Elastic imaging method and system based on scattering displacement gradient field

Abstract

The present application relates to the technical field of medical elastic imaging and material multi-scale mechanical measurement, and particularly discloses an elastic imaging method and system based on a scattering displacement gradient field, which comprises the following steps: generating a scattering displacement field by arranging an excitation device around a target material, measuring an out-of-plane displacement gradient field by using transverse shear interference imaging, selecting a single-frame instantaneous gradient field or a frequency-domain gradient field obtained by time-frequency domain Fourier transform as a target field; obtaining a global shear wave velocity distribution by adaptive sliding window interception, two-dimensional autocorrelation calculation and Rayleigh wave spatial autocorrelation theoretical model fitting, and then reconstructing viscoelastic modulus distribution by using an inversion algorithm. The present application supports single-frame scattering displacement gradient field inversion elastic imaging, can be used without high-frame-rate equipment, has strong anti-environmental vibration interference ability and high system stability, is suitable for scenes with poor isolation conditions, has low cost, high efficiency and high measurement precision, and can meet the requirements of medical clinical diagnosis and material multi-scale mechanical measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical elastography and material multi-scale mechanical measurement, in particular to an elastic imaging method and system based on a scattering displacement gradient field. BACKGROUND

[0002] In the field of medical elastography and material multi-scale mechanical measurement, the accurate measurement of elastic modulus as a core characterization parameter is of great significance to clinical diagnosis and material performance evaluation. The elastic imaging technology based on shear wave velocity measurement has been widely used due to its non-invasive and quantitative advantages, but the traditional technology has significant bottlenecks: the transient wave method relies on high frame rate imaging equipment with thousands to tens of thousands of hertz to acquire the space-time displacement field, resulting in high equipment cost and difficulty in popularization in primary medical institutions; the reverberation wave method also relies on high frame rate equipment, and multiple boundary reflections are needed to form reverberation, which prolongs the measurement time and brings inconvenience to patients in medical scenarios.

[0003] To break through the above bottlenecks, patent CN120636711A proposes an elastic imaging method and system based on instantaneous scattering displacement field, which has the core advantage of exciting scattering displacement field by passive or active method, only requiring low frame rate imaging equipment (such as ordinary ultrasound, optical or nuclear magnetic equipment) to measure a single frame of instantaneous scattering displacement field, and through local interception by sliding window, two-dimensional autocorrelation calculation and theoretical model fitting, the shear wave velocity and viscoelastic modulus can be inverted, effectively reducing the dependence on high frame rate equipment, realizing low-cost and high-efficiency elastic imaging, and supporting material surface, section and three-dimensional volume multi-scene measurement, with strong compatibility, providing a convenient path for upgrading existing imaging equipment.

[0004] However, this technical solution still has obvious limitations: the scattering displacement field elastic imaging based on optical measurement usually uses ordinary interference imaging method to measure the displacement field, such as optical coherence imaging OCT and holographic interference imaging. However, ordinary interference imaging needs an independent and high-quality reference light wavefront, which has weak anti-vibration interference ability, low system stability, fixed high sensitivity and is easily affected by environmental noise, which affects the final elastic imaging effect in clinical environment or industrial field.

[0005] Therefore, in the field of medical tissue elastography and material multi-scale mechanical characterization, it is urgent to develop an elastic imaging method that is more resistant to environmental vibration interference. SUMMARY

[0006] To this end, the present application aims to solve the problem that the conventional optical shear wave elastography relies on ordinary interference imaging, resulting in weak anti-vibration interference ability. Speckle interferometry mainly includes two major technical branches of speckle interference based on reference light and shear speckle interference based on shear interference. 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 interference imaging uses a part of the measured wave front itself for interference, and through common path design, the influence of vibration on the two beams of light is consistent, without the need for a high-precision reference mirror, simplifying the optical path, having strong anti-vibration interference ability, high system stability, and being more suitable for use in industrial sites or clinical environments with poor shock isolation conditions.

[0007] The present application first directly applies shear interference to elastography, measures the displacement gradient field using shear interference imaging, derives the spatial autocorrelation theoretical formula of the displacement gradient field under Rayleigh waves, uses the spatial correlation of the scattered displacement gradient field to invert the elasticity, and uses an adaptive sliding window to improve the inversion accuracy, finally realizing the elastography based on the scattered displacement gradient field. The present application has the characteristics of high inversion accuracy, strong anti-vibration interference ability and high system stability.

