ultrasound radiation force

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Transient MR elastography (t-MRE) using ultrasound radiation force: theory, safety, and initial experiments in vitro.

Transient MR elastography (t-MRE) using ultrasound radiation force: theory, safety, and initial experiments in vitro.

The concept of using ultrasound radiation force instead of an external vibrator for elasticity imaging – either ultrasound-based or MR-based – is not new (33, 12, 29, 36, 22, 5, 30). Radiation force is caused by the change of momentum of the ultrasound waves as they propagate, either because of wave absorption or of wave reflection (35, 7, 6, 34, 9, 8). The radiation force is localized and highly directional, its main axis being in the direction of propagation of the ultrasound beam. The force components in the other directions are at least an order of magnitude smaller (29). In the case of a focused transducer, the radiation force is usually negligible outside of the focal zone. The volumic force F (expressed in N/m 3 ) induced by an
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Analysis of index modulation in microembolic Doppler signals part I: radiation force as a new hypothesis-simulations

Analysis of index modulation in microembolic Doppler signals part I: radiation force as a new hypothesis-simulations

Abstract The purpose of this study was to reveal the cause of frequency modulation (FM) present in microembolic Doppler ultrasound signals. This novel explanation should help the development of sensitive microembolus discrimination techniques. We suggest that the frequency modulation detected is due to the ultrasonic radiation force (URF) acting directly on microemboli. The fre- quency modulation and the imposed displacement were calculated using a numerical dynamic model. By setting simulation parameters with practical values, it was possible to reproduce most microembolic frequency modulation signatures (FMS). The most interesting findings in this study were that: 1) the ultrasound radiation force acting on a gaseous microembolus and its corresponding cumulative displacement were far higher than those obtained for a solid mi- croembolus, and that is encouraging for discrimination purposes, and 2) the calculated frequency modulation indices (FMI) (≈ 20 kHz) were in good agreement with literature results. By taking into account the ultrasound radiation force, the flow pulsatility, the beam-to-flow angle and both the velocity and the US beam profiles, it was possible to explain all erratic FM signatures of a microbubble. Finally, by measuring FMI from simulated Doppler signals and by using a constant threshold of 1 KHz, it was possible to discriminate gaseous from solid microemboli with ease.
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Mathematical modelling of Acoustic Radiation Force in transient shear wave elastography in the heart

Mathematical modelling of Acoustic Radiation Force in transient shear wave elastography in the heart

to locally assess biomechanical properties highly sensitive to structural changes associated with physi- ological and pathological processes. The development of the first ARF-based shear wave elastography (SWE) technique dates back to late 1990s and was proposed under the name of Shear Wave Elastography Imaging (SWEI) [1]. Thereafter, several techniques based on impulsive acoustic radiation force were in- troduced, e.g. Vibro-acoustic Spectography [2], Acoustic Radiation Force Imaging (ARFI) [3], Supersonic Shear Imaging (SSI) [4], Spatially Modulated Ultrasound Radiation Force (SMURF) [5] and Comb-push Ultrasound Shear Elastography (CUSE) [6].
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Chiral drag force

Chiral drag force

Although the effects of the chiral drag force are small, we do not wish to underesti- mate the ingenuity of our experimentalist colleagues. Perhaps they can devise sufficiently sensitive correlation observables to see the small effects of the chiral drag force on heavy quarks. For example, it is worth constructing event-by-event observables that can see whether the B and D mesons in an event have picked up a net momentum perpendicular to the reaction plane in the “downward” (“upward”) direction in those events in which the chiral magnetic effect has resulted in an electric current “upwards” (“downwards”) with positive light hadrons pushed “upwards” (“downwards”) and negative light hadrons pushed “downwards” (“upwards”). A correlation observable like this uses the CME cur- rent to define the direction in which the heavy quarks should be pushed by the chiral drag force, and then checks whether a net push on all the heavy quarks and antiquarks in the event in this direction is seen. A nice feature of such a correlation observable is that the observable effects of both the CME current and the chiral drag force should each be equally suppressed by the partial cancellation between regions of the plasma with µ R > µ L and regions with µ R < µ L .
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Effect to the capillary force on force measurements in submerged micromanipulations.

Effect to the capillary force on force measurements in submerged micromanipulations.

