A method and system for cortical bone ultrasonic imaging based on frequency domain full-wave inversion

Abstract

The present invention relates to the technical field of cortical bone ultrasonic imaging, and provides a cortical bone ultrasonic imaging method based on frequency domain full-wave inversion, comprising the following steps: S1: arranging an acquisition environment for acquiring experimental wavefield signals of a cortical bone phantom model to be imaged; S2: acquiring the experimental wavefield signals of the cortical bone phantom model to be imaged; S3: setting an initial sound velocity model, forward modeling a simulated wavefield in the frequency domain, extrapolating the simulated wavefield, and recording the simulated wavefield signals in the frequency domain; S4: constructing a loss function required for full-wave inversion based on the experimental wavefield signals and the simulated wavefield signals, optimizing the loss function using a conjugate gradient method, and obtaining an optimized sound velocity distribution model; S5: increasing a fixed center frequency, assigning the initial sound velocity model to the optimized sound velocity distribution model, repeating steps S2-S4 until information iteration of all frequency points is completed, and outputting the final sound velocity model. Utilizing the full-wave inversion technique, the reliance on a priori sound velocity distribution model is greatly alleviated.

Description

Technical Field

[0001] The present invention relates to the technical field of cortical bone ultrasonic imaging, and in particular to a cortical bone ultrasonic imaging method and system based on frequency domain full-wave inversion. Background Art

[0002] Cortical bone is a type of bone tissue, also known as compact bone. It is part of the human skeletal system and is found in the outer regions of all long bones, including the femur, tibia, and ulna. Cortical bone has a very hard and dense structure, primarily composed of tightly packed bone cells, called osteocytes. These cells are distributed within the bone matrix, which is composed of collagen fibers and inorganic minerals. The main function of cortical bone is to provide mechanical support and protect internal organs. It has a high degree of strength and rigidity, capable of bearing the weight of the body and external stresses. In addition, cortical bone is involved in important physiological processes such as bone metabolism, storage of minerals (such as calcium and phosphorus), and red blood cell production. In summary, cortical bone is a dense bone tissue with strength and rigidity that performs the functions of supporting and protecting the body.

[0003] Cortical bone accounts for approximately 80% of human bone mass and is crucial for daily activities. However, due to its significant difference in acoustic impedance from surrounding soft tissue, ultrasound imaging is significantly more challenging, hindering bone diagnosis and treatment. Traditional soft tissue ultrasound imaging methods rely on the assumption of uniform sound velocity and, without a priori sound velocity models, struggle to provide clear images of biological hard tissues.

[0004] Currently, most commonly used medical ultrasound imaging methods are based on the pulse-echo method. This method assumes uniform sound velocity and is generally suitable for imaging soft tissues with minimal heterogeneity, such as Doppler imaging, brain imaging, and super-resolution imaging. However, when imaging hard tissues such as bone, where the sound velocity differs significantly from that of surrounding soft tissue, the pulse-echo method struggles to accurately image irregular bone or hard tissue without a prior model of the sound velocity distribution, easily leading to distortion and deformation of the ultrasound image.

[0005] The traditional ultrasonic pulse-echo method has the following limitations for cortical bone imaging: it requires a prior model of the sound velocity distribution of the target to be imaged. Without a known prior model of the sound velocity distribution, it is easy to cause image distortion and deformation. However, it is difficult to obtain a prior model of the sound velocity distribution in clinical applications; it is difficult to achieve clear structural imaging of cortical bone. The axial resolution of the pulse-echo based ultrasonic imaging method is determined by the transmitted pulse width, which is equal to half of the spatial pulse, and its lateral resolution is determined by the width of the ultrasonic beam, which is difficult to effectively improve in practical applications; the attenuation factor at the boundary between bone and soft tissue seriously affects the imaging quality, and the reverberation effect introduced by complex situations such as bone boundary reflection, diffraction, and scattering will seriously interfere with the pulse echo signal, causing obvious noise pollution, and thus seriously reducing the imaging quality.