[0008] The elastography method based on the scattered displacement gradient field comprises the following steps:

[0009] S1: According to the measurement site of the target material, a scattered displacement field excitation device is arranged on the periphery of the target material, and a scattered displacement field is generated in the target material region by driving the scattered displacement field excitation device with a driving signal;

[0010] S2: A lateral shear interference imaging technique is used to measure the out-of-plane displacement gradient field of the target material region with high spatial resolution, and an instantaneous scattered displacement gradient field or a time-space domain scattered displacement gradient field is obtained;

[0011] S3: For the instantaneous scattered displacement gradient field, a single frame of the instantaneous scattered displacement gradient field is selected as the target displacement gradient field; for the time-space domain scattered displacement gradient field, a time-frequency domain Fourier transform is performed on the time-space domain scattered displacement gradient field collected at a high frame rate to obtain a frequency domain displacement gradient field, which is used as the target displacement gradient field;

[0012] S4: The local scattered displacement gradient field in the target displacement gradient field is intercepted through an adaptive sliding window, two-dimensional autocorrelation calculation is performed 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;

[0013] S5: Based on the global shear wave velocity distribution, an inversion algorithm is used to reconstruct the viscoelastic modulus distribution of the target material region, and the characterization of the viscoelastic parameters of the material is realized.

[0014] In one embodiment of the present application, in S2, the method for measuring the lateral gradient field of the out-of-plane displacement of the target material region with high spatial resolution to obtain the instantaneous scattering displacement gradient field or the time-space domain scattering displacement gradient field is as follows:

[0015] S21: The lateral shearing interference image of the target material region is obtained by using the spatial carrier technology or the synchronous phase shift technology, and a phase extraction operation is performed on the lateral shearing interference image to obtain the wrapped phase difference ;

[0016] S22: The wrapped phase difference is judged for the fringe density: when the wrapped phase difference corresponding to the interference fringe density is not within the preset threshold range at any elastic wave driving frequency, the shearing amount of the shearing interference is adjusted , until the measurement requirement of the deformation of the target at any moment is met, and the adjusted wrapped phase difference information is obtained;

[0017] S23: The noise filtering processing is performed on the adjusted wrapped phase difference information to remove the environmental noise and the measurement noise, and the denoised wrapped phase difference information is obtained;

[0018] S24: The denoised wrapped phase difference information is unwrapped to obtain the global continuous phase difference information ; or the full-field phase value is constrained within the interval by reducing the scattering displacement field excitation amplitude, at which time the global phase is unwrapped, and the phase difference information is obtained;

[0019] S25: Based on the phase difference information , the shearing amount and the laser wavelength , the full-field out-of-plane displacement gradient field of the target material measurement region is obtained by the formula , which is the instantaneous scattering displacement gradient field corresponding to the deformation moment ; if the high-frame-rate continuous measurement mode is used, the time-space domain scattering displacement gradient field is obtained.

[0020] In one embodiment of the present application, in S21, the lateral shearing interference image of the target material region is obtained by using the spatial carrier technology or the synchronous phase shift technology, and a phase extraction operation is performed on the lateral shearing interference image to obtain the wrapped phase difference The method is as follows:

[0021] If the spatial carrier technology is used, a single exposure is used to collect a single frame of lateral shearing interference image , first Fourier transform the image, filter and extract the positive first-order spectrum component, then inverse Fourier transform the filtered spectrum component to obtain complex amplitude T; based on the complex amplitude of the initial moment and the complex amplitude of the current moment , calculate the wrapped phase difference between the two frames by formula , wherein represents the imaginary part of the complex amplitude, represents the real part of the complex amplitude;

[0022] If the synchronous phase shift technique is adopted, four frames of shearing interferograms with a single exposure are collected, and the four frames of shearing interferograms at the initial moment are denoted as , the four frames of shearing interferograms at the current moment are denoted as , , , , ; the phase information of the two groups of images is extracted by the four-step phase shift algorithm, and the wrapped phase difference between the two groups of data is calculated according to formula .

