Methods and device for focusing and measuring biological tissue shear vibration

Abstract

Disclosed herein are ultrasound shear elastography apparatuses that include a longitudinal shear vibration intensifier and a longitudinal shear vibration estimator. The longitudinal shear vibration estimator can be an ultrasound imaging array that is co-located at a surface of the longitudinal shear vibration intensifier. The longitudinal shear vibration intensifier can be a vibrating concave piston.

Description

METHODS AND DEVICE FOR FOCUSING AND MEASURING BIOLOGICAL TISSUE SHEAR VIBRATION CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No.63 / 631,159, filed April 8, 2024, which is incorporated herein by reference in its entirety. FIELD

[0002] The present disclosure relates to methods and devices for focusing and measuring biological tissue shear vibration. BACKGROUND

[0003] Ultrasound shear wave elastography is a clinically available method for detection of abnormalities and disease in soft tissues such as breast, liver, and muscle. Elastography detects changes in the mechanical properties of soft tissue associated with pathology, such as stiffening of otherwise soft tissue, by vibrating the tissues and imaging the response. Current technologies suffer from low tissue vibration amplitude in practice, resulting in measurement failure, especially when the imaging region is located deep within the body. SUMMARY

[0004] Disclosed herein are various devices and methods for focusing and measuring biological tissue shear vibration.

[0005] In one embodiment, an ultrasound shear elastography apparatus is disclosed. The apparatus comprises a longitudinal shear vibration intensifier and a longitudinal shear vibration estimator, the estimator incorporating an ultrasound imaging array positioned at a surface of the intensifier. In various embodiments, the intensifier may be configured as a vibrating concave piston, may consist of a single element, or may include a plurality of elements. When multiple elements are employed, they may vibrate out-of-plane transiently below 1000 Hz or with arbitrary phase and timing to steer and intensify vibration amplitude at a desired depth and orientation, and they may be actuated by a motor, an electromechanical transducer, and / or the piezoelectric effect. The ultrasound imaging array may comprise a plurality of ultrasonic transmitters and receivers configured to excite short ultrasonic pulses with a bandwidth within the range of 0.5 to 20 MHz, may be arranged in linear, circular, or irregular configurations, and may have a smaller width than the intensifier. In selectembodiments, the imaging array is co-aligned with a vibrating concave piston so that ultrasound pulses propagate along the same axis as the generated shear vibrations, and a data processing module may be included to receive ultrasound data and generate corresponding images.

[0006] In another embodiment, an ultrasound shear elastography apparatus is provided that focuses shear waves in biological tissue. In these embodiments, the longitudinal shear vibration intensifier is adapted to generate focused shear waves and comprises a plurality of vibrating elements arranged on a curved support surface, with the elements configured to vibrate out-of-plane below 1000 Hz and operable with arbitrary phase and timing to steer and intensify vibration amplitude at a desired depth and orientation. An ultrasound imaging array disposed coaxially with the intensifier is configured to excite and receive short ultrasonic pulses having a bandwidth within the range of 0.5 to 20 MHz, with certain embodiments specifying a bandwidth within 2 to 10 MHz. A control module is operatively connected to both the vibrating elements and the imaging array, generating drive signals for actuation and processing ultrasonic echo signals to form images of shear wave propagation within tissue. In some embodiments, the imaging array is co-aligned with a vibrating concave piston so that the ultrasound waves are directed along the same axis as the produced vibrations, and a data processing module may further process the received ultrasound information.

[0007] In further embodiments, a method for focusing and measuring shear vibration in biological tissue is disclosed. The method comprises actuating a longitudinal shear vibration intensifier that includes a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in tissue, and co-aligning an ultrasound imaging array with the intensifier so that ultrasound pulses propagate parallel to the shear waves. The method further involves transmitting short ultrasonic pulses into the biological tissue, receiving corresponding ultrasound echo signals, computing localized tissue displacement within image frames, and determining the propagation speed of the shear waves based on the computed displacements. In certain embodiments, the vibrating concave piston operates transiently below 1000 Hz, while the imaging array comprises multiple ultrasonic transmitters and receivers configured to excite pulses with a bandwidth between 0.5 and 20 MHz and may be arranged in a linear configuration. Additional aspects include filtering the received ultrasound echo signals with a bandpass filter, beamforming the signals using a delay-and-sum algorithm combined with one-dimensional normalized cross correlation, and calculating a temporalgradient of the tissue displacement, with the vibrator’s concave surface having a radius of curvature between about 30 mm and 50 mm.

[0008] The foregoing and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG.1 is a schematic of the configuration and boundary condition employed in the method for simulation of shear wave intensification.

[0010] FIG.2 illustrates an exemplary test setup.

[0011] FIG.3 is a schematic illustration of the exemplary test setup in FIG.2.

[0012] FIG.4 illustrates a flowchart for an exemplary method of signal processing.

[0013] FIG.5 illustrates a time snapshot of longitudinal displacement components of focused shear wavefields at different time frequencies.

[0014] FIG.6 is a cross-sectional schematic of an exemplary longitudinal shear vibration intensifier.

[0015] FIG.7 is a schematic illustration of a focused shear wave generated by an exemplary longitudinal shear vibration intensifier.

[0016] FIG.8 illustrates an exemplary device that includes a longitudinal shear vibration intensifier (i.e., a concave piston actuated by an electromagnetic vibrator), and a longitudinal shear vibration estimator (e.g., a US imaging array).

