The carotid arteries are major blood vessels located on either side of the neck, responsible for delivering oxygen-rich blood from the heart up to the brain. Carotid Artery Disease (CAD), also known as carotid stenosis, occurs when fatty deposits called plaque build up inside these arteries, causing them to narrow. Plaque buildup can reduce blood flow or break off and travel to the brain, which is a significant cause of ischemic stroke. Testing aims to measure this narrowing to quantify an individual’s stroke risk and guide preventive medical interventions.
When Carotid Artery Testing is Necessary
A healthcare provider typically orders a carotid artery test when specific symptoms or known risk factors raise concern for reduced blood flow. Symptoms that prompt testing often include a transient ischemic attack (TIA), sometimes called a “mini-stroke,” or unexplained neurological issues like temporary vision loss, sudden dizziness, or weakness on one side of the body. The presence of a carotid bruit, an abnormal “swooshing” sound heard over the neck artery during a physical exam, is another common trigger for testing. This sound indicates turbulent blood flow, although it does not definitively confirm severe narrowing. Testing is also frequently considered for individuals without symptoms but who have multiple long-standing risk factors, such as uncontrolled high blood pressure, high cholesterol, diabetes, a history of heavy smoking, or known coronary artery disease.
Carotid Ultrasound: The Standard Screening Method
The most common and non-invasive procedure for initial evaluation is the Carotid Duplex Ultrasound. This painless test uses a handheld device called a transducer, which is placed on the neck after a thin layer of gel is applied. The transducer emits high-frequency sound waves that bounce off the artery walls and blood cells, creating real-time images and flow measurements. The “Duplex” examination has two main components. B-mode imaging produces a two-dimensional image of the artery’s structure, allowing visualization of plaque deposits and measurement of the inner diameter. Doppler technology uses the change in the pitch of the returning sound waves to measure the speed and direction of blood flow.
Areas of narrowing cause blood to accelerate, creating a high-velocity jet stream that the Doppler can detect and quantify. These velocity measurements are translated into a percentage of narrowing, providing the most reliable data for diagnosing stenosis severity. Because the test is non-invasive and does not use radiation or contrast dye, it is the preferred first-line diagnostic tool for screening and monitoring the disease over time.
Advanced Imaging Techniques for Further Evaluation
When the results of the carotid ultrasound are inconclusive, or when a surgical procedure is being planned, advanced cross-sectional imaging may be ordered to confirm the diagnosis. Carotid Computed Tomography Angiography (CTA) uses a specialized X-ray machine and a rapid injection of an iodinated contrast agent to create detailed three-dimensional images of the arteries. CTA is particularly useful for visualizing the entire course of the artery and for detecting calcium deposits within the plaque. Magnetic Resonance Angiography (MRA) uses a strong magnetic field and radio waves to generate high-resolution images, often utilizing a gadolinium-based contrast agent. Both CTA and MRA provide greater anatomical detail than ultrasound, making them valuable for surgical planning by precisely mapping the location and extent of the stenosis.
Understanding the Test Results and Stenosis
The final test result is expressed as a percentage of stenosis, representing the degree of narrowing in the internal carotid artery. Stenosis is generally categorized into three clinical ranges to guide treatment decisions. Mild stenosis (less than 50% narrowing) is typically managed with aggressive lifestyle changes and medication. Moderate stenosis (50% to 69%) increases the risk of stroke, and medical therapy remains the standard approach with close monitoring. Severe stenosis (70% to 99%) carries a substantially higher risk of stroke, frequently leading to a discussion of surgical intervention, such as carotid endarterectomy or stenting.