Transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system and method

Abstract

The invention discloses a transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system and method, and relates to the technical field of biomedical engineering, and the system comprises a sound field effect simulation module which is used for calculating a brain sound field based on set ultrasonic parameters and a stimulation target in combination with a constructed human brain model; the biothermodynamic simulation is used for calculating the heat effect of different ultrasonic waves on the biological tissue on the main propagation path and the temperature change caused by the heat effect; the mechanical effect simulation is used for calculating the mechanical effect of the ultrasonic wave in the focusing area when the ultrasonic wave acts on the brain tissue, and calculating a mechanical index MI to evaluate the cavitation effect risk; evaluating the thermal injury of the soft tissue in the ultrasonic stimulation according to the cumulative energy model; according to the simulation system and method, sound field distribution and partial biological effects of transcranial focused ultrasound stimulation can be accurately analyzed.

Description

Technical Field

[0001] The present invention relates to the field of biomedical engineering technology, and in particular to a system and method for simulating thermal and mechanical effects of transcranial focused ultrasound stimulation. Background Art

[0002] Existing studies on human transcranial focused ultrasound stimulation have found that thermal and mechanical effects are the focus of attention during the stimulation process. Therefore, there is an urgent need for a precise method for simulating thermal and mechanical effects of transcranial acoustic fields that is closer to the physiological environment. As far as current simulation systems or methods are concerned, most patents are limited to the focusing and positioning of ultrasound, such as: Chinese patent CN105536156A uses time reversal technology to achieve precise focusing of ultrasound in the brain by building a three-dimensional head model, which can significantly improve the stimulation or regulation effect of ultrasound on specific brain areas. Although this technology can simulate the sound field, it lacks dynamic adjustment and real-time feedback capabilities, and it is difficult to maintain consistency between simulation and individual treatment in actual operation.

[0003] Chinese patent CN115317817A simulates the desynchronization effect of ultrasound on neurons by combining ultrasound data and neural network models, and explores the potential of ultrasound stimulation in inhibiting pathological neural activity (such as epilepsy or Parkinson's disease). This technology relies on the combination of ultrasound data and neural networks for simulation, but the parameters and data used in the model may not fully reflect the complex situation in biological tissues, especially the differences between different individuals.

[0004] Chinese patent CN118625698A simulates the echo signal of the ultrasonic sensor so that the controller under test can process the simulated signal, reducing the dependence on the real physical environment, thereby reducing the test cost and improving the development efficiency of the system. However, this technology mainly relies on the simulation of sensor signals rather than the simulation of the physical ultrasonic propagation process, and does not go deep into the physical process of the interaction between ultrasound and the environment. Although a few studies involve thermal effect simulation, they use linear models and simple methods, and do not accurately model the complex propagation process of the sound field. The modeling accuracy of the complex thermal phenomena and mechanical stress density changes of transcranial ultrasound stimulation is not enough. Therefore, a transcranial focused ultrasound thermal effect and mechanical effect simulation system based on the biophysical properties of ultrasound is needed.

[0005] In summary, the current simulations mainly focus on the ultrasonic propagation path, the ultrasonic focusing position, and the brief sound field distribution. On the contrary, the bio-thermal effects and mechanical effects involve multiple complex factors, such as the projection, reflection, and scattering of ultrasonic waves in different tissues, as well as the biophysical effects and biochemical reactions caused by the interaction of biological tissues, resulting in the need for complex mathematical models for related modeling. Performing these complex biophysical model calculations requires powerful computing capabilities and efficient computing methods. In summary, the simulation technology is complex, the verification is difficult, and the industry demand and multi-disciplinary intersection are insufficient, resulting in the slow development of the simulation of the thermal and mechanical effects of transcranial ultrasound stimulation. However, with the in-depth research and continuous progress of related technologies, the modeling of these effects will gradually become an important direction for future simulation research. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a simulation system and method for the thermal and mechanical effects of transcranial focused ultrasound stimulation, which can accurately analyze the sound field distribution and some biological effects of transcranial focused ultrasound stimulation.

[0007] A simulation system for the thermal and mechanical effects of transcranial focused ultrasound stimulation proposed by the present invention includes: Sound field effect simulation, which is used to calculate the brain sound field in the propagation direction and the focusing area based on the set ultrasonic parameters and the stimulation target, combined with the constructed human brain model; Bio-thermodynamic simulation, which is used to calculate the thermal effects of ultrasonic waves with different frequencies, sound pressures, and focusing characteristics on biological tissues on the main propagation path; Thermal damage assessment, which is used to evaluate the degree of thermal damage of biological tissues based on the time relationship between different temperatures and thermal damage, and evaluate the thermal damage of soft tissues during ultrasonic stimulation according to the cumulative energy model; Mechanical effect simulation, which is used to calculate the mechanical effects in the focusing area when ultrasonic waves act on the brain tissue, and calculate the mechanical index MI to evaluate the risk of cavitation effect; Multi-physical field coupling: Establish a coupling relationship between the sound field effect, the thermal effect, and the mechanical effect, calculate each part of the effect independently, and perform a linked calculation of each part of the effect and the remaining effects to achieve multi-physical field coupling simulation.

