Dynamic-aperture-based ultrasonic ct waveform inversion method and device

Abstract

The application discloses an ultrasonic CT waveform inversion method and device based on a dynamic aperture, and belongs to the technical field of ultrasonic image processing, and comprises the following steps: acquiring an observed sound pressure signal at a position of a receiving element of an ultrasonic CT data acquisition system; inputting a current sound velocity distribution into a wave equation to obtain a synthesized sound pressure signal at the position of the receiving element; for each transmitting element, extracting the synthesized sound pressure signals at the positions of M receiving elements away from the transmitting element; calculating the difference between the synthesized sound pressure signals at the positions of the M receiving elements corresponding to all the transmitting elements and the corresponding observed sound pressure signals; calculating the gradient of the current sound velocity distribution by using an adjoint state method according to the difference, and then obtaining an updated sound velocity distribution; re-substituting the updated sound velocity distribution into the wave equation for iteration, and simultaneously increasing the value of M until the iteration is stopped, and outputting the updated sound velocity distribution. The application can improve the accuracy of a reconstructed image under the condition of missing low-frequency information.

Description

Technical Field

[0001] This invention belongs to the field of ultrasound image processing technology, and more specifically, relates to a method and apparatus for ultrasound CT waveform inversion based on dynamic aperture. Background Technology

[0002] Ultrasound CT refers to the use of an ultrasound probe to emit ultrasound waves to the object being scanned and to receive ultrasound echoes from multiple directions that interact with the object through reflection, scattering, diffraction, etc. The ultrasound CT image is obtained by analyzing and processing these echo data.

[0003] Ultrasound CT image reconstruction is mainly divided into structural image reconstruction and functional image reconstruction. Functional image reconstruction has greater practical application significance. Functional image reconstruction includes sound velocity image reconstruction and attenuation coefficient image reconstruction. Functional image reconstruction methods include ray-based reconstruction methods and wave-based reconstruction methods. Compared to ray-based reconstruction methods, wave-based reconstruction methods can use all waveform data to reconstruct functional images, resulting in higher imaging resolution.

[0004] In existing technologies, full waveform inversion (FWI) is generally used to reconstruct functional images. However, this method suffers from a local minima problem, also known as cycle-skipping, which causes the inversion process to converge in the wrong direction, thus reducing the accuracy of the reconstructed image. To avoid cycle-skipping, sufficient low-frequency information is required in the acquired data. However, for ultrasound CT data, low-frequency information is often difficult to obtain, which poses a significant challenge to reconstructing accurate sound velocity images or attenuation coefficient images. Summary of the Invention

[0005] In view of the shortcomings of existing technologies and the need for improvement, this invention provides a method and apparatus for ultrasonic CT waveform inversion based on dynamic aperture, which aims to improve the accuracy of reconstructed images under the condition of missing low-frequency information.

[0006] To achieve the above objectives, according to a first aspect of the present invention, an ultrasonic CT waveform inversion method based on dynamic aperture is provided, comprising:

[0007] S1. Acquire the observed sound pressure signal at the location of each receiving element of the ultrasound CT data acquisition system; wherein, the ultrasound CT data acquisition system includes N elements, adopts a fully enclosed probe distribution, and adopts a single-shot N-connection mode;

[0008] S2. Input the current sound velocity distribution into the wave equation to simulate the process of transmitting and receiving ultrasound in the ultrasound CT data acquisition system, and obtain the synthetic sound pressure signal at the current location of each receiving array element.

[0009] S3. For each transmitting array element, select M array elements far away from the transmitting array element as receiving array elements, and extract the synthetic sound pressure signal at the location of each of the M receiving array elements according to the synthetic sound pressure signal described in S2; wherein, during initialization, M < N.

[0010] S4. Calculate the difference between the synthesized sound pressure signal and the corresponding observed sound pressure signal at the locations of the M receiving array elements corresponding to all transmitting array elements;

[0011] S5. Based on the differences described in S4, the gradient of the current sound speed distribution is calculated using the adjoint state method, and then the updated sound speed distribution is obtained.

[0012] S6. Take the updated sound speed distribution as the current sound speed distribution, and increase the value of M, M≤N, and jump to S2 until the difference in S4 is less than the set threshold or the set number of iterations is reached, stop the iteration, and output the updated sound speed distribution.

