Method for determining the viscoelastic properties of a biological medium, module and associated device

Abstract

The invention relates to a module for determining the viscoelastic properties, referred to as the module, of a moving biological medium of variable thickness, referred to as the medium, at least partially enclosed in an elastic biological environment. The module comprises a processing unit arranged to calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of the at least one shear wave in the medium, and to determine, from the dispersion curve of the at least one shear wave in the medium and a propagation mode of the at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium. Figure for the abstract: FIGURE 3

Description

Title of the invention: Method for determining the viscoelastic properties of a biological medium, module and associated device technical field

[0001] The present invention relates to the field of characterizing the properties of organic tissues in motion.

[0002] The present invention relates more specifically to the determination of viscoelastic properties of soft tissues in motion.

[0003] The invention falls within the field of non-invasive and non-intrusive tissue characterization techniques.

[0004] The invention belongs to the field of medical ultrasound imaging.

[0005] The invention relates, in particular, to ultrafast ultrasound imaging.

[0006] The invention relates, for example, to the fields of exercise physiology, rehabilitation science, or the control of artificial respirators. Prior art

[0007] Ultrafast ultrasound imaging is known from the prior art. This type of ultrasound scanner emits ultrasound waves and detects the ultrasound waves reflected by soft and / or elastic biological tissue at a frequency greater than 15 MHz. It allows for the characterization of an individual's soft and / or elastic tissues.

[0008] However, prior art methods have a number of limitations and drawbacks, particularly regarding the accuracy of the determined viscoelastic properties of moving media or media whose thickness varies over time. Prior art methods necessarily introduce a relative error in the estimation of the determined viscoelastic properties of the medium.

[0009] Furthermore, prior art methods require the use of ultrasound scanners in B-mode, i.e., in anatomical imaging mode, to determine the position of the target medium to be studied. This mode imposes significant hardware constraints, particularly with regard to the electronic device and the resources required for data processing.

[0010] One of the tissues of interest whose characterization of viscoelastic properties still needs to be improved is the diaphragm.

[0011] One object of the present invention is to remedy at least one of the drawbacks of the prior art.

[0012] Another object of the invention is to: - to allow for a more precise determination of the viscoelastic properties of a soft biological medium, and / or - to allow determination of the viscoelastic properties of a biological medium without using B-mode ultrasound imaging for positioning, and / or - to allow determination of the position of the biological medium within its environment, and / or - to allow determination of the position of the biological medium within its environment without using B-mode ultrasound imaging, and / or - to allow a determination of the thickness and / or the variation in thickness of the biological medium. Description of the invention

[0013] To this end, the invention proposes a method for determining viscoelastic properties, referred to as the method, of a biological medium, preferably soft or elastic, of variable thickness in motion, referred to as the medium, at least partially enveloped in an elastic or soft biological environment, referred to as the environment.

[0014] The process comprises the steps of: - to calculate, preferably by means of a processing unit, preferably the processing unit of the module or device according to the invention, from propagation data of at least one shear wave in the medium, preferably in a given or considered plane of the medium, a dispersion curve of at least one shear wave in the medium, preferably in a given or considered plane of the medium, - determine, preferably by means of a processing unit, preferably the processing unit of the module or device according to the invention, a thickness of the medium, preferably determined over a time period corresponding to the propagation of a shear wave in the medium, preferably in a given or considered plane of the medium, and / or the viscoelastic properties of the medium, preferably as a function of or relative to the thickness of the medium, from the dispersion curve of at least one shear wave in the medium and of one or more modes of propagation of at least one shear wave in the medium.

[0015] According to the invention, soft tissues can be understood to mean: tendons, ligaments, muscle tissues or vascular tissues.

[0016] The propagation of a shear wave in the medium can be defined as the spatial displacement of the disturbance in the medium generated by at least one shear wave.

[0017] It can be understood by at least one wave: a single wave or a wave at a given instant or several waves, or a set of waves, of successive shear (or propagating successively) in the medium.

[0018] Preferably, "propagation data of at least one shear wave in the medium" means: propagation data of at least one shear wave in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment.

[0019] Preferably, at least one shear wave in the medium is an acoustic shear wave propagating in the medium.

[0020] Propagation data may include: - the propagation speed of at least one shear wave in the medium, preferably in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment, and / or - the position, preferably the relative position, of the shear wave in the medium, preferably in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment, as a function of time, and / or - the amplitude of at least one shear wave in the medium, preferably in a given or considered plane of the medium, as a function of time and / or position; the position, preferably the relative position, of the shear wave in the medium, preferably in a given or considered plane of the medium and / or environment, preferably in several given or considered planes, preferably again in several given or considered planes corresponding to several depths of the medium and / or environment.

[0021] Preferably, the propagation mode(s) of at least one shear wave in the medium correspond to or constitute the solution(s) of the shear wave propagation equation in the medium.

[0022] The propagation mode(s) of at least one shear wave in the medium can be included in a database containing the propagation mode(s).

[0023] The propagation mode(s) of at least one shear wave in the medium can be calculated by a processing unit, preferably by means of a processing unit, preferably the processing unit of the module or device according to the invention.

[0024] Determining the viscoelastic properties of the medium from the propagation mode(s) of at least one shear wave makes it possible to improve the accuracy of the values ​​of the properties determined.

[0025] Determining the viscoelastic properties of the medium from the propagation modes of the propagation mode(s) of at least one shear wave allows the thickness of the medium to be determined.

