Elastic imaging method and system based on instantaneous scattering displacement 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 an instantaneous scattering displacement field, and the method comprises the steps: driving a passive / active method scattering displacement field excitation device through a frequency domain controllable sine wave signal, and generating a scattering displacement field on a target material, an instantaneous displacement field is obtained through high spatial resolution measurement, then sliding window local interception, two-dimensional autocorrelation calculation and nonlinear fitting based on the Rayleigh / shear wave spatial autocorrelation theory are performed on the single-frame instantaneous displacement field, shear wave velocity distribution is obtained, and then the viscoelasticity modulus of a target area is inverted to achieve comprehensive characterization of the viscoelasticity of the material. According to the scheme, the single-frame scattering displacement field is excited and collected, and the elasticity inversion is performed based on the instantaneous displacement field, so that the dependence of traditional elasticity imaging on high-frame-rate equipment is broken through, the material viscoelasticity evaluation can be efficiently completed at low cost, and the application prospect in the fields of clinical diagnosis and mechanical measurement is wide.

Description

Technical Field

[0001] The present invention relates to the technical fields of medical elastic imaging and multi-scale mechanical measurement of materials, and in particular to an elastic imaging method and system based on transient scattering displacement field. Background Art

[0002] The measurement of material elastic modulus is of great significance in clinical diagnosis and mechanical measurement: in medicine, abnormal changes in tissue elastic modulus can reflect pathological changes in tissue, often earlier than traditional imaging detection; in mechanical measurement, elastic modulus is a basic parameter for evaluating the mechanical properties of materials. Elastic imaging technology based on shear wave velocity measurement (such as transient wave method and reverberation wave method) has been applied in the medical field in scenarios such as liver fibrosis grading, differentiation of benign and malignant breast tumors, and muscle injury assessment due to its non-invasive and quantitative advantages. However, existing technologies have significant bottlenecks:

[0003] The transient wave method excites transient shear waves through a driving source and uses high-frame-rate imaging devices such as ultrasound, optical imaging, and magnetic resonance imaging (MRI) to capture the temporal and spatial displacement field. Wave velocity and elastic modulus are then calculated using time- or frequency-domain algorithms. While this method offers high accuracy, it requires an extremely high frame rate for the imaging device (typically thousands to tens of kilohertz), resulting in high equipment costs and limited widespread adoption in primary healthcare settings.

[0004] Existing reverberation wave methods use a small number of driving points (typically ≤7) to excite a reverberant displacement field. High-frame-rate imaging equipment is then used to acquire the spatiotemporal displacement field. The spatiotemporal displacement field is then subjected to Fourier transform, localized sliding window capture, and a two-dimensional autocorrelation algorithm to calculate the wave velocity and elasticity distribution. Although this method has found application in medical applications such as corneal elasticity measurement and liver elasticity imaging, it still relies on high-frame-rate equipment to acquire the spatiotemporal displacement field. Furthermore, the small number of driving points requires multiple boundary reflections to generate reverberation, resulting in long measurement times in medical settings and prolonged breath-holding time for patients.

[0005] Therefore, there is an urgent need to develop a low-cost, high-efficiency elastic imaging method to break through the cost and efficiency bottleneck of high-frame-rate equipment in medical tissue elastic imaging and multi-scale mechanical characterization of materials, while ensuring measurement accuracy. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problems that existing elastic imaging technologies all rely on high frame rate imaging equipment to collect spatiotemporal displacement fields, resulting in high equipment costs and long measurement times.

[0007] To solve the above technical problems, the present invention provides an elastic imaging method and system based on transient scattered displacement field, the method comprising the following steps:

[0008] S1: Depending on the measurement location of the target material, an excitation device that generates a scattering displacement field by a passive or active method is placed on the surface or periphery of the target material. The excitation device is driven by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in real time within the target material area.

[0009] S2: measuring the out-of-plane scattering displacement field or the in-plane scattering displacement field of the target material region with high spatial resolution to obtain an instantaneous scattering displacement field;

[0010] S3: selecting a single frame of instantaneous scattering displacement field from the instantaneous scattering displacement field, processing the single frame of instantaneous scattering displacement field by local interception with a sliding window and two-dimensional autocorrelation calculation, and performing nonlinear curve fitting based on a spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain a shear wave velocity distribution;

[0011] S4: Based on the shear wave velocity distribution, an inversion algorithm is used to reconstruct the viscoelastic modulus distribution of the target material area to achieve a comprehensive characterization of the viscoelastic parameters of the material.

[0012] In one embodiment of the present invention, in S1, depending on the measurement location of the target material, an excitation device for passively generating a scattering displacement field is disposed on the surface or periphery of the target material, and the excitation device is driven by a frequency-domain controllable sinusoidal wave signal. The method for generating a scattering displacement field in real time within the target material region includes:

[0013] The excitation device includes a surrounding excitation source and a plurality of scatterer units. The surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material area according to different measurement locations of the target material. The plurality of scatterer units are located in a space formed by the surrounding excitation source, and their geometric structure parameters satisfy Gaussian random distribution and disordered spatial arrangement.

[0014] The surround excitation source is driven by a sinusoidal signal controllable in the frequency domain, and the elastic wave generated generates a scattering displacement field in the target material area after being scattered by the multiple scatterer units.

[0015] In one embodiment of the present invention, according to different measurement locations of the target material, the method of arranging the surround excitation source and the plurality of scatterer units on the surface or periphery of the target material area is as follows:

[0016] When measuring the surface elastic modulus of a material, the scatterer unit adopts a ring-shaped envelope layout and is conformally attached along the outer contour of the target material area;

[0017] When measuring the cross-sectional elastic modulus of a material, a thin film structure comprising the plurality of scatterer units is prepared and attached to the surface of the target material region, wherein the thickness of the scatterer unit is smaller than the wavelength of the shear wave excited by the excitation source.