[0017] FIG.9 illustrates a block diagram of an exemplary system in which a function generator and audio amplifier are used to in connection with an electro-mechanical vibrator, and signals from an US imaging array are subsequently processed to obtain longitudinal shear vibration estimations.

[0018] FIG. 10 shows a circular longitudinal shear vibration intensifier (A) and a longitudinal shear vibration estimator (B).

[0019] FIG. 11 shows a rectangular longitudinal shear vibration intensifier (A) and a longitudinal shear vibration estimator (B).

[0020] FIG.12 illustrates the effectiveness of shear wave focusing over a range of liver stiffness in metabolic dysfunction-associated steatotic liver disease (MASLD).

[0021] FIG.13 illustrates measurements and best-fit simulations of longitudinal shear wave displacement amplitude along the beam axis versus propagation distance for the wave fields using phantoms with different percentages by weight of gelatin powder.

[0022] FIG.14 illustrates measurements showing the benefits of using focused shear waves to measure obstructed target regions (e.g., through ribs).

[0023] FIG.15 illustrates a simulation showing the benefits of using focused shear waves to measure obstructed target regions (e.g., through ribs).

[0024] Fig.16 is a flowchart of an example process 1600. In some implementations, one or more process blocks of Fig.16 may be performed by a device. DETAILED DESCRIPTION

[0025] Overview

[0026] The following explanations of terms are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. As used herein, “comprising” means “including” and the singular forms “a” or “an” or “the” include plural references unless the context clearly dictates otherwise. The term “or” refers to a single element of stated alternative elements or a combination of two or more elements unless the context clearly indicates otherwise.

[0027] The methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and non-obvious features and aspects of the present disclosure, alone and in various combinations and sub-combinations with one another. The disclosed methods are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed methods require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the methods are not limited to such theories of operation.

[0028] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity,the attached figures may not show the various ways in which the disclosed devices and methods can be used in conjunction with other devices and methods. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.

[0029] Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting, unless otherwise indicated. Other features of the disclosure are apparent from the following detailed description and the claims.

[0030] Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise indicated, implicitly or explicitly, the numerical parameters set forth are approximations that can depend on the desired properties sought and / or limits of detection under standard test conditions / methods. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited. Furthermore, not all alternatives recited herein are equivalents.

[0031] As used herein, the terms "ultrasound transducer" and "transducer" have their ordinary meanings as understood by those skilled in the art of ultrasound imaging technologies. Any suitable transducer may be used. For example, in some embodiments, an ultrasound transducer may comprise a piezoelectric device. The transducers described herein are configured in arrays of multiple individual transducer elements. As used herein, the terms "transducer array" or "array" refers to a collection of transducer elements attached to a common support structure.

[0032] As used herein, the terms "transmit element" and "receive element" have their ordinary meanings as understood by those skilled in the art of ultrasound imaging technologies. For example, the term "transmit element" refers without limitation to an ultrasound transducer element which at least momentarily performs a transmit function inwhich an electrical signal is converted into an ultrasound signal. Similarly, the term "receive element" refers without limitation to an ultrasound transducer element which at least momentarily performs a receive function in which an ultrasound signal impinging on the element is converted into an electrical signal.

[0033] As used herein, the term “ concave piston” refers to a mechanical component with a surface that curves inward. As described herein, a concave piston is used to generate focused shear waves by vibrating at the skin surface, directing the waves to converge towards a specific target region, such as the liver, to enhance the signal for tissue stiffness estimation. The concave shape aids in concentrating the wave energy, improving the effectiveness of the measurement.

[0034] As used herein, the term “longitudinal shear vibration intensifier” refers to a device or component that enhance the amplitude and focus of shear vibrations along the longitudinal axis within biological tissues. This intensifier can comprise elements that vibrate out-of-plane and that are arranged on a curved support surface, such as a concave piston. As described herein, the intensifier can be controlled to steer and intensify the vibration amplitude at desired depths and orientations.

[0035] As used herein, the term “longitudinal shear vibration estimator” refers to a component or system used to measure and evaluate the propagation of shear vibrations along the longitudinal axis within biological tissues. As described herein, the estimator can comprise an ultrasound imaging array that is co-located with a shear vibration intensifier.

[0036] Introduction

[0037] Ultrasound shear wave elastography is a diagnostic technique in which tissue stiffness is inferred from the propagation speed of shear waves as measured by ultrasound imaging. Tissue shear stiffness is a useful biomarker, for example, for the differentiation of benign and malignant breast lesions, for staging fibrosis in the progression of chronic liver disease, and for assessing and monitoring muscle and nerve health.

[0038] Two main strategies for ultrasound shear wave elastography are called two- dimensional (2D) shear wave elastography (2D SWE) and transient elastography (TE).2D SWE employs the acoustic radiation force produced by a tightly focused ultrasonic “push” beam to generate a short, approximately unipolar shear wave pulse that propagates away from the push beam focus. Shear wave propagation in 2D SWE is measured using high frame rateultrasound imaging with the same array used to generate the push beam.2DSWE is useful for generating images of tissue elasticity.

[0039] Shear waves in TE are generated by external vibration at the skin surface. Current clinical devices utilize low-frequency vibration of a small, flat piston at the skin surface to generate shear wave motion in the liver, which is measured using ultrasound imaging. The shear wave resulting from vibration of such a piston spreads in all directions from the source. Consequently, the vibration can diverge from the liver, resulting in a low shear wave signal in the liver stiffness measurement region and contributing to high failure rates and unreliability of TE.

