Search

In healthy subjects, spinal alignment varies with the variations of lung volume and the natural breathing perturbs physiologically the balance. The reciprocal action between respiratory postural perturbation and partial counteraction of cyclic movements of the spine, pelvis and lower limbs represents the posturo-respiratory interaction (PRI). The PRI is centrally controlled. In the Obstructive Sleep Apnoea Syndrome (OSAS) specifics postural dysfunctions related to an abnormal PRI is observed. Numerous tools exist to measure the PRI. We propose an alternative approach which is contactless and non-invasive using airborne ultrasound devices. This approach offers the advantages to simultaneously assess breathing and postural variations and to be easily implemented in clinical settings. We first evaluate the performance of our device to assess the breathing pattern compared to that of a spirometer. We secondly use our approach to qualify the PRI by measuring the postural variation at the level of the T7 vertebra. We introduce a new parameter named pseudo-emergence similar to the classical emergence parameter. This parameter gives a value of 8.33%. This value is close to the median emergence that was compute from predecessor. We have demonstrated that the proposed method allows a reliable measurement of breathing. We also offer a contactless approach of a respiratory pseudo-emergence parameter to evaluate the PRI. The obtained parameters seem promising and consistent with the literature, but need to be confirm. Programme SOUFFLE de l'Institut Universitaire d'Ingénierie en Santé (IUIS)

Non-contact ultrasound applications are raising more and more interests. However, very few applications have been reported, for now in medical applications. In this work, compact airborne piezotransducers have been designed, built and characterized for a novel medical application: contactless corneal imaging. The emission transducer is cylindrical with a 5.5 mm diameter and the reception transducer is a 2D array of 4x16 elements. A specific emission-reception electronic is also designed for these transducers to drive their high electric impedances that are larger than kiloOhms. The measured parameters - directivity, sensitivity and frequency bandwidth – of both transducers respond well to the needs of corneal imaging application.

The speed of the surface Rayleigh wave, which is related to the viscoelastic properties of the medium, can be measured by non-invasive and non-contact methods. This paper presents a new method for non-contact ultrasound surface wave elastography using airborne ultrasound surface motion camera (AUSMC). To demonstrate and validate the approach the experiments were carried out on different gelatin phantoms of different concentrations (3%, 5%, 8%) and ×12 scaled eye phantom. By studying the dispersion curve of the surface wave speed, shear modulus can be extracted. The study presents the preliminary results that support the capability of the AUSMC system to estimate without contact the shear modulus of semi-infinite media or thin layer over semi-infinite media.

International audience; The recent achievements in the accelerometer-based seismocardiography field indicate a strong potential for this technique to address wide variety of clinical needs. Recordings from different locations on the chest can give a more comprehensive observation and interpretation of wave propagation phenomena than a single-point recording, can validate existing modeling assumptions (such as the representation of the sternum as a single solid body), and provide better identifiability for models using richer recordings. Ultimately, the goal is to advance our physiological understanding of the processes to provide useful data to promote cardiovascular health. Accelerometer-based multichannel system is a contact method and laborious for use in practice, also even ultralight accelerometers can cause non-negligible loading effects. We propose a new contactless ultrasound imaging method to measure thoracic and abdominal surface motions, demonstrating that it is adequate for typical seismocardiogram use. The developed method extends non-contact surface-vibrometry to fast 2D mapping by originally combining multi-element airborne ultrasound arrays, a synthetic aperture implementation and pulsed-waves. Experimental results show the ability of the developed method to obtain 2D seismocardiographic maps of the body surface 30×40 cm 2 in dimension, with a temporal sampling rate of several hundred Hz, using ultrasound waves with the central frequency of 40 kHz. Our implementation was validated in-vivo on eight healthy human participants. The shape and position of the zone of maximal absolute acceleration and velocity during the cardiac cycle were also observed. This technology could potentially be used to obtain more complete cardio-vascular information than single-source SCG in and out of clinical environments, due to enhanced identifiability provided by distributed measurements, and observation of propagation phenomena.

Seismocardiography has been well studied in terms of analysis, applications, and methods of measurement. However, there remains a lack of research into the explanation and modelling of the involved phenomena. We propose a new contactless method to measure thoracic and sternal movements, demonstrate that it is adequate for typical seismocardiogram use. An ultrasonic diagnostic tool called ICARE (CArdio REspiratory Imager) was designed to perform non-contact ultrasonic waves imaging on the thorax and abdomen. In addition to ICARE measurements an accelerometer was placed above the xiphoid of 3 participants (male, age 39±11). Both ICARE and accelerometer measurements were performed concurrently. Experimental results show the ability of the ICARE system to obtain 3D seismocardiographic images with high frequency frame rate. Furthermore, this technology could potentially be used to obtain cardio-vascular information in and out of clinical environments, significantly lowering the required time and effort.

In security applications, several methods are used for detection of hidden objects. Metal detectors and palpation are the most common methods. Non-contact acoustic waves imaging of elastic heterogeneities in superficial body tissues could be an interesting alternative.

