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![(Color online) Coherent propagating shear wave profile extracted from stacked cross correlations of muscle noise recorded [in the frequency band ( 40 – 55 Hz ) only, see Fig. 1 , red line] between sensor pairs located on the middle third of the vastus lateralis muscle vs increasing sensor separation distance.](profile/Philippe-Roux-4/publication/234953327/figure/fig4/AS:307382421868561@1450297088925/Color-online-Coherent-propagating-shear-wave-profile-extracted-from-stacked-cross.png)
(Color online) Coherent propagating shear wave profile extracted from stacked cross correlations of muscle noise recorded [in the frequency band ( 40 – 55 Hz ) only, see Fig. 1 , red line] between sensor pairs located on the middle third of the vastus lateralis muscle vs increasing sensor separation distance.
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Measuring the in vivo elastic properties of muscles (e.g., stiffness) provides a means for diagnosing and monitoring muscular activity. The authors demonstrated a passive in vivo elastography technique without an active external radiation source. This technique instead uses cross correlations of contracting skeletal muscle noise recorded with skin-...
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... the best fit between the Voigt model Eq. 2 and the measured frequency dispersion Vf, in a least-mean square sense in the frequency band 40-55 Hz Ref. 19 see Fig. 3. The shear wave phase velocity dispersion Vf change of velocity versus frequency is estimated by 1 estimating the time-frequency distribution of each S-MMG cross-correlation wave forms Fig. 2, using a continuous Morlet wavelet transform, 21 and then 2 computing the slope of the shear wave arrival time for increasing sensor separation distances. The passive estimates of and appear highly corre- lated with weight load and hence muscle contraction level Fig. 4, in agreement with previously reported active iso- metric ...Citations
... As an alternative to the SWE, other elastography methods based exclusively on low-frequency (~100 Hz) surface waves propagation have recently emerged [26][27][28][29][30][31]. By eliminating ultrasound frequencies, the spatial information is lost, so it is not possible to construct an elastic map of the medium. ...
Introduction: In recent years, elastography has become a widely accepted methodology to assess the longitudinal shear elastic modulus of skeletal muscle. Ultrasound shear wave elastography is the gold standard used for such a purpose. However, its low sample rate (1-2 Hz) and the impossibility of being used in several muscles simultaneously limit potential biomechanical applications. In this work, we overcome such limitations by using a surface wave elastography method (NU-SWE). Methods: The NU-SWE comprises a wearable device suitable for measuring several muscles simultaneously. Elasticity can be measured at high-frequency rates (~15 Hz), by propagating several pulse trains of low-frequency (~100 Hz) superficial waves separated by a short time interval. These pulses propagate along the medium surface and are recorded by a linear array of vibration sensors placed on the skin of each measured muscle. In this context, this work carried out a proof of concept, showing how NU-SWE enables performing experimental protocols previously impracticable with ultrasound elastography. Thus, we measured the longitudinal shear elasticity of the biceps brachii and brachioradialis muscles simultaneously at 15 Hz during isometric elbow flexions exerted at different torque development rates. Furthermore, for comparison, we measured the electromyographic activity of both muscles. Results: Our results show that the maximum elasticity reached by the brachioradialis increases with contraction rate, while the biceps brachii behaves inversely. CITATION Grinspan GA, Oliveira LFD, Brandao MC and Benech N (2024), Widening the frontiers of elastography in biomechanics: simultaneous muscle elasticity measurements at high-sample rate with surface wave elastography.
... In addition to developments in imaging methods themselves, the most notable advances in recent years have focused on both in vivo soft tissue excitation methods and on methods for reconstructing mechanical maps. Even if they are not yet the most important developments, we can for example underline the emergence passive elastography [27][28][29] and Deep Learning [30,31] as excitation and reconstruction methods, respectively. Through in vivo mechanical characterizations across different scales and ranges of behavior of biological soft tissues, elastography enables today the exploration of a very wide spectrum of medical applications, ranging from diagnosis in clinical practice to the understanding and modeling of many healthy and pathological organs. ...
... The analogy 'seismology of the human body' (e.g. Obermann & Hillers, 2019) alludes to the Green's function retrieval in elastography that was introduced using surface waves along a human quadriceps muscle (Sabra et al., 2007). Shear wave reconstruction in soft tissues was first demonstrated using a gel phantom and mono-element transducers (Catheline et al., 2008). ...