[0006] The study of full-wave inversion imaging originated in the field of geophysics and is primarily used for underground resource exploration. By taking into account the full wavefield information and then iteratively matching the measured ultrasonic field with the numerically simulated wavefield calculated by the wave equation to perform wavefield reconstruction, extremely high inversion accuracy and resolution can be achieved, with a theoretical spatial resolution of up to half a wavelength. However, for biological hard tissues such as bone, imaging difficulties include large differences in acoustic impedance from surrounding tissues and complex wavefields in the edge regions, which are similar to the complex geological structures of the Earth's interior with their sound velocity distribution. Therefore, designing a full-wave inversion imaging method for cortical bone has high theoretical and practical value. Summary of the Invention

[0007] In response to the above problems, the purpose of the present invention is to provide a cortical bone ultrasonic imaging method and system based on frequency domain full-wave inversion. By utilizing full-wave inversion technology, the dependence on the prior model of sound velocity distribution is greatly alleviated; for cortical bone, a clear imaging effect can be presented on its structure and boundaries, which can significantly distinguish it from the surrounding soft tissue; at the same time, based on the inversion process in the frequency domain, while reducing data storage, it not only improves the data calculation efficiency, but also retains the high-resolution characteristics of full-wave inversion technology, and can provide high-resolution cortical bone images.

[0008] The above-mentioned object of the present invention is achieved through the following technical solutions:

[0009] A method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion comprises the following steps:

[0010] S1: Arranging an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom to be imaged, including two linear array ultrasonic transducers arranged opposite to each other;

[0011] S2: using the two linear array ultrasonic transducers arranged opposite to each other to sequentially transmit ultrasonic pulse signals with a fixed center frequency, collecting the experimental wave field signal of the cortical bone phantom model to be imaged, and completing the transformation of the experimental wave field signal from the time domain to the frequency domain;

[0012] S3: Setting a simulation wave field and an initial sound velocity model, performing forward modeling on the simulation wave field in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as in step S2, extrapolating the simulation wave field, and recording a simulation wave field signal in the frequency domain based on the current sound velocity model;

[0013] S4: constructing a loss function required for full-wave inversion based on the experimental wavefield signal and the simulated wavefield signal, and optimizing the loss function using a conjugate gradient method to obtain an optimized sound velocity distribution model;

[0014] S5: Increase the fixed center frequency, assign the initial sound speed model to the optimized sound speed distribution model, repeat steps S2-S4 until the information iteration of all frequency points is completed, and output the optimized sound speed distribution model as the final sound speed model.

[0015] Furthermore, in step S1, a collection environment for collecting the experimental wave field signal of the cortical bone phantom model to be imaged, including two linear array ultrasonic transducers arranged opposite to each other, is arranged as follows:

[0016] placing two identical linear array ultrasonic transducers parallely aligned and face to face, each of the linear array ultrasonic transducers comprising N array elements;

[0017] The cortical bone phantom model to be imaged is arranged between the two linear array ultrasonic transducers, and soft tissue is arranged around the cortical bone phantom model to be imaged.

[0018] Furthermore, in step S2, two linear array ultrasonic transducers arranged opposite to each other are used to sequentially transmit the ultrasonic pulse signals of the fixed center frequency, collect the experimental wave field signals of the cortical bone phantom model to be imaged, and complete the transformation of the experimental wave field signals from the time domain to the frequency domain, specifically as follows:

[0019] S21: All the array elements on one side of the linear array ultrasonic transducer sequentially transmit the fixed center frequency f cen Ultrasonic pulse signal;

[0020] S22: The acoustic field formed after the ultrasonic pulse signal passes through the cortical bone phantom to be imaged is received by the linear array ultrasonic transducer on the other side as the experimental wave field signal, wherein the experimental wave field signal includes N groups of dimensions of N×N t Experimental wave field data, N t is the sampling number of each group of experimental wave field data;

[0021] S23: For each set of dimensions, the size is N×N t The experimental wave field data in the time domain is subjected to Fourier transform at discrete frequency points to obtain a set of measured frequency domain wave field information in Represents a dimension of N×n f The complex matrix of the frequency points is the equally spaced frequency points within the -6dB bandwidth of the center frequency of the transmission, and the total number of frequency points is n f .

[0022] Furthermore, in step S3, the simulated wave field is set, and the initial sound velocity model is set. The simulated wave field in the frequency domain is forward modeled according to the same transceiver parameter settings of the linear array ultrasonic transducer as in step S2. The simulated wave field is extrapolated, and the simulated wave field signal in the frequency domain based on the current sound velocity model is recorded. Specifically,

[0023] S31: Setting a simulated wave field, wherein the transmitting and receiving parameters of the linear array ultrasonic transducer of the simulated wave field are set the same as those in step S2;

[0024] S32: Set the initial sound velocity model c(x,z)=c init , where x is the horizontal axis of the two-dimensional simulated wave field, and z is the vertical axis of the two-dimensional simulated wave field, i.e., the propagation direction;

[0025] S33: Start the forward modeling of the simulated wave field, and take the i-th array element as the emission source for each array element, and perform the forward modeling of the simulated wave field p from the wave field at z to the increment Δz. sim,i Make extrapolations.

