A medical ultrasound test is a diagnostic procedure that uses high-frequency sound waves to produce images of the organs and structures of the body. Because high-frequency sound cannot penetrate bone or air, they are especially useful for imaging the soft tissues and fluid-filled spaces of the human body (e.g., arteries and veins, blood vessels, fetus, gall bladder, heart, kidneys, liver, pelvis and reproductive organs, pancreas, and thyroid).

The test is simple and painless. A transducer (special probe), which produces and receives silent, high-frequency sound waves, is placed against the patient's body and slowly moved over the area that is being examined. Sound waves then pass through the skin into the body. As they strike various organs, they send echoes back to a transducer. The transducer is able to separate and identify the different echoes produced by different kinds of tissue, blood, bone, and fluid.