阅读说明：本技术 一种基于亥姆霍兹线圈阵列的心脏磁场模拟系统 (Heart magnetic field simulation system based on Helmholtz coil array ) 是由 马辛 窦帅 曹一荻 李君儒 张祎琛 于 2021-07-12 设计创作，主要内容包括：本发明涉及一种基于亥姆霍兹线圈阵列的心脏磁场模拟系统,该系统主要包括：磁屏蔽桶(房),低噪声程控电流源、亥姆霍兹线圈阵列。磁屏蔽桶(房)用于屏蔽地球磁场及其他外界磁场,同时也为使用原子磁强计测量产生的心脏磁场提供工作条件,低噪声程控电流源用于产生模拟心脏磁场所需要的电流,同时程控电流源也具有方便模拟动态信号系统的优点,亥姆霍兹线圈阵列用于产生心磁测量中胸腔表面法向的心脏磁场。本发明提出的系统可产生胸腔表面法向的心脏磁场应用于医学领域的研究,方便模拟病人的心脏磁场和原子磁强计探头的标定。(The invention relates to a heart magnetic field simulation system based on a Helmholtz coil array, which mainly comprises: magnetic shielding barrel (room), low-noise program-controlled current source and Helmholtz coil array. Magnetic shielding bucket (room) is used for shielding earth's magnetic field and other external magnetic fields, also provides operating condition for using the heart magnetic field that the atomic magnetometer measured the production simultaneously, and the programme-controlled current source of low noise is used for producing the required electric current of simulation heart magnetic field, and programme-controlled current source also has the advantage of conveniently simulating dynamic signal system simultaneously, and Helmholtz coil array is arranged in producing the heart magnetic field of thoracic cavity surface normal direction in the magnetocardiogram measurement. The system provided by the invention can generate a heart magnetic field normal to the surface of the thoracic cavity, is applied to the research in the medical field, and is convenient for simulating the heart magnetic field of a patient and calibrating the probe of the atomic magnetometer.)

1. A heart magnetic field simulation system based on a Helmholtz coil array is characterized in that: the system comprises: the device comprises a magnetic shielding barrel (room) (1), a Helmholtz coil array (2) and a low-noise program-controlled current source (3);

the magnetic shielding barrel (room) (1) is used for shielding a geomagnetic field and an environmental magnetic field, and the remanence of an internal working area needs to be within 20 nT;

the low-noise program-controlled current source (3) is arranged outside the magnetic shielding barrel (room) (1) and is used for providing current required by the Helmholtz coil array (2), outputting a synthesized magnetocardiogram signal, meeting the requirements of noise level and precision level and providing a human-computer interaction interface;

the Helmholtz coil array (2) is arranged in the magnetic shielding barrel (room) (1), and the array is arranged in a 4 x 4 mode to simulate and generate a magnetic field in the vertical direction of the heart, so that the use requirement of the multi-channel SERF atomic magnetometer is met.

2. The simulation system of claim 1, wherein: the magnetic shielding barrel (room) (1) comprises: the inner layer is epoxy or aluminum layer, the outer layer is aluminum layer, the middle is multi-layer permalloy with high magnetic permeability, one end is bottom, and the other end is a movable cover.

3. The simulation system of claim 1, wherein: the Helmholtz coil array (2) comprises: the coil form is selected to be Helmholtz coils, the number of turns of the upper and lower groups of coils is 1, namely, the coil is a single-wire coil, the diameter of a wire is set to be 1mm, the radius R of the coil is set to be 2cm, and therefore h is 2 cm; the distance between the central axes of two adjacent coils is set to be 5 cm; the coil power supply straight wire adopts a mode of an adjacent design, namely, a current inflow end power supply wire is attached to a current outflow end power supply wire.

4. The simulation system of claim 1, wherein: the low noise programmable current source (3) comprises: the power module, the AD module, the DA module, the power amplifier module, the MCU control module and the human-computer interaction module are connected in an integrated mode and are simultaneously designed on a PCB.

Technical Field

The invention belongs to the field of biomedicine, and relates to a heart magnetic field simulation system based on a Helmholtz coil array.

Background

The heart magnetic field of a human body contains a lot of bioelectricity physiology and pathology information, and a Magnetocardiogram (MCG) is a completely non-contact and non-invasive heart magnetic field passive measurement method. Because the magnetic permeability does not vary much in various parts of the human body, the resolution of the magnetocardiogram is higher than that of a conventional Electrocardiogram (ECG). The magnetocardiogram has extremely high exploration potential and wide application prospect in the fields of medical treatment, life science and the like, and has wide application in the aspects of diagnosing arrhythmia, myocardial ischemia, positioning of atrial fibrillation ablation and the like.

The magnetocardiograph for measuring the magnetocardiogram does not generate radiation, does not use a developer, is safer and more reliable compared with CT, does not generate an external strong magnetic field, does not contact with a patient, and therefore, the patient who has made the cardiac stent can safely use the magnetocardiograph. At present, the magnetocardiographs applied in the medical field mainly include SQUID (superconducting quantum interference) magnetocardiographs and SERF (Spin-Exchange Relaxation-Free) atomic magnetometer magnetocardiographs. When the SQUID magnetocardiograph is used, the SQUID magnetocardiograph needs to work in a low-temperature environment, and then liquid nitrogen is used for cooling, so that the SQUID magnetocardiograph is heavy and expensive in maintenance cost. The sensitivity of the SERF atomic magnetometer magnetocardiograph is higher than that of the SQUID magnetocardiograph, the SERF atomic magnetometer does not need to work in a low-temperature environment, the volume of the SERF atomic magnetometer has the advantages of miniaturization and integration, and the SERF atomic magnetometer is convenient for the design of multi-channel magnetocardiograph measurement, so that the SERF atomic magnetometer has wider application prospect at present.

