Electrical impedance frequency differential measurement method based on center driving measurement mode

Abstract

The invention relates to an electrical impedance frequency difference measurement method based on a center driving measurement mode, and belongs to the technical field of impedance measurement, and the method comprises the following steps: S1, taking a human body as a quasi-static field, taking a probe as an internal current source, taking body surface electrodes as a current sink in turn, and building a field equation of impedance frequency difference measurement of an operation region; s2, determining boundary conditions of impedance frequency difference measurement driven by the internal source electrode; s3, in the measurement process, current is injected from the internal source electrode and flows out from the external current, outflow electrodes are switched in sequence, the potential difference between the other body surface electrodes is measured, and a voltage difference matrix is generated; and S4, performing frequency difference calculation, and solving the change value of the conductivity of the diseased tissue caused by ablation in the operation process.

Description

Technical Field

[0001] This invention belongs to the field of impedance measurement technology and relates to a method for measuring impedance frequency difference based on center-driven measurement mode. Background Technology

[0002] Intraoperative monitoring and imaging are crucial for minimally invasive ablation surgery. Conventional medical imaging methods include postoperative CT, MRI, and intraoperative X-ray imaging. While ultrasound monitoring is portable, inexpensive, and provides real-time imaging, the high-echo cloud generated by water vaporization during microwave ablation can render the ultrasound sensor ineffective, hindering monitoring of the ablation process. Ultrasound elastography, although providing tissue stiffness information, has relatively low resolution and cannot clearly display the boundaries and internal structures of lesions smaller than 5 mm in diameter, leading to inaccurate assessments. Furthermore, tissue edema can cause the stiffness displayed by elastography to be lower than the actual stiffness of the ablated tissue, resulting in inaccurate assessments of ablation effectiveness due to edema interference. CT monitoring, while providing high-resolution tissue images, poses a risk of ionizing radiation to patients and medical staff, and requires intermittent imaging, failing to meet the need for continuous intraoperative monitoring. MRI monitoring faces compatibility issues with magnetic fields during microwave thermal ablation, and the expensive and bulky equipment is difficult to implement in routine surgical settings. Additionally, MRI monitoring requires the patient to remain still during ablation, increasing the complexity of the procedure. Traditional impedance measurement methods require injecting current into the body surface, and their mathematical models are boundary condition problems, making it difficult to accurately reflect real-time changes in the ablation area within the body. This technique cannot distinguish the impedance difference between the ablation area and surrounding tissues, leading to inaccurate judgments of the ablation range. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a method for differential measurement of impedance frequency based on a center-driven measurement mode.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for differential impedance frequency measurement based on a center-driven measurement mode includes the following steps: S1: Treat the human body as a quasi-static field, the probe as an internal current source, and the surface electrodes as current sinks in turn, and establish the field equation for measuring the impedance frequency difference in the surgical area. S2: Determine the boundary conditions for the impedance frequency difference measurement driven by the internal electrode; S3: During the measurement process, current is injected from the internal source electrode and flows out from the external current. The outflow electrode is switched in sequence to measure the potential difference between the remaining body surface electrodes and generate a voltage difference matrix. S4: Perform frequency difference calculations to solve for the change in conductivity of the lesion tissue caused by ablation during the operation.

[0006] Furthermore, the step S1, which involves establishing the field equation for the impedance frequency difference measurement of the surgical area, includes: S11: The differential form of the conduction current that satisfies Ohm's law, i.e.:

[0007] In the formula, It is the current density. It is electrical conductivity. It is the electric field strength; The equation for the continuity of current is:

[0008] The electric field strength and electric potential satisfy the following relationship:

[0009] S12: Combining the formulas in step S11, we obtain that the potential distribution satisfies the Poisson equation:

[0010] Represents the spatial conductivity distribution. Indicates the potential distribution. Indicates the injected current intensity. This represents the Dirac delta function, indicating that the current flows only at the internal source electrode location. Injected internally.

