A transfer function verification system and method for electromagnetic model of implantable medical device based on four-way parallel transmission

Abstract

The present invention provides a system and method for verifying the transfer function of an electromagnetic model of an implantable medical device based on four-way parallel transmission. Based on the response characteristics of the implantable medical device in the radio frequency field, a resonant electric field with different circular polarization characteristics is generated based on four-way parallel transmission lines to replace the traditional birdcage radio frequency coil and the electric field generator based on the cavity resonator, thereby achieving complete verification of the radio frequency heating transfer function of the implantable medical device. The system of the present invention not only solves the defects of the birdcage coil, such as large footprint, susceptibility to electromagnetic interference and high cost, but also makes up for the defect that the cavity resonator can only generate a single polarization electric field, thereby reducing the uncertainty of the verification test, and providing a solution for realizing fast and effective verification of the radio frequency heating transfer function.

Description

Technical Field

[0001] The invention belongs to the technical field of image detection, and relates to a system and method for verifying transfer functions of an electromagnetic model of an implantable medical device based on four-way parallel transmission. Background Art

[0002] In recent years, with the rapid development of bioelectronics technology, implantable medical devices have become an indispensable part of monitoring human health indicators, treating diseases and repairing human functions. Since the metal parts and electronic components inside implantable medical devices are very sensitive to the influence of external electromagnetic fields and are easily interfered by external electromagnetic fields, which may cause some unpredictable consequences to patients, patients wearing implantable medical devices are usually not allowed to enter environments with complex electromagnetic fields. This greatly limits the application scenarios of these implantable medical devices, especially when patients need other medical equipment and means to assist in diagnosis and treatment. For example, patients wearing implantable medical devices need to use magnetic resonance imaging (MRI) scans to help with high-quality imaging and diagnosis of the patient's internal tissues and organs.

[0003] As the most important clinical medical imaging method, MRI is not only of unique value for the evaluation of nervous system and soft tissue lesions, but also has no radioactive damage, no bone artifacts, and a high degree of soft tissue resolution compared to CT / PET. However, due to the extremely complex magnetic field environment of MRI, that is, the simultaneous presence of 0.5-7T strong static magnetic field (B0), low-frequency pulse gradient magnetic field (G) and 40-300MHz radio frequency (RF) magnetic field, when patients wearing implanted medical devices undergo MRI scans, the interaction between the implanted medical devices and the electromagnetic field of MRI will lead to many different potential safety issues, including mechanical movement and twisting of medical devices caused by static magnetic fields, circuit damage of medical devices caused by electromagnetic field radiation in MRI, and heating of human tissue caused by radio frequency magnetic fields. Among all the above safety hazards, the heating problem caused by the radio frequency magnetic field in patients wearing AIMD is one of the most serious safety issues. This is because the repetitive radio frequency pulses used for signal induction in MRI will generate a strong induced electric field in the patient's body and cause the energy density to be highly locally deposited in the tissue around the conductive end of the implant lead (such as the electrode), which causes the tissue temperature near the implanted medical device electrode to rise rapidly. Especially for AIMDs with thin and long wires (such as pacemakers, brain stimulators and neurostimulators, etc.), the tissue temperature rise caused by radio frequency may be very considerable, causing irreversible damage to the patient's tissue.

[0004] Therefore, MRI examinations have always been contraindicated for patients wearing implantable medical devices. However, due to the unique clinical diagnostic value of MRI, more than 50% of patients with implantable medical devices need MRI scans to help diagnose diseases. Under such demand contradictions, conducting scientific and effective "MR compatibility" assessments of implantable medical devices to ensure the safety and effectiveness of implantable medical device products is not only the goal of medical device manufacturers and regulatory authorities around the world, but also a research hotspot in the international academic field.

[0005] Since it is impossible to evaluate the RF-induced tissue temperature rise in patients by direct measurement, and the computer full-wave simulation process requires huge computing power and resources to resolve the multi-scale structure in the full-wave modeling of clinical scenarios, the scope of use of this method is greatly limited, resulting in this method being only applicable to the verification of individual clinical application scenarios. In order to model the response of implantable medical devices to RF fields, SM Park et al. proposed the concept of transfer function, which links the field incident on the implantable medical device with the RF-induced heating of the tip electrode. Combined with the incident electric field in the body, this transfer function can predict the RF-induced heating of the tip of the implant in a person undergoing MRI scanning.

