Tissue viscoelasticity calculation method and calculation system based on wavelet transform

Abstract

The invention provides a tissue viscoelasticity calculation method and system based on wavelet transform, and the method comprises the steps: exciting and generating shear waves at a target region of a tissue, and extracting shear wave information; carrying out wavelet transformation on the shear wave information, and extracting frequency domain information in the shear wave information, so as to obtain time-frequency domain information of shear waves; taking any point on the transverse tangent plane as a target point, and performing cross-correlation between the time-frequency domain information of the target point and the time-frequency domain information of the other points by using a cross-correlation algorithm to obtain phase differences between the target point and the other points under different frequencies; determining phase velocities of shear waves under different frequencies according to phase differences between the time-frequency domain signals of the target point and the time-frequency domain signals of other points under different frequencies; and fitting the phase velocities of the shear waves under different frequencies to obtain a viscosity value and an elasticity value corresponding to the target area of the tissue. The method does not need to collect data for many times, reduces errors caused by data collection, and improves the mechanical characteristic calculation precision of the tissue.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultrasonic elastography, and particularly relates to a tissue viscoelasticity calculation method and system based on wavelet transform. BACKGROUND

[0002] Ultrasound shear wave elastography, referred to as ultrasonic elastography, is an imaging technology for non-invasively quantitatively evaluating the mechanical properties of biological soft tissues. The technology excites a transversely propagating shear wave through ultrasonic radiation force, traces the wave velocity in the time-space domain, obtains the mechanical parameters of the biological soft tissues, and performs imaging. The core principle of ultrasonic elastography is to induce the elastic change of biological soft tissues through a specific pathological or physiological process.

[0003] Since the 1990s when the technology was first proposed, ultrasonic elastography has been widely applied in the non-invasive detection of the mechanical properties of biological soft tissues through continuous development and optimization in the application range of medical diagnosis and treatment monitoring devices. However, in the prior art, when the mechanical properties of biological soft tissues are imaged and monitored through ultrasonic elastography, the elastic assumption principle is generally used for elastic analysis only. However, the mechanical properties of biological soft tissues are actually viscoelastic, that is, in addition to elasticity, biological soft tissues also exhibit viscosity, resulting in the frequency dispersion of ultrasonic shear waves. If the viscosity of biological soft tissues is ignored during monitoring, information will be lost, and the monitoring result will be affected. Therefore, the viscoelasticity of biological soft tissues is the best indicator of the mechanical properties of biological soft tissues. The method of monitoring only elasticity in the prior art is no longer applicable, and the viscoelasticity of biological soft tissues needs to be analyzed through the dispersion curve of biological soft tissues.

[0004] At present, the commonly used method is to analyze and extract the dispersion curve of biological soft tissues by using a single tracking point method. The single tracking point method can reduce speckle noise through multiple beam offsets and single point tracking. However, the single tracking point method needs to collect dispersion data multiple times, and more noise will be introduced during the process of collecting dispersion data multiple times, resulting in a large error in the dispersion curve of biological soft tissues obtained. SUMMARY

[0005] In view of the technical problem in the prior art that the single tracking point method needs to be collected multiple times when analyzing and extracting the dispersion curve of biological soft tissues, resulting in a large error in the dispersion curve of biological soft tissues obtained, the application provides a tissue viscoelasticity calculation method and system based on wavelet transform.

[0006] The present application is to carry out wavelet transform analysis on the shear wave particle motion waveform (shear wave information), calculate the phase difference between any two points on the transverse section by the cross-correlation algorithm, thereby determine the phase velocity of the shear wave under different frequencies, finally fit the phase velocity of the shear wave under different frequencies, obtain the viscosity value and the elastic value corresponding to the target region of the tissue, without multiple data collection, reduce the error introduced by the data collection, and improve the calculation accuracy of the mechanical characteristics of the tissue.