[0040] Despite the lack of shear wave directivity, we classify shear waves used in TE as shear wave beams because they are generated at the skin surface using a finite-sized source and propagate into a half-space (the patient) subject to diffraction effects. As a result of wavefront curvature coupled with low tissue compressibility, shear wave beams are composed of both transverse and longitudinal displacements that are perpendicular and parallel to the propagation direction, respectively, and both propagate at the shear wave speed.

[0041] The methods and systems disclosed herein utilize focused shear wave TE, which operates through the vibration of a concave-shaped piston at the surface. The concave-shaped piston generates shear waves that converge towards the liver stiffness measurement region, thereby increasing the signal available for tissue stiffness estimation.

[0042] As described herein, the focused shear wave beams can provide more effective results, including, for example, over the entire stiffness range seen in fatty liver disease. In addition, the directionality of the narrow shear wave beams can also enable significant energy penetration through intercostal spaces due to the effect of shear wave aberration during propagation between ribs.

[0043] The propagation speed of the vibration can be measured using a co-localized highly sensitive ultrasound sensor array. The device can be used for assessing local mechanical properties of elasticity and viscosity of target tissues including but not limited to skeletal muscles, tendons, nerves, cartilages, liver, kidney, cardiovascular and lymphatic systems, as well as implanted tissue constructs. In some embodiments, the device can also be used for therapy, including but not limited to stimulation of muscles, nerves, and brains as well as enhancing drug delivery.

[0044] Exemplary Devices and Methods of Use

[0045] This disclosure relates to novel devices and methods for focusing the longitudinal component of shear vibration and measuring the propagation speed of the vibration remotely and noninvasively.

[0046] FIG.1 is a schematic illustration of the operation of the novel devices disclosed herein. When stress is applied to a target area at the skin surface by compression or shear waves, the tissue undergoes displacement or deformation. As shown in FIG.1, the novel devices described herein beneficially reduce displacement outside of the boundary of the area of contact between the device and the surface of the skin. In particular, the boundary outside of the source undergoes no, or very little, displacement.

[0047] By restricting the area of displacement as shown in FIG.1, the propagated field is easier to compute, using, for example, Fourier analysis (e.g., FFTs). Accurate displacement estimation is important for assessing soft tissue conditions (e.g., liver fibrosis or tumors). In addition, restricting the area of displacement as shown in FIG.1 can reduce the effect of Rayleigh waves at the skin surface. Using directional beams to focus shear waves as shown in FIG.1 to reduce the effect on boundary conditions outside of the source simplifies computations of the propagated field, by allowing the outer conditions to be treated as unimportant.

[0048] A mathematical model for determining displacement source conditions is shown in FIG.1. In particular, beginning with the Navier-Cauchy equation of motion for an isotropicelastic half-space with the displacement field ^^^, ^, ^^^^^^^ prescribed on the surface ^ ^ 0:where,

[0049] Thiswith the use of 2D spatial Fourier transform pair as indicated below.. p y p array provides focused shear wave generation and the shear waves were directed at tissue-mimicking gelatin phantoms. As shown in FIG.3, the US field of view of the linear array transducer measures the convergence of shear waves to the target stiffness measurement region.

[0051] FIG.4 illustrates a flowchart for an exemplary method of signal processing. In step 1, each frame of RF data is beamformed with a delay-and-sum (DAS) algorithm, in which each received signal is delayed based on the time it takes to travel from the transducer to the target area (delay) and the delayed signals are summed together to form an image pixel (sum). In step 2, localized displacements in each frame are computed using 1D normalized cross correlation. Then, in step 3, bandpass filters in time are applied to rejected unwanted signals. The passband can be defined based on the input pulse sent to the shaker.

[0052] FIG.5 illustrates a time snapshot of longitudinal displacement components of focused shear wavefields at different time frequencies (f = 200 Hz, 300 Hz, and 400 Hz).

[0053] FIG.6 is a cross-sectional schematic of an exemplary concave-shaped piston. In the example shown in FIG.6, the piston is about 50 mm wide (i.e., a 50 mm diameter) and has a concave surface with a 40 mm radius of curvature.

[0054] FIG.7 is a schematic illustration of a focused shear wave generated by a concave piston, such as that shown in FIG.6. The illustration shows a cylindrical coordinate system (r, z) and displacement polarizations of the focused shear wave. As shown in FIG.7, the anti- symmetrical shear wave coalescence results in a strong longitudinal (z-polarized) motion in the focal region. In this manner, the penetration of shear waves into a target region can be increased by focusing the field in the directional beam shown in FIG.7, thus forcing the wave to propagate into the target region more effectively.

[0055] FIG.8 illustrates an exemplary device that includes a longitudinal shear vibration intensifier (e.g., a concave piston actuated by an electromagnetic vibrator), and a longitudinal shear vibration estimator (e.g., a US imaging array). The electromagnetic vibrator enables longitudinal vibration of the piston in the z direction as depicted in FIG.7. In FIG.8, the concave piston is single-piece 3D piston with a 50 mm diameter and having a curved surfacewith a 40 mm radius of curvature, which is actuated by a voice-coil-type electromechanical vibrator by broad and narrow band signals in the frequency range 0 to 1000 Hz. The ultrasound imaging phased array in FIG.8 has a bandwidth of 2 to 4 MHz, and 64 piezoelectric transduction elements arranged linearly along 20 mm. As discussed in more detail below, the ultrasound sensor array and a vibrating element array of FIG.8 are co- aligned to intensify the vibration at a desired depths and orientations and measure the longitudinal shear propagation speed.