Tel: +33 (0) 381 402 810 - Fax: +33 (0) 381 402 809 Website: http://www.lab.cnrs.fr, E-mail: michael.gauthier@ens2m.fr Abstract— The subject of this article is to analyse the impact of liquid surface tension on force measurement in submerged micromanipulations. On the one hand, at the present, mechanical characterization of biological objects in biological liquid has significant interest. On the other hand, the reduction of the surface force, and adhesion forces in a submerged medium could be a good approach to perform reliable artificial objects mi- cromanipulations. In both cases, the micro-nano force measurement in a liquid is a great challenge. In case of a force sensor placed out of the liquid, the measurement is disturbed by the liquid surface tension. This article proposes an analysis of the disturbance of the surface tension on the force measurement. Some design rules are proposed to reduce disturbances. We shows that the major disturbances are induced by the contact angle hysteresis and a complete method is proposed to calculate these disturbances in a micromanipulation task.
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High-speed force spectroscopy: microsecond force measurements using ultrashort cantilevers

High-speed force spectroscopy: microsecond force measurements using ultrashort cantilevers

Bacteriorhodopsin (BR), a model membrane protein formed by seven transmembrane helices and homologous to biomedically important G protein-coupled receptors (GPCRs, important drug targets), has been extensively studied (Oesterhelt et al. 2000 ). Yu et al. ( 2017 ) applied HS-FS to this canonical system with the aim of quantifying the energetics of individual membrane proteins embedded in a native lipid bi- layer. Force extension curves recorded at 300 nm/s (Fig. 2a ) revealed the three major intermediates, corresponding to the unfolding of helices ED, CB, and A, described in the consen- sus unfolding pathway emerged over the past 15 years (Oesterhelt et al. 2000 ). However closer inspection of the unfolding traces uncovered “hidden” intermediates and a complex dynamic (un)folding network (Fig. 2b ). For instance, while only two nonobligate intermediates were described dur- ing unfolding the ED helix pair over the past 15 years (Fig. 2b ; left inset), HS-FS enabled to observe 14 intermediates. Changes in contour length between states could be derived from WLC fits to the data, with an estimated accuracy along the polypeptide of ± 1 amino acid. Transitions corresponding to the unwinding of just two amino acids and dwell times as short as 8 ms could be resolved. The higher resolution of HS- FS (~ 100 fold improvement in temporal resolution and ~ 10 fold improvement in force precision in comparison with pre- vious studies on BR) allowed detection of rapid, reversible back-and-forth transitions between two or even three states (Fig. 2b , bottom inset) while stretching. This indicates that the structural elements associated with BR unfolding are smaller than assumed from previous experiments (two or three amino acids vs. pairs of helices, single helix, or approximately half a helix) but these small changes in the molecular confor- mation are too fast to be detected in previous SMFS experi- ments due to the limited force and time resolution. The wide spreading of refolding events also suggests that the mechani- cal unfolding of BR at standard stretching rates is likely to occur close to equilibrium but usually masked by experimen- tal limitations when using standard force probes.
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Axial Casimir force

Axial Casimir force

However, to our best knowledge, all the proposed Casimir friction phenomena (motion-induced vacuum forces) are dis- sipative. A natural question then arises: Is it possible to find a dissipationless motion-induced vacuum force? This question is partially motivated by the recent progress in quantum Hall physics, where dissipationless Hall viscosity emerges as a new topological signature [ 10 ]. We address this question in this paper by examining a rotating particle near a bi-isotropic material (BIM) plate. Existing commonly in nature, BIMs include materials that break time-reversal symmetry (TRS) or parity symmetry (PS) or both (PTS) [ 11 ]. In recent years, the widely studied Chern insulators [ 12 ] and chiral metamaterials [ 13 ] can be classified as bi-isotropic materials breaking TRS and PS, respectively.
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COURS-Force centrale

COURS-Force centrale

Nous venons de voir que, pour un point matériel soumis à une force centrale, le moment cinétique est une constante du mouvement donc la grandeur r 2 ! • , notée C par la suite, est une constante du mouvement alors que r t ( ) et ! t ( ) sont des fonctions du temps évidemment. Cette grandeur joue un rôle important dans la trajectoire des planètes autour du soleil comme nous allons le voir dans la suite de ce chapitre. Nous retiendrons :

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16-Force de Laplace

16-Force de Laplace

La bobine qui reçoit une intensité électrique subit, en présence du champ magnétique, une force de Laplace qui la fait bouger et qui fait donc bouger la membrane. La membrane fait vibrer l’air ce qui produit le son. Le haut parleur est un convertisseur d’énergie électrique en énergie mécanique : il y a donc

