Ultrasound is an elastic mechanical wave in material medium. It is a wave form. Therefore, it can be used to detect the physiological and pathological information of human body, that is, diagnostic ultrasound. At the same time, it is also an energy form. When a certain dose of ultrasound propagates in organisms, through their interaction, it can cause changes in the function and structure of organisms, that is, ultrasonic biological effect.

The effects of ultrasound on cells mainly include thermal effect, cavitation effect and mechanical effect. The thermal effect is that when ultrasound propagates in the medium, the friction hinders the molecular vibration caused by ultrasound and converts part of the energy into local high heat (42-43 ℃). Because the critical lethal temperature of normal tissue is 45.7 ℃, and the sensitivity of swollen Liu tissue is higher than that of normal tissue, the metabolism of swollen Liu cells is impaired at this temperature, and the synthesis of DNA, RNA and protein is affected, Thus killing cancer cells without affecting normal tissues.

Cavitation effect is the formation of vacuoles in organisms under ultrasonic irradiation. With the vibration of vacuoles and their violent explosion, mechanical shear pressure and turbulence are generated, resulting in swelling Liu bleeding, tissue disintegration and necrosis.

In addition, when the cavitation bubble breaks, it produces instantaneous high temperature (about 5000 ℃) and high pressure (up to 500 ℃) × 104pa), which can thermally dissociate water vapor to produce. OH radical and. H atom. The redox reaction caused by. OH radical and. H atom can lead to polymer degradation, enzyme inactivation, lipid peroxidation and cell killing.