[0008] Furthermore, calculate the mechanical stress, mechanical index, and the energy absorption of biological tissues in the main propagation path and the focusing area, and evaluate the risk brought by the cavitation effect of intracranial tissue fluid and the thermal damage that may be caused by the increase in tissue temperature.

[0009] Furthermore, it also includes result visualization, which is specifically used for: Generating a visualized sound field sub-map of the intracranial stimulation sound field effect simulation result; Generating a visualized whole-brain heat map of the bio-thermodynamic simulation result; Generate the visual mechanical stress density and MI extreme values from the mechanical effect simulation results.

[0010] Furthermore, in the acoustic field effect simulation, the construction process of the human brain model is as follows: Obtain MRI / CT image data, perform image preprocessing such as denoising, registration, and segmentation, extract different tissues of the brain from the obtained image data to create a three-dimensional grid, and convert it into a three-dimensional skull model; Based on the physical properties of different media in the brain in the three-dimensional skull model, set the density, specific heat capacity, thermal conductivity, and blood perfusion rate in the brain for the skin, skull, and tissue solution, and obtain the absorption coefficient of ultrasonic waves in each layer of the medium, thereby constructing a human brain model.

[0011] Furthermore, in the stimulation target, specifically: Select the transducer to be used to determine the reference frequency, sound pressure, waveform, and focusing characteristics of the ultrasonic wave, import the human brain model to determine the position of the stimulation source on the scalp, the distance from the scalp, and the incident angle of the ultrasonic wave (usually perpendicular incidence), and set the incident direction as the main propagation path of the focused ultrasonic wave; Determine the three-dimensional coordinates of the stimulation target through slices in different dimensions in the human brain model, and set the central focus point of the transducer.

[0012] Furthermore, in the acoustic field effect simulation, based on the wave equation, the finite element method is applied to solve the propagation of ultrasonic waves and simulate the propagation process of ultrasonic waves in different media.

[0013] Furthermore, in the bio-thermodynamic simulation, the improved Pennes bio-heat conduction model is used to calculate the thermal effects of different ultrasonic waves on biological tissues. The improved Pennes bio-heat conduction model is specifically as follows: ; Among them, is the sound speed, is the specific heat capacity of the tissue, is the external heat, is the thermal conductivity, is the base temperature, is the density of the tissue, is the temperature gradient, is the blood perfusion rate, is the specific heat capacity of the blood, is the convective heat transfer coefficient, is the time, is the current temperature, is the rate of change of temperature with time, is the gradient operator; The cumulative energy model is specifically as follows: ; Among them, represents thermal damage, represents the temperature at time represents the attenuation coefficient related to temperature, represents the reference critical temperature, indicating that thermal damage will accumulate rapidly after exceeding this temperature.

[0014] Furthermore, in the mechanical effect simulation, the tissue strain distribution is obtained through the dynamic equilibrium equation, and the cavitation risk of ultrasonic stimulation is evaluated using the mechanical index MI. The specific dynamic equilibrium equation is as follows: ; The calculation formula of the mechanical index MI is as follows: ; Among them, is the stress density, is the sound pressure distance gradient, is the cosine waveform, is the distance from the surface after entering the skull, is the time, is the angular frequency, is the initial phase, is the sound pressure field.

[0015] A transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation method, including: Based on the set ultrasonic parameters and the attack target, combined with the reconstructed human brain model, calculate the brain sound field in the propagation direction (along the Z-axis) and the focal area to perform sound field effect simulation; Based on the sound field effect simulation, calculate the thermal effects of ultrasonic waves with different frequencies, sound pressures, and focusing characteristics on biological tissues on the main propagation path, perform bio-thermodynamic simulation, and evaluate the thermal damage of soft tissues during ultrasonic stimulation according to the cumulative energy model; Based on the sound field effect simulation, calculate the mechanical effects in the focal area when ultrasonic waves act on brain tissues, calculate the mechanical index MI to evaluate the cavitation effect risk, and perform mechanical effect simulation; Based on the bio-thermodynamic simulation and mechanical effect simulation, to achieve the simulation of stimulation area activation; Establish a coupling relationship among the sound field effect, thermal effect, and mechanical effect, calculate each part of the effect independently, and perform a linked calculation of each part of the effect and the remaining effects to achieve multi-physical field coupling simulation.