[0007] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] A tissue viscoelasticity calculation method based on wavelet transform, comprising the following steps:

[0009] S1: generating a shear wave at a target region of a tissue and extracting shear wave information;

[0010] S2: carrying out wavelet transform on the shear wave information, extracting frequency domain information in the shear wave information, thereby obtaining time-frequency domain information of the shear wave;

[0011] S3: taking any point on a transverse section as a target point, using the cross-correlation algorithm to cross-correlate the time-frequency domain information of the target point with the time-frequency domain information of the remaining points, obtaining the phase difference between the target point and the remaining points under different frequencies, wherein the transverse section refers to the cross section of the shear plane of the shear wave at a depth z;

[0012] S4: determining the phase velocity of the shear wave under different frequencies according to the phase difference between the time-frequency domain signals of the target point and the time-frequency domain signals of the remaining points under different frequencies;

[0013] S5: fitting the phase velocity of the shear wave under different frequencies, obtaining the viscosity value and the elastic value corresponding to the target region of the tissue.

[0014] Further limited, the step S1 specifically comprises:

[0015] S1.1: using an ultrasonic multi-focus shear wave excitation technology to generate a shear wave at a target region of a tissue;

[0016] S2.2: capturing the shear wave by using an ultrasonic fast plane wave imaging technology, and extracting the shear wave information.

[0017] Further limited, the step S1.1 is specifically: the ultrasonic multi-focus shear wave excitation technology is to continuously emit a sinusoidal wave as an excitation signal at the target region of the tissue, thereby generating a shear wave at the target region of the tissue.

[0018] Further limited, the step S4 is specifically:

[0019] S4.1: extract distance values between the target point and the rest of the points;

[0020] S4.2: calculate the ratio of the distance values between the target point and the rest of the points and the phase difference between the target point and the rest of the points at different frequencies, to obtain the phase velocity of the shear wave at different frequencies.

[0021] Further limitation, the step S5 is specifically: based on the viscoelastic model, the phase velocity of the shear wave at different frequencies is fitted by using the nonlinear least squares method, and the numerical inversion method is used to obtain the corresponding viscous value and elastic value of the target region of the tissue.

[0022] Further limitation, the number of points on the transverse section of the shear wave is 5 or 6.

[0023] Further limitation, in step S2, the wavelet transform is performed on the shear wave information to extract the frequency domain information in the shear wave information, which is specifically: taking a transverse section at the position of depth z=z0, and taking 6 points on the transverse section, the shear wave information corresponding to the 6 points is respectively SW(z0,x i ,t), SW(z0,x i+1 ,t), SW(z0,x i+2 ,t), SW(z0,x i+3 ,t), SW(z0,x i+4 ,t) and SW(z0,x i+5 ,t), and the wavelet transform is performed on the shear wave information corresponding to the 6 points respectively, to obtain the frequency domain information of the shear wave propagation corresponding to the 6 points SW(z0,x i ,f), SW(z0,x i+1 ,f), SW(z0,x i+2 ,f), SW(z0,x i+3 ,f), SW(z0,x i+4 ,f), SW(z0,x i+5 ,f), i is the serial number of the point, f is the frequency of the shear wave, x i is the position of the i-th point on the transverse section at the depth z0, and t is the time dimension variable.

[0024] Further limitation, the phase velocity of the shear wave at different frequencies is represented as:

[0025]

[0026] In the formula, C p (f ij ) is the phase velocity of the shear wave at different frequencies, the unit is m / s; f ij is the frequency of the j-th shear wave extracted at the i-th point, the unit is Hz, f ij∈f;ΔX is the distance between any two points on the transverse section, unit: m; is the phase difference between any two points on the transverse section, dimensionless.

