Method for determining velocity of natural shear wave propagating in medium

Abstract

At present, the interest of using ultrasound in the medical field has been completely established. Indeed, study of mechanical waves propagating in a medium generally allows the medium to be retrieved as a characteristic of an organ, such as a heart. These elastic characteristics may be determined based on propagation parameters such as the velocity of shear waves propagating in the medium. Shear waves may be generated in the medium either artificially or naturally (e.g., valve closure of the heart). In both cases, the generation and / or observation of such shear waves requires a highly complex and cost-effective system as well as a complex method for estimating the shear velocity with high precision. The present disclosure overcomes the above drawbacks by proposing a new method and detection system for estimating the velocity of shear waves propagating in a medium in a simple and efficient manner and having the high precision requirements required to determine the elastic properties of the medium.

Description

Technical Field

[0001] The present disclosure relates to ultrasonic measurement techniques, and more particularly to methods and apparatus for determining the velocity of natural shear waves propagating in a medium. Background Art

[0002] Today, the interest in using ultrasound in medicine no longer needs to be proven.

[0003] In fact, the study of mechanical waves propagating in a medium can allow the properties of this medium to be retrieved. For example, in the medical field, the study of mechanical waves (e.g. compression and / or shear waves) propagating in biological tissue (e.g. of an organ) can allow the elastic properties of this biological tissue to be retrieved and then, for example, the state of the organ to be determined. In fact, the state of an organ, such as the heart, can be related to its elastic properties, such as its stiffness.

[0004] Typically, elastic properties can be measured based on the speed of mechanical waves in a medium. Because compression waves propagate too fast in a medium, it is generally preferred to use shear waves to measure the elastic properties of a medium. The propagating shear waves can be artificially generated by an ultrasound probe (or ultrasonic transducer) that can then detect it, or can be generated by a natural source as an organ activity. The main disadvantage when using artificial shear waves is that a high-cost system suitable for generating shear waves in a medium and detecting its propagation with high precision is required, and its speed needs to be correctly measured and thus the elastic properties of biological tissues. The main disadvantage when using natural shear waves to measure elastic properties is that it is difficult to measure such natural shear waves in all dimensions, and the speed needs to be measured with high precision and thus the elastic properties. In fact, in contrast to artificial shear waves, the source of natural shear waves is essentially uncontrolled in terms of position, wavelength and amplitude. The propagation of shear waves from the source occurs in three dimensions along unknown directions. Therefore, quantifying elastic properties by using shear wave propagation requires a complex three-dimensional inverse problem, which is usually simplified in two dimensions. This simplification affects the accuracy of velocity measurement and therefore affects the accuracy of elastic properties of biological tissues.

[0005] Therefore, it is necessary to measure the velocity of the natural shear wave propagating in the medium with high accuracy. SUMMARY OF THE INVENTION

[0007] To this end, the present disclosure may be directed to a method for determining a velocity of a shear wave propagating in a medium, the shear wave having a wavelength, the method may include:

[0008] - generating at least one ultrasound beam into the medium, irradiating at least three respective observation points in the medium;

[0009] - collecting a plurality of backscattered signals backscattered respectively from the observation points irradiated by the at least one ultrasound beam;

[0010] - determining the respective arrival time of each observation point based on the backscattered signals respectively collected from the observation points;

[0011] - calculating the vector velocity component (c) of the shear wave based on the plurality of respective arrival times x 、c y 、c z );

[0012] - Based on the calculated vector velocity component (c x 、c y 、c z ) estimating the velocity of the shear wave (c);

[0013] wherein the respective observation points are different and not aligned.

[0014] Advantageously, the overall velocity of shear waves propagating in the medium can be determined in a simple and efficient manner without the need for complex imaging systems and methods.Furthermore, advantageously, the elastic properties of the medium can be determined based on the determined velocity of the shear waves.

[0015] Irradiation may be understood to include that an observation point in the medium is traversed by at least one ultrasound beam.

[0016] Vectors can be expressed in polar, cylindrical, or spherical coordinates.

[0017] The at least one ultrasound beam may be focused or defocused.

[0018] In one or more embodiments, the plurality of backscattered signals may be collected by a plurality of ultrasonic transducers, respectively, each ultrasonic transducer collecting a backscattered signal backscattered from a respective observation point.

[0019] Preferably, in one or several embodiments, the plurality of backscattered signals may be collected by at least three ultrasonic transducers among the plurality of ultrasonic transducers, respectively, and each ultrasonic transducer collects the backscattered signals backscattered from a respective observation point.

[0020] Advantageously, the more observation points and ultrasonic transducers there are for acquiring backscattered signals backscattered from the respective observation points, the higher the accuracy of the components along one or more X and Y axes and, therefore, the higher the accuracy of the shear wave velocity.

[0021] In one or more embodiments, the respective observation points may be separated from each other by a separation distance that is less than the wavelength of the shear waves in the medium.

[0022] Advantageously, this separation distance allows the shear wave to be considered as a planar shear wave.

[0023] In one or more embodiments, at least three ultrasound beams may be generated into the medium to irradiate at least three respective observation points in the medium.

[0024] In one or more embodiments, at least three ultrasound beams may be generated by a plurality of ultrasound transducers, respectively.

[0025] In one or more embodiments, at least three ultrasound beams may be generated by at least three ultrasound transducers of the plurality of ultrasound transducers, respectively.

[0026] Each of the at least three ultrasound beams may be focused or defocused.

[0027] In one or several embodiments, when the wave vector direction of the shear wave is known, the at least three observation points may not be aligned in the plane containing the wave vector of the shear wave, or when the wave vector direction of the shear wave is unknown, the at least three observation points may be at least four observation points that are not aligned and not all contained in the same plane.

