How does ultrasound work?
Sound waves are vibrations that occur at a specific frequency, are transmitted through a medium, and can be reflected off objects. Information about the direction from which the sound waves are reflected and the time taken for the sound to return from the object can be used to locate the object. Sound waves used in ultrasonography occur at frequencies of more than 20,000 Hz, which is beyond the range of human hearing. The ultrasound transducer both generates and receives sound waves to create images. Sound travels readily through liquid, whereas air causes distortion and reverberation of ultrasound waves. The ultrasound transducer at the tip of the echoendoscope must be immersed in a water-filled lumen or covered with a water-filled balloon to transmit and receive defined images.