High-discrimination nonlinear ultrasonic tomography image method based on phase shift technique

Abstract

The application discloses a high-differentiation nonlinear ultrasonic tomography image method based on phase shift technology, which radiates a medium or early disease biological tissue with microcosmic mechanical property change by using limited amplitude ultrasonic signals, obtains nonlinear ultrasonic signals carrying distortion of the medium property, processes the nonlinear ultrasonic signals, obtains phase shift of the relative linear signals, and calculates the nonlinear coefficient of the medium by using the phase shift; then, the nonlinear coefficient in the target is calculated by tomography through surrounding scanning of the target and transformation of the Radon principle, so that the high-differentiation nonlinear ultrasonic two-dimensional tomography image of the nonlinear coefficient of the medium is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to an ultrasonic imaging method, in particular, a high-differentiation nonlinear ultrasonic tomography imaging method based on phase shift technology. BACKGROUND

[0002] There are media with microscopic mechanical property changes and some pathological biological tissues, especially early pathological tissues, which have a sound impedance comparable to normal tissues, and conventional ultrasonic imaging cannot obtain good differentiation.

[0003] Nonlinear ultrasound is between power ultrasound and linear ultrasound, and has a good theory to refer to because it produces nonlinear phenomena without being too intense. Nonlinear ultrasound signals will produce distortion when propagating in the medium, that is, the phase will shift, and the characteristics of the generation of high harmonics can also be found after signal processing. The acoustic nonlinear coefficient of the medium is related to the high-order elastic parameters of the material, which is suitable for reflecting the microscopic mechanical property changes in the medium, especially in biological tissues. For example, the nonlinear elastic parameter changes of pathological biological tissues are 6 times higher than the linear parameter changes. Using nonlinear ultrasound for imaging is more conducive to the discovery and evaluation of early lesions and greatly improves the imaging differentiation. Using harmonics caused by nonlinearity for imaging can also improve the resolution of the image.

[0004] However, the traditional method for measuring the nonlinear coefficient is by comparing the amplitudes of the second harmonic and the fundamental frequency signal, and the second-order perturbation formula used is only suitable for small independent variables such as near-distance propagation and low excitation level, and the applicable range is narrow. When extracting the amplitudes of the fundamental frequency signal and the second harmonic, the frequency response of the hardware such as the filter and the near-field effect need to be considered, which introduces new interference factors. At the same time, the second harmonic is only a local characteristic of nonlinear properties, and more valuable nonlinear characteristics are discarded in the processing process, causing a waste of signal utilization. The above reasons cause the low reliability and poor efficiency of the second harmonic method for extracting the nonlinear coefficient.

[0005] The applicant has found that using phase shift, a more comprehensive nonlinear feature, to measure the nonlinear coefficient can be applied in a longer distance and higher excitation, improving the reliability and processing efficiency.

[0006] Discretizing the nonlinear coefficient of the medium, combining the phase shift formula and Radon transform, a two-dimensional tomographic image of the nonlinear coefficient of the medium can be obtained. Due to the high-differentiation property of the nonlinear coefficient, the high-differentiation property of the pathological tissue is ultimately improved, which is conducive to the discovery of early pathological tissues with low differentiation that are not easily discovered by conventional ultrasound. SUMMARY

[0007] The application aims to provide a high-differentiation nonlinear ultrasonic tomography image method based on phase shift technology.

[0008] The technical scheme of the application is as follows: a high-differentiation nonlinear ultrasonic tomography image method based on phase shift technology, which uses limited amplitude ultrasonic signals to obtain nonlinear ultrasonic signals carrying distortion of nonlinear properties of a medium with micro mechanical property changes, processes the nonlinear ultrasonic signals to obtain the phase of the nonlinear signals, simultaneously simulates the phase of linear signals according to the principle that the local position phase of nonlinear signals is constant, and obtains the phase shift of the nonlinear signals relative to the linear signals by difference, calculates the nonlinear coefficient of the medium by using the phase shift, uses an ultrasonic array to perform surrounding scanning on a detection target to obtain a two-dimensional matrix of the phase shift along a specific path, changes the two-dimensional matrix into a two-dimensional matrix of the integral of the nonlinear coefficient along the specific path through a formula, and finally obtains a nonlinear ultrasonic two-dimensional tomography image of the nonlinear coefficient of the medium with high differentiation by using Radon transform.