[0006] However, due to the numerical approximation of the electromagnetic model of implantable medical devices and the uncertainty of the transfer function during the testing process, experimental verification of the transfer function is necessary. The International Standards Organization (ISO) / TS 10974 standard requires that the transfer function model of implantable medical devices must be extensively verified before it is used in clinically relevant research.

[0007] The verification method of the transfer function is usually to place the implantable medical device in a test body membrane filled with tissue simulation fluid and test it under different incident electric fields. The incident field currently used is provided by a radio frequency magnetic field birdcage coil at the corresponding resonant frequency to simulate the radio frequency magnetic field environment of a real MRI. The radio frequency magnetic field test environment provided by this birdcage coil requires a special electromagnetic shielding laboratory to avoid external electromagnetic interference. In addition, due to the complex structure of the birdcage coil, the large size of the test equipment, and the high cost, the test cost is very high. Ji Chen et al. proposed using a cavity resonator to generate a specific electric field signal as the incident field for the verification test, but this method can only generate a specific mode of electric field distribution, and it is necessary to change the path of different implantable devices in the body membrane to complete the verification of the transfer function, which makes the verification test inefficient and has high uncertainty. Therefore, it is very necessary to provide a new verification system and method for the transfer function of the radio frequency electromagnetic model of implantable medical devices. Summary of the invention

[0008] The purpose of the present invention is to address the problems existing in the prior art and to provide a system and method for verifying the transfer function of the electromagnetic model of an implantable medical device based on four-way parallel transmission, which solves the need in the prior art to change the path of the implantable medical device in the body membrane to achieve diversity field testing, while also reducing the test error caused by changing the path of the implantable medical device and the uncertainty of the entire verification process.

[0009] To this end, the present invention adopts the following technical solutions:

[0010] A transfer function verification system for an electromagnetic model of an implantable medical device based on four-way parallel transmission, comprising a body membrane for containing tissue simulation fluid, a ring coil being arranged on the circumference of the body membrane, the coil comprising a shielding layer, the shielding layer being provided with four transmission lines, a signal generator and a power distributor being arranged on the side of the coil, and four phase shifters, four attenuators and four power amplifiers being arranged on the side of the power distributor, respectively, and the power amplifiers, attenuators, phase shifters and power distributor being electrically connected in sequence.

[0011] Furthermore, it also includes a control unit, which is electrically connected to the phase shifter and the attenuator respectively.

[0012] Furthermore, the signal generator is used to generate a 64-128 MHz electrical signal.

[0013] Furthermore, the power divider is used to equally divide the square wave signal generated by the signal generator into four signals with the same amplitude and phase.

[0014] Furthermore, the transmission line is made of copper and has a radius of 50-55 cm.

[0015] A verification method for the above-mentioned electromagnetic model transfer function verification system of implantable medical device based on four-way parallel transmission, characterized by comprising the following steps:

[0016] Step 1: Generate an electrical signal using a signal generator, and divide the electrical signal into four signals a1-a4 by a power divider, wherein the signals a1-a4 have the same amplitude and phase;

[0017] Step 2, the signals a1-a4 are respectively passed through phase shifters PS1-PS4 to change phases and generate signals b1-b4 respectively;

[0018] Step 3, the amplitudes of the signals b1-b4 are changed by attenuators A1-A4 respectively, and signals c1-c4 are generated respectively;

[0019] Step 4: Use the control unit to adjust the phase shifters PS1-PS4 and attenuators A1-A4 to adjust the phase shift and amplitude of the signals c1-c4;

[0020] Step 5: Use power amplifiers PA1-PA4 to amplify signals c1-c4 respectively, and generate signals d1-d4, which are input into four ring coils E1-E4 to generate 64MHz or 128MHz electric fields to form electric field resonators;

[0021] Step 6: Place the cylindrical body membrane filled with tissue simulation fluid into the electric field resonator, and fix the object to be tested along the pre-defined route and place it in the tissue simulation fluid, and use the control unit to adjust the phase shifters PS1~PS4 and attenuators A1~A4 to obtain different circularly polarized electric fields;

[0022] Step 7: Calculate the power deposition under each circular polarization field and compare it with the power deposition predicted by the transfer function In comparison, if the error If it is less than 3dB, the verification is passed.

[0023] Furthermore, the power deposition It is calculated by the specific absorption rate SAR distribution near the electrode, and its expression is: .

[0024] Furthermore, the power deposition predicted by the transfer function The expression is .

[0025] Furthermore, the specific absorption rate SAR distribution near the electrode is measured by a specific absorption rate probe.

