Doppler ultrasound is a technology that uses the Doppler effect (the change in frequency of sound waves reflected from moving objects) to measure and visualise blood flow within the heart and blood vessels. It is an essential component of echocardiography (cardiac ultrasound) and vascular ultrasound studies.
Whereas standard (B-mode) ultrasound produces still or moving images of anatomical structures, Doppler ultrasound detects the velocity and direction of blood flowing through those structures. This allows clinicians to assess valve function (detecting and quantifying leaking or narrowed valves by the velocity of blood jets across them), measure cardiac output and haemodynamics (estimating the volume ejected by the ventricles and evaluating pulmonary hypertension), identify abnormal shunts (blood flowing through holes in the heart or abnormal vessel connections), and assess coronary flow during stress echocardiography.
Colour-flow Doppler displays blood flow as colour-coded maps overlaid on the anatomical image (blue for flow away from the probe, red for flow towards it), allowing rapid visual assessment of valves and chambers. Pulsed-wave and continuous-wave Doppler provide precise velocity measurements at specific points.
For cardiac arrest survivors, Doppler echocardiography is routinely used to measure ejection fraction, assess valve function, detect myocardial stunning, and guide decisions about ICD implantation and medication.
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