Focusing and beam steering is achieved by using a time-reversal process and a single transducer coupled to a solid cavity that is immersed in water. This low-cost technique makes it possible to focus acoustic energy anywhere on a 3D domain with a spatio-temporal resolution comparable to that of multiple transducers array. A short pulse is emitted from a transducer stuck at the surface of the solid cavity. The multiple-scattered field is measured in front of the solid cavity using a hydrophone needle at a reference point. This signal is then time reversed and remitted by the transducer. Around the reference point, one can observe a spatio-temporal recompression. The sidelobe level as well as the focal width no longer depend on the transducer aperture but on the dimensions of the solid cavity and the multiple paths covered by the acoustic waves in the solid. Moreover, it is shown how the experimental impulse responses on the front face of the cavity can be used to control the emitting ultrasonic field. This “synthetic time-reversal” technique is shown to be as powerful as a real time-reversal process.

Lamb waves are extensively involved in plate structure inspection because of their guided nature. However, their dispersive nature often limits their use in flaw detection. In this paper we show that the use of a time-reversal mirror (TRM) allows to automatically compensate for the dispersive nature of Lamb waves. Experiments showing the spatial and temporal behavior of time-reversed Lamb waves, demonstrate the ability of TRMs to self-focus and to recompress dispersive pulses. This is demonstrated in a set of experiments in which a broadband ultrasonic laser source is used to simulate a point Lamb wave source and an optical interferometer is used to map the time reversed elastic field. We also show that TRM may work in pulse echo mode and allows to detect and to focus along large 2-D plates on any flaws located in the inspected area.

Generation of ultrasonic displacements under the thermoelastic effect has the advantage of being contactless and nondestructive. Unfortunately, the directivity and energy of the sound field of such a source are limited. In order to change these parameters the authors use a moving thermoelastic source by moving the laser beam on the solid surface. Moving the laser beam allows control of the ultrasonic beam directivity and an increase in the energy of the sound field. For this purpose, a large impulse of dye laser deflected by an acoustooptic cell working under the Bragg mode is used. Experimental results, in an aluminum sample give good agreement with the theoretical prediction. >

La generation acoustique par effet thermoelastique a l'avantage d'etre sans contact et non destructive. Cependant le diagramme de directivite de telle source est tres large entrainant une densite d'energie acoustique tres faible dans le faisceau. Afin de modifier ces parametres, nous utilisons un impact thermoelastique mobile en balayant le faisceau laser. Suivant la vitesse de balayage, un controle de la directivite ainsi qu'une amplification de l'intensite acoustique emise sont possibles. La realisation de telle source est obtenue en utilisant un deflecteur acousto-optique synchronise a un laser a colorant a impulsion longue. Les resultats experimentaux obtenus pour l'aluminium sont en bon accord avec les resultats numeriques.

Focusing and beam forming is achieved using a time-reversal process and a unique transducer coupled to a solid cavity. This technique allows one to focus acoustic energy anywhere on a 3D domain with a spatio-temporal resolution comparable to a multiple transducer array. We first record the signal emitted by the transducer and detected by a hydrophone needle at a reference point. The signal received is then time-reversed and remitted using the same transducer. At the reference point, one can observe a spatio-temporal recompression. Moreover, it is shown how the experimental Green's functions at the surface of the cavity can be used to control the emitting ultrasonic field. The solid cavity becomes a 2D pseudo-array. A careful study of this phenomenon leads to a better understanding of the resolution of the focusing system; according to diffraction theory, the focal width is no longer dependent on the transducer aperture but on the dimensions of the solid cavity. The signal-to-noise ratio of such a system is then explained by a modal theory and leads to four influencing parameters being defined: frequency bandwidth; number of transducers; cavity geometry; time reversed signal duration. Finally, a one channel inverse filter based on the frequency analysis is defined; its efficiency is compared to the time reversal one and linked to the modal theory.

Heterodyne interferometers using two‐wave mixing in photorefractive cubic crystals for ultrasound detection on rough surfaces are demonstrated. The speckled scattered beam from a rough surface sample interferes with a planar coherent pump beam inside a photorefractive crystal. A third frequency‐shifted beam is used to read the grating. The diffracted readout beam and the transmitted signal beam are wavefront matched, resulting in an optimal heterodyne interference signal. The signal to noise ratio for the two commonly used crystallographic configurations with cubic crystals, G∥〈110〉∥ and G∥〈001〉, where G is the grating wave vector, are investigated. Very good sensitivity is demonstrated for the detection of small amplitude ultrasonic surface displacements.

Detection of surface and subsurface flaws is achieved using the time reversal process leading to self‐focusing Rayleigh waves. The generation of surface waves is accomplished with an array of transducers coupled to the specimen with a Plexiglas wedge. The advantages of this technique are demonstrated with the detection of surface and subsurface holes of subwavelength dimensions. An optical interferometer is used to control the surface acoustic field obtained with such a time reversal process.