[0009] The aforementioned high-differentiation nonlinear ultrasonic tomography image method based on phase shift technology comprises the following steps:

[0010] 1) install an ultrasonic probe array around the medium with micro mechanical property changes to perform mechanical rotation or electronic rotation around the target to radiate limited amplitude ultrasonic signals in turn, and the corresponding ultrasonic probe array receives nonlinear signals and transmits the nonlinear signals to a computer for recording;

[0011] 2) according to the signals recorded in step 1), perform Hilbert transform on the signals to obtain the phase of the signals, simultaneously simulate the phase of linear signals according to the phase-time relationship of the recorded nonlinear signals and according to the principle that the position phase of the nonlinear signals with zero amplitude is constant, and obtain the phase shift of the nonlinear ultrasonic signals by difference;

[0012] 3) use the cumulative phase shift of the nonlinear ultrasonic signals along a straight line to calculate the spatial distribution of the nonlinear coefficient according to the following formula: combine Radon transform to calculate all the recorded scanning data, thereby obtaining a two-dimensional tomography image of the nonlinear coefficient of the medium; wherein, β, ρ0, c0, ω, dx, dy, p0 are the nonlinear coefficient of the medium, the density of the medium, the sound speed of the medium, the phase shift, the angular frequency of the excitation signal, the two-dimensional propagation path distance and the excitation sound pressure in sequence, x and y are spatial coordinates, l is a certain ultrasonic propagation path or integral path, θ is the angle between the origin and the x axis, and δ is an impulse function.

[0013] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein the limited-amplitude ultrasonic signal is at least a 10-cycle sinusoidal signal, and the average value mode is used for averaging more than 8 times to reduce the influence of noise on phase extraction.

[0014] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein when the medium with microscopic mechanical property changes is a solid medium, the ultrasonic probe array generating the limited-amplitude ultrasonic signal is attached to the solid medium, and the ultrasonic probe is sequentially excited by electronic rotation, and is received by the remaining probes.

[0015] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein when the medium with microscopic mechanical property changes is a condensed medium or a biological tissue with early symptoms, the ultrasonic probe array is surrounded around the target medium by a fixing device, and a fluid such as degassed water is used as a coupling medium to improve the radiated ultrasonic energy, and the degassed water can reduce the influence of microbubbles in water on the nonlinear property of the measured medium.

[0016] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein the fluid includes but is not limited to degassed water.

[0017] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein when the signal in step 2) is processed, Fourier transform and wavelet transform methods are included but are not limited thereto, so as to obtain the phase of the signal.

[0018] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein the phase of the linear signal is calculated according to the phase-time relationship of the recorded signal in step 2), which is based on the characteristic that the zero-amplitude signal of the nonlinear signal is not distorted, i.e., the phase is not shifted, and the phase at the zero-amplitude signal is consistent with the linear phase, the phase-time relationship of the linear signal is obtained, and the difference is obtained to obtain the phase shift of the nonlinear signal.

[0019] The high-discrimination nonlinear ultrasonic tomography imaging method based on phase shift technique as claimed in the preceding paragraph, wherein the calculation in step 3) selects the signal with a phase shift of 0.2-0.65 for calculation; because: when the phase shift is small, the noise signal will affect the accuracy of the obtained phase shift; and when the phase shift is large, the nonlinear acoustic signal is severely distorted, and the Hilbert transform has great difficulty in obtaining the signal phase or even errors occur.

[0020] The Radon transform in step 4) of the aforementioned high-differentiation nonlinear ultrasonic tomography image method based on the phase shift technique is a projection transform method of computer tomography, and a series of phase shifts of ultrasonic signals under different paths are obtained by discretizing the nonlinear coefficient of the medium, and a two-dimensional tomography image of the nonlinear coefficient is obtained by combining the phase shift formula and the Radon transform.

[0021] Advantages of the present application

[0022] The most commonly used nonlinear coefficient estimation method at present is the perturbation solution based on the second harmonic, and the phase shift of the finite amplitude signal is used to estimate the nonlinear coefficient, which has the following advantages over the second harmonic method:

[0023] 1. The second harmonic is only a local feature of the nonlinear nature of the finite amplitude signal, and the phase can present more comprehensive nonlinear characteristics, so that the nonlinear characteristics of the signal are more fully utilized.

[0024] 2. The second harmonic solution is a perturbation approximate solution, and according to mathematical theory, it is only valid for small independent variables, i.e. short distance, small nonlinear coefficient and low excitation level, while the application range of the phase shift is wider.

[0025] 3. The use of the phase shift method to estimate the nonlinear coefficient avoids the extraction process of the second harmonic, avoids the use of filters, and also avoids the influence of the frequency response of related instruments and equipment such as filters on the measurement results, so that the signal processing process is simpler and the results are more reliable.

