Tanter Mickael, Fink Mathias «Time reversal of acoustic waves in the nonlinear regime: application to harmonic imaging in medical ultrasound» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 5-11 (2005)

Harmonic imaging coupled to the use of contrast agents is a topic of wide interest in ultrasonic medical imaging. Images are built at twice the excitation frequency that corresponds to the resonance frequency of the bubbles embedded in the medium. Consequently, the contrast becomes important between areas of low and high concentration of bubbles. However, at a high mechanical index, the harmonic components of backscattered echoes depends on the intrinsic nonlinear properties of tissues as well as the bubble's resonance. The focused beam is generating harmonics during its nonlinear propagation. It results in a degradation of the harmonic image contrast. Time reversal is an elegant way to find the emission codes allowing us to cancel the harmonic components due to nonlinear propagation of the ultrasonic beam and so to recover an optimal image contrast. Indeed, the wave equation in a nonlinear regime remains time reversal invariant: in the absence of bubbles, if the backscattered echoes are time-reversed and reemitted by the array, the harmonic components of the resulting wavefront are transferred back to the fundamental frequency during propagation. Another way to calculate the optimal waveforms to be emitted for harmonics cancellation consists to achieve the first step of the time reversal experiment using simulations of the nonlinear wave propagation. The waveforms deduced from a KZK or finite differences code can be used as calibrated signals for the in vivo experiments. Experiments conducted with 1D-linear arrays illustrate these cancellation techniques. The contrast enhancement obtained emphasizes the great potential of fully programmable emission boards in multi-channels systems.

Preobrazhensky V., Pernod P., Bunkin F., Brysev A., Krutyansky L., Pyl'nov Yu., Preobrazhensky S. «Nonlinear acoustics of phase conjugate ultrasound beams. ten years of the russian-french collaboration» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 11-20 (2005)

Overview of nonlinear acoustics of phase conjugate waves (PCW) – the new domain of physical acoustics created by the participants of the Joint Russian–French laboratory LEMAC is presented. The original magneto-acoustic technique of supercritical parametric wave phase conjugation (WPC) is used as a basic method of generation of high intensity PCW. The results of experimental and theoretical studies of nonlinear propagation and interaction of PCW in liquids are considered. Compensation of phase distortions and high quality retro-focusing of PCW in nonlinear and inhomogeneous media in conditions of break of time reversal invariance (TRI) are observed experimentally and described theoretically. Selective WPC of the harmonics of nonlinear beams and its application for harmonic imaging are demonstrated on an example of the nonlinear acoustic microscopy. Detection of nonlinear inhomogeneities by means of WPC is described. Low frequency wave generation by nonlinear interaction of high frequency PCW and its use for velocimetry of scattering objects in liquid are discussed. Applications of TRI break for ultrasonic WPC-imaging of flows and the advantages of nonlinear modes of flow imaging are demonstrated.

Sapozhnikov O.A., Morozov A.V., Cathignol D. «Acoustic holography and laser vibrometry to characterize vibration of piezoceramic and piezocomposite transducers used in ultrasound therapy» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 20-29 (2005)

Acoustic pressure radiated by piezoelectric sources can be predicted based on the normal velocity distribution along vibrating surface. However, up to now, there are no reliable direct methods of surface vibration measurement in liquids. The transducer vibration is frequently considered as being uniform (thickness mode), which may be incorrect due to transducer structure or due to excitation of Lamb waves in it. In this work, a holographic method is developed and experimentally used that enables reconstruction of the radiator vibration pattern. The method includes a measurement of wave amplitude and phase in different points of a plane grid perpendicular to the acoustic axis at some distance from the source, theoretical time reversal of the waveform in each grid-point, and back propagation of the field to the source using the Rayleigh integral. In addition to the holographic approach, vibration of piezoelectric transducers was studied using laser vibrometry. It is demonstrated that the latter method gives wrong results when the transducer is in contact with liquid, because of strong acousto-optic interaction. It is shown that although the acoustic holographic approach has limited spatial resolution (of order of a wavelength), it allows fairly exact prediction of the radiated field pattern.