[0028] In one or more embodiments, the wavelength of the shear wave may be less than 0.7 meters, preferably less than 0.5 meters.

[0029] In one or more embodiments, each of a plurality of respective arrival times of a respective observation point may be determined using a motion estimator on a backscatter signal respectively collected from the respective observation point.

[0030] A motion estimator may be used to measure the backscattered signal to determine tissue displacement and / or tissue velocity.

[0031] In one or more embodiments, each of a plurality of respective arrival times for a respective observation point may be determined based on a respective change in tissue velocity determined by a motion estimator at the respective observation point.

[0032] Alternatively, the respective changes may be respective changes in tissue displacement.

[0033] In one or several embodiments, each of the plurality of respective arrival times of a respective observation point may be determined directly using the collected backscattered signal or radio signal frequency collected from the respective observation point.

[0034] In one or more embodiments, changes in tissue velocity at respective observation points may be calculated from a plurality of images constructed from backscattered signals acquired from the respective observation points.

[0035] In one or more embodiments, calculating the vector velocity component of the shear wave may also include determining a plurality of at least three delays, each delay (Δt) may be determined between two respective arrival times of a plurality of arrival times, and each vector velocity component may be a function of a respective delay (Δt) of the plurality of at least three delays.

[0036] In one or more embodiments, each vector velocity component may also be a function of the position of each observation point or the length between each observation point.

[0037] In one or more embodiments, each observation point may be defined by a respective depth in the medium.

[0038] In one or several embodiments, the depth of at least one observation point (S'; M'; P') in the medium can be scanned along the transport direction Z0.

[0039] Advantageously, this arrangement allows increasing the accuracy of the velocity component along the Z-axis (parallel to the transmission direction and the central axis of the ultrasound beam), and therefore increasing the accuracy of the velocity of the shear waves.

[0040] In one or several embodiments, each arrival time of a respective observation point determined based on the respective variation of tissue velocity at the respective observation point may be determined by detecting the maximum and / or minimum of the respective variation or by using a cross-correlation or artificial intelligence algorithm.

[0041] In one or more embodiments, estimating the velocity of the shear wave based on the calculated vector velocity components can be performed by using an inversion algorithm on the calculated vector velocity components.

[0042] Of course, other known techniques may be used to calculate the vector velocity components, such as function minimization, or regularization methods or artificial intelligence algorithms.

[0043] In one or more embodiments, multiple ultrasound transducers may be arranged in a 2D array.

[0044] In one or several embodiments, when at least one of the at least three ultrasound beams is focused, an observation point (S', M', P') may be defined along the transmission direction Z0 so as to be located in the focus of the focused ultrasound beam irradiating the observation point.

[0045] In one or more embodiments, the shear waves may be natural shear waves generated by a natural shear wave source contained in the medium, or artificial shear waves generated by an artificial shear wave source external to the medium.

[0046] In one or more embodiments, the natural shear wave source may be the movement of the closed valves of the heart or vibrations caused by sound or pulse waves propagating in the arterial wall.

[0047] In one or more embodiments, multiple ultrasonic transducers may be located on the surface of the medium and / or in the medium.

[0048] In one or more embodiments, an ultrasonic transducer of the plurality of ultrasonic transducers may be located at a distance of 0.001 to 0.1 meters from a natural shear wave source.

[0049] In one or more embodiments, the at least three ultrasonic transducers may be at least four ultrasonic transducers.

[0050] The present disclosure may also relate to a detection system for determining the velocity of a shear wave propagating in a medium using the method according to the present disclosure, the detection system may include:

[0051] - a plurality of ultrasonic transducers arranged in a 2D array for generating at least one ultrasonic beam into the medium and irradiating at least three respective observation points in the medium, and configured to acquire respective backscattered signals generated in response to an interaction between the at least one ultrasonic beam and the medium,

[0052] a control unit configured to cause an ultrasonic transducer of the plurality of ultrasonic transducers to generate the at least one ultrasonic beam, to collect a plurality of backscattered signals backscattered respectively from the at least three respective observation points irradiated by the at least one ultrasonic beam, to determine a respective arrival time of each observation point based on the backscattered signals collected respectively from the observation points, and to calculate a vector velocity component (c) of the shear wave based on the plurality of respective arrival times; x 、c y 、c z ) and is used to calculate the vector velocity component (c x 、c y 、c z ) estimating the velocity of the shear wave (c);

[0053] wherein the respective observation points are different and not aligned.

[0054] In one or more embodiments, the at least one ultrasound beam may be formed by emitting a plurality of ultrasound waves generated by respective ones of a plurality of ultrasound transducers in the medium.

[0055] In one or more embodiments, the ultrasonic wave may be transmitted at a rate of 100-30,000 / sec.

[0056] In one or more embodiments, the frequency of the at least one ultrasound beam may be 0.5-100 MHz.

[0057] In one or more embodiments, at least three ultrasound beams may be generated into the medium to irradiate at least three respective observation points (S', M', P') in the medium.

[0058] In one or more embodiments, at least three ultrasound beams may be generated by a plurality of ultrasound transducers.

[0059] In one or more embodiments, each of the plurality of ultrasound transducers may collect backscattered signals backscattered from a respective observation point.

[0060] Alternatively, or preferably, in one or several embodiments, each of the plurality of ultrasound transducers may acquire backscattered signals backscattered from only one respective observation point, respectively.

[0061] In one or several embodiments, when the wave vector direction of the shear wave is known, the at least three observation points may not be aligned in the plane containing the wave vector of the shear wave, or when the wave vector direction of the shear wave is unknown, the at least three observation points may be at least four observation points that are not aligned and not all contained in the same plane.

