Elastic imaging method and system based on scattering displacement gradient field

Abstract

The invention relates to the technical field of medical elastography and material multi-scale mechanical measurement, in particular to an elastography method and system based on a scattering displacement gradient field, and the method comprises the following steps: arranging an excitation device at the periphery of a target material to generate the scattering displacement field, and measuring an out-of-plane displacement gradient field by adopting lateral shear interference imaging; selecting a single-frame instantaneous gradient field or a frequency domain gradient field subjected to time-frequency domain Fourier transform as a target field; and through adaptive sliding window interception, two-dimensional autocorrelation calculation and Rayleigh wave space autocorrelation theoretical model fitting, global shear wave velocity distribution is obtained, and viscoelastic modulus distribution is reconstructed through an inversion algorithm. The method supports single-frame scattering displacement gradient field inversion elastic imaging, does not need high-frame-rate equipment, is high in environmental vibration interference resistance, is high in system stability, is suitable for scenes with poor shock isolation conditions, is low in cost, is high in efficiency, is high in measurement precision, and can meet the requirements of medical clinical diagnosis and material multi-scale mechanical measurement.

Description

Technical Field

[0001] This invention relates to the fields of medical elastography and multi-scale mechanical measurement of materials, and in particular to an elastography method and system based on a scattering displacement gradient field. Background Technology

[0002] In the fields of medical elastography and multi-scale mechanical measurement of materials, the elastic modulus, as a core characterization parameter, is crucial for accurate measurement in clinical diagnosis and material performance evaluation. Elastography based on shear wave velocity measurement has been widely used due to its non-invasive and quantitative advantages; however, traditional techniques suffer from significant bottlenecks: transient wave methods rely on high-frame-rate imaging equipment (thousands to tens of thousands of hertz) to acquire spatiotemporal displacement fields, resulting in high equipment costs and hindering widespread adoption in primary healthcare institutions; reverberant wave methods also remain dependent on high-frame-rate equipment and require multiple boundary reflections to generate reverberation, extending measurement time and causing inconvenience to patients in medical settings.

[0003] To overcome the aforementioned bottlenecks, patent CN120636711A proposes an elastic imaging method and system based on instantaneous scattering displacement field. Its core advantage lies in the fact that by using a passive or active method to excite the scattering displacement field, only a low frame rate imaging device (such as ordinary ultrasound, optical, or nuclear magnetic resonance equipment) is needed to measure the instantaneous scattering displacement field in a single frame. After local truncation through a sliding window, two-dimensional autocorrelation calculation, and fitting with a theoretical model, the shear wave velocity and viscoelastic modulus can be inverted, effectively reducing the dependence on high frame rate equipment. This achieves low-cost and high-efficiency elastic imaging and supports multi-scene measurement of material surfaces, cross-sections, and three-dimensional volumes. It has strong compatibility and provides a convenient path for upgrading existing imaging equipment.

[0004] However, this technical solution still has significant limitations: Elastic imaging of scattering displacement fields based on optical measurements typically employs conventional interferometric imaging methods to measure the displacement field, such as optical coherence physics (OCT) and holographic interferometry. However, conventional interferometric imaging requires an independent, high-quality reference wavefront, has weak resistance to vibration interference, low system stability, fixed high sensitivity, and is easily affected by environmental noise, impacting the final elastic imaging results in clinical or industrial settings.

[0005] Therefore, in medical tissue elastography and multi-scale mechanical characterization of materials, there is an urgent need to develop an elastography method that is more resistant to environmental vibration interference. Summary of the Invention

[0006] Therefore, this invention aims to address the problem that traditional optical shear wave elastography relies on conventional interferometry, resulting in weak resistance to environmental vibration interference. Speckle interferometry mainly includes two branches: reference-beam-based speckle interferometry and shear-interferometry-based speckle interferometry. The former measures the displacement field and is commonly used in current optical elastography, while the latter measures the displacement gradient field and is not applied to optical elastography. Shear interferometry utilizes a portion of the wavefront itself for interference, achieving consistent vibration effects on both beams through a common-path design. It eliminates the need for a high-precision reference mirror, simplifies the optical path, provides strong resistance to vibration interference, and exhibits high system stability, making it more suitable for use in industrial or clinical environments with poor vibration isolation.

[0007] This invention is the first to directly apply shear interferometry to elastic imaging. It measures the displacement gradient field using shear interferometry imaging, derives the spatial autocorrelation theory formula for the displacement gradient field under Rayleigh waves, inverts the elasticity using the spatial correlation of the scattered displacement gradient field, and employs an adaptive sliding window to improve inversion accuracy, ultimately achieving elastic imaging based on the scattered displacement gradient field. This invention features high inversion accuracy, strong resistance to vibration interference, and high system stability.

[0008] The elastic imaging method based on the scattering displacement gradient field includes the following steps: S1: Based on the measurement location of the target material, a scattering displacement field excitation device is set up around the target material. The scattering displacement field excitation device is driven by a driving signal to generate a scattering displacement field in the target material region. S2: Using transverse shearing interferometry imaging technology, the out-of-plane displacement gradient field of the target material region is measured with high spatial resolution to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field. S3: For the instantaneous scattering displacement gradient field, select a single-frame instantaneous scattering displacement gradient field from the instantaneous scattering displacement gradient field as the target displacement gradient field; for the spatiotemporal domain scattering displacement gradient field, perform a time-frequency domain Fourier transform on the spatiotemporal domain scattering displacement gradient field acquired at a high frame rate to obtain a frequency domain displacement gradient field, and use it as the target displacement gradient field; S4: The local scattered displacement gradient field in the target displacement gradient field is extracted by an adaptive sliding window, the local scattered displacement gradient field is subjected to two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. S5: Based on the global shear wave velocity distribution, the viscoelastic modulus distribution of the target material region is reconstructed using an inversion algorithm to characterize the viscoelastic parameters of the material.

