How to Read Vascular Ultrasound Results

A vascular ultrasound report typically contains a mix of velocity measurements, flow direction descriptions, vessel diameter readings, and waveform classifications that together tell your doctor whether blood is moving through your arteries and veins the way it should. Understanding these results does not require a medical degree, but it does help to know what the key numbers represent and when they signal a problem. The specific values that matter depend heavily on which vessels were examined, since a “normal” reading in a carotid artery looks nothing like a “normal” reading in a leg vein.

What the Colors and Images Actually Show

Most vascular ultrasound reports reference color Doppler, which overlays a color map onto a grayscale image of your blood vessels. The color-coding convention is straightforward: red indicates blood flowing toward the ultrasound probe, and blue indicates blood flowing away from it. Brighter shades of either color mean faster flow. This is sometimes called the BART convention (blue away, red toward), and it has nothing to do with whether blood is oxygenated or deoxygenated. Your report might also mention “power Doppler,” which shows the overall strength of blood flow signals regardless of direction, or “B-Flow,” which visualizes blood movement with high resolution and fewer imaging artifacts than standard color Doppler.¹

Beyond the color maps, the most information-dense part of your report comes from the spectral waveform, a graph that plots blood velocity over time. Picture a zigzag line that peaks with each heartbeat and dips between beats. The shape of that line tells the sonographer and your doctor a great deal about the health of the vessel. A tall, sharp peak followed by a brief reversal of flow and then a gentle forward drift is the classic healthy arterial pattern in your legs. A rounded, blunted peak without any reversal suggests something is restricting flow upstream.

The Velocity Numbers on Your Report

Two velocity readings dominate most vascular ultrasound reports. Peak systolic velocity (PSV) is the fastest speed blood reaches during the heart’s pumping phase. End diastolic velocity (EDV) is the speed of blood at the moment just before the next heartbeat, when the heart is relaxed. Both are measured in centimeters per second (cm/s). Of the two, PSV tends to be the workhorse measurement for grading arterial narrowing because it is less prone to measurement errors.² EDV becomes important for severe stenosis, where a persistently elevated diastolic velocity signals that the narrowing is tight enough to keep blood under high pressure even between heartbeats.

Another number you may encounter is the resistive index (RI). It is calculated from PSV and EDV and reflects how much resistance the smaller vessels downstream are putting up against blood flow. In the kidneys, for example, a normal RI typically falls between 0.50 and 0.70. A value above that range can suggest problems like narrowing of the renal artery or disease within the kidney itself.³ An RI close to 1.0 means almost no blood is flowing during the relaxation phase of the heartbeat, which is a red flag.

Reading Carotid Artery Results

If you had a carotid ultrasound, your report is focused on whether the arteries supplying blood to your brain have narrowed. The degree of narrowing (stenosis) is usually expressed as a percentage, but the raw numbers driving that percentage are the PSV and EDV in your internal carotid artery (ICA), often compared to the common carotid artery (CCA) just below it. This comparison is reported as the ICA/CCA ratio. A ratio below about 2.0 generally corresponds to less than 50% narrowing, while a ratio above 4.0 points to 70% or greater stenosis, a range where surgical intervention is often discussed.⁴

The absolute PSV matters too. In research comparing ultrasound to angiography, a PSV of 250 cm/s in the internal carotid artery was the strongest single predictor of a stenosis greater than 70%, though the accuracy varied between different vascular labs.⁵ That variability is worth knowing about: different hospitals use slightly different velocity thresholds, so a PSV of 230 cm/s might be classified differently depending on where the scan was performed. The standardized criteria your lab uses should be stated on or available alongside your report.

When CT angiography was compared head-to-head with color Doppler ultrasound for carotid stenosis in a study of 170 patients, CT angiography was more accurate overall, achieving about 97% accuracy compared with roughly 76% for Doppler ultrasound.⁶ This does not mean your carotid ultrasound is unreliable, but it does explain why your doctor may order a CT or MR angiogram to confirm findings before recommending surgery. Ultrasound serves as an excellent screening tool, and for mild or moderate stenosis the results are usually trustworthy on their own.

Venous Results and What “Compressibility” Means

If your ultrasound was ordered to look for a blood clot in your legs, the report centers on a deceptively simple test: can the vein be fully squeezed flat with the ultrasound probe? A healthy vein collapses easily under gentle pressure. A vein that refuses to compress has something solid inside it, which is the hallmark of deep vein thrombosis (DVT). The most commonly tested sites are the common femoral vein at the groin and the popliteal vein behind the knee.⁷ Your report will usually describe each vein as either “compressible” (good news) or “non-compressible” (evidence of clot).

A separate venous concern is reflux, which means the valves inside your veins are not closing properly and blood is leaking backward. This is the underlying problem in varicose veins and chronic venous insufficiency. During the exam, the sonographer provokes reflux by squeezing your calf or using a specialized maneuver, then measures how long backward flow lasts. For veins in the superficial system and the deep calf veins, backward flow lasting more than 500 milliseconds is considered abnormal. For the larger femoropopliteal veins (the deep veins of the thigh and behind the knee), the threshold is higher at more than 1,000 milliseconds. Perforator veins that connect the deep and superficial systems are flagged at more than 350 milliseconds of outward flow.⁸ If your report lists reflux durations, those are the benchmarks your doctor is comparing them against.