[0023] In one embodiment of the present application, in S4, the local scattering displacement gradient field in the target displacement gradient field is intercepted by an adaptive sliding window, two-dimensional autocorrelation calculation is performed on the local scattering displacement gradient field, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of the displacement gradient under Rayleigh wave to obtain the method for obtaining the global shear wave velocity distribution as follows:

[0024] S41: set the initial size of the adaptive sliding window as , move the adaptive sliding window to the current position to be processed in the target displacement gradient field, and intercept the local displacement gradient field data at the position;

[0025] S42: perform two-dimensional autocorrelation calculation on the local displacement gradient field data to obtain the first displacement gradient autocorrelation characteristic curve corresponding to the local area, wherein the curve takes the position difference as the horizontal coordinate, and the autocorrelation coefficient value corresponding to as the vertical coordinate;

[0026] S43: extract the horizontal coordinate value corresponding to the half peak height half peak width HWHM of the first displacement gradient autocorrelation characteristic curve to obtain the optimal sliding window size adapted to the current local area as , wherein is a preset constant for controlling the relationship between the adaptive sliding window size and the wavelength of the local area;

[0027] ​​S44: Based on the optimal sliding window size, re-intercepting the local displacement gradient field data of the current position, performing two-dimensional autocorrelation calculation on the data again to obtain the second displacement gradient autocorrelation characteristic curve corresponding to the local area;

[0028] S45: Introducing a spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave, fitting the second displacement gradient autocorrelation characteristic curve with the spatial autocorrelation theoretical model by using a nonlinear least squares fitting algorithm, and solving the shear wave velocity of the current local area through iterative calculation ;

[0029] S46: Controlling the adaptive sliding window to traverse the entire target material area by a preset step size, repeatedly executing steps S42-S45 for each traversed local area, sequentially solving the shear wave velocities of all local areas , and finally integrating the shear wave velocity data of all local areas to form the global shear wave velocity distribution of the target material area.

[0030] In an embodiment of the present application, the expression of the spatial autocorrelation theoretical model is as follows:

[0031] ; wherein, represents the two-dimensional autocorrelation function of the out-of-plane displacement transverse gradient , B0 is the zero-order Bessel function, B2 is the second-order Bessel function, k is the wave number, and ω is the angular frequency of the frequency-domain controllable sinusoidal wave signal of the driving scattered displacement field excitation device.

[0032] In an embodiment of the present application, in S5, based on the global shear wave velocity distribution, the method for reconstructing the viscoelastic modulus distribution of the target material area by using an inversion algorithm includes:

[0033] S51: Obtaining the density of the target material, establishing a nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus, and the expression is as follows:

[0034] , wherein, is the shear wave velocity, represents the elastic coefficient, and represents the viscosity coefficient;

[0035] S52: Keeping the local area division mode of the sliding window unchanged, changing the driving frequency of the driving signal, repeatedly executing steps S1-S4 to obtain the corresponding shear wave velocities of each local area at least two different driving frequencies​ , i.e. each local region corresponds to a set of shear wave velocity data , , n is the number of driving frequencies, and each value in the data set corresponds to a different driving frequency ;

[0036] S53: for each local region in the whole domain, the multi-frequency shear wave velocity data set of the region , and the driving signal angular frequency corresponding to each value is substituted into the nonlinear viscoelastic model, and a nonlinear fitting algorithm is used for fitting calculation to solve the viscoelastic parameters of the local region and , , is the spatial coordinate of the local region;

[0037] S54: traverse all local regions in the whole domain, integrate the and of each local region to form the elastic coefficient distribution and the viscosity coefficient distribution of the target material region, which together constitute the global viscoelastic modulus distribution.

[0038] In an embodiment of the present application, in S1, the method for generating a scattering displacement field in real time in the target material region is as follows:

[0039] Based on the type of the measurement site of the target material, a passive excitation method or an active excitation method is used to arrange an adaptive scattering displacement field excitation device in the peripheral region of the target material;

[0040] A sinusoidal wave signal with controllable frequency parameters is used as a driving source to apply a driving action to the scattering displacement field excitation device, so as to form a scattering displacement field in real time in the measurement region of the target material.