[0013] Furthermore, in S3, for each transmitting array element, M array elements directly opposite the transmitting array element are selected as receiving array elements.

[0014] Furthermore, S2 also includes inputting the current attenuation coefficient distribution into the wave equation; correspondingly, S5 also includes:

[0015] Based on the differences described in S4, the gradient of the current attenuation coefficient distribution is calculated using the adjoint state method, and then the updated attenuation coefficient distribution is obtained.

[0016] S6 also includes: taking the updated attenuation coefficient distribution as the current attenuation coefficient distribution, jumping back to S2, stopping the iteration, and outputting the updated attenuation coefficient distribution.

[0017] Furthermore, in S4, the difference is calculated by constructing an objective function;

[0018] The objective function is a L2 norm objective function, a deconvolution objective function, or a global cross-correlation objective function between the observed signal and the corresponding received signal;

[0019] Alternatively, the objective function may be a L2 norm objective function between the envelope of the observed signal and the envelope of the corresponding received signal;

[0020] Wherein, the observed signal is the observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements; the received signal is the synthesized sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements.

[0021] Furthermore, in S5, the gradient of the current sound speed distribution is calculated using the adjoint state method, thereby obtaining the updated sound speed distribution, including:

[0022] The gradient of the current sound speed distribution is calculated using the adjoint state method;

[0023] The gradient of the current sound speed distribution is multiplied by the current step size and then superimposed onto the current sound speed distribution to obtain the updated sound speed distribution.

[0024] According to a second aspect of the present invention, an ultrasonic CT waveform inversion device based on dynamic aperture is provided, comprising:

[0025] The acoustic pressure signal acquisition module is used to acquire the acoustic pressure signal at the location of each receiving element of the ultrasound CT data acquisition system; wherein, the ultrasound CT data acquisition system includes N array elements, adopts a fully enclosed probe distribution, and adopts a single-transmitter N-connection mode;

[0026] The synthetic sound pressure signal acquisition module is used to input the current sound velocity distribution into the wave equation to simulate the ultrasound CT data acquisition system's transmission and reception of ultrasound, and obtain the synthetic sound pressure signal at the current location of each receiving array element; the receiving array element selection module is used to select M array elements farthest from the transmitting array element as receiving array elements for each transmitting array element, and extract the synthetic sound pressure signal at the location of each of the M receiving array elements based on the synthetic sound pressure signal in the synthetic sound pressure signal acquisition module; wherein, during initialization, M < N;

[0027] The difference calculation module is used to calculate the difference between the synthesized sound pressure signal and the corresponding observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements;

[0028] The sound speed distribution update module is used to calculate the gradient of the current sound speed distribution based on the difference in the difference calculation module using the adjoint state method, and then obtain the updated sound speed distribution.

[0029] The iterative update module is used to take the updated sound velocity distribution as the current sound velocity distribution, while increasing the value of M, M≤N, and iteratively executing the synthesized sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module until the difference in the difference calculation module is less than a set threshold or the set number of iterations is reached, then the iteration stops and the updated sound velocity distribution is output.

[0030] Furthermore, in the receiving array element selection module, for each transmitting array element, M array elements directly opposite the transmitting array element are selected as receiving array elements.

[0031] Furthermore, the synthetic sound pressure signal acquisition module is also used to input the current attenuation coefficient distribution into the wave equation. Correspondingly, the sound velocity distribution update module is also used to calculate the gradient of the current attenuation coefficient distribution using the adjoint state method based on the difference in the difference calculation module, and then obtain the updated attenuation coefficient distribution.

[0032] The iterative update module is also used to take the updated attenuation coefficient distribution as the current attenuation coefficient distribution, and iteratively execute the synthetic sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module. When the iteration stops, it also outputs the updated attenuation coefficient distribution.

[0033] According to a third aspect of the present invention, an electronic device is provided, including a computer-readable storage medium and a processor;

[0034] The computer-readable storage medium is used to store executable instructions;

[0035] The processor is configured to read executable instructions stored in the computer-readable storage medium and execute the ultrasonic CT waveform inversion method based on dynamic aperture as described in any of the first aspects.