[0009] In one embodiment of the present invention, in S2, the method for performing high spatial resolution measurement on the out-of-plane displacement transverse gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field is as follows: S21: Using space carrier technology or synchronous phase shift technology, acquire the transverse shear interference image of the target material region, and perform phase extraction operation on the transverse shear interference image to obtain the encapsulation phase difference. ; S22: Determine the phase difference of the package Fringe density: When the fringe density corresponding to the phase difference at any elastic wave driving frequency is not within the preset threshold range, adjust the shearing amount of the shearing interference. This continues until the measurement requirements for the deformation of the target at any time are met, and the adjusted package phase difference information is obtained. S23: Perform noise filtering on the adjusted package phase difference information to remove environmental noise and measurement noise, and obtain the denoised package phase difference information; S24: Unwrap the denoised wrapped phase difference information to obtain continuous phase difference information over the entire domain. Alternatively, by reducing the excitation amplitude of the scattering displacement field, the phase value of the entire field can be constrained to... Within the interval, the entire phase is unenclosed, thus obtaining phase difference information. ; S25: Based on the phase difference information Combined with shear amount and laser wavelength Through formula The full-field out-of-plane displacement gradient field of the target material's measured region is obtained; this distribution is the instantaneous scattered displacement gradient field at the corresponding deformation moment. If a high frame rate continuous measurement method is used, the spatiotemporal scattering displacement gradient field can be obtained. .

[0010] In one embodiment of the present invention, in S21, a transverse shear interference image of the target material region is acquired using space carrier technology or synchronous phase shift technology, and a phase extraction operation is performed on the transverse shear interference image to obtain the encapsulation phase difference. The method is as follows: If space carrier technology is used, a single exposure acquires a single frame of transverse shearing interferometry image. First, a Fourier transform is performed on the image to filter and extract the positive first-order spectral components. Then, an inverse Fourier transform is performed on the filtered spectral components to obtain the complex amplitude T. Based on the complex amplitude at the initial time... and the complex amplitude at the current moment Through formula Calculate the wrap phase difference between two frames ,in This represents taking the imaginary part of the complex amplitude. This represents the real part of the complex amplitude; If synchronous phase shift technology is used, the phase shift amounts of the four frames acquired in a single exposure will differ sequentially. The shearing interferometry images, denoted as the four shearing interferometry images at the initial time, are as follows: The four frames of shearing interferometry images at the current moment are as follows: , , , The phase information of the two sets of images is extracted using a four-step phase-shifting algorithm, and then processed according to the formula. Calculate the package phase difference between the two sets of data .

[0011] In one embodiment of the present invention, in S4, the local scattered displacement gradient field in the target displacement gradient field is intercepted by an adaptive sliding window, two-dimensional autocorrelation is calculated on the local scattered displacement gradient field, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. The method is as follows: S41: Set the initial size of the adaptive sliding window to... The adaptive sliding window is moved to the current position to be processed in the target displacement gradient field, and the local displacement gradient field data at that position is captured. S42: Perform two-dimensional autocorrelation calculation on the local displacement gradient field data to obtain the first displacement gradient autocorrelation characteristic curve of the corresponding local region. This curve is based on the position difference. x-axis, corresponding The autocorrelation coefficient is the value on the ordinate; S43: Extract the abscissa value corresponding to the half-peak height and half-peak width (HWHM) of the first displacement gradient autocorrelation feature curve. The optimal sliding window size for the current local region is obtained as follows: ,in This is a preset constant used to control the relationship between the adaptive sliding window size and the wavelength of the local region; S44: Based on the optimal sliding window size, re-extract the local displacement gradient field data at the current position, and perform two-dimensional autocorrelation calculation on the data again to obtain the second displacement gradient autocorrelation characteristic curve of the corresponding local region; S45: Introducing the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave, and employing a nonlinear least squares fitting algorithm, the second displacement gradient autocorrelation characteristic curve is fitted to the spatial autocorrelation theoretical model. The shear wave velocity of the current local region is then calculated through iterative calculation. ; S46: Control the adaptive sliding window to traverse the entire target material region at a preset step size, and repeat steps S42~S45 for each traversed local region to solve the shear wave velocity of all local regions in sequence. Finally, the shear wave velocity data of all local regions are integrated to form the global shear wave velocity distribution of the target material region.

[0012] In one embodiment of the present invention, the expression of the spatial autocorrelation theoretical model is as follows: ;in, Represents the lateral gradient of out-of-plane displacement The two-dimensional autocorrelation function, It is a zero-order Bessel function. It is a second-order Bessel function. For wave number, The angular frequency of the frequency-domain controllable sinusoidal signal used to drive the scattering displacement field excitation device.

[0013] In one embodiment of the present invention, S5, the method for reconstructing the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm includes: S51: Obtain the density of the target material A nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established, and its expression is as follows: ,in, For shear wave velocity, Represents the elastic coefficient. Indicates the viscosity coefficient; S52: Keeping the local region division method of the sliding window unchanged, the driving frequency of the driving signal is changed. Repeat steps S1 to S4 to obtain the shear wave velocity of each local region at at least two different driving frequencies. That is, each local region corresponds to a set of shear wave velocity datasets. , n represents the number of driving frequencies, and each value in the dataset corresponds to a different driving frequency. ; S53: For each local region in the global domain, generate a multi-frequency shear wave velocity dataset for that region. and each The value corresponds to the angular frequency of the driving signal. Substituting the nonlinear viscoelastic model into the given data, a nonlinear fitting algorithm is used to perform fitting calculations, and the viscoelastic parameters of the local region are obtained. and , These are the spatial coordinates of a local region. S54: Traverse all local regions of the global domain and integrate each local region. and This forms the distribution of elastic coefficient and viscosity coefficient in the target material region, which together constitute the global viscoelastic modulus distribution.

[0014] In one embodiment of the present invention, in S1, the method for generating a scattering displacement field in real time within the target material region is as follows: Based on the type of the measurement location of the target material, a suitable scattering displacement field excitation device is deployed in the peripheral area of ​​the target material using either a passive excitation method or an active excitation method. A sinusoidal signal with controllable frequency parameters is used as the driving source to apply a driving action to the scattering displacement field excitation device, so that a scattering displacement field is formed in real time within the measurement area of ​​the target material.