[0041] In an embodiment of the present application, the method for forming a scattering displacement field in real time in the measurement region of the target material by using a passive excitation method includes:

[0042] The scattering displacement field excitation device is composed of a surrounding excitation source and a plurality of scatterer units; based on the spatial characteristics of the measurement site of the target material, the surrounding excitation source and the plurality of scatterer units are arranged in the peripheral region of the measurement region of the target material, and the plurality of scatterer units are all within the space range enclosed by the surrounding excitation source; wherein the geometric structure parameters of the scatterer units obey random distribution, and the spatial arrangement is in a disordered state;

[0043] The ring-around excitation source is driven by a frequency domain controllable sine wave signal; the elastic wave generated after the ring-around excitation source is driven propagates along the target material to the plurality of scatterer units, generates a scattering effect through the physical action of the scatterer units, and after scattering, the elastic waves are superimposed on each other in the target material to be measured area, and finally form a scattering displacement field in real time;

[0044] The ring-around excitation source and the plurality of scatterer units are arranged in the peripheral area of the target material to be measured area as follows:

[0045] The plurality of scatterer units adopt a ring-shaped envelope layout and are conformally attached along the peripheral contour of the target material to be measured area, so that the scatterer units adapt to the boundary form of the to-be-measured area and are all within the space range enclosed by the ring-around excitation source.

[0046] 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.

[0047] In an embodiment of the present application, the method for forming a scattering displacement field in the target material to be measured area in real time by using an active excitation method comprises:

[0048] A plurality of point excitation source arrays with random spatial distribution are arranged in the peripheral area of the target material to be measured area; the plurality of point excitation sources are synchronously driven by a frequency domain controllable sine wave signal, the elastic waves excited by the plurality of point excitation sources are superimposed on each other, and thus the scattering displacement field is directly generated in the target material to be measured area in real time.

[0049] The plurality of point excitation source arrays with random spatial distribution are arranged in the peripheral area of the target material to be measured area as follows:

[0050] The plurality of point excitation source arrays adopt a boundary circumferential ring-around configuration and are conformally attached along the boundary contour of the target material to be measured area; the spatial distribution of each excitation unit needs to maintain randomness, and the overall ring-around range needs to adapt to the surface boundary of the to-be-measured area, so as to ensure that the elastic waves excited by each excitation unit can be uniformly superimposed on the surface of the to-be-measured area.

[0051] The size of each excitation unit in the plurality of point excitation source arrays is 0.1-10 times the shear wave wavelength, and the spacing between adjacent excitation units is negatively correlated with the total number of excitation units.

[0052] Based on the same inventive concept, the present application also provides an elastic imaging system based on a scattering displacement gradient field, which comprises a scattering 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 solving module, and a material viscoelastic modulus representation module.

[0053] The scattering displacement field excitation generation module is configured to arrange a scattering displacement field excitation device around a measurement site of the target material, drive the scattering displacement field excitation device with a frequency-controllable sinusoidal wave signal, and generate a scattering displacement field in the target material region.

[0054] The displacement gradient field measurement module is configured to measure the out-of-plane displacement gradient field of the target material region at a high spatial resolution to obtain an instantaneous scattering displacement gradient field or a time-space domain scattering displacement gradient field.

[0055] The target displacement gradient field screening and construction module is configured to select a single-frame instantaneous scattering displacement gradient field from the instantaneous scattering displacement gradient field as a target displacement gradient field, and perform time-frequency domain Fourier transform on the time-space domain scattering displacement gradient field collected at a high frame rate to obtain a frequency domain displacement gradient field as a target displacement gradient field.

[0056] The global shear wave velocity distribution solving module is configured to obtain a local scattering displacement gradient field in the target displacement gradient field by adaptive sliding window cutting, perform two-dimensional autocorrelation calculation on the local scattering displacement gradient field, and perform nonlinear curve fitting based on a spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain a global shear wave velocity distribution.

[0057] The material viscoelastic modulus characterization module is configured to reconstruct a viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution by using an inversion algorithm to realize characterization of material viscoelastic parameters.

[0058] The application further provides a computer storage medium storing a computer software product, and the computer software product includes a plurality of instructions for enabling a computer device to execute the scattering displacement gradient field-based elastic imaging method.

[0059] The above technical solution of the application has the following beneficial effects compared with the prior art:

