Thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging

Abstract

The invention relates to a thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging. And a complete ablation and monitoring multi-physical field simulation process is constructed. Based on a COMSOL simulation platform, bidirectional coupling is carried out on electromagnetic waves and a biological heat transfer physical field in the ablation process, and tissue temperature and damage range solving under dynamic parameters is achieved. In the monitoring process, temperature distribution and dynamic parameters at a monitoring time point are introduced, electromagnetic waves, biological heat transfer and pressure acoustics physical field interfaces are sequentially coupled to realize visualization of the physical process of thermoacoustic monitoring thermal ablation, and detected thermoacoustic signals are subjected to image reconstruction. And finally, performing image processing to obtain information related to the ablation progress, such as tumor and ablation needle positioning, temperature distribution and ablation focus. Dynamic temperature detection and damage evaluation in the ablation process can be achieved, the ablation progress is quantitatively analyzed, the safety in microwave ablation treatment is improved, and the method has certain application value in the field of precise medical treatment.

Description

Technical Field

[0001] The present invention relates to the field of microwave thermoacoustic monitoring simulation, and in particular to a thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging. Background Art

[0002] The current means of monitoring thermal ablation mainly include CT, MRI, and ultrasound imaging. CT scanning can provide high spatial resolution but cannot perform real-time imaging; and it contains ionizing radiation and cannot be used for short-term large-scale detection. MRI can measure temperature to help assess the degree of tissue necrosis during ablation, but it also cannot perform real-time monitoring; and it has the limitations of being expensive and incompatible with metals. Ultrasound guidance is widely used, especially in soft tissue tumor ablation. It can provide relatively clear real-time image feedback and can qualitatively or quantitatively reflect the stiffness of the tissue, thereby judging the coagulative necrosis of the tumor. However, bubbles caused by heat in the high temperature range will cause artifacts in the ultrasound image. Therefore, the development of new imaging technologies that are portable, non-destructive, and can monitor the progress of thermal ablation in real time is particularly important for accurate thermal ablation treatment.

[0003] Microwave thermoacoustic imaging is a novel non-invasive biomedical imaging technology that combines the high resolution of ultrasound with the high tissue penetration of microwaves. Its imaging principle is based on the differences in the dielectric properties of biological tissues: the significant dielectric difference between malignant tumors and normal tissue enables precise identification of tumor boundaries, while the dielectric response characteristics of metallic foreign bodies enable precise positioning of the ablation antenna. These characteristics give it significant potential for monitoring in microwave tumor ablation. Numerical simulation, as a precursor to experimental research, can effectively reduce experimental costs and risks and provide critical prior guidance for practical applications.

[0004] COMSOL Multiphysics has become the mainstream platform for microwave thermoacoustic imaging simulation due to its excellent multi-physics coupling capabilities and modular operation advantages. The current research has preliminarily constructed a physical process model of this technology. By coupling the "electromagnetic wave frequency domain" and "pressure acoustic transient" modules, the Y.Deng team established a two-dimensional model for the generation of near-field microwave thermoacoustic signals, revealing the electromagnetic-acoustic coupling mechanism. Huang Lin and others focused on the characteristics of breast cancer tissue and systematically analyzed the influence of Young's modulus, excitation function and tumor size on thermoacoustic signals. The Hagness team developed a single-pulse microwave ablation-thermoacoustic monitoring dynamic model to quantify the specific absorption rate distribution of pure water under temperature changes and its thermoacoustic signal characteristics.

[0005] Although existing simulations have enabled visualization of fundamental physical processes, limitations exist in thermal ablation monitoring scenarios: There is a lack of real-time electromagnetic-thermal-acoustic multi-field coupled modeling of the dynamic evolution of the ablation region, and the correlation between monitored thermoacoustic signals and tissue temperature and thermal damage remains unclear. Therefore, constructing a complete dynamic coupled model of "thermal ablation-microwave thermoacoustic monitoring" that collaboratively simulates microwave thermal effects, tissue thermal expansion, and acoustic wave propagation can provide theoretical support and experimental design for precise ablation, with significant clinical application value.

[0006] The inventor's prior application, CN120052812, describes a microwave thermoacoustic imaging multi-physics simulation detection and monitoring method, which is used to establish a complete thermoacoustic multi-physics simulation detection and monitoring process. This method, based on COMSOL, sequentially couples the "Electromagnetic Waves, Frequency Domain," "Bioheat Transfer," "Solid Mechanics," and "Pressure Acoustics, Transient" physics interfaces to visualize the entire microwave thermoacoustic imaging process. The thermoacoustic image is reconstructed by calculating the thermoacoustic signal detected by each ultrasonic transducer. Furthermore, a steady-state solver and parametric sweep are combined to visualize the temporal variation of electromagnetic energy absorption in biological tissues. Multiple transient solvers are then used to calculate the thermoacoustic signal at each monitoring time point.

[0007] This patent realizes the visualization of the physical process of microwave thermoacoustic imaging by sequentially coupling the “Electromagnetic Waves, Frequency Domain”, “Bioheat Transfer”, “Solid Mechanics”, and “Pressure Acoustics, Transient” physical field interfaces based on COMSOL, and reconstructs the thermoacoustic image by calculating the thermoacoustic signal detected by each ultrasonic transducer, which only involves the relevant physical processes of microwave thermoacoustic imaging. This patent involves the physical process of thermal ablation and the physical process of microwave thermoacoustic imaging. By constructing the “electromagnetic-thermal” and “electromagnetic-thermal-acoustic” multi-physics field coupling models, it realizes the synchronous simulation of the evolution of tissue thermal damage and the thermoacoustic signal during thermal ablation and microwave thermoacoustic monitoring. Compared with the static model, the dynamic framework of the present invention can also accurately reflect the interaction mechanism between the temperature field and the acoustic wave characteristics of the ablation area.

[0008] This patent utilizes a one-way coupled solution in the "Electromagnetic Wave, Frequency Domain" and "Bioheat Transfer" modules. This patent takes into account the differences in excitation source configurations during thermal ablation and microwave thermoacoustic monitoring. Low-power continuous wave excitation is used during ablation, while high-power short-pulse width excitation is used during microwave thermoacoustic monitoring. Because the temperature-dependent variations of multiple parameters during ablation can negatively impact tissue absorption of microwaves, this patent utilizes a two-way coupled "electromagnetic-thermal" solution during thermal ablation. Summary of the Invention

[0009] The present invention aims to solve the above problems of the prior art. It proposes a thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging. The technical solution of the present invention is as follows:

[0010] A thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging includes the following steps:

[0011] S1. Constructing a simulation geometric model for thermal ablation and microwave thermoacoustic monitoring;

[0012] S2. Based on the microwave biothermal effect and thermoacoustic effect, set up the electromagnetic wave, frequency domain, bioheat transfer, transient, and transient pressure acoustics physics interfaces and corresponding boundary conditions.