[0015] In one embodiment of the present invention, a method for generating a scattering displacement field in real time within the measurement region of the target material using a passive excitation method includes: The scattering displacement field excitation device consists of an encircling excitation source and multiple scattering body units. Based on the spatial characteristics of the target material to be measured, the encircling excitation source and multiple scattering body units are set in the outer region of the target material to be measured area, and the multiple scattering body units are all within the space enclosed by the encircling excitation source. The geometric parameters of the scattering body units follow a random distribution, and their spatial arrangement is disordered. The surrounding excitation source is driven by a frequency-domain controllable sinusoidal signal; the elastic wave generated by the surrounding excitation source after being driven propagates along the target material to multiple scattering units, and the scattering effect is generated by the physical action of the scattering units. The scattered elastic waves are superimposed on each other in the target material to be measured area, and finally a scattering displacement field is formed in real time. The method for arranging the surrounding excitation source and the plurality of scattering units in the peripheral region of the target material to be measured is as follows: Multiple scatterer units are arranged in a ring-shaped envelope and conformally attached to the outer contour of the target material to be measured area, so that the scatterer units are adapted to the boundary shape of the area to be measured and are all within the space enclosed by the surrounding excitation source. The spacing between adjacent scatterer units is negatively correlated with the total number of scatterer units, and the elastic modulus of the scatterer unit is not less than 10 times the elastic modulus of the target material.

[0016] In one embodiment of the present invention, a method for generating a scattering displacement field in real time within the measurement region of the target material using an active excitation method includes: In the outer region of the target material to be measured area, a multi-point excitation source array is deployed in a spatially random distribution; the multi-point excitation sources are synchronously driven by a frequency-domain controllable sine wave signal, and the elastic waves excited by the multiple points are superimposed on each other, thereby directly generating a scattered displacement field in real time within the target material region; Among them, the method of deploying a multi-point excitation source array with random spatial distribution in the outer region of the target material to be measured area includes: The multi-point excitation source array adopts a boundary circumferential surrounding configuration, and is attached around the boundary contour of the target material to be measured area; the spatial distribution of each excitation unit needs to be random, and the overall surrounding range is adapted to the surface boundary of the area to be measured, so as to ensure that the elastic waves excited by each excitation unit can form a uniform superposition on the surface of the area to be measured. In the multi-point excitation source array, the size of each excitation unit is 0.1 to 10 times the shear wave wavelength, and the spacing between adjacent excitation units is negatively correlated with the total number of excitation units.

[0017] Based on the same inventive concept, the present invention also provides an elastic imaging system based on a scattered displacement gradient field, including: a scattered displacement field excitation generation module, a displacement gradient field measurement module, a target displacement gradient field screening and construction module, a global shear wave velocity distribution solution module, and a material viscoelastic modulus characterization module. The scattering displacement field excitation generation module is used to deploy a scattering displacement field excitation device around the target material according to the measurement location of the target material, and drive the scattering displacement field excitation device with a frequency-domain controllable sine wave signal to generate a scattering displacement field in the target material region. The displacement gradient field measurement module is used to perform high spatial resolution measurement of the out-of-plane displacement gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field. The target displacement gradient field filtering and construction module is used to select a single-frame instantaneous scattering displacement gradient field as the target displacement gradient field from the instantaneous scattering displacement gradient field; and to perform a time-frequency domain Fourier transform on the spatiotemporal domain scattering displacement gradient field acquired at a high frame rate to obtain a frequency domain displacement gradient field, which is then used as the target displacement gradient field. The global shear wave velocity distribution solution module is used to extract the local scattered displacement gradient field in the target displacement gradient field through an adaptive sliding window, perform two-dimensional autocorrelation calculation on the local scattered displacement gradient field, and perform nonlinear curve fitting based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. The material viscoelastic modulus characterization module is used to reconstruct the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm, thereby characterizing the viscoelastic parameters of the material.

[0018] The present invention also provides a computer storage medium storing a computer software product, the computer software product including several instructions for causing a computer device to execute the elastic imaging method based on the scattering displacement gradient field.

[0019] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: This invention breaks through the existing technical path of elastic imaging technology that relies on displacement field measurement. It innovatively combines shear interferometry imaging technology to directly measure the scattered displacement gradient field, giving full play to the advantages of this technology, such as compact structure, large field of view, strong anti-interference ability, no need for vibration isolation, and adaptability to non-light-avoiding environments. This significantly improves the environmental adaptability and ease of operation of elastic imaging. At the same time, it maintains the adaptability to low frame rate devices, and can perform elastic imaging by analyzing the instantaneous scattered displacement gradient field of a single frame, without the need for high-cost, high-frame-rate equipment, thus balancing low cost and high efficiency. By using adaptive sliding window local truncation, two-dimensional autocorrelation calculation, and nonlinear fitting of the theoretical model of displacement gradient space autocorrelation under Rayleigh wave, it can accurately obtain the global shear wave velocity distribution. Moreover, by using multi-frequency driving combined with a nonlinear viscoelastic model, it can achieve a comprehensive characterization of viscoelastic parameters, resulting in higher measurement accuracy. In addition, it is compatible with passive excitation methods and active excitation methods, adaptable to medical clinical diagnosis and multi-scale mechanical measurement of materials, and has the advantages of high measurement accuracy, vibration environment adaptability, and wide compatibility. Attached Figure Description

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0021] Figure 1 This is a schematic flowchart of an elastic imaging method based on a scattering displacement gradient field provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a specific process of an elastic imaging method based on a scattering displacement gradient field provided in an embodiment of the present invention; Figure 3This is a schematic diagram of the principle of material surface elastic imaging based on passive excitation method in the experiment, in which random scattering elements and surrounding excitation sources are deployed around the target region (ROI); Figure 4 It is the instantaneous displacement field on the material surface at different times of 10ms, 20ms, 30ms and 40ms obtained in the experiment; Figure 5 It is the shear wave velocity distribution and probability density distribution calculated by inversion from the displacement gradient field measured in the experiment; Figure 6 This is a schematic diagram of the structure of an elastic imaging system based on a scattering displacement gradient field provided in an embodiment of the present invention.

