CN116798638B - Three-dimensional temperature field simulation method for microwave ablation of liver tumor - Google Patents
Three-dimensional temperature field simulation method for microwave ablation of liver tumor Download PDFInfo
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Abstract
The application relates to the field of temperature field simulation, in particular to a three-dimensional temperature field simulation method for microwave ablation of liver tumors, which comprises the following steps: establishing a three-dimensional model of the liver part of the patient according to the liver image and dividing grids; establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by combining the two biological heat transfer equations; determining boundary conditions in a microwave ablation three-dimensional temperature field model according to different positions of the liver tumor at the liver part; determining model parameters in a microwave ablation three-dimensional temperature field model; three-dimensional simulation of the temperature field inside the tumor is generated in real time during the operation. The application considers the position of the liver part where the liver tumor is located, and accurately analyzes the boundary conditions to improve the accuracy of temperature simulation, so that the operation process is safer.
Description
Technical Field
The application relates to the field of temperature field simulation, in particular to a three-dimensional temperature field simulation method for microwave ablation of liver tumors.
Background
The microwave ablation technology for liver cancer is one kind of minimally invasive tumor ablation technology, and the specific treatment method is to puncture microwave antenna (microwave needle) to tumor site percutaneously under the guidance of B ultrasonic or CT, start microwave therapeutic apparatus, ablate tumor with microwave antenna, and has the features of accurate positioning and in situ inactivation, so that the polar molecules in tumor, such as water molecule protein molecule, are rotated repeatedly at high frequency, the mutual friction between polar molecules can raise the temperature inside tumor to over 110 deg.c fast, tumor death fast and tumor cell inactivation fast at 60 deg.c. Compared with the traditional operation, the tumor minimally invasive ablation treatment technology (microwaves, radio frequency and the like) has the characteristics of being minimally invasive, less in pain and high in safety, the operation recovery is quick, the patient can get out of the bed the next day after the operation, and no surgical scar exists. And for a plurality of focuses which cannot be excised in operation, the tumor can be inactivated one by utilizing a tumor minimally invasive ablation treatment technology, so that hope is brought to a tumor patient.
The microwave ablation preoperative scheme formulation relates to ablation thermal dose (ablation power and ablation time) setting and ablation needle puncture path planning, and relies on volume experimental data of an ex-vivo ablation model and experience of a clinician in puncturing an ablation needle, so that the precise operation scheme for different patients and the guidance of the clinician with less puncture experience are lacked. The existing liver tumor microwave ablation simulation method mostly ignores the influence of blood vessels and blood flow perfusion during in-vivo ablation, and a completely symmetrical ablation thermal field is calculated.
In addition, the position of the liver part where the liver tumor is located can influence model parameters and boundary conditions of a three-dimensional temperature field, and under the same conditions, the actual temperature can be different from the simulation temperature for the situation that the liver tumor is far away from the edge of the liver and the situation that the liver tumor is at the edge of the liver, so that errors of temperature judgment in the operation process can be caused, the liver tumor is possibly not completely ablated due to insufficient actual temperature, and normal stem tissue cells around the edge of the liver tumor can be inactivated due to excessive actual temperature, so that injury is caused to a patient. In the operation process, the change of the microwave ablation power and the change of the position of the microwave ablation needle can cause the change of the temperature field value, so that a method for updating the three-dimensional temperature field simulation in real time in the operation is also more needed, and the safety of the operation is improved.
The Chinese patent with the application publication number of CN110263489A discloses a three-dimensional temperature field simulation method for microwave ablation of liver tumor based on DICOM data, which comprises the following steps: reconstructing and repairing tumor and vascular models based on DICOM data, introducing the tumor and vascular models into a multi-physical-field simulation module, selecting a working plane to draw an ablation needle structure diagram, and constructing a simulation geometric model; setting different materials and parameters for a calculation domain in a simulation geometric model, wherein the specific material types are as follows: liver, tumor, PTFE; constructing a coupled electromagnetic wave radiation model and a biological heat transfer model; according to the constructed model, meshing the simulation geometric model according to the set microwave frequency, and setting a solver solving method; and carrying out visual processing on the simulation data obtained by solving to obtain temperature field distribution data. The simulation method can utilize preoperative image data of a patient to establish a three-dimensional finite element simulation model, calculate an ablation thermal field and guide the formulation of an operation scheme.