[0027] Further limited, the phase velocity of the shear wave at different frequencies is fitted based on the viscoelastic model using a nonlinear least squares method, and is expressed as:

[0028]

[0029] In the formula, μ1 is a shear elastic coefficient, unit: Pa; μ2 is a shear viscosity coefficient, unit: Pa·s; ρ is the density of the tissue, unit: kg / m 3 ; f is the frequency of the shear wave, unit: Hz; C P (f) is the phase velocity of the shear wave, unit: m / s, C p (f ij ) ∈ C P (f).

[0030] The present application forms a wavelet transform-based tissue viscoelasticity calculation system based on the wavelet transform-based tissue viscoelasticity calculation method described above, comprising:

[0031] A shear wave information acquisition module: for exciting a shear wave at a target region of the tissue and extracting shear wave information;

[0032] A wavelet transform module: for wavelet transforming the shear wave information and extracting frequency domain information in the shear wave information, thereby obtaining time-frequency domain information of the shear wave;

[0033] A phase difference calculation module: for taking any point on the transverse section as a target point, and using a cross-correlation algorithm to cross-correlate the time-frequency domain information of the target point with the time-frequency domain information of the remaining points, to obtain the phase difference between the target point and the remaining points at different frequencies, wherein the transverse section refers to the cross section of the shear plane of the shear wave at a depth z;

[0034] A phase velocity determination module: for determining the phase velocity of the shear wave at different frequencies according to the phase difference between the time-frequency domain signal of the target point and the time-frequency domain signal of the remaining points at different frequencies;

[0035] And a viscoelasticity calculation module: for fitting the phase velocity of the shear wave at different frequencies to obtain the viscosity value and the elasticity value corresponding to the target region of the tissue.

[0036] Compared with the prior art, the present application has the following advantages:

[0037] 1. The tissue viscoelasticity calculation method based on wavelet transform is wavelet transform analysis on the shear wave particle motion waveform (shear wave information), obtains the time-frequency domain information of the shear wave, calculates the phase difference between any two points on the transverse section through the cross-correlation algorithm, thereby determines the phase velocity of the shear wave under different frequencies, and finally fits the phase velocity of the shear wave under different frequencies, and obtains the viscosity value and the elasticity value corresponding to the target region of the tissue. The method can accurately determine the viscoelasticity (viscosity value and elasticity value) of the tissue, and provides a new method for non-invasive determination of the mechanical properties of the tissue. Compared with the prior art, the method does not need to collect data multiple times, reduces the error introduced by data collection, and improves the calculation accuracy of the mechanical characteristics of the tissue.

[0038] 2. The tissue viscoelasticity calculation method based on wavelet transform is to use the phase velocity of the shear wave under different frequencies to represent the viscoelasticity of the tissue, and the viscoelasticity calculation through the phase velocity of the shear wave can realize rapid non-destructive detection, non-invasive detection, simple operation, and greatly improves the detection efficiency. And the phase velocity of the shear wave of different frequencies will show different change rules when propagating in the medium, reflecting the frequency dependence of the viscoelasticity of the material. By detecting the phase velocity of the shear wave under different frequencies, the viscoelasticity characteristics of the material in a wide frequency range can be deeply understood. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a schematic diagram of the tissue viscoelasticity calculation method based on wavelet transform of the application;

[0040] Figure 2 It is a schematic diagram of the tissue viscoelasticity calculation system based on wavelet transform of the application;

[0041] Figure 3 It is a flowchart for making a viscoelastic cube;

[0042] Figure 4 It is a schematic diagram of the principle of generating shear wave;

[0043] Figure 5 It is a time domain information diagram of shear wave propagation;

[0044] Figure 6 It is a trajectory diagram of shear wave propagation in a uniform medium;

[0045] Figure 7 It is a signal change diagram of shear wave at different transverse displacement points under the same depth;

[0046] Figure 8 It is a time-frequency domain information diagram of shear wave propagation;

[0047] Figure 9 It is a phase difference trend diagram between multiple points on the transverse section under different frequencies;

[0048] Figure 10 To obtain a phase difference fitting map of corresponding points at multiple depths at a selected frequency;

[0049] Figure 11 The dispersion curve of the target area of ​​the tissue at the selected location;

[0050] Figure 12 The elastic and viscous values ​​calculated using the wavelet transform-based tissue viscoelasticity calculation method of this invention are shown in the figure. Shear elasticity refers to the elastic value, and shear viscosity refers to the viscous value. Detailed Implementation

[0051] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the embodiments described below.