[0022] Explanation of reference numerals in the accompanying drawings: 100, Scattered displacement field excitation generation module; 200, Displacement gradient field measurement module; 300, Target displacement gradient field screening and construction module; 400, Global shear wave velocity distribution solution module; 500, Material viscoelastic modulus characterization module; 1. Scattering element; 2. Surrounding excitation source. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0024] Example 1: Reference Figure 1 and Figure 2 As shown, this invention provides an elastic imaging method based on a scattering displacement gradient field, specifically including the following steps: S1: Based on the measurement location of the target material, a scattering displacement field excitation device is set up around the target material. The scattering displacement field excitation device is driven by a driving signal to generate a scattering displacement field in the target material region. S2: Using transverse shear interferometry imaging technology, the out-of-plane displacement gradient field of the target material region is measured with high spatial resolution to obtain the instantaneous scattered displacement gradient field. or the spatial-temporal domain scattering displacement gradient field ; S3: For the instantaneous scattering displacement gradient field, select a single-frame instantaneous scattering displacement gradient field from the instantaneous scattering displacement gradient field as the target displacement gradient field; for the spatiotemporal domain scattering displacement gradient field, perform a time-frequency domain Fourier transform on the spatiotemporal domain scattering displacement gradient field acquired at a high frame rate to obtain a frequency domain displacement gradient field, and use it as the target displacement gradient field; S4: The local scattered displacement gradient field in the target displacement gradient field is extracted by an adaptive sliding window, the local scattered displacement gradient field is subjected to two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. S5: Based on the global shear wave velocity distribution, the viscoelastic modulus distribution of the target material region is reconstructed using an inversion algorithm to characterize the viscoelastic parameters of the material.

[0025] As can be seen from the above technical solution, this invention flexibly generates a scattering displacement field by adapting to passive or active excitation methods for the target material measurement location. Utilizing shear interferometry, it directly obtains the instantaneous scattering displacement gradient field from a single shear interferometric image, exhibiting strong resistance to environmental vibration noise. It supports direct elastic imaging of the single-frame instantaneous gradient field, eliminating the need for high-cost, high-frame-rate equipment, thus balancing convenience and low cost. Alternatively, after high-frame-rate acquisition, it obtains the frequency-domain gradient field through time-frequency Fourier transform and performs elastic imaging. By adaptively sliding the window to extract the local gradient field, combining two-dimensional autocorrelation calculation with nonlinear fitting of the Rayleigh wave spatial autocorrelation theoretical model, it can accurately obtain the global shear wave velocity distribution. Then, through inversion algorithms and a nonlinear viscoelastic model driven by multiple frequencies, it achieves a comprehensive and accurate characterization of the material's viscoelastic modulus distribution, resulting in higher measurement accuracy. Furthermore, it is compatible with both passive and active excitation methods, adaptable to medical clinical diagnosis and multi-scale mechanical measurements of materials, possessing high measurement accuracy, vibration environment adaptability, and broad compatibility.

[0026] Furthermore, in step S1, the method for generating a scattering displacement field in real time within the target material region is the same as the principle of patent CN120636711A, as follows: Based on the type of the measurement location of the target material, a suitable scattering displacement field excitation device is deployed in the peripheral area of ​​the target material using either a passive excitation method or an active excitation method. A frequency-controllable sinusoidal signal is used as the excitation source to drive the scattering displacement field excitation device, so that a scattering displacement field is formed in real time within the measurement area of ​​the target material.

[0027] Specifically, methods for generating a scattering displacement field in real time within the measurement region of the target material using passive excitation include: The scattering displacement field excitation device consists of a surrounding excitation source and multiple scattering units. Based on the spatial characteristics of the target material to be measured, the surrounding excitation source and multiple scattering units are set in the outer region of the target material to be measured area, and the multiple scattering units are all within the space enclosed by the surrounding excitation source. The geometric parameters of the scattering units follow a random distribution, and their spatial arrangement is disordered. The geometric shape of the scattering units includes, but is not limited to, columnar structures, hole structures, triangular structures, grid structures, or ellipsoidal structures. The driving source is used to apply a driving action to the surrounding excitation source; the elastic wave generated by the surrounding excitation source after being driven propagates along the target material to the scatterer unit, and the scattering effect is generated by the physical action of the scatterer unit. The scattered elastic waves are superimposed on each other in the target material to be measured area, and finally a scattering displacement field is formed in real time.

[0028] Optionally, in the above technical solution, the method of arranging the surrounding excitation source and the plurality of scattering units in the peripheral region of the target material to be measured is as follows: Multiple scatterer units are arranged in a ring-shaped envelope and conformally attached to the outer contour of the target material to be measured area, so that the scatterer units are adapted to the boundary shape of the area to be measured and are all within the space enclosed by the surrounding excitation source. The spacing between adjacent scatterer units is negatively correlated with the total number of scatterer units; that is, the more scatterer units there are, the smaller the spacing between adjacent units. The elastic modulus of the scatterer unit is not less than 10 times the elastic modulus of the target material, preferably a polymer material such as epoxy resin or silicone rubber, to ensure that the scatterer unit has an effective scattering capability for elastic waves.

[0029] Specifically, methods for generating a scattered displacement field in real time within the measurement region of the target material using active excitation include: In the outer region of the target material to be measured area, a multi-point excitation source array is deployed in a spatially random distribution. The multi-point excitation sources are synchronously driven by a frequency-domain controllable sine wave signal. The elastic waves excited by the multiple points are superimposed on each other, thereby directly generating a scattering displacement field in real time within the target material region.

[0030] Optionally, in the above technical solution, the method of deploying a multi-point excitation source array with random spatial distribution in the peripheral region of the target material to be measured includes: The multi-point excitation source array adopts a boundary circumferential surrounding configuration, and is attached around the boundary contour of the target material to be measured area; the spatial distribution of each excitation unit needs to be random, and the overall surrounding range is adapted to the surface boundary of the area to be measured, so as to ensure that the elastic waves excited by each excitation unit can form a uniform superposition on the surface of the area to be measured. In this multi-point excitation source array, the size of each excitation unit is 0.1 to 10 times the shear wave wavelength, ensuring that a single excitation unit has the ability to effectively excite elastic waves. At the same time, the spacing between adjacent excitation units is negatively correlated with the total number of excitation units, that is, the more excitation units there are, the smaller the spacing between adjacent units, so as to ensure the superposition effect of multiple elastic waves through reasonable spatial density.

