TCD (Trans-Cranial Doppler)
A TCD test measures how slowly blood is moving through your cerebral (sir-EE-brol) arteries. Blood flows through these arteries to your brain. The brain needs a large supply of blood. The blood supplies the oxygen and glucose (sugar) that your brain needs for energy to work and stay healthy. So it’s very important to have enough blood flow to your brain. When a cerebral artery is narrowed, blocked, deformed, or spastic, blood flow slows down or is interrupted. If your brain does not get enough oxygen, brain tissue can become damaged.
How does TCD work?
TCD stands for trans-cranial (trans-KRAYnee-ol) Doppler. “Trans” means “through.” TCD sends sound waves through the skull, or cranium, to the arteries and veins. Then the sound waves bounce back. They are too high-pitched to hear or feel and are called ultrasound (UL-truh-sound). The Doppler method uses ultrasound to make an image of blood as it flows to your brain.
The device that sends and receives the sound waves is called a transducer (trans-DOO-sir). It is hand-held and about the size and shape of a microphone. When the sound waves strike red blood cells (RBCs) flowing in the blood, the sound waves change according to the speed of the RBCs. When the sound waves bounce back, TCD records how intense they are. The difference in intensity helps to detect problems in the arteries.
How do I prepare for the test?
- You may eat a regular meal or snack before your test.
- Before the day of the test, tell your doctor all the medicines you take. Do what your doctor tells you about taking your normal medicines.
What will happen during the test?
A technician will ask you to recline in a chair or lie on a bed. You will be asked to move into different positions during the test. It is important to do exactly as the technician tells you. A gel that washes off with water will be put on different areas of your scalp. Ultrasound does not travel well through air, so the gel is used to keep air bubbles from blocking the sound waves. The gel will feel cold on your scalp.
Usually 3 areas of your head are tested: your temples, your closed eyes, and the back of your skull. You may feel a slight pressure as the transducer is moved over these areas. The transducer makes blood flow audible. During the test, you may hear sounds of the blood flowing through your arteries. The technician will adjust the sound volume of the speaker to locate the blood vessels to be studied. The test usually lasts 45 to 60 minutes.
What happens after the test?
After the test, the technician will remove the gel from your scalp. You may return to your normal activities unless your doctor tells you otherwise.
How do I get my results?
Your doctor will discuss the results of the test with you. Check with your doctor or the testing center about how and when to get your test results.
Questions and Concerns
It’s normal to feel some anxiety before and during a test. But a diagnostic test should not be a frightening experience. A TCD test has no known risks. Feel free to express concerns about your test. Please ask the medical staff any questions you may have.
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