Numerical experiments of seismic wave propagation in a laterally homogeneous layered medium explore subsurface imaging at sub-wavelength distances for dense seismic arrays. We choose a time-reversal approach to simulate fundamental mode Rayleigh surface wavefields that are equivalent to the cross-correlation results of three-component ambient seismic field records. We demonstrate that the synthesized two-dimensional spatial auto-correlation fields in the time domain support local or so-called focal spot imaging. Systematic tests involving clean isotropic surface wavefields but also interfering body wave components and anisotropic incidence assess the accuracy of the phase velocity and dispersion estimates obtained from focal spot properties. The results suggest that data collected within half a wavelength around the origin is usually sufficient to constrain the employed Bessel functions models. Generally, the cleaner the surface wavefield the smaller the fitting distances that can be used to accurately estimate the local Rayleigh wave speed. Using models based on isotropic surface wave propagation we find that phase velocity estimates from vertical-radial component data are less biased by P wave energy compared to estimates obtained from vertical-vertical component data, that even strong anisotropic surface wave incidence yields phase velocity estimates with an accuracy of 1% or better , and that dispersion can be studied in the presence of noise. Estimates using a model to resolve potential medium anisotropy are significantly biased by anisotropic surface wave incidence. The overall accurate results obtained from near-field measurements using isotropic medium assumptions imply that dense array seismic Rayleigh wave focal spot imaging can increase the depth sensitivity compared to ambient noise surface wave tomography. The analogy to elastography focal spot medical imaging implies that a high station density and clean surface wavefields support sub-wavelength resolution of lateral medium variations.
... This allows reporting a numerical value about the bulk elasticity of the tissue. In this way, recent works refer to new elastography methods that use surface waves (or Rayleigh waves) to assess the mechanical properties of skeletal muscles (Benech et al., 2012;Courage, 2003;Grinspan et al., 2016;Sabra et al., 2007;Salman & Sabra, 2013). The general idea of these methods is to use a linear array of vibration sensors aligned with an external wave source, to record the surface displacement of the Rayleigh wave. ...
... However, the Timoshenko beam model employed in such work does not apply to the skeletal muscle (Timoshenko, 1921(Timoshenko, , 1922. Likewise, other low-frequency methods proposed to measure muscle shear elasticity do not consider the incidence of the diffraction, guided wave, and near-field effects (Benech et al., 2012;Courage, 2003;Sabra et al., 2007;Salman & Sabra, 2013;Zhang, 2016). In this sense, the new inversion algorithm of the NU-SWE can automatically correct the biases introduced for those effects, allowing reliable and robust estimates. ...
The shear elastic modulus is one of the most important parameters to characterize the mechanical behavior of soft tissues. In biomechanics, ultrasound elastography is the gold standard for measuring and mapping it locally in skeletal muscle in vivo. However, their applications are limited to the laboratory or clinic. Thus, low-frequency elastography methods have recently emerged as a novel alternative to ultrasound elastography. Avoiding the use of high frequencies, these methods allow obtaining a mean value of bulk shear elasticity. However, they are frequently susceptible to diffraction, guided waves, and near field effects, which introduces biases in the estimates. The goal of this work is to test the performance of the non-ultrasound surface wave elastography (NU-SWE), which is portable and is based on new algorithms designed to correct the incidence of such effects. Thus, we show its first application to muscle biomechanics. We performed two experiments to assess the relationships of muscle shear elasticity versus joint torque (experiment 1) and the electromyographic activity level (experiment 2). Our results were comparable regarding previous works using the reference ultrasonic methods. Thus, the NU-SWE showed its potentiality to get wide the biomechanical applications of elastography in many areas of health and sports sciences.
... Directional filtering has been proposed to solve this issue [4,5]. However, other researchers focused in developing alternative approaches to measure μ (or equivalently c s ) from a complex elastic wavefield [6][7][8][9][10][11][12][13][14][15][16][17][18]. For example, in the TREMR technique (Table-Resonance Elastography with MR), the elastic field created by the vibrations of the patient table of a MRI system was used to image the elasticity of a tissue phantom and the brain [7]. ...
... In this context, the goal of this short review is to cover the major developments in wave-physics involving elasticity imaging using time reversal and noise correlation of shear waves together with its latest applications. These include time reversal physics and near field effects of shear waves in soft tissues [15,28,29], passive brain elasticity imaging using MRI [20], cornea elasticity imaging using OCT [21], thyroid [14] and breast [18] elasticity imaging using low frame rate ultrasound scanners, liver elasticity imaging [13,30], passive muscle elasticity assessment [11,19] and most recently cellular elasticity imaging [31]. ...
... The work of Sabra et al. [11] was the first proof of concept in the field of passive elastography based on noise correlation. In [11] they used sixteen miniature skin-mounted accelerometer placed along the vastus lateralis to measure muscular noise in the 40-55 Hz frequency band. ...
