Elastic imaging method and system based on instantaneous scattering displacement 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 instantaneous scattering displacement field, which comprises the following steps: driving a passive / active scattering displacement field excitation device by a frequency domain controllable sinusoidal wave signal to generate a scattering displacement field on a target material, acquiring an instantaneous displacement field through high spatial resolution measurement, performing local interception on a single frame of instantaneous displacement field through a sliding window, performing two-dimensional autocorrelation calculation, and performing nonlinear fitting based on Rayleigh / shear wave spatial autocorrelation theory to obtain shear wave velocity distribution, and then inverting viscoelastic modulus of a target region to realize comprehensive characterization of material viscoelasticity. The scheme breaks through the dependence of traditional elastic imaging on high frame rate equipment by exciting and collecting a single frame of scattering displacement field and performing elastic inversion based on instantaneous displacement field, and can efficiently complete material viscoelasticity evaluation at low cost, and has wide application prospect in the fields of clinical diagnosis and mechanical measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical elastography and material multi-scale mechanical measurement, and particularly to an elastography method and system based on instantaneous scattering displacement field. BACKGROUND

[0002] 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 the tissue, and are often earlier than traditional imaging detection; in mechanical measurement, elastic modulus is a basic parameter for evaluating the mechanical properties of materials. Elastography technology based on shear wave velocity measurement (such as transient wave method and reverberation wave method) has been applied in medical fields such as liver fibrosis grading, breast tumor benign and malignant differentiation, muscle injury evaluation, etc. due to its non-invasive and quantitative advantages. However, the existing technology has significant bottlenecks:

[0003] The transient wave method excites a transient shear wave by a driving source, and uses high-frame-rate imaging devices such as ultrasound, optical imaging, and magnetic resonance imaging (MRI) devices to collect the spatiotemporal displacement field, and then calculates the wave velocity and elastic modulus through time-domain or frequency-domain algorithms. Although this method has high accuracy, it requires a very high frame rate of the imaging device (usually thousands to tens of thousands of hertz), resulting in high device cost and difficulty in popularization in primary medical institutions.

[0004] The existing reverberation wave method excites a reverberation displacement field by a small number of driving points (usually ≤7 points), and collects the spatiotemporal displacement field by a high-frame-rate imaging device, and then calculates the wave velocity and elastic distribution through Fourier transform, local interception by sliding window, and two-dimensional autocorrelation algorithm. Although this method has been applied in medical corneal elasticity measurement and liver elasticity imaging, it still relies on high-frame-rate devices to collect the spatiotemporal displacement field, and needs multiple boundary reflections to form reverberation due to the small number of driving points, resulting in a longer measurement time in medical scenarios and prolonging the patient's breath-holding time.

[0005] Therefore, it is urgent to develop a low-cost and high-efficiency elastography method to break through the cost and efficiency bottlenecks of high-frame-rate devices in medical tissue elastography and material multi-scale mechanical characterization, while ensuring measurement accuracy. SUMMARY

[0006] To this end, the technical problem to be solved by the present application is to overcome the problem that existing elastography technologies all rely on high-frame-rate imaging devices to collect the spatiotemporal displacement field, resulting in high device cost and long measurement time.

[0007] To solve the above technical problems, the present application provides an elastography method and system based on instantaneous scattering displacement field, which comprises the following steps:

[0008] S1: according to the measurement site of the target material, arranging excitation devices for generating a scattering displacement field by passive or active method on the surface or periphery thereof, driving the excitation devices by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in the target material region in real time;

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

[0010] S3: selecting a single-frame instantaneous scattering displacement field from the instantaneous scattering displacement field, locally intercepting the single-frame instantaneous scattering displacement field by a sliding window and processing the single-frame instantaneous scattering displacement field by 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, reconstructing the viscoelastic modulus distribution of the target material region by using an inversion algorithm to realize comprehensive characterization of the viscoelastic parameters of the material.