[0016] Furthermore, it also includes: Generate a visual sound field distribution map of the intracranial stimulation sound field effect simulation result; Generate a visual full-brain heat map from the results of biothermodynamic simulation and emulation; Generate a visual mechanical stress density and MI extreme value map from the results of mechanical effect simulation and emulation.

[0017] The advantages of a transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system and method provided by the present invention are as follows: Considering different stimulation parameters and stimulation scenarios, the wave equation is used to more accurately calculate the sound field change, the KZK equation is used to calculate the nonlinear change of the sound field caused by high-intensity ultrasound in the same medium, the exponential decay model is used to evaluate the change of sound pressure and mechanical stress density in space and time, the improved Pennes model is used to more accurately calculate the temperature change of tissues, and the finite element method (FEM) or the finite difference time domain method (FDTD) is used to accelerate the calculation of temperature change using GPU or distributed computing to improve the calculation efficiency. The interactive and visualization modules are used to more directly control the computer transcranial focused ultrasound stimulation, visually present and comprehensively analyze the stimulation results, so as to achieve the simulation purpose of accurately simulating the physiological environment of brain tissues. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of the present invention; Figure 2 It is a flowchart for implementing the sound field effect simulation; Figure 3 It is a flowchart for implementing the biothermodynamic simulation; Figure 4 It is a flowchart for implementing the mechanical effect and cavitation effect simulation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions of the present invention will be described in detail through specific embodiments. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0020] As Figures 1 to 4 shown, a transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system proposed by the present invention includes a sound field effect simulation, a biothermodynamic simulation, and a mechanical effect simulation.

[0021] The sound field effect simulation is used to calculate the brain sound field based on the set ultrasonic parameters and stimulation targets in combination with the constructed human brain model; The biothermodynamic simulation is used to calculate the thermal effect of ultrasonic waves with different frequencies, sound pressures, and focusing characteristics on biological tissues on the main propagation path; Mechanical effect simulation, used to calculate the mechanical effect of ultrasound on the focal area when it acts on brain tissue, and calculate the mechanical index MI to assess the risk of cavitation effect; Multi-physics coupling: Establish a close coupling relationship between the acoustic field, thermal effect and mechanical effect, calculate each part of the effect independently, and link the calculation of each part of the effect with other effects to realize multi-physics coupling simulation; Among them, consider the differences in sound wave propagation path, intensity and distribution caused by different ultrasonic frequencies, sound pressures and focusing methods, as well as the absorption and scattering effects of the complex structure of the human brain (including skin, skull, cerebrospinal fluid) on sound waves; and this multi-physics coupling calculation increases the complexity of the architecture and places high demands on the calculation methods and computing resources.

[0022] The main problems solved by this embodiment are as follows: The propagation of ultrasound in the skull and brain tissue, as well as the temperature changes and tissue deformation of biological tissues caused by ultrasonic stimulation are closely related to the ultrasound baseline frequency, sound pressure amplitude, waveform changes, ultrasonic focusing morphology, etc. The traditional method based on linear models, simple scenarios, a few fixed parameters and a large number of constant settings is difficult to conduct a relatively accurate analysis of the sound field distribution and some biological effects of transcranial focused ultrasound stimulation.

[0023] Therefore, the purpose of this embodiment is to consider different stimulation parameters and stimulation scenarios, use the wave equation to more accurately calculate the sound field changes, use the KZK equation to calculate the nonlinear changes of the sound field caused by high-intensity ultrasound in the same medium, use the exponential decay model to evaluate the changes in sound pressure and mechanical stress density in space and time, use the improved Pennes model to more accurately calculate the temperature changes of the tissue, use the finite element method (FEM) or the finite difference time domain method (FDTD) to use GPU to accelerate or distribute the temperature changes and improve the calculation efficiency. Use the interactive and visualization module to more directly control the computer transcranial focused ultrasound stimulation, visualize and comprehensively analyze the stimulation results, and achieve the simulation purpose of accurately simulating the physiological environment of brain tissue.

[0024] In this embodiment, various types of ultrasonic transducer configurations are provided, including parameter options such as different fundamental frequencies, sound pressure intensities, focusing ranges, and probe types. Users can choose planar transducers, spherical transducers, or array transducers to customize them according to experimental requirements. The system supports an event control mechanism that automatically switches transducer modes or adjusts parameters through preset trigger conditions (such as time, power adjustment, and frequency changes) to meet dynamic ultrasonic stimulation requirements. An interactive tool is provided for accurately setting the relative position and angle of the ultrasonic transducer on the skull surface. Users can adjust the spatial layout of the transducer based on the three-dimensional skull model to optimize the propagation path and focusing effect of the sound waves.

