Ultrasound imaging is based on the same principle as the sonar used by the bats, dolphins and fishermen on their boats. When a sound wave hits an object, it reflects which means that it produces an echo. By measuring such echo waves, it is possible to determine the distance of an object and its size, shape and firmness (whether the object is firm, filled with liquid or both).

In medicine, the ultrasound is used for detecting changes in the appearance of organs, tissue and vessels and detecting abnormal accumulations, such as tumours. During the ultrasound examination, transducer at the same time emits sound waves and records the waves that are being reflected. By pressing the transducer on the body, it emits a weak pulsation of inaudible high frequency sound waves into the body. As the sound waves bounce off the inside organs, fluids and tissues, the sensitive microphone inside the transducer records slight changes in the pitch and direction of the sound. Those recorded waves are immediately measured and shown on the computer, which creates the image using the live image technique on the screen. One or more frames of moving images are usually captured as still images.

Doppler ultrasound, a special appliance of the ultrasound, measures direction and the speed of blood cells as they flow through the vessels. The movement of blood cells causes a change in the height of the reflected sound waves (which is called Doppler’s effect). The computer collects and processes sounds and creates graphs or colour images that show the flow of blood through blood vessels.