An ultrasound scanner is a piece of medical equipment that provides images of most soft tissues without subjecting patients to ionizing radiation. In other words, it obtains diagnostic images from echoes obtained by emitting ultrasonic waves (the most common). A small instrument called a transducer, very similar to a microphone, emits ultrasound waves. These high-frequency sound waves are transmitted to the area of the body being studied, and their echo is received. The transducer picks up the echo of the sound waves and a computer converts it into an image that appears on the screen.

Ultrasound is a high-frequency sound wave (over 20,000 cycles per second, or 20 kHz) that cannot be heard by humans. Different tissues modify the waves in different ways, some reflecting them directly and others scattering them as echoes before they reach the transducer. Deeper reflected echoes are more attenuated than shallower ones. When the echoes return to the transducer, a two-dimensional tissue map can be reconstructed.

Ultrasound refers to sound waves emitted at frequencies beyond the range of human hearing. Frequencies ranging from 2 to 15 megahertz (MHz) are generally used for diagnostic imaging. Ultrasonic waves are mechanical (acoustic) vibrations that require a transmission medium and, as they exhibit the normal wave properties of reflection, refraction and diffraction, they can be directed, focused and reflected in a predictable manner.