[0013] S3. Set the dynamic temperature parameters of each model according to the selected physics interface;

[0014] S4. Set symmetric solution conditions and reasonably divide the grids of different solution domains into corresponding sizes according to simulation requirements;

[0015] S5. Add a steady-state-transient bidirectional coupling solver for solving the physical field of the ablation process, and add a steady-state and transient unidirectional coupling solver for solving the physical field of microwave thermoacoustic monitoring;

[0016] S6. Obtain the temperature distribution, biological damage score, thermoacoustic signal and acoustic pressure distribution during the ablation process, and export the data;

[0017] S7. Signal and image processing obtains information related to ablation progress, including tumor localization, ablation needle positioning, temperature distribution, and ablation lesions, which is compared and analyzed with the visualization results in S6.

[0018] Furthermore, the construction of the thermal ablation and microwave thermoacoustic monitoring simulation geometric model in S1 specifically includes the following steps:

[0019] S11. Thermal ablation geometric model construction: For thermal ablation, a two-dimensional axisymmetric model is selected in the geometric components to construct a coaxial slot ablation antenna geometric model and a biological tissue model.

[0020] S12. Constructing a geometric model for microwave thermoacoustic monitoring, specifically: selecting a three-dimensional model in the geometric component, and constructing a three-dimensional geometric model of a coaxial slot ablation antenna, biological tissue, rectangular waveguide, and oil cylinder.

[0021] Furthermore, the S2 includes the following steps:

[0022] S201, Thermal Ablation Physics Interface and Boundary Condition Settings:

[0023] S202, Microwave Thermoacoustic Monitoring Ablation Physics Interface and Boundary Condition Settings:

[0024] In step S201, the "Electromagnetic Wave, Frequency Domain" and "Bioheat Transfer, Transient" interfaces are bidirectionally coupled to solve the multi-physics process of microwave ablation. In the thermal ablation process, the "Electromagnetic Wave, Frequency Domain" interface is used to solve the electric field distribution and energy absorption density in biological tissues; and the "Bioheat Transfer, Transient" interface is used to solve the temperature rise of biological tissues due to the absorption of electromagnetic wave energy.

[0025] The boundary conditions in the thermal ablation process include electromagnetic boundary conditions and thermal boundary conditions; wherein the electromagnetic boundary conditions include port boundary conditions, ideal conductor boundary conditions and scattering boundary conditions;

[0026] The input power of the port boundary condition during the thermal ablation process is 10 W, the port type is set to coaxial, and the mode is transverse electromagnetic wave TEM mode;

[0027] The ideal boundary conductor boundary condition is:

[0028]

[0029] in, represents the unit normal vector, represents the electric field on the surface of an ideal conductor. This formula indicates that the tangential component of the electric field on the surface of an ideal conductor is 0;

[0030] The scattering boundary condition is:

[0031]

[0032] in, represents the unit normal vector, represents the electric field at the boundary of biological tissue, k is the wave number, and the formula as a whole is used to represent the antenna in radiation problems, describing the propagation and attenuation characteristics of electromagnetic waves at the boundary;

[0033] The thermal boundary condition is a heat flux boundary condition:

[0034]

[0035] in, represents the heat flux of biological tissue conduction, h represents the heat conductivity between biological tissue and the outside world, which is set to 5W / (m 2 K), where W represents power in watts, m represents distance in meters, and K represents temperature in Kelvin; T ext represents the external temperature, which is set to 310.15K, and T represents the temperature of biological tissue;

[0036] The step S202 microwave thermoacoustic monitoring process is coupled with "electromagnetic wave, frequency domain", "biological heat transfer, transient", "pressure acoustics, transient" physical field interfaces in sequence for multi-physical field process solving of microwave thermoacoustic monitoring; the "electromagnetic wave, frequency domain" and "biological heat transfer" physical field interfaces in the microwave thermoacoustic monitoring process are used for solving temperature rise of biological tissue due to absorption of electric field wave energy; the "biological heat transfer" and "pressure acoustics, transient" physical field are used for solving thermoacoustic signals generated by thermal elastic expansion of biological tissue;

[0037] In the step S202 microwave thermoacoustic monitoring process, the boundary conditions include electromagnetic boundary conditions, thermal boundary conditions and acoustic boundary conditions, wherein the electromagnetic boundary conditions include port boundary conditions, ideal electrical conductor boundary conditions and impedance boundary conditions;

[0038] In the thermoacoustic monitoring process, the input power of the port boundary condition is 500 kW / m, the port type is set to rectangular, and the port mode is set to TE10 mode.

[0039] The ideal electrical conductor boundary condition is:

[0040]

[0041] The impedance boundary condition is:

[0042]

[0043] wherein, denotes a unit normal vector, denotes a coupling oil boundary electric field, μ denotes a coupling oil permeability, ε denotes a coupling oil dielectric constant, σ denotes a coupling oil electrical conductivity, and ω denotes a microwave angular frequency, denotes a coupling oil boundary magnetic field, denotes a source electric field;

[0044] The thermal boundary condition is a heat flux boundary condition:

[0045]

[0046] The acoustic boundary condition is a plane wave radiation boundary condition:

[0047]

[0048] wherein, denotes a biological tissue conduction heat flux, h denotes a heat conduction coefficient between the biological tissue and the outside world, and is set to 5 W / (m 2 K), wherein W denotes power watt, m denotes distance unit meter, K denotes temperature unit Kelvin; T extrepresents the external temperature, which is set to 310.15K, and T represents the temperature of the biological tissue.

[0049] Where p represents the acoustic pressure generated by the microwave thermoacoustic effect on biological tissue, and ρ represents the density of the coupling oil, which is set to 860 kg / m 3 , v s represents the speed of sound in the coupling oil and is set to 1540 m / s.

[0050] Furthermore, the S3 thermal ablation process specifically includes the following steps:

[0051] S301 thermal ablation process parameter settings:

[0052] S302 Microwave Thermoacoustic Monitoring Process Parameter Settings:

[0053] The "Electromagnetic Waves, Frequency Domain" physics interface in the S301 thermal ablation process requires the definition of the electrical conductivity, magnetic permeability, and relative permittivity of the ablation needle and biological tissue; the "Bioheat Transfer, Transient" physics interface requires the definition of the constant-pressure heat capacity, thermal conductivity, and density of biological tissue. These parameters are all dynamic parameters that change with temperature.