The generation of acoustical waves in solids by pulsed laser irradiation has the advantage of being contactless and nondestructive in the case of the thermoelastic mode. Unfortunately, acoustical characteristics of such a source are limited. To modify these parameters, a phased array of thermooptical sources was made by moving the laser beam, and control of beam directivity was obtained. Achievement of such an array is accomplished with an acoustooptic deflector synchronized with a large pulse dye laser. The influence of the velocity and geometry of the moving source is studied, and comparison with a motionless source is made. >

The advantages of ultrasonic remote detection using a heterodyne photorefractive interferometer are demonstrated. The speckle nature of the light reflected by a rough surface (or after propagation through a multimode fiber) does not degrade the interferometer sensitivity. Thanks to the process of wave mixing in photorefractive crystals, this interferometer has a large etendue. Furthermore, the heterodyne detection provides an absolute measurement of the ultrasonic amplitudes. We investigate the influence of an applied ac electric field. Two photorefractive crystals, undoped BSO and BSO:Cr, which have different optical characteristics are compared. Finally, examples of application to NDE are demonstrated.

The time reversal process is used to detect surface and sub-surface flaws and leads to a self focusing process of Rayleigh waves. The surface waves are generated with an array of linear transducers coupled to a specimen surface with a Plexiglas wedge. The advantages of such a technique are demonstrated with the detection of surface and sub-surface holes of subwavelength dimensions. In a pulse-echo measurement, the signal to noise ratio is exponentially increased when the self focusing repetitive process is used Measurements are calibrated with an optical interferometer and results are compared with a surface focusing model to point out the sensitivity of such a detection method.

The D.O.R.T. method is an appropriate method to detect defects in complex and noisy solid samples. This method applies to any type of transducer array and linear waves. It is an efficient mean to separate the echo of a defect from the microstructure contribution or from another defect. The detection of defects in titanium alloy containing grain structure are shown. Results illustrating the detection at 5 MHz of flat bottom holes (FBH) with different diameters located at 140 mm depth in a titanium alloy sample are shown. Then we show that this method applies to imaging with Lamb waves. The detection of 0.6 and 0.8 mm holes in a 1 mm thick duralumin plate is presented.

Two-dimensional ultrasonic speckle correlation velocimetry (USV) is a new technique that allows to image moving scattering media, at a high frame-rate. In this paper we apply the. technique to determine two-dimensional particle velocity profiles of multiphase flows. Experiments are realized with suspensions of Sonazoid (medical contrast agent) and Magnetite (Fe/sub 3/O/sub 4/) in water. All measurements are performed in a vertical pipe with the flow moving downwards. The two-dimensional particle velocity profiles are then compared with a reference liquid volume flow velocity. As expected from theory, the heavier Magnetite particles have slightly higher velocity than the liquid whereas the contrast agent simply follows the liquid motion. The proposed technique can be used in combination with other techniques to measure the mass flow of the solid phase, in solid/liquid multiphase flow. This is generally more interesting than-measuring the bulk mass or volume flow. Godkänd; 2002; 20061024 (ysko)

This paper is devoted to imaging defects in liquid and solid ultrasonic waveguides. A new ultrasonic imaging technique, based on the spatio-temporal Green functions computation and cross-correlation, is presented. This technique extends the concept of matched field processing (MFP) used in ocean acoustics. Results of experiments conducted in water and in a solid Duralumin bar show that a strong improvement of the spatial resolution is observed with this MFP.

Conventional imaging techniques make the assumption that each scatterer is a source of a spherical wave propagating with a constant velocity towards the transducer array. Then, the processing reduces to the recognition of each of these spherical waves. Such a recognition process may be achieved by the cross correlation techniques but usually cross-correlation is only computed versus time variable. In some particular geometry problems, because of invariance by translation of the Green function, the cross correlation technique is still applicable but computations should be realized versus two variables: time and one spatial variables. In this paper, the two dimensional (2D) cross-correlation technique is demonstrated and used to image scatterers located inside a rectangular wave guide. In addition to the calculation flexibility, the ultrasonic images obtained present a better spatial resolution than that obtained using conventional techniques. Experimental results show that the spatial resolution is 5 times thinner than the usual one.

In previous work, it has been shown that ultrasonic speckle velocimetry can be used to measure local particle velocities in flows. So far the technique has been applied to monitor stationary processes. In this paper, we show how ultrasonic speckle velocimetry can be used to dynamically map the two-dimensional velocity profiles of vortices caused by an obstacle within a flow. Thanks to the great versatility of our multi-channel system, it is possible to capture as much as 5000 images per second, thus enabling us to monitor very fast moving processes. To date, two transducer arrays are used to estimate the 2D motion vector of local particles. We also discuss possible modifications and improvements of the system that could lead to the use of a single array of transducers to dynamically map the vectorial velocity fields of flows Godkänd; 2001; 20061101 (ysko)