Definition and Overview

Also known as TCD, transcranial doppler is a noninvasive diagnostic procedure that uses ultrasound waves to measure the blood flow in the brain.

The brain is considered as the center of the body’s activities. Although its function is interdependent with that of other organs, it controls many activities including those of the muscles. It's millions of cells and nerves are interconnected to other organs, allowing them to perform actions that are necessary for the continuance of life.

Because of its heavy metabolic function, the brain requires at least 20% of the oxygen coming from the heart. It also needs to maintain an ideal blood flow through the many blood vessels. If there’s too much blood supply, it increases the intracranial pressure that can lead to tissue damage. This type of damage can also occur, although usually gradually, if the blood supply is low, such as from 8 to 10 millimeters for every 100 grams per minute.

TCD can help evaluate whether a degenerative condition, stenosis (blockage of the artery) or other problems are affecting the blood flow. As a non-invasive imaging test, it uses a transducer that is moved around to different parts of the skull, its ultrasonic waves bouncing through the red blood cells that are passing through the blood vessels. This ultrasound doesn’t produce any image but rather sound waves that measure the speed of the blood flow. It is also portable, which means that the patient doesn’t have to leave the bedside to be tested. The patient also remains awake all throughout the procedure.

Who Needs It and Expected Results

TCD is recommended to patients who have:

  • High cholesterol level – People who have elevated triglyceride or blood cholesterol levels are more likely to suffer from stenosis due to the buildup of plaque in the walls of the arteries.

  • Cardiovascular disease – A person who has been diagnosed with cardiovascular disease may already have a damaged artery that can significantly affect the supply of blood to the brain.

  • Diabetes – Diabetes can lead to nerve damage and kidney disease, which can cause an abnormal increase in blood pressure. High blood pressure increases the risk of hypertension and stroke.

  • Sickle cell anemia – This is an inherited disease characterized by the presence of red blood cells that are shaped like a sickle rather than round. Sickle cell anemia reduces the number of red blood cells that carry oxygen. These cells can also block the blood vessels, which can lead to lower blood supply to the brain. People with this disease are also at a higher risk of developing pulmonary hypertension (high blood pressure of the lungs) and stroke.

  • Embolism – An embolism occurs when emboli (which can range from a blood clot to air bubbles, pus, or any other material produced by a certain part of the body) travel through the bloodstream and lodge themselves in the blood vessels.

TCD may also be recommended to those who have undergone trauma such as an accident or violence (e.g., being hit severely by a blunt object). These types of injuries can cause hemorrhage or internal bleeding of the brain. The copious amount of blood may then increase the intracranial pressure.

Further, it can be utilized to monitor surgical procedures or to determine the success of a particular treatment plan.

The procedure takes around 25 to 30 minutes. This is the only ultrasound test that produces sound, which can be heard by the doctors and the patient, although the sound waves themselves are inaudible.

How Does the Procedure Work?

TCD is a very straightforward imaging test. It is usually composed of a transducer and a computer that allows the doctor to monitor circulatory speed. It doesn’t require any preparation such as fasting. Moreover, the patient may wear normal clothes or a hospital gown. Unless the jewelry pieces are in the face, they also don’t have to be removed.

The test is often carried out in a hospital and supervised by a trained radiologist or neurologist. The patient may be lying on the examination or operation table or a hospital bed, or sitting on a chair. A specially formulated gel is then applied to various areas of the face, such as around the cheekbones, eyelids, the front of the ears, and nape. The patient is not allowed to move his or her head as well as talk while the test is ongoing. A transducer is then moved over the face and sends feedback to computer software. This allows the doctors to see blood flow information on the screen. Once the test is over, the gel is wiped off.

Possible Risks and Complications

As a non-invasive procedure, TCD is completely safe. There’s also no discomfort during and after the exam. Unless advised otherwise, patients can return to normal activities right after the procedure. Skin reaction due to the gel is also very rare.


  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
  • Roman AS (2013). Late pregnancy complications. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics & Gynecology, 11th ed., pp. 250–266. New York: McGraw-Hill.
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