For example, chinese patent with publication number CN107526928B discloses a method for simulating a microwave thermal ablation temperature field based on feedback of characteristic parameters, which comprises: setting preset initial conditions and boundary conditions in COMSOL software, and establishing a microwave thermal ablation temperature field simulation model; performing sensitivity analysis on the body model module characteristic parameters based on the simulation model; performing a microwave thermal ablation experiment, and performing actual measurement on seven points of an ablation zone by utilizing temperature measurement to obtain actual measurement temperature; based on the parameter sensitivity analysis result, obtaining an accurate characterization form of the characteristic parameter by using feedback needle actual measurement data; and carrying out temperature field simulation by using the accurate representation form of the characteristic parameters, and comparing the temperature field simulation with measured data to verify the accuracy of a temperature field distribution model. The technical scheme of the application can solve the problem that the temperature field distribution cannot be accurately obtained due to the uncertainty of the tissue characteristic parameters in the prior art.
The problems proposed in the background art exist in the above patents: the position of the liver part where the liver tumor is located can influence the error of the actual temperature and the simulated temperature, and the actual temperature is possibly insufficient to cause incomplete ablation of the liver tumor, and the actual temperature is possibly too high to cause inactivation of normal stem tissue cells around the edge of the liver tumor, so that the damage is caused to a patient. During the operation, the change of the microwave ablation power and the change of the position of the microwave ablation needle can cause the change of the temperature field value. In order to solve the problems, the application designs a three-dimensional temperature field simulation method for microwave ablation of liver tumors.
Disclosure of Invention
The application aims to solve the technical problem of providing a three-dimensional temperature field simulation method for microwave ablation of liver tumors aiming at the defects of the prior art.
In order to achieve the above purpose, the present application provides the following technical solutions:
the three-dimensional temperature field simulation method for microwave ablation of liver tumor is characterized by comprising the following steps:
step S1: establishing a three-dimensional model of the liver part of the patient according to the liver image and dividing grids;
step S2: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by combining the biological heat transfer equation based on the Fourier heat transfer rule and the biological heat transfer equation based on the non-Fourier heat transfer rule;
step S3: determining boundary conditions in a microwave ablation three-dimensional temperature field model according to different positions of the liver tumor at the liver part;
step S4: determining electric field model parameters and temperature field model parameters in a microwave ablation three-dimensional temperature field model;
step S5: three-dimensional simulation of the temperature field inside the tumor is generated in real time during the operation.
Further, the step S1 specifically includes the following steps:
step S1.1: collecting liver image data of a patient, and establishing a three-dimensional model of a liver part;
step S1.2: selecting a hexahedral unit as a unit type, and dividing grid units of the three-dimensional model of the liver part;
step S1.3: the cell mesh shape is checked and adjusted.
Further, step S1.2 specifically includes: the method comprises the steps of dividing the tip position of the ablation needle by adopting fine grids, dividing the edge part of the liver tumor and the central part of the liver tumor by adopting fine grids, dividing the part of the liver tumor except the central part and the edge part by adopting medium grids, and dividing the part of the whole liver except the liver tumor by adopting coarse grids.
Further, the step S2 specifically includes the following steps:
step S2.1: calculating temperature obtained by biological heat transfer equation based on Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,temperature, which is obtained by a biological heat transfer equation based on Fourier heat transfer law, is expressed>Representing biological tissue density,/->Representing the specific heat capacity of biological tissue->Superficial biological liver tissue heat conductivity coefficient, < >>Indicating blood density->Indicating blood perfusion rate,/->Represents the specific heat capacity of blood>Indicates blood temperature, < >>Representing the heat generated by the electric field applied by the ablation needle,time of presentation->Representing a gradient operator;
step S2.2: calculating the temperature obtained by a biological heat transfer equation based on a non-Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,representing the relaxation time, i.e. the characteristic time required for thermal energy transfer to the nearest unit within the biological tissue;
step S2.3: according to errors caused by the biological heat transfer equation, the weight of the biological heat transfer equation based on the Fourier heat transfer rule is set asThe weight of the biological heat transfer equation based on the non-Fourier heat transfer rule is set as +.>；
Step S2.4: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by taking the boundary point of the sickle ligament and the coronary ligament of the liver as the origin of coordinates of the three-dimensional temperature field model, wherein the calculation formula is as follows:
，
wherein ,the calculation formula of the ablation needle emission power is as follows: />, wherein />Represents the potential->Representing the conductivity of biological tissue, ">Representing the length-section proportional relationship of biological tissue, +.>Indicates ablation time,/->Specific point representing three-dimensional temperature field model +.>Temperature of>Three-dimensional temperature field model specific point of biological heat transfer equation based on Fourier heat transfer rule>Temperature of>Three-dimensional temperature field model specific point for representing biological heat transfer equation based on non-Fourier heat transfer rule>Is set in the temperature range of (a).