[0060] The present application breaks through the technical path of existing elastic imaging technology relying on displacement field measurement, innovatively combines the characteristics of directly measuring the scattering displacement gradient field by shear interference imaging technology, fully gives play to the advantages of compact structure, large field of view, strong anti-interference ability, no need for shock isolation and adaptation to non-light-avoiding environment of the technology, greatly improves the environmental adaptability and operation convenience of elastic imaging; at the same time, the low frame rate device adaptation capability is continued, the analysis can be carried out by single frame instantaneous scattering displacement gradient field to carry out elastic imaging, without high-cost high frame rate equipment, taking into account low cost and high efficiency; with the help of self-adaptive sliding window local interception, two-dimensional autocorrelation calculation and nonlinear fitting of the spatial autocorrelation theoretical model of the displacement gradient under Rayleigh wave, the global shear wave velocity distribution can be accurately obtained, and the comprehensive characterization of viscoelastic parameters is realized by multi-frequency driving combined with the nonlinear viscoelastic model, and the measurement precision is higher; in addition, the passive excitation method and the active excitation method are compatible, and the medical clinical diagnosis and material multi-scale mechanical measurement are adapted, and high measurement precision, vibration environment adaptability and wide compatibility are possessed. BRIEF DESCRIPTION OF DRAWINGS

[0061] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings.

[0062] Figure 1 is a flowchart of an elastic imaging method based on a scattering displacement gradient field provided in an embodiment of the present application;

[0063] Figure 2 is a specific flowchart of an elastic imaging method based on a scattering displacement gradient field provided in an embodiment of the present application;

[0064] Figure 3 is a schematic diagram of the principle of material surface elastic imaging based on the passive excitation method in the experiment, random scatterer units and surrounding excitation sources are deployed in the peripheral region of the target region (ROI);

[0065] Figure 4 is the instantaneous displacement field on the material surface at different time points of 10 ms, 20 ms, 30 ms and 40 ms obtained in the experiment;

[0066] Figure 5 is the displacement gradient field measured in the experiment, the shear wave velocity distribution and the probability density distribution calculated by inversion;

[0067] Figure 6 is a structural schematic diagram of an elastic imaging system based on a scattering displacement gradient field provided in an embodiment of the present application.

[0068] The description of the drawings is as follows: 100, a scattered displacement field excitation generation module; 200, a displacement gradient field measurement module; 300, a target displacement gradient field screening and constructing module; 400, a global shear wave velocity distribution solving module; 500, a material viscoelastic modulus representing module;

[0069] 1, a scatterer unit; 2, a surrounding excitation source. DETAILED DESCRIPTION

[0070] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0071] Embodiment one:

[0072] Reference Figure 1 and Figure 2 It is shown that the present application provides an elastic imaging method based on scattered displacement gradient field, which specifically includes the following steps:

[0073] S1: According to the measurement site of the target material, a scattered displacement field excitation device is arranged on the periphery of the target material, and a driving signal is used to drive the scattered displacement field excitation device to generate a scattered displacement field in the target material region;

[0074] S2: Using transverse shear interference imaging technology, the out-of-plane displacement gradient field of the target material region is measured with high spatial resolution to obtain an instantaneous scattered displacement gradient field or a time-space domain scattered displacement gradient field ;

[0075] S3: For the instantaneous scattered displacement gradient field, a single-frame instantaneous scattered displacement gradient field is selected from the instantaneous scattered displacement gradient field as the target displacement gradient field; for the time-space domain scattered displacement gradient field, the time-space domain scattered displacement gradient field collected at a high frame rate is subjected to Fourier transform in the time-frequency domain to obtain a frequency domain displacement gradient field, which is taken as the target displacement gradient field;

[0076] S4: By means of an adaptive sliding window, a local scattered displacement gradient field in the target displacement gradient field is intercepted, two-dimensional autocorrelation calculation is performed 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 a global shear wave velocity distribution;

[0077] S5: Based on the global shear wave velocity distribution, an inversion algorithm is used to reconstruct the viscoelastic modulus distribution of the target material region, so as to realize the representation of the material viscoelastic parameters.

[0078] From the above technical solutions, the present application flexibly generates a scattering displacement field by passive or active excitation method suitable for the measurement site of the target material, directly obtains the instantaneous scattering displacement gradient field from a single shear interference image by means of shear interference measurement, and is strong against environmental vibration noise; supports single-frame instantaneous gradient field for direct elastic imaging, without high-cost high-frame-rate equipment, and takes into account convenience and low cost, or obtains the frequency domain gradient field through time-frequency domain Fourier transform after high-frame-rate acquisition and performs elastic imaging; through adaptive sliding window interception of local gradient field, two-dimensional autocorrelation calculation, and nonlinear fitting of the spatial autocorrelation theoretical model under Rayleigh waves, the global shear wave velocity distribution can be accurately obtained, and then through inversion algorithm and nonlinear viscoelastic model under multi-frequency driving, the comprehensive and accurate characterization of the viscoelastic modulus distribution of the material is realized, and the measurement precision is higher; in addition, the passive excitation method and the active excitation method are compatible, suitable for medical clinical diagnosis and material multi-scale mechanical measurement, and have high measurement precision, vibration environment adaptability and wide compatibility.