[0025] Multiple configuration options for ultrasonic transducers are provided, allowing users to select the appropriate transducer type and parameters according to experimental requirements. Among them, the spherical transducer focuses sound waves on an ellipsoidal region, forming a local high-intensity sound field, which is suitable for areas that require precise stimulation. The array transducer is suitable for precise regulation of complex sound fields by achieving multi-point dynamic sound field focusing. In terms of key parameter options, the fundamental frequency range is 0.1 MHz - 2 MHz, the sound pressure intensity is 0.1 MPa - 2 MPa, the stimulation depth ranges from 40 mm to 120 mm, the major axis range of the focused area is 2 mm - 20 mm, and the minor axis range is 2 - 10 mm.

[0026] Event control mechanism: The system supports automated transducer operations triggered by events to meet the requirements of dynamic ultrasonic stimulation. Set time points or time intervals to trigger operations such as switching transducer modes or adjusting parameters. When the power output exceeds or is lower than the preset value, automatic adjustment is triggered. Change the fundamental frequency or sound field distribution according to external signals or preset conditions. The operations that can be performed mainly include switching transducer types, dynamically adjusting the fundamental frequency, sound pressure intensity, or focusing position.

[0027] Interactive transducer layout: An interactive tool based on a three-dimensional skull model is provided, allowing users to intuitively adjust the relative position and angle of the transducer on the cranial surface. Supports loading personalized head or skull MRI / CT data to generate a three-dimensional model specific to the experimental subject. Displays the propagation path of sound waves in the three-dimensional model and calculates the sound wave attenuation and focal position in real time. Integrates a multi-point calibration function to ensure the spatial matching accuracy between the transducer and the three-dimensional model.

[0028] Target setting: A function for setting the target area based on medical images such as MRI and CT is provided to support the precise implementation of transcranial focused ultrasound stimulation. Users can accurately label the stimulation target position through software such as Brainsight or 3D Slice using manual or automatic segmentation algorithms. This process first relies on high-resolution medical image data to ensure the accuracy and reliability of target identification.

[0029] After the target area is set, the system will enter the coordinate transformation stage. The main task of this stage is to align the sound source data, target data, and medical image data so that they coexist in the same coordinate system, facilitating further simulation analysis and effect evaluation. Through an accurate alignment process, users can better understand the relationship between sound wave propagation and the target, thereby optimizing the effect of ultrasonic stimulation.

[0030] For different tissue types (such as bone, soft tissue, and liquid), the propagation characteristics of sound waves are very different. Accurately setting the sound speed, density, and attenuation coefficient can reflect the transmission and attenuation effects of sound waves between different tissues in actual applications in the simulation model, thereby improving the accuracy and fidelity of ultrasonic stimulation.

[0031] (A)Simulation of sound field effect, such as Figure 2 shown; The construction process of the human brain model is as follows (1) to (2): (1) Obtain MRI / CT image data, perform image preprocessing, such as denoising, registration, and segmentation. Extract different tissues of the brain from the obtained image data to create a three-dimensional grid and convert it into a three-dimensional skull model; That is, first, read and process MRI / CT image data through SimpleITK or MITK tools. The skull CT data can also be generated based on a deep learning model (3D Residual U-Net). Perform image preprocessing, such as denoising, registration, and segmentation, to ensure high-quality data suitable for subsequent analysis. Use image processing techniques to extract different tissues of the brain (such as the cortex, white matter, and gray matter), create a three-dimensional grid, and convert it into a three-dimensional skull model to ensure that the three-dimensional skull model can accurately reflect the actual anatomical structure.

[0032] (2) Based on the physical properties of different media in the brain in the three-dimensional skull model, set the density, specific heat capacity, thermal conductivity, and blood perfusion rate in the brain for the skin, skull, and tissue solution, and obtain the absorption coefficient of ultrasonic waves in each layer of the medium, thereby constructing a human brain model; That is, in the three-dimensional skull model, set information such as the density, thickness, and specific heat capacity of the skull, skin, and brain tissue in the segmented area, calculate data such as the sound speed, attenuation coefficient, sound pressure, and sound field intensity, and obtain the absorption coefficient of brain tissue for ultrasonic energy, thereby constructing a human brain model under acoustic characteristics; That is, in establishing the human brain model, define physical properties for different tissues. For example, the thickness information of each layer of tissue can be obtained through image measurement. Set the density and sound speed for each tissue, and according to the acoustic characteristics of the material, obtain the absorption coefficient of ultrasonic waves in each layer of tissue. Set multiple parameters of the ultrasonic wave source to ensure the accuracy of the simulation, mainly including the reference frequency of the ultrasonic wave and the sound pressure of the ultrasonic wave source. Determine the focusing area of the ultrasonic wave to ensure that the ultrasonic wave energy is concentrated on the stimulation target.