Further, in step S2.1, heat generated by the electric field applied by the ablation needleThe calculation formula of (2) is as follows:
，
wherein ,indicating the heat generated by the electric field applied by the ablation needle, < >>Indicating the conductivity of the biological tissue as a function of temperature, < >>Representing the gradient operator.
Further, the boundary conditions in the microwave ablation three-dimensional temperature field model in step S3 include: boundary conditions imposed by liver tumors in the case of liver border are not present.
Further, the boundary conditions imposed in the case where the liver tumor is not at the edge of the liver include:
the ablation needle tip is considered as a voltage source and the liver edge is set to be grounded, i.e，/>Representing the edge potential;
setting the heat conduction between liver tissue and liver tumor to be linear continuous;
setting the initial temperature of the initial condition of the heat transfer equation to be。
Further, the boundary conditions imposed by the liver tumor in the case of liver edge include:
setting the edge potential of liver tumor asLiver tumor margin potential->The calculation formula of (2) is as follows:
，
wherein ,representing unit normal vector, ">Representing the liver tumor edge spatial position vector, +.>A position vector representing the center point of the tip of the ablation needle;
setting the initial temperature of the initial condition of the heat transfer equation to be；
Setting the heat conductivity coefficients of liver and tumor asThermal conductivity of liver and tumor->The calculation formula of (2) is as follows:
，
wherein ,indicating baseline temperature, +.>Representing the thermal conductivity of the liver or liver tumor at baseline temperature,/-for>Indicating the current temperature +_>Indicates the increase in liver or liver tumor thermal conductivity per one degree celsius rise, < >>Indicating the phase transition temperature, i.e. the upper limit of the temperature at which the substance transitions between different states.
Further, the electric field model parameters include: liver conductivity, liver tumor conductivity, baseline liver tumor conductivity, vapor conductivity, ablation needle tip conductivity, and ablation needle shaft conductivity.
Further, the temperature field model parameters include: liver heat conductivity, liver tumor heat conductivity, liver and tumor density, liver and tumor specific heat capacity, ablation needle tip heat conductivity, ablation needle tip density, ablation needle tip specific heat capacity, ablation needle shaft heat conductivity, ablation needle shaft density, ablation needle shaft specific heat capacity, blood density, blood specific heat capacity, baseline liver blood flow perfusion rate, baseline liver tumor blood flow perfusion rate, tissue water content and latent heat of vaporization.
Further, the step S4 specifically includes the following steps:
step S4.1: selecting boundary conditions according to the liver tumor position condition of the patient;
step S4.2: acquiring the real-time position of an ablation needle at a hepatic tumor part of a patient in operation, and transmitting power and ablation time of the ablation needle;
step S4.3: substituting the real-time position of the tip of the ablation needle, the emission power of the ablation needle, the ablation time, boundary conditions selected according to the position condition of the liver tumor of a patient and three-dimensional temperature field model parameters into a biological heat transfer equation to obtain the specific temperature of the three-dimensional temperature field grid, wherein the calculation formula is as follows:
，
wherein ,representing the temperature value of the grid in a three-dimensional temperature field simulation, < >>Indicating the number of selected temperature measuring points in the grid, < >>The distance between the real-time position of the tip of the ablation needle and the temperature measuring point is represented, and the calculation formula is as follows:，/>indicate->The position coordinates of the temperature measuring points,the table represents real-time position coordinates of the tip of the ablation needle;
step S4.4: outputting specific temperatures of each grid of the three-dimensional temperature field in the liver tumor and the grid temperature of the section of the liver tumor taking the ablation needle as an axis, and realizing real-time simulation of the three-dimensional temperature field.
A storage medium having instructions stored therein that, when read by a computer, cause the computer to perform a three-dimensional temperature field simulation method of microwave ablation of a liver tumor as described in any one of the preceding claims.
An electronic device comprising a processor and a storage medium as described above, the processor executing instructions in the storage medium.
Compared with the prior art, the application has the beneficial effects that:
1. according to the three-dimensional temperature field simulation method for microwave ablation of the liver tumor, the position of the liver part where the liver tumor is located is considered, the situation that the liver tumor is not at the edge of the liver and the situation that the liver tumor is at the edge of the liver are divided, the boundary condition setting is simplified under the situation that the liver tumor is not at the edge of the liver, the simulation speed and the efficiency can be improved, and the boundary condition is accurately analyzed under the situation that the liver tumor is at the edge of the liver so as to improve the accuracy of temperature simulation, so that the operation process is safer.