[0026] Determining the viscoelastic properties of the medium from the propagation modes of the propagation mode(s) of at least one shear wave makes it possible to improve the accuracy of the values ​​of the properties determined and / or to determine the thickness of the medium without using ultrasonic imaging in B-mode.

[0027] The viscoelastic properties of the medium may include: • one or more shear moduli of the medium, preferably parallel or perpendicular to fibers constituting the medium, • a shear viscosity of the medium, preferably parallel or perpendicular to the fibers constituting the medium, • one or more nonlinear shear moduli parallel or perpendicular to the fibers constituting the medium, • anisotropy factor of shear modulus, shear viscosity, or shear nonlinearity.

[0028] Preferably, the calculation step, preferably implemented by means of a processing unit, preferably the processing unit of the module or device according to the invention, of the dispersion curve of at least one shear wave in the medium, from propagation data of at least one shear wave in the medium and / or in the environment, propagating in the medium and / or in the environment according to the determined propagation mode, is implemented by Fourier transform of the propagation data of said at least one shear wave, propagating in the medium and / or in the environment according to the determined propagation mode, in the spatio-temporal domain.

[0029] According to the method, the calculation step, preferably implemented by means of a processing unit, preferably the processing unit of the module or device according to the invention, may further comprise, from propagation data of at least one shear wave propagating, according to the determined propagation mode, in the medium and / or in the environment, a Fourier transform of the propagation data of said at least one shear wave propagating, according to the determined propagation mode, in the medium and / or in the environment, in the spatial domain and a Fourier transform of the propagation data of said at least one shear wave propagating, according to the determined propagation mode, in the medium and / or in the environment, in the time domain. Preferably, the dispersion curve of at least one shear wave, propagating in the medium according to the determined mode of propagation, being calculated from the Fourier transforms in the spatial domain and in the time domain.

[0030] Preferably, the propagation mode of at least one shear wave in the medium is a dispersive propagation mode guided by the medium.

[0031] Preferably, the medium-guided dispersive propagation mode is understood to mean: the solution to the propagation equations of a medium-guided shear wave dispersing in the elastic biological environment in which the medium is at least partially enveloped.

[0032] Preferably, the determination step is implemented based on or from the shear modulus of the medium, the shear modulus of the environment, the density of the medium and the density of the environment.

[0033] The propagation modes of at least one shear wave in the medium may include or be a function of the shear modulus of the medium, the shear modulus of the environment, the density of the medium and / or the density of the environment.

[0034] Taking into account the environment, in particular environmental parameters, to determine the viscoelastic properties of the medium makes it possible to further improve the accuracy of the values ​​of the properties determined.

[0035] Taking into account the environment, in particular environmental parameters, makes it possible to improve the accuracy of the thickness of the medium determined.

[0036] Preferably, the propagation data of at least one shear wave in the medium include amplitude(s) and / or displacement data of at least one shear wave in the medium.

[0037] Preferably, the propagation data of at least one shear wave and / or the dispersion curve of at least one shear wave are, or correspond to or relate to, those of at least one shear wave in a given or considered plane or section of the medium.

[0038] Preferably, the method according to the invention is implemented for several, preferably for each, propagation data of at least one shear wave originating from a given plane or section or considered different from the medium.

[0039] Preferably, the environment is an organ of a subject.

[0040] Preferably, at least one shear wave is generated by: - a physiological process of the subject, - a voluntary action by the subject, and / or - an external stimulus.

[0041] A physiological process of the subject may be, by way of non-limiting example, the subject's heartbeat, the subject's blood circulation or the subject's borborygmi.

[0042] A voluntary action of the subject may be, by way of non-limiting example, a sound emitted by the voice of a subject or a snap of the fingers.

[0043] Preferably, the external stimulus comprises at least one ultrasonic wave emitted by an ultrafast ultrasonic imaging device.

[0044] Preferably, the method further comprises a step of calculating and / or determining the propagation data of at least one shear wave from ultrasonic waves reflected and detected by the ultrafast ultrasonic imaging device.

[0045] Preferably, the method further comprises a determination of the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device.

[0046] Preferably, the ultrafast ultrasonic imaging device is arranged to probe one, in particular a single, given or considered plane or one, in particular a single, given or considered section of the medium at a time.

[0047] The use of the propagation modes of at least one shear wave makes it possible to determine the presence of the medium in the, in particular the single or unique, plane or in the, in particular the single or unique, probed section of the medium.

[0048] The use of propagation modes of at least one shear wave makes it possible to determine the presence of the medium in the, in particular the single or unique, plane or in the, in particular the single or unique, probed section of the medium without using ultrasonic imaging in b-mode.

[0049] Preferably, the method includes determining the position of the medium in the environment from the data detected by said ultrafast ultrasonic imaging device.

[0050] The use of propagation modes of at least one shear wave associated with taking into account the environment, in particular environmental parameters, makes it possible to determine the position of the medium in its environment.

[0051] The use of propagation modes of at least one shear wave associated with taking into account the environment, in particular environmental parameters, makes it possible to determine the position of the medium in its environment without using ultrasonic imaging in b-mode.

[0052] Preferably, the middle is a diaphragm.

[0053] Preferably, when the medium is a diaphragm, the propagation data originate from or are those of several successive shear waves, or are data or correspond to the data of several successive shear waves propagating through the medium, and covering a continuous duration or extending over a period of at least one respiratory cycle.

