Modalities Part 4

Therapeutic ultrasound uses sound waves generated by piezoelectric effect at frequencies greater than 20 000?Hz to stimulate tissues and create physiologic effects. Therapeutic ultrasound devices may use short bursts of sound waves or a continuous stream to deliver ultrasonic energy to tissues. Cavitation is the most commonly cited mechanical effect of therapeutic ultrasound. Cavitation is a secondary effect of transmission of ultrasound waves in tissues, another secondary effect is acoustic streaming, which is flow of currents in tissue fluid. The microbubbles of cavitation are under high pressure and temperature just before they collapse. Absorption of ultrasound waves by a tissue represents a portion of the wave energy that is converted into heat. Phonophoresis is the use of ultrasound to enhance the delivery and absorption of topically applied drugs such as analgesics and anti-inflammatories.