• Le programme /The Program

  • Résumés/Abstracts

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    Les présentations invitées seront données par des chercheurs leaders du domaine:

  • Simon Arridge, Center for Medical Image Computing, University College London, UK

  • Title: Quantitative Photoacoustic Using the transport equation

    Abstract: Quantitative photoacoustic tomography involves the reconstruction of a photoacoustic image from surface measurements of photoacoustic wave pulses followed by the recovery of the optical properties of the imaged region. The latter is, in general, a nonlinear, ill-posed inverse problem, for which model-based inversion techniques have been proposed. Here, the full radiative transfer equation is used to model the light propagation, and the acoustic propagation and image reconstruction solved using a pseudo-spectal time-domain method. Direct inversion schemes are impractical when dealing with real, three-dimensional images. In this talk an adjoint field method is used to efficiently calculate the gradient in a gradient-based optimisation technique for simultaneous recovery of absorption and scattering coefficients. Joint work with B. Cox, T. Saratoon, T. Tarvainen.

  • Stefan Catheline, Lab. of Therapeutic Applications of Ultrasound, INSERM, Lyon

  • Title: Elastographie passive, élasto-tribologie, et élastographie par force de Lorentz: trois expériences à l'interface médecine-sismologie-physique.

    Abstract: L’élastographie, encore appelée sismologie du corps humain, est une modalité d’imagerie médicale récemment implémentée sur les échographes commerciaux. La fusion de deux thématiques de recherche fondamentales et appliquées que sont l’élastographie et le retournement temporel a profité aux deux parties. En effet, le champ élastique permanent qui existe dans le corps humain à cause d’activités musculaires recèle des informations sur les paramètres mécaniques (élasticité, viscosité) du corps humain. La clé pour extraire ces informations de ce champ physiologique complexe, diffus, réverbéré, est le retournement temporel. Cette technique est connue en sismologie sous le nom de corrélation de bruit sismique. Le second volet de cette présentation montre l'utilité de l'élastographie pour comprendre, dans des expériences de tribologie, comment les frictions faible et forte peuvent donner naissance à la propagation d'onde de cisaillement y compris en régime dit "super shear". Enfin dans la dernière partie, l'utilisation de densité de courant en présence d'un champ magnétique est à l'origine de force de Lorentz capable d'émettre des ondes cisaillement dans la matière molle. Les potentialités de cette nouvelle approche seront discutées.

  • Michel Dietrich , Institut des Sciences de la Terre, Grenoble

  • Title: Electroseismic: a natural bridge between seismology and electromagnetism for geological reservoir characterization

    Abstract: Transient electrokinetic coupling phenomena created at the microscopic scale by the passage of seismic waves through fluid-saturated porous media generate conversions between seismic and electromagnetic (EM) energy which can be observed at the macroscopic scale. Far from being a mere scientific curiosity, transient seismoelectric or electroseismic phenomena are especially appealing to oil and gas exploration and to hydrogeology as they open up the (fairly unique) possibility to characterize fluid-bearing geological formations with the resolution of seismic methods. Indeed, electrokinetic effects are likely to reconcile the sensitivity of electromagnetic exploration methods to fluids with the high resolving power of seismic prospecting techniques for structural imaging, thus naturally bridging the gap between these two important geophysical investigation means. Accounting for the electromagnetic dimension of the seismic wave propagation, or conversely, accounting for the seismic dimension of electromagnetic wave propagation gives new insights into the microstructure and physico-chemistry of fluid-filled porous or fractured media.

  • Mathias Fink , Institut Langevin, CNRS-ESPCI ParisTech, Paris

  • Title: Multiwave Imaging

    Abstract: Interactions between different kinds of waves can yield images that beat the single-wave diffraction limit. Multiwave Imaging consists of combining two different waves-- one to provide contrast, another to provide spatial resolution - in order to build a new kind of image. Contrary to single-wave imaging that is always limited by the contrast and resolution properties of the wave that generated it, multiwave imaging provides a unique image of the most interesting contrast with the most interesting resolution. Multiwave imaging opens new avenues in medical imaging and a large interest for this approach is now emerging in geophysics and non-destructive testing. We will describe the different potential interactions between waves that can give rise to multiwave imaging and we will emphasize the various multiwave approaches developed in the domain of medical and biological imaging. Common to all these approaches, ultrasonic waves are almost always used as one of the wave to provide spatial resolution, while optical, electromagnetic or sonic shear waves provide the contrast. Recently the multiwave approach have been extended by introducing optical wavefront shaping to get images that combine the best spatial resolution of optical waves to the optical contrast. We will discuss these new approaches.

