Acoustic cavitation, in a broad sense, refers to ultrasonically induced bubble activity occurring in a biological material that contains pre-existing gaseous inclusions. The non-thermal mechanism that has received the most attention is acoustically generated cavitation wherein ultrasonic energy by cavitation bubbles is concentrated. Current interest with thermally mediated ultrasound-induced bioeffects has focused on the thermal isoeffect concept.
Because the medium can absorb energy to produce heat, a temperature rise may occur as long as the rate of heat production is greater than the rate of heat removal. Absorption is a mechanism that represents that portion of ultrasonic wave that is converted into heat, and scattering can be thought of as that portion of the wave, which changes direction. This attenuation is due to either absorption or scattering. Whenever ultrasonic energy is propagated into an attenuating material such as tissue, the amplitude of the wave decreases with distance. Ultrasonic dosimetry is concerned with the quantitative determination of ultrasonic energy interaction with biological materials. Relative to the bioeffect or risk studies, that is, the biophysical mechanisms by which ultrasound affects biological materials, ultrasound-induced bioeffects are generally separated into thermal and nonthermal mechanisms. Thus, an understanding of the interaction of ultrasound with tissue provides the scientific basis for image production and risk assessment. On the other hand, when biological materials affect the ultrasonic wave, this can be viewed as the basis for diagnostic ultrasound. Ultrasound-induced bioeffect or risk studies focus on issues related to the effects of ultrasound on biological materials. Ultrasonic biophysics is the study of mechanisms responsible for how ultrasound and biological materials interact.
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