[0031] Furthermore, within the technical solution defined in this embodiment, the driving mode of the elastic wave excitation of the scattering displacement field excitation device in the process of realizing passive or active scattering displacement field excitation covers at least one of the following types: mechanical drive, piezoelectric ceramic or thin film drive, acoustic radiation force drive, metal plate / metal patch electromagnetic force drive, nanomagnetic particles, and laser thermoelastic drive.

[0032] In step S2, the method for performing high spatial resolution measurement on the out-of-plane displacement gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field is as follows: S21: Using space carrier technology or synchronous phase shift technology, acquire the transverse shear interference image of the target material region, and perform phase extraction operation on the transverse shear interference image according to the corresponding technical process to obtain the encapsulation phase difference. The specific implementation steps are as follows: If space carrier technology is used: a single exposure acquires a single frame of transverse shearing interference image. First, a Fourier transform is performed on the image to filter and extract the positive first-order spectral components. Then, an inverse Fourier transform is performed on the filtered spectral components to obtain the complex amplitude T. Based on the complex amplitude at the initial time... and the complex amplitude at the current moment Through formula Calculate the wrap phase difference between two frames ,in This represents taking the imaginary part of the complex amplitude. This represents the real part of the complex amplitude; If synchronous phase-shift technology is used: the phase shift of the four frames acquired in a single exposure is 0 in sequence. , , The shearing interferometry images, denoted as the four shearing interferometry images at the initial time, are as follows: The four frames of shearing interferometry images at the current moment are as follows: , , , The phase information of the two sets of images is extracted using a four-step phase-shifting algorithm, and then processed according to the formula. Calculate the package phase difference between the two sets of data ; S22: Determine the phase difference of the package Interference fringe density: When the interference fringe density corresponding to the phase difference is not within the preset threshold range at any elastic wave driving frequency, adjust the shearing amount of the shearing interference. This process continues until the required measurement accuracy for the deformation of the target at any given time is met, thus obtaining the adjusted wrapping phase difference information. S23: Perform noise filtering on the adjusted package phase difference information to remove noise caused by environmental vibration interference, equipment measurement errors, etc., and obtain the denoised package phase difference information. S24: Unwrap the denoised wrapped phase difference information to obtain continuous phase difference information over the entire domain. Alternatively, by reducing the excitation amplitude of the scattering displacement field, the phase value of the entire field can be constrained to... Within this interval, the entire phase is unwrapped, so there is no need to perform an unwrapping operation; the phase difference information can be obtained directly. This improves the real-time performance of phase measurements; S25: Based on the phase difference information Combined with shear amount and laser wavelength Through formula The full-field out-of-plane displacement gradient field of the target material's measured region is obtained; this distribution is the instantaneous scattered displacement gradient field at the corresponding deformation moment. If a high frame rate continuous measurement method is used, the spatiotemporal scattering displacement gradient field can be further obtained. .

[0033] Further, in step S24, for the denoised wrapping phase difference The phase difference can be obtained by unwrapping using the floor least squares method, resulting in a globally continuous phase difference. The specific implementation steps are as follows: S241: Construction Directional difference operator matrix and Directional difference operator matrix ,in for A 3D matrix, expressed as: ; for A 3D matrix, expressed as: M and N are the instantaneous wrapping phase differences, respectively. The number of rows and columns of the matrix; S242: Based on the difference operator matrix and the difference operator matrix Calculate the phase difference of the package Construct a gradient field using the x-axis and y-axis gradients. ,in, express The transpose of the matrix; S243: For the gradient field Divide all elements by 2π and then round down. Negate the rounded result to generate an integer gradient field. Where round is the floor operator. and These represent the integer gradient components in the x-direction and the integer gradient components in the y-direction, respectively. S244: Based on the integer jump gradient components in the x-direction The integer gradient components in the y-direction and difference operator matrix and Construct the Lyapunov equations: The coefficient matrices A and B of the equation are defined as follows: , The regular term matrix C is defined as follows: , express The transpose of the matrix; S245: Solve the Lyapunov equations using Singular Value Decomposition (SVD) to obtain the real jump matrix. ; S246: For the real number jump matrix Performing the floor operation yields the optimized integer transition matrix. : ; S247: Based on the denoised wrapping phase difference and the optimized integer jump matrix Phase compensation calculations are performed to obtain the globally continuous unwrapped phase difference. The calculation formula is as follows: .

[0034] Furthermore, in S4, the local scattered displacement gradient field in the target displacement gradient field is extracted by an adaptive sliding window, two-dimensional autocorrelation is calculated on the local scattered displacement gradient field, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution as follows: S41: Set the initial size of the adaptive sliding window to... The adaptive sliding window is moved to the current position to be processed in the target displacement gradient field, and the local displacement gradient field data at that position is captured. S42: Perform two-dimensional autocorrelation calculation on the local displacement gradient field data to obtain the first displacement gradient autocorrelation characteristic curve of the corresponding local region. This curve is based on the position difference. x-axis, corresponding The autocorrelation coefficient value is on the ordinate, which intuitively reflects the spatial correlation characteristics of the local gradient field; S43: Extract the abscissa value corresponding to the half-peak height and half-peak width (HWHM) of the first displacement gradient autocorrelation feature curve. The optimal sliding window size for the current local region is obtained as follows: ,in This is a preset constant used to control the relationship between the adaptive sliding window size and the wavelength of the local region; S44: Based on the optimal sliding window size, the local displacement gradient field data at the current position is re-extracted, and the two-dimensional autocorrelation is calculated again on the data to obtain the second displacement gradient autocorrelation characteristic curve of the corresponding local region. Due to the improved adaptability of the window size, the curve has higher correlation analysis accuracy. S45: Introducing the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave, and employing a nonlinear least squares fitting algorithm, the second displacement gradient autocorrelation characteristic curve is fitted to the spatial autocorrelation theoretical model. The shear wave velocity of the current local region is then calculated through iterative calculation. The expression for the spatial autocorrelation theoretical model is as follows: ;in, Represents the lateral gradient of out-of-plane displacement The two-dimensional autocorrelation function, It is a zero-order Bessel function. It is a second-order Bessel function. For wave number, The angular frequency of the frequency-domain controllable sinusoidal signal used to drive the scattering displacement field excitation device; S46: Control the adaptive sliding window to traverse the entire target material region at a preset step size, and repeat steps S42~S45 for each traversed local region to solve the shear wave velocity of all local regions in sequence. Finally, the shear wave velocity data of all local regions are integrated to form the global shear wave velocity distribution of the target material region.