[0033] In the simulation of sound field effect, based on the wave equation (1), the finite element method is applied to solve the propagation of sound waves and simulate the propagation process of sound waves in different media such as the skull and soft tissues.

[0034] ; (1) Among them, is the sound pressure, that is, the sound pressure value at a certain point in the sound pressure field at a certain moment, is the sound speed, indicating the propagation speed of ultrasonic waves in the medium, is the Laplace operator of the sound pressure, describing the spatial distribution of the sound pressure, The Dirichlet δ function as the wave source is an idealized function representing the spatial distribution of the wave source. When the function value is infinite and zero at other positions. is the intensity of the wave source, which is a constant representing the amplitude of the wave source. is the position of the wave source, which is a vector representing the position of the wave source in space. is the time function of the wave source, describing the variation of the wave source with time. Among them, represents the propagation of sound waves in the medium. represents the contribution of the wave source to the sound field.

[0035] Among them, in the case of high-intensity ultrasound, the KZK nonlinear model (2) can be used to describe the propagation of ultrasonic waves: ; (2) Among them, is the second-order derivative of the main axis space, is the axial coordinate, the direction perpendicular to the transducer surface, used to describe the propagation direction of ultrasonic waves. is the initial sound pressure. is the absorption coefficient, representing the energy loss when ultrasonic waves propagate in the medium, usually related to the viscosity and heat conduction of the medium. is the index of the time step, representing the discretized time points, used to describe the dynamic change of the sound field. is the wave number, related to the wavelength and frequency of ultrasonic waves, describing the spatial periodicity of ultrasonic waves.

[0036] Considering the attenuation coefficient of the skull to the sound field and the relationship between ultrasonic penetration and frequency, calculate the sound intensity (3): ; (3) Among them, is the sound intensity. is the initial sound pressure at time is the specific heat capacity of the tissue. is the frequency-dependent attenuation. is the distance.

[0037] Specifically: First, discretize the calculation area according to the anatomical structure of the brain and its surrounding tissues. For different calculation requirements, select different types of finite element meshes such as tetrahedral elements and hexahedral elements. In the problem of ultrasonic wave propagation, especially for higher-frequency ultrasonic waves, finer mesh division is carried out in key areas (such as the ultrasonic focusing area). Secondly, set an excitation source at the ultrasonic wave source position and use the Dirichlet boundary condition to represent the sound pressure Changes in the source location. Using Neumann boundary conditions (no-flux boundary conditions), assuming that the normal derivative of the ultrasonic wave is zero, the reflection of the ultrasonic wave at the tissue boundary is simulated. In the external region of the computational domain, an absorbing boundary condition (such as Perfectly Matched Layer, PML) can be used to simulate the radiation effect of the ultrasonic wave. For multi-point stimulation, the finite difference method (FDM) is used to solve the wave equation to improve the efficiency of solving the sparse matrix. By solving the wave equation, the acoustic pressure field distribution within the computational domain is obtained, laying the foundation for thermal simulation, mechanical stress, and the calculation of the MI value.

[0038] ; (4) where is the distance, is the acoustic pressure value in the acoustic pressure field at position and time , where is the index of the spatial position, usually a three-dimensional spatial coordinate , is the index of the time step, representing the discretized time point, is the position and time acoustic pressure value. is the time step, representing the size of the discretized time interval, is the spatial step, respectively representing the discretized spatial intervals in the directions, is the source term, representing the sound source excitation at position and time .

[0039] (B) Bio-thermodynamic simulation and mechanical effect simulation, as shown in Figure 3 and 4 ; Combining factors such as metabolic heat, blood cooling effect, and heat exchange with surrounding tissues, the improved Pennes bioheat conduction model (5) is used to calculate the thermal effects of different ultrasounds on biological tissues. According to the cumulative energy model (CEM), the thermal damage of soft tissues during ultrasound stimulation is evaluated, that is, according to the energy accumulation characteristics at different temperatures, the potential damage of temperature rise to tissues is evaluated. The finite element method (FEM) or the finite difference time domain method (FDTD) is used to accelerate the temperature change calculation using GPU or distributed computing (6).

[0040] ; (5) ; (6) Cumulative Energy Model (CEM) The details are as follows: ; Among them, is the speed of sound, is the specific heat capacity of the tissue, is the external heat, is the thermal conductivity, is the basal blood temperature (37 °C), is the density of the tissue, is the temperature gradient, is the blood perfusion rate, is the specific heat capacity of the blood, is the convective heat transfer coefficient, is the time, is the current temperature, is the rate of change of temperature with time, is the gradient operator. is the temperature at position , is the heat source intensity per unit volume, represents thermal damage, represents the temperature at time is the attenuation coefficient related to temperature, usually taken as 0.5 when the temperature is greater than 42 °C, represents the reference critical temperature, generally taken as 42 °C in the cranial cavity, indicating that thermal damage will accumulate rapidly after exceeding this temperature.