[0062] In one or more embodiments, ultrasonic transducers in the plurality of ultrasonic transducers that respectively generate at least three ultrasonic beams may not be aligned with each other.

[0063] In one or more embodiments, the shear waves may be natural shear waves generated by a natural shear wave source contained in the medium, or artificial shear waves generated by an artificial shear wave source external to the medium.

[0064] In one or more embodiments, the natural shear wave source may be the movement of the closed valves of the heart or vibrations caused by sound or pulse waves propagating in the arterial wall.

[0065] In one or more embodiments, the at least three ultrasonic transducers may be at least four ultrasonic transducers.

[0066] In one or more embodiments, multiple ultrasonic transducers may be located on the surface of the medium and / or in the medium.

[0067] In one or more embodiments, multiple ultrasound transducers arranged in a 2D array may be included in the ultrasound probe.

[0068] In one or several embodiments, each ultrasonic transducer may be formed of a matrix of transducer elements adapted to be independently controlled, and the control system may be configured to control the ultrasonic transducer elements so as to emulate an ultrasonic transducer generating an ultrasonic beam in a medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Additional features, details and advantages will be seen in the following detailed description and accompanying drawings, in which:

[0070] Figure 1

[0071] [ Figure 1 ] schematically shows an overall schematic diagram of the detection system according to the present disclosure.

[0072] Figure 2a

[0073] [ Figure 2a ] shows a flow chart of the method according to the present disclosure.

[0074] Figure 2b

[0075] [ Figure 2b ] shows the principle of detecting two arrival times.

[0076] Figure 2c &2d

[0077] [ Figure 2c and Figure 2d ] show the propagation of shear waves in the medium along the XY plane and XZ plane respectively.

[0078] Figure 3a

[0079] [ Figure 3a ] shows an experimental setup for measuring the velocity of shear waves propagating in a medium.

[0080] Figure 3b

[0081] [ Figure 3b ] shows the results of changes in tissue velocity signals measured based on backscattered signals collected from observation points respectively by the experimental device. DETAILED DESCRIPTION

[0082] Figure 1 The overall schematic diagram of the detection system according to the present disclosure is schematically shown.

[0083] In the various drawings, the same reference numbers refer to the same or similar items.

[0084] Figure 1 The illustrated detection system 100 is capable of detecting shear waves, such as natural or artificial shear waves propagating in a medium 101 (eg, an organ included in a patient's chest), and is capable of determining (or evaluating) the overall velocity (or rate) of the shear waves.

[0085] The medium (e.g. an organ or a medium comprising an organ) may include a shear wave source 102 that allows the generation of shear waves 105 that propagate in all directions (x, y, z) in the medium. The shear wave source may be a natural shear wave source (or an artificial shear wave source) that allows the generation of natural shear waves (or artificial shear waves when an artificial source is used) in the medium. According to one example, the natural shear wave source may correspond to the movement of a heart valve, such as the closure of a valve, or the contraction of a heart atrium or electrical wave propagation.

[0086] In one or several embodiments, the shear wave source may be an artificial shear wave source external to the medium suitable for generating shear waves in the medium, such as an artificial vibration source with a frequency of 1-1000 Hz.

[0087] The detection system 100 may include a plurality of (e.g., at least three ultrasonic transducers or at least four ultrasonic transducers) ultrasonic transducers 107a, 107b, 107c, respectively located at positions S, M, P around a shear wave source (e.g., a natural shear wave source), and a control system 111. Each ultrasonic transducer 107a, 107b, 107c may be configured to generate a respective ultrasonic beam 113a, 113b, 113c in a medium, which irradiates a respective observation point S', M', P' (but not necessarily) defined in the medium (e.g., defined by the detection system) according to respective coordinates (x, y, z). For example, at least three (or, for example, at least four) ultrasonic transducers may generate at least three ultrasonic beams, respectively. For example, ultrasonic transducer 107a may generate ultrasonic beam 113a, ultrasonic transducer 107b may generate ultrasonic beam 113b, and ultrasonic transducer 107c may generate ultrasonic beam 113c.

[0088] In addition, each ultrasonic transducer 107a; 107b; 107c can be configured to collect (or receive) a respective backscattered signal generated in response to the interaction between the medium at the respective observation point S', M', P' and the respective ultrasonic beam 113a, 113b, 113c generated by the ultrasonic transducer 107a, 107b, 107c.

[0089] For example, the ultrasonic transducer 107a may generate an ultrasonic beam 113a and may collect backscattered signals generated by the interaction between the ultrasonic beam 113a and the medium 101 at respective observation points S′ in the medium.

[0090] In one or more embodiments, only one ultrasonic transducer among the plurality of transducers may be used to generate an ultrasonic beam so as to simultaneously irradiate observation points (e.g., at least two or three or more) contained in the medium, and the plurality of ultrasonic transducers (e.g., at least two or three ultrasonic transducers) may collect a plurality of backscattered signals respectively backscattered from the observation points irradiated by the ultrasonic beam. For example, the ultrasonic transducer 107b among the plurality of ultrasonic transducers may generate an ultrasonic beam 113b that simultaneously irradiates respective observation points S', M', P'. Then, each ultrasonic transducer 107a; 107b; 107c may collect respective backscattered signals generated at respective observation points S', M', P' in response to the interaction between the medium and the ultrasonic beam 113b generated by the ultrasonic transducer 107b.

[0091] In one or more embodiments, two or more ultrasonic transducers of the plurality of ultrasonic transducers may be used, for example, to illuminate three or more (e.g., four) observation points. For example, the first ultrasonic transducer 107a may be used to illuminate observation points S' and M', and the second ultrasonic transducer 107c may be used to illuminate observation point P' (or when more observation points are defined, to illuminate observation point P' and another observation point).

