What can a continuous wave Doppler assess that a pulsed Doppler cannot?

Continuous wave Doppler ultrasound is particularly designed to assess higher velocities of blood flow and provides values without range resolution. This means that it can measure extremely high velocities, such as those encountered in stenosis or other areas of high-grade arterial disease, where the speed of the flowing blood can exceed the limits of pulsed Doppler.

In contrast, pulsed Doppler has limitations regarding measuring high velocities due to its sampling method, which uses specific intervals to obtain data. When blood flow velocities exceed the Nyquist limit (often around 2 m/s), pulsed Doppler cannot accurately measure those velocities and can lead to aliasing, obscuring the true nature of the flow. Continuous wave Doppler, however, does not have this limitation as it continuously transmits and receives ultrasound signals, allowing for the identification of high-velocity flows without the additional complication of range resolution, which can lead to mixing velocities from different depths.

Thus, the unique aspect of continuous wave Doppler that allows for the assessment of higher velocities makes it invaluable in vascular sonography, particularly for assessing conditions such as significant stenosis or other abnormalities where blood flow is expected to be rapid.