[0054] The S302 microwave thermoacoustic monitoring process requires the definition of the dielectric constant, magnetic permeability, and electrical conductivity for the "Electromagnetic Waves, Frequency Domain" physics interface; the definition of the constant-pressure heat capacity, thermal conductivity, and density of biological tissue for the "Bioheat Transfer" physics interface; and the definition of the sound velocity and density in the coupling oil and the thermal expansion coefficient in biological tissue for the "Pressure Acoustics, Transient" physics interface. All of the above parameters, except those in the coupling oil, are dynamic parameters that change with temperature.

[0055] Furthermore, the S4 includes the following steps:

[0056] S401 symmetric solution settings:

[0057] S402 Reasonably divide the grids of different solution domains into corresponding sizes:

[0058] The physical fields that need to be solved symmetrically in the thermal ablation in S401 include "electromagnetic waves, frequency domain" and "biological heat transfer". The symmetry condition is to make the model rotationally symmetrical along the axis Z=0.

[0059] Among them, the symmetry conditions of "Electromagnetic Waves, Frequency Domain" are:

[0060]

[0061] Where, In the cylindrical coordinate system, the electric field is at the azimuth angle The field component under the formula represents the transverse component of the electric field by E r、E z Determine,satisfy the constraint of no lateral rotation;

[0062] Among them, the symmetry condition of "biological heat transfer" is:

[0063] -n·q=0

[0064] Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ;

[0065] In the S401 microwave thermoacoustic monitoring ablation, the physical fields that need to be solved symmetrically include "bioheat transfer" and "pressure acoustics, transient". The symmetry condition is to divide the model into four equal parts along the X=0, YZ plane and the Y=0, XZ plane.

[0066] Among them, the symmetry conditions in the bioheat transfer module are:

[0067] -n·q=0

[0068] Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ;

[0069] The symmetry condition in the Pressure Acoustics Module is:

[0070]

[0071] Where n is the unit normal vector of the boundary, ρ is the fluid density, and p t is the total sound pressure, q d The sound source term represents the externally applied dipole sound source, with the unit of N / m 3 , is the gradient operator;

[0072] In the S402 thermal ablation process, the maximum unit size of the grid is set to 3mm, the minimum unit size is 0.5mm, and the grid shape is a free triangle grid. In the S402 microwave thermoacoustic monitoring process, the maximum unit size of the "electromagnetic wave, frequency domain" and "biological heat transfer field" grids is set to 3mm, the minimum unit size is 0.5mm, and the grid shape is a free tetrahedron grid by weighing the simulation time and solution accuracy. The maximum grid size h is set for "pressure acoustics, transient". max The following conditions must be met:

[0073]

[0074] Among them, f max The maximum ultrasonic frequency for which the Pressure Acoustics, Transient physics is to be solved is set to 0.5 MHz.

[0075] Further, the S5 comprises the following steps:

[0076] S501 thermal ablation multi-physics simulation solution setting:

[0077] S502 microwave thermoacoustic monitoring ablation multi-physics simulation solution setting:

[0078] Wherein, in the S501 thermal ablation multi-physics, a frequency domain-transient solver is used to calculate the "electromagnetic wave, frequency domain" and "biological heat transfer, transient" physical field interface, and the center frequency is set to 2.45GHz. The absorption of microwave energy by biological tissue causes temperature rise, which changes the electrical and thermal parameters of the tissue, which in turn affects the absorption of electromagnetic waves and temperature changes in the tissue at the next moment; for the "biological heat transfer" physical field interface, the "backward difference formula" method is selected in the solver configuration; the time step is set to 0.5S, and the solution time is set to 600S;

[0079] Wherein, in the S502 microwave thermoacoustic monitoring ablation, a steady-state solver is used to calculate the "electromagnetic wave, frequency domain" physical field interface, and the center frequency of the solution is 3GHz; two transient solvers are used to solve the "biological heat transfer" and "pressure acoustics, transient" physical field interfaces; for the "biological heat transfer" physical field interface, the "backward difference formula" method is selected in the solver configuration; the time step is set to 0.1us, and the solution time is set to 100us. For the "pressure acoustics, transient" physical field interface, the "generalized alpha" method is selected in the solver configuration, and the time step is set to 0.033us.

[0080] Further, the S6 mainly comprises the following steps:

[0081] S601 thermal ablation visualization simulation result acquisition:

[0082] S602 microwave thermoacoustic monitoring ablation visualization simulation result acquisition and thermoacoustic image reconstruction:

[0083] Wherein, in the S601 microwave tumor ablation process, the visualization results of temperature distribution and damage score after microwave ablation are as follows:

[0084] After the simulation calculation is completed, in the two-dimensional rotation, select the data set "study 1 / solution 1", the axis definition method is point 1(0, 0), point 2(0, 1), the number of rotation layers is selected to be 360 layers, and the starting angle and the rotation angle are set to 0° and 360°; add a three-dimensional drawing group in the result and select the body, the data set is selected to be "study 1 / solution 1", the expression is changed to T, select the time, and add the exported drawing data to export the three-dimensional temperature distribution at the corresponding time point.

[0085] In the microwave thermoacoustic monitoring process S602, the thermoacoustic signal of the physical field calculation result is obtained and the thermoacoustic image reconstruction is performed based on it as follows:

[0086] After the simulation calculation is completed, add a three-dimensional mirror to the data set, select "Pressure Acoustics, Transient" for the data set, and mirror the solved thermoacoustic data into complete three-dimensional data; enter the three-dimensional coordinate position of the transducer in the three-dimensional cutoff point, replace the expression with "actd.p_t" in the derived value, select two-dimensional mirror for the data set, and perform point calculations to obtain the sound pressure information at all transducers. The obtained data is exported, and the delayed superposition algorithm is used in MATLAB to reconstruct the corresponding monitoring thermoacoustic image at this moment.

[0087] Furthermore, in process S7, the obtained simulation data and thermoacoustic images are processed, and thermoacoustic image reconstruction is performed in step S7 to obtain positioning information of the tumor and ablation needle. The thermoacoustic image reconstructed in step S7 is converted from sound pressure to temperature. The initial thermoacoustic image and the thermoacoustic image during the ablation process are input and regionalized. The sound pressure and temperature fitting is performed for the tumor and liver regions respectively. Finally, the "Arrhenius equation" is used to substitute the temperature distribution obtained at multiple monitoring time points into the equation for calculation to obtain the corresponding biological thermal damage range at the last monitoring moment, that is, the range of the ablation lesion.

