A carotid ultrasound is a non-invasive diagnostic test that uses high-frequency sound waves to create images of the two large arteries located on each side of your neck. These blood vessels, known as the carotid arteries, are responsible for delivering oxygen-rich blood directly from the heart to the brain. Specifically, the test is designed to evaluate the structure of the artery walls and measure the speed and direction of blood flowing through them.
Why Doctors Order a Carotid Ultrasound
Physicians most often request a carotid ultrasound to assess a patient’s risk for experiencing a stroke. Blockage or significant narrowing in the carotid arteries is a major cause of ischemic stroke, which occurs when a clot prevents blood flow to the brain. Early detection of problems allows for immediate intervention to lower this risk.
The test is frequently ordered for individuals who have already experienced stroke-like symptoms, such as a transient ischemic attack (TIA) or unexplained dizziness and fainting. A TIA, or “mini-stroke,” is a temporary event that signals a high risk of a future, more serious stroke. The ultrasound helps determine if the carotid arteries were the source of the temporary event.
Screening may also be recommended for people without symptoms but who possess medical conditions that increase their risk of arterial disease. These risk factors include high blood pressure, elevated cholesterol levels, diabetes, or existing coronary artery disease. A physician may also order the test if they hear an abnormal sound, called a carotid bruit, while listening to the neck with a stethoscope. This sound can suggest a partial blockage is present in the artery.
The Step-by-Step Procedure
The carotid ultrasound is a simple and generally painless examination performed by a specialized technician called a sonographer. The patient lies on their back on an examination table, and their head may be turned slightly to the side to give the technician better access to the neck. The test is completely external, meaning nothing is inserted into the body.
The sonographer applies a small amount of warm, water-based gel to the skin over the area of the carotid arteries. This gel helps eliminate air pockets and ensures the sound waves travel efficiently between the skin and the transducer. The technician gently presses the transducer against the skin on the side of the neck and moves it to capture images from different angles.
The test uses a specialized technique called Doppler ultrasound to measure the flow of blood. As the technician scans, the movement of blood cells causes a change in the pitch of the returning sound waves, known as the Doppler effect. This information is translated into graphs and color images on a monitor, which indicate the speed and direction of blood flow. During this part of the exam, the patient may hear a distinct whooshing or pulsing sound that represents the blood moving through the vessel. The entire procedure typically takes between 30 and 45 minutes to complete.
What the Ultrasound Results Reveal
The primary purpose of the ultrasound is to detect two specific conditions: the presence of plaque and the degree of stenosis, or narrowing, in the artery. Plaque is a buildup of fatty substances, cholesterol, and calcium on the inner walls of the arteries. The ultrasound images allow the physician to analyze the characteristics and stability of this plaque.
Stenosis is a measurement of how much the plaque has narrowed the artery, which restricts blood flow to the brain. The degree of narrowing is measured in percentages and is directly linked to stroke risk and subsequent treatment decisions. For instance, a blockage below 50% often suggests treatment can focus on lifestyle changes and preventative medications, such as statins or blood thinners.
If the ultrasound reveals moderate to severe stenosis, typically defined as a blockage of 50% or more, a more aggressive treatment plan may be necessary. For blockages over 60%, especially in patients with symptoms, a physician may recommend surgical interventions, such as a carotid endarterectomy to remove the plaque, or angioplasty and stenting to hold the artery open.
Preparing for the Exam
Preparation for a carotid ultrasound is minimal. Patients are generally advised to wear a shirt that has a comfortable, open neck to allow easy access for the sonographer to place the transducer. Any necklaces, chains, or large earrings should be removed before the appointment to prevent interference with the scanning area.
There is usually no requirement to fast or alter one’s diet before the test. However, some facilities may ask patients to avoid consuming caffeine or smoking for a few hours prior to the exam, as these substances can temporarily constrict blood vessels and potentially affect the accuracy of the blood flow measurements.