Ultrasound surgery

In surgical practice, ultrasound can be used for its cavitational and thermal effects. The controlled intensity is 10-20 W/cm2.

The application can take place in a time limit of 1-20 s at an operating frequency of 20-40 kHz and 1-7 MHz. The most common use is in ophthalmic surgery under the term phacoemulsification - ultrasound grinds the lens of the eye followed by its suction through a channel in the phacoemulsifier attachment, which takes place before the implementation of the artificial lens. In conventional surgery, the so-called harmonic scalpel plays the main role. This device uses longitudinal ultrasound waves with a frequency of e.g. 20kHz. Its application is accompanied by heating of the cutting surface up to a temperature of 50-100 °C, which facilitates cutting and coagulation of soft tissues or reduces bleeding from small vessels. Ultrasound can also be used in osteosynthesis, where it is used to accelerate the curing of a special synthetic bone binder. Ultrasound disintegration of kidney stones is also possible as an alternative to extracorporeal shock wave lithotripsy. The concrement is targeted by X-ray or ultrasound imaging, then a nephroscope with a sonotrode is introduced and the concrement is crushed in direct contact with the sonotrode at a working frequency of about 25 kHz. Last but not least, it is necessary to mention tumour therapy using ultrasound-induced hyperthermia, where temperature differences occur at the interface of different acoustic impedances. The absorption of ultrasound in tissues depends mainly on its frequency and the kinematic viscosity of the environment. The basic principle is to maintain a constant elevated temperature of about 42 °C for 20 min. In practice, it is imperative to focus the ultrasound beams directly into the tumour focus to avoid damage to the surrounding tissue.