[0012] In an embodiment of the present application, in S1, according to the measurement site of the target material, arranging excitation devices for generating a scattering displacement field by passive method on the surface or periphery thereof, driving the excitation devices by a frequency-domain controllable sinusoidal wave signal to generate a scattering displacement field in the target material region in real time, the method comprising:

[0013] The excitation device comprises a surrounding excitation source and a plurality of scatterer units, and according to the measurement site of the target material, the surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material region; wherein the plurality of scatterer units are in a space formed by the surrounding excitation source, and the geometric structure parameters thereof satisfy Gaussian random distribution and spatial arrangement disorder;

[0014] The surrounding excitation source is driven by a frequency-domain controllable sinusoidal wave signal, and the generated elastic wave generates a scattering displacement field in the target material region after scattering effect of the plurality of scatterer units.

[0015] In an embodiment of the present application, according to the measurement site of the target material, the surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material region as follows:

[0016] When measuring the surface elastic modulus of the material, the scatterer units adopt a ring envelope type layout and conformally attach along the periphery contour of the target material region;

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

[0018] In an embodiment of the present application, the size of the scatterer unit is 0.1-10 times the shear wave wavelength, and the spacing of the scatterer unit is negatively correlated with the number thereof.

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

[0020] In an embodiment of the present application, in S1, according to the measurement site of the target material, an excitation device for generating a scattering displacement field by an active method is arranged on the surface or periphery thereof, and a frequency domain controllable sinusoidal wave signal is used to drive the excitation device to generate a scattering displacement field in the target material region in real time.

[0021] A plurality of randomly distributed point excitation sources are arranged on the surface or periphery of the target material, and a frequency domain controllable sinusoidal wave signal is used to drive the plurality of point excitation sources, so that the elastic waves excited by the plurality of point excitation sources are superimposed on each other, thereby directly generating a scattering displacement field in the target material region in real time.

[0022] In an embodiment of the present application, according to the measurement site of the target material, an excitation device for generating a scattering displacement field by an active method is arranged on the surface or periphery thereof.

[0023] When measuring the elastic modulus of the material surface, the plurality of point excitation sources are arranged around the boundary of the target region; when measuring the elastic modulus of the material cross section, the plurality of point excitation sources are attached to the surface of the target material region.

[0024] In an embodiment of the present application, the size of each excitation unit in the plurality of point excitation sources is 0.1-10 times the shear wave wavelength, and the spacing of the excitation unit is negatively correlated with the number thereof.

[0025] In an embodiment of the present application, the driving mode of the excitation device for generating an elastic wave at least includes one of mechanical driving, piezoelectric ceramic driving, acoustic radiation force driving, metal plate or metal patch electromagnetic force driving, and laser thermal elastic driving.

[0026] In an embodiment of the present application, in S2, the off-plane scattering displacement field or the in-plane scattering displacement field of the target material region is measured at a high spatial resolution to obtain an instantaneous scattering displacement field.

[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 is configured to reconstruct a viscoelastic modulus distribution of the target material region based on the shear wave velocity distribution by using an inversion algorithm, so as to comprehensively characterize the viscoelastic parameters of the material.

[0050] The application further provides an electronic device, which comprises a processor, a memory and a bus system, the processor and the memory are connected through the bus system, the memory is used for storing instructions, and the processor is used for executing the instructions stored in the memory to realize the elastic imaging method based on the instantaneous scattering displacement field.

[0051] The application further provides a computer storage medium, which stores a computer software product, and the computer software product comprises a plurality of instructions to make a computer device execute the elastic imaging method based on the instantaneous scattering displacement field.