[0088] The advantages and beneficial effects of the present invention are as follows:

[0089] By constructing a dynamic coupled electromagnetic, thermal, and acoustic multiphysics model, this paper achieves simultaneous simulation of the evolution of tissue thermal damage and thermoacoustic signals during thermal ablation and thermoacoustic monitoring. Compared to traditional static models, this dynamic framework accurately reflects the interaction between the temperature field and acoustic wave characteristics in the ablation area.

[0090] By post-processing the simulation signal and thermoacoustic images, this paper effectively extracts ablation progress information, including tumor boundaries, ablation needle positioning, temperature distribution, and ablation lesions. This provides a theoretical basis and experimental guidance for real-time microwave thermoacoustic monitoring of ablation.

[0091] The present invention provides a thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging. Step S2 is based on COMSOL. During the thermal ablation process, the "electromagnetic wave, frequency domain" and "bioheat transfer" physical field interfaces are coupled. During the microwave thermoacoustic monitoring process, the "electromagnetic wave, frequency domain", "bioheat transfer" and "pressure acoustics, transient" multi-physics field interfaces are coupled. In conjunction with step S3, synchronous simulation of the evolution of tissue thermal damage and the thermoacoustic signal during thermal ablation and microwave thermoacoustic monitoring is achieved. In the thermal ablation physical field solution process of step S5, a two-way coupling solution method is adopted, which can effectively correlate the mutual influence between the thermal parameter changes caused by the temperature distribution and the microwave absorption characteristics. Finally, the thermoacoustic image is reconstructed by the detected thermoacoustic signal, and the thermoacoustic image is post-processed in combination with steps S6 and S7 to effectively extract ablation progress information such as tumor boundary, ablation needle positioning, temperature distribution, and ablation lesions. It provides a theoretical basis and experimental guidance for real-time monitoring of thermal ablation by microwave thermoacoustics.

[0092] The ingenuity of the present invention lies in: (1) Compared with the traditional static simulation model, the dynamic framework of the present invention can also accurately reflect the interaction mechanism between the temperature field and acoustic wave characteristics of the ablation area. (2) The present invention introduces the "electromagnetic-thermal" bidirectional coupling solution and dynamic parameters in the thermal ablation process, which can accurately reflect the temperature changes and microwave absorption characteristics during the thermal ablation process. (3) The image processing method proposed in the present invention can extract information related to the ablation progress, such as the ablation needle position, tumor boundary, temperature gradient distribution and damage range, from the thermoacoustic signal and thermoacoustic image, to provide feedback and quantitative evaluation for real-time monitoring of thermal ablation by microwave thermoacoustics, thereby improving the accuracy and effectiveness of thermal ablation treatment and reducing treatment risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 This is a flow chart of a thermal ablation monitoring simulation method based on microwave thermoacoustic imaging according to a preferred embodiment of the present invention;

[0094] Figure 2 A schematic diagram of a thermal ablation process simulation model and physical field boundary conditions provided for an embodiment of the present invention;

[0095] Figure 3 A schematic diagram of a microwave thermoacoustic monitoring ablation process simulation model and physical field boundary conditions provided for an embodiment of the present invention;

[0096] Figure 4 This is a flowchart of the image processing based on simulation results of the present invention. DETAILED DESCRIPTION

[0097] The following will describe the technical solutions in the embodiments of the present invention in detail with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention.

[0098] The technical solution of the present invention to solve the above technical problems is:

[0099] Please see the attached Figure 1 , the present invention has dealt with a thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging, and constructed a complete multi-physics field simulation process of thermal ablation and microwave thermoacoustic monitoring ablation. The present invention is based on COMSOL simulation software, and performs bidirectional coupling of the "electromagnetic wave, frequency domain" and "bioheat transfer" physical field interfaces during the ablation process to achieve the solution of liver tissue temperature and damage range under dynamic temperature parameters. In the microwave thermoacoustic monitoring process, the temperature distribution and dynamic temperature parameters corresponding to the monitoring time point are first introduced, and the "electromagnetic wave, frequency domain", "bioheat transfer" and "pressure acoustics, transient" physical field interfaces are coupled in sequence to realize the visualization of the physical process of microwave thermoacoustic monitoring ablation, and the thermoacoustic image is reconstructed through the thermoacoustic signal detected by each ultrasonic transducer, and the obtained thermoacoustic signal and thermoacoustic image are finally processed to obtain information related to the ablation progress, such as tumor positioning, ablation needle positioning, temperature distribution and ablation lesions. Specifically comprising the following steps:

[0100] S1. Construct a geometric model for thermal and thermoacoustic monitoring simulation.

[0101] Based on the actual microwave thermoacoustic imaging experimental configuration, in order to simulate the actual physical process of ablation and thermoacoustic monitoring, we chose to construct a two-dimensional rotationally symmetric and three-dimensional model for calculation. The details are as follows:

[0102] S101 thermal ablation geometric model construction:

[0103] S102 Microwave Thermoacoustic Monitoring Ablation Geometric Model Construction:

[0104] Please refer to the attached Figure 2 The thermal ablation model consists of a coaxial ablation antenna, liver tissue, and tumor tissue. The liver tissue size is set as a semicircle with a radius of 30 mm, and the tumor size is set as a semicircle with a radius of 10 mm.

[0105] Please refer to the attached Figure 3 The microwave thermoacoustic monitoring model consists of a rectangular waveguide, a coupled oil cylinder, an ablation antenna, liver tissue, tumor tissue, and a ring-shaped ultrasonic transducer. The rectangular waveguide is sized as a 100mm×74mm×36mm cuboid, the oil cylinder is sized as a 100mm×100mm×100mm cube, the liver is sized as a 30mm-radius sphere, and the tumor is sized as a 10mm-radius sphere.

[0106] S2. Based on the microwave biothermal effect and thermoacoustic effect, set up the electromagnetic wave, frequency domain, bioheat transfer, transient, and transient pressure acoustics physics interfaces and corresponding boundary conditions. Specifically, it includes:

[0107] S201 Thermal Ablation Physics Interface and Boundary Condition Settings:

[0108] S202 Microwave Thermoacoustic Monitoring Ablation Physics Interface and Boundary Condition Settings:

[0109] Specifically, the thermal ablation in step S201 involves the following two physical processes:

[0110] (1) Coaxial antenna radiates microwaves into biological tissues

[0111] (2) Biological tissue absorbs electromagnetic wave energy and generates temperature rise

[0112] Therefore, the physics interfaces for this process include the "Electromagnetic Waves, Frequency Domain" and "Bioheat Transfer" physics interfaces. After selecting the physics interface, set the boundary conditions based on the respective physical model and physics interface. The details are as follows:

[0113] Please refer to Figure Attachment 2. In the thermal ablation physics model, the "Electromagnetic Waves, Frequency Domain" physics interface acts on the entire geometric model; the upper dielectric of the coaxial antenna is set as a port boundary condition, the boundary between the dielectric and copper is set as an ideal conductor boundary condition, and the liver tissue boundary is set as a scattering boundary condition. "Bioheat Transfer" acts on the biological tissue and the ablation antenna, considering that there is also heat exchange between the biological tissue and the antenna. Therefore, a heat flux boundary is set at the boundary between the biological tissue and the antenna, as shown below;

[0114] The input power of the port boundary condition is 10 W, the port type is set to coaxial, and the mode is transverse electromagnetic wave TEM mode.