[0079] Further, in step S1, the method for generating a scattering displacement field in real time in the target material region is the same as that of patent CN120636711A, as follows:

[0080] Based on the type of the measurement site of the target material, passive excitation method or active excitation method is adopted, and an adaptive scattering displacement field excitation device is arranged in the peripheral region of the target material;

[0081] A frequency-controllable sinusoidal wave signal is used as an excitation source to drive the scattering displacement field excitation device, so as to form a scattering displacement field in real time in the target material to be measured.

[0082] Specifically, the method for forming a scattering displacement field in real time in the target material to be measured by using passive excitation method includes:

[0083] The scattering displacement field excitation device is composed of a surrounding excitation source and a plurality of scatterer units; based on the spatial characteristics of the target material to be measured, the surrounding excitation source and a plurality of scatterer units are arranged in the peripheral region of the target material to be measured, and the plurality of scatterer units are all within the space range surrounded by the surrounding excitation source; wherein the geometric structure parameters of the scatterer units obey random distribution, and the spatial arrangement is in a disordered state; the geometric shape of the scatterer unit includes but is not limited to columnar structure, hole structure, triangular structure, grid structure or ellipsoidal structure, etc.

[0084] The driving source is used to apply driving action to the surrounding excitation source; the elastic wave generated after the surrounding excitation source is driven propagates to the scatterer unit along the target material, produces scattering effect through the physical action of the scatterer unit, the scattered elastic wave is superimposed in the target material to be measured, and finally a scattering displacement field is formed in real time.

[0085] Optionally, in the above technical solution, the method of arranging the surround excitation source and the plurality of scatterer units in the peripheral region of the target material measurement region is as follows:

[0086] The plurality of scatterer units adopt a ring envelope layout and conformally attach along the peripheral contour of the target material measurement region, so that the scatterer units adapt to the boundary form of the measurement region and are all within the space range enclosed by the surround excitation source.

[0087] The spacing between adjacent scatterer units is negatively correlated with the total number of scatterer units, that is, the more the number of scatterer units, 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 high polymer material such as epoxy resin or silicone rubber, to ensure that the scatterer unit has effective scattering ability for elastic waves.

[0088] Specifically, the method of actively exciting to form a scatter displacement field in the target material measurement region includes:

[0089] In the peripheral region of the target material measurement region, a multi-point excitation source array with random spatial distribution is arranged; the multi-point excitation source is synchronously driven by a frequency domain controllable sine wave signal, and the elastic waves excited by multiple points are superimposed, thereby directly generating a scatter displacement field in the target material region in real time.

[0090] Optionally, in the above technical solution, the method of arranging the multi-point excitation source array with random spatial distribution in the peripheral region of the target material measurement region includes:

[0091] The multi-point excitation source array adopts a boundary circumferential surround configuration and realizes surround attachment along the boundary contour of the target material measurement region; the spatial distribution of each excitation unit needs to maintain randomness, and the overall surround range is adapted to the surface boundary of the measurement region, to ensure that the elastic waves excited by each excitation unit can form uniform superposition on the surface of the measurement region.

[0092] The size of each excitation unit in the multi-point excitation source array is 0.1-10 times the shear wave wavelength, to ensure that a single excitation unit has effective elastic wave excitation capability; at the same time, the spacing between adjacent excitation units is negatively correlated with the total number of excitation units, that is, the more the total number of excitation units, the smaller the spacing between adjacent units, to ensure the superposition effect of multiple elastic waves through reasonable spatial density.

[0093] Further, in the technical solution defined in the embodiment, the elastic wave excitation driving mode of the scattering displacement field excitation device at least covers any one of the following types in the process of realizing passive or active scattering displacement field excitation: mechanical driving, piezoelectric ceramic or thin film driving, acoustic radiation force driving, metal plate / metal patch type electromagnetic force driving, nano magnetic particles, laser thermal elastic driving.