[0018] In one embodiment of the present invention, the size of the scatterer units is 0.1 to 10 times the shear wave wavelength, and the spacing between the scatterer units is negatively correlated with the number of the scatterer units.

[0019] In one embodiment of the present invention, the elastic modulus of the scatterer unit is at least 10 times greater than that of the target material.

[0020] In one embodiment of the present invention, in S1, depending on the measurement location of the target material, an excitation device for generating a scattering displacement field by an active method is arranged on the surface or periphery of the target material, and the excitation device is driven by a frequency-domain controllable sinusoidal wave signal. The method for generating a scattering displacement field in real time within the target material region includes:

[0021] Multi-point excitation sources with random distribution are deployed on the surface or periphery of the target material. The multi-point excitation sources are driven by a frequency-domain controllable sinusoidal wave signal, so that the elastic waves excited by the multi-points are superimposed on each other, thereby directly generating a scattering displacement field in the target material area in real time.

[0022] In one embodiment of the present invention, a method for disposing an excitation device for generating a scattered displacement field by an active method on the surface or periphery of a target material according to different measurement locations thereof includes:

[0023] When measuring the elastic modulus of the material surface, the multi-point excitation source is attached around the boundary of the target area; when measuring the elastic modulus of the material section, the multi-point excitation source is attached to the surface of the target material area;

[0024] The size of each excitation unit in the multi-point excitation source is 0.1 to 10 times the shear wave wavelength, and the spacing between the excitation units is negatively correlated with the number of the excitation units.

[0025] In one embodiment of the present invention, the driving mode of the excitation device for generating elastic waves includes at least one of mechanical drive, piezoelectric ceramic drive, acoustic radiation force drive, metal plate or metal patch driven by electromagnetic force, and laser thermoelastic drive.

[0026] In one embodiment of the present invention, in S2, the method of performing high spatial resolution measurement on the out-of-plane scattering displacement field or the in-plane scattering displacement field of the target material region to obtain the instantaneous scattering displacement field includes:

[0027] Ultrasonic imaging, magnetic resonance imaging or optical imaging systems are used to measure the out-of-plane displacement field or in-plane displacement field of the target area with high spatial resolution to obtain the surface, two-dimensional cross-section or three-dimensional volume displacement distribution.

[0028] In one embodiment of the present invention, in S3, the single-frame instantaneous scattering displacement field is processed by local sliding window interception and two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain the shear wave velocity distribution as follows:

[0029] The instantaneous scattered displacement field is segmented into local regions by a sliding window convolution operator to obtain a local scattered displacement field. The local scattered displacement field is processed by a two-dimensional autocorrelation algorithm, and the Rayleigh wave cylindrical coordinate autocorrelation function or the shear wave rectangular coordinate autocorrelation function is selected according to the material measurement location:

[0030] For the off-plane displacement field measurement of the material surface, the measurement direction is perpendicular to the material surface, and the Rayleigh wave spatial autocorrelation model uses a cylindrical coordinate system:

[0031] ;

[0032] The Rayleigh wave velocity distribution is obtained by performing nonlinear least square fitting on the Rayleigh wave spatial autocorrelation function. , and then through the conversion formula , and obtain the shear wave velocity on the material surface ;

[0033] Calculating the shear wave velocity distribution of the entire field through the sliding window;

[0034] in, is the position difference in cylindrical coordinates, is the zero-order Bessel function, is the angular frequency, represents the out-of-plane displacement field, is Poisson's ratio;

[0035] For the off-plane displacement field measurement of the material section, the measurement direction is perpendicular to the material surface, and the shear wave spatial autocorrelation model uses a rectangular coordinate system:

[0036] ;

[0037] The shear wave velocity of the material section is obtained by performing nonlinear least square fitting on the shear wave spatial autocorrelation function. ;

[0038] Calculating the shear wave velocity distribution of the entire field through the sliding window;

[0039] in, is the horizontal position difference, and are zero-order and first-order spherical Bessel functions, is the angular frequency, represents the out-of-plane displacement field.

[0040] In one embodiment of the present invention, in S4, the method of reconstructing the viscoelastic modulus distribution of the target material region using an inversion algorithm based on the shear wave velocity distribution includes:

[0041] A nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established as follows:

[0042] ,in, is the shear wave velocity, and are the elastic and viscous coefficients, is the material density;

[0043] By changing the driving frequency of the sinusoidal wave signal, elastic waves of different frequencies are excited to propagate in the target material area, thereby calculating the shear wave velocity at different driving frequencies. ;

[0044] The nonlinear viscoelastic model is used to calculate the shear wave velocity at different frequencies actually measured. Perform nonlinear fitting to calculate the viscoelastic parameters of the target material area and .

[0045] Based on the same inventive concept, the present invention also provides an elastic imaging system based on transient scattered displacement field, comprising the following modules:

[0046] A scattering displacement field excitation generation module is used to deploy an excitation device that generates a scattering displacement field by a passive or active method on the surface or periphery of the target material according to the different measurement locations. The excitation device is driven by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in real time within the target material area.

[0047] An instantaneous displacement field measurement module is used to measure the out-of-plane displacement field or the in-plane displacement field of the target material area with high spatial resolution to obtain an instantaneous scattered displacement field;

[0048] a wave velocity inversion module, configured to select a single-frame instantaneous scattering displacement field from the instantaneous scattering displacement field, process the single-frame instantaneous scattering displacement field by local sliding window interception and two-dimensional autocorrelation calculation, and perform nonlinear curve fitting based on a spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain a shear wave velocity distribution;

[0049] and an elastic modulus quantitative evaluation module for reconstructing the viscoelastic modulus distribution of the target material region based on the shear wave velocity distribution using an inversion algorithm to achieve a comprehensive characterization of the material's viscoelastic parameters.

[0050] The present invention also provides an electronic device, which includes a processor, a memory and a bus system. The processor and the memory are connected via the bus system. The memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to implement the elastic imaging method based on the transient scattering displacement field.

