Optimization of gain settings. (a) Duplex US image obtained with spectral Doppler US as the active scanning mode and too low a gain setting (0%) falsely suggests absent flow. (b-d) Duplex US images obtained with a gain setting of 38% (b), 77% (c), and 100% (d) demonstrate gradual artificial filling in of the spectral waveform, yielding a false finding of increased flow with little meaningful quantitative flow data. The gain settings function independently of other parameters; therefore, changing the gain setting will not alter any other parameter. Changing the color gain does not alter the spectral gain (and vice versa), and the PRF remains unchanged. Whether the color or spectral component is active, the gain setting should be adjusted to outline the contour of the depicted waveform or color flow depiction. 
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