[0026] 4. The method of the present application is simple, and the phase shift is proportional to the distance, which provides feasibility for computer two-dimensional tomography imaging by Radon transform.

[0027] Because the acoustic impedance of early lesion tissue changes little, conventional ultrasound cannot form a high-differentiation image, but the change of the high-order elastic parameter related to the nonlinear coefficient is 6 times higher than that of the linear elastic parameter, so imaging of the nonlinear coefficient can greatly improve the differentiation of the image; at the same time, by using Radon transform, computer two-dimensional tomography imaging of biological tissues can be realized, which is beneficial to the early diagnosis of early lesion tissue. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The outermost medium of the assumed data model of the egg in water is water; the oval is egg white and yolk.

[0029] Figure 2 It is a phase shift data matrix diagram of an egg in water after ultrasonic 180° scanning by using nonlinear ultrasonic.

[0030] Figure 3 It is a two-dimensional tomography image of the nonlinear coefficient of the egg in water by using Radon transform.Figure 2 The results of two-dimensional tomographic imaging of an egg after mid-phase shift data processing, i.e., the spatial distribution of the nonlinear coefficients of the egg.

[0031] Figure 4 This is a data model of a hypothetical diseased human liver.

[0032] Figure 5 This is the phase shift data after performing a 180° ultrasound scan of the human liver using nonlinear ultrasound.

[0033] Figure 6 To utilize the Radon transform Figure 5 The results of two-dimensional tomographic imaging of the human kidney after mid-phase shift data processing, i.e. the spatial distribution of the nonlinear coefficient of the human liver. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0035] Embodiments of the present invention

[0036] Example 1

[0037] 1) Using computational software to simulate, such as Figure 1 The data model of the egg shown is provided, in which the density is set to 1.00 g / cm³ to maintain consistent acoustic impedance across all media. 3 The sound speed was 1500 m / s, the nonlinear coefficient of water was set to 5, the nonlinear coefficient of egg white was set to 5.25, and the nonlinear coefficient of egg yolk was set to 5.5; the signal excitation frequency was 5 MHz. An ultrasonic probe array was installed around the egg and radiated a sinusoidal ultrasonic signal for 10 cycles in a mechanical or electronic rotation around the egg; the corresponding ultrasonic probe array received and recorded the nonlinear signal.

[0038] 2) Based on the signal recorded in step 1), perform a Hilbert transform on it to obtain the phase matrix of the signal. Then, calculate the phase of the linear signal based on the phase-time relationship of the recorded signal, and subtract the phase from the phase matrix to obtain the phase shift matrix of the recorded nonlinear ultrasound signal, such as... Figure 2 As shown;

[0039] 3) Select a phase shift signal with a phase shift between 0.2 and 0.65, and utilize the spatial distribution relationship between the cumulative phase shift of the nonlinear ultrasonic signal along a certain straight line and the nonlinear coefficient: By combining Radon transform with calculations on all recorded scan data, a two-dimensional tomographic image of the medium's nonlinear coefficients is obtained, such as... Figure 3 As shown, where β,ρ0,c0, ω, d, p0 are the nonlinear coefficients of the medium, the density of the medium, the speed of sound in the medium, the phase shift, the angular frequency of the excitation signal, the propagation distance, and the excitation sound pressure, respectively. x, y are the spatial coordinates, l is a certain ultrasonic propagation path or integration path, θ is the angle between the origin and the propagation path and the x-axis, and δ is the impulse function.

[0040] Example 2

[0041] 1) Using computational software to simulate, such as Figure 4 The liver data model shown has a surrounding water density of 1.00 g / cm³. 3 The sound velocity is 1500 m / s, and the nonlinear coefficient is set to 5; the reference parameters for the liver are: density 1.05 g / cm³. 3 The sound velocity was 1588 m / s; the nonlinear coefficient of a normal liver was 7.2, and that of a diseased liver portion was 7.5; the signal excitation frequency was 5 MHz. An array of ultrasound probes was mounted around the liver and rotated mechanically or electronically to radiate a sinusoidal ultrasound signal for 10 cycles; the corresponding ultrasound probe array received and recorded the nonlinear signal.