[0052] See Figure 1 This invention proposes a method for calculating tissue viscoelasticity based on wavelet transform, comprising the following steps:

[0053] S1: Excite and generate shear waves at the target area of ​​the tissue, and extract shear wave information;

[0054] Specifically, step S1 includes: S1.1: Using ultrasonic multifocal shear wave excitation technology, shear waves are generated at the target area of ​​the tissue; wherein, ultrasonic multifocal shear wave excitation technology generates shear waves at the target area of ​​the tissue by continuously emitting sinusoidal waves as excitation signals; the target area of ​​the tissue refers to the area to be detected. See also Figure 4 In the target area of ​​the tissue, multiple points are selected along the longitudinal section to generate shear waves using ultrasonic multifocal shear wave excitation technology. The plane containing these multiple points is the transverse section; S2.2: Ultrafast plane wave imaging technology is used to capture the shear waves and extract the shear wave information; see [link to relevant documentation] Figure 5 The shear wave information is the time-domain information of the time dimension variable SW(z,x,t), where z represents the axial dimension variable or the depth dimension variable, x represents the transverse dimension variable, and t represents the time dimension variable. That is, the shear wave information of a point on the transverse section is represented as SW(z0,x,t), where z0 is the depth value of the transverse section, x represents the transverse dimension variable, and t represents the time dimension variable.

[0055] S2: Perform wavelet transform on the shear wave information to extract the frequency domain information, thereby obtaining the time-frequency domain information of the shear wave. Normalize the time-frequency domain information of the shear wave to obtain, as shown below. Figure 8 The diagram shows the time-frequency domain information of shear wave propagation.

[0056] Specifically, the shear wave information of six different points at the depth value z0 of the transverse section, SW(z0, x i ,t), SW(z0, x i+1 ,t), SW(z0, x i+2 ,t), SW(z0, x i+3 ,t), SW(z0, x i+4 ,t) and SW(z0, x i+5 ,t) are sequentially subjected to wavelet transform to obtain time-frequency domain signals SW(z0, x i ,f), SW(z0, x i+1 ,f), SW(z0, x i+2 ,f), SW(z0, x i+3 ,f), SW(z0, x i+4 ,f), SW(z0, x i+5 ,f), i is the serial number of the point, f is the frequency of the shear wave, x i is the position of the i-th point on the transverse section at the depth z0, and t is the time dimension variable.

[0057] S3: taking any point on the transverse section as a target point, the time-frequency domain information of the target point is cross-correlated with the time-frequency domain information of the remaining points by using the cross-correlation algorithm to obtain the phase difference between the target point and the remaining points at different frequencies, wherein the transverse section refers to the cross section of the shear plane of the shear wave at the depth z;

[0058] wherein the cross-correlation formula of the time-frequency domain information at two different positions is as follows:

[0059]

[0060] According to the maximum value of the cross-correlation result, the phase difference between the two points on the transverse section at different frequencies is obtained as follows:

[0061]

[0062] In the formula, R(τ) is the cross-correlation function, which is dimensionless; τ is the time delay, the unit is s; T is the time length of the time-frequency domain information, the unit is s; and are the phases of the two time-frequency domain information of the cross-correlation, which are dimensionless; is the phase difference between the two points on the transverse section at different frequencies; f0 is the carrier frequency of the time-frequency domain information in the shear wave, the unit is Hz; j is the imaginary unit, which is dimensionless.

