Forces acting in the direction of propagation in pulsed ultrasound fields

Abstract

This paper considers some non-thermal effects resulting from absorption of acoustic energy from an ultrasound beam. An experimental investigation of the location of the 'source pump', responsible for the generation of streaming in high amplitude diagnostic fields in water, is reported. Acoustically transparent membranes were inserted in the ultrasound field in order to restrict the streaming volume. It is shown that the major contribution to an acoustic stream is generated in the region near to the focus of a transducer where the intensity in the beam and the degree of non-linear distortion are both high. In the second part of the paper a simple model of non-linear propagation is used to predict the magnitude of the maximum pressure gradient induced in a medium by the absorption of acoustic energy from a beam. Propagation in water, in tissue and in amniotic fluid are considered. Within the limitations of this model it is shown that the pressure gradients induced in pulsed acoustic fields do not result in the ultimate shear stress of tissue being exceeded.

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…Convective acceleration ðu Á rÞu is potentially significant (compared to one-dimensional Eckart streaming). Starritt et al (1991) showed that even when controlling for acoustic intensity, nonlinear distortion in the acoustic wave can cause far larger acoustic streaming amplitudes, about a 1 order of magnitude increase due to the presence of harmonics and their consequent attenuation in the fluid.…”

Approach to breast cancer early detection via tracking of secondary speckle patterns reflected from the skin with artificial intradermal impurity

“…This group of imaging techniques is called elasticity imaging [28]. The general approach in elasticity imaging is to measure the response of tissue to an excitation force [29]. The excitation force used in current work is an acoustic pulse of specific frequency.…”

Physical Principles of Microbubbles for Ultrasound Imaging and Therapy

“…Just pushing the bubbles against the cell repetitively, may be sufficient to stimulate cell uptake [24]. At high ultrasound pressures, bubbles have been shown to translate very rapidly in vitro (5–10 cm/s) and to be capable of destroying cells upon impact [79, 80]. However, in vivo, this ‘bubble bullet’ effect does not appear to be significant, possibly because a very high bubble:cell ratio is required [81 ]or because the presence of carbon dioxide in the blood has a damping effect upon bubble activity [74].…”