What are the best practices for measuring blood flow and velocity using Doppler ultrasound?

1 Choose the right probe

The probe is the device that emits and receives the sound waves from your skin. Depending on the type and location of the vessel you want to examine, you may need a different probe with a specific frequency, shape, or size. For example, a lower frequency probe can penetrate deeper into your tissues, while a higher frequency probe can provide better resolution for superficial vessels. A curved or linear probe can cover a larger area, while a phased array probe can steer the sound beam in different directions. Consult your device manual or your supervisor for guidance on selecting the appropriate probe for your exam.

2 Apply enough gel

The gel is the substance that helps create a smooth contact between the probe and your skin. It also reduces the air gaps that can interfere with the sound transmission and reflection. Without enough gel, you may get poor image quality, artifacts, or inaccurate measurements. Apply a generous amount of gel to the probe and the skin surface, and spread it evenly to cover the entire area of interest. You may need to reapply more gel during the exam if it dries out or gets wiped off.

3 Adjust the angle

The angle is the angle between the direction of the sound beam and the direction of the blood flow in the vessel. It affects how the Doppler effect changes the frequency of the reflected sound waves, which is how the device calculates the blood velocity. Ideally, you want to align the probe parallel to the vessel, so that the angle is zero. This will give you the most accurate measurement of the blood velocity. However, this is not always possible or practical, especially for deep or curved vessels. In that case, you should try to keep the angle as small as possible, preferably less than 60 degrees. You can adjust the angle by tilting, rotating, or sliding the probe along the skin. You can also use the device settings to correct for the angle if you know it.

4 Optimize the image

The image is the visual representation of the blood flow and the surrounding tissues on the device screen. It can help you identify the vessel of interest, locate any abnormalities, and guide your measurements. To optimize the image quality, you should adjust the device settings according to the type and depth of the vessel, the amount of blood flow, and the ambient lighting. Some of the settings you may need to tweak include the gain, the depth, the scale, the filter, and the color map. You should aim for a clear, bright, and contrasted image that shows the blood flow as a distinct color from the background.