[0054] Preferably, the determination step further includes the determination of a variation in the thickness of the medium over time and / or a variation in the thickness of the medium in space.

[0055] According to another aspect of the invention, a computer program is proposed comprising executable instructions which, when executed by computer, implement the steps of the process according to the invention.

[0056] The computer program can be in any computer language, such as for example in machine language, in C, C++, JAVA, Python, etc.

[0057] According to another aspect of the invention, a computer-readable medium is proposed comprising instructions which, when executed by a computer, lead the computer to implement the process according to the invention.

[0058] According to another aspect of the invention, a data processing device programmed and / or configured and / or arranged to implement the process according to the invention is proposed.

[0059] The data processing device can be a server, a computer, a tablet, a calculator, a processor, a computer chip, programmed to implement the method according to the invention, for example by executing the computer program according to the invention.

[0060] According to the invention, a module for determining viscoelastic properties, referred to as the module, of a biological medium of variable thickness in motion, referred to as the medium, at least partially enveloped in an elastic biological environment, is also proposed.

[0061] Preferably, the module is suitable and / or intended to and / or arranged to be connected, by wire or wireless means, to an ultrasound imaging device, preferably to an ultrafast ultrasound imaging device.

[0062] The module includes a processing unit arranged for: - calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0063] Preferably, the module includes communication means and / or a connector arranged to communicate with an ultrafast ultrasound imaging device and to receive propagation data from at least one wave shear in the medium originating from said ultrafast ultrasonic imaging device.

[0064] "Communicate" can be understood as: transferring, receiving and / or transmitting data.

[0065] An ultrafast ultrasonic imaging device may be understood to mean a high-frequency imaging device. High frequency may be understood to mean the emission and detection of ultrasonic waves at a frequency greater than or equal to 15 MHz, typically greater than or equal to 20 MHz.

[0066] Typically, the propagation time of a shear wave in the medium within an imaging field is on the order of a few microseconds for soft tissues with high stiffness, and on the order of a few tens of microseconds, typically around one hundred microseconds, for soft tissues with low stiffness. Therefore, given the imaging frequency of ultrafast ultrasound imaging devices (capable of producing 20,000 images per second), it is possible to obtain, during the propagation of a shear wave through the medium, propagation data from at least 10 x 10⁷ images of the shear wave propagating through the medium.

[0067] By way of non-limiting example, high hardness may be understood as: a hardness close to or on the order of 100 kPa. By way of non-limiting example, low hardness may be understood as: a hardness close to or on the order of 10 Pa.

[0068] Preferably, the processing unit of the module is arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasound imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasound imaging device.

[0069] According to the invention, an ultrafast ultrasonic imaging device, referred to as the device, is also proposed for determining the viscoelastic properties of a moving biological medium of variable thickness, referred to as the medium, at least partially enveloped in an elastic biological environment, referred to as the environment.

[0070] The device includes a probe arranged to emit at least one ultrasonic wave and detect reflected ultrasonic waves.

[0071] Preferably, the ultrafast ultrasonic imaging device is arranged to detect ultrasonic waves reflected by the medium and the environment.

[0072] According to a first alternative, the device comprises the module according to the invention.

[0073] According to the first alternative, the module can be further arranged to calculate and / or determine propagation data for at least one shear wave in the medium from ultrasound waves reflected and detected by said ultrafast ultrasound imaging device.

[0074] According to a second alternative, the device comprises a processing unit arranged to: - calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0075] Preferably, the processing unit of the device is further arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasound imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasound imaging device.

[0076] Preferably, the probe is arranged, in addition, to emit at least one ultrasonic wave capable of generating at least one shear wave in the medium.

[0077] Preferably, the module for determining the viscoelastic properties of the medium, more preferably the processing unit of the module for determining the viscoelastic properties of the medium, and / or the device for determining the viscoelastic properties of the medium, more preferably the processing unit of the device for determining the viscoelastic properties of the medium, according to the invention is suitable, more preferably is particularly suitable, more preferably is designed and more advantageously is specially designed, to implement the process of stabilizing molten samples and / or the process of determining the viscoelastic properties of the medium.Therefore, any characteristic of the device for determining the viscoelastic properties of the medium and / or of the device for determining the viscoelastic properties of the medium according to the invention is directly transposable to the method for determining the viscoelastic properties of the medium and vice versa. Brief description of the FIGURES

[0078] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which: - Fig. 1 is a schematic representation of a three-layer model comprising the medium or soft tissue and its environment, - Figure 2 includes two graphs illustrating the dispersion relationship of a shear wave propagating in two distinct biological environments, - Figure 3 includes two schematic representations of non-limiting examples of embodiments of the viscoelastic property determination module according to the invention, - [Fig.4] is a schematic representation of a non-limiting example embodiment of an ultrafast ultrasonic imaging device for determining viscoelastic properties according to the invention.

[0079] In the figures and in the rest of the description, elements common to several figures retain the same reference. Description of a method of implementation

[0080] The embodiments described below are in no way limiting; variants of the invention may include, in particular, a selection of the described features, isolated from the other described features (even if this selection is isolated within a sentence containing these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably a functional one without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0081] A non-limiting embodiment of the invention is presented.

[0082] The invention aims to determine the viscoelastic properties of a medium of variable thickness over time whose viscoelastic properties also change over time.