[0041] Specifically: Based on the Pennes bioheat conduction equation, considering complex biological heat exchange, heat cooling and other effects, as well as differences in different ultrasonic stimulation parameters and acoustic characteristics of different skulls and brains, initialize the acoustic and thermal parameters of the tissue, set the boundary conditions of the scalp, skull and brain tissue, and use methods such as finite difference and finite element to solve the thermal effects and temperature changes when ultrasonic waves propagate in the brain. Among them, the acoustic parameters mainly include the speed of sound, density, absorption coefficient, scattering coefficient, and the thermal parameters mainly include thermal conductivity, specific heat capacity, tissue metabolic rate (blood flow heat source term), etc. In the boundary setting, the scalp usually adopts the boundary condition of heat conduction and is set in combination with the external environmental temperature. During the calculation, the calculation area is meshed, and the change of tissue temperature with time is solved by the time-domain difference method in space, and finally the temperature situation of the target area is obtained.

[0042] ; (7) ; (8) Among them, is the sound intensity, is the external heat, is the time step, is the duty cycle, representing the time ratio of the sound field action. It is a dimensionless parameter, usually used to describe the characteristics of the pulsed sound field. is at the position and time is the temperature, is at the position and time is the temperature.

[0043] In the module architecture design, the idea of object-oriented design (OOP) is adopted. The grid generation and processing module is developed to handle the grid division and grid optimization of the computational domain, and the data input and output module is developed to handle the input (such as ultrasonic parameters, tissue characteristics, boundary conditions, etc.) and output (such as temperature field, stress field, thermal effects, etc.) of the simulation model. The GPU parallel computing and optimization module is developed to support parallel computing and improve the efficiency of large-scale simulation calculations. The heat absorption value is calculated using the sound field intensity data generated by the sound field effect simulation module, or the heat change is calculated according to the selected parameters, and then the temperature change in a specific area is obtained.

[0044] The acoustic radiation force value is obtained based on the linear elastic or nonlinear viscoelastic model, and then the mechanical stress caused by the sound wave is further solved to evaluate the potential damage to the tissue. The linear elastic model is applicable to the case of small deformation and is also the main change in transcranial focused ultrasound stimulation. In the simulation, the tissue strain distribution can be obtained through the dynamic equilibrium equation (including the inertia term, damping term, and external force term), and then the potential impact of the mechanical stress on the tissue can be evaluated. The MI in the propagation path is solved to evaluate the potential damage of the cavitation effect to the neurons.

[0045] That is, the dynamic equilibrium equation is specifically as follows: ; (9) The calculation formula of the mechanical index MI is as follows: ; (10) Among them, is the stress density, is the sound pressure distance gradient, is the cosine waveform, is the distance from the surface after entering the skull. The attenuation is considered after penetrating the skull and entering the skull, is the time, is the angular frequency, is the initial phase, is the sound pressure field.

[0046] (C) Interactive and visualization design; First, use SimpleITK to read medical image data. Remove image noise through filters (such as Gaussian filtering, median filtering, etc.). Adopt uniform grid resampling or non-uniform resampling to ensure the consistency of the image at different scales. Register multiple images to ensure the alignment of different images (such as CT and MRI) in the same spatial coordinate system and convert them into a suitable format. Generate isosurfaces through the vtkMarchingCubes algorithm to display the boundaries of anatomical structures or certain specific physical quantities (such as temperature distribution, sound pressure, etc.). Use the vtkContourFilter to generate contour lines, or use color mapping to display different physical quantities in the image (such as sound pressure, temperature change, etc.). By adjusting the Color Map, users can clearly see the distribution of the data. For the mechanical stress distribution caused by ultrasound, it can be displayed through isosurfaces, vector fields, or through color mapping. Design a graphical user interface (GUI) using PySide 6. Dynamically update the simulation results according to the ultrasonic parameters input by the user. Users can view the changes in physical quantities such as sound pressure, temperature, and stress in real time through the interactive controls of the system. Develop a data export function that allows users to save the simulation results (such as temperature fields, stress fields) in different formats (such as images, data files, videos, etc.) for subsequent analysis.