[0056] In some embodiment, the vibrating concave piston can have a concave surface with a radius of curvature between about 20 mm and 70 mm, or between about 30 mm and 50 mm.

[0057] In one embodiment, a waveform generator (e.g., Agilent 33250 A, Keysight Technologies, Santa Rosa, CA, USA) can be used to produce the driving signal, which can first passed through an audio amplifier (e.g., APA150, Dayton Audio, Springboro, OH, USA). The driving signal can be given by where the pulse duration iseven integer that controls the pulse ramp-up and rampdown times and ω = 2πf is the angular frequency. Values of T = 4 / f and m = 4 can be employed such that s(t) has approximately 5 cycles. Parameters T and m can be chosen to enable separation of the resulting shear and compressional wave fields temporally while also ensuring that the pulse is sufficiently narrowband that the vibrator natural frequency at approximately 20 Hz is avoided.

[0058] The amplified signal can drive the vibrator, which moves the piston longitudinally (in the z direction), thus generating focused shear wave motion in the region of interest. Piston vibration frequencies of 200, 300, and 400 Hz can be used such that sufficiently short shear wavelengths compared to the piston radius were produced to ensure effective focusing of the beam. FIG.9 illustrates a block diagram of an exemplary system in which a function generator and audio amplifier are used to in connection with an electro-mechanical vibrator, and signals from an US imaging array are subsequently processed to obtain longitudinal shear vibration estimations.

[0059] The longitudinal piston vibration excites both compressional and shear waves in the target area. In a test, for example, longitudinal vibration of the piston resulted in compression of the gelatin along the z direction, which appears as quasistatic compression of the gelatindue to the long compressional wavelengths at audio frequencies. Transverse stretching in the r direction away from the z axis accompanies compression due to the low compressibility of the gelatin. The transverse stretch results in a shear stress, launching a shear wave that propagates into the gelatin with approximately radial displacement polarization.

[0060] The curved surface of the piston yields conical shear wavefronts that eventually converge along the z axis, thus focusing the shear wave field as depicted in Fig.7. The region where the conical shear wave converges along the z axis is referred to as the focal region. Curvature of the focused shear wavefronts results in radial normal strain that is balanced by longitudinal normal strain in the z direction because of the nearly incompressible behavior of the gelatin at audio frequencies. Thus the shear wave displacement vector u has components in both the r and z directions that propagate together at the shear wave speed ct, i.e., u = urer + uzez, where erand ezare unit vectors in the r and z directions. Symmetry requires that ur= 0 along the z axis. The transverse ur and longitudinal uz displacement components of the shear wave are referred to herein as the transverse and longitudinal shear waves, respectively. The longitudinal shearwave is the subject of this disclosure due to its accessibility for ultrasound elastography applications, as in TE, in which the ultrasonic sensor used for shear wave imaging is aligned coaxially with the piston source.

[0061] The longitudinal shear vibration intensifiers disclosed herein can comprise a single element or array of elements. Each element vibrates out of plane transiently with a bandwidth that is above 0 Hz and below, for example, 1000 Hz. The total array size can be between 10 mm and 100 mm in a lateral dimension, and the array can have a circular, rectangular, square, or elliptical shape. Elements can vibrate with arbitrary phase / timing to steer and intensify vibration amplitude at the desired depths and orientations. Elements can be actuated by a motor, an electromechanical transducers such as capacitive plates, or the piezoelectric effect. Individual elements have curved or flat faces. The overall surface of the array can be curved or flat.

[0062] FIGS.10 and 11 show exemplary co-aligned longitudinal shear vibration intensifiers and estimators. For example, the ultrasound sensor array and a vibrating element arrays can be co-aligned to intensify the vibration at a desired depths and orientations and measure the longitudinal shear propagation speed. In FIG.10, a circular longitudinal shear vibration intensifier (A) and a longitudinal shear vibration estimator (B) are shown. FIG.10 illustrates another exemplary co-aligned device in which the shear vibration intensifier (A) and a longitudinal shear vibration estimator (B) have a rectangular shape.

[0063] The longitudinal shear vibration estimators can be ultrasonic transmitter / receivers that excite short ultrasonic pulses with bandwidth in a range, for example, of 0.5 and 20 MHz. Active materials of the ultrasonic elements can be piezoelectric. Ultrasonic elements can receive echoes individually from which tissue vibration estimation is performed. Ultrasonic array can be linear, circular, or irregularly arranged. The overall size of the ultrasonic array can be less than that of the intensifier so that it can be located within the intensifier.

[0064] Focused shear wave generation and propagation was demonstrated in silico using a novel analytical model and on the benchtop in tissue-mimicking gelatin phantoms shown in FIG.2. FIG.12 illustrates the effectiveness of shear wave focusing over a range of liver stiffness in metabolic dysfunction-associated steatotic liver disease (MASLD). FIG.13 illustrates measurements (black) and best-fit simulations (blue) of longitudinal shear wave displacement amplitude | uz | along the beam axis (r = 0) versus propagation distance for the wave fields using phantoms with different percentages by weight of gelatin powder (e.g., at (a) 3%, (b) 5%, and (c) 7% ). As shown in these figures, focusing was insensitive to different stiffnesses and the model-measurement was in agreement across the entire stiffness range.

