You will be asked to remove any jewelry that might interfere with the test, especially around the neck area. You may need to remove some of your clothes; if not, wearing a loose-fitting shirt with an open neck would be best. Do not smoke for a few hours before the test.
What happens during the test?
You will lie down on your back on an examination table. Your head may be turned to one side, and you will have to stay still. A clear gel will be applied to the left and right sides of your neck where the carotid arteries are located. The gel helps the device glide around on your skin, making it easier for the sound waves to pass through. The doctor or technician will press the device against your neck and move it back and forth over the length of your neck several times to get many different views of the carotid artery. You may hear a sound like a heartbeat while the machine monitors and measures the blood flow through the artery. The process is then repeated on the carotid artery on the other side of your neck. The entire procedure usually takes about 30 minutes.
What happens after the test?
You may go back to your normal activities after the test. The technician will record the test so that it can be reviewed by a radiologist, who will contact your doctor with the results.
What do the results mean?
Your doctor will compare the images of your left and right carotid arteries to look for any differences in blood flow. Irregular or disrupted blood flow on the images means that you may be at risk for stroke. The greater the narrowing is, the higher your risk. Your doctor may recommend medications or another imaging test to determine if you should have surgery to open your carotid arteries and prevent a stroke.
If you are having the test to evaluate the results of a procedure, the doctor will examine the images to make sure the blood is flowing freely.3 If the test shows irregular blood flow or new narrowing, the artery may have re-narrowed because of plaque buildup or clots.
The carotid Doppler ultrasound test is very accurate at evaluating blood flow in the carotid arteries in the neck. One study of 503 patients (31% were women) found that for detecting severe narrowing the ultrasound results agreed with the results of an angiogram 96% of the time.5
Arteries that have large deposits of calcium are more difficult to see on the ultrasound image, making the test less accurate.6 Arrhythmias (heart rhythm problems) and some other kinds of heart disease can also affect the accuracy of the test.6
A complete blockage of the carotid artery can't always be detected by carotid Doppler ultrasound alone.4 When the results of this test are not conclusive, additional tests such as CT angiography or MR angiography may be performed.6