  • Vitaly Gusev, Laboratoire d'Acoustique de l'Université du Maine, Le Mans

  • Title: Depth-profiling of the acoustic, optic and acousto-optic spatial inhomogeneities by techniques of laser-based nanoacoustics

    Abstract: In picosecond laser ultrasonics or laser-based nanoacoustics ultra-short laser pulses are used both for the generation and detection of the acoustic pulses with a typical length from 100 nm down to several nanometres. These acoustic pulses could be applied for the depth profiling, i.e., spatially resolved imaging, of the inhomogeneous materials. Monitoring the reflection of these wide-frequency-band acoustic pulses, incident on the interface between a solid and a liquid, it is possible to determine the near-interface structuring of liquid caused by its interaction with the solid with a nm spatial resolution. Picosecond acoustic interferometry or time-resolved Brillouin scattering technique, which monitors temporal evolution a single frequency component of these wide-frequency-band acoustic pulses, provides opportunity for the depth-profiling of the optically transparent spatially inhomogeneous materials, for revealing individual micro-crystallites in optically isotropic polycrystalline materials and for monitoring the nonlinear transformation of the finite amplitude acoustic pulses of GHz frequency range. The spatial resolution of the method can be controlled either by the spatial scale of the linear laser-generated picosecond acoustic pulse propagating inside the tested material or the spatial width of the weak shock front in the nonlinear acoustic pulse. These scales are much shorter than optical wavelength.
    [1] C. Mechri, P. Ruello, J. M. Breteau, M. R. Baklanov, P. Verdonck, V. Gusev, Appl. Phys. Lett. 95, 091907 (2009). [2] V. Gusev, A. M. Lomonosov, P. Ruello, A. Ayouch, G. Vaudel, J. Appl. Phys. 110, 124908 (2011). [3] A. M. Lomonosov, A. Ayouch, P. Ruello, G. Vaudel, M. R. Baklanov, P. Verdonck, L. Zhao, and V. E. Gusev, ACS Nano 6, 1410 (2012). [4] C. Klieber, V. E. Gusev, T. Pezeril, K. A. Nelson, http://arxiv.org/abs/1403.3222 [5] V. E. Gusev, http://archive.org/details/TheoryNLBrillouinScattering

  • Otmar Scherzer, Université de Vienne, Autriche

  • Title: Quantitive Estimation of Imaging Parameters in Photoacoustics using Focusing or Assuming Piecewise Constant Imaging Parameters

    Abstract: In this talk we will discuss mathematical possibilities of estimating imaging parameters quantitatively via photoacoustic imaging. We derive backprojection formulas for focused illumination and detection. Moreover,we consider parallel estimation of the wave speed function and the absorption density, the later is the standard imaging parameter of photoacoustics. The second part of the talk is concerned with quantitative imaging of piecewise constant parameters in photoacoustic imaging. As we show, the numerical realization can be based on edge detection algorithms. The talk is based on joint work with Peter Elbau, Wolf Naetar (Vienna) and Andreas Kirsch (Karlsruhe).

  • John Schotland, Michigan University, USA

  • Title: Acousto-optic imaging and related inverse problems

    Abstract: A method to reconstruct the optical properties of a highly-scattering medium from acousto-optic measurements is proposed. The method is based on the solution to an inverse problem for the radiative transport equation with internal data. I will also discuss a related inverse source problem with applications to molecular imaging.

  • Laurent Seppecher, Ecole Normale Supérieure, Paris

  • Title: Mathematical modeling of hybrid biomedical imaging by mechanic perturbation

    Abstract: We see how an ill posed problem posed by biomedical imaging can by accurately solve using additionnal mechanical perturbations. From the coupled physics problem, we deduce an internal data from which it is possible to start a recovering procedure for the physical parameter that we want to image. Finding this internal data is based on Radon type geometric integral operator inversion. The reconstruction step involve a non linear coupled system of elliptic PDEs. To deal with hybrid problems, we need a smoothness a priori hypothesis of the unknown parameter. This hypothesis assures that the collected measurements are meaningful. Here, we see that these methods still work if the unknown parameter only belongs to a certain class of bounded variation functions.

  • Gunther Uhlmann, Washington University, USA

  • Title: Recovering the index of refraction from travel times

    Abstract: We will consider the problem of recovering the index of refraction or sound speed of a medium by measuring the travel times of sound waves going through the medium. We will report on recent results the case of partial or incomplete data.

    Les participants peuvent proposer des exposés courts de 15-20 mn en lien avec les thèmes des journées. Dans les limites du budget disponible, le GDR Ondes pourra participer aux frais de transports ou d'hébergement de quelques doctorants.