[0092] Each ultrasonic beam 113a; 113b; 113c may all be parallel to the same transmission direction (Z0), but not necessarily (for example, they may be inclined along the transmission direction), and may be formed (or generated) by emitting a plurality of ultrasonic waves generated by respective ultrasonic transducers 107a, 107b, 107c included in the plurality of ultrasonic transducers into a medium. In addition, the ultrasonic beams 115a, 115b, and 115c may be generated so that they are different from each other and do not overlap with each other.

[0093] Each irradiated observation point S', M', P' can be defined (for example by a control system) so that its coordinates (x, y) in the XY plane correspond to the coordinates (x, y) of the ultrasonic transducer, which collects the backscattered signal backscattered from the irradiated observation point (or the ultrasonic transducer has irradiated the observation point when each observation point is irradiated by its respective ultrasonic beam).

[0094] For example, the observation position S' may have the same coordinates in the plane XY as the coordinates of an ultrasound transducer located at a point S in the plane XY for collecting backscattered signals backscattered from the illuminated observation point S'.

[0095] Furthermore, each irradiated observation point S', M', P' may be defined such that its coordinate (z) may be defined by a depth in the medium. For example, the depth may be defined along the transmission direction Z0 or along the central axis 120a; 120b; 120c of the ultrasonic transducer used to collect backscattered signals from the irradiated observation point. For example, the coordinate z of the observation point S' may be defined along the central axis 120a of the ultrasonic transducer 107a.

[0096] Furthermore, the respective observation points may be included in the same plane or not all in the same plane, and / or not aligned between them. In fact, depending on the type of shear wave source and its position on or in the medium, such a plane may be a plane containing the wave vector direction of the shear wave and may be known in advance. Moreover, when the wave vector direction of the shear wave is known, such a plane may be a plane containing the wave vector of the shear wave. For example, the plane containing the wave vector may be the inner wall of the heart. In this case, when the wave vector direction of the shear wave is known, three observation points may be sufficient (for example, using three ultrasonic transducers) to determine the speed of the shear wave in the medium. In contrast, when attempting to determine the speed of a shear wave in a medium that may propagate along an unknown plane and direction, or / and when the wave vector direction of the shear wave is unknown, it may be preferred (but not necessary) to use at least four observation points (for example, using at least four ultrasonic transducers), which are not aligned and are not all included in the same plane.

[0097] Such misalignment between observation points (e.g., in the same plane) can be achieved by positioning multiple ultrasonic transducers used to collect multiple backscattered signals so that they are misaligned with each other in the XY plane (e.g., perpendicular to the transmission direction Z0 of the ultrasonic transducer) because, as previously described, the observation points can have the same coordinates as the ultrasonic transducers in the XY plane.

[0098] For example, the ultrasonic transducers 107a, 107b, and 107c may be located on the surface of the medium 101, around or / and near a natural shear wave source, so that they are not aligned with each other in the XY plane (e.g., perpendicular to the transmission direction Z0). For example, the ultrasonic transducer 107a may be located at a first position S (x1, y1), the ultrasonic transducer 107b may be located at a second position M (x2, y2), and the ultrasonic transducer 107c may be located at a third position P (x3, y3), with different coordinates for each position. This arrangement may allow multiple respective ultrasonic beams or respective observation points to be misaligned between them in the XY plane (e.g., perpendicular to the transmission direction Z0).

[0099] This misalignment may allow each component x and y of the shear wave velocity to be determined with high accuracy, which is required to determine the shear wave velocity with high accuracy.

[0100] In addition, the respective observation points S', M', P' (or ultrasound beams 115a, 115b, 115c) can be separated from each other by a separation distance that is less than the wavelength of the shear wave. This constraint on the separation distance can allow the assumption that the shear waves propagating in the medium can be considered as wave planes. For example, the separation distance can be less than 0.7 meters, and preferably less than 0.3 meters. In practice, shear waves can typically present a wavelength of less than 0.7 meters in the medium.

[0101] The frequency (or centre frequency) of the ultrasound wave or ultrasound beam may be, for example, 0.5-100 MHz, or, for example, 1-10 MHz.

[0102] In one or more embodiments, the plurality of ultrasonic transducers 107a, 107b, 107c may include a plurality of transducers ranging from 3 to 100 transducers.The ultrasonic transducers may be defined by a diameter of 0.05-10 centimeters.

[0103] In addition, the ultrasound beam can be focused or defocused. For this purpose, the ultrasonic transducer can present a concave surface of its surface so as to allow the ultrasound beam to be focused in the medium and produce a focus in the medium. Therefore, each focused ultrasound beam 113a, 113b, 113c can include respective focuses 115a, 115b, 115c, which can be in the form of an ellipse. For example, at a given depth, the size of the focus can have a diameter of 0.1-10 mm along the X axis and a diameter of 0.1-10 mm along the Z axis. When one or all ultrasound beams are focused, respective observation points S', M', P' (but not necessarily) can be defined so that each respective observation point or at least one of them is located in the respective focus 115a, 115b, 115c of the focused ultrasound beam irradiating the observation point along the transmission direction. For example, for the respective observation point S', the coordinate Z can be defined as being located in the focus 115a of the focused ultrasound beam 113a.

[0104] Multiple ultrasonic transducers can be located around a shear wave source or multiple shear wave sources contained in a medium. For example, multiple ultrasonic transducers 107a; 107b; 107c can be located on the surface of the medium 101 so as to be located near the natural shear wave source 102 as a closed valve of the patient's heart. For example, the ultrasonic transducers can be at a distance of 0.001 to 0.1 meters from the natural shear wave source (i.e., a proximity distance).

