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Transcranial Doppler Ultrasound

Overview

Transcranial Doppler ultrasound (TCD) uses sound waves to evaluate blood flow in the circle of Willis, an important junction of blood vessels at the base of the brain. Vascular neurologists use the real-time information provided by TCD in the diagnosis and monitoring of a variety of vascular conditions. These include:

Unlike CT scans or MRIs, TCD focuses on the movement of blood through the brain rather than looking at the brain’s structure.

illustration of the blood vessels at the base of the brain where aneurysms are more common.
An illustration showing the arteries of the base of the brain.

What is transcranial Doppler ultrasound used for?

TCD is used extensively in the management of patients following hemorrhagic strokes due to its ability to detect vasospasm. This sudden narrowing of blood vessels is a common complication of subarachnoid hemorrhage (SAH) and can cause a secondary stroke. SAH describes bleeding between the brain and the thin tissues covering it. Doctors also use diagnostic TCD to assess sickle cell disease, in which misshapen red blood cells can get stuck in blood vessels and cause strokes.

Embolic monitoring is another use for TCD. By detecting the presence of small clots or bubbles in the blood, TCD can help your doctors gauge your risk for stroke or other circulatory problems like patent foramen ovale (PFO). Early detection of PFO is critical, as the condition can allow blood clots to pass into the brain and cause an ischemic stroke.

TCD can also help evaluate head injuries, migraines, or conditions that affect blood clotting. In some cases, it’s even used during surgeries to ensure proper blood flow to the brain.

How does the test work?

The test uses high-frequency sound waves to measure how fast blood moves through your brain’s blood vessels. A device called a transducer sends these sound waves into your head, and as the waves bounce back, they create images and measurements of blood flow. The sound waves used in TCD are safe and don’t cause discomfort.

Unlike other types of ultrasound, TCD requires specific techniques because the skull can block sound waves. To circumvent this, the technician performing the test will place the transducer on areas of your head where the skull is thinner. These areas, known as acoustic windows, include spots near your temples, the back of your head, or even around your eyes. By carefully positioning the transducer, the technician can see the blood vessels clearly.

Your care team will ask you to sit or lie down for the procedure. A gel is applied to the skin to better conduct the sound waves, and the technician moves the transducer to different positions to get a complete picture of your blood flow. You might hear some whooshing or pulsing sounds during the test. This results from the transducer converting the sound waves into audible signals.

The entire procedure usually takes about 30 to 60 minutes, depending on the complexity of the test and the specific areas examined. Once it’s complete, the technician will wipe off the gel, and you’ll be free to go about your day. There’s no downtime or recovery period, so you can resume your normal activities immediately.

What does TCD feel like?

TCD is non-invasive and painless. You won’t feel the sound waves; the gel is water-based and easily wiped off afterward. The transducer may feel slightly cool initially, and you might notice slight pressure as the technician moves it around. Still, most people find the test very comfortable. There’s no need for needles, dyes, or any special preparation, so you can rest and relax during the procedure.

stroke neurologist daniel gonzalez treats a patient in at the petznick strock center

Interpreting the Results of TCD

The results of your TCD will provide valuable information about how blood flows through your brain. If the test shows that blood flow is normal, it indicates that your blood vessels are healthy and functioning properly. However, if the results reveal areas where blood flow is reduced or blocked, your doctor will use this information to determine the next steps.

For example, if blood flow is slower than it should be, it might indicate a narrowing or blockage in one of the blood vessels. This can increase the risk of stroke and may require further tests or treatments. Conversely, blood that is moving too fast could suggest an abnormal connection between blood vessels or other issues that require medical treatment. In some cases, TCD can also detect tiny clots or air bubbles in the bloodstream, which can help prevent complications before they occur.

Your doctor will explain the results in detail and discuss their benefits for your health. Depending on the findings, they may recommend lifestyle changes, medications, or additional tests to address your concerns. If you have transcranial Doppler ultrasound to monitor a known condition, the results can help guide treatment and ensure that your care plan is working as intended.

Benefits and Limitations of TCD

TCD is a safe, simple procedure. Unlike other imaging tests, it doesn’t involve radiation, dyes, or invasive procedures, making it suitable for children and people of all ages. It’s also relatively quick and affordable compared to other diagnostic methods.

However, there are some limitations to keep in mind. Because sound waves don’t travel well through bone, the test relies on accessing specific areas of the skull where the bone is thinner. This means that it may not always provide a complete picture of blood flow in certain parts of the brain. Additionally, the quality of the images can sometimes be affected by the thickness of your skull.

Despite these limitations, transcranial Doppler ultrasound remains an invaluable tool for diagnosing and monitoring various conditions. Its ability to measure blood flow in real time provides unique insights that other tests can’t offer, making it an essential part of modern medical care.

Preparing for Transcranial Doppler Ultrasound

One of the great things about TCD is that it requires no special preparation. Before the test, you can eat, drink, and take your usual medications. It’s a good idea to wear comfortable clothing and avoid hair products, like gels or sprays, which could interfere with the procedure.

After the test, no recovery time is necessary. You can go straight back to work, school, or any other activities you have planned. If your doctor has any specific instructions based on your results, they’ll let you know what to do next. In most cases, the test is just one piece of the puzzle, and your doctor will use it along with other information to develop a complete picture of your health.

Summary

Transcranial Doppler ultrasound is a safe, painless, and effective way to evaluate blood flow in the brain. Whether you’re being tested for a specific condition or as part of a routine check-up, it provides valuable insights that can help guide your care. The procedure is quick and easy, with no downtime or side effects, making it an ideal choice for people of all ages.

Medically Reviewed by Bryan Franzen, DO on February 5, 2025

Resources

National Library of Medicine

MedlinePlus

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