An arterial duplex ultrasound is a non-invasive imaging technique used to visualize blood flow and the structure of arteries throughout the body. This vascular ultrasound assesses the circulatory system without using X-rays or injecting dyes. The “duplex” name signifies that the test combines two separate modes of ultrasound to deliver a comprehensive evaluation. It provides both a live, two-dimensional image of the vessel and a quantitative measurement of the blood moving within it.
How the Duplex Technology Works
The technology is based on high-frequency sound waves transmitted into the body by a handheld device called a transducer. The first component is the B-mode, or brightness mode, which creates a grayscale image of the artery’s walls and surrounding tissues. This allows for the visualization of the vessel’s structure, including any plaque buildup, vessel wall thickness, or narrowing of the internal passageway.
The second, equally important component is the Doppler ultrasound, which uses the physical principle of the Doppler effect. This mode records the frequency shift of the sound waves as they reflect off moving red blood cells. By analyzing this shift, the system calculates the speed and direction of blood flow in real-time. This combination of structural imaging and flow dynamics is what makes the arterial duplex scan a powerful diagnostic tool.
The Doppler data is often presented as a spectral waveform or a color map overlaid on the B-mode image. Color Doppler assigns different hues, typically red and blue, to blood flow moving toward or away from the transducer, providing an immediate visual assessment of flow patterns. The audible “swishing” sound sometimes heard during the exam is the raw Doppler signal being converted to sound, representing the actual flow of blood through the vessel.
Medical Conditions Diagnosed
This diagnostic tool is frequently used to identify and characterize Peripheral Artery Disease (PAD), which involves the buildup of atherosclerotic plaque that narrows the arteries, especially in the legs. By scanning arteries in the extremities, the test can pinpoint the exact location and extent of the blockage. It is also routinely used to evaluate the carotid arteries in the neck, where plaque can lead to stenosis and increase the risk of stroke.
Another common application is the detection of arterial occlusions, which are complete blockages that stop blood flow entirely. The test can also identify aneurysms, which are abnormal bulges or enlargements in the wall of an artery that carry a risk of rupture. Specific scans, such as renal duplex ultrasound, are used to examine the arteries supplying the kidneys, checking for narrowing that could contribute to high blood pressure.
The arterial duplex scan evaluates arteries in various parts of the body, including those supplying the arms, abdomen, and brain. For example, it helps determine the cause of leg pain during walking, known as claudication, by assessing blood flow in the femoral and popliteal arteries. This assessment of blood vessel health guides treatment decisions for numerous vascular conditions.
What Happens During the Procedure
The arterial duplex ultrasound is a straightforward procedure that requires little special preparation. Patients lie comfortably on an examination table, and the vascular technologist exposes the area being examined. A water-soluble gel is applied to the skin to transmit sound waves from the transducer into the body.
The handheld transducer is pressed gently against the skin and moved along the path of the artery being studied. Patients may feel slight pressure but should not experience pain. The examination often takes between 30 and 45 minutes, depending on the area being scanned. The technologist may ask the patient to change positions or briefly hold their breath to optimize the blood flow signal.
Understanding the Test Results
The interpretation of arterial duplex results relies on analysis of the images and velocity measurements. The grayscale image allows the physician to visualize the arterial wall, determining if plaque is present and noting its location. The Doppler velocity data is then used to quantify the severity of any narrowing observed.
When an artery narrows due to stenosis, the blood flow speed, known as the Peak Systolic Velocity (PSV), increases as it squeezes through the smaller opening. This velocity increase is measured precisely and is the primary parameter used to grade the blockage. For instance, an elevated PSV or a velocity ratio exceeding 2:1 compared to a normal segment often indicates a hemodynamically significant stenosis, meaning the artery is narrowed by 50% or more.
The waveform pattern provides substantial information about the health of the artery. Normal arteries in the limbs exhibit a triphasic waveform, which includes forward flow, a brief flow reversal, and a small forward flow during the cardiac cycle. As arterial disease progresses, this smooth pattern degrades into a biphasic or monophasic waveform, indicating reduced elasticity or a significant blockage upstream. Spectral broadening or aliasing in the Doppler signal signifies turbulent, disorganized flow, which is common immediately downstream from a severe stenosis.