How to utilize the basic buttons on a duplex ultrasound machine

The duplex ultrasound machine may look complex, but only a few buttons are used for a basic lower extremity arterial study:

• Power and sleep
• Probe and preset
• Trackball, freeze, and save (e.g., acquire 1)
• Caliper and depth
• Doppler gain, two-dimensional gain, and color gain
• Color scale
• Steering
• Pulsed-wave

Let’s get familiarized with each of these buttons so that you can feel confident using a Doppler probe.

As is true for all the buttons covered in this article, the power button will be located in different places depending on the machine. We’ll demonstrate examples of where each button may be found on the keyboard. But, keep in mind that their locations vary.

There is usually a sleep button next to the power button that can be used when the machine needs to be transported. Sleep mode decreases battery use, and the power usually lasts about 20–30 minutes for off-outlet scanning time.

As you get started, you will be prompted to pick a probe and a preset. Choose the 12 MHz linear transducer and the arterial lower extremity preset.

Most machines have a trackball in the middle of the keyboard with freeze and save buttons around it. Save is labeled as the acquire 1 button.

The freeze button is used to freeze images, which are then scrolled back with the trackball to get an optimal image, and then saved with the acquire 1 button.

Once an image is frozen, you can use the caliper button on the main keyboard to measure the distance between the arterial walls to diagnose an aneurysm, or to measure the peak systolic velocity (e.g., the highest peak on the waveform) to diagnose an obstruction.

The depth button will allow you to increase the image depth to see deeper vessels and decrease the image depth to more clearly see superficial vessels.

An additional set of buttons frequently used during a lower extremity examination are the gain buttons. These consist of two-dimensional (2D) gain, color gain, and Doppler gain (pulsed-wave or PW button). Gain buttons control the brightness of an image and can be adjusted throughout the exam.

Adjusting the Doppler gain will affect the brightness of the ultrasound. Changing the Doppler gain can affect the brightness so much that, at some levels, the waveforms can completely disappear. A slight adjustment will bring it into view again—but too much of an adjustment will create background changes!

Two-dimensional gain adjusts the visual volume of the black-and-white screen. Keep in mind that if the gain is too high, you can sometimes get artifacts that can affect the image quality.

Here’s a video example from our Ultrasound Masterclass: Arteries of the Legs Course showing the results of 2D gain adjustments:

As color gain is adjusted, the color appearance changes. It can fade away so that no color flow is seen or becomes so bright that it overwhelms the image, which makes the duplex difficult to evaluate. Fine adjustments to the color gain will affect how well you see the color flow.

Check out this example of color gain adjustments from our Ultrasound Masterclass: Arteries of the Legs Course:

Another color gain function is color scale, which can also be adjusted as you examine a vessel. Initially, it should be set around 30–40 cm / s. Color scale controls the color sensitivity, meaning that it allows a specific range of blood flow velocities to be translated into color. The gain helps amplify this data.

A lower color scale reads slower blood flow and must be adjusted. It can be adjusted along with gain throughout the examination. You can turn the color scale up or, if you are not seeing color very well in what seems like a patent artery, you can turn it down and increase your color gain. This is especially helpful if the area of concern is distal to significant stenosis and only has a trickle of blood flow.

If the scale is appropriately low but the gain is also too low, you still won’t see the blood flow. Thus, gain and scale are often adjusted depending on the need at each particular vessel.

In contrast, you can turn the color scale up to exclude low velocities and focus on high velocities, such as velocities that create aliasing and bruits. Turning the color scale up should make the color less sensitive to stenotic vibrations, decrease artifacts, and give better color fill.

The Doppler angle should be set at 60° with the angle parallel to the vessel wall. The steering button is used to make this adjustment.

If the vessel is at a slant where the Doppler angle cannot be parallel to the walls at 60°, then the angle can be adjusted to less than 60° for an accurate measurement. But, you ideally want to keep a 45–60° angle. If the Doppler angle is over 60°, the machine overestimates the velocity and thus the degree of stenosis.

As you measure the velocities, turn the direction of the color box so that it follows the slant of the vessel. The steering button controls the slant of the color box and the sample volume. Knowing how to maneuver these controls is helpful when measuring velocities.

When measuring velocities, press the PW button. This is the same PW button as mentioned under Doppler gain.

In addition to controlling gain (e.g., darkness or brightness), the PW button controls the waveform scale (e.g., size of the waveforms) on the velocity graph. This is extremely helpful for more accurate measurements of velocity. Keep in mind that you may have to increase your PW scale to accommodate high velocities in stenosis.