Definition: Ultrasound machines are a treatment modality used by physical therapists that utilize high or low frequency sound waves. These sound waves are transmitted to the surrounding tissue and vasculature. They penetrate the muscles to cause deep tissue/muscle warming. This promotes tissue relaxation and therefore is useful in treating muscle tightness and spasms. The warming effect of the sound waves also cause vessel vasodilatation and increase circulation to the area that assists in healing. The physical therapist can also adjust the frequency on the machine to use waves that will decrease inflammation.