The carotid arteries are a pair of major blood vessels located on either side of the neck, delivering oxygen-rich blood from the heart to the brain and head. Each common carotid artery divides into the external carotid artery, which supplies the face and scalp, and the internal carotid artery, which nourishes the brain. Testing is used to determine if plaque has built up inside these vessels, causing narrowing or blockage, a condition known as carotid artery stenosis. Stenosis restricts blood flow and can lead to serious neurological events. Testing methods focus on visualizing the vessel walls and measuring the speed and volume of blood moving toward the brain.
Indications for Testing
A physician orders carotid artery testing based on a patient’s medical history, specific symptoms, or findings during a physical examination. Patients with established risk factors for atherosclerosis, such as high blood pressure, high cholesterol, or diabetes, are candidates for evaluation. Smoking history and a family history of early-onset heart disease or stroke also increase the need for screening.
Testing is indicated if a patient experiences symptoms suggesting temporary brain ischemia, such as a transient ischemic attack (TIA). Symptoms include sudden weakness, temporary vision loss, or difficulty speaking. Unexplained dizziness, fainting, or sudden vision changes also prompt investigation. During a physical exam, a physician may detect a whooshing sound called a carotid bruit, created by turbulent blood flow passing through a narrowed artery.
Carotid Duplex Ultrasound Procedure
The Carotid Duplex Ultrasound is the most common and non-invasive method used to assess the vessels in the neck. This procedure employs high-frequency sound waves to create images and measure blood flow, without the use of radiation or injections. The patient lies down, and a clear gel is applied to the neck. A handheld transducer is then moved along the path of the arteries. This device transmits sound waves and captures the returning echoes, allowing the technician to visualize the structure of the artery walls and any plaque buildup.
The “duplex” test combines two modes: B-mode imaging and Doppler technology. B-mode provides a two-dimensional image of the artery wall and the size of any plaque. The Doppler component measures the velocity of blood flow within the vessel, translating the flow into a spectral waveform or color-coded map. Significant narrowing causes the blood to accelerate, resulting in a higher velocity reading and an audible “whooshing” sound, which helps quantify the degree of blockage.
Supplemental Imaging Techniques
While the duplex ultrasound provides substantial information, other advanced methods may be used if the results are unclear or when planning a surgical intervention. Computed Tomography Angiography (CTA) uses X-rays and computer processing to create detailed cross-sectional images of the arteries. This technique involves the injection of an iodine-based contrast dye to highlight the blood vessels and the extent of the narrowing.
Magnetic Resonance Angiography (MRA) uses magnetic fields and radio waves to generate detailed images of the blood vessels. MRA requires a contrast agent, usually gadolinium, to enhance clarity. Both CTA and MRA offer a broader view of the neck and brain circulation. They are useful for evaluating complex plaque characteristics or blockages high up in the neck or near the base of the skull, areas difficult to view with ultrasound alone.
Interpreting Stenosis Results
The primary result from a carotid artery test is the degree of stenosis, which is the percentage of the artery’s diameter that is blocked or narrowed by plaque. Stenosis results are grouped into ranges that guide subsequent medical decisions.
Mild stenosis is considered less than 50% blockage. Management focuses on controlling risk factors through medication and lifestyle changes.
Moderate stenosis is defined by a narrowing between 50% and 69% of the artery’s diameter. This range is determined by the visual image and a measured peak systolic velocity (PSV) of blood flow in the internal carotid artery, frequently exceeding 180 cm/second. Patients in this category require more aggressive medical therapy and regular monitoring with follow-up ultrasounds to track any progression of the disease.
Severe stenosis is classified as 70% or greater narrowing, or near-total occlusion of the vessel. This high degree of blockage significantly increases the risk of stroke and prompts discussion about surgical intervention, such as carotid endarterectomy or stenting. The specific percentage of narrowing dictates the urgency and nature of the treatment plan to prevent a future neurological event.