-MediSave for Seniors; or
• Outpatient scans for diagnosis or treatment of a medical condition.

Please refer to the Ministry of Health's Outpatient Care page for the latest claim limits and eligibility criteria.

The information is correct as of July 2026 and subject to revisions without notice.
Content adapted from NNI Neurodiagnostic Laboratory (NDL), NNI@TTSH.