[0094] In step S2, the out-of-plane displacement gradient field of the target material region is measured at a high spatial resolution, and the method for obtaining the instantaneous scattering displacement gradient field or the time-space domain scattering displacement gradient field is as follows:

[0095] S21: The spatial carrier wave technology or the synchronous phase shift technology is used to obtain the lateral shearing interference image of the target material region, and the phase extraction operation is performed on the lateral shearing interference image according to the corresponding technical process to obtain the wrapped phase difference , and the specific implementation steps are as follows:

[0096] If the spatial carrier wave technology is used: a single exposure is used to collect a single frame of lateral shearing interference image , the Fourier transform is first performed on the image, the positive first-order spectral component is extracted by filtering, and then the inverse Fourier transform is performed on the filtered spectral component to obtain the complex amplitude T; based on the complex amplitude at the initial moment and the complex amplitude at the current moment, the wrapped phase difference between the two frames is calculated by the formula , wherein represents the imaginary part of the complex amplitude, represents the real part of the complex amplitude;

[0097] If the synchronous phase shift technology is used: four frames of shearing interference images with phase shifts of 0、 、 、 in turn are collected by a single exposure, the four frames of shearing interference images at the initial moment are denoted as , and the four frames of shearing interference images at the current moment are denoted as 、 、 、 ; the phase information of the two groups of images is extracted by the four-step phase shift algorithm, and the wrapped phase difference between the two groups of data is calculated by the formula ;

[0098] S22: The interference fringe density of the wrapped phase difference is judged: when the interference fringe density corresponding to the wrapped phase difference at any elastic wave driving frequency is not within the preset threshold range, the shearing amount of the shearing interference is adjusted , until the measurement accuracy requirement of the deformation of the target at any time is met, and the adjusted wrapped phase difference information is obtained;

[0099] S23: Noise filtering processing is performed on the adjusted wrapped phase difference information, noise caused by environmental vibration interference, device measurement error, etc. is removed, and denoised wrapped phase difference information is obtained;

[0100] S24: The denoised wrapped phase difference information is unwrapped to obtain globally continuous phase difference information ; or by reducing the scattering displacement field excitation amplitude, the full-field phase value is constrained in interval, at this time, the full-field phase is unwrapped, and unwrapping operation is not needed, and the phase difference information is directly obtained, so that the real-time performance of phase measurement is improved;

[0101] S25: Based on the phase difference information , combined with the shear quantity and the laser wavelength , the full-field out-of-plane displacement gradient field of the target material to be measured is obtained through formula , which is the instantaneous scattering displacement gradient field corresponding to the deformation moment ; if a high frame rate continuous measurement method is used, the space-time domain scattering displacement gradient field can be further obtained.

[0102] Further, in step S24, for the denoised wrapped phase difference , the least square rounding method can be used for unwrapping operation to obtain globally continuous phase difference The specific implementation steps are as follows:

[0103] S241: Construct direction difference operator matrix and direction difference operator matrix , wherein is a dimensional matrix, and the expression is ; is a dimensional matrix, and the expression is , M and N are respectively the matrix row number and column number of the instantaneous wrapped phase difference .

[0104] S242: Based on the difference operator matrix and the difference operator matrix , the x-direction gradient and y-direction gradient of the wrapped phase difference are calculated, and the gradient field is constructed, wherein, denotes the transpose matrix of ;

[0105] S243: divide all elements in the gradient field by 2π and take the integer part, and take the negative of the integer part to generate the integer jump gradient field , where round is the rounding operator, and denote the x-direction integer jump gradient component and the y-direction integer jump gradient component, respectively;

[0106] S244: based on the x-direction integer jump gradient component , the y-direction integer jump gradient component , and the difference operator matrix and , construct the Lyapunov equation: , where the equation coefficient matrices A and B are defined as , , and the normal term matrix C is defined as , denotes the transpose matrix of ;

[0107] S245: solve the Lyapunov equation using the singular value decomposition method (SVD) to obtain the real jump matrix ;

[0108] S246: perform rounding operation on the real jump matrix to obtain the optimized integer jump matrix : ;

[0109] S247: based on the denoised wrapped phase difference and the optimized integer jump matrix , perform phase compensation operation to obtain the globally continuous unwrapped phase difference , and the calculation formula is: .

[0110] Further, in S4, the method for obtaining the global shear wave velocity distribution by adaptively sliding window to intercept the local scattering displacement gradient field in the target displacement gradient field, performing two-dimensional autocorrelation calculation on the local scattering displacement gradient field, and performing nonlinear curve fitting based on the spatial autocorrelation theoretical model of the displacement gradient under Rayleigh wave is as follows:

[0111] 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.

