What is the Doppler-based medical test for measuring blood flow in vessels called?

The Doppler-based medical test for measuring blood flow in vessels is called Doppler sonography.

Also known as Doppler ultrasonography or a Doppler ultrasound, it uses high-frequency sound waves to examine moving blood. A transducer sends ultrasound into the body and receives echoes returning from blood cells. Because those cells are moving, their echoes shift in frequency; the size and direction of that shift reveal blood-flow speed and direction.

Clinicians commonly use the test to assess arteries and veins in the neck, limbs, abdomen, and during pregnancy. It can help identify narrowed or blocked vessels, blood clots, abnormal circulation, and problems such as peripheral artery disease. Colour Doppler displays flow direction and relative speed visually, while spectral Doppler presents movement as a waveform.

Doppler sonography is non-invasive and does not use ionising radiation. It is not the same as endoscopy, which uses a camera to inspect internal surfaces, or radiography, which uses X-rays. The test is named for the Doppler effect, the same frequency-shift principle used in radar and astronomy.