A Doppler ultrasound is a noninvasive test that can be used to estimate the blood flow through your blood vessels by bouncing high-frequency sound waves (ultrasound) off circulating red blood cells. A regular ultrasound uses sound waves to produce images, but can't show blood flow.
A Doppler ultrasound may help diagnose many conditions, including:
Blood clots
Poorly functioning valves in your leg veins, which can cause blood or other fluids to pool in your legs (venous insufficiency)
Heart valve defects and congenital heart disease
A blocked artery (arterial occlusion)
Decreased blood circulation into your legs (peripheral artery disease)
Bulging arteries (aneurysms)
Narrowing of an artery, such as in your neck (carotid artery stenosis)
A Doppler ultrasound can estimate how fast blood flows by measuring the rate of change in its pitch (frequency). During a Doppler ultrasound, a technician trained in ultrasound imaging (sonographer) presses a small hand-held device (transducer), about the size of a bar of soap, against your skin over the area of your body being examined, moving from one area to another as necessary.