[0036] According to a fourth aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the ultrasonic CT waveform inversion method based on dynamic aperture as described in any of the first aspects.

[0037] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0038] (1) The ultrasonic CT waveform inversion method based on dynamic aperture of the present invention selects M array elements far away from the transmitting array elements as receiving array elements. In the early stage of iteration, the low wavenumber information (i.e., long wavelength signal) provided by the N*M transmission signals received by the M receiving array elements far away from the transmitting array elements is first focused on. As the number of iterations increases, M dynamically increases (i.e., the number of receiving array elements gradually increases), and more attention is paid to the high wavenumber information provided by the transmitting signals received by the receiving array elements. In the image reconstruction process, the low wavenumber information is reconstructed first, making the reconstruction process smoother. Therefore, the method of the present invention can make the inversion process smoother and create low frequency information for the signal, effectively alleviate the cycle-skipping problem, ensure the correct convergence direction, and improve the accuracy of the reconstructed image.

[0039] Meanwhile, in the iterative calculation process, the method of the present invention selects the signals of M receiving array elements for calculation each time. Compared with the prior art, which requires N receiving array elements to participate in the calculation for each iteration, the method of the present invention can effectively accelerate the iteration, reduce the amount of calculation, improve the calculation efficiency, and has no additional consumption, making it simple and efficient.

[0040] (2) Preferably, in S3, the M array elements directly opposite the transmitting array element are selected as the M receiving array elements selected at the beginning of the iteration. At this time, the M receiving array elements are farthest from the transmitting array element, which can obtain more low wavenumber information at the beginning of the iteration and further improve the accuracy of the reconstructed image.

[0041] (3) Furthermore, when the input of the wave equation in S2 also includes the current attenuation coefficient distribution, the attenuation coefficient distribution can be accurately inverted using the method of the present invention.

[0042] (4) Furthermore, when the objective function is constructed by using the difference between the envelope corresponding to the synthesized sound pressure signal and the envelope corresponding to the observed sound pressure signal to solve the difference, the method of the present invention can work together with the envelope inversion method to further improve the accuracy of the reconstructed image.

[0043] The dynamic aperture-based ultrasound CT waveform inversion of this invention can provide low wavenumber information for the signal while reducing some computational load, making the inversion process smoother and avoiding cycle-skipping problems, ensuring the correct convergence direction and obtaining high-resolution ultrasound CT sound velocity distribution images or attenuation coefficient distribution images. Attached Figure Description

[0044] Figure 1 This is a flowchart of the ultrasonic CT waveform inversion method based on dynamic aperture in Embodiment 1 of the present invention.

[0045] Figure 2 This is a schematic diagram illustrating the selection process of the corresponding receiving array element for each transmitting array element in the iterative process of the ultrasonic CT waveform inversion method based on dynamic aperture in Embodiment 1 of the present invention.

[0046] Figure 3 This is a real-world example of sound velocity distribution in the brain.

[0047] Figure 4 This is the reconstructed sound velocity distribution obtained from simulation in Embodiment 2 of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0049] In this invention, the terms "first," "second," etc., used in the invention and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0050] like Figure 1 As shown, the ultrasonic CT waveform inversion method based on dynamic aperture of the present invention mainly includes:

[0051] S1. Acquire the observed acoustic pressure signal d at the location of each receiving element in the ultrasound CT data acquisition system. obs (x s ,x r ,t), x s (1≤s≤N) represents the coordinates of the transmitting element, x r (1≤r≤N) represents the coordinates of the receiving array element, t represents the sampling time, and N represents the number of ultrasound probes, i.e., the total number of array elements in the ultrasound CT data acquisition system. The ultrasound CT data acquisition system employs a fully enclosed probe distribution, including N array elements, using a single-transmitter-N-connected mode, meaning one array element transmits and N array elements receive. Each receiving array element can receive N observation sound pressure signals, for a total of N... 2 A data record. In this embodiment of the invention, an ultrasound CT data acquisition system with a ring-shaped, fully enclosed probe distribution is used. In other embodiments, other ultrasound CT data acquisition systems with fully enclosed probe distributions may also be selected.

