Ultrasound scanning, also called sonography, is a technique used to see tissues and organs inside the body. It uses high-frequency sound waves, which cannot be heard by humans, to produce images of structures inside the body. The process is very similar to the way sonar is used by dolphins or submarines to detect objects. When sound waves are aimed into the body, some are absorbed by body tissues and others bounce back. The sound waves that bounce back are measured by the ultrasound machine, and are transformed into an image of a particular body area.
Ultrasound produces excellent images of organs that are soft or filled with fluid, but it is less effective for examining air-filled organs or bones. Ultrasound is a safe and painless test that usually takes 15 to 30 minutes.