[0042] 2) Based on the signal recorded in step 1), perform a Hilbert transform on it to obtain the phase matrix of the signal. Then, calculate the phase of the linear signal based on the phase-time relationship of the recorded signal, and subtract the phase from the phase matrix to obtain the phase shift matrix of the recorded nonlinear ultrasound signal, such as... Figure 5 As shown;

[0043] 3) Select a phase shift signal with a phase shift between 0.2 and 0.65, and utilize the spatial distribution relationship between the cumulative phase shift of the nonlinear ultrasonic signal along a certain straight line and the nonlinear coefficient: By combining Radon transform with calculations on all recorded scan data, a two-dimensional tomographic image of the medium's nonlinear coefficients is obtained, such as... Figure 6 As shown, where β,ρ0,c0, ω, d, p0 are the nonlinear coefficients of the medium, the density of the medium, the speed of sound in the medium, the phase shift, the angular frequency of the excitation signal, the propagation distance, and the excitation sound pressure, respectively. x, y are the spatial coordinates, l is a certain ultrasonic propagation path or integration path, θ is the angle between the origin and the propagation path and the x-axis, and δ is the impulse function.

[0044] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology, characterized in that: By radiating a medium with microscopic mechanical property changes using a finite amplitude ultrasonic signal, a nonlinear ultrasonic signal carrying the distortion of the medium's properties is obtained. This nonlinear signal is then subjected to Hilbert transform to obtain its phase. Simultaneously, the phase of a linear signal is simulated using the principle that the phase of a nonlinear signal remains unchanged at local positions, and the phase shift of the nonlinear signal relative to the linear signal is obtained by subtraction. The nonlinear coefficient of the medium is calculated using this phase shift. An ultrasonic array is then used to perform a circumferential scan of the target, obtaining a two-dimensional matrix of the phase shift along a specific path. This two-dimensional matrix is ​​then transformed into a matrix of nonlinear coefficients integral along the specific path using the relationship between phase shift and distance. Finally, a Radon transform is used to obtain a nonlinear ultrasonic two-dimensional tomographic image with high resolution of the medium's nonlinear coefficients.

2. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 1, characterized in that, The method includes the following steps: 1) An array of ultrasonic probes is installed around a medium with varying microscopic mechanical properties and rotates mechanically or electronically around the target to radiate ultrasonic signals with limited amplitudes in sequence; the corresponding ultrasonic probe array receives nonlinear signals and transmits them to a computer for recording. 2) Based on the signal recorded in step 1), perform a Hilbert transform on it to obtain the phase of the signal; at the same time, based on the recorded phase-time relationship of the nonlinear signal, and based on the principle that the phase remains unchanged when the amplitude of the nonlinear signal is zero, simulate the phase of the linear signal, and calculate the difference to obtain the phase shift of the nonlinear ultrasonic signal. 3) Utilizing the relationship between the cumulative phase shift of a nonlinear ultrasound signal along a certain straight line and the spatial distribution of the nonlinear coefficient: By combining Radon transform with calculations on all recorded scan data, a two-dimensional tomographic image of the medium's nonlinear coefficients is obtained; among which, The parameters are, in order: nonlinear coefficient of the medium, medium density, medium sound velocity, phase shift, excitation signal angular frequency, two-dimensional propagation path distance, and excitation sound pressure. l For a certain ultrasound propagation path or integration path, The angle between the origin, the propagation path, and the x-axis. Let be the impulse function.

3. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 1 or 2, characterized in that: The finite amplitude ultrasonic signal is a sinusoidal signal with at least 10 cycles, and is averaged more than 8 times using an average value mode to reduce the impact of noise on phase extraction.

4. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 1 or 2, characterized in that: The medium exhibiting changes in micromechanical properties is a solid medium. An array of ultrasonic probes that generates finite amplitude ultrasonic signals is attached to the solid medium. The ultrasonic probes are sequentially excited by electronic rotation and received by the remaining probes.

5. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 1 or 2, characterized in that: When the medium exhibiting changes in micromechanical properties is a condensed medium or biological tissue, the ultrasonic probe array surrounds the target medium through a fixing device, using fluid as a coupling medium to enhance the radiated ultrasonic energy.

6. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 5, characterized in that: The fluid includes, but is not limited to, degassed water.

7. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 2, characterized in that: When performing phase processing on the signal described in step 2), Fourier transform and wavelet transform are also included, among other things.

8. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 2, characterized in that: Step 3) The calculation is performed using a signal with a phase shift between 0.2 and 0.

65.

9. The high-resolution nonlinear ultrasound tomography imaging method based on phase-shifting technology according to claim 2, characterized in that: Step 4) The Radon transform is a projection transformation method for computed tomography. By discretizing the nonlinear coefficients of the medium, a series of phase shifts of the ultrasound signal under different paths are obtained. Combining the phase shift formula and the Radon transform, a two-dimensional tomographic image with nonlinear coefficients is obtained.

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