[0051] The present invention also provides a computer storage medium storing a computer software product. The computer software product includes several instructions for enabling a computer device to execute the elastic imaging method based on transient scattering displacement field.

[0052] The above technical solution of the present invention has the following advantages over the prior art:

[0053] The present invention sets randomly distributed scatterer boundaries on the periphery or surface of the target area, and combines with an external driving source to instantly generate a high-quality scattering displacement field. Only low-frame-rate imaging equipment (such as ordinary ultrasound, optical or nuclear magnetic resonance equipment) is required to measure the instantaneous displacement field, without the need for high-frame-rate acquisition of spatiotemporal data, thus bypassing the bottleneck of high-cost equipment. The local displacement field is intercepted by a sliding window, and the shear wave velocity and elastic modulus are inverted through two-dimensional autocorrelation calculation and theoretical model fitting. Viscoelasticity evaluation can also be achieved through multi-frequency drive combined with the Voigt viscoelastic model. The invention has the advantages of low cost, compatibility with ordinary imaging equipment, high measurement efficiency, and the ability to achieve surface / cross-section / three-dimensional elastic imaging. It is expected that existing imaging equipment can be upgraded by adding scatterer accessories, showing broad application prospects and social and economic benefits in the fields of medical clinical screening and composite material quality control. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0055] Figure 1 1 is a flow chart of an elastic imaging method based on transient scattering displacement field provided in an embodiment of the present invention;

[0056] Figure 2 1 is a schematic diagram of a specific process of an elastic imaging method based on transient scattering displacement field provided in an embodiment of the present invention;

[0057] Figure 3This is a schematic diagram of the principle of material surface elastic imaging in Experiment 1 (passive scattering displacement field excitation device), in which random scatterer units and surrounding excitation sources are deployed outside the target region (ROI);

[0058] Figure 4 is the instantaneous displacement field on the material surface at different times of 9ms, 18ms, 27ms, and 36ms obtained in Experiment 1;

[0059] Figure 5 is the shear wave velocity distribution and probability density distribution calculated by inversion from the displacement field measured in Experiment 1;

[0060] Figure 6 This is a schematic diagram of the principle of material cross-section elastic imaging in Experiment 2 (passive method to excite the scattered displacement field), in which random scatterer units and surrounding excitation sources are deployed on the material surface;

[0061] Figure 7 is the instantaneous displacement field on the material section obtained in Experiment 2 at different times of 5ms, 10ms, 15ms, and 20ms;

[0062] Figure 8 The shear wave velocity distribution and probability density distribution are calculated by inverting the displacement field measured in Experiment 2;

[0063] Figure 9 This is a schematic diagram of the principle of material surface elastic imaging in Experiment 3 (active method to excite the scattered displacement field). In this method, multiple randomly distributed metal patches are deployed around the target material area as excitation sources. The metal coil is energized to generate electromagnetic force that drives the metal patches to directly generate the scattered displacement field.

[0064] Figure 10 is the instantaneous displacement field on the material surface at different times of 5ms, 10ms, 15ms, and 20ms obtained in Experiment 3;

[0065] Figure 11 The shear wave velocity distribution and probability density distribution are calculated by inverting the displacement field measured in Experiment 3;

[0066] Figure 12 This is a schematic diagram of the principle of material cross-section elastic imaging in Experiment 4 (active method to excite the scattered displacement field). In this method, multiple metal patches are randomly distributed on the surface of the target material as the excitation source. The electromagnetic force generated by energizing the metal coil drives the metal patches to directly generate the scattered displacement field.

[0067] Figure 13 is the instantaneous displacement field on the material section obtained in Experiment 4 at different times of 5ms, 10ms, 15ms, and 20ms;

[0068] Figure 14 The shear wave velocity distribution and probability density distribution are calculated by inverting the displacement field measured in Experiment 4;

[0069] Figure 15 is a structural schematic diagram of an elastic imaging system based on transient scattering displacement field provided in an embodiment of the present invention;

[0070] Description of the accompanying drawings: 1. Scattering unit; 2. Surrounding excitation source; 3. Metal coil; 4. Metal patch;

[0071] 100. Scattering displacement field excitation generation module; 200. Instantaneous scattering displacement field measurement module; 300. Wave velocity inversion module; 400. Elastic modulus quantitative evaluation module. DETAILED DESCRIPTION

[0072] 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 the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0073] Example 1:

[0074] like Figure 1 and Figure 2 As shown, the present invention provides an elastic imaging method and system based on transient scattering displacement field, the method comprising the following steps:

[0075] S1: Depending on the measurement location of the target material, an excitation device that generates a scattering displacement field by a passive or active method is placed on the surface or periphery of the target material. The excitation device is driven by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in real time within the target material area.

[0076] S2: measuring the out-of-plane scattering displacement field or the in-plane scattering displacement field of the target material region with high spatial resolution to obtain an instantaneous scattering displacement field;

[0077] S3: selecting a single frame of instantaneous scattering displacement field from the instantaneous scattering displacement field, performing local interception with a sliding window and two-dimensional autocorrelation calculation processing, and performing nonlinear curve fitting based on a spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain a shear wave velocity distribution;

[0078] S4: Based on the shear wave velocity distribution, an inversion algorithm is used to reconstruct the viscoelastic modulus distribution of the target material area to achieve a comprehensive characterization of the viscoelastic parameters of the material.

[0079] It can be seen from the above technical solutions that the present invention adopts a frequency-domain controllable sinusoidal wave signal to drive a passive or active scattering displacement field excitation device, instantly generates an isotropic high-quality scattering displacement field, and inverts the elastic distribution through a single-frame instantaneous scattering displacement field, avoiding the high-frame-rate time-space displacement field measurement that the transient wave method and the reverberation wave method rely on, and avoiding the long waiting time of multiple reflections that the traditional reverberation wave method relies on, thereby improving measurement efficiency; supporting high-spatial resolution measurement of off-plane displacement fields or in-plane displacement fields, covering multiple scenes of surfaces, sections and three-dimensional volumes, and realizing stereo elastic imaging; performing nonlinear fitting to calculate the shear wave velocity based on the Rayleigh wave / shear wave spatial autocorrelation theoretical model; combining the shear wave velocities at different frequencies obtained under multi-frequency excitation, introducing a viscoelastic model to invert the viscoelastic modulus, and realizing quantitative analysis of the viscoelasticity of the material.