[0047] As an embodiment: (a1) Precise personalized three-dimensional human brain model: Use a CT scanning device to obtain the bone structure data of the patient's skull, especially important information such as the thickness and shape of the skull. The CT image resolution is recommended to be below 1 mm to ensure sufficient details. Use an MRI device to obtain the soft tissue structure data of the patient's brain, especially the distribution of brain tissue, blood vessels, and intracranial fluids. The resolution and slice thickness of MRI match that of CT for easy subsequent image fusion. Use medical image processing software to register and fuse the CT and MRI data to generate a personalized three-dimensional human brain model of the patient, and set parameters such as specific heat capacity, density, sound speed, and acoustic impedance rate layer by layer and medium by medium.

[0048] (a2) Stimulus source and stimulus target (i.e., stimulus target) setting: Select the transducer to be used to determine the fundamental frequency, sound pressure, waveform, and focusing range of the ultrasound. Import the human brain model to determine the position of the stimulus source on the scalp, the distance from the scalp, and the incident angle of the ultrasound (usually perpendicular incidence), and set the incident direction as the main propagation path of the focused ultrasound. Determine the three-dimensional coordinates of the stimulus target through slices in different dimensions in the human brain model and set the central focus point of the transducer.

[0049] In focused ultrasound, the pressure and energy are the strongest along the main propagation path and in the focal region, while being very weak elsewhere. Therefore, the incident direction is set as the main propagation path of the focused ultrasound, thus avoiding the problem that calculating the thermal effects of the whole brain requires a large amount of computing resources.

[0050] (a3)Ultrasound sound field simulation: According to the mechanical vibration characteristics of ultrasound and the acoustic physical characteristics such as the density, thickness, and specific heat capacity of each medium, simulate the propagation process of ultrasound, calculate the sound pressure change in the main propagation direction, and the sound pressure, mechanical stress density, and sound field intensity in the focal region, and use the matplot tool to draw the distribution diagrams of the sound pressure and sound field intensity in the propagation direction and the focal region; That is, calculate the mechanical stress, mechanical index, and biological tissue energy absorption in the main propagation path and the focal region, and evaluate the risks brought by the cavitation effect of intracranial tissue fluid and the thermal damage that may be caused by the increase in tissue temperature.

[0051] (a4)Effect analysis and safety assessment: Import the heat conduction module, determine parameters such as the pulse time, pulse interval, duration, and duration interval of the ultrasonic stimulation, combine the previously set parameters such as the blood perfusion rate and specific heat capacity, and the sound field intensity values obtained during the sound field effect simulation process, calculate the heat absorption, further calculate the temperature changes in the main propagation path, especially on the cranial surface and the target area, calculate the CEM (Cumulative Equivalent Minutes) value to evaluate the thermal damage suffered by the tissue due to temperature changes during ultrasonic stimulation. Calculate the mechanical stress density in the focal region when the ultrasonic wave acts on the brain tissue, evaluate the risk of mechanical effects and irreversible tissue deformation, and calculate the MI to evaluate the risk of cavitation effect. Use the vtkMarchingCubes algorithm to generate isosurfaces, and use the vtkContourFilter to generate contour lines to visually display the distribution of the above values.

[0052] In this embodiment, the wave equation is used to comprehensively consider the propagation of sound waves and the influence of continuous stimulation of the sound source on the sound field at different positions, and a multi-point synthesis algorithm is developed to calculate the influence of multi-point stimulation on the sound field distribution, realizing a more accurate simulation of the sound field distribution. For high-intensity ultrasound, the KZK nonlinear model is used to comprehensively consider the influence of medium density changes on ultrasonic propagation and attenuation. In terms of thermal effect simulation, the nonlinear attenuation is used to calculate the change in sound field intensity, and the influence of thermal conductivity, blood perfusion, tissue metabolism, and tissue heat exchange at different temperatures on temperature is comprehensively considered. The CEM method is used to evaluate thermal damage, further improving the accuracy and fidelity of thermal simulation.

[0053] This system combines medical imaging and acoustic simulation technology through precise target setting and acoustic parameter adjustment, providing a more accurate and personalized simulation solution for transcranial focused ultrasound therapy, improving the treatment effect and safety of patients.

[0054] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system, characterized in that: include: Acoustic field effect simulation, which is used to calculate the brain acoustic field in the propagation direction and focal area based on the set ultrasound parameters and stimulation targets combined with the constructed human brain model; Biothermodynamic simulation, used to calculate the thermal effects of ultrasound waves of different frequencies, sound pressures and focusing characteristics on biological tissues in the main propagation path, and to evaluate the thermal damage of soft tissues during ultrasound stimulation based on the cumulative energy model; Mechanical effect simulation is used to calculate the mechanical effect of ultrasound in the focal area when it acts on brain tissue, and to calculate the mechanical index MI to assess the risk of cavitation effect. Multi-physics coupling: Establish coupling relationships between acoustic, thermal, and mechanical effects, calculate each part of the effect independently, and link each part of the effect with the remaining effect to achieve multi-physics coupling simulation.

2. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: The mechanical stress, mechanical index and energy absorption of biological tissue in the main propagation path and focal area were calculated to evaluate the risks brought by intracranial tissue fluid cavitation effect and the thermal damage that may be caused by increased tissue temperature.

3. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: Also included is result visualization, specifically for: Generate a visual sound field distribution diagram based on the simulation results of intracranial stimulation sound field effect; Generate a visual whole-brain heat map from the biothermodynamic simulation results; The mechanical effect simulation results are used to generate visual mechanical stress density and MI extreme value diagrams.

4. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: In the simulation of the acoustic field effect, the construction process of the human brain model is as follows: Acquire MRI / CT image data, perform image preprocessing, such as denoising, registration, and segmentation, extract different brain tissues from the image data to create a three-dimensional mesh, and convert it into a three-dimensional skull model; Based on the physical properties of different brain media in the three-dimensional skull model, the density, specific heat capacity, thermal conductivity and intracranial blood perfusion rate are set for the skin, skull and tissue solution, and the absorption coefficient of ultrasound in each layer of media is obtained to construct a human brain model.

5. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: Among the stimulation targets, specifically: The transducer to be used is selected to determine the reference frequency, sound pressure, waveform and focusing characteristics of the ultrasound, and the human brain model is introduced to determine the location of the stimulus source on the scalp, the distance from the scalp and the incident angle of the ultrasound, and the incident direction is set as the main propagation path of the focused ultrasound; In the human brain model, the three-dimensional coordinates of the stimulation target are determined through slices of different dimensions, and the central focusing point of the transducer is set.

6. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 4, characterized in that: In the simulation of acoustic field effects, based on the wave equation, the finite element method is used to solve the ultrasonic propagation and simulate the propagation process of ultrasonic waves in different media.

7. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: In the biothermodynamic simulation, the improved Pennes bioheat conduction model is used to calculate the thermal effects of different ultrasound waves on biological tissues. The improved Pennes bioheat conduction model is as follows: Where c is the speed of sound, ρ is the specific heat capacity of the tissue, is the external heat, κ(T) is the thermal conductivity, T b is the basic temperature of blood, p is the density of tissue, is the temperature gradient, ω is the blood perfusion rate, c s is the specific heat capacity of blood, h is the convective heat transfer coefficient, t is the time, T is the current temperature, is the rate of change of temperature with time, is the gradient operator; The cumulative energy model is as follows: Among them, D total (t) represents thermal damage, T(τ) represents the temperature at time τ, k(T(τ)) represents the temperature-related attenuation coefficient, T ref Represents the reference critical temperature, indicating the temperature above which thermal damage will accumulate rapidly.

8. The transcranial focused ultrasound stimulation thermal effect and mechanical effect simulation system according to claim 1, characterized in that: In the mechanical effect simulation, the tissue strain distribution is obtained by the dynamic balance equation, and the mechanical index MI is used to evaluate the cavitation risk of ultrasound stimulation. The dynamic balance equation is as follows: The mechanical index MI calculation formula is as follows: Where f is the stress density, is the sound pressure distance gradient, cos(wt+φ) is the cosine waveform, r is the distance from the surface after entering the skull, t is the time, w is the angular frequency, φ is the initial phase, and p(r,t) is the sound pressure field.

9. A method for simulating thermal and mechanical effects of transcranial focused ultrasound stimulation, characterized in that: include: Based on the set ultrasound parameters and stimulation targets, combined with the reconstructed human brain model, the propagation direction (along the Z axis) and the brain acoustic field of the focal area are calculated to simulate the acoustic field effect; Based on the simulation of acoustic field effects, the thermal effects of ultrasound waves with different frequencies, sound pressures and focusing characteristics on biological tissues on the main propagation path are calculated, biothermodynamic simulation is performed, and the thermal damage of soft tissues during ultrasound stimulation is evaluated according to the cumulative energy model. Based on the simulation of the acoustic field effect, the mechanical effect of ultrasound on the focal area when it acts on the brain tissue is calculated, the mechanical index MI is calculated to evaluate the risk of cavitation effect, and the mechanical effect simulation is performed; A coupling relationship is established between the acoustic field effect, thermal effect and mechanical effect, each partial effect is calculated independently, and each partial effect is linked with the remaining effect to achieve multi-physics field coupling simulation.

10. The method for simulating thermal and mechanical effects of transcranial focused ultrasound stimulation according to claim 9, characterized in that: Also includes: Generate a visual sound field distribution diagram based on the simulation results of intracranial stimulation sound field effect; Generate a visual whole-brain heat map from the biothermodynamic simulation results; The mechanical effect simulation results are used to generate visual mechanical stress density and MI extreme value diagrams.

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