Transcranial Doppler (TCD)

Fig - TCD

A TCD test uses ultrasound waves to measure the blood flow rate and direction in the main (cerebral) arteries of the brain. It helps detect blockages, narrowing or spasms of the arteries.

Risk Factors

TCD is noninvasive and has no risks. A compression test is occasionally, though very rarely, hazardous for a patient with narrowed arteries (atherosclerosis), since the increased pressure may dislodge a piece of the substance that causes the narrowing (plaque).

What to Expect

Fig - PMD Unit with Remote Control

No special precautions are necessary. No special preparation is needed. There is no diet or activity restriction before this test. The patient should remove contact lenses, and may wish to avoid the use of eye makeup, since the gel is likely to smear it.

The test does not involve the use of needles or injections. TCD is done with either one or two probes placed against the skin. The examiner spreads a clear gel on the areas of the head where the probe will be placed:

  • On each side of your head.
  • Under your chin.
  • Over your closed eyelid.
  • At the back of your neck.

In these places, there is the last amount of thick protective bone and the sound waves can penetrate the best. The examiner adjusts the probe position and orientation to direct the sound waves toward the blood vessels of interest. Finding the best approach may take some time. A compression test may be performed during the exam. In this test, the main artery in the neck (carotid artery) is briefly compressed, and changes in blood flow patterns are observed. A full TCD exam may last 30-45 minutes, and often longer in patients with disease.

The gel is washed off with soap and water. No other after care is needed.

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