[0052] The above technical scheme of the application has the following advantages compared with the prior art:

[0053] The application generates a high-quality scattering displacement field in real time by setting a random distribution of scatterer boundaries on the periphery or surface of a target region in combination with an external driving source, only needs to measure an instantaneous displacement field by using a low-frame-rate imaging device (such as a common ultrasound, optical or nuclear magnetic device), does not need to acquire space-time domain data at a high frame rate, bypasses a high-cost device bottleneck, intercepts a local displacement field by using a sliding window, and calculates a two-dimensional autocorrelation and a theoretical model fitting inversion shear wave velocity and elastic modulus, and can also realize viscoelastic evaluation by using a multi-frequency driving in combination with a Voigt viscoelastic model, has the advantages of low cost, adaptation to common imaging devices, high measurement efficiency, realization of surface / cut surface / three-dimensional elastic imaging and the like, and is expected to upgrade existing imaging devices by adding a scatterer accessory, and has broad application prospects and social and economic benefits in the fields of medical clinical screening and composite material quality control. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to make the content of the application more easily understood, the application is further described in detail below according to specific embodiments of the application and in combination with the drawings, in which,

[0055] Figure 1 is a flowchart of an elastic imaging method based on an instantaneous scattering displacement field provided in an embodiment of the application;

[0056] Figure 2 is a specific flowchart of an elastic imaging method based on an instantaneous scattering displacement field provided in an embodiment of the application;

[0057] Figure 3is the principle sketch of material surface elastic imaging in experiment 1 (passive method to excite scattering displacement field), in which random scatterer units and surrounding excitation source are deployed in the peripheral of target region (ROI);

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

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

[0060] Figure 6 is the principle sketch of material surface elastic imaging in experiment 2 (passive method to excite scattering displacement field), in which random scatterer units and surrounding excitation source are deployed on the surface of material;

[0061] Figure 7 is the instantaneous displacement field of material surface at different time of 9ms, 18ms, 27ms and 36ms in experiment 1;

[0062] Figure 8 is the measured displacement field in experiment 2, the inversion calculated shear wave velocity distribution and probability density distribution;

[0063] Figure 9 is the principle sketch of material surface elastic imaging in experiment 3 (active method to excite scattering displacement field), in which random distributed multi-point metal patches are deployed in the peripheral of target material region as excitation source, and the electromagnetic force generated by the power on metal coil drives metal patch to directly generate scattering displacement field;

[0064] Figure 10 is the instantaneous displacement field of material surface at different time of 9ms, 18ms, 27ms and 36ms in experiment 1;

[0065] Figure 11 is the measured displacement field in experiment 3, the inversion calculated shear wave velocity distribution and probability density distribution;

[0066] Figure 12 is the principle sketch of material surface elastic imaging in experiment 4 (active method to excite scattering displacement field), in which random distributed multi-point metal patches are deployed on the surface of target material as excitation source, and the electromagnetic force generated by the power on metal coil drives metal patch to directly generate scattering displacement field;

[0067] Figure 13 is the instantaneous displacement field of material surface at different time of 9ms, 18ms, 27ms and 36ms in experiment 1;

[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] From the above technical solutions, the present application adopts a frequency domain controllable sinusoidal signal to drive passive or active scattering displacement field excitation devices, instantaneously generates isotropic high-quality scattering displacement fields, inverts the elastic distribution through a single frame of instantaneous scattering displacement field, avoids the high frame rate time-space displacement field measurement dependent on the transient wave method and the reverberation wave method, avoids the long waiting time dependent on multiple reflections of the traditional reverberation wave method, improves the measurement efficiency, supports high spatial resolution measurement of off-plane displacement fields or in-plane displacement fields, covers multiple scenes such as a surface, a section and a three-dimensional volume, and realizes three-dimensional elastic imaging; based on the Rayleigh wave / shear wave spatial autocorrelation theory model, the shear wave velocity is calculated through nonlinear fitting; in combination with the shear wave velocities at different frequencies obtained under multi-frequency excitation, a viscoelastic model is introduced to invert the viscoelastic modulus, and quantitative analysis of material viscoelasticity is realized.

