1.8.1.3 Practical Issues of Spectral Doppler

Several factors must be considered if one wishes to obtain good spectral tracings. The quality of the Doppler signal is greatly dependent on the quality of the 2D image. Therefore, optimize the image before you use Doppler. Use color Doppler to guide the positioning of your sample volume (PW Doppler) and Doppler line (CW Doppler). It will help you to observe the location of the flow as well as the direction of the jet. To obtain best results, align the Doppler wave parallel to flow.

As on the 2D image, artifacts are encountered with the Doppler technique as well (prosthetic valves). To avoid such artifacts you may need to reposition your Doppler sample volume or use a different 2D reference image. Use the "focus" when performing CW Doppler. The point of focus is depicted on the CW Doppler line. The focus point should be at the origin of the jet. Baseline shift and sweep speed should be adjusted accordingly. All machines are equipped with a baseline filter which can be used to disregard low-velocity signals and artifacts. However, beware: you may filter away signals that are important for analysis, especially when you are recording low-velocity flow (i.e. venous flow, retrograde flow in the descending aorta, ASD flow).