Color coding with the aliasing effect. The aliasing effect, shown here with a white arrow is characterized by a transition of the orange and yellow shades at one end of the color scale to light blue and green shades at the other end of the scale (а)

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... The correct answer is aliasing (Fig. 2 ). Aliasing arises when the Doppler shift of the moving blood is higher than half of the PRF (Nyquist limit). Aliased signals are displayed with the wrong direction (red instead of blue and vice versa) and velocity (the hue of the color). An aliasing artifact is usually associated with the increased flow velocity in the stenotic segment. ...