Dopplerultralydsignal

Dopplerultralydsignal refers to the frequency and amplitude information obtained by Doppler ultrasound when it interrogates moving targets, most commonly red blood cells, within the body. The Doppler effect causes reflected ultrasound waves to shift in frequency in proportion to the velocity of the target along the beam direction. The Doppler shift Δf is approximately 2 f0 v cos θ divided by the speed of sound c in tissue, where f0 is the transmitted frequency, v the target velocity and θ the angle between the flow and the ultrasound beam. In clinical ultrasound, f0 typically ranges from 2 to 15 MHz and c is about 1540 m/s.

Doppler ultrasound is implemented in several modes. Continuous-wave (CW) Doppler uses separate transmit and receive elements and can measure high-velocity flow without aliases, but lacks range resolution. Pulsed-wave (PW) Doppler uses a single transducer element and a listening gate to obtain velocity information from a defined sample volume, but can suffer from aliasing if velocities exceed the Nyquist limit. The raw Doppler signal is processed into different formats: spectral Doppler presents velocity over time as a waveform; color Doppler overlays velocity information on a B-mode image with color indicating direction and relative speed; and power Doppler displays the strength of the Doppler signal, showing flow presence without direction.

Applications include assessment of blood flow in cardiovascular and vascular studies, detection of stenosis, regurgitation, perfusion abnormalities, and fetal well-being. Important limitations are angle dependence (velocity estimation is most accurate when θ is small), sensitivity to motion artifacts, and aliasing in PW Doppler. Safety is generally high, as ultrasound is non-ionizing and regulated to keep acoustic exposure within recommended limits.