[0115] The ideal boundary conductor boundary condition is:

[0116]

[0117] The scattering boundary condition is:

[0118]

[0119] in, represents the unit normal vector, represents the electric field at the boundary of biological tissue, k is the wave number (propagation constant), and the formula as a whole is used to represent the antenna in radiation problems, describing the propagation and attenuation characteristics of electromagnetic waves at the boundary.

[0120] The heat flux boundary condition is:

[0121]

[0122] in, represents the heat flux conducted by the biological tissue, h represents the heat conduction coefficient between the biological tissue and the outside world, and is set to 5 W / (m 2 K), where W represents power in watts, m represents distance in meters, and K represents temperature in kelvin; T ext represents the temperature of the outside world, and is set to 310.15 K, and T represents the temperature of the biological tissue.

[0123] Specifically, the S202 thermoacoustic monitoring ablation process involves the following three physical processes:

[0124] (1) microwave radiation into the biological tissue, the biological tissue absorbs electromagnetic wave energy to produce temperature rise;

[0125] (2) the biological tissue expands elastically due to the temperature rise and emits ultrasonic waves;

[0126] (3) ultrasonic waves propagate to the surrounding medium

[0127] Therefore, the physical field interfaces of this process include the "electromagnetic wave, frequency domain", "biological heat transfer", and "pressure acoustics, transient" physical field interfaces. After selecting the physical field interfaces, the boundary conditions are set according to the respective physical models and the physical field interfaces. Specifically as follows:

[0128] Please refer to FIG. 3, in the microwave thermoacoustic monitoring ablation physical model, the "electromagnetic wave, frequency domain" acts on the entire geometric model; the right opening of the rectangular waveguide is used to radiate electromagnetic waves, the left side of the rectangular waveguide is set as a port boundary condition, the remaining surfaces of the waveguide are set as ideal electrical conductor boundary conditions, and the boundaries of the oil cylinder are set as impedance boundary conditions. The "biological heat transfer" acts on the liver and tumor tissue, and the heat exchange between the biological tissue and the coupling oil boundary is considered, so the heat flux boundary condition should be set at the boundary between the biological tissue and the coupling oil. The "pressure acoustics, transient" acts on the geometric model except the rectangular waveguide; in order to minimize the reflection of the boundary to the acoustic wave, the boundaries of the oil cylinder are set as "plane wave radiation" boundaries; specifically as follows:

[0129] The input power of the port boundary condition is 500 kW / m, the port type is set as rectangular, and the port mode is set as TE10 mode;

[0130] The boundary condition of the ideal electrical conductor is:

[0131]

[0132] The impedance boundary condition is:

[0133]

[0134] wherein, represents the unit normal vector, represents the electric field at the coupling oil boundary, μ represents the magnetic permeability of the coupling oil, ε represents the dielectric constant of the coupling oil, σ represents the electrical conductivity of the coupling oil, ω represents the microwave angular frequency, represents the magnetic field at the coupled oil boundary, represents the source electric field;

[0135] The thermal boundary condition is a heat flux boundary condition:

[0136]

[0137] in, represents the heat flux of biological tissue conduction, h represents the heat conductivity between biological tissue and the outside world, which is set to 5W / (m 2 K), where W represents power in watts, m represents distance in meters, and K represents temperature in Kelvin; T ext represents the external temperature, which is set to 310.15K, and T represents the temperature of the biological tissue.

[0138] The acoustic boundary condition is a plane wave radiation boundary condition:

[0139]

[0140] Where p represents the acoustic pressure generated by the thermoacoustic effect in biological tissue, and ρ represents the density of the coupling oil, which is set to 860 kg / m 3 , v s represents the speed of sound in the coupling oil and is set to 1540 m / s.

[0141] S3. Set the dynamic temperature parameters of each model based on the selected physics interface.

[0142] First, input the 3D temperature distribution at the monitoring time. Then, based on the selected physics interface, set the model's material parameters and the biological tissue parameters at dynamic temperature. Specifically, these parameters include:

[0143] During the thermal ablation process, the "Electromagnetic Waves, Frequency Domain" physical field interface needs to define the electrical conductivity, magnetic permeability, and relative dielectric constant of the ablation needle and biological tissue; the "Bioheat Transfer, Transient" physical field interface needs to define the constant-pressure heat capacity, thermal conductivity coefficient, and density of the biological tissue. The above parameters are all dynamic parameters that change with temperature.

[0144] During the microwave thermoacoustic monitoring ablation process, the "Electromagnetic Waves, Frequency Domain" physical field interface needs to define the dielectric constant, magnetic permeability, and electrical conductivity; the "Bioheat Transfer" physical field interface needs to define the constant-pressure heat capacity, thermal conductivity, and density of biological tissue; the "Pressure Acoustics, Transient" needs to define the sound velocity and density in the coupling oil, and the thermal expansion coefficient in the biological tissue. Except for the parameters in the coupling oil, all of the above parameters are dynamic parameters that change with temperature.

[0145] S4. Set symmetrical solution conditions and reasonably divide the grids of different solution domains into corresponding sizes according to the simulation requirements to reduce the amount of calculation. Specifically, the following steps are included:

[0146] S401 symmetric solution settings:

[0147] S402 Reasonably divide the grids of different solution domains into corresponding sizes:

[0148] Specifically, the physical fields that need to be solved symmetrically in the thermal ablation in S401 include "electromagnetic waves, frequency domain" and "biological heat transfer". The symmetry condition is to make the model rotationally symmetric along the axis of Z=0.

[0149] Among them, the symmetry conditions of "Electromagnetic Waves, Frequency Domain" are:

[0150]

[0151] Where, In the cylindrical coordinate system, the electric field is in the azimuth The field component under the formula represents the transverse component of the electric field by E r 、E z Determine that the lateral no-rotation constraint is satisfied.