[0105] According to one or several embodiments, multiple ultrasound transducers may be positioned (on the surface of or in a medium) along a trajectory (eg, propagation direction or trajectory) that a shear wave may follow, such as along an artery or along the myocardium of a heart.

[0106] In one or more embodiments, multiple ultrasound transducers can be directly contained in the medium and located around the natural shear wave source. For example, multiple transducers can be positioned intravascularly so as to surround / adjacent to an organ containing a natural shear wave source. For example, the ultrasound transducer can be at a distance of 0.001 to 0.1 meters from the natural shear wave source (i.e., a proximity distance).

[0107] In one or more embodiments, some of the plurality of transducers may be located on the surface of the medium and some other of the plurality of transducers may be located in the medium (ie, below the surface of the medium and / or near a natural shear wave source).

[0108] In one or more embodiments, multiple transducers may be included in a matrix (e.g., 2D) of transducers integrated into an ultrasound probe. The ultrasound probe may be located on the surface of a medium surrounding / adjacent to a natural shear wave source, and some transducers of the transducer matrix are used to generate multiple ultrasound beams in the medium, respectively.

[0109] In one or more embodiments, each ultrasonic transducer can be integrated in a respective ultrasonic probe located on the surface of the medium. For example, at least three ultrasonic probes can be located on the surface of the medium, each ultrasonic probe comprising a single or multiple transducers that can be independently controlled (e.g., by a control system).

[0110] In one or several embodiments, each transducer may be formed of a matrix of transducer elements adapted to be independently controlled, and the control system may be configured to control the transducer elements so as to emulate an ultrasonic transducer generating an ultrasonic beam in a medium.

[0111] The control system can be programmed (or configured) so that the ultrasonic waves (used to form an ultrasonic beam in the medium) emitted by each ultrasonic transducer 107a, 107b, 107c can be emitted at a rate greater than 100 ultrasonic waves per second (e.g., hundreds to thousands of ultrasonic waves per second). The control system can, for example, include a control unit 111a and a computer 111b. In this example, the control unit 111a can be used to control each ultrasonic transducer 107a, 107b, 107c, and the computer 111b can be used to control the control unit 111a, for generating at least one ultrasonic beam, for collecting backscattered signals through each ultrasonic transducer, for detecting changes based on the collected backscattered signals, for calculating the velocity component of the shear wave (or the vector velocity component of the shear wave), and for estimating the velocity of the shear wave. In a variant, a single electronic device can implement all the functions of the control unit 111a and the computer 111b.

[0112] According to one example, the control system or / and control unit may comprise an electronic unit comprising as many channels as there are transducers, for example 3 channels respectively connected to the transducers 107a; 107b; 107c. Each of these channels may comprise an analog-to-digital converter associated with a memory and in communication with a central unit electronics such as a microprocessor or the like, which itself may communicate, for example, with a memory and a signal processing circuit such as a DSP, and with a computer 111b.

[0113] Figures 2a to 2d The method of the present disclosure in one or several embodiments is shown.

[0114] Figure 2a A flow chart of a method according to the present disclosure is shown.

[0115] refer to Figure 2a , a method for determining the velocity of a shear wave propagating in a medium may include:

[0116] - generating 201 at least one ultrasound beam 113a, 113b, 113c into the medium, irradiating at least three respective observation points S', M', P' in the medium;

[0117] - collecting 203 a plurality of backscattered signals backscattered respectively from said observation points illuminated by said at least one ultrasound beam.

[0118] The ultrasound beam can be used by using Figure 1 For example, in the case presented in the figures of the present disclosure, at least one ultrasound beam or multiple ultrasound beams can be generated by multiple ultrasound transducers located around a natural shear wave source 102, such as on the surface of a medium such as the chest of the patient P and along a trajectory such as an arterial trajectory or a myocardial trajectory of the patient P (i.e., the wave vector direction of the shear wave is known), respectively at points S, M and P (or into the medium according to another example).

[0119] The shear waves may be generated by a natural shear wave source contained in the medium (or may be an external artificial shear wave source). The natural shear wave source may be contained in an organ. For example, the natural shear wave source may be the movement of a closed valve of a patient's heart.

[0120] Each ultrasonic transducer 107a; 107b; 107c located at points S, M and P, respectively, can be configured to emit ultrasonic waves in the medium to form (or generate) a respective ultrasonic beam 113a; 113b; 113c, which illuminates the respective observation points S', M' and P' (or several observation points), and can be configured to collect respective backscattered signals from the respective observation points, wherein the respective backscattered signals are generated in response to the interaction between the ultrasonic beam 113a; 113b; 113c and the medium at the respective observation points.

[0121] The backscatter signal associated with an observation point illuminated by the ultrasound beam may be retrieved (eg, by signal processing and performed by the control system 111) from all backscatter signals emitted by the region in the medium illuminated by the ultrasound beam (including the observation point).

[0122] The method may then include:

[0123] - For each observation point 205, a respective arrival time 207 is determined based on the backscattered signals respectively acquired from the observation point.

[0124] Figure 2b The principle of detecting two arrival times is shown.

[0125] refer to Figure 2b , which presents two changes of tissue velocity signals determined based on backscattered signals collected from observation points, respectively.

[0126] Each arrival time of a respective observation point can be determined by using a motion estimator on the backscattered signals respectively collected from the respective observation point.

[0127] In one or more embodiments, a motion estimator may be used to determine the velocity or displacement of the tissue (or the change in velocity or displacement of the tissue) from backscattered signals backscattered from respective observation points.