[0063] Taking x i as the target point, the time-frequency domain signals at x i are respectively cross-correlated with the time-frequency domain signals at the remaining points x i+1 , xi+2 ,x i+3 ,x i+4 ,x i+5 The phase difference is calculated by cross-correlation algorithm between the time-frequency domain signals at the target point and the time-frequency domain signals at the other points;

[0064] S4: determining the phase velocity of the shear wave at different frequencies according to the phase difference between the time-frequency domain signals at the target point and the time-frequency domain signals at the other points at different frequencies;

[0065] Specifically, step S4 includes: S4.1: extracting the distance value between the target point and the other points; S4.2: calculating the ratio of the distance value between the target point and the other points to the phase difference between the target point and the other points at different frequencies, to obtain the phase velocity of the shear wave at different frequencies.

[0066] The phase velocity of the shear wave at different frequencies is represented as:

[0067]

[0068] In the formula, C p (f ij ) is the phase velocity of the shear wave at different frequencies, with the unit of m / s; f ij is the frequency of the jth shear wave extracted at the ith point, with the unit of Hz, f ij ∈f; ΔX is the distance value between any two points on the transverse section, with the unit of m; is the phase difference between any two points on the transverse section, dimensionless.

[0069] S5: fitting the phase velocity of the shear wave at different frequencies to obtain the viscosity value and the elasticity value corresponding to the target region of the tissue; specifically, step S5 is: fitting the phase velocity of the shear wave at different frequencies based on the viscoelastic model using the nonlinear least squares method, which is represented as:

[0070]

[0071] In the formula, μ1 is the shear elasticity coefficient, with the unit of Pa; μ2 is the shear viscosity coefficient, with the unit of Pa·s; ρ is the density of the tissue, with the unit of kg / m 3 ; f is the frequency of the shear wave, with the unit of Hz; C P (f) is the phase velocity of the shear wave, with the unit of m / s, C p (f ij ) ∈ C P (f).

[0072] The viscosity value and the elasticity value corresponding to the target region of the tissue are obtained by using the numerical inversion method.

[0073] Preferably, in the present application, the number of points in the lateral section of the shear wave is 5 or 6.

[0074] The present application is based on the phase velocity of shear waves at different frequencies generated by ultrasonic radiation force to characterize the viscoelasticity of tissue, and the biological tissue is a viscoelastic medium, the wave velocity of which changes with frequency, resulting in frequency dispersion phenomenon, and the corresponding phase velocity of shear waves at each frequency needs to be accurately calculated. The present application uses ultrasonic multi-focus shear wave excitation technology to excite shear waves in the tissue, extracts shear wave information, performs wavelet transform analysis on the shear wave information, calculates the phase difference between any two points in the lateral section at different frequencies through cross-correlation algorithm, thereby calculates the phase velocity of shear waves at different frequencies, and fits the phase velocity of shear waves at different frequencies to obtain the corresponding viscosity value and elasticity value of the target region of the tissue. The present application provides the possibility for non-invasive calculation of the mechanical properties of tissue, and can accurately evaluate the viscoelasticity of tissue.

[0075] In the present application, the shear wave information includes wavelength, excitation frequency, excitation duration, ultrasonic radiation force excitation element number, excitation focus position, ROI (lateral section), excitation voltage, tracking frequency, tracking focus configuration, channel data sampling frequency, beam synthesis resolution, per-frame acquisition interval and captured shear wave frame number.

[0076] The following will take the prepared phantom as an example to specifically describe a tissue viscoelasticity calculation method based on wavelet transform.

[0077] The preparation instrument and materials of the phantom are as follows: gelatin, nano-titanium dioxide powder, castor oil, digital constant temperature magnetic stirring oil bath and constant temperature explosion-proof refrigerator.