Lafon C., Gelet A., Cathignol D., Prat F., Chapelon J.Y. «Interstitial and intracavitary therapeutic ultrasound» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 30-35 (2005)

The non invasive nature of High Intensity Focused Ultrasound (HIFU) for thermal ablation of in-depth tumors is very promising and several medical devices are currently commercially available. Techniques using intracavitary or interstitial applicators have been proposed because extracorporeal HIFU techniques are not always suitable for deepseated tumors. Bones or gaseous pockets may indeed be located in the intervening tissue. The objective is to bring the ultrasound source as close as possible to the target through natural routes in order to minimize the effects of attenuation and phase aberration along the ultrasound pathway. Under these circumstances, it becomes possible to use higher frequency, thus increasing the ultrasonic absorption coefficient and resulting in more efficient heating of the treatment region. In contrast to extra-corporeal applicators, the design of intracavitary probes imposes additional constraints relative to size and ergonomy. When associated to modern imaging modalities, these minimally invasive therapeutic devices offer very promising options for cancer treatment.

Maksimov A.O. «Effect of the shock wave envelope on cavitation bubble dynamics» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 35-40 (2005)

The Rayleigh equation describing nonlinear oscillations of a gas bubble in a liquid has been analyzed using the theory of groups. The group of scale transformations was calculated and then used as the basis for constructing the solutions to the Rayleigh equation. The analytical description of the essentially nonlinear dynamics of a bubble allows one to use the aforementioned solutions as a model for analyzing such phenomena as shock wave propagation in liquids with phase inclusions. The study of effectiveness of expansion and collapse of a single bubble driven by periodically prolonged scaling acoustical field has been performed. The key to understanding the transition from weakly oscillating to strongly collapsing bubbles lies in the existence of a threshold for spontaneous bubble expansion known as the Blake threshold. Blake threshold is never achieved at this form of driving and this is the main reason for ineffectiveness of bubble extension.. The small, in comparison with the pressure drop at the leading edge, stretching pressure at the trailing edge of the scaling pulse increases insignificantly bubble radius, thus decreasing the probability of tissue damage due to cavitation that can occur at this phase of the shock wave.

Khokhlova V.A., Blanc-Benon P., Averiyanov M.V., Cleveland R.O. «Diffraction of nonlinear waves in randomly inhomogeneous moving media» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 41-47 (2005)

The combined effects of acoustic nonlinearity and diffraction on the propagation of intense acoustic waves in an inhomogeneous moving medium are investigated Л nonlinear parabolic equation that accounts for diffraction, nonlinearity, absorption, scalar inhomogeneities (density and sound speed) and vectorial inhomogeneities (flaw) is employed, A 2D numerical algorithm is used to solve the equation and to investigate the propagation of initially harmonic waves in media with random inhomogeneities of different types. The results are compared with those obtained using ray theory (within the paradigm of nonlinear geometrical acoustics) in order to investigate the impact of diffraction on focusing in inhomogeneous media. It is shown that the prediction of caustics and shadow zones by nonlinear geometrical acoustics only partially corresponds to the regions of high and low pressure levels predicted with the nonlinear parabolic wave equation. The discrepancy between the results of the models increases for smaller size of inhomogeneities and for longer distances in randomly inhomogeneous media. When nonlinearity is present distorted waveforms are obtained in the diffraction field even in the shadow zones of decreased pressure due to scattering of higher frequencies from the areas of focusing.

