Therapeutic ultrasound refers generally to the use of ultrasound for the treatment of a medical condition or for therapeutic benefit. Physiotherapeutic ultrasound was introduced into clinical practice in the 1950s, with lithotripsy introduced in the 1980s. Other uses of ultrasound for therapeutic benefit are at various stages in transitioning from research to clinical use and include: high-intensity focused ultrasound (HIFU), targeted ultrasound drug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis, cancer therapy, and ultrasound assisted thrombolysis Ultrasound used for therapeutic benefit often use focused ultrasound waves, however, unfocused ultrasound waves may also be used.
In the above applications, the ultrasound passes through human tissue where it is the main source of the observed biological effect (the oscillation of abrasive dental tools at ultrasonic frequencies therefore do not belong to this class). The ultrasound within tissue consists of very high frequency sound waves, between 800,000 Hz and 20,000,000 Hz, which cannot be heard by humans.