[0026] Furthermore, the forward simulation wave field p from the wave field at z to the increment Δz is sim,i The extrapolation formula is as follows:

[0027]

[0028] in, is the set of discrete frequency points of the Fourier transform in step S2, Δz is the z-axis increment in the propagation direction, m(x,z)=1 / c(x,z) represents the slowness of the cortical bone phantom model to be imaged at the coordinate (x,z) in the two-dimensional simulated wave field, is the average slowness at propagation depth z, and They represent the Fourier transform and inverse transform operators in the x direction, exp is the exponential function symbol, j is the imaginary unit, and k x is the transverse spatial frequency of the simulated wave field in the frequency domain, p sim,i (x, z, f) is the frequency domain wavefield information based on the current discrete frequency point f at the position coordinate (x, z) in the two-dimensional simulated wavefield. After the simulated wavefield extrapolation is completed, all the simulated wavefield signals in the frequency domain based on the current sound velocity model c are recorded.

[0029] Furthermore, in step S4, based on the experimental wavefield signal and the simulated wavefield signal, the loss function required for full-wave inversion is constructed, and the conjugate gradient method is used to optimize the loss function to obtain the optimized sound velocity distribution model, specifically:

[0030] S41: Based on the experimental wavefield signal and the simulated wavefield signal, the loss function required for full-wave inversion is constructed as follows:

[0031]

[0032] Wherein, J(c) is the loss function constructed based on the current sound speed model c, N is the total number of the array elements transmitted, and p sim,i (c, f) The transmitted simulated wave field signal obtained based on the array element of the i-th emission and the current sound velocity model c, p mea,i (f) is the experimental wave field signal in the frequency domain obtained based on the array element of the ith emission in the simulation experiment. The frequency point set used in Fourier transform is

[0033] S42: Optimize the loss function using the conjugate gradient method to obtain the optimized sound velocity distribution model c k .

[0034] Furthermore, the conjugate gradient method is expressed as follows:

[0035]

[0036] Among them, c k with c k+1 are the sound velocity distribution models obtained by the kth iteration and the k+1th iteration optimization, α k is the step size of the k-th iteration update, Indicates the J(c k+1 ) find the gradient of the sound velocity distribution model c, where J(c k+1 ) represents the sound velocity distribution model c k+1 The loss function constructed, d k+1 with d k They represent the search directions of the k+1th iteration and the kth iteration update, β k is the momentum coefficient in the k-th iterative update.

[0037] A cortical bone ultrasonic imaging system based on frequency domain full wave inversion for performing the above-mentioned cortical bone ultrasonic imaging method based on frequency domain full wave inversion comprises:

[0038] An acquisition environment arrangement module, for arranging an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom to be imaged, including two linear array ultrasonic transducers arranged opposite to each other;

[0039] an experimental wavefield signal acquisition module, configured to use the two linear array ultrasonic transducers arranged opposite to each other to sequentially transmit ultrasonic pulse signals of a fixed center frequency, acquire the experimental wavefield signal of the cortical bone phantom to be imaged, and complete the transformation of the experimental wavefield signal from the time domain to the frequency domain;

[0040] a simulated wavefield signal acquisition module, configured to set a simulated wavefield and an initial sound velocity model, perform forward modeling of the simulated wavefield in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as those in the experimental wavefield signal acquisition module, extrapolate the simulated wavefield, and record a simulated wavefield signal in the frequency domain based on the current sound velocity model;

[0041] A sound velocity distribution model optimization model is used to construct a loss function required for full-wave inversion based on the experimental wave field signal and the simulated wave field signal, and to optimize the loss function using a conjugate gradient method to obtain an optimized sound velocity distribution model;

[0042] The final sound velocity model output module is used to increase the fixed center frequency, assign the initial sound velocity model to the optimized sound velocity distribution model, repeat the experimental wave field signal acquisition module, the simulation wave field signal acquisition module and the sound velocity distribution model optimization model until the information iteration of all frequency points is completed, and output the optimized sound velocity distribution model as the final sound velocity model.

[0043] A computer device includes a memory and one or more processors, wherein the memory stores computer code, and when the computer code is executed by the one or more processors, the one or more processors execute the above method.

[0044] A computer-readable storage medium stores computer code. When the computer code is executed, the above method is performed.