[0078] As shown in Figure 3 , the manufacturing process of the phantom is as follows:

[0079] 1) In a beaker, the nano-titanium dioxide powder and anhydrous ethanol are magnetically stirred for not less than 30 minutes to fully mix them to form a titanium dioxide mixture;

[0080] 2) The gelatin particles and deionized water are subjected to constant temperature water bath stirring in the digital constant temperature magnetic stirring oil bath for at least 30 minutes to fully mix them to form a gelatin solution;

[0081] 3) The titanium dioxide mixture, the gelatin solution and the castor oil are mixed and stirred, and the constant temperature stirring is not less than 1 hour to fully mix them to form a mixed solution;

[0082] 4) The mixed solution is introduced into a square container, the surface suspended bubbles are removed and cooled to room temperature (about 20 degrees Celsius), and then placed in a constant temperature explosion-proof refrigerator for 24 hours to form a phantom.

[0083] Shear wave is excited at the target region of tissue using a Verasonics ultrasound experimental system, which can excite, collect and image shear wave. The ultrasound multi-focus shear wave excitation technology is that the Verasonics ultrasound experimental system uses a L11-4V ultrasound linear array probe with a center frequency of 6.25 MHz to dynamically focus and emit continuous sinusoidal waves as excitation signals. The shear wave is captured by using an ultrafast plane wave imaging technology, and shear wave information as shown in Table 1 is extracted.

[0084] Table 1: Shear wave information

[0085]

[0086]

[0087] Shear wave is excited at the target region of tissue using a Verasonics ultrasound experimental system, which can excite, collect and image shear wave. The ultrasound multi-focus shear wave excitation technology is that the Verasonics ultrasound experimental system uses a L11-4V ultrasound linear array probe with a center frequency of 6.25 MHz to dynamically focus and emit continuous sinusoidal waves as excitation signals. The shear wave is captured by using an ultrafast plane wave imaging technology, and shear wave information as shown in Table 1 is extracted. Figure 6 Figure 7 i ,f ij ) and the time-frequency domain signals SW(z0,x i+1 ,f ij ), SW(z0,x i+2 ,f ij ), SW(z0,x i+3 ,f ij ), SW(z0,x i+4 ,f ij ) and SW(z0,x i+5 ,f ij ) of the other five points on the transverse section, the time-frequency domain signal SW(z0,x i ,f ij ) of the target point is calculated, and the time-frequency domain signals SW(z0,x i ,f ij ), SW(z0,x i+1 ,f ij ), SW(z0,x i+2 ,f ij ), SW(z0,x i+3 ,f ij ), SW(z0,x i+4 ,f ij ) and SW(z0,x i+5 ,f​​ij ) between the phase difference trend chart as shown in Figure 9 ; according to the phase difference between the time-frequency domain signals of the target point and the time-frequency domain signals of the remaining points at different frequencies, the phase velocity of the shear wave at different frequencies is determined to be fitted, and the slope of the fitted straight line is as shown in Figure 10 ; as shown in Figure 11 , the phase velocity of the shear wave at different frequencies is fitted based on the viscoelastic model using the nonlinear least squares method; as shown in Figure 12 , the numerical inversion method is used to obtain the corresponding viscous value and elastic value of the target region of the tissue.

[0088] The above calculation and graphic processing are realized by using MATLAB 2022a in the above calculation process.

[0089] Table 2: Comparison of shear wave phase velocity calculation results for uniform viscoelastic tissue

[0090] Frequency QIBA theoretical shear wave phase velocity Wavelet transform calculated shear wave phase velocity Relative error 200 (Hz) 1.7414 (m / s) 1.7942 (m / s) 3.03％ 290 (Hz) 1.9487 (m / s) 1.9468 (m / s) 0.098％ 340 (Hz) 2.0495 (m / s) 2.0293 (m / s) 0.99％ 430 (Hz) 2.2052 (m / s) 2.2238 (m / s) 0.84％ 530 (Hz) 2.3393 (m / s) 2.3369 (m / s) 0.1％

[0091] As shown in Table 2, the QIBA data shear wave phase velocity calculated by the wavelet transform-based tissue viscoelasticity calculation method of the present application is compared with the QIBA theoretical shear wave phase velocity, and the overall relative error is small, thereby indicating that the method of the present application can accurately detect the phase velocity of the shear wave, thereby accurately inverting the viscoelasticity.