[0052] S2. Input the current sound velocity distribution into the wave equation to simulate the process of transmitting and receiving ultrasound in the ultrasound CT data acquisition system, and obtain the synthetic sound pressure signal at the current location of each receiving array element; correspondingly, each receiving array element can obtain N corresponding synthetic sound pressure data; wherein, during initialization, the current sound velocity distribution is set;

[0053] S3. For each transmitting element, select M receiving elements that are far away from the transmitting element. Based on the synthetic sound pressure signal at the current location of each receiving element, extract the synthetic sound pressure signal at the location of each of the selected M receiving elements. Wherein, during initialization, M < N.

[0054] S4. Calculate the difference between the synthesized sound pressure signal at the location of the selected M receiving array elements corresponding to all transmitting array elements and the observed sound pressure signal at the location of the selected M receiving array elements corresponding to all transmitting array elements.

[0055] S5. Based on the differences in S4, the gradient of the current sound speed distribution is calculated using the adjoint state method, and then the updated sound speed distribution is obtained.

[0056] S6. Use the updated sound velocity distribution as the current sound velocity distribution, and increase the value of M, M≤N, and jump to S2 until the difference calculated in S4 is less than the set threshold or the set number of iterations is reached. Stop the iteration and output the updated sound velocity distribution.

[0057] The ultrasonic CT waveform inversion method based on dynamic aperture of this invention selects M array elements farthest from the transmitting array elements as receiving array elements. In the initial iteration stage, it focuses on the low wavenumber information (i.e., long wavelength signals) provided by the N*M transmitted signals received by the M receiving array elements farthest from the transmitting array elements. As the number of iterations increases, M dynamically increases (i.e., the number of receiving array elements gradually increases), gradually focusing more on the high wavenumber information provided by the transmitted signals received by the receiving array elements. During image reconstruction, low wavenumber information is reconstructed preferentially, making the reconstruction process smoother. Therefore, the method of this invention can make the inversion process smoother, create low-frequency information for the signal, effectively alleviate the cycle-skipping problem, ensure the correct convergence direction, and improve the accuracy of the reconstructed image.

[0058] Meanwhile, in the iterative calculation process, the method of the present invention selects the signals of M receiving array elements for calculation each time. Compared with the prior art, which requires N receiving array elements to participate in the calculation for each iteration, the method of the present invention can effectively accelerate the iteration, reduce the amount of calculation, improve the calculation efficiency, and has no additional consumption, making it simple and efficient.

[0059] As a preferred option, in S3, the M array elements directly opposite the transmitting array element are selected as the M receiving array elements selected at the beginning of the iteration. At this time, the selected M receiving array elements are the farthest from the transmitting array element, which can obtain more low wavenumber information at the beginning of the iteration and further improve the accuracy of the reconstructed image.

[0060] Specifically, in S1, the observed acoustic pressure signal at the location of each receiving element of the ultrasound CT data acquisition system is acquired, including:

[0061] The ultrasonic CT data acquisition system transmits and receives ultrasonic signals to obtain real three-dimensional spatial data, which is the observed sound pressure signal at the location of each receiving array element.

[0062] Specifically, in S2, the wave equation used in this embodiment of the invention is:

[0063]

[0064] Where x is the coordinate of any point in the spatial domain, v is the sound velocity distribution model in the spatial domain, p(x,t) represents the synthesized sound pressure signal at any point x in space at time t, and s(x,t) is the source term.

[0065] Given the position information x of the transmitting array element s Given the sound velocity distribution, the synthesized sound pressure signal p(x) at any point x and any time t in the entire computational space is discretely solved using numerical simulation methods (such as finite difference, finite element, etc.). s (x, t).

[0066] Specifically, in S3, for the selected M receiving array elements x that are far away from the transmitting array element... r (1+L≤r≤M+L), the synthesized sound pressure signal at the location of each receiving array element is:

[0067] d cal (x s x r ,t)=p(x s , x = x r ,t)

[0068] Where L represents the number of array elements that are not selected on one side of the current transmitting array element, that is, the number of array elements that do not participate in the calculation during the iteration process. When M≠N, L, M and N satisfy the following relationship: N=2*L+1+M.