[0065] The effect of shear wave aberration during propagation between ribs was also investigated in simulation and on the benchtop using anatomically realistic 3D printed human ribs, where it is found that the directionality of the narrow shear wave beam enables significant energy penetration through the intercostal space. FIGS.14 and 15, for example, illustrates the benefits of using focused shear waves, as described herein, to measure obstructed target regions.

[0066] Accordingly, the devices and methods described herein provide a co-aligned ultrasound sensor array and a vibrating element array to intensify the vibration at a desired depths and orientations and measure the longitudinal shear propagation speed. These uniquely designed vibrating elements can be activated by electrical pulses, including but not limited to piezo ceramic crystals and capacitive plates, or motor-driven plates, and vibration focusing algorithms. The array elements can be in any form of annular, oval, square, rectangular shapes.

[0067] The acoustic sensor array disclosed herein can more effectively to steer beams to the vibration focused area. In addition, uniquely designed encoded pulses within the safety range can be provided to measure the frequency dependent propagation speed and amplitude.

[0068] The devices and methods described herein can be used to assess local mechanical properties of elasticity and viscosity of target tissues including but not limited to skeletal muscles, tendons, nerves, cartilages, liver, kidney, cardiovascular and lymphatic systems, as well as implanted tissue constructs.

[0069] Fig.16 is a flowchart of an example process 1600. In some implementations, one or more process blocks of Fig.16 may be performed by a device.

[0070] As shown in Fig.16, process 1600 may include actuating a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in a biological tissue (block 1602). For example, device may actuate a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in a biological tissue, as described above. As also shown in Fig.16, process 1600 may include co-aligning an ultrasound imaging array with the longitudinal shear vibration intensifier such that the ultrasound pulses emitted by the imaging array propagate along an axis parallel to the generated shear waves (block 1604). For example, device may co-align an ultrasound imaging array with the longitudinal shear vibration intensifier such that the ultrasound pulses emitted by the imaging array propagate along an axis parallel to the generated shear waves, as described above. As further shown in Fig.16, process 1600 may include transmitting short ultrasonic pulses from the ultrasound imaging array into the biological tissue and receiving corresponding ultrasound echo signals reflecting from the focused shear waves (block 1606). For example, device may transmit short ultrasonic pulses from the ultrasound imaging array into the biological tissue and receiving corresponding ultrasound echo signals reflecting from the focused shear waves, as described above. As also shown in Fig.16, process 1600 may include computing localized tissue displacement within the image frames and determining a propagation speed of the focused shear waves based on the computed displacements (block 1608). For example, device may compute localized tissue displacement within the image frames and determining a propagation speed of the focused shear waves based on the computed displacements, as described above.

[0071] Although Fig.16 shows example blocks of process 1600, in some implementations, process 1600 may include additional blocks, fewer blocks, different blocks, or differently arranged blocks than those depicted in Fig.16. Additionally, or alternatively, two or more of the blocks of process 1600 may be performed in parallel.

[0072] Summary

[0073] Ultrasound shear wave elastography is a widely used diagnostic technique for assessing the mechanical properties of soft tissues, such as the liver, breast, and muscle. This method is particularly useful for detecting abnormalities and diseases by measuring tissue stiffness, which can indicate pathological changes like fibrosis or tumors. However, current elastography technologies face significant challenges, particularly in achieving sufficient tissue vibration amplitude for accurate measurements. This issue is exacerbated when the imaging region is located deep within the body, leading to frequent measurement failures and unreliable results.

[0074] Ultrasound shear wave elastography typically employs low-frequency vibration of a small, flat piston at the skin surface to generate shear wave motion. While this approach is clinically available, it suffers from several disadvantages. The shear waves generated by such pistons tend to spread in all directions from the source, resulting in a divergence of the wave energy from the target region, such as the liver. This divergence leads to a low shear wave signal in the measurement region, contributing to high failure rates and unreliable assessments of tissue stiffness. Additionally, the lack of shear wave directivity in these systems limits their effectiveness, particularly in cases where precise localization and increased amplitude of shear waves are required for accurate diagnosis.

[0075] The present approach addresses these challenges by introducing a novel method for focusing and measuring biological tissue shear vibration. The method utilizes a concave- shaped piston to generate focused shear waves that converge towards the target stiffness measurement region, thereby increasing the signal available for tissue stiffness estimation. This focused shear wave transient elastography (TE) technique enhances the directionality of the shear wave beams, enabling significant energy penetration through intercostal spaces and improving measurement accuracy across a range of tissue stiffnesses. The method further incorporates a co-localized ultrasound sensor array to measure the propagation speed and amplitude of the shear waves, providing a comprehensive assessment of the mechanical properties of target tissues. This innovative approach not only improves the reliability of elastography measurements but also expands the potential applications of the technology in both diagnostic and therapeutic contexts.

[0076] Further Embodiments

[0077] As discussed above, the present disclosure is directed toward all novel and non- obvious features and aspects of the present disclosure, alone and in various combinations and sub-combinations with one another. The following paragraphs illustrate certain sub- combinations that are part of present disclosure.