[0092] Referring to Figure 2 , the present application also provides a wavelet transform-based tissue viscoelasticity calculation system, which is formed based on the above wavelet transform-based tissue viscoelasticity calculation method, comprising:

[0093] a shear wave information acquisition module for exciting a shear wave at a target region of the tissue and extracting shear wave information;

[0094] a wavelet transform module for wavelet transforming the shear wave information to extract frequency domain information in the shear wave information, thereby obtaining time-frequency domain information of the shear wave;

[0095] a phase difference calculation module for taking any point on a transverse section as a target point, and using a cross-correlation algorithm to cross-correlate the time-frequency domain information of the target point with the time-frequency domain information of the remaining points to obtain the phase difference between the target point and the remaining points at different frequencies, wherein the transverse section refers to a cross section of the shear plane of the shear wave at a depth z;

[0096] a phase velocity determination module for determining the phase velocity of the shear wave at different frequencies according to the phase difference between the time-frequency domain signals of the target point and the time-frequency domain signals of the remaining points at different frequencies;

[0097] and a viscoelasticity calculation module: used for fitting the phase velocity of the shear wave at different frequencies to obtain the corresponding viscous value and elastic value of the target region of the tissue.

[0098] It should be noted that the content of the wavelet transform-based tissue viscoelasticity calculation system in the present application corresponds to the content of the wavelet transform-based tissue viscoelasticity calculation method described above. For the specific content of the shear wave information acquisition module, the wavelet transform module, the phase difference calculation module, the phase velocity determination module and the viscoelasticity calculation module which are not described in detail in the wavelet transform-based tissue viscoelasticity calculation system, please refer to the description of the wavelet transform-based tissue viscoelasticity calculation method part described above. The present application does not repeat here.

[0099] It should be noted that the tissue in the present application refers to an ex vivo biological soft tissue.

[0100] The above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the present application. Although the present application has been described in detail above, those skilled in the art should understand that they can still modify the technical solutions described above, or make equivalent substitutions for part or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for calculating viscoelasticity of a tissue based on wavelet transform, characterized by, The method comprises the following steps: S1: exciting a shear wave at a target region of a tissue and extracting shear wave information; S2: performing wavelet transform on the shear wave information to extract frequency domain information in the shear wave information, thereby obtaining time-frequency domain information of the shear wave; S3: taking any point on a transverse section as a target point, and using a cross-correlation algorithm to cross-correlate the time-frequency domain information of the target point with the time-frequency domain information of the remaining points, thereby obtaining phase differences between the target point and the remaining points at different frequencies, wherein the transverse section refers to a cross section of a shear plane of the shear wave at a depth z; S4: determining phase velocities of the shear wave at different frequencies according to the phase differences between the time-frequency domain signals of the target point and the time-frequency domain signals of the remaining points at different frequencies; S5: fitting the phase velocities of the shear wave at different frequencies to obtain a viscous value and an elastic value corresponding to the target region of the tissue.

2. The method of claim 1, wherein, The step S1 specifically comprises: S1.1: exciting a shear wave at a target region of a tissue using an ultrasonic multi-focus shear wave excitation technology; S2.2: capturing the shear wave using an ultrasonic fast plane wave imaging technology and extracting shear wave information.

3. The method of claim 2, wherein, The step S1.1 specifically refers to exciting a shear wave at a target region of a tissue by continuously transmitting a sinusoidal wave as an excitation signal, thereby exciting a shear wave at the target region of the tissue.