[0045] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0046] (1) A cortical bone ultrasonic imaging method based on frequency domain full-wave inversion is provided, comprising: S1: arranging an acquisition environment for acquiring an experimental wave field signal of a cortical bone phantom model to be imaged, including two linear array ultrasonic transducers arranged relatively to each other; S2: using the two linear array ultrasonic transducers arranged relatively to each other, sequentially emitting ultrasonic pulse signals of a fixed center frequency, acquiring the experimental wave field signal of the cortical bone phantom model to be imaged, and completing the transformation of the experimental wave field signal from the time domain to the frequency domain; S3: setting a simulation wave field, and setting an initial sound velocity model, according to the same transceiver parameters of the linear array ultrasonic transducer as in step S2. The simulated wave field in the frequency domain is forward modeled, the simulated wave field is extrapolated, and the simulated wave field signal in the frequency domain based on the current sound velocity model is recorded; S4: based on the experimental wave field signal and the simulated wave field signal, a loss function required for full-wave inversion is constructed, and the loss function is optimized using the conjugate gradient method to obtain an optimized sound velocity distribution model; S5: the fixed center frequency is increased, the initial sound velocity model is assigned to the optimized sound velocity distribution model, and steps S2-S4 are repeated until the information iteration of all frequency points is completed, and the optimized sound velocity distribution model is output as the final sound velocity model. The above technical solution, because the fixed center frequency of the emission covers information of various frequency bands, especially the low-frequency part, allows a wide range of sound velocity changes, which greatly reduces the dependence of cortical bone imaging on the prior sound velocity model; in addition, the full-wave waveform information in the frequency domain is used for full-wave inversion, which not only greatly reduces the data storage and processing burden compared to the time-domain full-wave inversion technology, but also ensures the high-resolution characteristics of the full-wave inversion imaging technology.

[0047] (2) The present invention utilizes the frequency domain full-wave inversion cortical bone ultrasound imaging algorithm to image the cortical bone at different angles. It can not only realize axial cross-sectional imaging of the cortical bone, but also jump angles to realize radial cross-sectional imaging, and has high applicability for cortical bone.

[0048] (3) In order to obtain clear and accurate cortical bone imaging, the present invention performs full-wave inversion on the simulated measurement data based on frequency domain data, and uses the angular spectrum method to accurately and quickly realize wave field extrapolation. Finally, after iterating the data at different frequency points, high-quality full-wave inversion results of the cortical bone are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is an overall flow chart of the cortical bone ultrasonic imaging method based on frequency domain full-wave inversion of the present invention;

[0050] Figure 2 This is a schematic diagram of the placement of the cortical bone phantom model to be imaged and two linear array ultrasonic transducers of the present invention;

[0051] Figure 3 Schematic diagram of the sound velocity model of the cortical bone phantom model to be imaged according to the present invention;

[0052] Figure 4 The present invention is aimed at Figure 3 Schematic diagram of the imaging results obtained from the cortical bone phantom target;

[0053] Figure 5 This is a schematic diagram of the sound velocity distribution in the radial section of the additional cortical bone phantom according to the present invention;

[0054] Figure 6 The present invention utilizes Figure 5 Schematic diagram of the inversion imaging results obtained from the mid-cortical bone phantom experiment;

[0055] Figure 7 This is the overall structural diagram of the cortical bone ultrasonic imaging system based on frequency domain full-wave inversion of the present invention. DETAILED DESCRIPTION

[0056] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0057] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a," "an," "said," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0058] First embodiment

[0059] like Figure 1 As shown, this embodiment provides a cortical bone ultrasonic imaging method based on frequency domain full-wave inversion, comprising the following steps:

[0060] S1: Arranging an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom model to be imaged, including two linear array ultrasonic transducers arranged opposite to each other.

[0061] In this embodiment, to obtain experimental wavefield signal data for a cortical bone phantom to be imaged, the first step is to arrange an acquisition environment for the experimental wavefield signal. This includes: placing two identical linear array ultrasonic transducers in parallel and aligned face to face, each comprising N array elements; placing the cortical bone phantom to be imaged between the two linear array ultrasonic transducers; and surrounding the cortical bone phantom to be imaged with soft tissue. For example, each linear array ultrasonic transducer may have 128 array elements.