2. According to the three-dimensional temperature field simulation method for microwave ablation of liver tumors, disclosed by the application, the human liver is simulated by utilizing fresh isolated pig livers through a biological heat transfer equation based on a Fourier heat transfer rule and a biological heat transfer equation based on a non-Fourier heat transfer rule, errors of the two heat transfer equations are calculated, weights are distributed, the accuracy of the calculated temperatures of the biological heat transfer equation based on the Fourier heat transfer rule and the biological heat transfer equation based on the non-Fourier heat transfer rule is improved, the discrete degree is lower, and the simulation accuracy of the three-dimensional temperature field for ablation is improved.
3. According to the three-dimensional temperature field simulation method for microwave ablation of the liver tumor, provided by the application, the real-time three-dimensional temperature field simulation is carried out in the operation process of microwave ablation of the liver tumor by acquiring the real-time position of the ablation needle in the operation, the real-time power of microwave ablation, the time of microwave ablation and the boundary conditions and model parameters generated in real time, and the three-dimensional temperature field simulation is carried out, and display output is carried out, so that a doctor can be helped to judge the specific condition of the microwave ablation of the liver tumor, and the reliability of the microwave ablation operation of the liver tumor is improved.
4. According to the three-dimensional temperature field simulation method for microwave ablation of the liver tumor, disclosed by the application, the tip position of the ablation needle, namely the central part of the liver tumor, is divided by adopting fine grids, and the edge part of the liver tumor is divided by adopting fine grids, so that the accuracy of temperature calculation of the edge and the central position can be improved, and the reliability of three-dimensional temperature field simulation is improved; the central part and the edge part of the liver tumor are divided by adopting medium grids, and the whole liver tumor removing part is divided by adopting coarse grids, so that the speed of calculation simulation of a non-important part temperature field can be increased, and the simulation efficiency is improved.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the detailed description of non-limiting embodiments, made with reference to the following drawings in which:
FIG. 1 is a schematic flow chart of a three-dimensional temperature field simulation method for microwave ablation of liver tumor in embodiment 1 of the application;
FIG. 2 is a schematic diagram of an ablation needle working section of a three-dimensional temperature field simulation method for microwave ablation of liver tumors in embodiment 2 of the present application;
fig. 3 is a schematic diagram of hexahedral mesh temperature measurement points of a three-dimensional temperature field simulation method for microwave ablation of liver tumor in embodiment 3 of the present application;
FIG. 4 is a data flow diagram of a three-dimensional temperature field simulation method for microwave ablation of liver tumors according to embodiment 4 of the present application;
fig. 5 is an electronic device diagram of a three-dimensional temperature field simulation method for microwave ablation of liver tumor in embodiment 5 of the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments.
Example 1
Referring to fig. 1, an embodiment of the present application is provided: the three-dimensional temperature field simulation method for microwave ablation of liver tumor is characterized by comprising the following steps:
step S1: establishing a three-dimensional model of the liver part of the patient according to the liver image and dividing grids;
step S2: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by combining the biological heat transfer equation based on the Fourier heat transfer rule and the biological heat transfer equation based on the non-Fourier heat transfer rule;
step S3: determining boundary conditions in a microwave ablation three-dimensional temperature field model according to different positions of the liver tumor at the liver part;
step S4: determining electric field model parameters and temperature field model parameters in a microwave ablation three-dimensional temperature field model;
step S5: three-dimensional simulation of the temperature field inside the tumor is generated in real time during the operation.
The step S1 specifically comprises the following steps:
step S1.1: collecting liver image data of a patient, and establishing a three-dimensional model of a liver part;
step S1.2: selecting a hexahedral unit as a unit type, and dividing grid units of the three-dimensional model of the liver part;
step S1.3: the cell mesh shape is checked and adjusted.
The step S1.2 specifically comprises the following steps: the method comprises the steps of dividing the tip position of the ablation needle by adopting fine grids, dividing the edge part of the liver tumor and the central part of the liver tumor by adopting fine grids, dividing the part of the liver tumor except the central part and the edge part by adopting medium grids, and dividing the part of the whole liver except the liver tumor by adopting coarse grids.