Shear wave elastography (SWE) relies on the generation and tracking of coherent shear waves to image the tissue's shear elasticity. Recent technological developments have allowed SWE to be implemented in commercial ultrasound and magnetic resonance imaging systems, quickly becoming a new imaging modality in medicine and biology. However, coherent shear wave tracking sets a limitation to SWE because it either requires ultrafast frame rates (of up to 20 kHz), or alternatively, a phase-lock synchronization between shear wave-source and imaging device. Moreover, there are many applications where coherent shear wave tracking is not possible because scattered waves from tissue’s inhomogeneities, waves coming from muscular activity, heart beating or external vibrations interfere with the coherent shear wave. To overcome these limitations, several authors developed an alternative approach to extract the shear elasticity of tissues from a complex elastic wavefield. To control the wavefield, this approach relies on the analogy between time reversal and seismic noise cross-correlation. By cross-correlating the elastic field at different positions, which can be interpreted as a time reversal experiment performed in the computer, shear waves are virtually focused on any point of the imaging plane. Then, different independent methods can be used to image the shear elasticity, for example, tracking the coherent shear wave as it focuses, measuring the focus size or simply evaluating the amplitude at the focusing point. The main advantage of this approach is its compatibility with low imaging rates modalities, which has led to innovative developments and new challenges in the field of multi-modality elastography. The goal of this short review is to cover the major developments in wave-physics involving shear elasticity imaging using a complex elastic wavefield and its latest applications including slow imaging rate modalities and passive shear elasticity imaging based on physiological noise correlation.
... Using the shear wave speed c S = 1.67 m/s, the 511 compression wave speed c P = 1500 m/s, the medium density 512 ρ = 10 3 kg/m 3 , and a dipole pulse force of period T = 10 ms, 513 theoretical calculation of the x -component displacement in the 514 medium using the analytical Green's function (8) (Fig. 11-b). The large difference in the velocity means among different 555 target parts of the same stiffness mainly comes from the dif-556 ference in the distances of the target parts to the shear wave 557 displacement sources, which produces difference in the set of 558 frames having shear wave displacements in the target parts and 559 finally results in large difference in the velocity means computed 560 through (18). ...
Objective:
This article presents shear wave generation by remotely stimulating aluminum patches through a transient magnetic field and its preliminary application in the cross-correlation approach based ultrasound elastography.
Methods:
A transient magnetic field is employed to remotely vibrate the patch actuators through the Lorentz force. The origin and the characteristics of the Lorentz force are confirmed using an interferometric laser probe. The shear wave displacement fields generated in the soft medium are studied through the ultrafast ultrasound imaging. The potential of the shear wave fields generated through the patch actuators for the cross-correlation approach based elastography is confirmed through experiments on an agar phantom sample.
Results:
Under a transient magnetic field of changing rate of 10.44 kT/s, the patch actuator generates a shear wave source of an amplitude of 100 μm in a polyvinyl alcohol (PVA) phantom sample. The shear wave fields created by experiments agree qualitatively well with those by theory. From the shear wave velocity map computed from 100 frames of shear wave fields, the boundaries of cylindrical regions of different stiffness can be clearly recognized, which are completely concealed in the ultrasound image.
Conclusion:
Shear wave fields in the level of 100 μm can be remotely generated in soft medium through stimulating aluminum patches with a transient magnetic field, and qualitative shear wave velocity maps can be reconstructed from the shear wave fields generated.
Significance:
The proposed method allows potential application of the cross-correlation approach based elastography in intravascular-based or catheter-based cardiology.
... Computing their ratio point by point finally gives the shear-wave speed imaging ( fig. 2). Inspired by seismic noise correlation [25][26][27][28], a complete description of the elastography method is available in [23,29]. ...
When a wave field is measured within a propagative medium, it is widely accepted that the resulting image resolution depends on the measuring point density, and no longer on the wavelength. Indeed, in situ measurements allow the near-field details needed for super-resolution to be retrieved. Rarely studied in elastography, this is supported here by experiments. A passive elastography imaging of two inclusions in a tissue mimicking phantom is shown with a resolution down to 1/45 of a shear wavelength.
... In seismology, Chaves [12] used the cross-correlation of ambient seismic noise to extract direct seismic response between two points on the earth's surface. Artman [13] and Campillo [14] pointed out the feasibility of extracting Green's function extraction from the noise correlation function (NCF) in many fields, including ultrasonic [15,16], underwater acoustics [17,18], and medical imaging [19]. However, application of the Green's function reconstruction method in the post-processing of ultrasonic full matrix signals is hardly ever reported. ...
