pulssidoppler

Pulssidoppler, or pulsed Doppler, is an ultrasound technique that uses pulsed acoustic waves to measure the Doppler shift from moving targets, typically red blood cells, within a defined sample volume at a specific depth. The result is a velocity spectrum representing blood flow along the ultrasound beam.

Principle: A transducer emits short pulses of ultrasound; echoes from moving blood are Doppler-shifted in frequency. The system samples the returned signal at a defined depth (gate). The measured Doppler shift Δf is related to the velocity component along the beam by Δf ≈ 2 f0 v cos θ / c, where f0 is transmit frequency, c is the speed of sound, and θ is the angle between the beam and flow. The device converts Δf to velocity and displays it as a spectral waveform over time.

Pulsed Doppler can be performed in pulsed-wave mode, which can measure velocity at a single depth but suffers from limited unambiguous velocity range due to aliasing; continuous-wave Doppler can measure higher velocities but lacks depth discrimination. With pulsed Doppler, operators place a sample volume in a vessel to obtain velocity-time curves and peak systolic/diastolic velocities.

Applications: It is widely used in cardiology to assess valvular disease and cardiac output, in vascular studies to evaluate stenosis or occlusion, and in obstetrics to assess fetal and placental circulation. It is often combined with color Doppler imaging to localize flow regions.

Limitations and safety: Results depend on the insonation angle, with accuracy highest when the beam is parallel to flow. Aliasing may occur if velocities exceed the Nyquist limit. Image quality may be affected by patient habitus and instrument settings. Pulsed Doppler uses diagnostic ultrasound within recommended safety limits.