4. The method of claim 1, wherein, The step S4 specifically comprises: S4.1: extracting distance values between the target point and the remaining points; S4.2: calculating ratios of the distance values between the target point and the remaining points to the phase differences between the target point and the remaining points at different frequencies, thereby obtaining phase velocities of the shear wave at different frequencies.

5. The method of claim 1, wherein, The step S5 specifically refers to fitting the phase velocities of the shear wave at different frequencies based on a viscoelastic model using a nonlinear least squares method, and obtaining a viscous value and an elastic value corresponding to the target region of the tissue using a numerical inversion method.

6. The method of claim 1, wherein, The number of points on the transverse section of the shear wave is 5 or 6.

7. The method of claim 1, wherein the wavelet transform-based tissue viscoelasticity calculation method is characterized by, The step S2 is to perform wavelet transform on the shear wave information, and extract frequency domain information in the shear wave information. Specifically, a transverse section is taken at the position of depth z=z0, and six points are taken on the transverse section. The shear wave information corresponding to the six points is respectively SW(z0,x i ,t), SW(z0,x i+1 ,t), SW(z0,x i+2 ,t), SW(z0,x i+3 ,t), SW(z0,x i+4 ,t) and SW(z0,x i+5 ,t). The wavelet transform is performed on the shear wave information corresponding to the six points respectively, to obtain the frequency domain information of shear wave propagation corresponding to the six points, which is SW(z0,x i ,f), SW(z0,x i+1 ,f), SW(z0,x i+2 ,f), SW(z0,x i+3 ,f), SW(z0,x i+4 ,f), SW(z0,x i+5 ,f), i is the serial number of the point, f is the frequency of the shear wave, x i is the position of the i-th point on the transverse section at the depth z0, and t is a time dimension variable.

8. The method of claim 4, wherein the wavelet transform-based calculation of tissue viscoelasticity is characterized by, The phase velocities of the shear wave at different frequencies are represented as: where C p (f ij ) is the phase velocity of the shear wave at different frequencies, unit: m / s; f ij is the frequency of the jth shear wave extracted at the ith point, unit: Hz, f ij ∈f; AX is the distance between any two points on the lateral section, unit: m; is the phase difference between any two points on the lateral section, dimensionless.

9. The method of claim 5, wherein the wavelet transform-based tissue viscoelasticity calculation method is characterized by, Fitting the phase velocities of the shear wave at different frequencies based on a viscoelastic model using a nonlinear least squares method is represented as: In the formula, μ1 is a shear elastic coefficient, unit: Pa; μ2 is a shear viscous coefficient, unit: Pa·s; ρ is the density of the tissue, unit: kg / m 3 ; f is the frequency of the shear wave, unit: Hz; C P (f) is the phase velocity of the shear wave, unit: m / s, C p (f ij ) ∈ C P (f).

10. A wavelet transform-based tissue viscoelasticity calculation system formed based on the wavelet transform-based tissue viscoelasticity calculation method according to claim 1, characterized by, It comprises: a shear wave information acquisition module for exciting a shear wave at a target region of a tissue and extracting shear wave information; a wavelet transform module for performing wavelet transform on the shear wave information to extract frequency domain information in the shear wave information, thereby obtaining time-frequency domain information of the shear wave; a phase difference calculation module for taking any point on a transverse section as a target point, and using a cross-correlation algorithm to cross-correlate the time-frequency domain information of the target point with the time-frequency domain information of the remaining points, thereby obtaining phase differences between the target point and the remaining points at different frequencies, wherein the transverse section refers to a cross section of a shear plane of the shear wave at a depth z; a phase velocity determination module for determining phase velocities of the shear wave at different frequencies according to the phase differences between the time-frequency domain signals of the target point and the time-frequency domain signals of the remaining points at different frequencies; and a viscoelasticity calculation module for fitting the phase velocities of the shear wave at different frequencies to obtain a viscous value and an elastic value corresponding to the target region of the tissue.

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