Doppler ultrasound is a noninvasive test that can be used to measure the blood flow through your blood vessels. It works by bouncing high-frequency sound waves off red blood cells that are circulating in the bloodstream. 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, known as venous insufficiency.
• Heart valve defects and congenital heart disease.
• A blocked artery, called arterial occlusion.
• Decreased blood circulation into your legs, called peripheral artery disease.
• Bulging arteries, known as aneurysms.
• Narrowing of an artery in the neck, called carotid artery stenosis.

A Doppler ultrasound can estimate how fast blood flows by measuring the rate of change in its pitch, also called frequency. A technician trained in ultrasound imaging, called a sonographer, performs the Doppler ultrasound. The sonographer presses a small hand-held device against the skin over the area of your body being examined. The device moves from one area to another as necessary.

This test may be done as an alternative to more-invasive procedures, such as angiography. An angiography involves injecting dye into the blood vessels so that they show up clearly on X-ray images.

A Doppler ultrasound test also may help check for injuries to your arteries or to monitor certain treatments to your veins and arteries.