Changing the spectral baseline to avoid aliasing. (a) Duplex US image demonstrates aliasing of the spectral waveform, which results in the production of inaccurate waveform data and an inability to obtain accurate quantitative flow data. (b) On a duplex US image obtained after the spectral baseline was lowered, the spectral waveform falls within the range of velocities being evaluated, so that accurate quantitative data can be obtained. Note that changing the baseline does not change the velocity scale (PRF = 1,515 Hz), making this adjustment a logical initial change when reducing aliasing. 
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