The step S2 specifically comprises the following steps:
step S2.1: calculating temperature obtained by biological heat transfer equation based on Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,temperature, which is obtained by a biological heat transfer equation based on Fourier heat transfer law, is expressed>Representing biological tissue density,/->Representing the specific heat capacity of biological tissue->Indicating the thermal conductivity of biological tissue,/-)>Indicating blood density->Indicating blood perfusion rate,/->Represents the specific heat capacity of blood>Indicates blood temperature, < >>Representing the heat generated by the electric field applied by the ablation needle,time of presentation->Representing a gradient operator;
step S2.2: calculating the temperature obtained by a biological heat transfer equation based on a non-Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,representing the relaxation time, i.e. the characteristic time required for the transfer of thermal energy to the nearest unit in the biological tissue, for liver tissue +.>；
Step S2.3: calculating an error caused by a biological heat transfer equation, and setting biological heat transfer based on a Fourier heat transfer ruleThe weight of the equation isThe weight of the biological heat transfer equation based on the non-Fourier heat transfer rule is set as +.>；
Step S2.4: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by taking the boundary point of the sickle ligament and the coronary ligament of the liver as the origin of coordinates of the three-dimensional temperature field model, wherein the calculation formula is as follows:
，
wherein ,the calculation formula of the ablation needle emission power is as follows: />, wherein />Represents the potential->Representing the conductivity of biological tissue, ">Representing the length-section proportional relationship of biological tissue, +.>Indicates ablation time,/->Specific point representing three-dimensional temperature field model +.>Temperature of>Three-dimensional temperature field model specific point of biological heat transfer equation based on Fourier heat transfer rule>Temperature of>Three-dimensional temperature field model specific point for representing biological heat transfer equation based on non-Fourier heat transfer rule>Is set in the temperature range of (a).
In step S2.1, heat generated by the electric field applied by the ablation needleThe calculation formula of (2) is as follows:
，
wherein ,indicating the heat generated by the electric field applied by the ablation needle, < >>Indicating the conductivity of the biological tissue as a function of temperature, < >>Representing gradient operators, wherein ∈>The calculation formula of (2) is as follows:
，
wherein ,represents liver conductivity or liver tumor conductivity, < ->Represents baseline liver conductivity or liver tumor conductivity, < ->An upper limit representing the phase transition temperature, i.e. the temperature at which a substance transitions between different states, +.>Indicating the lower limit of the phase transition temperature.
In step S2.3, the specific steps for calculating the error caused by the biological heat transfer equation are as follows:
step S2.3.1: performing simulation test with fresh isolated pig liver, controlling the ambient temperature to 37 deg.C, selectingInserting ablation needles at different points to perform heating treatment;
step S2.3.2: twenty points are selected from the surrounding part of the tip of the ablation needle at each different point position to carry out temperature measurement;
step S2.3.3: using a biological heat transfer equation based on a Fourier heat transfer rule and a biological heat transfer equation based on a non-Fourier heat transfer rule to calculate the temperature of twenty points around the tip of the ablation needle at each different point;
step S2.3.4: calculating the percentage error of a biological heat transfer equation based on a Fourier heat transfer ruleAnd mean square error->Percentage error of biological heat transfer equation based on non-Fourier heat transfer rule>Sum mean square errorThe calculation formula is as follows:
，
，
wherein ,indicating the number of different spots of insertion of ablation needle, < >>One of twenty temperature measurement points representing the peripheral portion of the tip of the ablation needle at each different point,/->Represents one of the different points of insertion of the ablation needle,/->Representing the measured temperature true value, +.>Is indicated at +.>The +.f. of different points of the individual ablation needles>Calculating temperature according to biological heat transfer equation based on Fourier heat transfer rule of each temperature measuring point, < >>Is indicated at +.>The +.f. of different points of the individual ablation needles>Calculating temperature according to a biological heat transfer equation based on a non-Fourier heat transfer rule of each temperature measuring point, wherein the temperature is +.> and />Respectively representing the percentage error and the mean square error of the calculated temperature of the biological heat transfer equation based on the Fourier heat transfer rule,/and-> and />Respectively representing the percentage error and the mean square error of the calculated temperature of the biological heat transfer equation based on the non-Fourier heat transfer rule;
step S2.3.5: calculating weight based on errors, wherein the calculation formula is as follows:
，
wherein ,weights representing biological heat transfer equations based on fourier heat transfer law,/->Weights representing biological heat transfer equations based on non-fourier heat transfer laws, +.>Represents constraint constant, and the value range is [ 0-1 ]]。
In step S3, boundary conditions in the microwave ablation three-dimensional temperature field model include: boundary conditions imposed by liver tumors in the case of liver border are not present.