[0062] like Figure 2 The figure shows the placement of the cortical bone phantom model to be imaged and two linear array ultrasonic transducers according to the present invention. Figure 3 As shown, the sound velocity is 2900 m / s, and the surrounding area is soft tissue (sound velocity 1525 m / s). The experimental wave field data in this embodiment is obtained by simulation experiment using the k-Wave toolkit. Each linear array ultrasonic transducer has 128 array elements, and the center spacing of the array elements is 0.3 mm. The linear array ultrasonic transducer on one side is selected, and each array element on it is set to transmit the initial center frequency f in sequence. cen =0.6Mhz, -6dB bandwidth is 0.1-1.1Mhz pulse signal, and the linear array ultrasonic transducer on the other side is responsible for receiving it.

[0063] S2: using the two linear array ultrasonic transducers arranged opposite to each other, sequentially emitting ultrasonic pulse signals with a fixed center frequency, collecting the experimental wave field signal of the cortical bone phantom to be imaged, and completing the transformation of the experimental wave field signal from the time domain to the frequency domain, specifically:

[0064] S21: All the array elements on one side of the linear array ultrasonic transducer sequentially transmit the fixed center frequency f cen ultrasonic pulse signal.

[0065] S22: The acoustic field formed after the ultrasonic pulse signal passes through the cortical bone phantom to be imaged is received by the linear array ultrasonic transducer on the other side as the experimental wave field signal, wherein the experimental wave field signal includes N groups of dimensions of N×N t Experimental wave field data, N t is the sampling number of each set of experimental wavefield data.

[0066] S23: For each set of dimensions, the size is N×N t The experimental wave field data in the time domain is subjected to Fourier transform at discrete frequency points to obtain a set of measured frequency domain wave field information in Represents a dimension of N×n fThe complex matrix of the frequency points is the equally spaced frequency points within the -6dB bandwidth of the center frequency of the transmission, and the total number of frequency points is n f .

[0067] For example, in this embodiment, a linear array ultrasonic transducer comprising 128 array elements is used, and each array element sequentially transmits a fixed center frequency of f cen The -6dB bandwidth is 1Mhz ultrasonic pulse signal, and the 128 array elements on the other side are responsible for recording the projected sound field information, and finally record 128 sets of experimental wave field data measured in the time domain where N t is the number of sampling times, Indicates a dimension of 128×N t The real number matrix, then at the current transmission center frequency f cen 21 frequency points are taken at equal intervals within the -6dB bandwidth, and all p t,i (t) Perform Fourier transform to obtain the current center frequency f cen 128 sets of frequency domain experimental wave field data under Represents a complex matrix of dimension 128×21.

[0068] S3: Setting a simulated wave field and an initial sound velocity model, forward modeling the simulated wave field in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as in step S2, extrapolating the simulated wave field, and recording the simulated wave field signal in the frequency domain based on the current sound velocity model, specifically:

[0069] S31: Setting a simulated wave field, wherein the transmitting and receiving parameters of the linear array ultrasonic transducer of the simulated wave field are set the same as those in step S2.

[0070] S32: Set the initial sound velocity model c(x,z)=c init , where x is the horizontal axis of the two-dimensional simulated wave field, and z is the vertical axis of the two-dimensional simulated wave field, i.e., the propagation direction.

[0071] S33: Start the forward modeling of the simulated wave field, and take the i-th array element as the emission source for each array element, and perform the forward modeling of the simulated wave field p from the wave field at z to the increment Δz. sim,i Extrapolate, the extrapolation formula is:

[0072]

[0073] in, is the set of discrete frequency points of the Fourier transform in step S2, Δz is the z-axis increment in the propagation direction, m(x,z)=1 / c(x,z) represents the slowness of the cortical bone phantom model to be imaged at the coordinate (x,z) in the two-dimensional simulated wave field, is the average slowness at propagation depth z, and They represent the Fourier transform and inverse transform operators in the x direction, exp is the exponential function symbol, j is the imaginary unit, and k x is the transverse spatial frequency of the simulated wave field in the frequency domain, p sim,i (x, z, f) is the frequency domain wave field information based on the current discrete frequency point f at the position coordinate (x, z) in the two-dimensional simulated wave field. After the simulated wave field is extrapolated, all the simulated wave field signals based on the frequency domain of the current sound velocity model c are recorded. For example, for a linear array ultrasonic transducer with 128 elements, all the simulated wave field signals based on the current sound velocity model c are recorded. Represents a complex matrix of dimension 128×21.