[0026] The beneficial effects of the present invention are:

[0027] The purpose of the present invention is to propose a novel implantable medical device radio frequency heating transfer function verification system. The verification system generates a resonant electric field with different circular polarization characteristics based on four parallel transmission lines according to the response characteristics of the implantable medical device in the radio frequency field to replace the traditional bird cage radio frequency coil and the electric field generator based on the cavity resonator, thereby realizing the complete verification of the radio frequency heating transfer function of the implantable medical device. The verification system not only solves the defects of the bird cage coil, such as large footprint, susceptibility to electromagnetic interference and high cost, but also makes up for the defect that the cavity resonator can only generate a single polarization electric field, thereby reducing the uncertainty of the verification test and realizing the complete verification of the radio frequency heating transfer function of the implantable medical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1It is a schematic diagram of the system structure of the present invention;

[0029] Figure 2 It is a structural schematic diagram of the annular coil in the present invention;

[0030] Figure 3 Schematic diagram of circular polarization electric field in the present invention;

[0031] Figure 4 The power deposition in the present invention Theoretical power deposition Schematic diagram of comparison under 8 different polarization fields. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described below in conjunction with the accompanying drawings and embodiments.

[0033] A transfer function verification system for electromagnetic models of implantable medical devices based on four-way parallel transmission, such as Figure 1 As shown, it includes a body membrane for containing tissue simulation fluid, the body membrane has a radius of 44 cm and a height of 20 cm, a ring coil is provided on the circumference of the body membrane, the coil includes a shielding layer, the shielding layer is provided with four transmission wires, the transmission wires are made of copper, and the radius is 50-55 cm.

[0034] A signal generator and a power divider are provided on the side of the coil, wherein the signal generator is used to generate a 64 MHz or 128 MHz electrical signal, and the power divider is used to evenly divide the square wave signal generated by the signal generator into four signals of the same amplitude and phase; four phase shifters, four attenuators and four power amplifiers are provided on the side of the power divider, respectively, and each phase shifter, attenuator and power amplifier are set as a group, totaling four groups, and the power amplifier, attenuator, phase shifter and power divider are electrically connected in sequence.

[0035] The system also includes a control unit, which is electrically connected to the four phase shifters and the four attenuators respectively. The control unit adjusts the phase and amplitude of each transmission signal to achieve a resonant electric field with different circular polarization characteristics.

[0036] The electric field generated by the above system can be used as an incident electric field signal. By controlling the amplitude and phase of the four signals in the above electric field generating system, electric fields of different circular polarizations can be generated to excite the implanted medical device in the body membrane.

[0037] In order to stimulate the body membrane containing the tissue simulation fluid, a verification method for the above-mentioned electromagnetic model transfer function verification system of the implantable medical device based on four-way parallel transmission is adopted, which is characterized by comprising the following steps:

[0038] Step 1: Generate an electrical signal using a signal generator, and divide the electrical signal into four signals a1-a4 by a power divider, wherein the signals a1-a4 have the same amplitude and phase;

[0039] Step 2, the signals a1-a4 are respectively passed through phase shifters PS1-PS4 to change phases and generate signals b1-b4 respectively;

[0040] Step 3, the amplitudes of the signals b1-b4 are changed by attenuators A1-A4 respectively, and signals c1-c4 are generated respectively;

[0041] Step 4: Use the control unit to adjust the phase shifters PS1-PS4 and attenuators A1-A4 to adjust the phase shift and amplitude of the signals c1-c4;

[0042] Step 5: Use power amplifiers PA1-PA4 to amplify signals c1-c4 respectively, and generate signals d1-d4, which are input into four ring coils E1-E4 to generate 64MHz or 128MHz electric fields to form electric field resonators;

[0043] Step 6: Place the cylindrical body membrane filled with tissue simulation fluid into the electric field resonator, fix the implant to be tested according to the predetermined route and place it into the tissue simulation fluid, and use the control unit to adjust the phase shifters PS1~PS4 and attenuators A1~A4 to obtain Figure 3 Different circularly polarized electric fields are shown;

[0044] Step 7: Calculate the power deposition under each circular polarization field and power deposition through transfer function theory .

[0045] Wherein, the power deposition The calculation expression is , the power deposition predicted by the transfer function The expression is: .

[0046] The power deposition Theoretical power deposition In comparison, if the error If it is less than 3dB, the verification is passed.

