DopplerUltraschalluntersuchung

Doppler ultrasound is a noninvasive medical imaging technique that uses the Doppler effect of ultrasound waves to assess blood flow within the body. It combines conventional gray-scale imaging with Doppler information to evaluate the presence, direction, and velocity of blood in vessels and cardiac chambers.

Principle: An ultrasound transducer emits high-frequency sound waves that reflect off moving blood cells. The reflected waves undergo a frequency shift Δf proportional to the velocity v of the target and the cosine of the angle θ between the flow direction and the beam, approximately Δf = 2 f0 v cos θ / c, where f0 is the transmitted frequency and c is the speed of sound in tissue. By measuring the Doppler shift, the device can estimate flow velocity and, with angle correction, flow direction.

Types: Color Doppler encodes velocity and direction as colors over a grayscale image; spectral Doppler provides a graph of velocity versus time and may be pulsed-wave (range-gated) or continuous-wave (no range information).

Applications: Obstetric Doppler is used to monitor fetal and placental circulation; echocardiography assesses intracardiac flow and valvular function; vascular studies evaluate carotid, peripheral, and hepatic vessels for stenosis or occlusion; Doppler is also used to assess venous insufficiency and deep vein thrombosis.

Limitations and safety: Doppler ultrasound is noninvasive and does not involve ionizing radiation. Its accuracy depends on operator skill and proper insonation angle; image quality may be limited by body habitus or bowel gas. Artifacts include spectral aliasing, angle-dependent velocity estimates, and blooming. It provides relative rather than absolute velocity without careful calibration.