Spectral Doppler Ultrasound Filters:
©Walter Rasmussen, R.D.C.S.
Spectral Doppler ultrasound filters remove lower frequency echoes the result of which is easily observed on the spectral Doppler recording. Low velocity blood flow, moving cardiac structures and noise are most affected by spectral Doppler filters.
Low velocities cluttering the baseline can make precise measurements at the beginning and end of events difficult, and can also make it difficult to hear and clearly see higher velocity blood flow.
Low velocity blood flow such as is typically recorded from the normal pulmonic valve, tricuspid valve and pulmonary veins require minimal filtering of low velocities whereas, high velocities such as in mitral regurgitation and aortic stenosis require more filtering.
Generally, the velocity profile should be shown clearly touching the baseline and not floating high above it. If there is a lot of low frequency noise, or the gain needs to be at a high level, more filtering will be needed.
The spectral Doppler velocity profile should touching the baseline.
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