[0083] In particular, the invention proposes a determination of viscoelastic properties which is non-invasive and painless.

[0084] The invention relates to the determination of viscoelastic properties of any type of soft tissue in motion at least partially enveloped in an elastic biological environment.

[0085] To this end, a method for determining the viscoelastic properties, referred to as the method, of a moving biological medium of variable thickness, referred to as the medium, at least partially enveloped in an elastic biological environment, referred to as the environment, is proposed. The method comprises the step of calculating, from propagation data of at least one shear wave in the medium, the curve, The equation or dispersion relation of at least one shear wave in the medium. The dispersion relation allows us to obtain a relationship between the angular frequency (eu) and the wave vector (k) of at least one shear wave.

[0086] The method further includes a step of determining, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

[0087] By way of non-limiting example, the determination step is implemented based on or from the shear modulus of the medium, the shear modulus of the environment, the density of the medium and / or the density of the environment.

[0088] Preferably, the density, expressed in kg / m³, of the soft tissues according to the embodiment is considered to be between 1000 and 1100 kg / m³. The soft tissues are also considered to be virtually incompressible. The Poisson's ratio of the soft media according to the embodiment is close to 0.5.

[0089] Advantageously, the method is implemented using propagation data of several shear waves in the medium and / or in the environment, preferably a set of shear waves in the medium and / or in the environment, preferably even a set or several successive shear waves in the medium and / or in the environment.

[0090] According to a preferred ingenious, non-limiting embodiment, for at least one propagation mode of at least one shear wave in the medium, the inventors have considered the shear waves as guided in the medium. Thus, according to the embodiment, the guidance of the shear waves has been expressed by means of guided wave theory or Lamb waves. It should be noted that other models, derived or arising from, for example, Maxwell's equations or the telegrapher's equations, could have been used.

[0091] A direct advantage of using such a description of shear wave guidance is to introduce a correspondence between the viscoelastic properties of two semi-infinite environments surrounding the medium, the viscoelastic properties of the medium, and the thickness of the medium. In other words, according to such a consideration, the environment / medium system constitutes a three-layer. The three-layer medium is shown in [Fig. 1].

[0092] With reference to the three-layered medium illustrated in [Fig. 1], the biological medium 2 of variable thickness in motion and the elastic biological environment comprising a first layer 1, enveloping, at least in part, the medium 2 and the elastic biological environment comprising a second layer 3 are illustrated. enveloping, at least in part, the medium 2. Layers 1 and 3 can constitute a distinct environment.

[0093] The coefficient p (pl, p2 and p3) represents the density (volumetric mass) in kg / m3, the coefficients q (ql, q2, q3) represent the shear modulus (where the first Lamé coefficient) in kPa and X (XI, X2 and X3) represent the second Lamé coefficient in Pa.

[0094] A semi-infinite solid three-layer structure (1, 2, 3) is considered. The three-layer consists of a plate of thickness h with interfaces (considered rigid) corresponding to two semi-infinite solids and with lateral dimensions assumed to be infinite. Considering an orthonormal coordinate system (O, z) with ez the normal to the three-layer and ëx the direction of propagation of elastic waves, each layer is associated with a density (p1, p2, and p3).

[0095] Thus, longitudinal velocities V Lj and transverse velocities V Tjdc propagation of elastic waves propagating in each of the three layers 1, 2, 3 can be considered.

[0096] In other words, the medium 2 is composed of an elastic structure forming a plate 2 surrounded by two semi-infinite elastic solids 1, 3, which have the effect of generating flowing longitudinal and transverse waves. The shear waves arriving from environment 1, from above, (L*, Sp) or arriving from environment 3, from below, (L^ S-^) of the two infinite half-spaces are, and must be, zero according to the chosen model. Each layer j_ i>2,3 is viscoelastic and the complex Lamé coefficients can be expressed as: j = j + i on] j, where co corresponds to the angular frequency of the shear wave and qj corresponds to the shear viscosity in Pa.s.

[0097] The scalar potentials are sought in the form of harmonic waves, propagating along the x-direction. Consequently, the scalar potentials (pj and vectors j) are expressed according to the following equation 1: ' çpi (æ, z, t) = fi = Au fi(æ, z, t) = = Au < — IAîocos ( kin> z^ æ ' wAa z, t) - 72 - [Aa cos + B2t sm ip3(x, Z, A = = An A^-^1 where Z; - z + h, . 17 w \2 I ”, , / 7 w , 2 * ” the coefficients of kx kfv = V7^) ■ kx Lamé for layer ii 23: , / >,2 ->tz2 ) and (T72 ), A and B are the respective amplitudes of normal and transverse displacements in the layer j, Aji and Bji are the amplitudes of the displacements of layer j along the longitudinal polarization direction of the shear wave and Ajt and Bjt are the amplitudes of the displacements of layer j-1.2.3 along the transverse polarization direction of the shear wave, x and z are the coordinates in the (0%z) frame, z being the depth in medium 2 and in the biological environment 1, 3, zj corresponds to the depth of the layer j considered plus or minus the thickness of the biological medium 2, t is the time, k is the wavenumber and k[z and kt- correspond respectively to the wavenumber of the shear wave along the longitudinal direction and to the wavenumber of the shear wave along the vertical direction.