Boundary conditions imposed by liver tumors without liver edges include:
the ablation needle tip is considered as a voltage source and the liver edge is set to be grounded, i.e，/>Representing the edge potential;
setting the heat conduction between liver tissue and liver tumor to be linear continuous;
setting the initial temperature of the initial condition of the heat transfer equation to be，/>。
Boundary conditions imposed by liver tumors in the case of liver edges include:
setting the edge potential of liver tumor asLiver tumor margin potential->The calculation formula of (2) is as follows:
，
wherein ,representing unit normal vector, ">Representing the liver tumor edge spatial position vector, +.>A position vector representing the center point of the tip of the ablation needle;
setting the initial temperature of the initial condition of the heat transfer equation to be，/>；
Setting the heat conductivity coefficients of liver and tumor asThermal conductivity of liver and tumor->The calculation formula of (2) is as follows:
，
wherein ,indicating baseline temperature, +.>Representing the thermal conductivity of the liver or liver tumor at baseline temperature,/-for>Indicating the current temperature +_>Indicates the increase in liver or liver tumor thermal conductivity per one degree celsius rise, < >>Indicating the phase transition temperature, i.e. the upper limit of the temperature at which the substance transitions between different states.
Example 2
Referring to fig. 2, an embodiment of the present application is provided: an ablation needle working section schematic diagram of a three-dimensional temperature field simulation method for microwave ablation of liver tumor, A1 represents an ablation needle, A2 represents an ablation needle tip part, A3 represents an ablation needle shaft part, A4 represents liver tissue, A5 represents liver tumor tissue, A6 represents blood vessels in liver tumor, B1 represents boundary conditions selected according to the situation of the liver tumor position, B2 represents boundary conditions generated by thermal effects of blood flow, wherein the boundary conditions generated by the thermal effects of the blood flow comprise blood and tissue edgesHeat transfer coefficient of boundary convectionConvection heat transfer coefficient->The calculation formula of (2) is as follows:
，
wherein ,convection coefficient representing tissue blood and tissue boundary, < ->Representing the radius of the blood vessel>Representing gradient operators +_>Indicating the thermal conductivity of the liver and tumor.
The electric field model parameters include: liver conductivity, liver tumor conductivity, baseline liver tumor conductivity, steam conductivity, ablation needle tip conductivity and ablation needle shaft conductivity, the specific values are shown in the following table:
table 1 electric field model parameter values
The temperature field model parameters include: the specific values of the liver heat conductivity coefficient, the liver tumor heat conductivity coefficient, the liver and tumor density, the liver and tumor specific heat capacity, the ablation needle tip heat conductivity coefficient, the ablation needle tip specific heat capacity, the ablation needle shaft heat conductivity coefficient, the ablation needle shaft density, the ablation needle shaft specific heat capacity, the blood density, the blood specific heat capacity, the baseline liver blood flow perfusion rate, the baseline liver tumor blood flow perfusion rate, the tissue water content and the vaporization latent heat are shown in the following table:
table 2 temperature field model parameter values
The step S4 specifically comprises the following steps:
step S4.1: selecting boundary conditions according to the liver tumor position condition of the patient;
step S4.2: acquiring the real-time position of an ablation needle at a hepatic tumor part of a patient in operation, and transmitting power and ablation time of the ablation needle;
step S4.3: substituting the real-time position of the tip of the ablation needle, the emission power of the ablation needle, the ablation time, boundary conditions selected according to the position condition of the liver tumor of a patient and three-dimensional temperature field model parameters into a biological heat transfer equation to obtain the specific temperature of the three-dimensional temperature field grid, wherein the calculation formula is as follows:
，
wherein ,representing the temperature value of the grid in a three-dimensional temperature field simulation, < >>Indicating the number of selected temperature measuring points in the grid, < >>The distance between the real-time position of the tip of the ablation needle and the temperature measuring point is represented, and the calculation formula is as follows:，/>indicate->The position coordinates of the temperature measuring points,the table represents real-time position coordinates of the tip of the ablation needle;
step S4.4: outputting specific temperatures of each grid of the three-dimensional temperature field in the liver tumor and the grid temperature of the section of the liver tumor taking the ablation needle as an axis, and realizing real-time simulation of the three-dimensional temperature field.
Example 3
Referring to fig. 3, an embodiment of the present application is provided: a hexahedral mesh temperature measurement point schematic diagram of a three-dimensional temperature field simulation method for microwave ablation of liver tumors, wherein gray dots represent specific positions of an ablation needle tip in the hexahedral mesh, black dots represent temperature measurement points of the hexahedral mesh where the ablation needle tip is located, and the method comprises the following steps: five vertexes of the hexahedron, a center point of each of six faces of the hexahedron, and a middle point of each of nine edges of the hexahedron, which are twenty temperature measuring points in total.