[0152] Among them, the symmetry condition of "biological heat transfer" is:

[0153] -n·q=0

[0154] Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ;

[0155] Specifically, in the S401 microwave thermoacoustic monitoring ablation, the physical fields that need to be solved symmetrically include "bioheat transfer" and "pressure acoustics, transient"; wherein, the symmetry condition is to evenly divide the model into 4 parts along the X=0, YZ plane and the Y=0, XZ plane.

[0156] Among them, the symmetry conditions in the bioheat transfer module are:

[0157] -n·q=0

[0158] Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ;

[0159] The symmetry condition in the Pressure Acoustics Module is:

[0160]

[0161] Where n is the unit normal vector of the boundary, ρ is the fluid density, and p t is the total sound pressure, q d The sound source term represents the externally applied dipole sound source, with the unit of N / m 3 , is the gradient operator.

[0162] During the S402 thermal ablation process, the quality of the mesh division is related to the validity of the simulation results. Generally, the denser the mesh, the closer the numerical solution obtained by the simulation is to the real essence, but the corresponding time consumption is also greatly increased. By weighing the simulation time and solution accuracy, the maximum unit size of the mesh is set to 3mm, the minimum unit size is set to 0.5mm, and the mesh shape is a free triangle mesh. During the S402 microwave thermoacoustic monitoring process, by weighing the simulation time and solution accuracy, the maximum unit size of the "electromagnetic wave, frequency domain" and "biological heat transfer field" mesh is set to 3mm, the minimum unit size is set to 0.5mm, and the mesh shape is a free tetrahedral mesh. The maximum mesh size of "pressure acoustics, transient" is set to h max The following conditions need to be met:

[0163]

[0164] Among them, f max The maximum ultrasonic frequency for which the Pressure Acoustics, Transient physics is to be solved is set to 0.5 MHz.

[0165] S5. Add a steady-state-transient bidirectional coupling solver for solving the physical field of the ablation process, and add a steady-state and transient unidirectional coupling solver for solving the physical field of microwave thermoacoustic monitoring. Specifically, the following steps are included:

[0166] S501 thermal ablation multi-physics simulation solution settings:

[0167] S502 Microwave Thermoacoustic Monitoring Multiphysics Simulation Solution Settings:

[0168] Specifically, the S501 thermal ablation multi-physics field adopts a frequency domain-transient solver to calculate the "electromagnetic wave, frequency domain" and "biological heat transfer, transient" physical field interface, and the center frequency is set to 2.45GHz. The absorption of microwave energy by biological tissue causes temperature rise, which changes the electrical and thermal parameters of the tissue, which in turn affects the absorption of electromagnetic waves and temperature changes in the tissue at the next moment. For the "biological heat transfer" physical field interface, the "backward difference formula" method is selected in the solver configuration; the time step is set to 0.5S, and the solving time is set to 600S.

[0169] Specifically, in the S502 microwave thermoacoustic monitoring ablation, a steady-state solver is used to calculate the "electromagnetic wave, frequency domain" physical field interface, and the center frequency of the solution is 3GHz; two transient solvers are used to solve the "biological heat transfer" and "pressure acoustics, transient" physical field interfaces; for the "biological heat transfer" physical field interface, the "backward difference formula" method is selected in the solver configuration; the time step is set to 0.1us, and the solving time is set to 100us. For the "pressure acoustics, transient" physical field interface, the "generalized alpha" method is selected in the solver configuration, and the time step is set to 0.033us.

[0170] S6, obtain the temperature distribution, biological damage score, microwave thermoacoustic monitoring process, and acoustic pressure distribution during the ablation process, and export the data. Specifically, it includes:

[0171] S601 thermal ablation visualization simulation result acquisition:

[0172] S602 microwave thermoacoustic monitoring visualization simulation result acquisition and thermoacoustic image reconstruction:

[0173] Specifically, in the S601, the visualization results of the temperature distribution and damage score after microwave ablation are as follows:

[0174] After the simulation calculation is completed, select the dataset "Study 1 / Solution 1" in the two-dimensional rotation, the axis definition method is point 1(0, 0), point 2(0, 1), the number of rotation layers is selected as 360 layers, and the start angle and rotation angle are set to 0° and 360°. Add a three-dimensional drawing group to the results and select the body, the dataset is "Study 1 / Solution 1", the expression is changed to T, select the time, and add the exported drawing data to export the three-dimensional temperature distribution at the corresponding time point.

[0175] Specifically, in the S602, the thermoacoustic signal of the physical field calculation result is obtained, and the thermoacoustic image reconstruction is as follows:

[0176] After the simulation is complete, add a 3D mirror image to the dataset. Select "Pressure Acoustics, Transient" for the dataset to mirror the solved thermoacoustic data into complete 3D data. Enter the 3D coordinate position of the transducer in the 3D cut point field, replace the expression with "actd.p_t" in the derived value field, select 2D mirror for the dataset, and perform point calculations to obtain the sound pressure information at all transducers. Export the resulting data and use the delayed superposition algorithm in MATLAB to reconstruct the corresponding monitored thermoacoustic image at that moment.

[0177] S7. Signal and image processing obtains information related to ablation progress, such as tumor localization, ablation needle positioning, temperature distribution, and ablation lesions, and compares and analyzes them with the visualization results in S6.

[0178] Referring to FIG. 4 , in the process S6 , the positioning information of the tumor and the ablation needle can be obtained by reconstructing the thermoacoustic images obtained from different monitoring time points, and image processing is performed on the obtained simulation data and thermoacoustic images as follows;

[0179] Perform temperature-sound pressure curve fitting on the sound pressure information and temperature information obtained in step S6;

[0180]

[0181] ΔT=T-T0

[0182] Among them, B is the vertical coordinate of the sound pressure growth ratio curve, ΔT is the horizontal coordinate of the temperature difference curve, T is the current temperature, T0 is the reference temperature before ablation, which is 310.15K, and P T is the sound pressure amplitude at temperature T, is the acoustic pressure amplitude at 310.15K before ablation.

[0183] The reconstructed thermoacoustic image from step S6 is converted from sound pressure to temperature. The initial thermoacoustic image and the thermoacoustic image during the ablation process are input to calculate the sound pressure ratio matrix. The area requiring sound pressure-temperature fitting is divided into a tumor area (Mask_tumor) and a normal area (Mask_normal), and fitting is performed separately.

[0184] By using the "Arrhenius equation", the temperature distribution obtained at multiple monitoring time points is substituted into the equation for calculation to obtain the corresponding biological thermal damage range at the last monitoring moment, that is, the range of the ablation lesion.