[0069] Specifically, in S4, the difference *f* between the synthesized sound pressure signal at the location of the selected M receiving array elements corresponding to all transmitting array elements and the observed sound pressure signal at the location of the selected M receiving array elements corresponding to all transmitting array elements is calculated by constructing an objective function. The corresponding calculation formula is:

[0070]

[0071] In the formula, F(d) obs (x s x r ,t),d cal (x s x r Let ,t)) represent the objective function representing the difference between the synthesized sound pressure signal and the observed sound pressure signal at the corresponding location; for example, this objective function could be a L2 norm objective function representing the difference between the synthesized sound pressure signal and the observed sound pressure signal at the corresponding location:

[0072]

[0073] Alternatively, the objective function can also be a L2 objective function representing the difference between the envelope corresponding to the synthesized sound pressure signal and the envelope corresponding to the observed sound pressure signal. In this case, the method of the present invention can work together with the envelope inversion method to further improve the accuracy of the reconstructed image.

[0074] In other embodiments, the objective function may also be a deconvolution objective function or a global cross-correlation objective function representing the difference between the synthesized sound pressure signal and the observed sound pressure signal at the corresponding location, etc., which are not limited in the embodiments of the present invention.

[0075] Specifically, in S5, the gradient of the current sound velocity distribution is calculated using the adjoint state method, and then the updated sound velocity distribution is obtained, including:

[0076] The gradient of the current sound speed distribution is multiplied by the current step size and then superimposed onto the current sound speed distribution to obtain the updated sound speed distribution.

[0077] In S6, it should be noted that as the number of iterations increases, M gradually increases. When M increases to be the same as N, the data recorded by all array elements (N) at this point... 2 All of them participate in the calculation. If the iteration termination condition has not been met, the next iteration will continue. In subsequent iterations, M = N.

[0078] As a further design of the present invention, S2 also includes inputting the current attenuation coefficient distribution into the wave equation; in this case, in the embodiment of the present invention, a multi-parameter viscous acoustic wave equation is adopted.

[0079] S5 also includes: based on the differences in S4, the gradient of the current attenuation coefficient distribution is calculated using the adjoint state method, and then the updated attenuation coefficient distribution is obtained;

[0080] S6 also includes: using the updated attenuation coefficient distribution as the current attenuation coefficient distribution and jumping to S2; when the iteration stops, it also outputs the updated attenuation coefficient distribution.

[0081] In the embodiment of the present invention, the selection process of the corresponding receiving array element for each transmitting array element in the dynamic aperture-based ultrasound CT waveform inversion method is illustrated in the following diagram. Figure 2 As shown, Figure 2 In the diagram, the red elements represent the corresponding transmitting elements, the solid blue elements represent the M receiving elements selected in each iteration, and the hollow blue elements represent elements that did not participate in the calculation during the iteration. Figure 2 In the diagram, 'n' represents the nth transmitting element.

[0082] Example 2

[0083] This invention provides an ultrasonic CT waveform inversion device based on dynamic aperture, mainly comprising:

[0084] The acoustic pressure signal acquisition module is used to acquire the acoustic pressure signal at the location of each receiving element of the ultrasound CT data acquisition system; the ultrasound CT data acquisition system includes N array elements, adopts a fully enclosed probe distribution, and adopts a single-transmitter N-connection mode;

[0085] The synthetic sound pressure signal acquisition module is used to input the current sound velocity distribution into the wave equation to simulate the ultrasound transmission and reception process of the ultrasound CT data acquisition system, and obtain the synthetic sound pressure signal at the current location of each receiving array element; the receiving array element selection module is used to select M array elements far away from the transmitting array element as receiving array elements for each transmitting array element, and extract the synthetic sound pressure signal at the location of each of the M receiving array elements based on the synthetic sound pressure signal in the synthetic sound pressure signal acquisition module; wherein, during initialization, M < N;

[0086] The difference calculation module is used to calculate the difference between the synthesized sound pressure signal and the corresponding observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements;

[0087] The sound velocity distribution update module is used to calculate the gradient of the current sound velocity distribution based on the differences in the difference calculation module, and then obtain the updated sound velocity distribution.

[0088] The iterative update module is used to take the updated sound velocity distribution as the current sound velocity distribution, while increasing the value of M, M≤N, and iteratively executing the synthesized sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module until the difference in the difference calculation module is less than the set threshold or the set number of iterations is reached, then the iteration stops and the updated sound velocity distribution is output.