Example 4
Referring to fig. 4, an embodiment of the present application is provided: a dataflow graph of a three-dimensional temperature field simulation method of microwave ablation of liver tumors, comprising:
firstly, extracting liver part image data of a patient to be operated, and suggesting a three-dimensional model diagram of the liver of the patient through the image data; according to different liver tumor parts of a patient, boundary conditions are selected, and a determined heat transfer equation is brought into to generate a model of a microwave ablation three-dimensional temperature field; bringing the biological tissue parameters and the real-time position parameters of the ablation needle into a model of a microwave ablation three-dimensional temperature field to generate a real-time simulation result; and finally, displaying and outputting the simulation result through an output display screen.
Example 5
Referring to fig. 5, an embodiment of the present application is provided: an electronic equipment diagram of a three-dimensional temperature field simulation method for microwave ablation of liver tumors comprises a processor and the storage medium, wherein the processor executes instructions in the storage medium.
Any combination of one or more computer readable media may be employed. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium can be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of the computer-readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
The foregoing description is only of preferred embodiments of the application and is not intended to limit the application to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application.
Claims (12)
1. The three-dimensional temperature field simulation method for microwave ablation of liver tumor is characterized by comprising the following steps:
step S1: establishing a three-dimensional model of the liver part of the patient according to the liver image and dividing grids;
step S2: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by combining the biological heat transfer equation based on the Fourier heat transfer rule and the biological heat transfer equation based on the non-Fourier heat transfer rule;
the step S2 specifically includes the following steps:
step S2.1: calculating temperature obtained by biological heat transfer equation based on Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,temperature, which is obtained by a biological heat transfer equation based on Fourier heat transfer law, is expressed>Representing the density of the biological tissue,representing the specific heat capacity of biological tissue->Indicating the thermal conductivity of biological tissue,/-)>Indicating blood density->The blood perfusion rate is indicated by the ratio,represents the specific heat capacity of blood>Indicates blood temperature, < >>Indicating the heat generated by the electric field applied by the ablation needle, < >>Time of presentation->Representing a gradient operator;
step S2.2: calculating the temperature obtained by a biological heat transfer equation based on a non-Fourier heat transfer ruleThe calculation formula is as follows:
，
wherein ,representing the relaxation time, i.e. the characteristic time required for thermal energy transfer to the nearest unit within the biological tissue;
step S2.3: according to errors caused by the biological heat transfer equation, the weight of the biological heat transfer equation based on the Fourier heat transfer rule is set asThe weight of the biological heat transfer equation based on the non-Fourier heat transfer rule is set as +.>；
Step S2.4: establishing a biological heat transfer equation of the microwave ablation three-dimensional temperature field model by taking the boundary point of the sickle ligament and the coronary ligament of the liver as the origin of coordinates of the three-dimensional temperature field model, wherein the calculation formula is as follows:
，
wherein ,the calculation formula of the ablation needle emission power is as follows: />, wherein />Representing the potential of the biological tissue,representing the conductivity of biological tissue, ">Representing the length-section proportional relationship of biological tissue, +.>Indicates ablation time,/->Specific point representing three-dimensional temperature field model +.>Temperature of>Three-dimensional temperature field model specific point of biological heat transfer equation based on Fourier heat transfer rule>Temperature of>Three-dimensional temperature field model specific point for representing biological heat transfer equation based on non-Fourier heat transfer rule>Is set at a temperature of (2);
step S3: determining boundary conditions in a microwave ablation three-dimensional temperature field model according to different positions of the liver tumor at the liver part;
step S4: determining electric field model parameters and temperature field model parameters in a microwave ablation three-dimensional temperature field model;
step S5: three-dimensional simulation of the temperature field inside the tumor is generated in real time during the operation.
2. The method for simulating a three-dimensional temperature field for microwave ablation of liver tumor according to claim 1, wherein said step S1 comprises the steps of:
step S1.1: collecting liver image data of a patient, and establishing a three-dimensional model of a liver part;
step S1.2: selecting a hexahedral unit as a unit type, and dividing grid units of the three-dimensional model of the liver part;
step S1.3: the cell mesh shape is checked and adjusted.
3. The method for simulating a three-dimensional temperature field for microwave ablation of liver tumors according to claim 2, wherein the step S1.2 specifically comprises: the method comprises the steps of dividing the tip position of the ablation needle by adopting fine grids, dividing the edge part of the liver tumor and the central part of the liver tumor by adopting fine grids, dividing the part of the liver tumor except the central part and the edge part by adopting medium grids, and dividing the part of the whole liver except the liver tumor by adopting coarse grids.