[0128] For example, tissue velocity (or tissue velocity change) can be determined by using a motion estimator on the backscattered signals collected by the respective ultrasonic transducers 107a, 107b from the respective observation points S', M', respectively, and the respective ultrasonic transducers can be (but not necessarily) the ultrasonic transducers that have generated the respective ultrasonic beams that illuminate the respective observation points.

[0129] For example, the change 213a can be determined by calculating the backscattered signal generated by the interaction of the ultrasound beam 113a with the medium 101 at the respective observation point S' (irradiated by the ultrasound beam 113a) and collected by the ultrasound transducer 107a. Similarly, the change 213b can be determined by calculating the backscattered signal generated by the interaction of the ultrasound beam 113b with the medium 101 at the respective observation point M' (irradiated by the ultrasound beam 113b) and collected by the ultrasound transducer 107b.

[0130] Each detected tissue velocity (or tissue displacement) change 213a, 213b can reflect the passage of the shear wave at the respective observation point being irradiated. In fact, when the shear wave passes through a medium having a defined respective observation point, it temporarily modifies the intrinsic properties (e.g., physical properties) of the medium, resulting in a change in the backscattered signal monitored at the respective observation point, which is generated by the irradiation and thus results in a change in the tissue velocity calculated at the respective observation point.

[0131] In one or more embodiments, each change in tissue velocity at a respective observation point may be calculated from a plurality of images (e.g., 1D, 2D, or 3D) constructed from backscatter signals acquired from the respective observation points, respectively. According to an example, an observation point may correspond to a pixel in a spatiotemporal image obtained based on a backscatter signal generated in response to a respective ultrasound beam acquired at a given frame rate.

[0132] therefore, Figure 2b Each curve of may present the amplitude variation as a function of time of the tissue velocity signal calculated for the respective observation point.

[0133] From these variations, the respective arrival time at each observation point can then be determined by detecting the maximum of each curve or by cross-correlation or any suitable known technique, for example. For example, for each variation, a maximum value (e.g., a maximum or minimum peak value) or a minimum value can be detected. Thus, with reference to Figure 2b , the arrival time t0 can be detected in the change 213a corresponding to its maximum value, and the arrival time t1 can be detected in the change 213b corresponding to its maximum value.

[0134] Since the individual observation points are different and separated from one another, the delay in time or phase between two detected arrival times can be determined.

[0135] In one or more embodiments, the arrival times may be detected directly from the multiple backscattered signals by using an artificial intelligence algorithm, thus, without the need to use a motion estimator (eg, tissue velocity or tissue displacement).

[0136] Therefore, reference Figure 2b , the time delay Δt between the two arrival times t0 and t1 detected from the respective maximum value of each variation can be determined.

[0137] This time delay may represent the time (eg, time of flight) it takes for a shear wave to propagate from point S' to point M' for a given speed (or velocity) in the medium.

[0138] The method may then include calculating 209 a vector velocity component (c x 、c y 、c z ).

[0139] To retrieve each component of the shear wave velocity (or each vector velocity component), in one or more embodiments, such calculations may be performed as follows.

[0140] Figure 2c and 2d The propagation of the shear wave in the medium along the XY plane (eg, a plane perpendicular to the transmission direction) and the XZ plane (eg, including the transmission direction Z0 ) are respectively shown.

[0141] refer to Figure 2c and 2d , the natural shear wave can be regarded as a plane wave according to the following formula:

[0142]

[0143] The assumption of a wane plane may be true when the distance between the ultrasound beams of the plurality of ultrasound beams is smaller than the wavelength of the shear waves in the medium. For example, the distance between the respective observation points or between the respective ultrasound transducers may be smaller than 0.5 m, preferably smaller than 0.3 m (i.e., corresponding to 0.3 m, the wavelength of the shear waves in the medium).

[0144] This plane wave can be represented by a wave with three components (c x 、c y 、c z ) (or three vector components) of velocity c and wave number k (k x , k y , k z ) to limit.

[0145] The phase difference between the two plane waves defined by equation (1) along the x-axis is It can be written as follows:

[0146]

[0147] From the generalization of this equation (2) in all directions (x, y, z), the phase difference between the two changes in the tissue velocity signal at the respective observation points S' and M' of the shear wave propagating in the medium and detected by the ultrasonic transducers located at points S and M can be written as follows:

[0148]

[0149] Likewise, the phase difference between two changes in tissue velocity signals at respective observation points M' and P' of a shear wave propagating in a medium and detected by ultrasonic transducers located at points M and P can be written as follows:

[0150]

[0151] Finally, the phase difference between the two changes in the tissue velocity signal at the respective observation points S' and P' of the shear wave propagating in the medium and detected by the ultrasonic transducers located at points S and P can be written as follows:

[0152]

[0153] Equations (3), (4) and (5) can be written in matrix form as follows:

[0154]

[0155] according to Where T is the period of the shear wave, the phase difference can be written as a function of the time delay Δt. By using the equation and λ=cT, where c is the velocity of the shear wave in the medium and λ is the wavelength of the shear wave, the matrix (6) can be written as follows:

[0156]

[0157] Finally, equation (7) can be written as follows and leads to:

[0158]

[0159] Therefore, equation (8) can be used to express the vector component of the shear wave velocity (c x 、c y 、c z ) is defined as a function of the delays along three perpendicular axes. The function depends on the multiple delays and the position of each observation point or the length between each observation point.

[0160] Each delay (or time difference or time delay) Δt S′M′ , Δt M′P′ and Δt S′P′ may be known and may correspond to Figure 2b The time delay (eg, time of flight) measured at the observation point is determined based on multiple arrival times detected in the change of the tissue velocity signal at the respective observation points.