[0080] Specifically, in this embodiment, in S1, depending on the measurement location of the target material, an excitation device for passively generating a scattering displacement field is disposed on the surface or periphery of the target material, and the excitation device is driven by a frequency-domain controllable sinusoidal wave signal. The method for generating a scattering displacement field in real time within the target material region includes:

[0081] The excitation device includes a surrounding excitation source and a plurality of scatterer units. The surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material area according to different measurement locations of the target material. The plurality of scatterer units are located in a space formed by the surrounding excitation source, and their geometric structure parameters (including size, azimuth angle, etc.) and material parameters satisfy Gaussian random distribution and disordered spatial arrangement. The geometric shape of the scatterer units includes but is not limited to a columnar structure, a hole structure, a triangular structure, a grating structure, or an ellipsoidal structure.

[0082] The surround excitation source is driven by a sinusoidal signal controllable in the frequency domain, and the elastic wave generated generates a scattering displacement field in the target material area after being scattered by the multiple scatterer units.

[0083] Specifically, in the above technical solution, according to different measurement locations of the target material, the method of arranging the surround excitation source and the plurality of scatterer units on the surface or periphery of the target material area is as follows:

[0084] When measuring the surface elastic modulus of a material, the plurality of scatterer units are arranged in an annular envelope and conformally attached along the outer contour of the target material area;

[0085] When measuring the cross-sectional elastic modulus of a material, a thin film structure comprising the plurality of scatterer units is prepared and attached to the surface of the target material region, wherein the thickness of the scatterer unit is smaller than the wavelength of the shear wave excited by the excitation source.

[0086] The size of the scatterer unit is 0.1-10 times the shear wave wavelength, and the spacing between adjacent scatterer units is negatively correlated with their number, that is, the spacing between the scatterer units decreases accordingly as the number of scatterers increases. The higher the number of scatterer units, the more significant the scattering effect, and it is easier to construct a high-quality scattering displacement field in real time.

[0087] The elastic modulus of the scatterer unit must be at least 10 times that of the medium being measured. Typical material systems include polymer materials such as epoxy resin and silicone rubber.

[0088] In addition to setting up a passive scattering displacement field excitation device on the surface or periphery of the target material to generate a scattering displacement field, an active scattering displacement field excitation device can also be used, as follows:

[0089] Deploying randomly distributed multi-point excitation sources on the surface or periphery of a target material, including: when measuring the surface elastic modulus of a material, the multi-point excitation sources are attached around the boundary of the target area; when measuring the cross-sectional elastic modulus of a material, the multi-point excitation sources are attached to the surface of the target material area; wherein the size of each excitation unit in the multi-point excitation source is 0.1 to 10 times the shear wave wavelength, and the spacing between the excitation units is negatively correlated with the number of the excitation units;

[0090] The multi-point excitation source is driven by a frequency-domain controllable sinusoidal wave signal, so that elastic waves excited at multiple points are superimposed on each other, thereby directly generating a scattering displacement field in the target material area in real time.

[0091] Furthermore, in this embodiment, the driving mode of the excitation device for generating elastic waves by passive or active methods includes at least one of mechanical drive, piezoelectric ceramic drive, acoustic radiation force drive, metal plate or metal patch driven by electromagnetic force, and laser thermoelastic drive.

[0092] Specifically, in this embodiment, in S2, an ultrasonic phased array tomography, a magnetic resonance elastography sequence or an optical imaging system is used to measure the out-of-plane displacement field ( or , displacement field perpendicular to the surface) or in-plane displacement field ( or , displacement field parallel to the surface) to perform high spatial resolution measurements and obtain surface, two-dimensional cross-sectional or three-dimensional volume displacement distributions.

[0093] Among them, surface measurement Used to characterize the two-dimensional displacement field of the material surface, z represents the direction of the out-of-plane displacement. In the field of medical ultrasound elastography, this characterization method is suitable for evaluating the biomechanical properties of superficial tissues such as the skin stratum corneum and corneal stroma. It is used to characterize the displacement distribution of the internal section of the material. The displacement component in the z-axis depth direction can be used to quantify the elastic parameters of deep tissue. This technology can be used in clinical applications to examine organs such as the liver and breast. Used to characterize the complete three-dimensional displacement field, realize stereo elastic imaging, and be used for the evaluation of complex anatomical structures.

[0094] Specifically, in this embodiment, in S3, the single-frame instantaneous scattering displacement field is processed by local sliding window interception and two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain the shear wave velocity distribution as follows:

[0095] The instantaneous scattered displacement field is segmented into local regions by a sliding window convolution operator to obtain a local scattered displacement field. The local scattered displacement field is processed by a two-dimensional autocorrelation algorithm, and the Rayleigh wave cylindrical coordinate autocorrelation function or the shear wave rectangular coordinate autocorrelation function is selected according to the material measurement location:

[0096] For the off-plane displacement field measurement of the material surface, the measurement direction is perpendicular to the material surface, and the Rayleigh wave spatial autocorrelation model uses a cylindrical coordinate system:

[0097] ;

[0098] The Rayleigh wave velocity distribution is obtained by performing nonlinear least square fitting on the Rayleigh wave spatial autocorrelation function. , and then through the conversion formula , and obtain the shear wave velocity on the material surface ; Calculate the shear wave velocity distribution of the entire field through the sliding window;

[0099] in, is the position difference in cylindrical coordinates, is the zero-order Bessel function, is the angular frequency, represents the out-of-plane displacement field; is Poisson's ratio.

