Ultrasound–biophysics mechanisms

Abstract

Ultrasonic biophysics is the study of mechanisms responsible for how ultrasound and biological materials interact. Ultrasound-induced bioeffect or risk studies focus on issues related to the effects of ultrasound on biological materials. On the other hand, when biological materials affect the ultrasonic wave, this can be viewed as the basis for diagnostic ultrasound. Thus, an understanding of the interaction of ultrasound with tissue provides the scientific basis for image production and risk assessment. 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. Ultrasonic dosimetry is concerned with the quantitative determination of ultrasonic energy interaction with biological materials. Whenever ultrasonic energy is propagated into an attenuating material such as tissue, the amplitude of the wave decreases with distance. This attenuation is due to either absorption or scattering. 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. 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. Current interest with thermally mediated ultrasound-induced bioeffects has focused on the thermal isoeffect concept. The non-thermal mechanism that has received the most attention is acoustically generated cavitation wherein ultrasonic energy by cavitation bubbles is concentrated. Acoustic cavitation, in a broad sense, refers to ultrasonically induced bubble activity occurring in a biological material that contains pre-existing gaseous inclusions. Cavitation-related mechanisms include radiation force, microstreaming, shock waves, free radicals, microjets and strain. It is more challenging to deduce the causes of mechanical effects in tissues that do not contain gas bodies. These ultrasonic biophysics mechanisms will be discussed in the context of diagnostic ultrasound exposure risk concerns.

New Zealand sonographers do not outperform their European or American colleagues in the knowledge of ultrasound safety

“…Safety considerations in diagnostic ultrasound have been broadly published in numerous science and review papers 3 , 4 , 5 , 6 , 7 . Professional organisations such as the ASUM 8 , 9 , 10 , 11 , 12 , 13 , 14 , American Institute for Ultrasound in Medicine (AIUM) 15 , British Medical Ultrasound Society (BMUS) 16 , 17 and others provide prolific references to the safe use of ultrasound, ALARA and in some cases, recommended TI and MI values 17 .…”

The characteristics of novel bimodal Ag–TiO2 nanoparticles generated by hybrid laser-ultrasonic technique

“…12 Image of plasma plume and nanoparticles dispersing in deionised water during picosecond laser ablation of a target (without using ultrasonic waves). The photograph is taken after recording the ablation process by a normal camera wave interacts with a solid material, its amplitude will be decreased in the material due to absorption or scattering which means that the some energy will be absorbed by nanoparticles which leads to a change in their direction which acts as a driving force [44]. Here, it can be said that the ultrasonic waves might have not effected the generation mechanism of nanoparticles such as phase transition, thermodynamic, and kinetic growth, but they have an effect on the combination of two different types of nanoparticles while they are still hot (during the laser ablation) that have different physical properties.…”

Interplay Between Mechanochemistry and Sonochemistry

“…In general, prolonged sonication will be detrimental, lead to extensive cellular damage and chemical biomolecule modification via cavitation processes. Ultrasonic biophysics deals with the study of mechanisms which account for the interaction of ultrasound and biological materials [91]. This damage can however be harnessed for specific therapeutic applications [92,93].…”