[0098] A normal axis corresponds to an axis parallel to or coinciding with the z-axis; for example, normal displacements are displacements along a normal axis, that is, along an axis perpendicular to the biological medium 2. A transverse axis corresponds to an axis parallel to or coinciding with the x-axis; for example, transverse displacements are displacements along a transverse axis, that is, along an axis included in or coinciding with the plane in which the biological medium 2 extends. A longitudinal axis corresponds to an axis parallel to or coinciding with the y-axis (perpendicular to the x and z axes); for example, longitudinal displacements are displacements along a longitudinal axis, that is, along an axis included in or coinciding with the plane in which the biological medium 2 extends.

[0099] The solutions associated with the amplitudes By, B16 B3! and B3t are not physically admissible because they diverge in depth. Waves arriving from above (Lp) or from below (Ly) must therefore be considered as zero.

[0100] The idea is to look for solutions representing waves propagating parallel to the interfaces or surface of the medium 2, which corresponds to solutions describing evanescent waves along the z direction.

[0101] From here, it is possible to express a displacement field u (^ and üj), after Helmholtz decomposition (i.e., by expressing: Uxj = gradet U~j — rot ( ipj ) ). The expressions for the stresses, denoted and in terms of the scalar potentials (pj and vectors ipj), can be expressed according to the following equation (2): ( duxj duZj \ axzj = B; ( “ + ” / _ , / àuXi duzj \ 3¾ , equation (2). &zzj = Ài\ dx + az

[0102] Considering that the boundary conditions allow continuity of normal and tangential stresses and continuity of normal and tangential displacements at the interfaces in z = z ±h, a system of eight equations and eight unknowns is obtained, denoted (Au, Au, Aa, B-^ A^, B^ A^ A^).

[0103] From here, it is possible to obtain the expressions for the normal and transverse displacements in z = z + (π / 2) as well as the expressions for the normal and transverse stresses. From these expressions, it is possible to draw up the transcendental equation, denoted MU, of a semi-infinite solid three-layer, which can be presented in 8x8 matrix form according to the following equation (3): — .Ad - —2iu?kxki:P> shiAO] ~2ifl2kie^tx2 WS[klz2h] — 2? ki^ (?) -2 / (10 ik. rl - 2kx) cosOa'M --- Zkx COS ; kl,2 2fcj) sixi[L;:2 ikx sillOA] with M the determinant of the matrix and A^ A2b B^, A^ B2b Ay, A^] where U* corresponds to the amplitudes of the displacement field.

[0104] Finally, to obtain the dispersion curves (i.e., the relationship between the angular frequency (œ) and the wave vector (k) of the shear waves), it suffices to search for the values ​​for which the determinant is zero (i.e., M = 0) using, for example, the Newton-Raphson, bisection, or Muller method. Solving the dispersion equation allows us to obtain the pairs (eu, k).

[0105] Layers 1 and 3, i.e., the elastic biological environment in which the medium is enveloped, may be different. In this case, it is not possible to divide M into two submatrices to separate the symmetric modes from the antisymmetric modes. Nevertheless, when the 1, 2, 3 tri-layer is asymmetric, it can be observed that the modes of the same family never intersect. Consequently, this will not pose a problem when searching for a branch (mode) using a zero-finding algorithm (Muller type or other).

[0106] If the semi-infinite solid 1 is identical to the semi-infinite solid 3, that is, if the medium 2 is enclosed within the same biological environment 1,3, then it is possible to divide M into two submatrices, thus allowing the family to be separated symmetrical modes S, antisymmetrical modes A. We will have AiL = A3L, BiT = B3T, An = -A3t, Bil = -B3l, and A2T = B2L = 0 for symmetrical modes S, and similarly, we will have AiL = -A3L, B[T = -B3T, AiT = A3T, B[L = B3L, and A2L = B2T = 0 for antisymmetrical modes A.

[0107] These two submatrices are almost identical since it would suffice to add a factor, denoted a, to the cosines and sines of the matrix M. From here, for a = 0 we obtain the submatrix of symmetric modes and for a = n / 2 the antisymmetric modes.

[0108] Also, it is important to note that the invention is not limited to the particular embodiment based on the guided wave model as described above but may be carried out by means of any model or calculation enabling the establishment or comprising a solution of the equation (therefore at least one mode of propagation) of a shear wave propagating, at least partially, in a biological medium 2 and in a biological environment 1,3, at least partially enveloping said biological medium 2.

[0109] Furthermore, the model or calculation (i.e. the solution of the equation, or at least one mode of propagation, of a shear wave propagating in the medium includes or is a function of the thickness of the medium and of physico-chemical parameters (viscosity, density...) and / or mechanical parameters (Young's modulus, shear modulus, Poisson's ratio...) depending on the medium.

[0110] The shear wave propagation data in the medium and / or in the environment, referred to as propagation data in the following description, include or are a function of the depth of the shear wave in the medium (and possibly in the environment).The propagation data consist of, include, correspond to, or are proportional to the propagation velocity of at least one shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or the position, or the change in position as a function of time, of the shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or the amplitude, or the change in amplitude, of at least one shear wave (in medium 2, or in medium 2 and environment 1, 3) and / or any other parameter, characteristic or indicator representative of or function of the propagation of the shear wave, preferably as a function of time, (in medium 2, or in medium 2 and environment 1, 3).

[0111] According to the invention, it is advantageous that the propagation data include shear wave propagation data in medium 2 and in environment 1,3.