[0161] Similarly, according to Figure 2c , since the position of each ultrasonic transducer is known, the difference between two respective observation points along the X and Y axes can be known. In fact, as mentioned above, for example, the coordinates (x, y) of the respective observation points S', P', M' in a plane perpendicular to the transmission direction can correspond to the coordinates (x, y) of the positions S, P, M of the ultrasonic transducers 107a, 107b, 107c in a plane perpendicular to the transmission direction, for example, at which the ultrasonic transducers 107a, 107b, 107c have collected a plurality of backscattered signals.

[0162] Thus, for example, the values ​​Δx2x1 and Δy2y1 between the observation points S' and M' can be determined based on the known positions of the two ultrasonic transducers at points S and M, respectively. Similarly, the values ​​Δx3x2 and Δy3y2 between the observation points M' and P' can be determined based on the known positions of the two ultrasonic transducers at points M and P, respectively. Finally, the values ​​Δx3x2 and Δy3y2 between the observation points M' and P' can be determined based on the also known positions of the two ultrasonic transducers at points S and P, respectively. Figure 2c The values ​​Δx3x1 and Δy3y1 between the observation points S' and P' are determined by the positions of the two ultrasonic transducers (not shown).

[0163] Likewise, the coordinates (z) of the respective observation points S', P', M' defined by the depth in the medium (e.g., along the transmission direction or along the central axis 120a; 120b; 120c of the ultrasonic transducer S, M, P) are known, and the values ​​Δz2z1, Δz3z1 and Δz3z1 may also be known. In practice, the depth of each respective observation point is known in advance, for example, because it is defined by the detection system.

[0164] Furthermore, in one or several embodiments, the depth of the observation point can be scanned along the central axis of the ultrasonic transducer, which collects the backscattered signal backscattered from the observation point, so as to obtain different variations of the backscattered signal for the same coordinates x and y of the respective observation point (or the position of the ultrasonic transducer). Advantageously, using several depths for the same respective observation point can allow increasing the accuracy of the velocity component along the Z axis, and therefore increasing the accuracy of the velocity (or overall velocity) of the shear wave.

[0165] In one or more embodiments, the depth of each respective observation point may be the same or may be different, or may be the same for some respective observation points and different for other observation points. Figure 2d, the respective observation point S' may have the same depth as the respective observation point M' (z1=z2), and the respective observation point P' may have a depth z3 different from the depth of S' and / or M'.

[0166] Furthermore, the number of respective observation points may be increased by increasing the number of ultrasonic transducers around / near the shear wave source in order to increase the accuracy of the velocity components along the X and Y axes, and hence the velocity (or overall velocity) of the shear wave.

[0167] The method may then include calculating the velocity vector component (c x 、c y 、c z ) Estimate 211 (or calculate) the velocity of the shear wave (c).

[0168] This estimation can be done according to the following formula:

[0169]

[0170] By calculating the velocity (or overall velocity) of the shear wave generated by the natural shear wave source using equation (9), the elastic properties of the medium (e.g., biological tissue) surrounding the natural shear wave source can be determined. For example, when the natural shear wave source is the heart, the elastic properties of the biological tissue of the patient's heart and, for example, the directions of the myocardial fibers at different depths can be determined. The elastic properties can be, for example, the Young's modulus and / or the shear modulus of the medium (i.e., the biological tissue).

[0171] Figure 3a and Figure 3b An example of measuring shear wave velocity using a matrix ultrasound array probe commonly used for 3D imaging is shown.

[0172] More precisely, Figure 3a shows an experimental setup for measuring the velocity of a shear wave propagating in a medium, and Figure 3b The results of changes in tissue velocity signals measured based on backscattered signals collected from observation points by the experimental device are shown.

[0173] refer to Figure 3a , the experimental device 300 may include a matrix array probe 310 coupled to an ultrasound imaging system or a control system including, for example, a control unit and a computer (not shown). The ultrasound array probe may include a plurality of transducers in a matrix form (e.g., 2D). The ultrasound probe may be located on the surface (or inside) of a medium 320, and some transducers of the transducer matrix are used to generate a plurality of ultrasound beams in the medium, respectively. Typically, such an ultrasound probe is used in ultrasound imaging such as 3D echography (or ultrasound images).

[0174] In this example, the medium 320 is a gelatin phantom, and at least one shear wave 330 is generated by a vibrating plate 340 at a frequency of 40 Hz placed inside the medium.

[0175] Several transducers of the ultrasound probe can be configured to emit ultrasound waves in the medium to form (or generate) an ultrasound beam 350 for irradiating nine observation points in the medium, and can be configured to collect backscattered signals from these observation points as described above. The backscattered signals can then be processed by the experimental device as described above.

[0176] Figure 3b Results 360 of changes in tissue velocity signals measured at nine observation points using the experimental setup are shown. Figure 2b As described, Figure 3b Each (of the nine) curves may present amplitude variations as a function of time of the tissue velocity signal calculated for a respective one of the nine observation points.

[0177] From these variations, the respective arrival time at each observation point can then be determined by detecting the maximum of each curve and then determining the time delay Δt between the two arrival times and inverting according to equation (8).

[0178] Based on the average of the determined time delays, the components of the shear wave may be calculated as previously described, and the velocity (or speed) of the shear wave may be determined by using an inversion method based on the calculated components of the shear wave.

[0179] With this experimental setup, the velocity of the shear waves propagating in the medium was determined to be about 4.66 m / s.

[0180] Thus, advantageously, the present method may use existing (or conventional) ultrasound imaging including a conventional ultrasound probe or use an imaging system utilizing a conventional ultrasound probe (having an ultrasound transducer) to determine the velocity of shear waves propagating in a medium (eg, biological tissue of the heart).

