Ultrasound Radiation Pressure Research Articles

Estimation of the Crushed Ore Particles Density in the Pulp Flow Basedon the Dynamic Effects of High-Energy Ultrasound

The method of automatic measurement of the ore particles density in the pulp flow by measuring the amount of high-frequency volume ultrasonic oscillations attenuation, which have passed a fixed distance in the test medium under the influence of high-energy ultrasound dynamic effects is considered. The results of ultrasonic field parameters calculation and spatial simulation of high-energy ultrasound radiation pressure effect on the pulp flow, as well as the results of modeling the trajectory of ore particles displacement of three fractions in the pulp flow under the influence of high-energy ultrasound radiation pressure are presented.

Airborne ultrasound pulse amplification based on acoustic resonance switching

Airborne ultrasound radiation pressure, a nonlinear effect that appears as a static force in mid-air in the presence of strong ultrasound, has recently been applied in novel scientific and industrial fields. However, the output power of an ultrasound transducer remains low mainly due to the significant mismatch in acoustic impedance between a solid diaphragm and air. To circumvent this fundamental challenge, we propose to emit amplified airborne ultrasound pulses by instantaneously releasing stored acoustic energy into free-space. Specifically, we implement an acoustic cavity with a mechanically rotating shutter covering its open top. Once the acoustic cavity is fully charged, the stored energy is released by opening the shutter. By developing a choke structure that reduces leakage of the stored energy, we generate ultrasound pulses with 2.5 times higher peak power than the input continuous waves at 40 kHz. This preliminary result has a great potential to generate high-power ultrasound pulses using a conventional air-coupled transducer by separating the storage and radiation process, thus circumventing the fundamental limitation brought by impedance mismatch.

Array formation by ultrasound standing waves with solidification of liquid-suspended micro-particles

In the present article, ultrasound technology is proposed using the spatial periodic force distribution of radiation pressure. For applying ultrasound to the solidification of suspended microparticles, the details of a periodicity array of composite materials and its construction methodology are described. Suspended particles of polyethylene and silica with a concentration of less than 1.0 wt. % were used. A periodic arrangement of particles in distilled water using the ultrasound radiation pressure distribution was confirmed. A solidification process from liquid to solid under this periodic arrangement was also observed and was related to temperature. In the case of silica particles, the dendrites in primary ice crystals and their growth conditions were investigated. The ice crystals grew parallel to the periodically arranged particles.

Passive elastography: Extracting mechanical properties of soft tissues from natural elastic waves

Clinical devices that give elastography imaging from a shear wave speed measurement within tissues uses controlled sources for elastic wave generation. It can be a mechanical vibrator for transient elastography and magnetic resonance elastography (MRE) or ultrasound radiation pressure for ARFI and shear wave elastography technique. Generally speaking, the main drawback of all these methods is the drop of efficiency for deep regions and obese patient. Delivering robust elastic waves in depth is an issue. We have proposed in the past a solution that avoid the problem of shear wave penetration using active sources. It consists in using natural shear waves that exist everywhere in living tissues. These natural shear wave are created thanks to heart beating, to pulse wave within arteries or to muscle activities. Since a few years now, we have been tracking natural shear waves in different soft tissues of the human body and we have not yet been disappointed. Using uncontrolled shear wave needs a change in the group velocity measurement paradigm. This approach is the so-called noise correlation technique developed in the field of seismology.

Explosive Instability of Gravity-Capillary Waves under Ultrasound Radiation Pressure

The parametric interaction of ultrasonic and gravity-capillary waves (GCWs) on a liquid surface has been investigated. Harmonic modulation of the intensity of a plane ultrasonic wave incident on the liquid surface from the depth provides nonlinear parametric coupling of GCW wave triads. We determined the resonance conditions, providing spatiotemporal synchronism of interacting waves, and the threshold ultrasound intensities, at which an explosive-type instability develops in the system of standing and traveling GCWs.

Characterization and modeling of the acoustic field generated by a curved ultrasound transducer for non-contact structural excitation

Conventional excitation techniques typically use an impact hammer, piezoelectric actuator, or mechanical shaker excitation for experimental modal testing. However, the use of these devices may be challenging if accurate high-frequency dynamic measurements on small or lightweight structural parts have to be performed. To overcome these problems, the high-frequency radiation force generated by focused ultrasonic transducers (FUTs) can be used. This approach has shown potential to be used as a non-contact method for modal excitation of small-sized or flexible structures such as MEMS devices, small turbine blades, integral blade rotors (IBR), and biological structures. However, the sound radiation in the air of these ultrasonic transducers and the resulting radiation force imparted onto a structure is not well understood and critically crucial for performing accurate modal analysis and system identification. In this research, the technical development of ultrasound radiation pressure mapping and simulation is presented. Starting from the calibrated sound pressure fields generated by the spherically FUT, driven by amplitude modulated signals, the dynamic focused ultrasound radiation force is modeled and estimated. The acoustic pressure field of a FUT operating in the air is measured and used for validating the accuracy of a new numerical boundary element method (BEM) model in predicting the direct acoustic force generated in the high-frequency range (i.e., 300–400 kHz). The results show that an excellent agreement is found regarding both the pressure profile and amplitude. Pressure fields up to 1200 Pa can be generated as the transducer is driven at 400 kHz. Experiments also prove that the FUT is capable of creating a focal spot size of nearly 3 mm in diameter. To finish, the FUT's dynamic focused ultrasound radiation force is quantified and could be used to quantify a force-response relationship for experimental modal analysis purposes.

