1.8.1 Spectral Doppler
Spectral Doppler permits graphic display of velocities over time. Velocity curves provide information about absolute velocities and the direction of blood flow as well as how velocity changes in a certain region (pulsed-wave Doppler) or along a certain Doppler line (continuous-wave Doppler). The Doppler tracing has a "y axis" which represents velocity (m/sec) and an "x axis" which shows time. Velocities towards the transducer are depicted above, and velocities away from the transducer below, the "zero line". Doppler signals are also converted to audio signals, which enable the investigator to "hear" blood flow during the investigation. Higher velocities are heard as high-pitched sounds while lower velocities are perceived as low-pitched sounds.