Bou Matar O., Preobrazhensky V., Pernod P. «2D axisymmetric pseudospectral simulation of supercritical phase conjugation of ultrasound in active solid media» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 48-56 (2005)

The problem of supercritical wave phase conjugation (WPC) has no analytical solution far geometry and operation conditions of real conjugators. Hence, to study the influence of reverberations and multiple mode conversions inside the active element of the conjugator on the parametric WPC processus, a 2D axisymmetric numerical modal in developed for supercritical parametric phase conjugation of ultrasound in a solid active element of cylindrical shape and finite length immersed in water. The pseudo-spectral time domain algorithm (PSTD) is used. PSTD solves elastic wave equation in time dependent heterogeneous isotropic and axisymmetric anisotropic solids using FFTs for high order approximation of the spatial differential operator an staggered grid. Complex frequency shifted perfectly matched layers are introduced to truncate the computational domain. It is shown, that retro-focusing of the incident pulse taken place even in the case of mode conversions inside the active zone. Nevertheless, amplitude and form of the obtained conjugate pulse depend on the simulated configuration. Numerical simulation correctly describes the parametric amplification and retro-focusing of ultrasound observed in experiments, when the conjugator is loaded at one end by water, and is free on the opposite one.

Blanc-Benon P., Marx D. «Nonlinear effects in a standing wave thermoacoustics refrigerator» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 57-65 (2005)

In thermoacoustic refrigerators, the acoustic energy provided by an acoustic source is used to pump heat from a cold reservoir. Such refrigerators may possibly be miniaturized, offering an application to microelectronic refrigeration. The knowledge of temperature and flow fields in the microchannels and at the edges of the stack plates becomes an increasingly important issue in the design of heat exchangers for thermoacoustic engines. On these topics we have developed numerical simulations and conducted experiments in a resonant standing wave thermoacoustic refrigerator model. In this paper the full compressible Navier–Stokes equations are solved numerically, and the flow and heat transfer around a 2-D stack plate immerged in an acoustic standing wave are computed. Non-harmonic temperature variations are found and are explained using the results of a former nonlinear analysis. The effects of the acoustic Mach number and geometrical parameters on refrigerator performance are investigated.

Penelet G., Gusev V., Lotton P., Bruneau M. «Experimental and theoretical studies of nonlinear saturation processes in annular thermoacoustic prime movers» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 65-74 (2005)

The present study gives a simplified analytical description of spontaneous generation and finite amplitude saturation of sound in annular thermoacoustic engines, and also provides comparison with experiments. The model includes the description of thermoacoustic amplification of sound (induced by interaction between an heterogeneously heated stack of solid plates and resonant gas oscillations), which accounts for the details of the temperature distribution in the whole thermoacoustic device. The saturation of the acoustic wave amplitude is described by taking into account both the reverse influence of the acoustic field on the temperature field, and the dissipation of acoustic power due to higher harmonics generation and minor losses (vortex generation). From the comparison between simulation results and experiments, it is demonstrated that the dynamical behavior observed in our experimental device is predominantly controlled by the effects of acoustic streaming and acoustically enhanced thermal conductivity tending not only to reduce the externally imposed temperature gradient along the stack, but also to change the shape of the temperature field in such a way that additional thermoacoustic amplification may occur.

Haumesser L., Bou Matar O., Dos Santos S., Vander Meulen F. «Transmission through and reflection from a fluid elastic layer: quasi-linear approximation» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 75-80 (2005)

Second Harmonic Generation (SHG) in a three fluid layer system, is investigated in the quasi-linear approximation. Considering an initially sinusoidal plane wave normally incident upon the central layer, the pressure radiated from the later is evaluated at double frequency. Analytical expressions for the reflected and transmitted pressure fields are derived from series of reflected and refracted waves. Results are discussed as a function of the geometrical and material characteristics of the system.

Catheline Stefan, Tanter Mickael, Gennisson Jean-Luc, Fink Mathias «Nonlinear propagation of shear waves in soft solids» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 81-85 (2005)