Peripheral Arterial Disease in the Legs

When ultrasound is used to evaluate the arteries in your legs, the report pays close attention to the waveform shape at each segment. In a healthy leg artery, the waveform has a sharp peak, a brief dip below the baseline (indicating a momentary reversal of flow), and then a small forward bump. This multi-phase pattern means blood flow is pulsing normally through a vessel with good elasticity and no major obstruction. When a significant blockage is present upstream, the waveform loses that reversal component and becomes a smooth, rounded single hump, described as “monophasic.” In one study of patients with confirmed peripheral arterial disease, monophasic flow was found in 76% of affected limbs.⁹

Your report may also mention “spectral broadening” and “turbulent flow.” In a normal artery, most red blood cells move at similar speeds, producing a crisp waveform with a clear window underneath the peak. When a narrowing creates turbulence, cells scatter in different directions and speeds, filling in that window. This spectral broadening is one of the earliest signs of developing stenosis, sometimes appearing before the narrowing is severe enough to register as a dramatic velocity change. Compared to CT angiography across all leg artery segments, duplex ultrasound has demonstrated a sensitivity around 93% and an overall accuracy near 86%.¹⁰

Abdominal Aortic Aneurysm Measurements

Screening for an abdominal aortic aneurysm (AAA) is one of the most common reasons for a vascular ultrasound, particularly in older men who have ever smoked. The key number on your report is the maximum diameter of the aorta, measured in centimeters. A normal abdominal aorta is generally under 3 cm in diameter. Once it reaches 3 cm, it is classified as aneurysmal. Repair is typically discussed once the diameter reaches about 5.5 cm in men or 5.0 cm in women, or if the aneurysm is growing rapidly.

One important nuance: how the diameter is measured matters more than you might expect. There are several methods that differ in where the measurement calipers are placed on the vessel wall (inner edge to inner edge, outer edge to outer edge, or leading edge to leading edge). A review of measurement practices found a wide range of definitions in use, with no single standardized approach.¹¹ A direct comparison of the three leading methods showed that ultrasound consistently underestimates aortic size compared to CT. The inner-to-inner method underestimated the most, by an average of about 5 mm, while the outer-to-outer method came closest to CT, underestimating by only about 1 mm.¹² If your report gives a diameter close to a surgical threshold, your doctor may order a CT scan for a more precise measurement before making any decisions.

Renal Artery Findings

If your ultrasound evaluated blood flow to your kidneys, the report focuses on whether the renal arteries are narrowed, a condition that can cause hard-to-control high blood pressure or declining kidney function. The primary measurement is the PSV within the renal artery itself. Most studies have found that a PSV above roughly 180 to 200 cm/s suggests a stenosis of more than 50%.¹³ For more severe narrowing of 60% or greater, one study identified 285 cm/s as the PSV threshold offering the best balance of accuracy, catching about two-thirds of significant stenoses while correctly clearing nine out of ten normal arteries.¹⁴

Your report may also include the renal-aortic ratio (RAR), which compares the PSV in the renal artery to the PSV in the aorta. A ratio above about 3.5 to 3.7 raises suspicion for significant stenosis. The resistive index measured within the kidney itself, as described earlier, adds another layer. If the RI is markedly different between your two kidneys, the one with the lower RI on the affected side may be receiving less blood due to upstream narrowing, while the opposite kidney may show a higher RI from chronic damage. However, accuracy of these various criteria is quite variable across studies, which is why vascular labs often use several parameters together rather than relying on any single number.¹³

Pseudoaneurysms and Post-Procedure Complications

If you recently had a cardiac catheterization or another procedure that involved puncturing an artery in your groin, your doctor may order an ultrasound to check for a pseudoaneurysm. Unlike a true aneurysm, which involves stretching of the vessel wall, a pseudoaneurysm is essentially a contained leak: blood escapes through the puncture site and collects in a sac next to the artery, connected by a narrow channel called a neck. On ultrasound, the telltale sign is a “to-and-fro” waveform in that neck, meaning blood flows into the sac during the heartbeat’s pumping phase and then partially flows back out during relaxation. Duplex ultrasound is the go-to test for this diagnosis, with reported sensitivity around 94% and specificity around 97%.¹⁵

Your report will describe the sac’s size, the length and width of the neck, and whether there is active flow within it. Small pseudoaneurysms sometimes clot off on their own. Larger ones, or those with a wide neck, may need treatment, which can range from ultrasound-guided compression to injection of thrombin directly into the sac. The size and neck dimensions on the report guide that decision.

