Transcranial Doppler

Basic Facts

  • Transcranial Doppler ultrasound (TCD) is a safe, painless, noninvasive method for assessing blood flow in the arteries that supply blood to the brain.
  • TCD measures the velocity of the blood flowing through an artery.
  • This test is used to help diagnose arterial narrowing or blockage, vessel malformation, or the sudden constriction of a blood vessel.
Transcranial Doppler (TCD) is a safe, noninvasive ultrasound test. Physicians use TCD to check or monitor blood flow in the vessels inside the skull that supply blood to the brain. The test is useful in diagnosing the following:
  • Narrowing or blockage of arteries in the neck or brain;
  • Arteriovenous malformations; and
  • Vasospasm in the neck or brain arteries.
TCD works by directing ultrasound waves (high-frequency sound waves that people cannot hear) at a blood vessel. The ultrasound waves bounce off of moving red blood cells. The difference between the sound wave frequency and the frequency of the echoes is used to calculate the speed of blood flow. TCD can also reveal what direction the blood is flowing in a vessel.


TCD requires no special patient preparation.


Using an ultrasound transducer, the physician aims the sound waves through relatively thin areas or natural openings (called windows) in the skull, such as the eye socket, the temple, and the base of the skull. A clear gel may be applied to the skin before the transducer is placed to help conduct the ultrasound waves. Depending on which window is used, the patient may be required to sit upright or lie back.

An ultrasound signal is emitted from the transducer to the blood vessel being examined. A machine records the signal frequencies and produces a graph called a waveform that a radiologist analyzes.

  • Can be performed as an outpatient procedure;
  • Does not require the patient to change clothes or disrobe;
  • Is relatively inexpensive;
  • Takes approximately 30 to 60 minutes; and
  • Gives immediate results.

TCD has no complications and is safe and painless.

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