Transient elastography has shown its efficiency to map the elastic properties of soft tissues. Now like other elastic imaging techniques (sonoelastography or magnetic resonance elastography) transient elastography is faced to the following problem: in order to properly discriminate tumors, additional information such as viscosity, anisotropy or nonlinearity is needed. If nonlinearity has long been studied in metals, crystals or rocks, only a few experimental works are found in the literature concerning soft tissues and none on shear waves. Thanks to the ultrafast scanner that can map the displacement field of shear waves, we present in this paper an overview of three experiments that allow to illustrate and quantify the nonlinear behavior of soft tissue phantoms. In the first one, a static stress is applied on an Agar-gelatin based sample. The change on the shear wave speed characterizes the nonlinear elastic Landau moduli (A = 50 kPa, B = 7 GPa, C = 11 GPa). The surprising difference found between these constants are thought to be closely related to the huge difference between the linear Lame coefficients (λ>>μ). It is the acoustoelasticity experiment. In the second one, we present an experimental observation of a shock shear wave. The very weak Young’s modulus of the tissue phantom allows one to generate plane shear wave with a Mach number as high as unity. In this extreme configuration, the agreement with the numerical simulation of the modified Burgers equation is remarkable. It is the finite-amplitude shear wave experiment. At last, the interaction between two plane transverse waves with frequencies ω1 and ω2 is carefully studied. Harmonics and secondary waves are created during the propagation at the frequencies (3ω1, 3ω2, ω1+2ω2, ω1–2ω2, ω2+2ω1, ω 2–2ω1). It is the nonlinear interaction experiment. The nonlinear coefficients deduced from the two latter experiments are comparable to the order of magnitude of the Landau coefficients found from the first experiment.

Tournat V., Gusev V.E., Zaitsev V.Yu., Nazarov V.E., Castagnede B., Bequin Ph., Inserra C. «Nonlinear acoustic effects in unconsolidated granular media» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 86-92 (2005)

This paper deals with various manifestations of classical and non classical nonlinear acoustic effects that have been observed recently in unconsolidated assemblages of glass beads: operation of the parametric antenna with shear pump waves, non monotonous amplitude dynamics of the longitudinal second harmonic generated from a shear fundamental wave, cross-modulation of propagating waves. Theoretical interpretations of each of these non linear effects demonstrate the important role of the so-called weak contacts, i.e. contacts that support weaker static loads than the average one in the medium. In contrast, the linear wave propagation is mainly affected by the average and strong contacts. As a consequence, nonlinear acoustic methods are found to be much more sensitive than the linear methods for the evaluation of the granular materials in general, and may contribute to a better understanding of their peculiar properties.

Sebaa N., Fellah Z.E.A., Depollier C., Lauriks W. «Direct and inverse scattering problem in cancellous bone: application of biot theory» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 92-99 (2005)

In this paper direct and inverse scattering problems of ultrasonic pulses from cancellous bone are investigated. Reflection and transmission coefficients are derived for a slab of cancellous bone having an elastic frame using Biot’s theory. The inverse problem for waves transmitted by cancellous bone is solved at normal incidence. Experimental results for slow and fast waves transmitted through cancellous bone samples are given and compared with theoretical predictions.

Gurbatov S.N., Demin I.Yu., Pronchatov-Rubtsov N.V. «The use bispectral analysis for nonlinear diagnosis of soft tissues» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 100-104 (2005)

The evolution of higher-order spectral functions of random waves propagating in a nonlinear medium are investigated. The possibility of recovering the input spectrum from the measured spectrum and bispectrum at the output of the nonlinear medium is discussed. A method of measurement of nonlinear propagation characteristics of low frequency vibration in the tissues by using bispectral analysis has been described.

Lasaygues P. «Imaging the shape of long bones using ultrasound tomography» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 105-111 (2005)

In this paper, we investigate ultrasound measurement of the cortical thickness of child long bones. Due to the acoustic impedance mismatch between surrounding tissues and bone, the higher the frequency, the smaller the portion of energy going through and the lesser the resolution of the shaft. To estimate the cortical thickness, we propose ultrasonic tomography, with frequencies lower than those of conventional echography and especially adapted to the strong contrast medium. The ultrasonic tomographic imaging techniques produce cross-sectional images of the spatial distribution of some physical parameters of an object from scattered ultrasonic measures. The measurements are made for more or less dense sets of transmitter and receiver positions and of frequencies of the interrogating wave. We solved this inverse scattering problem by using a Born approximation, which leads to a simple and attractive linear relation between the object function and the scattered field, particularly in the far-field. This approach makes it possible, in principle, to reconstruct the object almost in real time for a large set of scattering data. We investigated wide-band acoustical tomography experimentally.