[0074] S4: Based on the experimental wavefield signal and the simulated wavefield signal, a loss function required for full-wave inversion is constructed, and the conjugate gradient method is used to optimize the loss function to obtain an optimized sound velocity distribution model, specifically:

[0075] S41: Based on the experimental wavefield signal and the simulated wavefield signal, the loss function required for full-wave inversion is constructed as follows:

[0076]

[0077] Wherein, J(c) is the loss function constructed based on the current sound speed model c, N is the total number of the array elements transmitted, and p sim,i (c, f) The transmitted simulated wave field signal obtained based on the array element of the i-th emission and the current sound velocity model c, p mea,i (f) is the experimental wave field signal in the frequency domain obtained based on the array element of the ith emission in the simulation experiment. The frequency point set used in Fourier transform is

[0078] S42: Optimize the loss function using the conjugate gradient method to obtain the optimized sound velocity distribution model c k The conjugate gradient method is expressed as follows:

[0079]

[0080] Among them, c k with c k+1are the sound velocity distribution models obtained by the kth iteration and the k+1th iteration optimization, α k is the step size of the kth iteration update, ▽ c J(c k+1 ) represents the J(c k+1 ) find the gradient of the sound velocity distribution model c, where J(c k+1 ) represents the sound velocity distribution model c k+1 The loss function constructed, d k+1 with d k They represent the search directions of the k+1th iteration and the kth iteration update, β k is the momentum coefficient in the k-th iterative update.

[0081] S5: Increase the fixed center frequency, assign the initial sound speed model to the optimized sound speed distribution model, repeat steps S2-S4 until the information iteration of all frequency points is completed, and output the optimized sound speed distribution model as the final sound speed model.

[0082] For example, increase the fixed center frequency by 0.5Mhz and use the currently optimized sound velocity distribution model as the new inversion initial sound velocity, i.e., f cen =f cen +0.5Mhz with c init =c k Repeat steps S2-S4 until the transmission center frequency reaches 2.1 MHz. Record the final sound velocity model and complete the final imaging based on the final sound velocity model.

[0083] Figure 3 4 is a sound velocity distribution diagram of the cortical bone phantom according to an embodiment of the present invention. Figure 4 The embodiment of the present invention is directed to Figure 3 Cortical bone phantom target, imaging results obtained using the above method. Figure 4 As shown, the imaging results have clear inner and outer boundaries, and the imaging position and shape are consistent with Figure 3 The cortical bone phantom model is highly matched. Figure 5 It is based on the sound velocity distribution of the radial section of the additional cortical bone phantom. Figure 6 This method utilizes Figure 5 Inversion imaging results obtained from the cortical bone phantom experiment. Figure 6 As can be clearly seen in the figure, the final inversion result not only highly overlaps with the phantom target in terms of position, but also well reflects the phantom's contour and sound velocity distribution. In summary, the method proposed in this paper not only achieves high-resolution axial imaging of cortical bone, but also effectively inverts the sound velocity distribution along its radial cross-section, demonstrating its high adaptability and robustness for cortical bone imaging.

[0084] In the embodiments, the present invention utilizes a frequency-domain full-wave inversion-based cortical bone ultrasound imaging algorithm to achieve high-resolution imaging of cortical bone. As can be seen from the embodiments, the present invention utilizes full-wave inversion to achieve not only clear imaging of the axial direction of cortical bone but also high-resolution imaging of its radial cross-sections, successfully achieving high-resolution imaging of a cortical bone phantom.

[0085] Second embodiment

[0086] like Figure 7 As shown, this embodiment provides a cortical bone ultrasonic imaging system based on frequency domain full wave inversion for performing the cortical bone ultrasonic imaging method based on frequency domain full wave inversion in the first embodiment, comprising:

[0087] An acquisition environment arrangement module 1 is used to arrange an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom model to be imaged, including two linear array ultrasonic transducers arranged opposite to each other;

[0088] The experimental wave field signal acquisition module 2 is used to use the two linear array ultrasonic transducers arranged opposite to each other to sequentially transmit ultrasonic pulse signals with a fixed center frequency, collect the experimental wave field signal of the cortical bone phantom to be imaged, and complete the transformation of the experimental wave field signal from the time domain to the frequency domain;

[0089] The simulated wavefield signal acquisition module 3 is used to set the simulated wavefield and the initial sound velocity model, perform forward modeling on the simulated wavefield in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as those in the experimental wavefield signal acquisition module, extrapolate the simulated wavefield, and record the simulated wavefield signal in the frequency domain based on the current sound velocity model;

[0090] The sound velocity distribution model optimization model 4 is used to construct a loss function required for full-wave inversion based on the experimental wave field signal and the simulated wave field signal, and optimize the loss function using the conjugate gradient method to obtain an optimized sound velocity distribution model;

[0091] The final sound velocity model output module 5 is used to increase the fixed center frequency, assign the initial sound velocity model to the optimized sound velocity distribution model, repeat the experimental wave field signal acquisition module, the simulation wave field signal acquisition module and the sound velocity distribution model optimization model until the information iteration of all frequency points is completed, and output the optimized sound velocity distribution model as the final sound velocity model.