[0035] Furthermore, in S5, the method for reconstructing the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm includes: S51: Obtain the density of the target material A nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established, and its expression is as follows: ,in, For shear wave velocity, Represents the elastic coefficient. Indicates the viscosity coefficient; S52: Keeping the local region division method of the sliding window unchanged, the driving frequency of the driving signal is changed. Repeat steps S1 to S4 to obtain the shear wave velocity of each local region at at least two different driving frequencies. That is, each local region corresponds to a set of shear wave velocity datasets. , n represents the number of driving frequencies, and each value in the dataset corresponds to a different driving frequency. ; S53: For each local region in the global domain, generate a multi-frequency shear wave velocity dataset for that region. and each The value corresponds to the angular frequency of the driving signal. Substituting the nonlinear viscoelastic model into the given data, a nonlinear fitting algorithm is used to perform fitting calculations, and the viscoelastic parameters of the local region are obtained. and , These are the spatial coordinates of a local region. S54: Traverse all local regions of the global domain and integrate each local region. and This forms the distribution of elastic coefficient and viscosity coefficient in the target material region, which together constitute the global viscoelastic modulus distribution.

[0036] To further verify the effectiveness of the method in this application, a passive excitation method is used to excite the scattering displacement field: a scattering body unit 1 and an encircling excitation source 2 are arranged around the target material region. The encircling excitation source 2 is driven by a frequency-controllable sinusoidal wave signal. The elastic wave generated by the source is scattered by the scattering body unit 1 and then superimposed in real time within the target material region to form a scattering displacement field.

[0037] A finite element model is constructed to numerically simulate the propagation process of elastic waves on the material surface, and the distribution of the material's elastic parameters is inverted based on the displacement gradient field obtained from the simulation. For example... Figure 3 As shown, the geometric and mechanical parameters of the simulated material are set as follows: thickness 2cm, diameter 4cm, density... Shear modulus 3 kPa, corresponding to theoretical shear wave velocity =1m / s; The scatterer unit 1 adopts a distributed structure design, consisting of 64 cuboid units, which are distributed in a ring around the target material area. The size of a single scatterer unit 1 is 0.7mm×0.7mm×2mm, and the shear modulus is 70kPa. Its spatial layout follows a random distribution law; A sinusoidal wave signal with a frequency of 800Hz is used to drive the surrounding excitation source 2. The generated Rayleigh wave is scattered by the scatterer unit 1 and propagates to the entire target area.

[0038] Figure 4 For the out-of-plane displacement gradient field at different times ( The distribution cloud map shows that at t=27ms, a spatially uniform and signal-quality stable scattering displacement gradient field has been formed within the target material region. An adaptive window size of 6* was selected. In a local region, two-dimensional autocorrelation calculations are performed on the displacement gradient field data to obtain the displacement gradient autocorrelation characteristic curve; this characteristic curve is then compared with the Rayleigh wave autocorrelation theoretical model. Nonlinear least squares fitting is performed to invert and obtain the shear wave velocity of the local region; the adaptive sliding window is controlled to traverse the entire target material domain at a preset step size, and the above local region calculation process is repeated to integrate and obtain the global shear wave velocity distribution and probability density distribution (e.g., ...). Figure 5 (As shown). Statistical results show that the statistical mean of shear wave velocity is in high agreement with the theoretical value of 1 m / s, verifying the effectiveness and reliability of the method of this invention.

[0039] The numerical simulation results above confirm that by measuring the out-of-plane displacement gradient field of the target material through transverse shear interferometry imaging, and combining the two-dimensional autocorrelation algorithm with the nonlinear fitting of the Rayleigh wave spatial autocorrelation theoretical model, high-precision inversion of the elastic parameters of the material surface can be achieved, providing solid theoretical and data support for subsequent practical applications.

[0040] Example 2: Based on the same inventive concept as Embodiment 1, such as Figure 6 As shown, the present invention also provides an elastic imaging system based on a scattered displacement gradient field, including: a scattered displacement field excitation generation module 100, a displacement gradient field measurement module 200, a target displacement gradient field screening and construction module 300, a global shear wave velocity distribution solution module 400, and a material viscoelastic modulus characterization module 500. The scattering displacement field excitation generation module 100 is used to deploy a scattering displacement field excitation device around the target material according to the measurement location of the target material, and drive the scattering displacement field excitation device with a frequency-domain controllable sine wave signal to generate a scattering displacement field in the target material region. The displacement gradient field measurement module 200 is used to perform high spatial resolution measurement of the out-of-plane displacement gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field. The target displacement gradient field screening and construction module 300 is used to select a single-frame instantaneous scattering displacement gradient field as the target displacement gradient field from the instantaneous scattering displacement gradient field; and to perform a time-frequency domain Fourier transform on the high frame rate acquired time-frequency domain scattering displacement gradient field to obtain a frequency domain displacement gradient field, which is then used as the target displacement gradient field. The global shear wave velocity distribution solution module 400 is used to extract the local scattered displacement gradient field in the target displacement gradient field through a sliding window, perform two-dimensional autocorrelation calculation on the local scattered displacement gradient field, and perform nonlinear curve fitting based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. The material viscoelastic modulus characterization module 500 is used to reconstruct the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm, thereby characterizing the viscoelastic parameters of the material.