[0078] 1: An ultrasound shear elastography apparatus may include: a longitudinal shear vibration intensifier; and a longitudinal shear vibration estimator, where the longitudinal shear vibration estimator may include an ultrasound imaging array, and the ultrasound imaging array is co-located at a surface of the longitudinal shear vibration intensifier.

[0079] 2: The ultrasound shear elastography apparatus as paragraph 1 describes, where the longitudinal shear vibration intensifier may include a vibrating concave piston, and optionally, where the vibrating concave piston has a concave surface with a radius of curvature between about 20 mm and 70 mm, or between about 30 mm and 50 mm.

[0080] 3: The ultrasound shear elastography apparatus as either of paragraphs 1 or 2 describe, where the US imaging array and the vibrating concave piston are co-aligned such that the ultrasound waves emitted by a plurality of transducers of the US imaging array are directed along the same axis as the vibrations generated by the vibrating concave piston.

[0081] 4: The ultrasound shear elastography apparatus as any of paragraphs 1-3 describe, where the longitudinal shear vibration intensifier may include a single element.

[0082] 5: The ultrasound shear elastography apparatus as any of paragraphs 1-4 describe, where the longitudinal shear vibration intensifier may include a plurality of elements.

[0083] 6: The ultrasound shear elastography apparatus as any of paragraphs 1-5 describe, where the plurality of elements vibrate out of plane transiently below 1000 Hz.

[0084] 7: The ultrasound shear elastography apparatus as any of paragraphs 1-6 describe, where the plurality of elements vibrates with arbitrary phase / timing to steer and intensify vibration amplitude at a desired depth and orientation.

[0085] 8: The ultrasound shear elastography apparatus as any of paragraphs 1-7 describe, where the plurality of elements are actuated by a motor, an electromechanical transducer, or the piezeoelectric effect.

[0086] 9: The ultrasound shear elastography apparatus as any of paragraphs 1-8 describe, where the ultrasound imaging array may include a plurality of ultrasonic transmitters andreceivers that excite short ultrasonic pulses with a bandwidth within the range of 0.5 and 20 MHz.

[0087] 10: The ultrasound shear elastography apparatus as any of paragraphs 1-9 describe, where the ultrasound imaging array is linear, circular, or irregularly arranged.

[0088] 11: The ultrasound shear elastography apparatus as any of paragraphs 1-10 describe, where the ultrasound imaging array has a smaller width than a width of the longitudinal shear vibration intensifier.

[0089] 12: The ultrasound shear elastography apparatus as any of paragraphs 1-11 describe, where the ultrasound imaging array is linear, circular, or irregularly arranged.

[0090] 13: The ultrasound shear elastography apparatus as any of paragraphs 1-12 describe, further may include a data processing module that receives ultrasound data from the US imaging array and processes it to generate images.

[0091] 14: The ultrasound shear elastography apparatus as any of paragraphs 1-13 describe, where the ultrasound imaging array has a smaller width than a width of the longitudinal shear vibration intensifier.

[0092] 15: An ultrasound shear elastography apparatus may include: a longitudinal shear vibration intensifier configured to generate focused shear waves in biological tissue, the longitudinal shear vibration intensifier may include: a plurality of vibrating elements arranged on a curved support surface, the vibrating elements configured to vibrate out-of- plane at frequencies below 1000 Hz and operable with arbitrary phase and timing to steer and intensify vibration amplitude at a desired depth and orientation; an ultrasound imaging array disposed coaxially with the longitudinal shear vibration intensifier and configured to excite and receive short ultrasonic pulses having a bandwidth within the range of 0.5 to 20 MHz; and a control module operatively connected to the plurality of vibrating elements and the ultrasound imaging array, the control module configured to generate drive signals for actuating the vibrating elements and to process ultrasonic echo signals from the ultrasound imaging array to generate images of shear wave propagation in the tissue.

[0093] 16: The ultrasound shear elastography apparatus as paragraph 15 describes, where the longitudinal shear vibration intensifier may include: a vibrating concave piston.

[0094] 17: The ultrasound shear elastography apparatus as either of paragraphs 15 or 16 describe, where the ultrasound imaging array and the vibrating concave piston are co-alignedsuch that the ultrasound waves emitted by a plurality of transducers of the ultrasound imaging array are directed along the same axis as the vibrations generated by the vibrating concave piston.

[0095] 18: The ultrasound shear elastography apparatus as any of paragraphs 15-17 describe, where the longitudinal shear vibration intensifier is a single element.

[0096] 19: The ultrasound shear elastography apparatus as any of paragraphs 15-18 describe, where the longitudinal shear vibration intensifier may include a plurality of elements.

[0097] 20: The ultrasound shear elastography apparatus as any of paragraphs 15-19 describe, where the plurality of elements vibrate out of plane transiently below 1000 Hz.

[0098] 21: The ultrasound shear elastography apparatus as any of paragraphs 15-20 describe, where the plurality of elements vibrate with arbitrary phase / timing to steer and intensify vibration amplitude at a desired depth and orientation.

[0099] 22: The ultrasound shear elastography apparatus as any of paragraphs 15-21 describe, where the plurality of elements are actuated by a motor, an electromechanical transducer, and / or the piezoelectric effect.

[0100] 23: The ultrasound shear elastography apparatus as any of paragraphs 15-22 describe, where the ultrasound imaging array may include a plurality of ultrasonic transmitters and receivers that excite short ultrasonic pulses with a bandwidth within the range of 0.5 and 20 MHz.