Wavenumber imaging with Green’s function reconstruction of ultrasonic diffuse fields is used to realize fast imaging of near-surface defects in rails. Ultrasonic phased array has been widely used in industries because of its high sensitivity and strong flexibility. However, the directly measured signal is always complicated by noise caused by physical limitations of the acquisition system. To overcome this problem, the cross-correlations of the diffuse field signals captured by the probe are performed to reconstruct the Green’s function. These reconstructed signals can restore the early time information from the noise. Experiments were conducted on rails with near-surface defects. The results confirm the effectiveness of the cross-correlation method to reconstruct the Green’s function for the detection of near-surface defects. Different kinds of ultrasonic phased array probes were applied to collect experimental data on the surface of the rails. The Green’s function recovery is related to the number of phased array elements and the excitation frequency. In addition, the duration and starting time of the time-windowed diffuse signals were explored in order to achieve high-quality defect images.
... Note that a low value of API is desirable. SNR = 10 log 10 I max I average (10) where I max is the maximum value of the defect signal and I average is the average amplitude of the background noise level. A rectangular region (from −7.5 to 7.5 mm in the X-axis, from 0 to 15 mm in the Z-axis) of specimen 1 is shown in Figure 10. ...
In this paper, phase coherence imaging is proposed to improve spatial resolution and signal-to-noise ratio (SNR) of near-surface defects in rails using cross-correlation of ultrasonic diffuse fields. The direct signals acquired by the phased array are often obscured by nonlinear effects. Thus, the output image processed by conventional post-processing algorithms, like total focus method (TFM), has a blind zone close to the array. To overcome this problem, the diffuse fields, which contain spatial phase correlations, are applied to recover Green’s function. In addition, with the purpose of improving image quality, the Green’s function is further weighted by a special coherent factor, sign coherence factor (SCF), for grating and side lobes suppression. Experiments are conducted on two rails and data acquisition is completed by a commercial 32-element phased array. The quantitative performance comparison of TFM and SCF images is implemented in terms of the array performance indicator (API) and SNR. The results show that the API of SCF is significantly lower than that of TFM. As for SNR, SCF achieved a better SNR than that of TFM. The study in this paper provides an experimental reference for detecting near-surface defects in the rails.
... To perform MR elastography, a continuous shear wave needs to be generated inside the organ under consideration. In this subsection, only active MR elastography techniques are considered, in which shear waves are externally applied to the organ, in opposition with passive elastography techniques, where the shear waves are generated through natural physiological processes 391 (pulsatile blood flow, physiological motions, …). Usually, a monochromatic continuous shear wave is generated during the whole imaging process thanks to an external excitation system. ...
The respiratory function in human cannot be separated from the deformation motion of the lung: the gas exchanges between the organism and its environment are made possible, during the inspiration, by the swelling of the alveoli in the pulmonary parenchyma, and during the expiration, by a passive return to the static equilibrium state of the lung. The viscoelastic properties of lung tissue play a key role in the function of this organ. These elements of respiratory mechanics may prove to be very sensitive biomarkers of the pathophysiological state of the lung since they depend on the structure of tissues and biological conditions that are considerably altered by most pulmonary diseases such as cancer, emphysema, asthma or interstitial fibrosis. Magnetic resonance imaging enables non-invasive measurement of three-dimensional anatomical images that allow, thanks to the accessible spatial and temporal resolutions as well as the rich contrasts observed in the soft tissues, the measurement of the deformation state of an organ at a given moment. Moreover, by applying motion encoding gradients, magnetic resonance elastography gives the possibility to follow, onto to the magnetic resonance phase signal, the mechanical strain response of organs to an external mechanical stress in order to reveal their viscoelastic properties, which makes possible a quantitative and spatially-resolved exploration of deep organs that are nor reachable by the medical doctor's hand. In the lung, conventional MRI is, however, relatively difficult: the low tissue density, the large differences in magnetic susceptibility at the interface between gas and tissue and, correlatively, the very short lifetimes of the magnetic resonance signal, lead to signal-to-noise ratios that are difficult to exploit. In addition, the durations of three-dimensional MRI scans are generally longer than the period of the respiratory motion, which requires consideration of this motion within the imaging process. This PhD project, carried out in collaboration with GE Healthcare, aims at circumventing the limitations mentioned above by using UTE and ZTE sub-millisecond echo-time acquisition techniques, combined with original and innovative approaches of intrinsic physiological motions monitoring as well as four-dimensional image reconstruction techniques taking into account the respiratory motion, the redundancy of information between the different data acquisition channels and the sparsity of the reconstructed images through some mathematical representations. The ultimate goal of this project is the development and the validation of local and quantitative techniques to explore the respiratory function, as well as dynamic magnetic resonance lung elastography, in order to extract local ventilation parameters and viscoelastic shear moduli in the lung during the breathing cycle.