[0092] A computer-readable storage medium stores computer code. When the computer code is executed, the above-described method is performed. A person skilled in the art will appreciate that all or part of the steps in the various methods of the above-described embodiments can be performed by a program instructing related hardware. The program can be stored in a computer-readable storage medium. The storage medium may include a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0093] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

[0094] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion, characterized in that: The following steps are involved: S1: Arranging an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom to be imaged, including two linear array ultrasonic transducers arranged opposite to each other; S2: using the two linear array ultrasonic transducers arranged opposite to each other to sequentially transmit ultrasonic pulse signals with a fixed center frequency, collecting the experimental wave field signal of the cortical bone phantom model to be imaged, and completing the transformation of the experimental wave field signal from the time domain to the frequency domain; S3: Setting a simulation wave field and an initial sound velocity model, performing forward modeling on the simulation wave field in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as in step S2, extrapolating the simulation wave field, and recording a simulation wave field signal in the frequency domain based on the current sound velocity model; S4: constructing a loss function required for full-wave inversion based on the experimental wavefield signal and the simulated wavefield signal, and optimizing the loss function using a conjugate gradient method to obtain an optimized sound velocity distribution model; S5: increasing the fixed center frequency, assigning the initial sound velocity model to the optimized sound velocity distribution model, repeating steps S2-S4 until all frequency point information iterations are completed, and outputting the optimized sound velocity distribution model as the final sound velocity model; In step S3, the simulated wave field is set, and the initial sound velocity model is set. The simulated wave field in the frequency domain is forward modeled according to the same transceiver parameter settings of the linear array ultrasonic transducer as in step S2. The simulated wave field is extrapolated, and the simulated wave field signal in the frequency domain based on the current sound velocity model is recorded. Specifically, S31: Setting a simulated wave field, wherein the transmitting and receiving parameters of the linear array ultrasonic transducer of the simulated wave field are set the same as those in step S2; S32: Set the initial sound velocity model c(x,z)=c init , where x is the horizontal axis of the two-dimensional simulated wave field, and z is the vertical axis of the two-dimensional simulated wave field, i.e., the propagation direction; S33: Start the forward modeling of the simulated wave field, and take the i-th array element as the emission source for each array element, and perform the forward modeling of the simulated wave field p from the wave field at z to the increment Δz. sim,i Make extrapolations; The simulated wave field p from the wave field at z to the increment Δz is sim,i The extrapolation formula is as follows: in, is the set of discrete frequency points of the Fourier transform in step S2, Δz is the z-axis increment in the propagation direction, m(x,z)=1 / c(x,z) represents the slowness of the cortical bone phantom model to be imaged at the coordinate (x,z) in the two-dimensional simulated wave field, is the average slowness at propagation depth z, and They represent the Fourier transform and inverse transform operators in the x direction, exp is the exponential function symbol, j is the imaginary unit, and k x is the transverse spatial frequency of the simulated wave field in the frequency domain, p sim,i (x, z, f) is the frequency domain wavefield information based on the current discrete frequency point f at the position coordinate (x, z) in the two-dimensional simulated wavefield. After the simulated wavefield extrapolation is completed, all the simulated wavefield signals in the frequency domain based on the current sound velocity model c are recorded.

2. The method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion according to claim 1, characterized in that: In step S1, a collection environment for collecting the experimental wave field signal of the cortical bone phantom model to be imaged, including two linear array ultrasonic transducers arranged opposite to each other, is arranged, specifically: placing two identical linear array ultrasonic transducers parallely aligned and face to face, each of the linear array ultrasonic transducers comprising N array elements; The cortical bone phantom model to be imaged is arranged between the two linear array ultrasonic transducers, and soft tissue is arranged around the cortical bone phantom model to be imaged.