[0101] 24: The ultrasound shear elastography apparatus as any of paragraphs 15-23 describe, where the ultrasound imaging array may include a plurality of ultrasonic transmitters and receivers that excite short ultrasonic pulses with a bandwidth within the range of 2 and 10 MHz.

[0102] 25: The ultrasound shear elastography apparatus as any of paragraphs 15-24 describe, further may include a data processing module that receives ultrasound data from the ultrasound imaging array and processes the data to generate images.

[0103] 26: A method for focusing and measuring biological tissue shear vibration, may include: actuating a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in a biological tissue; co-aligning an ultrasound imaging array with the longitudinal shear vibration intensifier such that the ultrasound pulses emitted by the imaging array propagatealong an axis parallel to the generated shear waves; transmitting short ultrasonic pulses from the ultrasound imaging array into the biological tissue and receiving corresponding ultrasound echo signals reflecting from the focused shear waves; and computing localized tissue displacement within the image frames and determining a propagation speed of the focused shear waves based on the computed displacements.

[0104] 27: The method as paragraph 26 describes, where the vibrating concave piston vibrates transiently at a frequency below 1000 Hz.

[0105] 28: The method as either of paragraphs 26 or 27 describe, where the ultrasound imaging array may include a plurality of ultrasonic transmitters and receivers configured to excite short ultrasonic pulses having a bandwidth within the range of 0.5 to 20 MHz.

[0106] 29: The method as any of paragraphs 26-28 describe, further may include: filtering the received ultrasound echo signals with a bandpass filter prior to computing the localized tissue displacement.

[0107] 30: The method as any of paragraphs 26-29 describe, where computing the localized tissue displacement may include: beamforming the received ultrasound echo signals using a delay-and-sum algorithm; and employing one-dimensional normalized cross correlation.

[0108] 31: The method as any of paragraphs 26-30 describe, where determining the propagation speed of the focused shear waves may include: calculating a temporal gradient of the computed tissue displacements.

[0109] 32: The method as any of paragraphs 26-31 describe, where the ultrasound imaging array is co-aligned with the vibrating concave piston such that the ultrasound pulses are emitted along the same axis as the vibrations generated by the concave piston.

[0110] 33: The method as any of paragraphs 26-32 describe, where the vibrating concave piston has a concave surface with a radius of curvature between about 20 mm and 70 mm, or between about 30 mm and 50 mm.

[0111] 34: The method as any of paragraphs 26-33 describe, where the ultrasound imaging array is arranged in a linear configuration.

[0112] 35: A method for focusing and measuring biological tissue shear vibration, may include: providing a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in biological tissue; providing a longitudinal shear vibration estimator may include anultrasound imaging array; co-locating said ultrasound imaging array at a surface of said longitudinal shear vibration intensifier; and measuring biological tissue shear vibration using said ultrasound imaging array co-located at the surface of said longitudinal shear vibration intensifier.

[0113] While preferred aspects of the present disclosure have been shown and described herein, it will be apparent to a person of ordinary skill in the art that such aspects are provided by way of example only. Variations, changes, and substitutions to these disclosed aspects will be apparent to a person of ordinary skill in the art without departing from the present disclosure. It should be understood that all such various alternatives to the aspects described herein may be employed in practicing the present disclosure. The following claims define the scope of the disclosure.

Claims

We claim:

1. An ultrasound shear elastography apparatus comprising: a longitudinal shear vibration intensifier; and a longitudinal shear vibration estimator, wherein the longitudinal shear vibration estimator comprises an ultrasound imaging array, and the ultrasound imaging array is co-located at a surface of the longitudinal shear vibration intensifier.

2. The ultrasound shear elastography apparatus of claim 1, wherein the longitudinal shear vibration intensifier comprises a vibrating concave piston.

3. The ultrasound shear elastography apparatus of claim 1, wherein the longitudinal shear vibration intensifier comprises a single element.

4. The ultrasound shear elastography apparatus of claim 1, wherein the longitudinal shear vibration intensifier comprises a plurality of elements.

5. The ultrasound shear elastography apparatus of claim 4, wherein the plurality of elements vibrate out of plane transiently below 1000 Hz.

6. The ultrasound shear elastography apparatus of claim 4, wherein the plurality of elements vibrates with arbitrary phase / timing to steer and intensify vibration amplitude at a desired depth and orientation.

7. The ultrasound shear elastography apparatus of claim 4, wherein the plurality of elements are actuated by a motor, an electromechanical transducer, or the piezeoelectric effect.

8. The ultrasound shear elastography apparatus of claim 1, wherein the ultrasound imaging array comprises a plurality of ultrasonic transmitters and receivers that excite short ultrasonic pulses with a bandwidth within the range of 0.5 and 20 MHz.

9. The ultrasound shear elastography apparatus of claim 8, wherein the ultrasound imaging array is linear, circular, or irregularly arranged.

10. The ultrasound shear elastography apparatus of claim 8, wherein the ultrasound imaging array has a smaller width than a width of the longitudinal shear vibration intensifier.

11. The ultrasound shear elastography apparatus of claim 2, wherein the US imaging array and the vibrating concave piston are co-aligned such that the ultrasound waves emitted by a plurality of transducers of the US imaging array are directed along the same axis as the vibrations generated by the vibrating concave piston.