Gavrilov L.R. «Improvement of the performance of high-intensity linear and spherical phased arrays for application in surgery» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 111-119 (2005)

Disadvantages of powerful phased arrays designed for noninvasive surgery include the unwanted presence of grating lobes and other secondary intensity maxima in acoustic fields. Methods for improvement the quality of the acoustic fields generated by the arrays are discussed and the efficacy of these approaches is illustrated by the results of measurements and computer modeling. For linear arrays, it was shown that optimization of number of active elements with the values of aperture, focal distance, shift of the focus and other focusing conditions permits to reduce the level of secondary maxima. For two dimensional spherical phased array, it was shown that randomization of elements distributions on the surface of the array improved significantly the performance of the arrays by suppressing grating lobes in the acoustic field. The other necessary condition is that the diameter of circular elements of the array should not be larger than 5 wavelengths. The sparseness of the random array should be within a range, approximately, 40–60%. Randomization increased essentially the ability of the array to steer the single focus or the multiple foci (for example, 25 foci) off the array axis. The parameters and characteristics of random spherical arrays for application in surgery are discussed.

Goursolle T., Dos Santos S., Vander Meulen F., Haumesser L., Bou Matar O. «Ultrasonic parametric imaging of metallic samples using nonlinear acoustic measurements» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 120-128 (2005)

A calibrated contact phase modulation method [Vila M., Vander Meulen F., Dos Santos S., Haumesser L. and Bou Matar O. Contact phase modulation method for acoustic nonlinear parameter measurement in solid // Ultrasonics 2004, V.42(1-9) P.1061–1065] have been developed in the laboratory. Nonlinear effects coming from parametric interaction of an high and a low frequency waves can be measured as a phase modulation of the HF acoustic beam. According to the NDE needs, the nonlinearity in samples with interfaces, coming from aeronautic industries (two layers of aluminum bonded by an epoxy thin layer), must be measured. In order to meet these needs, our method has been extended. Thanks to additional measurements of reflection coefficient, calibration procedure, based on the selfreciprocity principle applied to the LF transducer, has led us to obtain absolute value of the LF particle velocity at the bonded interface. To know the feasibility of this extension, preliminary results of nonlinear parameter have been obtained in bi-layer samples considering the propagation inside the layer only. An image has been created by slope values of phase modulation obtained from 25 regularly spaced measurements.

Didenkulov I.N., Kustov L.M., Pronchatov-Rubtsov N.V., Stromkov A.A. «Methods of the nonlinear acoustic vision of objects and defects» High intensity acoustic waves in modern technological and medical applications. Joint Workshop of Russian Acoustical Society (RAS) and French Acoustical Society (SFA). Special Session of the XVI Meeting of Russian Acoustical Society (Moscow. 14–18 November 2005), с. 128-134 (2005)

Nonlinear acoustic methods are found increasing applications during the last decade. In this paper we describe methods of acoustic imaging based on the nonlinear effects: the combination acoustic scattering and the modulation of high-frequency acoustic wave by low-frequency wave. Acoustic vision of objects at the difference frequency was studied using bubbles as strongly nonlinear scatterers. The experiments were carried out in a water tank with metal objects covered with electrolysis microbubbles to produce highly nonlinear scattering from the object surfaces. Images of the objects were obtained. The nonlinear scattering by bubbles was also used to obtain an image of the cavitation flow. Nonlinear acoustic vision of small (in the scale of wavelength) defects is possible when tomography schemes are applied. We used the method of nonlinear modulation modal spectroscopy for defectoscopy of cracks in metal samples. Results of investigation demonstrate possibilities of the nonlinear acoustic techniques in nondestructive testing of different media.