Claims

1. A method for determining the velocity of a shear wave (105) propagating in a medium (101), the shear wave having a wavelength, the method comprising: - generating (201) at least one ultrasound beam (113a, 113b, 113c) into the medium, irradiating at least three respective observation points (S', M', P') in the medium; - collecting (203) a plurality of backscattered signals backscattered respectively from said observation points irradiated by said at least one ultrasound beam; - determining (207) the respective arrival time of each observation point (205) based on the backscattered signals respectively collected from the observation points; - calculating (209) the vector velocity component (c) of the shear wave based on the plurality of respective arrival times x 、c y 、c z ); - Based on the calculated vector velocity component (c x 、c y 、c z ) estimating (211) the velocity (c) of the shear wave; wherein the respective observation points are different and not aligned.

2. The method according to claim 1, wherein at least three ultrasound beams (113a, 113b, 113c) are generated into the medium, respectively irradiating at least three respective observation points (S', M', P') in the medium.

3. The method according to claim 1 or 2, wherein the multiple backscattered signals are collected by multiple ultrasonic transducers respectively, and each ultrasonic transducer collects the backscattered signals backscattered from its own observation point.

4. The method according to claim 3, wherein the at least three ultrasound beams (113a, 113b, 113c) are respectively generated by a plurality of ultrasonic transducers.

5. The method according to claim 3 or 4, wherein the at least three ultrasound beams (113a, 113b, 113c) are respectively generated by at least three ultrasound transducers of the plurality of ultrasound transducers.

6. A method according to any one of the preceding claims, wherein the respective observation points are separated from each other by a separation distance which is less than the wavelength of the shear waves in the medium.

7. The method according to claim 6, wherein the wavelength of the shear wave is less than 0.7 meters, preferably less than 0.5 meters.

8. A method according to any one of the preceding claims, wherein when the wave vector direction of the shear wave is known, the at least three observation points may not be aligned in a plane containing the wave vector of the shear wave, or when the wave vector direction of the shear wave is unknown, the at least three observation points may be at least four observation points that are not aligned and not all contained in the same plane.

9. The method according to any one of claims 1 to 8, wherein a motion estimator is used on backscatter signals respectively collected from the respective observation points to determine each of a plurality of respective arrival times of the respective observation points.

10. The method of claim 9, wherein each of a plurality of respective arrival times for a respective observation point is determined based on a respective change in tissue velocity determined by a motion estimator at the respective observation point.

11. A method according to any of the preceding claims, wherein calculating the vector velocity component of the shear wave also includes determining a plurality of at least three delays, each delay (Δt) can be determined between two respective arrival times of a plurality of arrival times, and each vector velocity component can be a function of a respective delay (Δt) of the plurality of at least three delays.

12. A method according to any of the preceding claims 9-11, wherein each arrival time of a respective observation point determined based on the respective change in tissue velocity at the respective observation point is determined by detecting the maximum and / or minimum of the respective change or by using a cross-correlation or an artificial intelligence algorithm.

13. A method according to any one of the preceding claims, wherein estimating the velocity of the shear wave based on the calculated vector velocity components is performed by using an inversion algorithm on the calculated vector velocity components.

14. The method according to any of the preceding claims, wherein the shear waves are natural shear waves generated by a natural shear wave source contained in the medium, or artificial shear waves generated by an artificial shear wave source external to the medium.

15. The method of claim 14, wherein the natural shear wave source is the movement of a closed valve of the heart or vibrations caused by sound or pulse waves propagating in an arterial wall.

16. The method according to any of the preceding claims 3-5, wherein the plurality of ultrasonic transducers are located on the surface of the medium and / or in the medium.

17. A detection system (100) for determining the velocity of a shear wave (105) propagating in a medium (101) using the method according to claims 1 to 16, the detection system comprising: a plurality of ultrasonic transducers arranged in a 2D array (107a, 107b, 107c) for generating at least one ultrasonic beam (113a, 113b, 113c) into the medium and illuminating at least three respective observation points (S', M', P') in the medium, and configured to acquire respective backscattered signals generated in response to an interaction between the at least one ultrasonic beam and the medium, - a control unit configured to cause an ultrasonic transducer of the plurality of ultrasonic transducers to generate the at least one ultrasonic beam, to collect a plurality of backscattered signals backscattered respectively from the at least three respective observation points irradiated by the at least one ultrasonic beam, to determine a respective arrival time of each observation point based on the backscattered signals collected respectively from the observation points, and to calculate (209) a vector velocity component (c 209) of the shear wave based on the plurality of respective arrival times. x 、c y 、c z ) and is used to calculate the vector velocity component (c x 、c y 、c z ) estimating (211) the velocity (c) of the shear wave; wherein the respective observation points are different and not aligned.

18. The detection system according to claim 17, wherein at least three ultrasound beams (113a, 113b, 113c) are generated into the medium to illuminate at least three respective observation points (S', M', P') in the medium.

19. The detection system according to claim 17 or 18, wherein each of the plurality of ultrasonic transducers collects backscattered signals backscattered from a respective observation point.

20. The detection system according to any one of the preceding claims 17-19, wherein the shear wave is a natural shear wave generated by a natural shear wave source contained in the medium, or an artificial shear wave generated by an artificial shear wave source outside the medium.

21. The detection system of claim 20, wherein the natural shear wave source is the movement of a closed valve of the heart or vibrations caused by sound or pulse waves propagating in an arterial wall.

22. A detection system according to any of the preceding claims 17-21, wherein each ultrasonic transducer is formed by a matrix of transducer elements adapted to be independently controlled, and the control system is configured to control the ultrasonic transducer elements so as to simulate an ultrasonic transducer generating an ultrasonic beam in a medium.

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