[0112] Thus, from the model or calculation and the shear wave propagation data, it is established, calculated, determined or chosen (for example in a basis of given) the equation or formula of the mode of propagation of the shear wave in the medium.

[0113] The method may include a step of obtaining shear wave propagation data and / or data in the environment.

[0114] The shear wave propagation data in the medium and / or the environment are stored data. Therefore, the method can be implemented without a propagation data acquisition step. This allows for the systematic or static study or comparison of the viscoelastic properties of a biological medium based on available (previously acquired) data.

[0115] The method further includes the step of calculating, from shear wave propagation data in the medium and at least one shear wave propagation mode in the medium, the calculation of the dispersion curve of at least one shear wave in the medium.

[0116] According to the embodiment, the calculation of the shear wave dispersion curve in the medium is implemented by Fourier transformation, in the spatio-temporal domain, of the shear wave propagation data propagating in the medium according to the determined propagation mode.

[0117] With reference to [Fig.2], examples of dispersion curves obtained in the case of a soft plate immersed in a liquid, water according to the examples, or loaded on one side by water and on the other by a soft elastic solid are illustrated.

[0118] The left-hand graph of [Fig. 2] illustrates the dispersion curve for a submerged soft plate for shear waves propagating in medium 2 (according to the determined principal propagation mode) with (i.e., shear wave propagation data propagating in medium a) longitudinal velocities VLj and transverse velocities VTj of elastic wave propagation of 1500 m / s and 5 m / s respectively (corresponding to typical velocities of viscoelastic biological media). Medium 2 has a thickness of 3.6 mm according to the embodiment. The soft plate 2 is completely immersed in water 1, 3 exhibiting longitudinal velocities VLj and transverse velocities V Tj of propagation of elastic waves (i.e. shear wave propagation data in the medium) of 1500 m / s and 0 m / s respectively.The points correspond to the dispersion curves calculated by spatio-temporal analysis, by Fourier transformation according to the realization mode, of the shear waves propagating in medium 2 (according to the determined principal propagation mode) (corresponding to the solution of the transcendental equation).

[0119] The graph on the right of [Fig.2] illustrates the dispersion curve for a soft plate exhibiting longitudinal velocities VL2 and transverse velocities Vr2 of elastic shear wave propagation of 1500 m / s and 2 respectively. m / s (corresponding to typical speeds of viscoelastic biological media). Medium 2 has a thickness of 3.6 mm according to the embodiment. The soft plate 2 is half-enclosed in water 1 on one side (with VL1 and VTi of 1500 m / s and 5 m / s, respectively) and half-enclosed in a soft solid 3 on the other side (with Vet V T3 of 1500 m / s and 15 m / s, respectively). The points correspond to the dispersion curves calculated by spatio-temporal analysis, using Fourier transform according to the embodiment, of the shear waves propagating in medium 2 (according to the determined principal propagation mode) (corresponding to the solution of the transcendental equation).

[0120] According to a particularly advantageous but non-limiting embodiment of the invention, the propagation data of at least one shear wave in medium 2 and / or in environment 1, 3 originate or are derived from an ultrafast ultrasound imaging device. The propagation data may be stored digital data or data acquired in real time and processed in real time, according to the invention.

[0121] With reference to [Fig. 3], the invention also proposes a module 4 for determining the viscoelastic properties, referred to as module 4, of a moving biological medium 2 of variable thickness, referred to as medium 2, at least partially enveloped in an elastic biological environment 1, 3. Module 4 comprises a processing unit arranged and / or configured and / or programmed to implement the method according to the invention. The schematic representation on the left of [Fig. 3] illustrates module 4 according to the embodiment, and the schematic representation on the right of [Fig. 3] shows the module connected by wire to an external ultrafast ultrasound imaging device 5.

[0122] Advantageously, module 4 includes means for communication / reception with (for example, wireless communication means via radio waves) and / or a connector arranged to communicate / receive data from an external or remote device 5.

[0123] The connection means of module 4 are suitable and / or arranged to communicate and / or transmit and / or receive data from the external or remote device 5. According to a non-limiting advantageous embodiment, the external or remote device 5 is an ultrafast ultrasound imaging device 5. The propagation data of at least one shear wave in the medium 2 originate from, or are provided by, said ultrafast ultrasound imaging device 5.

[0124] According to one envisaged embodiment, the module 4 may include an ultrasonic probe 6 arranged to emit and detect ultrasound reflected by the medium and / or the environment. Preferably, in this case, the module 4 is arranged to perform the instructions from an ultrafast ultrasound imaging device 5 enabling the emission and reception of ultrasound waves.

[0125] Advantageously, module 4 and / or the method is arranged to determine, by implementation of the method, the position of and / or locate the (or confirm or detect the presence of) biological medium 2 in the area probed (i.e. in one or more planes of) the area probed by the ultrafast ultrasonic imaging device 5. Indeed, the determination or selection of the shear wave propagation equation, from the propagation data, allows the discrimination (or identification) of medium 2 and environment 1, 3.

[0126] With reference to [Fig.4], an ultrafast ultrasonic imaging device 7, referred to as device 7, is presented for the determination of viscoelastic properties according to the invention.

[0127] The device 7 is arranged and / configured and / or programmed to implement the process according to the invention.

[0128] The device 7 includes one or more probe(s) 8 arranged to emit ultrasonic waves and detect reflected ultrasonic waves (by the medium and / or by the environment).