[0011] Furthermore, the boundary conditions described in step S2 include: Neumann boundary condition: only applies at the boundary where the current flows out. At that point, the current satisfies:

[0012] Zero current boundary condition: at the remaining electrodeless boundary No current flows out, satisfying:

[0013] Dirichlet boundary conditions: at the boundary of the measuring electrode At that point, the boundary potential satisfies:

[0014] in Indicates electrode Boundary potential, It is the normal direction. It is the potential gradient along the normal direction, and the current. From intrinsic electrodes Injection, from surface electrodes Outflow, =1,..., , This represents the number of external electrodes.

[0015] Furthermore, in step S3, current is injected from the internal source electrode and flows out from the external current, with the outflow electrode being switched sequentially. Measure the remaining body surface electrodes Potential difference between , =1, 2, …, ,and As shown in the following formula:

[0016] choose and For two adjacent electrode pairs, the voltage difference matrix generated after traversing all current flows out of the electrodes is denoted as . :

[0017] In the formula Voltage measurement vector of column This indicates that when the current flows out at the numbered point... When measuring electrodes, the vector consists of the voltage measurements between all electrode pairs, with each component being the voltage value of a set of current-measuring electrode pairs. These components together form a complete voltage measurement matrix. This is the total number of external electrodes.

[0018] Furthermore, step S4 specifically includes the following steps: S41: Perform finite element discretization; S42: Solve for the stiffness matrix and potential distribution; S43: Frequency differential calculation; S44: Linearize the voltage difference and solve for the conductivity.

[0019] Furthermore, step S41, which involves finite element discretization, specifically includes: The solution domain Discretized The element is a tetrahedral element in three-dimensional space. The approximate solution of the finite element method is represented by basis functions, and the conductivity distribution is shown. and electric potential As shown in the following formula:

[0020] In the formula, Let be the conductivity basis function. Given the potential basis functions, the final control equations after finite element discretization are shown below:

[0021] This represents the stiffness matrix calculated based on the conductivity distribution after finite element discretization. Represents the nodal potential vector. This indicates the source term, i.e., the term at the internal source electrode. The outflow electrode is .

[0022] Furthermore, the solution to the stiffness matrix and potential distribution in step S42 is as follows: .

[0023] Furthermore, the frequency difference calculation in step S43 includes: After establishing the governing equations and boundary conditions, and determining the electrode potential sampling strategy, frequency difference calculation begins. The current frequency changes over time, denoted as... ; First, we decompose the conductivity, assuming that the change in conductivity during ablation consists of two parts, as shown in the following equation:

[0024] in For background conductivity, For time-varying perturbations caused by ablation; In frequency and Measure the voltage and calculate the voltage difference:

[0025] in Electrode In frequency The potential below.

[0026] Furthermore, the linearization and conductivity solution in step S44 include: Linearize the sensitivity matrix to account for perturbations in the conductivity of the tumor region during ablation. The voltage difference is linearized as follows:

[0027] in It is the first The Jacobian matrix under the secondary current injection configuration was calculated using the finite element method. This represents noise introduced by minute perturbations; Finally, the inverse dynamic frequency difference problem is solved to reconstruct the data from multi-time-point and multi-frequency measurement data. The regularization model is shown in the following equation:

[0028] in This is a time-smoothing regularization term that constrains the continuity between adjacent time points; This is a spatial total variation regularization term that preserves the conductivity jump boundary; This refers to the change in electrical conductivity of the diseased tissue caused by ablation during the surgical procedure.

[0029] The beneficial effects of this invention are as follows: This invention achieves impedance measurement through the center-driven frequency difference method. By using the probe that needs to be injected during the minimally invasive ablation surgery, the excitation current is carried into the body, so that the current source appears directly on the right side of the control equation and becomes a non-homogeneous term. Its mathematical essence is a boundary value problem of the Poisson equation with point source. This method realizes real-time impedance monitoring of tumor ablation, and provides a comprehensive, timely and convenient understanding of the surgical situation.