[0100] For the off-plane displacement field measurement of the material section, the measurement direction is perpendicular to the material surface, and the shear wave spatial autocorrelation model uses a rectangular coordinate system:

[0101] ;

[0102] The shear wave velocity of the material section is obtained by performing nonlinear least square fitting on the corresponding spatial autocorrelation function. ;

[0103] Calculating the shear wave velocity distribution of the entire field through the sliding window;

[0104] in, is the horizontal position difference, and are zero-order and first-order spherical Bessel functions, is the angular frequency, Specifically, in this embodiment, in S4, the method of reconstructing the viscoelastic modulus distribution of the target material region using an inversion algorithm based on the shear wave velocity includes:

[0105] The Voigt-Kelvin nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established as follows:

[0106] ,in, is the shear wave velocity, and are the elastic and viscous coefficients, is the material density;

[0107] By changing the driving frequency of the sinusoidal wave signal, elastic waves of different frequencies are excited to propagate in the target material area, thereby calculating the shear wave velocity at different driving frequencies. ;

[0108] The nonlinear viscoelastic model is used to calculate the shear wave velocity at different frequencies actually measured. Perform nonlinear fitting to calculate the viscoelastic parameters of the target material area and .

[0109] To further validate the effectiveness of this method, a passive method was first employed to excite the scattered displacement field. Scattering units 1 and surrounding excitation sources 2 were deployed on the surface or periphery of the target material region. Excitation source 2 was driven by a frequency-domain controllable sinusoidal signal. The generated elastic waves, after being scattered by scattering units 1, generated a scattered displacement field in real time within the target material region. Multiple sets of experiments were designed to verify the method's high measurement efficiency and its ability to perform surface, cross-section, and three-dimensional multimodal elastic imaging.

[0110] Experiment 1: Tissue Surface Elasticity Imaging (Passive Excitation Scattering Displacement Field)

[0111] The scattering displacement field is excited by the passive method, and a finite element model is established to numerically simulate the wave propagation process on the tissue surface, and the elastic distribution is inverted based on the displacement field obtained by simulation. Figure 3 As shown, the geometric parameters of the simulated material are: thickness 2cm, diameter 4cm, density , shear modulus 1kPa, corresponding to the theoretical shear wave velocity =1m / s. The scatterer unit is a distributed scatterer unit structure, consisting of 64 rectangular scatterer units 1, distributed in a ring around the target material area. The dimensions of a single scatterer unit 1 are 0.7mm × 0.7mm × 2mm, with a shear modulus of 70kPa. The spatial layout of the scatterer units satisfies the random distribution characteristics of a two-dimensional Poisson point process. The surround excitation source 2 is driven by an 800Hz sinusoidal signal, and the generated Rayleigh waves are scattered by the scatterer units and propagate toward the target area.

[0112] Figure 4 Shows the out-of-plane displacement field at different times ( ) cloud map, the results show that: the scatterer unit can effectively scatter regular elastic waves with high quality, and a high-quality scattered displacement field has been formed at t=26ms. A local area with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and a two-dimensional autocorrelation calculation is performed on the displacement field of this area. Based on the Rayleigh wave autocorrelation theoretical model Perform nonlinear least squares fitting and invert to obtain the shear wave velocity distribution. By sliding the window across the entire field, the shear wave velocity probability density distribution is obtained, such as Figure 5 As shown in the figure, its statistical mean is highly consistent with the theoretical value of 1m / s, which verifies the effectiveness and reliability of the algorithm.

[0113] The simulation results show that the Rayleigh waves driven by the surround excitation source 2 can generate a high-quality scattering displacement field through the scatterer unit 1. Combined with the two-dimensional autocorrelation algorithm and the Rayleigh wave spatial autocorrelation theoretical model, accurate inversion of tissue surface elastic parameters can be achieved.

[0114] Experiment 2: Material Cross-Section Elasticity Imaging (Passive Excitation Scattering Displacement Field)

[0115] The passive method is used to excite the scattered displacement field, and a finite element model is established to carry out numerical simulation of the wave propagation characteristics inside the tissue, and the elastic distribution is inverted based on the displacement field obtained by simulation. Figure 6 As shown, the geometric size of the simulated material is 3.7cm×3.7cm×2cm, and the material parameters are set as follows: density , shear modulus μ = 1kPa, corresponding to the theoretical shear wave velocity =1m / s. The scatterer unit utilizes a thin layer structure containing scattering elements (equivalent to the topology of a QR code), with overall dimensions of 3.7cm×3.7cm×0.05cm and a shear modulus of 70kPa. The hollowed-out area consists of square scatterer elements 1 (1.25mm side length, 0.5mm depth). The spatial distribution of the scatterer elements follows a two-dimensional Gaussian random process. A sinusoidal signal with a frequency of f=800Hz drives the surrounding excitation source 2 on the surface. The generated elastic waves are scattered by the scatterer elements and propagate into the material.

[0116] Figure 7 Shows the out-of-plane displacement field on the section at different times ( ) distribution, the results show that: the scatterer unit can effectively scatter regular elastic waves with high quality, and a high-quality scattering displacement field has been formed at t=17ms. A local area with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and a two-dimensional autocorrelation calculation is performed on the displacement field of this area. Based on the shear wave autocorrelation theoretical model Perform nonlinear fitting and inversion to obtain the shear wave velocity distribution. Slide the window across the entire section to generate a shear wave velocity probability density map, such as Figure 8 As shown in Figure 3, the statistical results are highly consistent with the theoretical value of 1 m / s, which verifies the effectiveness of this method in inverting the internal elastic parameters of the material.

[0117] The simulation results show that the shear waves driven by the surrounding excitation source can generate high-quality scattered displacement fields through scatterer units. Combined with the two-dimensional autocorrelation algorithm and the shear wave spatial autocorrelation theoretical model, it is possible to achieve accurate quantitative evaluation of the elastic modulus of materials inside tissues.

