Doppler ultrasound

Doppler ultrasound uses frequency shifts in reflected sound waves to estimate the direction and speed of moving blood.

Doppler effect: A change in observed wave frequency caused by relative motion between a wave source and an observer. Moving blood shifts reflected ultrasound frequencies, providing the measurement principle.
Carotid ultrasonography: Ultrasound examination of the carotid arteries in the neck to assess their structure and blood flow. Doppler measurements help detect and grade flow disturbances associated with narrowing.
Medical ultrasonography: A medical imaging technique that uses high-frequency sound waves and their echoes to visualize internal structures. Doppler measurements are collected from returning ultrasound echoes.
B-mode ultrasonography: A grayscale ultrasound imaging mode that displays the strength of returning echoes as points in a two-dimensional image. B-mode depicts anatomy, whereas Doppler adds information about motion and flow.
Peak systolic velocity: The highest blood-flow velocity measured during the heart’s contraction phase. It is a common Doppler metric for assessing stenosis in selected arteries.
Continuous-wave Doppler: A Doppler ultrasound mode that transmits and receives continuously, measuring velocities along the beam without depth selection. It measures very high blood-flow velocities but cannot locate them along the beam.
Venous duplex ultrasonography: An ultrasound examination combining vein imaging with Doppler assessment of blood flow. Flow and compressibility findings help evaluate suspected deep vein thrombosis.
Acoustic impedance: A material property equal to density multiplied by sound speed, affecting how sound reflects at boundaries. Reflections from tissue and blood cells provide the echoes used for Doppler analysis.
Power Doppler: A Doppler mode that displays the strength of Doppler signals rather than their direction or velocity. It is more sensitive to weak flow signals but does not show flow direction.
Resistive index: An ultrasound-derived index calculated as peak systolic velocity minus end-diastolic velocity, divided by peak systolic velocity. It summarizes the arterial waveform and is used in renal and other vascular assessments.

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Blood flowRelated: It estimates flow direction and velocity without inserting a probe into the vessel.