3. The method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion according to claim 2, characterized in that: In step S2, two linear array ultrasonic transducers arranged opposite to each other are used to sequentially transmit the ultrasonic pulse signals of the fixed center frequency, collect the experimental wave field signals of the cortical bone phantom model to be imaged, and complete the transformation of the experimental wave field signals from the time domain to the frequency domain, specifically: S21: All the array elements on one side of the linear array ultrasonic transducer sequentially transmit the fixed center frequency f cen Ultrasonic pulse signal; S22: The acoustic field formed after the ultrasonic pulse signal passes through the cortical bone phantom to be imaged is received by the linear array ultrasonic transducer on the other side as the experimental wave field signal, wherein the experimental wave field signal includes N groups of dimensions of N×N t Experimental wave field data, N t is the sampling number of each group of experimental wave field data; S23: For each set of dimensions, the size is N×N t The experimental wave field data in the time domain is subjected to Fourier transform at discrete frequency points to obtain a set of measured frequency domain wave field information in Represents a dimension of N×n f The complex matrix of the frequency points is the equally spaced frequency points within the -6dB bandwidth of the center frequency of the transmission, and the total number of frequency points is n f .

4. The method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion according to claim 1, characterized in that: In step S4, based on the experimental wavefield signal and the simulated wavefield signal, the loss function required for full-wave inversion is constructed, and the conjugate gradient method is used to optimize the loss function to obtain the optimized sound velocity distribution model, specifically: S41: Based on the experimental wavefield signal and the simulated wavefield signal, the loss function required for full-wave inversion is constructed as follows: Wherein, J(c) is the loss function constructed based on the current sound speed model c, N is the number of total transmitted array elements, and p sim,i (c, f) The transmitted simulated wave field signal obtained based on the array element of the i-th emission and the current sound velocity model c, p mea,i (f) is the experimental wave field signal in the frequency domain obtained based on the array element of the ith emission in the simulation experiment. The frequency point set used in Fourier transform is S42: Optimize the loss function using the conjugate gradient method to obtain the optimized sound velocity distribution model c k .

5. The method for cortical bone ultrasonic imaging based on frequency domain full-wave inversion according to claim 1, characterized in that: The conjugate gradient method is expressed as follows: Among them, c k with c k+1 are the sound velocity distribution models obtained by the kth iteration and the k+1th iteration optimization, α k is the step size of the kth iteration update, ▽ c J(c k+1 ) represents the J(c k+1 ) find the gradient of the sound velocity distribution model c, where J(c k+1 ) represents the sound velocity distribution model c k+1 The loss function constructed, d k+1 with d k They represent the search directions of the k+1th iteration and the kth iteration update, β k is the momentum coefficient in the k-th iterative update.

6. A cortical bone ultrasonic imaging system based on frequency domain full wave inversion for executing the cortical bone ultrasonic imaging method based on frequency domain full wave inversion according to any one of claims 1 to 5, characterized in that: include: An acquisition environment arrangement module, for arranging an acquisition environment for acquiring experimental wave field signals of a cortical bone phantom to be imaged, including two linear array ultrasonic transducers arranged opposite to each other; an experimental wavefield signal acquisition module, configured to use the two linear array ultrasonic transducers arranged opposite to each other to sequentially transmit ultrasonic pulse signals of a fixed center frequency, acquire the experimental wavefield signal of the cortical bone phantom to be imaged, and complete the transformation of the experimental wavefield signal from the time domain to the frequency domain; a simulated wavefield signal acquisition module, configured to set a simulated wavefield and an initial sound velocity model, perform forward modeling of the simulated wavefield in the frequency domain according to the same transceiver parameter settings of the linear array ultrasonic transducer as those in the experimental wavefield signal acquisition module, extrapolate the simulated wavefield, and record a simulated wavefield signal in the frequency domain based on the current sound velocity model; A sound velocity distribution model optimization model is used to construct a loss function required for full-wave inversion based on the experimental wave field signal and the simulated wave field signal, and to optimize the loss function using a conjugate gradient method to obtain an optimized sound velocity distribution model; The final sound velocity model output module is used to increase the fixed center frequency, assign the initial sound velocity model to the optimized sound velocity distribution model, repeat the experimental wave field signal acquisition module, the simulation wave field signal acquisition module and the sound velocity distribution model optimization model until the information iteration of all frequency points is completed, and output the optimized sound velocity distribution model as the final sound velocity model.

7. A computer device comprising a memory and one or more processors, wherein the memory stores computer code, and when the computer code is executed by the one or more processors, the one or more processors are caused to perform the method according to any one of claims 1 to 5. 8 . A computer-readable storage medium storing computer code, wherein when the computer code is executed, the method according to claim 1 is performed.

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