The carotid arteries are major blood vessels located on either side of the neck, functioning as the primary pathway for oxygenated blood traveling from the heart to the brain and head. Given the brain’s high demand for blood, the condition of these arteries is closely linked to neurological health. A carotid ultrasound is a non-invasive imaging procedure that uses sound waves to create pictures of the vessels and assess the flow of blood within them. This examination provides a detailed view of the artery walls, helping medical professionals determine if there is any narrowing, blockage, or structural abnormality, which is a major factor in determining an individual’s risk for cerebrovascular events.
How the Carotid Ultrasound Works
The procedure uses a small, handheld device called a transducer, which a technician gently moves across the skin of the neck after applying a water-based gel. The transducer emits high-frequency sound waves that travel through the tissues and bounce back as echoes when they encounter surfaces like blood cells and artery walls. A computer translates these echoes into real-time images displayed on a monitor, creating a visual map of the carotid arteries.
A specialized technique, known as Doppler ultrasound, is integrated into the scan to measure the speed and direction of blood flow. Color flow Doppler overlays the standard image with colors (typically red and blue) to indicate the direction of blood movement relative to the transducer. Spectral Doppler generates a graph that allows clinicians to calculate the velocity of the blood flow, which is a direct indicator of obstruction. This process is quick, painless, usually takes about 30 minutes, and requires no radiation or injections.
Primary Findings: Detecting Carotid Artery Stenosis
The most frequent and clinically significant finding is carotid artery stenosis, a narrowing of the vessel. This narrowing is most commonly caused by atherosclerosis, where plaque—a sticky substance made up of fat, cholesterol, calcium, and other materials—builds up on the inner walls of the artery. The ultrasound identifies the precise location and size of this plaque buildup, providing a visual assessment of its extent, contour, and structure.
Beyond measuring the obstruction, the scan characterizes the plaque’s composition, determining its stability and risk profile. Plaque that is soft, irregular, or hypoechoic (darker on the image) is considered more “vulnerable” to rupture. This vulnerability stems from features such as intraplaque hemorrhage or a thin fibrous cap, which are associated with a higher risk of fragmentation. If a piece of unstable plaque breaks off, it can travel downstream and block a smaller artery in the brain, leading directly to an ischemic stroke.
Stenosis reduces the space for blood flow, forcing the blood to speed up as it passes through the constricted area. Doppler velocity measurements correlate directly with this narrowing; a higher velocity reading indicates a more severe stenosis. Combining the visual image of the plaque with the velocity data assesses the risk of reduced blood flow and potential embolization to the brain. This analysis of plaque morphology and hemodynamic changes is central to stroke risk stratification.
Other Conditions Revealed by the Scan
While stenosis is the main focus, the carotid ultrasound is a versatile tool that can identify several other vascular conditions. One condition is carotid artery dissection, involving a tear in the inner layer of the artery wall that separates the layers. The scan may reveal a “dissection flap”—a membrane floating within the artery—or a “double lumen,” representing the true and false channels created by the tear. A dissection can also be inferred from a thickened, hypoechoic vessel wall, signifying an intramural hematoma, or a sudden, unexplained absence of flow.
The scan can also detect an aneurysm, an abnormal dilation of the artery wall. A true aneurysm involves all three layers of the vessel wall, appearing as a distinct, enlarged segment of the vessel. A pseudoaneurysm, or false aneurysm, is also visible, often presenting as a sac-like structure adjacent to the artery with blood flow spiraling inside, sometimes displaying a characteristic “yin-yang” pattern on color Doppler. Furthermore, the ultrasound can identify vessel tortuosity, which is an excessive kinking or coiling of the artery. Severe kinking can lead to flow disturbances or, in some cases, predispose an individual to a dissection.
Interpreting the Degree of Blockage and Next Steps
The velocity measurements obtained from the Doppler analysis categorize the severity of carotid artery stenosis. Classification schemes use the Peak Systolic Velocity (PSV) at the point of maximum narrowing, the End Diastolic Velocity (EDV), and the ratio of the Internal Carotid Artery (ICA) velocity to the Common Carotid Artery (CCA) velocity. Stenosis is typically categorized as mild (less than 50% diameter reduction), moderate (50% to 69%), or severe (70% to 99%).
A mild blockage, usually indicated by normal or near-normal velocities, often leads to recommendations for lifestyle modifications and aggressive medical management, such as cholesterol-lowering drugs. As the degree of stenosis reaches the moderate range (50-69%), the PSV typically increases above 125 cm/s, and physicians may intensify medication or consider more frequent monitoring. Severe stenosis, generally associated with a PSV greater than 230 cm/s or a high ICA/CCA ratio, significantly increases stroke risk and may prompt a discussion about interventional procedures.
The ultimate decision for intervention depends on the severity of the stenosis and whether the patient has experienced symptoms. For severe blockages, procedures like carotid endarterectomy (plaque removal) or carotid artery stenting (inserting a mesh tube) may be recommended to reduce the risk of a future stroke. Regular follow-up scans monitor the progression of the disease or check for restenosis following a procedure.