[0030] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of impedance frequency differential measurement based on center-driven measurement mode; Figure 2 This refers to the electrode potential sampling strategy of the method described in this invention; Figure 3 This is a flowchart of the impedance frequency differential measurement method based on the center-driven measurement mode described in this invention. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0034] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0035] Example 1: like Figure 1-3 As shown, this invention provides a impedance frequency differential measurement method based on a center-driven measurement mode. It is used for the evaluation and monitoring of intraoperative tumor ablation efficacy. This method uses an endogenous electrode in conjunction with multiple surface electrodes to measure the impedance of the surgical area. By applying multi-frequency current excitation, the real and imaginary parts of the impedance are extracted separately. Simultaneously, a specific center-driven measurement mode focuses on the change of regional impedance over time. The measurement device mainly consists of a probe that needs to be injected during the minimally invasive ablation procedure to carry the excitation current into the body as the source electrode, and multiple non-invasive external measurement electrode sensors, thereby achieving real-time impedance monitoring of tumor ablation.

[0036] like Figure 1 As shown, based on the different changes in conductivity and capacitance of different tissues (tumor tissue and normal tissue) in the surgical area with time and frequency during the ablation process, regional imaging of tumor ablation is achieved through the impedance-frequency difference method. A probe is used as the intrinsic electrode, in conjunction with external measuring electrodes to achieve measurement. The intrinsic electrode reaches the tumor lesion area along the pre-planned puncture path, and the external measuring electrodes are attached to the body surface in a certain array arrangement. The current amplitude is 0.1mA and the frequency is 50Hz-2MHz. The current is injected into the human body through the intrinsic electrode and then flows out through one of the external electrodes. The potential of the remaining external electrodes is measured. At this time, the next external electrode is alternately switched as the current outflow electrode, and the potential of the remaining external electrodes is measured. This cycle is repeated until all body surface electrodes are traversed, and the measurement data is recorded, thereby reconstructing the impedance distribution and changes of the tumor area during the ablation process.

[0037] This method specifically includes the following steps: ① Construct a mathematical calculation model: In studies of bioelectromagnetic effects, the frequency is typically less than 1 MHz. The human body can be considered a quasi-static field, and the influence of displacement current is neglected. The surgical probe serves as an internal current source, and the surface electrodes alternately act as current sinks. Assume the probe tip is located at... Injected current magnitude The current angular frequency is The current outflow electrode (measuring electrode) is located at ( =1,2,…, , If the number of electrodes on the body surface is given, then the potential distribution satisfies the Poisson equation:

[0038] Indicates frequency Spatial conductivity distribution, Indicates frequency Under the potential distribution, Indicates the injected current intensity. This represents the Dirac delta function, indicating that the current flows only at the internal source electrode location. Injected internally.

[0039] ② Determine the boundary conditions: The boundary conditions for impedance frequency difference measurement driven by internal electrodes are: Neumann boundary condition: only applies at the boundary where the current flows out. At that point, the current satisfies:

[0040] Zero current boundary condition (at the electrodeless location): at the remaining electrodeless boundary. No current flows out, satisfying:

[0041] Dirichlet boundary conditions: at the boundary of the measuring electrode At that point, the boundary potential satisfies:

[0042] in Indicates electrode Boundary potential, It is the normal direction. It is the potential gradient along the normal direction. Current From the intrinsic electrode (probe tip) Injected from surface electrodes ( =1, 2, ... , (Number of external electrodes) flows out.

[0043] ③ Potential measurement mode: Sequentially switch outflow electrodes Measure the remaining body surface electrodes Potential difference between , ( =1, 2, …, ,and ), as shown in the following formula.

[0044]

[0045] In the measurement mode of this method, select and For two adjacent electrode pairs, for ease of notation, the voltage difference matrix generated after traversing all current flows out of the electrodes is denoted as . .

[0046]

[0047] In the formula Voltage measurement vector of column This indicates that when the current flows out at the numbered point... When measuring electrodes, the vector consists of the voltage measurements between all electrode pairs, with each component being the voltage value of a set of current-measuring electrode pairs. These components together form a complete voltage measurement matrix. This is the total number of external electrodes.

