RIU 324 Lecture Notes - Lecture 20: Flow Velocity, Laminar Flow, High-Pass Filter
29 Mar 2020
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Document Summary
Amplifies the received signal, also amplifies noise. If output power is too low, more gain will be needed which will increase noise and reduce quality of spectrum. Maximum velocity that can be displayed without aliasing. Limit in both directions established by nyquist, which is one-half prf. Higher sweep speed to show more detail, used for tracing waveforms such as carotid or heart valves. Lower sweep speed to show more time, such as venous response to compressions and breathing. A high pass filter that eliminates low-frequency doppler shift frequencies associated with slow-moving structures such as vessel walls. Control that eliminates low-amplitude signals to suppress noise in the spectral display. The threshold for rejection is based on signal level rather than frequency. Doppler gain set too high causes artifactual spectral broadening of the true doppler spectrum and displays a mirror image of the doppler spectrum on opposite sides of the baseline.