[0080] Specifically, in the present embodiment, in S1, according to the measurement site of the target material, an excitation device for generating a scattering displacement field by a passive method is arranged on the surface or periphery of the target material, a frequency domain controllable sinusoidal signal is used to drive the excitation device, and a method for instantaneously generating a scattering displacement field in the target material region includes:

[0081] The excitation device includes a surrounding excitation source and a plurality of scatterer units, and according to the measurement site of the target material, the surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material region; wherein the plurality of scatterer units are in a space formed by the surrounding excitation source, and the geometric structure parameters (including size, azimuth angle, etc.), material parameters thereof satisfy Gaussian random distribution and spatial arrangement disorder; the geometric shape of the scatterer unit includes but is not limited to a columnar structure, a hole structure, a triangular structure, a grid structure or an ellipsoidal structure, etc.

[0082] The surrounding excitation source is driven by a frequency domain controllable sinusoidal signal, and the generated elastic wave generates a scattering displacement field in the target material region after scattering effect of the plurality of scatterer units.

[0083] Specifically, in the above technical solution, according to the measurement site of the target material, the surrounding excitation source and the plurality of scatterer units are arranged on the surface or periphery of the target material region as follows:

[0084] When measuring the elastic modulus of the material surface, the plurality of scatterer units adopt a ring envelope type layout and conformally attach along the periphery contour of the target material region.

[0085] When measuring the elastic modulus of the material section, a film-like structure containing the plurality of scatterer units is prepared and attached to the surface of the target material region, and the thickness of the scatterer unit is less than the shear wave wavelength excited by the excitation source.

[0086] The scatterer unit size is 0.1-10 times the shear wave wavelength, and the spacing between adjacent scatterer units is negatively correlated with the number of scatterer units, that is, the spacing between the scatterer units decreases as the number of scatterer units increases, and 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 needs to be at least 10 times that of the measured medium, and typical material systems are high molecular materials such as epoxy resin and silicone rubber.

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

[0089] A plurality of excitation sources in random distribution are deployed on the surface or periphery of the target material, including: when measuring the elastic modulus of the material surface, the plurality of excitation sources are attached around the boundary of the target area; when measuring the elastic modulus of the material section, the plurality of excitation sources are attached to the surface of the target material area; wherein the size of each excitation unit in the plurality of excitation sources is 0.1-10 times the shear wave wavelength, and the spacing of the excitation units is negatively correlated with the number of excitation units.

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

[0091] Further, in the embodiment, the excitation device is used to generate an elastic wave by at least one of passive method or active method, including mechanical driving, piezoelectric ceramic driving, acoustic radiation force driving, metal plate or metal patch electromagnetic force driving, and laser thermal elastic driving.

[0092] Specifically, 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 (z or , displacement field perpendicular to the surface) or in-plane displacement field (x or , displacement field parallel to the surface) of the target area with high spatial resolution, and obtain the surface, two-dimensional cross-sectional, or three-dimensional volume displacement distribution.

[0093] Wherein, the surface measurement is used to characterize the two-dimensional displacement field of the material surface, and z represents the out-of-plane displacement direction. In the field of medical ultrasonic elastography, this characterization method is suitable for the biomechanical property evaluation of superficial tissues such as the stratum corneum and corneal stroma. The two-dimensional cross-sectional For characterizing displacement distribution of internal section of material, displacement component in z-axis depth direction can quantify elastic parameters of deep tissue, which can be used in clinical application for organ examination of liver, breast and the like. Three-dimensional volume For characterizing complete three-dimensional displacement field, three-dimensional elastic imaging is realized, which is used for complex anatomical structure evaluation.

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

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

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

[0097] ;

[0098] Nonlinear least square fitting is performed on the Rayleigh wave spatial autocorrelation function to obtain Rayleigh wave velocity distribution , and a conversion formula is used to obtain shear wave velocity of the material surface ; the shear wave velocity distribution of the whole field is calculated through the sliding window;

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

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

[0101] ;

[0102] Nonlinear least square fitting is performed on the corresponding spatial autocorrelation function to obtain shear wave velocity of the material section ;

[0103] The shear wave velocity distribution of the whole field is calculated through the sliding window;

[0104] wherein, is the position difference in the horizontal direction, and are the zeroth and first order spherical Bessel functions, is the angular frequency, represents the out-of-plane displacement field. Specifically, in the present embodiment, in S4, the method for reconstructing the viscoelastic modulus distribution of the target material region based on the shear wave velocity using an inversion algorithm includes:

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

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

[0107] By changing the driving frequency of the sinusoidal signal, elastic waves of different frequencies are excited to propagate in the target material region, and the shear wave velocities at different driving frequencies are calculated .