[0089] As a preferred embodiment, in the receiving array element selection module, for each transmitting array element, M array elements directly opposite the transmitting array element are selected as receiving array elements.

[0090] Furthermore, the synthesized sound pressure signal acquisition module is also used to input the current attenuation coefficient distribution into the wave equation. Correspondingly, the sound velocity distribution update module is also used to calculate the gradient of the current attenuation coefficient distribution using the adjoint state method based on the difference in the difference calculation module, and then obtain the updated attenuation coefficient distribution.

[0091] The iterative update module is also used to take the updated attenuation coefficient distribution as the current attenuation coefficient distribution and iteratively execute the synthetic sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module. When the iteration stops, it also outputs the updated attenuation coefficient distribution.

[0092] The steps corresponding to the ultrasonic CT waveform inversion method based on dynamic aperture in Implementation Example 1 for each of the above modules will not be repeated here.

[0093] A simulation experiment was conducted using the ultrasonic CT waveform inversion device based on dynamic aperture provided in Example 2, taking sound velocity reconstruction as an example. Figure 3 The image shown is a true distribution map of sound velocity in the brain. Figure 3 The blue background in the image also represents the reconstructed portion. Figure 4 The reconstructed sound velocity distribution map, obtained by using the dynamic aperture-based ultrasonic CT waveform inversion device in this embodiment of the invention, shows that the invention has high accuracy.

[0094] Example 3

[0095] This invention provides an electronic device, including a computer-readable storage medium and a processor;

[0096] Computer-readable storage media are used to store executable instructions;

[0097] The processor is used to read executable instructions stored in a computer-readable storage medium and execute the ultrasonic CT waveform inversion method based on dynamic aperture in Embodiment 1 above.

[0098] Example 4

[0099] This invention provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the ultrasonic CT waveform inversion method based on dynamic aperture as described in Embodiment 1 above.

[0100] This invention addresses the problem of acquiring high-resolution ultrasound CT sound velocity images under conditions of missing low-frequency information in ultrasound CT data. The method of this invention can create low-frequency information for the signal, making the inversion process smoother and avoiding cycle-skipping problems, ensuring the correct convergence direction and obtaining high-resolution ultrasound CT sound velocity images. Furthermore, the method of this invention has strong adaptability and can be used in conjunction with existing inversion methods and strategies, such as envelope inversion, adaptive waveform inversion, and multi-scale frequency waveform inversion strategies, to further improve the accuracy of the reconstructed images.

[0101] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for inverting ultrasound CT waveforms based on dynamic aperture, characterized in that, include: S1. Acquire the observed sound pressure signal at the location of each receiving element of the ultrasound CT data acquisition system; wherein, the ultrasound CT data acquisition system includes N elements, adopts a fully enclosed probe distribution, and adopts a single-shot N-connection mode; S2. Input the current sound velocity distribution into the wave equation to simulate the process of transmitting and receiving ultrasound in the ultrasound CT data acquisition system, and obtain the synthetic sound pressure signal at the current location of each receiving array element. S3. For each transmitting array element, select M array elements far away from the transmitting array element as receiving array elements, and extract the synthetic sound pressure signal at the location of each of the M receiving array elements according to the synthetic sound pressure signal described in S2; wherein, during initialization, M < N. S4. Calculate the difference between the synthesized sound pressure signal and the corresponding observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements; S5. Based on the differences described in S4, the gradient of the current sound speed distribution is calculated using the adjoint state method, and then the updated sound speed distribution is obtained. S6. Take the updated sound speed distribution as the current sound speed distribution, and increase the value of M, M≤N, and jump to S2 until the difference in S4 is less than the set threshold or the set number of iterations is reached, stop the iteration, and output the updated sound speed distribution.

2. The ultrasonic CT waveform inversion method based on dynamic aperture according to claim 1, characterized in that, In S3, for each transmitting array element, M array elements directly opposite the transmitting array element are selected as receiving array elements.