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COURS-Force-Centrale

COURS-Force-Centrale

IV – Mouvement d’un point matériel soumis à la force de gravité 4.1 Hypothèse de l’étude Nous allons étudier le mouvement d’un point matériel de masse m (le satellite) soumis à la force de gravité d’un autre objet (l’astre attracteur) de masse M . L’astre sera situé au centre du référentiel galiléen O et considéré comme immobile car on supposera que M  m . Cette situation est une bonne approximation quand on veut décrire le mouvement des planètes autour du soleil ou de satellites autour de la Terre. En général, les états liés du satellite sont des ellipses mais quand M  m , les ellipses deviennent des cercles. C’est pourquoi nous allons étudier uniquement les trajectoires circulaires. Dans ce cas également, la situation est une bonne approximation pour décrire le mouvement des planètes autour du soleil ou de satellites autour de la Terre.
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La force exclusive de la norme

La force exclusive de la norme

distinction absolue que Kelsen instaure du contenu de la norme et de l’acte qui la pose. Et, ce faisant, s'il se peut rencontrer des normes dont la force contraignante soit rendue explicite par le biais contradictoire. En outre, je me réfère au livre 14 du De l’interprétation d’Aristote : Cela étant, le bon est à la fois bon et non-mal ; la première de ces déterminations lui appartient par essence, et la seconde, seulement par accident, car c’est bien par accident qu’il est non-mal. Mais si le jugement vrai est plus vrai quand il porte sur l’essence même d’un sujet, le jugement faux est alors aussi plus faux. Or le jugement le bon n’est pas bon est un jugement faux portant sur ce qui appartient au bon par essence, tandis que le jugement le bon est mal porte sur ce qui appartient au bon par accident. Il en résulte que le jugement qui énonce la négation du bon sera plus faux que celui qui énonce le contraire du bon. 36
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Recent Advances on Ultrasound Contrast Agents for Blood-Brain Barrier Opening with Focused Ultrasound

Recent Advances on Ultrasound Contrast Agents for Blood-Brain Barrier Opening with Focused Ultrasound

The addition of microbubbles has reduced the amount of ultrasound energy required to open the BBB by 100-fold [2,3]. Upon sonication, microbubbles start oscillating at the frequency of ultrasound. Above a certain acoustic pressure, the previously symmetrical oscillations of the bubble become unstable [23]. Those two different regimens are respectively called stable and inertial cavitation. Inertial cavitation can induce microbubble collapse accompanied by micro-jetting, fragmentation, and shock-wave formation, which may induce vascular endothelium damages [20,22,24,25]. On the other hand, the mechanical stress generated by the stable cavitation can locally and reversibly disrupt the tight junctions present in the vascular endothelial tissue, which increases the BBB permeability [26]. It is generally accepted that stable cavitation is the preferred regime for a safe BBB opening [26]. Figure 1 schematically presents the two oscillation regimens of microbubbles and their potential effects on BBB. The use of low acoustic pressure (few hundreds of kPa) ensures the safety of the technique by limiting any potential damages such as erythrocyte extravasation, hemorrhage, and necrotic damage [27] resulting from local thermal [28] or mechanical effects [24,27].
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Adaptive multigroup radiation diffusion

Adaptive multigroup radiation diffusion

The physical interpretation of equation 3.11 is that the time rate of change of monochromatic radiation momentum density for photons at frequency v is equal to the [r]

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Contrast-enhanced and targeted ultrasound

Contrast-enhanced and targeted ultrasound

Ultrasound The sound that humans can perceive lies within the fre- quency range 20 Hz-20 kHz. Ultrasound is by definition all sound higher than 20 kHz. The ultrasound frequen- cies utilized in medical imaging are mainly in the range 1-40 MHz. Such high frequencies cannot be transmitted through air but can be transmitted satisfactorily through solid or fluid materials. An ultrasonic transducer serves a dual function as both transmitter and receiver of ultra- sound. A signal generated by an ultrasonic transducer typi- cally consists of a pulse of a few μs with a certain center frequency. Part of this signal propagates through target tissue, part is reflected by macroscopic tissue structures, part is absorbed by tissue, and part is scattered by struc- tures in the tissue smaller than the acoustic wavelength. Only a small portion of the transmitted acoustic energy is received by the transducer, but this portion is used to build an ultrasonic image. The received signal is the su- perposition of specular reflections at tissue boundaries and echoes from tissue backscattering [3] . Current real-time
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Real time ultrasound image denoising

Real time ultrasound image denoising

the date of receipt and acceptance should be inserted later Abstract Image denoising is the process of removing the noise that per- turbs image analysis methods. In some applications like segmentation or registration, denoising is intended to smooth homogeneous areas while pre- serving the contours. In many applications like video analysis, visual servo- ing or image-guided surgical interventions, real-time denoising is required. This paper presents a method for real-time denoising of ultrasound images: a modified version of the NL-means method is presented that incorporates an ultrasound dedicated noise model, as well as a GPU implementation of the algorithm. Results demonstrate that the proposed method is very efficient in terms of denoising quality and is real-time.
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Physical principles of medical ultrasound