[0108] The actually measured shear wave velocities at different frequencies are nonlinearly fitted by the nonlinear viscoelastic model, and the viscoelastic parameters and of the target material region are calculated.

[0109] To further verify the effectiveness of the method of the present application, a passive method is used to excite a scattering displacement field, and a scattering body unit 1 and a surrounding excitation source 2 are arranged on the surface or periphery of the target material region. The technical solution generates a scattering displacement field in the target material region in real time by driving the excitation source 2 with a frequency-domain controllable sinusoidal signal, and the generated elastic wave is scattered by the scattering body unit 1. A plurality of experiments are designed to verify that it has high measurement efficiency and surface / cut surface / three-dimensional multi-modal elastic imaging capability.

[0110] Experiment 1: tissue surface elastic imaging (passive method to excite scattering displacement field)

[0111] The passive method is used to excite the scattering displacement field, a finite element model is established to numerically simulate the wave propagation process on the tissue surface, and the elastic distribution is inverted according to the simulated displacement field. As Figure 3 shown, the simulation material geometric parameters are: thickness 2 cm, diameter 4 cm, density , shear modulus 1 kPa, corresponding to the theoretical shear wave velocity =1m / s. The scatterer unit is a distributed scatter unit structure, which is composed of 64 cuboid scatterer units 1 and is annularly distributed outside the target material region. The size of a single scatterer unit 1 is 0.7mm x 0.7mm x 2mm, the shear modulus is 70kPa, and the spatial layout of the scatterer unit satisfies the random distribution characteristics of the two-dimensional Poisson point process. The annular excitation source 2 is driven by a sinusoidal wave signal with a frequency of 800Hz, and the generated Rayleigh wave propagates towards the target region after being scattered by the scatterer unit.

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

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

[0114] Experiment 2: Material section elastic imaging (passive method to excite scattered displacement field)

[0115] The passive method is used to excite the scattered displacement field, a finite element model is established to simulate the wave propagation characteristics in the tissue, and the elastic distribution is inverted according to the simulated displacement field. As shown in Figure 6 , the geometric size of the simulated material is 3.7cm x 3.7cm x 2cm, the material parameters are set as: density , shear modulus μ=1kPa, and the corresponding theoretical shear wave velocity =1m / s. The scatterer unit adopts a thin layer structure containing scatter units (equivalent to a two-dimensional code topology), with an overall size of 3.7cm x 3.7cm x 0.05cm, a shear modulus of 70kPa, and a square scatterer unit 1 (1.25mm in length and 0.5mm in depth) in the hollow area. The spatial distribution of the scatterer unit follows a two-dimensional Gaussian random process. The annular excitation source 2 on the surface is driven by a sinusoidal wave signal with a frequency of f=800Hz, and the generated elastic wave propagates into the material after being scattered by the scatterer unit.

[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 ( ) and the results show that the electromagnetic force driven randomly distributed metal patches 4 can effectively induce scattered elastic waves, and a high-quality scattered displacement field has been formed at t = 26 ms. A local region with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and the two-dimensional autocorrelation calculation is performed on the displacement field in this region, and based on the Rayleigh wave autocorrelation theoretical model , nonlinear least squares fitting is performed, and the shear wave velocity distribution is obtained. By traversing the whole field with a sliding window, the wave velocity probability density distribution is obtained, as shown in Figure 11 , the statistical mean value is highly consistent with the theoretical value of 1 m / s, which verifies the effectiveness of the method for material surface elastic parameter inversion.

[0122] The simulation results show that the electromagnetic force driven randomly distributed metal patches 4 can directly generate a high-quality scattered displacement field, and combined with the two-dimensional autocorrelation algorithm and the Rayleigh wave spatial autocorrelation theoretical model, the precise inversion of the elastic parameters of the tissue surface can be realized.

