Ultrasound uses sound waves instead of radiation to generate snapshots or moving pictures of structures inside the body. This imaging technique works in a manner similar to radar and sonar, developed in World War II to detect airplanes, missiles, and submarines that were otherwise invisible.
A radiologist or ultrasound technician places an ultrasound transducer, which looks like a microphone. The transducer sends sound waves into your body and picks up the echoes of the sound waves as they bounce off internal organs and tissue. A computer transforms these echoes into an image that is displayed on a small screen.
Doppler ultrasound is a variation of this technique that not only shows internal structures but also examines the flow of blood through blood vessels. Doppler ultrasound is useful in detecting blockages to blood flow, such as a blood clot blocking a vein, or narrowing of the blood vessels due to cardiovascular disease.