Edelmen's Sonography Principles and Instrumentation (SPI) Practice Exam

Pulsed Doppler provides depth information by emitting short ultrasound pulses and gating the received signal to a specific time after emission. That time delay corresponds to a particular depth, so you can place a sample volume at a chosen location along the beam and measure flow there. Continuous-wave Doppler lacks range discrimination; it continuously transmits and receives with no depth gating, so the Doppler signal is integrated along the entire path of the beam and you can’t tell exactly where the flow is located. Both modalities can derive velocity from the Doppler shift, but only pulsed Doppler lets you know the location of the flow along the beam. Speed (magnitude of velocity) isn’t unique to pulsed Doppler, so the key differentiator is location.