[0123] Experiment 4: Elastic imaging of material cross section (active method to excite scattered displacement field)

[0124] An active method is used to excite the scattered displacement field, a finite element model is established to simulate the wave propagation characteristics in the tissue, and the elastic distribution is obtained according to the simulated displacement field. As shown in Figure 12 , the geometric size of the simulated material is 3.7 cm x 3.7 cm x 2 cm, and the material parameters are set as: density ρ = 10 3 kg / m 3 , shear modulus μ = 1 kPa, corresponding to the theoretical shear wave velocity = 1 m / s. Randomly distributed metal patches 4 are attached to the surface of the material, and the size of a single metal patch 4 is 1.25 mm x 1.25 mm x 0.5 mm, 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 patch 4 is driven to excite a shear wave of 800 Hz, and the scattered displacement field generated by the multi-point driven shear wave propagates to the target area.

[0125] Figure 13 shows the out-of-plane displacement field distribution on the cross section at different times , and the results show that the electromagnetic force driven randomly distributed metal patches 4 can effectively excite scattered shear waves, and a high-quality scattered displacement field has been formed at t = 17 ms. A local region with a window size of 1.5λ (λ is the shear wave wavelength) is selected, and the two-dimensional autocorrelation calculation is performed on the displacement field in this region, and based on the shear wave autocorrelation theoretical model , nonlinear fitting is performed, and the shear wave velocity distribution is obtained. By traversing the whole cross section with a sliding window, the wave velocity probability density map is generated, as shown in 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 for setting passive or active scattering displacement field excitation devices on the periphery or surface of the target material region, and instantaneously generating a scattering displacement field on the target material region;

[0133] The instantaneous scattering displacement field measurement module 200 is used for measuring the out-of-plane displacement field or in-plane displacement field of the target material region at a high spatial resolution, and obtaining an instantaneous scattering displacement field.

[0134] The wave velocity inversion module 300 is used for selecting a single frame of the instantaneous scattering displacement field from the instantaneous scattering displacement field, performing local interception through 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.

[0135] The elastic modulus quantitative evaluation module 400 is used for inverting the elastic modulus distribution of the target material region based on the shear wave velocity, to realize comprehensive characterization of material viscoelasticity.

[0136] The embodiment provides an elastic imaging system based on an instantaneous scattering displacement field, which is used for implementing the foregoing elastic imaging method based on the instantaneous scattering displacement field.

[0137] Embodiment three:

[0138] The embodiment also provides an electronic device, which comprises a processor, a memory and a bus system, the processor and the memory are connected through the bus system, the memory is used for storing instructions, and the processor is used for executing the instructions stored in the memory, so as to implement the elastic imaging method based on the instantaneous scattering displacement field in the foregoing embodiment.

[0139] Embodiment four:

[0140] The embodiment also provides a computer storage medium, which stores a computer software product, the computer software product comprises a plurality of instructions, and the instructions are used to make a computer device execute the elastic imaging method based on the instantaneous scattering displacement field in the foregoing embodiment.

[0141] Those skilled in the art will appreciate that embodiments of the present application can be devised for a method, a system, or a computer program product. Accordingly, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer readable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code thereon for use by or in connection with an instruction execution system. For the purposes of this description, a computer usable or computer readable storage medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

[0142] Obviously, the above-described embodiments are only examples for clearly illustrating the present application, and are not intended to limit the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

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: Select a single frame of instantaneous scattering displacement field from the instantaneous scattering displacement field, process the single frame of instantaneous scattering displacement field by local sliding window interception and two-dimensional autocorrelation calculation, 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, the method is 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; 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 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 .

9. 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 using an inversion algorithm based on the shear wave velocity distribution, thereby achieving a comprehensive characterization of the material's viscoelastic parameters; The shear wave velocity distribution is obtained by: 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.

10. 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 8.

11. 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 8.

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