Ultrasound uses a high-frequency sound wave emitted from the sound head when electricity is passed through a quartz crystal. The sound waves cause the vibration of water molecules deep within tissue causing a heating effect. When the sound waves are pulsed, they cause a vibration of the tissue rather than heating. The stream of sound waves helps with nutrition exchange at the cellular level and healing. Studies have shown that ultrasound is helpful for ligament healing and clinically, for carpal tunnel syndrome, and muscle spasm.