High-frequency sound waves which can be bounced off body tissues using special devices during which echoes are converted into a picture called a sonogram.

Ultrasound imaging, referred to as ultrasonography, allows physicians and patients to get an inside view of soft tissues and body cavities, without using invasive techniques.

Ultrasound is often used to examine a fetus during pregnancy and so far there is no convincing evidence for any danger from ultrasound during pregnancy.