12. The ultrasound shear elastography apparatus of claim 1, further comprising a data processing module that receives ultrasound data from the US imaging array and processes it to generate images.

13. An ultrasound shear elastography apparatus comprising: a longitudinal shear vibration intensifier configured to generate focused shear waves in biological tissue, the longitudinal shear vibration intensifier comprising: a plurality of vibrating elements arranged on a curved support surface, the vibrating elements configured to vibrate out-of-plane at frequencies below 1000 Hz and operable with arbitrary phase and timing to steer and intensify vibration amplitude at a desired depth and orientation; an ultrasound imaging array disposed coaxially with the longitudinal shear vibration intensifier and configured to excite and receive short ultrasonic pulses having a bandwidth within the range of 0.5 to 20 MHz; and a control module operatively connected to the plurality of vibrating elements and the ultrasound imaging array, the control module configured to generate drive signals for actuating the vibrating elements and to process ultrasonic echo signals from the ultrasound imaging array to generate images of shear wave propagation in the tissue.

14. The ultrasound shear elastography apparatus of claim 13, wherein the longitudinal shear vibration intensifier comprises: a vibrating concave piston.

15. The ultrasound shear elastography apparatus of claim 13, wherein the longitudinal shear vibration intensifier is a single element.

16. The ultrasound shear elastography apparatus of claim 13, wherein the longitudinal shear vibration intensifier comprises a plurality of elements.

17. The ultrasound shear elastography apparatus of claim 16, wherein the plurality of elements vibrate out of plane transiently below 1000 Hz.

18. The ultrasound shear elastography apparatus of claim 16, wherein the plurality of elements vibrate with arbitrary phase / timing to steer and intensify vibration amplitude at a desired depth and orientation.

19. The ultrasound shear elastography apparatus of claim 16, wherein the plurality of elements are actuated by a motor, an electromechanical transducer, and / or the piezoelectric effect.

20. The ultrasound shear elastography apparatus of claim 13, wherein the ultrasound imaging array comprises a plurality of ultrasonic transmitters and receivers that excite short ultrasonic pulses with a bandwidth within the range of 0.5 and 20 MHz.

21. The ultrasound shear elastography apparatus of claim 13, wherein the ultrasound imaging array comprises a plurality of ultrasonic transmitters and receivers that excite short ultrasonic pulses with a bandwidth within the range of 2 and 10 MHz.

22. The ultrasound shear elastography apparatus of claim 8, wherein the ultrasound imaging array is linear, circular, or irregularly arranged.

23. The ultrasound shear elastography apparatus of claim 1, wherein the ultrasound imaging array has a smaller width than a width of the longitudinal shear vibration intensifier.

24. The ultrasound shear elastography apparatus of claim 14, wherein the ultrasound imaging array and the vibrating concave piston are co-aligned such that theultrasound waves emitted by a plurality of transducers of the ultrasound imaging array are directed along the same axis as the vibrations generated by the vibrating concave piston.

25. The ultrasound shear elastography apparatus of claim 13, further comprising a data processing module that receives ultrasound data from the ultrasound imaging array and processes the data to generate images.

26. A method for focusing and measuring biological tissue shear vibration, comprising: actuating a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in a biological tissue; co-aligning an ultrasound imaging array with the longitudinal shear vibration intensifier such that the ultrasound pulses emitted by the imaging array propagate along an axis parallel to the generated shear waves; transmitting short ultrasonic pulses from the ultrasound imaging array into the biological tissue and receiving corresponding ultrasound echo signals reflecting from the focused shear waves; and computing localized tissue displacement within the image frames and determining a propagation speed of the focused shear waves based on the computed displacements.

27. The method of claim 26, wherein the vibrating concave piston vibrates transiently at a frequency below 1000 Hz.

28. The method of claim 26, wherein the ultrasound imaging array comprises a plurality of ultrasonic transmitters and receivers configured to excite short ultrasonic pulses having a bandwidth within the range of 0.5 to 20 MHz.

29. The method of claim 26, further comprising: filtering the received ultrasound echo signals with a bandpass filter prior to computing the localized tissue displacement.

30. The method of claim 26, wherein computing the localized tissue displacement comprises: beamforming the received ultrasound echo signals using a delay-and-sum algorithm; and employing one-dimensional normalized cross correlation.

31. The method of claim 26, wherein determining the propagation speed of the focused shear waves comprises: calculating a temporal gradient of the computed tissue displacements.

32. The method of claim 26, wherein the ultrasound imaging array is co-aligned with the vibrating concave piston such that the ultrasound pulses are emitted along the same axis as the vibrations generated by the concave piston.

33. The method of claim 26, wherein the vibrating concave piston has a concave surface with a radius of curvature between about 30 mm and 50 mm.

34. The method of claim 26, wherein the ultrasound imaging array is arranged in a linear configuration.

35. A method for focusing and measuring biological tissue shear vibration, comprising: providing a longitudinal shear vibration intensifier, the intensifier including a vibrating concave piston configured to vibrate out-of-plane to generate focused shear waves in biological tissue; providing a longitudinal shear vibration estimator comprising an ultrasound imaging array; co-locating said ultrasound imaging array at a surface of said longitudinal shear vibration intensifier; and measuring biological tissue shear vibration using said ultrasound imaging array co- located at the surface of said longitudinal shear vibration intensifier.

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