Site-specific sonoporation of human melanoma cells at the cellular level using high lateral-resolution ultrasonic micro-transducer arrays

We developed a new instrumental method by which human melanoma cells (LU1205) are sonoporated via radiation pressures exerted by highly-confined ultrasonic waves produced by high lateral-resolution ultrasonic micro-transducer arrays (UMTAs). The method enables cellular-level site-specific sonoporation within the cell monolayer due to UMTAs and can be applicable in the delivery of drugs and gene products in cellular assays. In this method, cells are seeded on the biochip that employs UMTAs for high spatial resolution and specificity. UMTAs are driven by 30-MHz sinusoidal signals and the resulting radiation pressures induce sonoporation in the targeted cells. The sonoporation degree and the effective lateral resolution of UMTAs are determined by performing fluorescent microscopy and analysis of carboxylic-acid-derivatized CdSe/ZnS quantum dots passively transported into the cells. Models representing the transducer-generated ultrasound radiation pressure, the ultrasound-inflicted cell membrane wound, and the transmembrane transport through the wound are developed to determine the ultrasound-pressure-dependent wound size and enhanced cellular uptake of nanoparticles. Model-based calculations show that the effective wound size and cellular uptake of nanoparticles increase linearly with increasing ultrasound pressure (i.e., at applied radiation pressures of 0.21, 0.29, and 0.40 MPa, the ultrasound-induced initial effective wound radii are 150, 460, and 650 nm, respectively, and the post-sonoporation intracellular quantum-dot concentrations are 7.8, 22.8, and 29.9 nM, respectively) and the threshold pressure required to induce sonoporation in LU1205 cells is ∼0.12 MPa.

Ultrasound stimulated vibrometry for measuring tissue properties

Harmonic or pulsed radiation pressure and subsequent measurement of the tissue response can be used to accurately quantitatively measure fundamental material properties of tissue. The measurement of shear wave dispersion can be used to estimate elastic shear moduli of tissue using an appropriate model. Fundamental model free properties such as complex modulus can also be measured. Ultrasound radiation pressure is used to induce free propagating shear waves. The measurable properties of the shear waves such as speed are sensitive to only the local material properties of the tissue under certain circumstances. A model relating the shear wave speed as a function of frequency is related to the elastic and viscous moduli within small regions of tissue according to, for instance, the Voigt model. Shear and elastic moduli in tissue are measured with high accuracy and precision given appropriate models of wave propagation within the geometry of the tissue. Complex modulus in liver of live pig and other tissues have been made. Careful use of shear wave propagation and subsequent measurements can provide fundamental quantitative measurements of tissue mechanical properties if models are accurate. An application of this method is the noninvasive measurement of liver stiffness as a surrogate for fibrosis.

TH-B-L100E-01: Ultrasound Stimulated Vibrometry for Measuring Tissue Properties

Background: Ultrasound stimulated Vibro-acoustography has been used to image tissues using the acoustic response of tissues to localized harmonic radiation pressure. The method provides high resolution and high dynamic range images of tissues. The parameter being imaged is a complex combination of scattering, attenuation, and nonlinearity. However specific use of harmonic or pulsed radiation pressure and subsequent measurement of the tissue response can be used to measure fundamental material properties of tissue. The measurement of shear wave dispersion can be used to estimate elastic shear moduli of tissue. Fundamental model free properties such as elastic storage and loss constants can also be measured. Methods: Ultrasound radiation pressure is used to induce free propagating shear waves. The measurable properties of the shear waves are sensitive to only the material properties of the tissue under certain circumstances. A model relating the shear wave speed as a function of frequency is related to the elastic and viscous moduli within small regions of tissue. Results: Shear and elastic moduli in tissue are measured with high accuracy and precision given appropriate models of wave propagation within the geometry of the tissue. Conclusion: Careful use of shear wave propagation and subsequent measurements can provide fundamental measurements of tissue mechanical properties if models are accurate. An application of this method is the noninvasive measurement of liver stiffness as a surrogate for fibrosis. Educational Objectives 1. Understand Shear Wave moduli. 2. Understand Vibrometry. 3. Understand measurement of elasticity and viscosity with ultrasound.