[0185] The Arrhenius equation is:

[0186]

[0187] θ d =1-exp(-α)

[0188] Where A is the frequency factor, dE represents the activation of irreversible damage reflection (6.68×10 5 J.mol -1 ), R represents the flux gas constant (8.3 J·mol -1 ·K -1 ), T represents the temperature of liver tissue. When α = 1, it means that the biological tissue has been completely thermally damaged, and when α = 0, it means that the biological tissue has not been thermally damaged at all. The larger the α, the more severe the tissue damage, and it can also represent the degree of damage in the application of microwave thermal ablation to tumors. θ d The percentage of necrotic tissue is 63%. When about 63% of the cells in the tissue are damaged by heat, it can be determined that irreversible thermal damage has occurred.

[0189] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions.

[0190] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0191] The above embodiments should be understood as merely illustrating the present invention and not as limiting the scope of protection of the present invention. After reading the contents of the present invention, technicians may make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging, characterized in that: The following steps are involved: S1. Constructing a simulation geometric model for thermal ablation and microwave thermoacoustic monitoring; S2. Based on the microwave biothermal effect and thermoacoustic effect, set up the electromagnetic wave, frequency domain, bioheat transfer, transient, and transient pressure acoustics physics interfaces and corresponding boundary conditions. S3. Set the dynamic temperature parameters of each model according to the selected physics interface; S4. Set symmetric solution conditions and reasonably divide the grids of different solution domains into corresponding sizes according to simulation requirements; S5. Add a steady-state-transient bidirectional coupling solver for solving the physical field of the ablation process, and add a steady-state and transient unidirectional coupling solver for solving the physical field of microwave thermoacoustic monitoring; S6. Obtain the temperature distribution, biological damage score, thermoacoustic signal and acoustic pressure distribution during the ablation process, and export the data; S7. Signal and image processing obtains information related to ablation progress, including tumor localization, ablation needle positioning, temperature distribution, and ablation lesions, which is compared and analyzed with the visualization results in S6.

2. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1, characterized in that: The S1 constructs a thermal ablation and microwave thermoacoustic monitoring simulation geometric model, specifically including the following steps: S11. Thermal ablation geometric model construction: For thermal ablation, a two-dimensional axisymmetric model is selected in the geometric components to construct a coaxial slot ablation antenna geometric model and a biological tissue model. S12. Constructing a geometric model for microwave thermoacoustic monitoring, specifically: selecting a three-dimensional model in the geometric component, and constructing a three-dimensional geometric model of a coaxial slot ablation antenna, biological tissue, rectangular waveguide, and oil cylinder.

3. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1 is characterized in that: The S2 comprises the following steps: S201, Thermal Ablation Physics Interface and Boundary Condition Settings: S202, Microwave Thermoacoustic Monitoring Ablation Physics Interface and Boundary Condition Settings: In step S201, during thermal ablation, bidirectional coupling is performed between "Electromagnetic Waves, Frequency Domain" and "Bioheat Transfer, Transient" to solve the multi-physics process of microwave ablation. During the thermal ablation process, the "Electromagnetic Waves, Frequency Domain" physics interface is used to solve the electric field distribution and energy absorption density in biological tissues; and the "Bioheat Transfer, Transient" interface is used to solve the temperature rise caused by the absorption of electromagnetic wave energy in biological tissues. The boundary conditions in the thermal ablation process include electromagnetic boundary conditions and thermal boundary conditions; wherein the electromagnetic boundary conditions include port boundary conditions, ideal conductor boundary conditions and scattering boundary conditions; The input power of the port boundary condition during the thermal ablation process is 10 W, the port type is set to coaxial, and the mode is transverse electromagnetic wave TEM mode; The ideal boundary conductor boundary condition is: in, represents the unit normal vector, represents the electric field on the surface of an ideal conductor. This formula indicates that the tangential component of the electric field on the surface of an ideal conductor is 0; The scattering boundary condition is: in, represents the unit normal vector, represents the electric field at the boundary of biological tissue, k is the wave number, and the formula as a whole is used to represent the antenna in radiation problems, describing the propagation and attenuation characteristics of electromagnetic waves at the boundary; The thermal boundary condition is a heat flux boundary condition: in, represents the heat flux of biological tissue conduction, h represents the heat conductivity between biological tissue and the outside world, which is set to 5W / (m 2 K), where W represents power in watts, m represents distance in meters, and K represents temperature in Kelvin; T ext represents the external temperature, which is set to 310.15K, and T represents the temperature of biological tissue; In step S202, the "Electromagnetic Waves, Frequency Domain," "Bioheat Transfer, Transient," and "Pressure Acoustics, Transient" physical field interfaces are sequentially coupled during the microwave thermoacoustic monitoring process to solve the multi-physics process of microwave thermoacoustic monitoring. During the microwave thermoacoustic monitoring process, the "Electromagnetic Waves, Frequency Domain" and "Bioheat Transfer" physical field interfaces are used to solve the temperature rise caused by the absorption of electric field wave energy by biological tissues. The "Bioheat Transfer" and "Pressure Acoustics, Transient" physical fields are used to solve the thermoacoustic signal generated by the thermoelastic expansion of biological tissues. In step S202 of the microwave thermoacoustic monitoring process, the boundary conditions include electromagnetic boundary conditions, thermal boundary conditions, and acoustic boundary conditions, wherein the electromagnetic boundary conditions include port boundary conditions, ideal conductor boundary conditions, and impedance boundary conditions; The input power of the port boundary condition in the thermal acoustic monitoring process is 500 kW / m, the port type is set to rectangular, and the port mode is set to TE10 mode. The boundary conditions of the ideal conductor are: The impedance boundary condition is: in, represents the unit normal vector, represents the electric field at the coupling oil boundary, μ represents the magnetic permeability of the coupling oil, ε represents the dielectric constant of the coupling oil, σ represents the electrical conductivity of the coupling oil, ω represents the microwave angular frequency, represents the magnetic field at the coupled oil boundary, represents the source electric field; The thermal boundary condition is a heat flux boundary condition: The acoustic boundary condition is a plane wave radiation boundary condition: in, represents the heat flux of biological tissue conduction, h represents the heat conductivity between biological tissue and the outside world, which is set to 5W / (m 2 K), where W represents power in watts, m represents distance in meters, and K represents temperature in Kelvin; T ext represents the external temperature, which is set to 310.15K, and T represents the temperature of the biological tissue. Where p represents the acoustic pressure generated by the microwave thermoacoustic effect on biological tissue, and ρ represents the density of the coupling oil, which is set to 860 kg / m 3 , v s represents the speed of sound in the coupling oil and is set to 1540 m / s.

4. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1, characterized in that: The S3 thermal ablation process specifically includes the following steps: S301 thermal ablation process parameter settings: S302 Microwave Thermoacoustic Monitoring Process Parameter Settings: The "Electromagnetic Waves, Frequency Domain" physics interface in the S301 thermal ablation process requires the definition of the electrical conductivity, magnetic permeability, and relative permittivity of the ablation needle and biological tissue; the "Bioheat Transfer, Transient" physics interface requires the definition of the constant-pressure heat capacity, thermal conductivity, and density of biological tissue. These parameters are dynamic parameters that change with temperature. During the S302 microwave thermoacoustic monitoring process, the "Electromagnetic Waves, Frequency Domain" physics interface requires the definition of the dielectric constant, magnetic permeability, and electrical conductivity; the "Bioheat Transfer" physics interface requires the definition of the constant-pressure heat capacity, thermal conductivity, and density of biological tissue; and the "Pressure Acoustics, Transient" physics interface requires the definition of the speed of sound and density in the coupling oil and the thermal expansion coefficient of the biological tissue. All of these parameters, except those in the coupling oil, are dynamic and change with temperature.

5. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1, characterized in that: The S4 comprises the following steps: S401 symmetric solution settings: S402 Reasonably divide the grids of different solution domains into corresponding sizes: The physical fields that need to be solved symmetrically in the thermal ablation step S401 include "electromagnetic waves, frequency domain" and "bioheat transfer". The symmetry condition is to make the model rotationally symmetrical along the axis Z=0. The symmetry conditions for "Electromagnetic Waves, Frequency Domain" are: Where, In the cylindrical coordinate system, the electric field is at the azimuth angle The field component under the formula represents the transverse component of the electric field by E r 、E z Determine,satisfy the constraint of no lateral rotation; Among them, the symmetry condition of "bioheat transfer" is: -n·q=0 Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ; In the S401 microwave thermoacoustic monitoring ablation, the physical fields that require symmetric solutions include "bioheat transfer" and "pressure acoustics, transient." The symmetry condition is to divide the model into four equal parts along the X=0, YZ plane and the Y=0, XZ plane. Among them, the symmetry conditions in the bioheat transfer module are: -n·q=0 Where n is the unit normal vector of the boundary, q is the heat flux in W / m 2 ; The symmetry condition in the Pressure Acoustics Module is: Where n is the unit normal vector of the boundary, ρ is the fluid density, and p t is the total sound pressure, q d The sound source term represents the externally applied dipole sound source, with the unit of N / m 3 , is the gradient operator; In the S402 thermal ablation process, the maximum unit size of the grid is set to 3mm, the minimum unit size is 0.5mm, and the grid shape is a free triangle grid. In the S402 microwave thermoacoustic monitoring process, the maximum unit size of the grid for "electromagnetic waves, frequency domain" and "bioheat transfer field" is set to 3mm, the minimum unit size is 0.5mm, and the grid shape is a free tetrahedron grid by weighing the simulation time and solution accuracy. The maximum grid size h for "pressure acoustics, transient" is set to max The following conditions must be met: Among them, f max This indicates the maximum ultrasonic frequency that the Pressure Acoustics, Transient physics needs to solve for, and is set to 0.5 MHz.

6. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1, characterized in that: The S5 comprises the following steps: S501 thermal ablation multi-physics simulation solution settings: S502 Microwave Thermoacoustic Monitoring Ablation Multiphysics Simulation Solution Settings: The S501 Thermal Ablation multiphysics model uses a frequency-domain-transient solver to calculate the "Electromagnetic Waves, Frequency Domain" and "Bioheat Transfer, Transient" physics interfaces, with a center frequency set to 2.45 GHz. Biological tissue absorbs microwave energy, causing a temperature rise that changes the electrical and thermal parameters within the tissue, which in turn affects the absorption of electromagnetic waves and temperature changes within the tissue at the next moment. For the "Bioheat Transfer" physics interface, the "Backward Difference Formulation" solver configuration is selected, with a time step of 0.5 seconds and a solution time of 600 seconds. In the S502 microwave thermoacoustic monitoring ablation, a steady-state solver was used to calculate the "Electromagnetic Waves, Frequency Domain" physics interface, with a central frequency of 3 GHz. Two transient solvers were used to solve the "Bioheat Transfer" and "Pressure Acoustics, Transient" physics interfaces. For the "Bioheat Transfer" physics interface, the "Backward Difference Formulation" method was selected in the solver configuration, with a time step of 0.1 μs and a solution time of 100 μs. For the "Pressure Acoustics, Transient" physics interface, the "Generalized Alpha" method was selected in the solver configuration, with a time step of 0.033 μs.

7. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1, characterized in that: The S6 mainly includes the following steps: S601 thermal ablation visualization simulation results acquisition: S602 Microwave Thermoacoustic Monitoring Ablation Visualization Simulation Results Acquisition and Thermoacoustic Image Reconstruction: During the thermal ablation step S601, the visualization results of the temperature distribution and damage score after the microwave ablation are obtained are as follows: After the simulation is complete, select the "Study 1 / Solution 1" data set in the 2D Rotation section, define the axes as Point 1 (0, 0) and Point 2 (0, 1), select 360 layers for the rotation, and set the start angle and rotation angle to 0° and 360° respectively. In the Results section, add a 3D plot group and select Volume. Select "Study 1 / Solution 1" as the data set, change the expression to T, select Time, and add the plot data to be exported. This will export the 3D temperature distribution at the corresponding time points. In the microwave thermoacoustic monitoring process S602, the thermoacoustic signal of the physical field calculation result is obtained and the thermoacoustic image reconstruction is performed based on it as follows: After the simulation is complete, add a 3D mirror image to the data set. Select "Pressure Acoustics, Transient" for the data set to mirror the solved thermoacoustic data into complete 3D data. Enter the 3D coordinate position of the transducer in the 3D cut point field, replace the expression with "actd.p_t" in the derived value field, select "2D mirror" for the data set, and perform point calculations to obtain the sound pressure information at all transducers. Export the obtained data and use the delayed superposition algorithm in MATLAB to reconstruct the corresponding monitored thermoacoustic image at that moment.

8. The thermal ablation monitoring simulation and image processing method based on microwave thermoacoustic imaging according to claim 1 is characterized in that: In process S7, the obtained simulation data and thermoacoustic images are processed, and thermoacoustic image reconstruction is performed in step S7 to obtain tumor and ablation needle positioning information. The thermoacoustic image reconstructed in step S7 is converted from sound pressure to temperature. The initial thermoacoustic image and the thermoacoustic image during the ablation process are input and regionalized. The sound pressure and temperature fitting is performed for the tumor and liver regions respectively. Finally, the "Arrhenius equation" is used to calculate the corresponding biological thermal damage range at the last monitoring moment, i.e., the range of the ablation lesion.

Images