When Contrast Is Used

Standard vascular ultrasound does not require an injection, but in some situations your doctor may use a contrast agent, tiny gas-filled microbubbles injected into a vein that make blood flow much more visible. Contrast-enhanced ultrasound (CEUS) is particularly useful after aortic stent-graft repair. One of the main concerns after stent repair is an endoleak, where blood continues to seep into the aneurysm sac around the graft. Research has shown that CEUS is at least as good as CT for detecting endoleaks and may actually be more sensitive.¹⁶ Because CEUS avoids radiation and iodinated contrast dye (which can be hard on the kidneys), it is increasingly used for long-term surveillance in patients who need repeated imaging after stent placement.

Artifacts and Limitations to Watch For

Your ultrasound report is only as good as the quality of the images obtained, and certain artifacts can trip up the interpretation. The most common one in vascular studies is aliasing, which happens when blood is moving so fast that the machine cannot accurately track the velocity. On the color map, aliasing looks like a sudden flip from red to blue (or vice versa) in the middle of a vessel, creating a confusing mosaic of colors that could be mistaken for turbulent or abnormal flow. In reality, it is just a technical limitation that occurs when the machine’s sampling rate is set too low for the actual velocities present. It is particularly common in high-flow areas like dialysis fistulas.¹⁷ A skilled sonographer adjusts for this during the exam, but if it is mentioned in the report, it means the operator was aware and either corrected for it or flagged it as a potential source of error.

Body habitus (your body size and shape) also matters. Ultrasound waves have a harder time penetrating through thicker tissue, and bowel gas can completely block the view of deep abdominal vessels. If your report says something like “limited study due to body habitus” or “aorta not visualized due to overlying bowel gas,” it is not a reflection of the technologist’s skill. It is an inherent limitation of the technology. In those cases, CT or MR angiography may be recommended as an alternative. Similarly, heavily calcified arteries can cast acoustic shadows that obscure the vessel wall and make velocity measurements unreliable. Your report should note when calcification limited the assessment.

Hemodialysis Access Monitoring

For patients on hemodialysis, vascular ultrasound plays a unique role in evaluating the arteriovenous fistula (AVF) or graft used for dialysis. These are surgically created connections between an artery and a vein, and they are prone to complications like narrowing at the connection site, failure to mature, or blood clot formation. Duplex ultrasound is the only imaging method that gives both anatomical information (vessel diameter, wall thickness) and functional data (flow velocities, flow volume) in a single noninvasive exam, which makes it uniquely valuable for tracking fistula health over time.¹⁸ If you have a dialysis access, your report will include flow volumes (usually in milliliters per minute) and note any areas of stenosis or abnormal turbulence within the fistula circuit. A declining flow volume over serial exams is one of the earliest warnings that the access may be developing a problem that needs intervention.

Because flow speeds in a fistula are much higher than in normal vessels, aliasing artifacts (as described above) are especially common in these studies, and the sonographer needs to adjust the machine settings accordingly. If your report mentions aliasing near the arterial anastomosis, that is not necessarily abnormal; it may simply reflect the expected high-velocity jet at the surgical connection point.

Why Your Report Might Differ From Someone Else’s

One frustrating reality of vascular ultrasound is that the field has not fully standardized the language used in reports. A joint effort by the Society for Vascular Medicine and the Society for Vascular Ultrasound produced a consensus statement proposing standardized terminology for describing arterial and venous waveforms, replacing a patchwork of older classification systems that varied between institutions.¹⁹ In practice, adoption has been uneven. You may see terms like “triphasic,” “biphasic,” or “monophasic” on one report and entirely different descriptors on another for the same type of finding. A comparison of older waveform classification systems found that different schemes could categorize as few as 77% or as many as 98% of the same set of waveforms, depending on which system was used.²⁰

The practical takeaway: if you are comparing results from two different vascular labs, be cautious about drawing your own conclusions from differences in wording or even from small differences in velocity numbers. Ask your doctor whether the two reports used the same criteria. And if your report describes a borderline finding using velocity thresholds, remember that those thresholds can vary between institutions, as illustrated by the carotid stenosis data discussed earlier. The trend over time, measured at the same lab with the same protocol, is usually more informative than any single snapshot.

When Ultrasound Leads to Further Testing

In emergency settings, point-of-care vascular ultrasound performed at the bedside can rapidly identify serious problems like arterial occlusion, aneurysm, or DVT. Case series from emergency departments have documented that bedside vascular ultrasound changed clinical management by speeding up diagnoses and preventing harmful delays.²¹ But even in non-urgent scenarios, your vascular ultrasound often serves as a first step rather than the final word. A finding of moderate or severe stenosis on carotid Doppler will typically prompt a CT or MR angiogram before any surgical planning, given that CT angiography is more accurate for grading stenosis. An aortic diameter that sits near the repair threshold on ultrasound will usually get a confirmatory CT measurement, because ultrasound tends to underestimate the true size. A DVT found on compression ultrasound, on the other hand, is usually considered definitive enough to start treatment immediately without further imaging. Understanding where your ultrasound fits in the diagnostic chain helps you anticipate what comes next and ask better questions of your care team.