Which Doppler ultrasound mode displays velocity information as a graph over time?

Spectral Doppler displays velocity information as a graph over time. The vertical axis represents flow direction and velocity, while the horizontal axis represents time.

Unlike color Doppler, which overlays directional flow information on a two-dimensional anatomical image, spectral Doppler produces a waveform. This lets clinicians examine how quickly blood is moving at different moments in the cardiac cycle and identify patterns such as pulsatility, acceleration, and reversed flow.

The waveform is generated from Doppler frequency shifts caused by moving red blood cells. Pulsed-wave Doppler can sample flow at a selected depth, while continuous-wave Doppler measures velocities along the ultrasound beam without precise depth selection. Spectral broadening can indicate that blood cells are moving at a wider range of velocities, as occurs with turbulence or narrowing in a vessel.

M-mode is different: it tracks motion along a single ultrasound line, commonly for cardiac structures. B-mode creates a grayscale anatomical image, and elastography estimates tissue stiffness rather than plotting blood velocity.