[0048] ④ Perform finite element discretization: The solution domain Discretized The element is a tetrahedral element in three-dimensional space. The approximate solution of the finite element method is represented by basis functions, and the conductivity distribution is shown. and electric potential As shown in the following formula:

[0049] In the formula, Let be the conductivity basis function. Given the potential basis functions, the final control equations after finite element discretization are shown below:

[0050] This represents the stiffness matrix calculated based on the conductivity distribution after finite element discretization. Represents the nodal potential vector. This indicates the source term, i.e., the term at the internal source electrode. The outflow electrode is .

[0051] ⑤ Solve for the stiffness matrix and potential distribution: Multiplying both sides of the above equation by the inverse of a stiffness matrix on the left, we obtain the potential distribution at this point:

[0052] ⑥ Frequency difference calculation: After establishing the governing equations and boundary conditions, and determining the electrode potential sampling strategy, frequency difference calculation begins. The current frequency changes over time, denoted as... .

[0053] First, we decompose the conductivity, assuming that the change in conductivity during ablation consists of two parts, as shown in the following equation:

[0054] in The background conductivity (initial state). This refers to time-varying perturbations caused by ablation.

[0055] In frequency and Measure the voltage and calculate the voltage difference:

[0056] in Electrode In frequency The potential below.

[0057] ⑦ Linearization and conductivity solution: Secondly, the sensitivity matrix is ​​linearized to account for perturbations in the conductivity of the tumor region during ablation. The voltage difference can be linearized as follows:

[0058] in It is the first The Jacobian matrix (sensitivity matrix) under the secondary current injection configuration was calculated using the finite element method. This represents noise introduced by a small disturbance.

[0059] Finally, the inverse dynamic frequency difference problem is solved to reconstruct the data from multi-time-point and multi-frequency measurement data. The regularization model is shown in the following equation:

[0060] in The time smoothing regularization term (L2 norm) constrains the continuity between adjacent time points; The total spatial variation regularization term (TV) preserves the conductivity jump boundary.

[0061] The above This refers to the change in electrical conductivity of the lesion tissue caused by ablation during the surgical procedure.

[0062] Example 2: An electronic device, comprising a memory and a processor; The memory is used to store computer programs; The processor is configured to implement the method described in Embodiment 1 when executing the computer program.

[0063] Example 3: A computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in Embodiment 1.

[0064] Example 4: A computer program product includes a computer program that, when executed by a processor, implements the method described in Example 1.

[0065] In the above embodiments, the reference to "this embodiment" in the specification indicates that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least some embodiments, but not necessarily all embodiments. Multiple appearances of "this embodiment" do not necessarily all refer to the same embodiment.

[0066] In the above embodiments, although the invention has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. For example, other memory structures (e.g., dynamic RAM (DRAM)) may be used with the embodiments discussed. The embodiments of the invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims.

[0067] As will be understood by those skilled in the art, the computer-readable storage medium described in this embodiment allows for the implementation of all or part of the steps in the above method embodiments by computer program-related hardware. The aforementioned computer program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0068] The electronic terminal provided in this embodiment includes a processor, a memory, a transceiver, and a communication interface. The memory and the communication interface are connected to the processor and the transceiver and complete communication between them. The memory is used to store computer programs, the communication interface is used to perform communication, and the processor and the transceiver are used to run the computer programs, so that the electronic terminal performs the steps of the above method.

[0069] In this embodiment, the memory may include random access memory (RAM) and may also include non-volatile memory, such as at least one disk storage device.

[0070] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0071] This invention can be used in a wide range of general-purpose or special-purpose computing system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices, etc.

[0072] This invention can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. This invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for differential impedance-frequency measurement based on a center-driven measurement mode, characterized in that: Includes the following steps: S1: Treat the human body as a quasi-static field, the probe as an internal current source, and the surface electrodes as current sinks in turn, and establish the field equation for measuring the impedance frequency difference in the surgical area. S2: Determine the boundary conditions for the impedance frequency difference measurement driven by the internal electrode; S3: During the measurement process, current is injected from the internal source electrode and flows out from the external current. The outflow electrode is switched in sequence to measure the potential difference between the remaining body surface electrodes and generate a voltage difference matrix. S4: Perform frequency difference calculations to solve for the change in conductivity of the lesion tissue caused by ablation during the operation.

2. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 1, characterized in that: Step S1, the step of establishing the field equation for the impedance frequency difference measurement of the surgical area, includes: S11: The differential form of the conduction current that satisfies Ohm's law, i.e.: In the formula, It is the current density. It is electrical conductivity. It is the electric field strength; The equation for the continuity of current is: The electric field strength and electric potential satisfy the following relationship: S12: Combining the formulas in step S11, we obtain that the potential distribution satisfies the Poisson equation: Represents the spatial conductivity distribution. Indicates the potential distribution. Indicates the injected current intensity. This represents the Dirac delta function, indicating that the current flows only at the internal source electrode location. Injected internally.

3. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 1, characterized in that: The boundary conditions mentioned in step S2 include: Neumann boundary condition: only applies at the boundary where the current flows out. At that point, the current satisfies: Zero current boundary condition: at the remaining electrodeless boundary No current flows out, satisfying: Dirichlet boundary conditions: at the boundary of the measuring electrode At that point, the boundary potential satisfies: in Indicates electrode Boundary potential, It is the normal direction. It is the potential gradient along the normal direction, and the current. From intrinsic electrodes Injection, from surface electrodes Outflow, =1,..., , This represents the number of external electrodes.

4. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 1, characterized in that: In step S3, current is injected from the internal source electrode and flows out from the external current electrode, with the outflow electrode being switched sequentially. Measure the remaining body surface electrodes Potential difference between , =1, 2, …, ,and As shown in the following formula: choose and For two adjacent electrode pairs, the voltage difference matrix generated after traversing all current flows out of the electrodes is denoted as . : In the formula Voltage measurement vector of column This indicates that when the current flows out at the numbered point... When measuring electrodes, the vector consists of the voltage measurements between all electrode pairs, with each component being the voltage value of a set of current-measuring electrode pairs. These components together form a complete voltage measurement matrix. This is the total number of external electrodes.

5. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 1, characterized in that: Step S4 Specifically, the following steps are included: S41: Perform finite element discretization; S42: Solve for the stiffness matrix and potential distribution; S43: Frequency differential calculation; S44: Linearize the voltage difference and solve for the conductivity.

6. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 5, characterized in that: Step S41, which involves finite element discretization, specifically includes: The solution domain Discretized The element is a tetrahedral element in three-dimensional space. The approximate solution of the finite element method is represented by basis functions, and the conductivity distribution is shown. and electric potential As shown in the following formula: In the formula, It is the basis function of conductivity. Given the potential basis functions, the final control equations after finite element discretization are shown below: This represents the stiffness matrix calculated based on the conductivity distribution after finite element discretization. Represents the nodal potential vector. This indicates the source term, i.e., the term at the internal source electrode. The outflow electrode is .

7. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 6, characterized in that: Step S42, which involves solving for the stiffness matrix and potential distribution, is as follows: 。 8. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 7, characterized in that: The frequency difference calculation in step S43 includes: After establishing the governing equations and boundary conditions, and determining the electrode potential sampling strategy, frequency difference calculation begins. The current frequency changes over time, denoted as... ; First, we decompose the conductivity, assuming that the change in conductivity during ablation consists of two parts, as shown in the following equation: in For background conductivity, For time-varying perturbations caused by ablation; In frequency and Measure the voltage and calculate the voltage difference: in Electrode In frequency The potential below.

9. The impedance-frequency differential measurement method based on center-driven measurement mode according to claim 8, characterized in that: Step S44, the linearization and conductivity solution, includes: Linearize the sensitivity matrix to account for perturbations in the conductivity of the tumor region during ablation. The voltage difference is linearized as follows: in It is the first The Jacobian matrix under the secondary current injection configuration was calculated using the finite element method. This represents noise introduced by minute perturbations; Finally, the inverse dynamic frequency difference problem is solved to reconstruct the data from multi-time-point and multi-frequency measurement data. The regularization model is shown in the following equation: in This is a time smoothing regularization term that constrains the continuity between adjacent time points; This is a spatial total variation regularization term that preserves the conductivity jump boundary; This refers to the change in electrical conductivity of the lesion tissue caused by ablation during the surgical procedure.

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