[0041] Example 3: The present invention also provides a computer storage medium storing a computer software product, the computer software product including several instructions for causing a computer device to execute the elastic imaging method based on the scattering displacement gradient field described in Embodiment 1.

[0042] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0043] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0044] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0045] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An elastic imaging method based on a scattering displacement gradient field, characterized in that, Includes the following steps: S1: Based on the measurement location of the target material, a scattering displacement field excitation device is set up around the target material. The scattering displacement field excitation device is driven by a driving signal to generate a scattering displacement field in the target material region. S2: Using transverse shearing interferometry imaging technology, the out-of-plane displacement gradient field of the target material region is measured with high spatial resolution to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field. S3: For the instantaneous scattering displacement gradient field, select a single-frame instantaneous scattering displacement gradient field from the instantaneous scattering displacement gradient field as the target displacement gradient field; for the spatiotemporal domain scattering displacement gradient field, perform a time-frequency domain Fourier transform on the spatiotemporal domain scattering displacement gradient field acquired at a high frame rate to obtain a frequency domain displacement gradient field, and use it as the target displacement gradient field; S4: The local scattered displacement gradient field in the target displacement gradient field is extracted by an adaptive sliding window, the local scattered displacement gradient field is subjected to two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. S5: Based on the global shear wave velocity distribution, the viscoelastic modulus distribution of the target material region is reconstructed using an inversion algorithm to characterize the viscoelastic parameters of the material.

2. The elastic imaging method based on the scattering displacement gradient field according to claim 1, characterized in that, In S2, the method for performing high spatial resolution measurement of the out-of-plane displacement transverse gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field is as follows: S21: Using space carrier technology or synchronous phase shift technology, acquire the transverse shear interference image of the target material region, and perform phase extraction operation on the transverse shear interference image to obtain the encapsulation phase difference. ; S22: Determine the phase difference of the package Fringe density: When the fringe density corresponding to the phase difference at any elastic wave driving frequency is not within the preset threshold range, adjust the shearing amount of the shearing interference. This continues until the measurement requirements for the deformation of the target at any time are met, and the adjusted package phase difference information is obtained. S23: Perform noise filtering on the adjusted package phase difference information to remove environmental noise and measurement noise, and obtain the denoised package phase difference information; S24: Unwrap the denoised wrapped phase difference information to obtain continuous phase difference information over the entire domain. Alternatively, by reducing the excitation amplitude of the scattering displacement field, the phase value of the entire field can be constrained to... Within the interval, the entire phase is unenclosed, thus obtaining phase difference information. ; S25: Based on the phase difference information Combined with shear amount and laser wavelength Through formula The full-field out-of-plane displacement gradient field of the target material's measured region is obtained; this distribution is the instantaneous scattered displacement gradient field at the corresponding deformation moment. ; If a high frame rate continuous measurement method is used, the spatiotemporal scattering displacement gradient field can be obtained. .

3. The elastic imaging method based on the scattering displacement gradient field according to claim 2, characterized in that, In step S21, a transverse shear interference image of the target material region is acquired using space carrier technology or synchronous phase shift technology, and a phase extraction operation is performed on the transverse shear interference image to obtain the encapsulation phase difference. The method is as follows: If space carrier technology is used, a single exposure acquires a single frame of transverse shearing interferometry image. First, a Fourier transform is performed on the image to filter and extract the positive first-order spectral components. Then, an inverse Fourier transform is performed on the filtered spectral components to obtain the complex amplitude T. Based on the complex amplitude at the initial time... and the complex amplitude at the current moment Through formula Calculate the wrap phase difference between two frames ,in This represents taking the imaginary part of the complex amplitude. This represents the real part of the complex amplitude; If synchronous phase shift technology is used, the phase shift amounts of the four frames acquired in a single exposure will differ sequentially. The shearing interferometry images, denoted as the four shearing interferometry images at the initial time, are as follows: The four frames of shearing interferometry images at the current moment are as follows: , , , The phase information of the two sets of images is extracted using a four-step phase-shifting algorithm, and then processed according to the formula. Calculate the package phase difference between the two sets of data .

4. The elastic imaging method based on the scattering displacement gradient field according to claim 1, characterized in that, In S4, the local scattered displacement gradient field in the target displacement gradient field is extracted by an adaptive sliding window. Two-dimensional autocorrelation is calculated on the local scattered displacement gradient field, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of the displacement gradient under Rayleigh waves to obtain the global shear wave velocity distribution. The method is as follows: S41: Set the initial size of the adaptive sliding window to... The adaptive sliding window is moved to the current position to be processed in the target displacement gradient field, and the local displacement gradient field data at that position is captured. S42: Perform two-dimensional autocorrelation calculation on the local displacement gradient field data to obtain the first displacement gradient autocorrelation characteristic curve of the corresponding local region. This curve is based on the position difference. x-axis, corresponding The autocorrelation coefficient is the value on the ordinate; S43: Extract the abscissa value corresponding to the half-peak height and half-peak width (HWHM) of the first displacement gradient autocorrelation feature curve. The optimal sliding window size for the current local region is obtained as follows: ,in This is a preset constant used to control the relationship between the adaptive sliding window size and the wavelength of the local region; S44: Based on the optimal sliding window size, re-extract the local displacement gradient field data at the current position, and perform two-dimensional autocorrelation calculation on the data again to obtain the second displacement gradient autocorrelation characteristic curve of the corresponding local region; S45: Introducing the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave, and employing a nonlinear least squares fitting algorithm, the second displacement gradient autocorrelation characteristic curve is fitted to the spatial autocorrelation theoretical model. The shear wave velocity of the current local region is then calculated through iterative calculation. ; S46: Control the adaptive sliding window to traverse the entire target material region at a preset step size, and repeat steps S42~S45 for each traversed local region to solve the shear wave velocity of all local regions in sequence. Finally, the shear wave velocity data of all local regions are integrated to form the global shear wave velocity distribution of the target material region.

