Carotid ultrasound is a non—invasive diagnostic imaging tool used to visualize the inside of a carotid artery.
Carotid ultrasound, also called carotid duplex ultrasonography (CUS), or Doppler ultrasonography, is a diagnostic imaging technique that uses ultrasound waves instead of radiation (as used by x ray) to generate color snapshots or moving images of the interior of the carotid arteries, the major arteries of the neck that supply blood to the brain. Since the technique also allows to measure blood flow velocity, carotid ultrasound results can show whether buildup of a fatty material called plaque has narrowed one or both carotid arteries and impaired blood flow to the brain.
Carotid ultrasound is used to help diagnose and evaluate carotid disease , characterized by narrowing or blockage of the carotid arteries, resulting from the accumulation of plaque on the inner walls of these arteries. A carotid ultrasound may be performed to see whether carotid disease treatment, especially surgery such as carotid endarterectomy, has restored normal blood flow. It can also help evaluate the effects of antihypertensive drugs on blood flow.
Carotid ultrasound is a well-validated technique used to study the presence and progression of cardiovascular disease. Carotid ultrasound can also be used as a preventive screening test in people who have medical conditions that increase their risk of stroke , including high blood pressure and diabetes. People with these conditions, especially in the senior population, may benefit from undergoing regular carotid ultrasound tests even if they show no signs of plaque buildup.
Carotid ultrasound images are collected with an ultrasound instrument that consists of the following components:
- The pulser: This device generates electrical pulses for conversion into ultrasound waves.
- The transducer: The transducer contains a piezoelectric crystal that converts the electrical pulses into ultrasound waves that pass into the body and bounce off the carotid arteries. The device detects the different reflections of the ultrasound waves, which are then converted by a computer into live images of the arteries and the blood flow.
- The receiver: The receiver amplifies the ultrasound signals and rejects noise signals.
Carotid duplex ultrasound is usually performed with a high frequency transducer (5–10 mHz), color flow imaging, with Doppler velocity measurement capabilities.
Patients can undergo a carotid ultrasound without any special preparation being required. It is usually performed in a health clinic or hospital. The test is painless and usually takes from 30 minutes to one hour. The patient is asked by an ultrasound technician to lie on an examination table, and a gel is applied to the neck to provide lubrication and help transmit the sound waves. The transducer is moved back and forth over one side of the neck to obtain different views of the carotid artery. The other side of the neck is then scanned. Once clear images are obtained, they are recorded on film or video by the technician for later analysis by the radiologist. A typical carotid ultrasound takes from 15 to 30 minutes to complete.
Doppler ultrasound is a variation of the technique that additionally examines the flow of blood through the carotids. It is based on the Doppler effect, which changes the frequency of the sound waves as they bounce off the moving blood, thus providing an image of blood in motion.
Test results can be normal or abnormal. A normal ultrasound shows no significant narrowing or other abnormality in the arteries examined. An abnormal ultrasound may show an image or irregular blood flow that indicates a blocked or narrowed artery.
Ultrasound machines are usually maintained by the operating technicians. Representatives from the company that manufactured the equipment may assist with scheduled maintenance, urgent repairs, equipment upgrades, and in many instances, actual training of technicians.
A carotid ultrasound is performed by a doctor specialized in performing and interpreting imaging tests (radiologist) or by an ultrasound technologist (sonographer) who is supervised by a radiologist. Most ultrasonography training programs are hospital—based. Currently, certification in diagnostic sonography is achieved by passing the American Registry for Diagnostic Medical Sonography (ARDMS) exams. This is the certification most widely recognized by the American (and Canadian) medical communities. The course of studies consists of ultrasound physics and medical sonography, followed by clinical training, in which instructors organize scanning modules on various organ systems with emphasis on proper technique and recognition of normal anatomy. Students can usually start scanning within the first clinical week. Progress is monitored by regular clinical evaluations that include assessment of skill level and professional conduct.
Carotid artery —A blood vessel that supplies the brain with oxygenated blood.
Carotid disease —Carotid disease occurs when the major arteries of the neck that supply blood to the brain become narrowed or blocked.
Carotid endarterectomy —Surgical procedure performed to remove plaque from a carotid artery.
Doppler effect —Change in the frequency of sound or light waves as they bounce off a moving object.
Plaque —A semi—hardened accumulation of substances from fluids that bathe an area. Plaques on the inner walls of blood vessels can lead to blood clot formation, heart attacks, and stroke.
Sonographer —A medical technician trained in performing ultrasound exams.
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National Institute of Neurological Disorders and Stroke (NINDS), P.O. Box 5801, Bethesda, MD, 20824, (301) 496-5751, (800) 352-9424, http://www.ninds.nih.gov.
National Stroke Association, 9707 East Easter Lane, Englewood, CO, 80112-3747, (303) 649-9299, (800) STROKES, (303) 649-1328, [email protected], http//www.stroke.org.
Monique Laberge Ph.D.