[0118] To further verify the effectiveness of the method of this application, an active method is used to excite the scattered displacement field. Multi-point metal patches 4 are randomly distributed on the surface or periphery of the target material as excitation sources. The metal coil 3 is energized to generate electromagnetic force to drive the metal patches 4 to directly generate a scattered displacement field. Multiple sets of experiments are designed to verify its high measurement efficiency and surface / cross-section / three-dimensional multimodal elastic imaging capabilities.

[0119] Experiment 3: Material Surface Elastic Imaging (Active Method Exciting Scattering Displacement Field)

[0120] The active method is used to excite the scattered displacement field, and a finite element model is established to numerically simulate the wave propagation process on the tissue surface, and the elastic distribution is inverted based on the simulated displacement field. Figure 9 As shown, the geometric parameters of the simulated material are: thickness 2cm, diameter 4cm, density , shear modulus 1kPa, corresponding to the theoretical shear wave velocity =1m / s. 64 rectangular metal patches 4 are attached to the surface, distributed in a ring shape around the periphery of the target material area. The size of a single metal patch 4 is Its spatial layout satisfies the random distribution characteristics of a two-dimensional Poisson point process. By energizing the metal coil 3 to generate a periodic magnetic field, the metal patch 4 is driven to excite 800Hz Rayleigh waves. The multi-point driven Rayleigh waves ultimately generate a scattered displacement field that propagates toward the target area.

[0121] Figure 10 Shows the out-of-plane displacement field at different times ( ) cloud map, the results show that: electromagnetic force driving the randomly distributed metal patch 4 can effectively induce scattered elastic waves, and a high-quality scattered displacement field has been formed at t = 26ms. A local area with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and a two-dimensional autocorrelation calculation of the displacement field in this area is performed. Based on the Rayleigh wave autocorrelation theoretical model Perform nonlinear least squares fitting and invert to obtain the shear wave velocity distribution. Slide the window across the entire field to obtain the velocity probability density distribution, such as Figure 11 As shown in Figure 3, its statistical mean is highly consistent with the theoretical value of 1 m / s, which verifies the effectiveness of this method in inverting the surface elastic parameters of materials.

[0122] The simulation results show that electromagnetic force driving randomly distributed metal patches 4 can directly generate high-quality scattering displacement fields. Combined with the two-dimensional autocorrelation algorithm and the Rayleigh wave spatial autocorrelation theoretical model, it can achieve accurate inversion of tissue surface elastic parameters.

[0123] Experiment 4: Material Section Elasticity Imaging (Active Excitation Scattering Displacement Field)

[0124] The active method is used to excite the scattered displacement field, and a finite element model is established to carry out numerical simulation of the wave propagation characteristics inside the tissue, and the elastic distribution is inverted based on the displacement field obtained by simulation. Figure 12 As shown, the geometric size of the simulated material is 3.7cm×3.7cm×2cm, and the material parameters are set as follows: density ρ=10 3 kg / m 3 , shear modulus μ = 1kPa, corresponding to the theoretical shear wave velocity = 1m / s. Randomly distributed metal patches 4 are attached to the material surface. Each metal patch 4 measures 1.25mm × 1.25mm × 0.5mm, and its spatial distribution follows a two-dimensional Gaussian random process. By energizing the metal coil 3 to generate a periodic magnetic field, the metal patches 4 are driven to excite 800Hz shear waves. These multi-point driven shear waves ultimately generate a scattered displacement field that propagates toward the target area.

[0125] Figure 13 Shows the out-of-plane displacement field on the section at different times ( ) distribution, the results show that the electromagnetic force driving the randomly distributed metal patch 4 can effectively excite the scattered shear wave, and a high-quality scattered displacement field is formed at t=17ms. A local area with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and the two-dimensional autocorrelation calculation of the displacement field in this area is performed. Based on the shear wave autocorrelation theoretical model Perform nonlinear fitting and inversion to obtain the shear wave velocity distribution. Slide the window across the entire section to generate a velocity probability density map, such as Figure 14As shown in Figure 3, the statistical results are highly consistent with the theoretical value of 1 m / s, which verifies the effectiveness of this method in inverting the internal elastic parameters of the material.

[0126] This simulation result also proves that electromagnetic force driving randomly distributed metal patches 4 can directly generate high-quality scattering displacement fields. Combined with the two-dimensional autocorrelation algorithm and the shear wave spatial autocorrelation theoretical model, it can achieve accurate quantitative evaluation of the elastic modulus inside the tissue.

[0127] In summary, the elastic imaging technology described in the present invention, due to its low cost, high efficiency, compatibility, and the absence of high-frame-rate equipment, can be widely expanded to the following scenarios, significantly improving the universality and clinical value of material elasticity assessment:

[0128] Based on the application scenario of medical elastography, when evaluating superficial tissues, such as in the field of dermatology, the elasticity test of the skin can assist in the diagnosis of skin aging, pathological changes in the skin, etc. In ophthalmology, it can be used to measure corneal elasticity, help diagnose corneal diseases such as keratoconus, and provide a basis for early screening and accurate diagnosis of corneal diseases. For deep organs, such as in the diagnosis of liver diseases, by measuring the elasticity of liver tissue, it can help in the early detection and disease monitoring of liver fibrosis, cirrhosis and liver tumors; in the diagnosis and treatment of breast diseases, it can assist in distinguishing between benign and malignant breast tumors, improve the accuracy of early diagnosis of breast cancer, and provide key information for the formulation of subsequent treatment plans.