[0129] Alternatively, the device 7 can be defined as comprising the module 4 according to the invention. In this case, the device 7 can be defined as the external or remote ultrafast ultrasound imaging device 5.

[0130] According to the invention, advantageously, at least one shear wave propagating in the medium 2 is generated by a non-therapeutic process or stimulus.

[0131] The (non-therapeutic) stimulus may be an unprovoked physiological process (the subject's breathing, the subject's heartbeat, the subject's blood circulation, or the subject's borborygmi).

[0132] The (non-therapeutic) stimulus may be a voluntary action of the subject, by way of non-limiting example, a sound emitted by the subject's voice or a snap of the fingers or a voluntary action of the subject or expectoration.

[0133] The (non-therapeutic) stimulus may be an external stimulus, for example a ultrasonic wave (preferably emitted by an ultrafast ultrasound imaging ultrasound scanner).

[0134] The (non-therapeutic) stimulus may be an external stimulus, for example, electrical and / or magnetic stimulation. Electrical and / or magnetic stimulation may be delivered to the nervous system by: - transcranial stimulation, and / or - cervico-medullary stimulation, and / or - stimulation of the phrenic roots, and / or - stimulation of one or two of the main trunks of the phrenic nerve, and / or - stimulation of the diaphragm itself.

[0135] Ultrasonic probes are known to those skilled in the art. The ultrasonic probe 6 (of module 4), the ultrasound probe 8 (of device 7) or the probe 9 of the remote ultrafast ultrasound imaging device 5 may include a set of sensors, for example piezoelectric, suitable and / or arranged to emit ultrasound and to capture / detect ultrasound echoes from the probed area 2 and suitable for ultrafast ultrasound imaging.

[0136] According to an advantageous but non-limiting embodiment of the invention, at least one shear wave is generated in the medium 2 by one or more ultrasonic waves emitted by the ultrasonic probe 6, 8 or 9 (of the module 4, of the device 7 or remote ultrafast ultrasound imaging device 5).

[0137] This embodiment is advantageous because the propagation data of at least one shear wave in the medium 2 (and in the environment 1, 3) are obtained or acquired, in real time, by the module 4, by the device 7 or by the remote device 5.

[0138] In this case, the Shear Bottom propagation data can be considered as the raw data acquired by module 4, device 7 or remote device 5. Alternatively, the Shear Bottom propagation data can be determined or calculated from the raw data acquired or from the ultrasonic images.

[0139] Preferably, the thickness of the medium 2 and the viscoelastic properties of the medium 2 are determined from the propagation data of several successive shear waves.

[0140] According to the non-limiting embodiment, the medium 2 is the diaphragm 2. This organ typically illustrates a medium whose thickness is constantly modified over time and whose viscoelastic properties also change over time, in particular during the ventilatory cycle.

[0141] According to the embodiment presented, the determination of viscoelastic properties makes it possible to evaluate diaphragmatic function during ventilatory tasks. Diaphragmatic function can include or be characterized by several parameters or indicators.

[0142] By way of non-limiting examples, diaphragmatic function may include contractility and / or diaphragmatic pressure and / or diaphragmatic function and / or diaphragmatic effort and / or diaphragmatic work and / or nerve conduction velocity and / or identification of the spatial organization of the muscle fascicle(s).

[0143] A person skilled in the art will be able to transpose and / or adapt the parameters or indicators of the diaphragm, or of the diaphragmatic function, to other soft tissues according to the invention and will also be able to supplement the viscoelastic properties of other soft tissues with other parameters specific to each soft tissue considered.

[0144] The present idea of ​​the invention therefore consists of using ultrafast ultrasound coupled with the prior generation of shear waves generated by ultrasound radiation pressure (shear wave elastography) to quantify the viscoelastic properties of the diaphragm during ventilation. As described in detail above, the shear waves can also be generated by alternative means, such as one or more external vibrators, by the body's natural shear waves (heartbeat, blood circulation, respiration), or by the voice. Due to the geometry of the diaphragm in the intercostal imaging zone, a plate of finite thickness (from 500 sq m to 10 mm) surrounded by two distinct semi-infinite media (the liver 1 and the intercostal muscle 3), the shear waves propagate dispersively and in a guided manner within the diaphragm 2.Thus, the model described according to the embodiment (Guided Wave Theory or Lamb waves) applies to the tri-layer liver 1, diaphragm 2 and intercostal muscles 3. The guidance of these waves then depends on the viscoelastic properties of two semi-infinite media surrounding the plate (here the diaphragm), the viscoelastic properties of the diaphragm 2 and its thickness.

[0145] A computer program is also proposed comprising executable instructions which, when executed by a computer, implement all or part (but at least part) of the steps of the process according to the invention. In particular, the computer program can be executed or implemented by module 4, by a device 7 and / or by a remote device 5 according to the invention.

[0146] A computer-readable medium is also proposed, comprising instructions which, when executed by a computer, cause the computer to implement the method according to the invention. In particular, the readable medium can be executed or implemented by module 4, by a device 7, and / or by a remote device 5 according to the invention.

[0147] A data processing device programmed and / or configured and / or arranged to implement the method according to the invention is also proposed. In particular, the data processing device may be a component or element of module 4, a device 7, and / or a remote device 5 according to the invention. By way of example, the data processing device may be a processing unit or a computing unit, such as a microprocessor.

