Ultrasonography is the second most commonly used imaging format in veterinary practice. It uses ultrasonic sound waves in the frequency range of 1.5–15 megahertz (MHz) to create images of body structures based on the pattern of echoes reflected from the tissues and organs being imaged. Several types of image formats can be displayed. The most familiar one (and the one that creates the actual image of anatomy) is B-mode grayscale scanning. The sound beam is produced by a transducer placed in contact with and acoustically coupled by means of a transmission gel to the animal. An ultrashort pulse of sound is directed into the animal, after which the transducer switches to the receive mode. Echoes occur as the sound beam changes velocity while passing from a tissue of one density to one of another density, even when the change occurs at nearly microscopic levels.