A vascular ultrasound, often referred to as a duplex study, is a non-invasive test that uses high-frequency sound waves to evaluate the body’s circulatory system. This procedure allows physicians to assess the structure of the vessels and the speed and direction of blood flow within them. The primary purpose of the test is to identify blockages, narrowing, or other structural problems in arteries and veins throughout the neck, limbs, and abdomen. Understanding the technical language within the resulting report is the first step toward grasping the findings.
Decoding the Vascular Ultrasound Report Structure
A typical vascular ultrasound report is divided into several sections. The initial part contains basic patient and demographic information, followed by an outline of the specific vessels examined. Paired body parts, such as the arteries in the legs or arms, will have findings separated by laterality, labeled “Left” or “Right.”
The main body of the report is the Technical Findings or Data Section, which contains the raw measurements and observations made by the sonographer. This section is filled with abbreviations and numerical values that quantify the blood flow characteristics at various points along the vessel. These raw measurements form the foundation of the diagnosis.
The Impression or Summary section is typically found near the end of the document. This is where the interpreting physician, often a radiologist or vascular specialist, translates the technical data into a concise, clinical conclusion. The impression summarizes the presence and severity of any disease found, directly addressing the reason the test was ordered.
Essential Terminology and Doppler Metrics
Interpreting the data section requires familiarity with the specific measurements used to quantify blood flow. The most frequently cited measurement is the Peak Systolic Velocity (PSV), which represents the highest speed the blood achieves inside the vessel during systole (the heart’s contraction phase). Measured in centimeters per second (cm/s), PSV is the most effective parameter for detecting arterial narrowing.
Another measurement is the End Diastolic Velocity (EDV), which records the blood flow speed during diastole (the heart’s relaxation phase). Both PSV and EDV increase significantly when blood flow encounters a restriction. The Velocity Ratio, or PSV Ratio, provides a comparison by dividing the PSV measured in the narrowed segment by the PSV measured in a nearby, normal segment of the same vessel.
The report will also discuss the Spectral Doppler Waveform, a visual tracing of the blood flow pattern over time. Normal arterial flow in the limbs is “triphasic,” meaning it has three phases: brisk forward flow in systole, brief reversal in early diastole, and a small forward flow component in late diastole. A loss of this characteristic pattern, such as a “monophasic” waveform, suggests increased resistance or upstream disease.
Interpreting Arterial Stenosis Severity
The primary application of arterial duplex ultrasound is to grade the severity of stenosis, which is the narrowing of an artery usually caused by plaque buildup. The technical data is correlated with a standardized grading scale to categorize the blockage based on the increase in PSV and velocity ratio at the site of narrowing.
A minimal blockage (0-19% stenosis) shows a normal PSV and no significant increase in the velocity ratio. As the disease progresses to a mild or moderate stage (20-49% stenosis), the PSV may slightly increase, but the velocity ratio remains below two.
The next threshold, 50-69% stenosis, is considered clinically significant. This is typically indicated by a PSV exceeding 125 cm/s and a velocity ratio between two and four. Severe narrowing (70-99% stenosis) requires the blood velocity to increase dramatically, often diagnosed when the PSV exceeds 230 cm/s and the velocity ratio is greater than four.
A complete blockage, or 100% occlusion, is reported when there is no measurable blood flow, meaning both PSV and EDV are absent. In cases of near-total occlusion, the velocities might drop again, showing a tiny, slow stream of flow sometimes referred to as a “trickle.” The interpreting physician uses these established velocity thresholds to translate the raw numbers into the final percentage of arterial blockage.
Identifying Non-Stenotic Abnormalities
Vascular ultrasound identifies abnormalities that do not involve arterial narrowing, particularly issues within the venous system. The most common is Deep Vein Thrombosis (DVT), a blood clot in a deep vein, most frequently in the legs. The definitive finding for an acute DVT is the lack of compressibility of the vein when pressure is applied with the ultrasound probe.
A healthy vein collapses completely under slight external pressure, but a vein containing a solid blood clot remains open. The report may mention the clot’s appearance, describing an acute thrombus as relatively dark (“hypoechoic”), while an older, chronic clot appears brighter (“echogenic”) due to organization and fibrosis. The spectral Doppler may also show a continuous, non-phasic flow pattern instead of normal respiratory-related flow variations.
Another non-stenotic abnormality is an Aneurysm, a localized, abnormal dilation of an artery or vein. The report defines an aneurysm by providing its maximum diameter measurement, comparing it to the normal size of the vessel at nearby points. An aneurysm may also be associated with turbulent blood flow, which the Doppler study visualizes as a chaotic mixture of colors.
The report may also detail Valvular Incompetence, primarily in the leg veins, which indicates chronic venous insufficiency. Veins contain one-way valves that prevent blood from flowing backward. If these valves are damaged, the ultrasound will show “reflux,” meaning blood flows backward when the patient performs a maneuver that increases venous pressure, such as the Valsalva maneuver or calf compression. The duration and velocity of this reverse flow quantify the severity of the venous valve dysfunction.