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Transcranial Doppler Ultrasound (TCD)

What is a transcranial Doppler ultrasound?

Transcranial Doppler (TCD) is a painless, non-invasive ultrasound test that measures blood flow inside the brain. It can detect if there is a high risk of having a stroke.  

TCD uses a small device (probe) placed on the outside of the head. It records images or waveforms to show how blood is flowing through blood vessels in the brain. Like other types of ultrasound or sonography, this test uses sound waves to see inside the body or detect blood flow.

Both types of TCD machines measure blood flow.

Child undergoing tcd ultrasound

Transcranial Doppler (TCD) ultrasound is a painless test that measures blood flow in the brain.

TCD can help find problems that affect blood flow to the brain such as:

  • Blood clots or other blockage of blood vessels
  • Blood vessels that are getting narrow

Types of TCD machines include: 

  • TCD with imaging (TCDi) 
  • TCD without imaging (TCD) 

Both types of TCD machines measure blood flow.

Transcranial Doppler ultrasound and sickle cell disease

All children with sickle cell anemia (HbSS) or sickle beta thalassemia (SB-0) need routine TCD tests starting at age 2.  This test is an important part of your child’s care.

Regular TCD screening tests help to monitor the risk of stroke. A stroke is an injury to the brain that happens when a blood vessel is blocked.  

People with sickle cell disease have red blood cells that are hard, sticky, and shaped like a banana. This can cause red blood cells to block blood vessels. This increases your child’s risk of stroke.

What to expect during the test

TCD and TCDi are safe and painless. No special preparation is needed. Your child can eat and drink normally before the test. The test usually takes up to one hour.

Your child should wear comfortable, loose-fitting clothing. Your child does not need to change into a medical gown. Remove hats, glasses, hair clips, and earrings.

Your child will lie on their back. Your child may be able to watch a show on a tablet during the exam.

A trained TCD technologist will perform the test. The technologist will put a clear gel on the side of your child’s head. This helps the ultrasound probe work better on the skin. The gel might feel cold at first. The technologist will wipe it off when the ultrasound is over.

Next, the technologist will press the ultrasound probe firmly on your child’s skin. This should not cause any pain or discomfort. Your child might feel some pressure. Your child will hear a “swooshing” sound during the test. This is the sound of blood flowing through the arteries.

The technologist might move the probe back and forth in a certain place or press more firmly in some places. This helps get the best measurement of blood flow.

Your child will be awake during the exam. It is important for your child to:

  • Lie still
  • Be as quiet as possible
  • Stay awake for the entire exam

Your child cannot eat, drink, suck on a pacifier, or talk during the exam. If your child has trouble lying still or being quiet, let the care team know.  

After the test

A doctor called a radiologist will review the scans. They will look carefully at how fast blood is moving through your child’s brain. Results will be shared with other members of your child’s care team.

TCD results

Below is a list of the possible test results and what each generally means. Your care team will explain your child’s results and let you know what follow up care is needed. Always follow the specific recommendations given by your care team.

  • Normal TCD: Your child has a low chance of having a stroke. The test will be repeated in 1 year or sooner if needed.
  • Conditional TCD: Your child has a medium chance of having a stroke. Another test will be done in 3 to 6 months or sooner if recommended by the care team. A care team member may also talk with you about your child’s stroke risk and ways to reduce stroke risk.
  • Abnormal TCD: Your child has a high chance of having a stroke. They will need another TCD in 2 to 4 weeks or sooner depending on what the care team decides. A care team member may talk with you about your child’s stroke risk and treatments to reduce the chance of having a stroke. 
  • Limited or Inadequate TCD: The technologist could not take all the pictures or waveforms needed. This means your child’s stroke risk is not known. If this happens, your care team will repeat the test or recommend other tests.

Benefits and risks of TCD and TCDi


  • Transcranial Doppler ultrasound (both imaging and non-imaging) gives a clear idea of blood flow in the brain.
  • Ultrasound is safe and does not have side effects. It does not use radiation.
  • TCD and TCDi tests are not invasive. The probe stays on the surface of the skin. It does not go inside the body. It does not use needles.


  • Transcranial Doppler ultrasound with or without imaging do not have any harmful effects.
  • Your child will need to avoid talking and keep their head still while the test is done. They cannot fall asleep during the exam.

Questions to ask your care team about TCD

  • How long will the test take?
  • How will I find out my child’s results?
  • Who will explain the results to me?
  • How often will my child need this test?
  • What other tests may my child need?

Key points about TCD and TCDi

  • Transcranial Doppler ultrasound, with or without imaging, is a test that uses sound waves to examine blood flow in the brain.
  • Children with certain types of sickle cell disease should have routine scans as recommended by their care team.
  • This test can help determine your child’s risk for stroke.
  • Your child’s care team will talk about the results with you and let you know when another scan is needed.

Reviewed: April 2024