Ultrasound is
sound of
vibrations with
frequencies too high to be audible by the human
ear, above approximately 20
kilohertz. Some sound that is ultrasound to the human ear can be heard by animals, such as
dogs. Ultrasound has
industrial[?] and medical applications.
Medical ultrasonography can visualise muscle and soft tissue, making them useful for scanning the organs. However, they will not penetrate
bone so they are not a substitute for conventional
X-rays in many cases.
See also physics, light.