The most common carotid artery test is a duplex ultrasound, a painless scan that takes 15 to 30 minutes and requires no needles, no fasting, and no recovery time. You lie on your back, a technician applies warm gel to your neck, and a small handheld probe captures images of blood flow through the two carotid arteries that supply your brain. If your doctor needs more detailed imaging, other options include CT angiography, MR angiography, or, rarely, catheter-based angiography.
What Happens During a Carotid Ultrasound
You’ll lie face-up on an exam table, and the technician may tilt your head to one side to expose your neck more fully. A clear, water-based gel goes on the skin over each carotid artery. The gel eliminates tiny air pockets between the probe and your skin so sound waves can pass through cleanly.
The technician then presses a small device called a transducer gently against the side of your neck. It sends high-frequency sound waves into the tissue, and a computer translates the returning echoes into a real-time image of the artery. Part of the test shows the structure of the vessel wall and any plaque buildup. The other part, called Doppler imaging, measures the speed and direction of blood flowing through the artery. Combining both views is what makes it a “duplex” ultrasound. The whole scan typically takes 15 to 30 minutes, and you can go straight back to your normal activities afterward. There is no radiation involved, and the test carries no known risks.
Preparation for the Test
There is almost nothing you need to do ahead of time. No fasting is required, and there are no restrictions on caffeine or medications. Wearing a shirt with an open or low neckline can make it easier for the technician to access the area, but that’s the extent of the preparation. If you experience any discomfort during the scan, which is uncommon, you can simply tell the technician and they’ll adjust the probe.
What the Results Tell You
The key measurement is how fast blood is moving through the artery. When plaque narrows the vessel, blood has to squeeze through a tighter space, which increases its velocity, much like water speeds up when you partially cover the end of a garden hose. Doctors use these velocity readings to estimate the degree of narrowing, or stenosis.
A peak blood flow speed around 125 cm/s or higher generally flags moderate narrowing (50% or more of the artery blocked), while speeds around 230 cm/s or higher suggest severe narrowing (70% or more blocked). These thresholds can vary somewhat between labs, which is why vascular labs calibrate their own equipment against standardized benchmarks. The test’s accuracy for detecting severe stenosis ranges from roughly 81% to 92%, depending on the specific velocity criteria a lab uses. Results are typically reviewed by a radiologist or vascular specialist and sent to the doctor who ordered the test.
Intima-Media Thickness Testing
A specialized version of the ultrasound measures the thickness of the inner two layers of the carotid artery wall. This measurement, called carotid intima-media thickness, can detect early signs of vascular disease before significant plaque has formed. A reading at or above the 75th percentile for your age, sex, and race signals increased cardiovascular risk. Plaque is typically defined as a focal thickening of the artery wall of at least 1.2 mm. This test uses the same ultrasound equipment and feels identical to a standard carotid scan.
CT Angiography of the Carotid Arteries
CT angiography, or CTA, pairs a CT scan with an injection of iodine-based contrast dye delivered through a vein in your hand or forearm. The dye makes the blood vessels stand out sharply on the images, giving doctors a detailed three-dimensional map of the arteries from the chest up through the brain. The scan itself takes only a few minutes, though the full visit, including the IV setup and a short monitoring period afterward, is longer.
CTA does involve radiation, though modern scanners use techniques to keep the dose as low as possible. The iodine contrast can cause mild reactions in some people, including nausea, itching, or hives, especially if you have a known iodine allergy. If you have kidney disease or diabetes, your care team may provide extra fluids after the test to help your kidneys flush the dye. Doctors typically order CTA when they need a wider view of the arteries than ultrasound can provide, or when ultrasound results are inconclusive.
MR Angiography of the Carotid Arteries
Magnetic resonance angiography, or MRA, uses a powerful magnet and radio waves instead of radiation. You lie inside an MRI machine while it captures images of blood flow. Some versions of the test require an injection of a contrast agent containing gadolinium, which highlights the arteries. Other techniques can image blood flow without any contrast at all.
The main drawback is time. MRA scans take longer than CT scans, and the confined space of the machine can be uncomfortable for people with claustrophobia. Ultrasound can show real-time blood flow dynamics that MRA misses, while CTA and MRA both offer broader anatomical coverage, imaging the arteries from the chest all the way through the head in a single session. Your doctor chooses between these based on what clinical question needs answering.
Catheter-Based Angiography
For decades, catheter angiography (also called digital subtraction angiography, or DSA) was the only way to image the carotid arteries. A catheter is threaded through a puncture in the femoral artery near the groin, guided up to the carotid arteries, and contrast dye is injected directly into the vessel. The resulting images offer the highest spatial resolution of any method, revealing fine details like plaque ulcerations and subtle irregularities in the artery wall.
This test is invasive, more expensive, and requires a period of bed rest afterward. The primary concern has historically been the risk of neurological complications. In the 1990s, the rate of permanent neurological injury was roughly 0.9%, with transient complications around 2%. Modern techniques using smaller catheters have driven that risk dramatically lower. A study of over 1,700 patients at a high-volume center between 2000 and 2008 found zero strokes or permanent deficits.
Still, non-invasive tests have largely replaced catheter angiography for routine diagnosis. Doctors reserve it for complex cases involving multiple narrowed vessels, when they need to assess the direction of blood flow and collateral circulation patterns, or when non-invasive imaging results are unclear.
Which Test You’re Most Likely to Get
For the vast majority of people, the first and often only test is the duplex ultrasound. It’s quick, painless, inexpensive, requires no contrast dye or radiation, and provides both structural images and real-time blood flow data. If the ultrasound reveals significant narrowing or the results are ambiguous, your doctor may follow up with CTA or MRA to get a more comprehensive picture before making treatment decisions. Catheter angiography is reserved for the small number of cases where non-invasive tools fall short.