Ultrasound stimulated vibroacoustography and vibrometry for measuring tissue properties

Ultrasound stimulated vibroacoustography has been used to image tissues using the acoustic response of tissues to localized harmonic radiation pressure. The method provides high resolution and high dynamic range images of tissues. The parameter being imaged is a complex combination of scattering, attenuation, and nonlinearity. However, specific use of harmonic or pulsed radiation pressure and subsequent measurement of the tissue response can be used to measure fundamental material properties of tissue. The measurement of shear wave dispersion can be used to estimate elastic shear moduli of tissue. Fundamental model free properties such as elastic storage and loss constants can also be measured. Ultrasound radiation pressure is used to induce free propagating shear waves. The measurable properties of the shear waves are sensitive to only the material properties of the tissue under certain circumstances. Shear moduli in tissue are measured with high accuracy and precision given appropriate models of wave propagation within the geometry of the tissue. Careful use of shear wave propagation and subsequent measurements can provide fundamental measurements of tissue mechanical properties if models are accurate.

Nonconventional approaches to ultrasonic assessment of skeletal system

Conventional bone ultrasonometry is based on the transmission mode measurement of the linear acoustic parameters of bone (speed of sound and broadband attenuation). It is a well-established technique specifically for osteoporosis diagnostics though it is highly limited in its applications. It cannot be used for the assessment of the hip bone which is the most important area in characterization of the skeletal system and can hardly be used in pediatric applications, particularly in neonatology, for the assessment of newborns and premature and low-birth-weight infants skeletal systems, which became especially vital during the last few decades. There are several new ideas on acoustic assessment of the skeletal sites hardly accessible by the conventional bone ultrasonometry and on principles of the acoustic characterization of bone quality, fracture risk evaluation, and monitoring of therapeutic interventions. New approaches are based on the use of the ultrasound radiation pressure for the remote generation of acoustic waves in bones, on the use of various modes of guided acoustic waves having a propagation speed dependent on both the elasticity modulus and the bone thickness, on the use of geometrical dispersion of sound velocity for bone characterization, and the use of principles of nonlinear acoustic spectroscopy for remote bone testing. [Work supported by NIH.]

Ultrasonically induced motion in tissue during fracture treatment?

Objective: Ultrasound has been shown to increase mechanical strength of the callus of healing fractures in animal models. In human trials, the time to healing has been decreased using low-power pulsed ultrasound. The mechanism both physical and biological for this phenomenon is not known. We have reported accelerated endochondral ossification in the callus after ultrasound exposure, whereas other authors have reported that ultrasound exposure changes the calcium content of cultured cells. We report here the first measurement of movement of bone and tissue caused by the low power ultrasound signal (30 mW/cm∧2 average at 1.5 MHz, tone pulsed 200ux every 800 us). Methods: Fresh cadaveric human forearms were cut down over the distal radius to expose the bone. The radius was cut through to simulate a fracture. The underside of the arm was exposed to the healing signal mentioned above. A laser interferometer was used to measure the 1 kHz motion of the distal and proximal edges of the bone cut. The interferometer was also used to measure the motion of the tissue and fluid surface between the cut ends of the bone. Results: The ends of the bone moved at a velocity of 1 to 2 microns per second at 1 kHz. The tissue was found to move 3 to 5 microns per second. Movies of the motion of the bones were made with a scanning laser interferometer and showed modes of vibration. Conclusions: Small cyclic motion of the fractured bone is induced by ultrasound treatment. Because it has been shown that CW treatment does not accelerate healing but that pulsed ultrasound does, this ultrasound radiation pressure induced tissue motion may contribute to the healing effect of ultrasound.

Vibro‐acoustography: The sound of tissue

Palpation is routinely used for detecting pathology using the stiffness of the tissue and is more than 2000 years old. Palpation is subjective and limited to individual experience and to the accessibility of the tissue region to touch. Noninvasive images of elastic modulus may be useful to distinguish tissues and pathologic processes based on mechanical properties such as elastic modulus. Static, quasistatic, or cyclic stresses have been applied while strains have been measured using ultrasound or MRI. The related elastic modulus has been estimated from visco‐elastic models of tissue mechanics. Recently we have developed a new ultrasound technique that produces speckle free images related to both tissue stiffness and reflectivity. This method, termed Ultrasound Stimulated Vibro‐acoustography [Science 280, 83–85 (1998); PNAS 96, 6603–6608 (1999)], uses ultrasound radiation pressure to produce sound vibrations from a small region of the tissue that depend on the scattering and elastic characteristics of the tissue. The method can detect microcalcification within breasts, and promises to provide high‐quality images of calcification within the arteries. Vibro‐acoustography can detect mechanical defects in prostheses such as artificial mitral and aortic valves. The method may also be used in nondestructive evaluation. [Work supported by HL 61451, DBI 7980‐4.]