Physical principles of medical ultrasound

medical ultrasound, which are handy especially if the sound waves are asymmetric.. 66.[r]

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Structured ultrasound-modulated optical tomography

Structured ultrasound-modulated optical tomography

Received 19 September 2018; revised 11 January 2019; accepted 31 January 2019; posted 1 February 2019 (Doc. ID 346368); published 6 March 2019 Ultrasound-modulated optical tomography (UOT) is an imaging technique that couples light and ultrasound in order to perform in-depth imaging of highly scattering media. In previous work, we introduced plane wave UOT, an imaging method analogous to x-ray tomography based on the filtered backprojection for image reconstruction. Angle-limited measurements, however, led to drastic loss of lateral spatial resolution. Here, we present a new structured ultrasonic plane wave UOT method that allows partial recovery of the resolution. For image reconstruction, we present a generalization of the Fourier slice theorem along with a generalized filtered back- projection formalism. The method is successfully tested on simulated and experimental data. © 2019 Optical Society of America
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View of Ultrasound hemodynamic evaluation

View of Ultrasound hemodynamic evaluation

Par analogie à l’évaluation des pressions de remplissage cardiaque gauche habituellement estimées par le rapport E/ Ea mitral, nous proposons dans ce travail d’évaluer la corrélation en[r]

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La force obligatoire du contrat de travail

La force obligatoire du contrat de travail

domaine matériel de la force obligatoire, la nouvelle organisation du Code civil en consacre une vision maximaliste. Le principe de la force obligatoire du contrat doit participer de « l’interprétation de l’ensemble des règles du contrat, et au besoin à en combler les lacunes » 108 . De manière cohérente avec l’essence normative du contrat, la force obligatoire du contrat se pose désormais comme faisant partie « des définitions du contrats » 109 . Le futur article 1193 du Code civil constitue une manifestation concrète de ce principe, mais non son intégralité. La composition de la Sous-section consacrée à la force obligatoire ne peut d’ailleurs pas s’expliquer autrement. A ce titre il convient de comparer l’articulation entre les articles 1134 et 1135 actuels et entre les futurs articles 1193 et 1194. L’alinéa 1er de l’article 1134 fait directement référence à l’essence normative des conventions. L’article 1135 se trouve donc logiquement à la suite puisqu’il indique que « les conventions obligent non seulement à ce qui y est exprimé, mais encore à toutes les suites que l'équité, l'usage ou la loi donnent à l'obligation d'après sa nature ». Les suites données au contrat reçoivent tout autant force obligatoire que les prévisions des parties puisqu’elles « obligent » au même titre. Par forçage du contrat, la Loi nationale peut devenir la loi des parties. A partir du 1er octobre 2016, il faudra revenir quatre-vingt-dix articles en arrière pour comprendre l’article 1194, dont la signification ne peut pas découler du futur article 1193 selon lequel « les contrats ne peuvent être modifiés ou révoqués que du consentement mutuel des parties, ou pour les causes que la loi autorise ». En effet, c’est bien parce que le contrat est une loi pour les parties que son contenu, même forcé par la loi, l’usage ou l’équité, les oblige. La présence du futur article 1194 du Code civil dans la partie consacrée à la force obligatoire du contrat est un aveu du législateur : le principe de la force obligatoire du contrat garde sa philosophie et n’est pas réduit aux seules intangibilité et irrévocabilités unilatérales 110 .
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Displacement Reconstructions in Ultrasound Elastography

Displacement Reconstructions in Ultrasound Elastography

1 Introduction Elastography has established itself as an important imaging modality to quantify the elastic proper- ties of biological tissues [ 8 , 9 , 16 , 18 , 19 , 20 , 21 ]. In most settings of elastography, the first step in the modality is the reconstruction of internal elastic displacements or strain tensors. This paper is concerned with Ultrasound Elastography, which includes Strain Elastography [ 18 , 19 ] and Transient Elastography (or Shear-wave Elastography) [ 8 , 9 ], and aims to reconstruct the elastic displacements from ultrasonic echoes. Internal displacements may also be obtained by another method, not con- sidered in this paper, which combines elastic displacements with magnetic resonance imaging; see [ 14 , 15 , 16 , 17 , 21 ] for additional information on Magnetic Resonance Elastography.
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