[0129] In the application scenario of multi-scale mechanical measurement of materials, the method described in the present invention can be used to achieve multi-scale mechanical property measurement of materials. For example, by embedding silica particles with a size comparable to the shear wave wavelength of the measured material on the surface of the material as scatterers, and laying thin-film metal patches on the surface of the material, sine wave signals of different frequencies are used to act on the metal coil to generate electromagnetic forces to drive elastic waves. After the elastic waves are scattered, a scattering displacement field is formed. After sub-micron-level measurement of the scattering displacement field, the shear wave velocity distribution is obtained through two-dimensional spatial autocorrelation calculation and nonlinear fitting, and then the viscoelastic modulus distribution of the material is inverted, thereby achieving multi-scale mechanical property characterization from micron to centimeter level.

[0130] Example 2:

[0131] Based on the same inventive concept as that of the first embodiment, the present invention further provides an elastic imaging system based on a transient scattering displacement field, which is used to implement the steps of the elastic imaging method based on a transient scattering displacement field described in the first embodiment. Figure 15 As shown, the elastic imaging system based on the instantaneous scattering displacement field includes: a scattering displacement field excitation generation module 100, an instantaneous scattering displacement field measurement module 200, a wave velocity inversion module 300 and an elastic modulus quantitative evaluation module 400; wherein,

[0132] The scattering displacement field excitation generation module 100 is used to set a passive or active scattering displacement field excitation device on the periphery or surface of the target material area to instantly generate a scattering displacement field on the target material area;

[0133] The instantaneous scattered displacement field measurement module 200 is used to perform high spatial resolution measurement on the out-of-plane displacement field or in-plane displacement field of the target material area to obtain the instantaneous scattered displacement field;

[0134] The velocity inversion module 300 is used to select a single frame of the instantaneous scattering displacement field from the instantaneous scattering displacement field, perform local interception with a sliding window and two-dimensional autocorrelation calculation processing, and perform nonlinear curve fitting based on the spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain the shear wave velocity distribution;

[0135] The elastic modulus quantitative evaluation module 400 is used to invert the elastic modulus distribution of the target material region based on the shear wave velocity, thereby achieving a comprehensive characterization of the material's viscoelasticity.

[0136] This embodiment proposes an elastic imaging system based on an instantaneous scattering displacement field, which is used to implement the aforementioned elastic imaging method based on an instantaneous scattering displacement field. Therefore, the specific implementation of the elastic imaging system based on an instantaneous scattering displacement field can be found in the aforementioned embodiment of the elastic imaging method based on an instantaneous scattering displacement field. For example, the scattering displacement field excitation generation module 100, the scattering displacement field measurement module 200, the wave velocity inversion module 300, and the elastic modulus quantitative evaluation module 400 are respectively used to implement steps S1, S2, S3, and S4 of the elastic imaging method based on an instantaneous scattering displacement field in the first embodiment. Therefore, the specific implementation of the system can refer to the description of the corresponding embodiments. To avoid redundancy, it will not be repeated here.

[0137] Example 3:

[0138] The present invention also provides an electronic device, comprising a processor, a memory, and a bus system, wherein the processor and the memory are connected via the bus system, the memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to implement the elastic imaging method based on the transient scattering displacement field described in Example 1.

[0139] Example 4:

[0140] The present invention also provides a computer storage medium storing a computer software product. The computer software product includes several instructions for enabling a computer device to execute the elastic imaging method based on transient scattering displacement field described in Example 1.

[0141] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0142] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for elastic imaging based on transient scattering displacement field, characterized in that: The following steps are involved: S1: Depending on the measurement location of the target material, an excitation device that generates a scattering displacement field by a passive or active method is placed on the surface or periphery of the target material. The excitation device is driven by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in real time within the target material area. S2: measuring the out-of-plane scattering displacement field or the in-plane scattering displacement field of the target material region with high spatial resolution to obtain an instantaneous scattering displacement field; S3: selecting a single frame of instantaneous scattering displacement field from the instantaneous scattering displacement field, processing the single frame of instantaneous scattering displacement field by local interception with a sliding window and two-dimensional autocorrelation calculation, and performing nonlinear curve fitting based on a spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain a shear wave velocity distribution; S4: Based on the shear wave velocity distribution, an inversion algorithm is used to reconstruct the viscoelastic modulus distribution of the target material area to achieve a comprehensive characterization of the viscoelastic parameters of the material.

2. The elastic imaging method based on transient scattered displacement field according to claim 1, characterized in that: In S1, depending on the measurement location of the target material, an excitation device for passively generating a scattering displacement field is arranged on the surface or periphery of the target material, and the excitation device is driven by a frequency-domain controllable sinusoidal wave signal. The method for generating a scattering displacement field in real time within the target material region includes: The excitation device includes a surrounding excitation source and a plurality of scatterer units. The surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material area according to different measurement locations of the target material. The plurality of scatterer units are located in a space formed by the surrounding excitation source, and their geometric structure parameters satisfy Gaussian random distribution and disordered spatial arrangement. The surround excitation source is driven by a sinusoidal signal controllable in the frequency domain, and the elastic wave generated generates a scattering displacement field in the target material area after being scattered by the multiple scatterer units.

3. The elastic imaging method based on transient scattering displacement field according to claim 2, characterized in that: Depending on the measurement location of the target material, the method of arranging the surround excitation source and the plurality of scatterer units on the surface or periphery of the target material area is as follows: When measuring the surface elastic modulus of a material, the plurality of scatterer units are arranged in an annular envelope and conformally attached along the outer contour of the target material area; When measuring the cross-sectional elastic modulus of the material, a thin film structure comprising the plurality of scatterer units is prepared and attached to the surface of the target material region, wherein the thickness of the scatterer unit is less than the wavelength of the shear wave excited by the excitation source; The size of the scatterer unit is 0.1 to 10 times the shear wave wavelength, and the spacing between the scatterer units is negatively correlated with the number of the scatterer units; the elastic modulus of the scatterer unit is at least 10 times greater than that of the target material.