[0148] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

[0149] In particular, all the variants and embodiments described are combinable with each other if there is no technical obstacle to this combination.

[0150] Thus, in combinable variants of the embodiments described above: - the process includes a step for determining and / or the processing unit is arranged to determine: • the presence of medium 2 in a plane probed by the ultrasonic waves emitted by the probe 6, 8 or 9; indeed, the equation or formula of the propagation mode of the shear wave in the medium (corresponding to the solution of the transcendental equation) is a function of the thickness of the medium and the position of the waves in medium 2 and in the environment 1, 3, and / or • the position of medium 2 from the data detected by probe 6, 8 or 9; indeed, the equation or formula of the propagation mode of the shear wave in the medium (corresponding to the solution of the transcendental equation) is a function of the thickness of the medium and the position of the waves in medium 2 and in the environment 1, 3, - the propagation data of at least one shear wave and / or the dispersion curve of at least one shear wave (preferably in medium 2, or in medium 2 and in environment 1, 3) are those of at least one shear wave in a given or considered plane or section of medium 2, or of medium 2 and environment 1, 3, and / or - the process further includes (or the determination step further includes) the determination of a variation in thickness of medium 2 over time.

Claims

Demands

1. A module for determining the viscoelastic properties, referred to as the module, of a moving biological medium of variable thickness, referred to as the medium, at least partially enveloped in an elastic biological environment, said module comprises a processing unit arranged to: - calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

2. Module according to the preceding claim, comprising communication means and / or a connector arranged to communicate with an ultrafast ultrasound imaging device and to receive propagation data of at least one shear wave in the medium from said ultrafast ultrasound imaging device.

3. Module according to the preceding claim, wherein the processing unit is arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device.

4. An ultrafast ultrasonic imaging device, said device, for determining the viscoelastic properties of a moving biological medium of variable thickness, said medium, at least partially enveloped in an elastic biological environment, said environment, said device comprising: - a probe arranged to emit at least one ultrasonic wave and detect reflected ultrasonic waves, and - the module according to any one of claims 1 to 3; said module being further arranged to calculate and / or determine propagation data of at least one shear wave in the medium from ultrasonic waves reflected and detected by said ultrafast ultrasonic imaging device, or - a processing unit arranged to: • calculate, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, • determine, from the dispersion curve of at least one shear wave in the medium and a propagation mode of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

5. Ultrafast ultrasonic imaging device according to the preceding claim, wherein the processing unit of the device is further arranged to determine: - the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device, and / or - the position of the medium from the data detected by the ultrafast ultrasonic imaging device.

6. Ultrafast ultrasonic imaging device according to claim 4 or 5, wherein the probe is further arranged to emit at least one ultrasonic wave capable of generating at least one shear wave in the medium.

7. A method for determining the viscoelastic properties, said method, of a moving biological medium of variable thickness, said medium, at least partially enclosed in an elastic biological environment, said environment, said method comprising the steps of: - calculating, from propagation data of at least one shear wave in the medium, a dispersion curve of at least one shear wave in the medium, - determining, from the dispersion curve of at least one shear wave in the medium and a mode propagation of at least one shear wave in the medium, a thickness of the medium and / or the viscoelastic properties of the medium.

8. A method according to the preceding claim, wherein the step of calculating the dispersion curve of at least one shear wave in the medium, from propagation data of at least one shear wave in the medium, propagating in the medium according to the determined propagation mode, is implemented by Fourier transform of the propagation data of said at least one shear wave in the medium, propagating in the medium according to the determined propagation mode, in the spatio-temporal domain.

9. A method according to claim 7 or 8, wherein the propagation mode of at least one shear wave in the medium is a dispersive propagation mode guided by the medium.

10. A method according to any one of claims 7 to 9, wherein the propagation data of at least one shear wave in the medium include amplitude(s) and / or displacement data of at least one shear wave in the medium.

11. A method according to any one of claims 7 to 10, wherein the propagation data of at least one shear wave and the dispersion curve of at least one shear wave are those of at least one shear wave in a given or considered plane or section of the medium.

12. A method according to any one of claims 7 to 11, wherein the medium is an organ of a subject and at least one shear wave is generated by: - ​​a physiological process of the subject, - a voluntary action of the subject, and / or - an external stimulus.

13. A method according to the preceding claim, wherein the external stimulus comprises at least one ultrasonic wave emitted by an ultrafast ultrasonic imaging device; the method further comprises a step of calculating and / or determining the propagation data of at least one shear wave from ultrasonic waves reflected and detected by said ultrafast ultrasonic imaging device.

14. A method according to the preceding claim, further comprising a determination of the presence of the medium in a plane probed by the ultrafast ultrasonic imaging device.

15. A method according to claim 13 or 14, further comprising a determination of the position of the medium in the environment from the data detected by said ultrafast ultrasonic imaging device.

16. A method according to any one of claims 7 to 15, wherein the medium is a diaphragm.

17. A method according to the preceding claim, wherein the propagation data originate from several successive shear waves and cover a continuous duration or extend over a period of at least one breathing cycle.

18. A method according to the preceding claim, wherein the determination step further comprises determining a variation in the thickness of the medium over time.

19. A computer program comprising executable instructions which, when executed by a computer, implement the steps of the process according to any one of claims 7 to

20. 1 O. Computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 7 to 18.

21. Data processing apparatus programmed and / or configured and / or arranged to carry out the process of any one of claims 7 to 18.

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