5. The elastic imaging method based on the scattering displacement gradient field according to claim 3, characterized in that, The expression for the spatial autocorrelation theoretical model is as follows: ； in, Represents the lateral gradient of out-of-plane displacement The two-dimensional autocorrelation function, It is a zero-order Bessel function. It is a second-order Bessel function. For wave number, The angular frequency of the frequency-domain controllable sinusoidal signal used to drive the scattering displacement field excitation device.

6. The elastic imaging method based on the scattering displacement gradient field according to claim 1, characterized in that, In S5, the method for reconstructing the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm includes: S51: Obtain the density of the target material A nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established, and its expression is as follows: ,in, For shear wave velocity, Represents the elastic coefficient. Indicates the viscosity coefficient; S52: Keeping the local region division method of the sliding window unchanged, the driving frequency of the driving signal is changed. Repeat steps S1 to S4 to obtain the shear wave velocity of each local region at at least two different driving frequencies. That is, each local region corresponds to a set of shear wave velocity datasets. , n represents the number of driving frequencies, and each value in the dataset corresponds to a different driving frequency. ; S53: For each local region in the global domain, generate a multi-frequency shear wave velocity dataset for that region. and each The value corresponds to the angular frequency of the driving signal. Substituting the nonlinear viscoelastic model into the solution and using a nonlinear fitting algorithm, the viscoelastic parameters of the local region are obtained. and , These are the spatial coordinates of a local region. S54: Traverse all local regions of the global domain and integrate each local region. and This forms the distribution of elastic coefficient and viscosity coefficient in the target material region, which together constitute the global viscoelastic modulus distribution.

7. The elastic imaging method based on scattering displacement gradient field according to claim 1, characterized in that, In S1, the method for generating the scattering displacement field in real time within the target material region is as follows: Based on the type of the measurement location of the target material, a suitable scattering displacement field excitation device is deployed in the peripheral area of ​​the target material using either a passive excitation method or an active excitation method. A sinusoidal signal with controllable frequency parameters is used as the driving source to apply a driving action to the scattering displacement field excitation device, so that a scattering displacement field is formed in real time within the measurement area of ​​the target material.

8. The elastic imaging method based on the scattering displacement gradient field according to claim 7, characterized in that, Methods for generating a scattered displacement field in real time within the measurement region of the target material using passive excitation include: The scattering displacement field excitation device consists of an encircling excitation source and multiple scattering body units. Based on the spatial characteristics of the target material to be measured, the encircling excitation source and multiple scattering body units are set in the outer region of the target material to be measured area, and the multiple scattering body units are all within the space enclosed by the encircling excitation source. The geometric parameters of the scattering body units follow a random distribution, and their spatial arrangement is disordered. The surrounding excitation source is driven by a frequency-domain controllable sinusoidal signal; the elastic wave generated by the surrounding excitation source after being driven propagates along the target material to multiple scattering units, and the scattering effect is generated by the physical action of the scattering units. The scattered elastic waves are superimposed on each other in the target material to be measured area, and finally a scattering displacement field is formed in real time. The method for arranging the surrounding excitation source and the plurality of scattering units in the peripheral region of the target material to be measured is as follows: Multiple scatterer units are arranged in a ring-shaped envelope and conformally attached to the outer contour of the target material to be measured area, so that the scatterer units are adapted to the boundary shape of the area to be measured and are all within the space enclosed by the surrounding excitation source. The spacing between adjacent scatterer units is negatively correlated with the total number of scatterer units, and the elastic modulus of the scatterer units is not less than 10 times the elastic modulus of the target material.

9. The elastic imaging method based on the scattering displacement gradient field according to claim 7, characterized in that, Methods for generating a scattered displacement field in real time within the measurement region of the target material using active excitation include: In the outer region of the target material to be measured area, a multi-point excitation source array is deployed in a spatially random distribution; the multi-point excitation sources are synchronously driven by a frequency-controllable sinusoidal wave signal; the elastic waves excited by the multiple points are superimposed on each other, thereby directly generating a scattered displacement field in real time within the target material region; Among them, the method of deploying a multi-point excitation source array with random spatial distribution in the outer region of the target material to be measured area includes: The multi-point excitation source array adopts a boundary circumferential surrounding configuration, and is attached around the boundary contour of the target material to be measured area; the spatial distribution of each excitation unit needs to be random, and the overall surrounding range is adapted to the surface boundary of the area to be measured, so as to ensure that the elastic waves excited by each excitation unit can form a uniform superposition on the surface of the area to be measured. In the multi-point excitation source array, the size of each excitation unit is 0.1 to 10 times the shear wave wavelength, and the spacing between adjacent excitation units is negatively correlated with the total number of excitation units.

10. An elastic imaging system based on a scattering displacement gradient field, characterized in that, Includes the following modules: A scattering displacement field excitation generation module is used to deploy a scattering displacement field excitation device around the target material according to the measurement location of the target material, and drive the scattering displacement field excitation device with a frequency-domain controllable sine wave signal to generate a scattering displacement field in the target material region. The displacement gradient field measurement module is used to perform high spatial resolution measurement of the out-of-plane displacement gradient field of the target material region to obtain the instantaneous scattered displacement gradient field or the spatiotemporal scattered displacement gradient field. The target displacement gradient field filtering and construction module is used to select a single-frame instantaneous scattering displacement gradient field as the target displacement gradient field from the instantaneous scattering displacement gradient field; and to perform a time-frequency domain Fourier transform on the spatiotemporal domain scattering displacement gradient field acquired at a high frame rate to obtain a frequency domain displacement gradient field, which is then used as the target displacement gradient field. The global shear wave velocity distribution solution module is used to extract the local scattered displacement gradient field in the target displacement gradient field through an adaptive sliding window, perform two-dimensional autocorrelation calculation on the local scattered displacement gradient field, and perform nonlinear curve fitting based on the spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain the global shear wave velocity distribution. And a material viscoelastic modulus characterization module, which is used to reconstruct the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution using an inversion algorithm, thereby characterizing the viscoelastic parameters of the material.

11. A computer storage medium, characterized in that, The computer storage medium stores a computer software product, the computer software product including several instructions for causing a computer device to execute the elastic imaging method based on the scattering displacement gradient field as described in any one of claims 1 to 9.

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