Doppler studies use ultrasound waves to assess structures and processes inside the body. One of the most familiar uses of ultrasound is in obstetrics where the technique is used to evaluate the developing fetus. Doppler ultrasound studies are also used in other areas of medicine, including neurology, where they can be useful in assessing blood flow to and in the brain. Carotid Doppler studies use ultrasound energy to look for blockages or narrowing in the two carotid arteries that supply the brain with oxygen-rich blood. The carotid arteries are located on either side of the neck. A transcranial Doppler study evaluates the flow of blood inside the skull.
Carotid and transcranial Doppler studies usually are performed to assess a person’s risk of having a stroke of transient ischemic attack (TIA or “mini-stroke”), emboli or other issues related to blood flow in the brain, or to manage treatment in patients at risk for these issues. When assessing stroke risk, they’re often ordered in patients who have:
high blood pressure (hypertension)
a history of smoking
coronary artery disease or other vascular disease
a personal or family history of strokes or TIAs
unusual sounds detected with a stethoscope that may indicate a partial blockage or narrowing in the carotid arteries
Both tests are performed on an outpatient basis. Carotid ultrasounds are completely noninvasive. Transcranial ultrasound tests may include other tests like a “bubble study” that tracks tiny, microscopic bubbles injected into the bloodstream to determine if these bubbles are able to make it to the brain or if they’re trapped prior to reaching the brain. The bubble study can be useful in determining if clots that form elsewhere in the body could potentially travel to the brain, causing stroke. Both tests use a handheld device called a transducer that’s placed against the skin and moved over the evaluation site. The transducer sends ultrasound waves through the skin, “capturing” the waves as they bounce back and then sending data to the ultrasound machine, which creates detailed images based on that data.