A Doppler ultrasound is a painless, noninvasive test that uses sound waves to determine the amount of blood flowing through the arteries and veins. During the test, an ultrasound technician will pass a handheld device called a transducer over the skin covering the affected blood vessel. The transducer then sends sound waves to a computer for processing. The computer can create graphs or images to depict the amount of blood flow in the affected vessel. This test is helpful in evaluating arteries in the brain or leading to the brain to determine blockages or spasms in the blood vessels, such as:

• Stroke
• Fibromuscular dysplasia
• Moyamoya disease