3. The ultrasonic CT waveform inversion method based on dynamic aperture according to claim 1 or 2, characterized in that, S2 also includes inputting the current attenuation coefficient distribution into the wave equation; correspondingly, S5 also includes: Based on the differences described in S4, the gradient of the current attenuation coefficient distribution is calculated using the adjoint state method, and then the updated attenuation coefficient distribution is obtained. S6 also includes: taking the updated attenuation coefficient distribution as the current attenuation coefficient distribution, jumping back to S2, stopping the iteration, and outputting the updated attenuation coefficient distribution.

4. The ultrasonic CT waveform inversion method based on dynamic aperture according to claim 1 or 2, characterized in that, In S4, the difference is calculated by constructing an objective function; The objective function is a L2 norm objective function, a deconvolution objective function, or a global cross-correlation objective function between the observed signal and the corresponding received signal; Alternatively, the objective function may be a L2 norm objective function between the envelope of the observed signal and the envelope of the corresponding received signal; Wherein, the observed signal is the observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements; the received signal is the synthesized sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements.

5. The ultrasonic CT waveform inversion method based on dynamic aperture according to claim 1 or 2, characterized in that, In S5, the gradient of the current sound velocity distribution is calculated using the adjoint state method, and then the updated sound velocity distribution is obtained, including: The gradient of the current sound speed distribution is calculated using the adjoint state method; The gradient of the current sound speed distribution is multiplied by the current step size and then superimposed onto the current sound speed distribution to obtain the updated sound speed distribution.

6. An ultrasonic CT waveform inversion device based on dynamic aperture, characterized in that, include: The acoustic pressure signal acquisition module is used to acquire the acoustic pressure signal at the location of each receiving element of the ultrasound CT data acquisition system; wherein, the ultrasound CT data acquisition system includes N array elements, adopts a fully enclosed probe distribution, and adopts a single-transmitter N-connection mode; The synthetic sound pressure signal acquisition module is used to input the current sound velocity distribution into the wave equation to simulate the ultrasound CT data acquisition system's transmission and reception of ultrasound, and obtain the synthetic sound pressure signal at the current location of each receiving array element; the receiving array element selection module is used to select M array elements farthest from the transmitting array element as receiving array elements for each transmitting array element, and extract the synthetic sound pressure signal at the location of each of the M receiving array elements based on the synthetic sound pressure signal in the synthetic sound pressure signal acquisition module; wherein, during initialization, M < N; The difference calculation module is used to calculate the difference between the synthesized sound pressure signal and the corresponding observed sound pressure signal at the location of the M receiving array elements corresponding to all transmitting array elements; The sound speed distribution update module is used to calculate the gradient of the current sound speed distribution based on the difference in the difference calculation module using the adjoint state method, and then obtain the updated sound speed distribution. The iterative update module is used to take the updated sound velocity distribution as the current sound velocity distribution, while increasing the value of M, M≤N, and iteratively executing the synthesized sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module until the difference in the difference calculation module is less than a set threshold or the set number of iterations is reached, then the iteration stops and the updated sound velocity distribution is output.

7. The ultrasonic CT waveform inversion device based on dynamic aperture according to claim 6, characterized in that, In the receiving array element selection module, for each transmitting array element, M array elements directly opposite the transmitting array element are selected as receiving array elements.

8. The ultrasonic CT waveform inversion device based on dynamic aperture according to claim 6 or 7, characterized in that, The synthesized sound pressure signal acquisition module is also used to input the current attenuation coefficient distribution into the wave equation. Correspondingly, the sound velocity distribution update module is also used to calculate the gradient of the current attenuation coefficient distribution using the adjoint state method based on the difference in the difference calculation module, and then obtain the updated attenuation coefficient distribution. The iterative update module is also used to take the updated attenuation coefficient distribution as the current attenuation coefficient distribution, and iteratively execute the synthetic sound pressure signal acquisition module, the receiving array element selection module, the difference calculation module, and the sound velocity distribution update module. When the iteration stops, it also outputs the updated attenuation coefficient distribution.

9. An electronic device, characterized in that, Includes computer-readable storage media and processors; The computer-readable storage medium is used to store executable instructions; The processor is used to read executable instructions stored in the computer-readable storage medium and execute the ultrasonic CT waveform inversion method based on dynamic aperture as described in any one of claims 1-5.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the ultrasonic CT waveform inversion method based on dynamic aperture as described in any one of claims 1-5.

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