What does "ultrasound" mean and what is it used for?

Ultrasound, also called sonography, uses high-frequency sound waves to create real-time images of internal body structures. The term combines ultra meaning beyond and sound, referring to frequencies above human hearing. A transducer emits sound waves that bounce off tissues and return as echoes, which a computer converts into images. Ultrasound is used for pregnancy monitoring, abdominal imaging of the liver, gallbladder, and kidneys, cardiac assessment called echocardiography, vascular evaluation of blood flow, and guiding needle biopsies.