4. A method according to claim 3, wherein in step S2.1, the heat generated by the electric field applied by the ablation needle is generatedThe calculation formula of (2) is as follows:
，
wherein ,indicating the heat generated by the electric field applied by the ablation needle, < >>Indicating the conductivity of the biological tissue as a function of temperature, < >>Representing the gradient operator.
5. The method according to claim 4, wherein the boundary conditions in the microwave ablation three-dimensional temperature field model in step S3 include: boundary conditions imposed by liver tumors in the case of liver border are not present.
6. The method of three-dimensional temperature field simulation of microwave ablation of a liver tumor according to claim 5, wherein the boundary conditions imposed by the liver tumor without the liver edge include:
the ablation needle tip is considered as a voltage source and the liver edge is set to be grounded, i.e，/>Representing the edge potential;
setting the heat conduction between liver tissue and liver tumor to be linear continuous;
setting the initial temperature of the initial condition of the heat transfer equation to be。
7. The method of three-dimensional temperature field simulation of microwave ablation of a liver tumor according to claim 6, wherein the boundary conditions imposed by the liver tumor in the case of a liver margin include:
setting the edge potential of liver tumor asLiver tumor margin potential->The calculation formula of (2) is as follows:
，
wherein ,representing unit normal vector, ">Representing the liver tumor edge spatial position vector, +.>A position vector representing the center point of the tip of the ablation needle;
setting the initial temperature of the initial condition of the heat transfer equation to be；
Setting the heat conductivity coefficients of liver and tumor asThermal conductivity of liver and tumor->The calculation formula of (2) is as follows:
，
wherein ,indicating baseline temperature, +.>Representing the thermal conductivity of the liver or liver tumor at baseline temperature,/-for>Indicating the current temperature of the device and,indicates the increase in liver or liver tumor thermal conductivity per one degree celsius rise, < >>Indicating the phase transition temperature, i.e. the upper limit of the temperature at which the substance transitions between different states.
8. The method for three-dimensional temperature field simulation of microwave ablation of liver tumors according to claim 7, wherein the electric field model parameters comprise: liver conductivity, liver tumor conductivity, baseline liver tumor conductivity, vapor conductivity, ablation needle tip conductivity, and ablation needle shaft conductivity.
9. The method for three-dimensional temperature field simulation of microwave ablation of liver tumors according to claim 8, wherein the temperature field model parameters comprise: liver heat conductivity, liver tumor heat conductivity, liver and tumor density, liver and tumor specific heat capacity, ablation needle tip heat conductivity, ablation needle tip density, ablation needle tip specific heat capacity, ablation needle shaft heat conductivity, ablation needle shaft density, ablation needle shaft specific heat capacity, blood density, blood specific heat capacity, baseline liver blood flow perfusion rate, baseline liver tumor blood flow perfusion rate, tissue water content and latent heat of vaporization.
10. The method for simulating a three-dimensional temperature field for microwave ablation of liver tumor according to claim 9, wherein said step S4 comprises the steps of:
step S4.1: selecting boundary conditions according to the liver tumor position condition of the patient;
step S4.2: acquiring the real-time position of an ablation needle at a hepatic tumor part of a patient in operation, and transmitting power and ablation time of the ablation needle;
step S4.3: substituting the real-time position of the tip of the ablation needle, the emission power of the ablation needle, the ablation time, boundary conditions selected according to the position condition of the liver tumor of a patient and three-dimensional temperature field model parameters into a biological heat transfer equation to obtain the specific temperature of the three-dimensional temperature field grid, wherein the calculation formula is as follows:
，
wherein ,representing the temperature value of the grid in a three-dimensional temperature field simulation, < >>The number of selected temperature measuring points in the grid is represented,the distance between the real-time position of the tip of the ablation needle and the temperature measuring point is represented, and the calculation formula is as follows:，/>indicate->Position coordinates of the temperature measuring points, < >>Representing real-time position coordinates of the tip of the ablation needle;
step S4.4: outputting specific temperatures of each grid of the three-dimensional temperature field in the liver tumor and the grid temperature of the section of the liver tumor taking the ablation needle as an axis, and realizing real-time simulation of the three-dimensional temperature field.
11. A storage medium having instructions stored therein which, when read by a computer, cause the computer to perform a method of three-dimensional temperature field simulation of microwave ablation of a liver tumor according to any one of claims 1-10.
12. An electronic device comprising a processor and the storage medium of claim 11, the processor executing instructions in the storage medium.
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