4. The elastic imaging method based on transient scattering displacement field according to claim 1, characterized in that: In S1, depending on the measurement location of the target material, an excitation device for generating a scattered displacement field by an active method is arranged on the surface or periphery of the target material, and the excitation device is driven by a frequency-domain controllable sinusoidal wave signal. The method for generating a scattered displacement field in real time within the target material area includes: Multi-point excitation sources with random distribution are deployed on the surface or periphery of the target material. The multi-point excitation sources are driven by a frequency-domain controllable sinusoidal wave signal, so that the elastic waves excited by the multi-points are superimposed on each other, thereby directly generating a scattering displacement field in the target material area in real time.

5. The elastic imaging method based on transient scattered displacement field according to claim 4, characterized in that: Depending on the measurement location of the target material, the methods for arranging an excitation device on its surface or periphery to generate a scattered displacement field by an active method include: When measuring the surface elastic modulus of a material, the multi-point excitation source is attached around the boundary of the target area; When measuring the elastic modulus of a material section, the multi-point excitation source is attached to the surface of the target material area; The size of each excitation unit in the multi-point excitation source is 0.1 to 10 times the shear wave wavelength, and the spacing between the excitation units is negatively correlated with the number of the excitation units.

6. The elastic imaging method based on transient scattered displacement field according to claim 1, characterized in that: The driving mode of the excitation device for generating elastic waves includes at least one of mechanical driving, piezoelectric ceramic driving, acoustic radiation force driving, electromagnetic force driving of a metal plate or metal patch, and laser thermoelastic driving.

7. The elastic imaging method based on transient scattered displacement field according to claim 1, characterized in that: In S2, the method of performing high spatial resolution measurement on the out-of-plane scattering displacement field or the in-plane scattering displacement field of the target material region to obtain the instantaneous scattering displacement field includes: Ultrasonic imaging, magnetic resonance imaging or optical imaging systems are used to measure the out-of-plane displacement field or in-plane displacement field of the target area with high spatial resolution to obtain the surface, two-dimensional cross-section or three-dimensional volume displacement distribution.

8. The elastic imaging method based on transient scattering displacement field according to claim 1, characterized in that: In S3, the single-frame instantaneous scattering displacement field is processed by local sliding window interception and two-dimensional autocorrelation calculation, and nonlinear curve fitting is performed based on the spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain the shear wave velocity distribution as follows: The instantaneous scattered displacement field is segmented into local regions by a sliding window convolution operator to obtain a local scattered displacement field. The local scattered displacement field is processed by a two-dimensional autocorrelation algorithm, and the Rayleigh wave cylindrical coordinate autocorrelation function or the shear wave rectangular coordinate autocorrelation function is selected according to the material measurement location: For the off-plane displacement field measurement of the material surface, the measurement direction is perpendicular to the material surface, and the Rayleigh wave spatial autocorrelation function uses the cylindrical coordinate system: ； The Rayleigh wave velocity distribution is obtained by performing nonlinear least square fitting on the Rayleigh wave spatial autocorrelation function. , and then through the conversion formula , and obtain the shear wave velocity on the material surface ; Calculating the shear wave velocity distribution of the entire field through the sliding window; in, is the position difference in cylindrical coordinates, is the zero-order Bessel function, is the angular frequency, represents the out-of-plane displacement field, is Poisson's ratio; For the off-plane displacement field measurement of the material section, the measurement direction is perpendicular to the material surface, and the shear wave spatial autocorrelation function uses the rectangular coordinate system: ； The shear wave velocity of the material section is obtained by performing nonlinear least square fitting on the shear wave spatial autocorrelation function. ; Calculating the shear wave velocity distribution of the entire field through the sliding window; in, is the horizontal position difference, and are zero-order and first-order spherical Bessel functions, is the angular frequency, represents the out-of-plane displacement field.

9. The elastic imaging method based on transient scattered displacement field according to claim 8, characterized in that: In S4, based on the shear wave velocity distribution, the method of reconstructing the viscoelastic modulus distribution of the target material region using an inversion algorithm includes: A nonlinear viscoelastic model of shear wave velocity and material viscoelastic modulus is established as follows: ,in, is the shear wave velocity, and are the elastic and viscous coefficients, is the material density; By changing the driving frequency of the sinusoidal wave signal, elastic waves of different frequencies are excited to propagate in the target material area, thereby calculating the shear wave velocity at different driving frequencies. ; The nonlinear viscoelastic model is used to calculate the shear wave velocity at different frequencies actually measured. Perform nonlinear fitting to calculate the viscoelastic parameters of the target material area and .

10. An elastic imaging system based on transient scattering displacement field, characterized in that: Includes the following modules: A scattering displacement field excitation generation module is used to deploy an excitation device that generates a scattering displacement field by a passive or active method on the surface or periphery of the target material according to the different measurement locations. The excitation device is driven by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in real time within the target material area. An instantaneous displacement field measurement module is used to measure the out-of-plane displacement field or the in-plane displacement field of the target material area with high spatial resolution to obtain an instantaneous scattered displacement field; a wave velocity inversion module, configured to select a single-frame instantaneous scattering displacement field from the instantaneous scattering displacement field, process the single-frame instantaneous scattering displacement field by local sliding window interception and two-dimensional autocorrelation calculation, and perform nonlinear curve fitting based on a spatial autocorrelation theoretical model of Rayleigh waves or shear waves to obtain a shear wave velocity distribution; and an elastic modulus quantitative evaluation module for reconstructing the viscoelastic modulus distribution of the target material region based on the shear wave velocity distribution using an inversion algorithm to achieve a comprehensive characterization of the material's viscoelastic parameters.

11. An electronic device, characterized in that: The electronic device includes a processor, a memory, and a bus system, wherein the processor and the memory are connected via the bus system, the memory is used to store instructions, and the processor is used to execute the instructions stored in the memory to implement the elastic imaging method based on the transient scattered displacement field according to any one of claims 1 to 9.

12. A computer storage medium, characterized in that The computer storage medium stores a computer software product, and the computer software product includes several instructions for enabling a computer device to execute the elastic imaging method based on transient scattered displacement field according to any one of claims 1 to 9.

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