[0112] 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;

[0113] 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;

[0114] 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.

[0115] 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:

[0116] ;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;

[0117] 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.

[0118] Further, in S5, based on the global shear wave velocity distribution, the method for reconstructing the viscoelastic modulus distribution of the target material region by using an inversion algorithm includes:

[0119] S51: Obtain the density of the target material , and establish a nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus, which is expressed as follows:

[0120] , wherein, is the shear wave velocity, represents the elastic coefficient, represents the viscosity coefficient;

[0121] S52: Keep the local region division mode of the sliding window unchanged, and repeat steps S1-S4 by changing the driving frequency of the driving signal , to obtain the corresponding shear wave velocity of each local region under at least two different driving frequencies , that is, each local region corresponds to a set of shear wave velocity data , , n is the number of driving frequencies, and each value in the data set corresponds to a different driving frequency ;

[0122] S53: For each local region in the global region, the multi-frequency shear wave velocity data set of the region, and the driving signal angular frequency corresponding to each value are substituted into the nonlinear viscoelastic model, and a nonlinear fitting algorithm is used for fitting calculation to obtain the viscoelastic parameters and , of the local region.

[0123] S54: Traverse all local regions in the global region, integrate and of each local region to form the elastic coefficient distribution and the viscosity coefficient distribution of the target material region, which together constitute the global viscoelastic modulus distribution.

[0124] To further verify the effectiveness of the method, a passive excitation method is used to excite the scattering displacement field: scattering body units 1 and a surrounding excitation source 2 are arranged on the periphery of the target material region, and a frequency-domain controllable sinusoidal signal is used to drive the surrounding excitation source 2, which generates elastic waves that are scattered by the scattering body units 1 and then superimposed in real time in the target material region to form a scattering displacement field.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] Example 2:

[0129] 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.

[0130] The scattering displacement field excitation generation module 100 is configured to arrange a scattering displacement field excitation device around a measurement site of a target material, drive the scattering displacement field excitation device with a frequency-controllable sinusoidal wave signal, and generate a scattering displacement field in the target material region.

[0131] The displacement gradient field measurement module 200 is configured to measure the out-of-plane displacement gradient field of the target material region at a high spatial resolution to obtain an instantaneous scattering displacement gradient field or a time-space domain scattering displacement gradient field.

[0132] The target displacement gradient field screening and constructing module 300 is configured to select a single-frame instantaneous scattering displacement gradient field from the instantaneous scattering displacement gradient field as a target displacement gradient field, and perform time-frequency domain Fourier transform on the time-space domain scattering displacement gradient field collected at a high frame rate to obtain a frequency domain displacement gradient field as a target displacement gradient field.

[0133] The global shear wave velocity distribution solving module 400 is configured to obtain a local scattering displacement gradient field in the target displacement gradient field by sliding window interception, perform two-dimensional autocorrelation calculation on the local scattering displacement gradient field, and perform nonlinear curve fitting based on a spatial autocorrelation theoretical model of displacement gradient under Rayleigh wave to obtain a global shear wave velocity distribution.

[0134] The material viscoelastic modulus representing module 500 is configured to reconstruct the viscoelastic modulus distribution of the target material region based on the global shear wave velocity distribution by using an inversion algorithm to realize the representation of the material viscoelastic parameters.

[0135] Embodiment three:

[0136] The application further provides a computer storage medium storing a computer software product, and the computer software product includes a plurality of instructions for causing a computer device to execute the scattering displacement gradient field-based elastic imaging method in embodiment one.

[0137] Those skilled in the art should understand that the embodiments of the application can be provided as a method, a system, or a computer program product. Therefore, the application can adopt a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the application can adopt a computer program product in the form of one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0138] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flow or blocks Figure 1 one or more flow or blocks

[0139] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flow or blocks Figure 1 one or more flow or blocks

[0140] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flow or blocks Figure 1 one or more flow or blocks

[0141] Obviously, the above-described embodiments are only examples for clarity of description and are not limiting on the embodiments. Based on the above description, one of ordinary skill in the art can further make other different forms of changes or modifications. Here, all the embodiments are not required to be exhausted. The obvious changes or modifications derived from the above are still within the protection scope of the present application.

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 scattering displacement gradient field, perform a time-frequency domain Fourier transform on the spatiotemporal 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 region, 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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