[0047] Specifically, the power deposition The specific absorption rate SAR distribution near the electrode is calculated and then integrated to obtain the specific absorption rate SAR distribution, where the specific absorption rate SAR distribution is measured by a specific absorption rate probe.

[0048] In order to demonstrate the use of the system, the present invention obtains the transfer function h(l) of an implantable wire with a length of 30 cm through numerical simulation, such as Figure 2 Place it in the designed test system as shown and Figure 3 As shown, the simulation is performed under 8 different polarization fields and the power deposition is calculated. , which corresponds to the power deposition obtained in the actual test, and then through the following formula:

[0049]

[0050] The theoretical power deposition is obtained by integrating the transfer function and the tangential electric field along the implant. .

[0051] Figure 4 Power Deposition Theoretical power deposition Comparison under 8 different polarization fields shows that the error between the two is less than 1.9dB, which is within the range of system uncertainty, so the transfer function is successfully verified.

Claims

1. A transfer function verification system for electromagnetic model of implantable medical device based on four-way parallel transmission, characterized in that: The invention comprises a body membrane for containing tissue simulation fluid, wherein the body membrane has a radius of 44 cm and a height of 20 cm, a ring coil is arranged on the circumference of the body membrane, the coil comprises a shielding layer, the shielding layer is provided with four transmission lines, a signal generator and a power distributor are arranged on the side of the coil, and four phase shifters, four attenuators and four power amplifiers are arranged on the side of the power distributor, respectively, and the power amplifiers, attenuators, phase shifters and power distributors are electrically connected in sequence; A verification method for the above-mentioned electromagnetic model transfer function verification system of an implantable medical device based on four-way parallel transmission comprises the following steps: Step 1: Generate an electrical signal using a signal generator, and divide the electrical signal into four signals a1-a4 by a power divider, wherein the signals a1-a4 have the same amplitude and phase; Step 2, the signals a1-a4 are respectively passed through phase shifters PS1-PS4 to change phases and generate signals b1-b4 respectively; Step 3, the amplitudes of the signals b1-b4 are changed by attenuators A1-A4 respectively, and signals c1-c4 are generated respectively; Step 4: Use the control unit to adjust the phase shifters PS1-PS4 and the attenuators A1-A4 to adjust the phase shift and amplitude of the signals c1-c4; Step 5: Use power amplifiers PA1-PA4 to amplify signals c1-c4 respectively, and generate signals d1-d4, which are input into four ring coils E1-E4 to generate 64MHz or 128MHz electric fields to form electric field resonators; Step 6: Place the cylindrical body membrane filled with tissue simulation fluid into the electric field resonator, and fix the object to be tested along the pre-defined route and place it in the tissue simulation fluid, and use the control unit to adjust the phase shifters PS1~PS4 and attenuators A1~A4 to obtain different circularly polarized electric fields; Step 7: Calculate the power deposition under each circular polarization field and compare it with the power deposition predicted by the transfer function In comparison, if the error If it is less than 3dB, the verification is passed.

2. According to claim 1, the electromagnetic model transfer function verification system of implantable medical device based on four-way parallel transmission is characterized in that: It also includes a control unit, which is electrically connected to the phase shifter and the attenuator respectively.

3. The electromagnetic model transfer function verification system for implantable medical devices based on four-way parallel transmission according to claim 1, characterized in that: The signal generator is used to generate a 64-128 MHz electrical signal.

4. The electromagnetic model transfer function verification system for implantable medical devices based on four-way parallel transmission according to claim 1, characterized in that: The power divider is used to equally divide the square wave signal generated by the signal generator into four signals with the same amplitude and phase.

5. The electromagnetic model transfer function verification system for implantable medical devices based on four-way parallel transmission according to claim 1, characterized in that: The transmission line is made of copper and has a radius of 50-55 cm.

6. The verification method of the electromagnetic model transfer function verification system of an implantable medical device based on four-way parallel transmission according to claim 1 is characterized in that: The power deposition It is calculated by the specific absorption rate SAR distribution near the electrode, and its expression is: .

7. The verification method of the electromagnetic model transfer function verification system of an implantable medical device based on four-way parallel transmission according to claim 1 is characterized in that: The power deposition predicted by the transfer function The expression is ,in, Refers to the length of the implant.

8. The verification method of the electromagnetic model transfer function verification system of an implantable medical device based on four-way parallel transmission according to claim 6 is characterized in that: The specific absorption rate (SAR) distribution near the electrode is measured by a specific absorption rate probe.

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