The Helmholtz coil array is used for simulating a magnetic field in the vertical direction of the heart, and under the working condition of a magnetic shielding barrel (room), a current simulating the magnetic field of the heart is generated by a low-noise program-controlled current source, so that a magnetic field simulating the strength of the heart in the vertical direction in the pT magnitude is generated.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the Helmholtz coil array is utilized to generate a uniform magnetic field for simulating a biological magnetic field, and particularly, the Helmholtz coil array is utilized to simulate the magnetic field in the vertical direction of the heart, so that the probe of the SERF atomic magnetometer is conveniently calibrated, the integrity of MCG signals is verified, and the accuracy of SERF atomic magnetometer disease diagnosis is tested. Meanwhile, when the SERF atomic magnetometer is researched, the problem that a human body needs to repeatedly carry out experiments is solved by using the method.

The invention adopts the following technical scheme:

a helmholtz-coil-array-based cardiac magnetic field simulation system, the system comprising: a magnetic shielding barrel (room) 1, a Helmholtz coil array 2 and a low-noise program-controlled current source 3; the magnetic shielding barrel (room) 1 is used for shielding a geomagnetic field and an environmental magnetic field, and the remanence of an internal working area needs to be within 20 nT; the low-noise program-controlled current source 3 is arranged outside the magnetic shielding barrel (room) 1 and used for providing current required by the Helmholtz coil array 2, outputting a synthesized magnetocardiogram signal, meeting the requirements of noise level and precision level and providing a human-computer interaction interface; the Helmholtz coil array 2 is arranged in the magnetic shielding barrel (room) 1 and is arranged in a 4 x 4 mode to simulate and generate a vertical magnetic field of the heart, so that the use requirement of the multichannel SERF atomic magnetometer is met.

Further, the magnetic shield bucket (room) 1 includes: the inner layer is epoxy or aluminum layer, the outer layer is aluminum layer, the middle is multi-layer permalloy with high magnetic permeability, one end is bottom, and the other end is a movable cover.

Further, the helmholtz coil array 2 includes: the coil form is selected to be Helmholtz coils, the number of turns of the upper and lower groups of coils is 1, namely, the coil is a single-wire coil, the diameter of a wire is set to be 1mm, the radius R of the coil is set to be 2cm, and therefore h is 2 cm; the distance between the central axes of two adjacent coils is set to be 5 cm. The coil power supply straight wire adopts a close design mode, namely, a current inflow end power supply wire is tightly attached to a current outflow end power supply wire. The purpose of this design is to minimize the effect on the coil field by offsetting the supply conductor fields from each other, while accommodating the requirements of multi-channel SERF atomic magnetometer measurements in an array format.

Further, the low-noise programmable current source 3 includes: the power module, the AD module, the DA module, the power amplifier module, the MCU control module and the human-computer interaction module are connected in an integrated mode and are simultaneously designed on a PCB. The simulation system can meet the requirement of generating a current value required by meeting the requirement of simulating a cardiac magnetic field, has the advantage of a simulation dynamic signal system, simulates and generates a cardiac magnetic signal in the vertical direction of the heart, can also adjust the duration and amplitude of each wave group, and simultaneously meets the requirements of low noise and high precision for generating the cardiac magnetic field by using the low-noise program-controlled current source.

In particular, the present invention is realized by:

a heart magnetic field simulation system based on a Helmholtz coil array mainly comprises: a magnetic shielding barrel (room) 1, a low-noise program-controlled current source 3 and a Helmholtz coil array 2. Low-noise program-controlled current source 3 is arranged outside shielding barrel (room) 1, Helmholtz coil array 2 is arranged in shielding barrel (room) 1, low-noise program-controlled current source 3 generates a simulation cardiac current signal, and Helmholtz coil array 2 generates a magnetic field in the vertical direction of the heart. The synthesized magnetocardiogram signal is input into a Microcontroller (MCU) of a program-controlled current source, and then output to a Helmholtz coil array through the program-controlled current source to generate a magnetic field simulating the vertical direction of the heart.

1) Magnetic shielding barrel or magnetic shielding room

The strength of the heart magnetic field is in the pT order, and the strength of the earth magnetic field is 6 x 10⁷pT or so, so the measurement of the heart magnetic field needs to be in a magnetically shielded environment, and the magnetically shielded bucket (room) 1 is used for shielding the earth magnetic field and the environmental magnetic field. The remanence of the working area inside the magnetic shielding barrel (room) 1 needs to be within 20nT so as to provide a working environment for the SERF atomic magnetometer. The magnetic shielding barrel is made of three layers of permalloy, and has extremely high magnetic conductivity and good plasticity to a weak magnetic field.

2) Low-noise program-controlled current source

Because the cardiac magnetic field signal is different from a normal sinusoidal signal or other simple signal, the input of the cardiac magnetic field signal is facilitated by using a programmed current source. Meanwhile, because the magnitude of the intensity of the cardiac magnetic field is in the pT magnitude, a low-noise programmed current source is needed to prevent noise from influencing the output magnetic field. The low-noise programmable current source 3 is adopted, so that the influence of extra output impedance caused by designing the Helmholtz coil array 2 and the input lead of the Helmholtz coil array 2 is avoided. The low-noise program-controlled current source 3 used by the invention has continuous and adjustable functions, has a large output range, can realize constant current output and arbitrary waveform output, and is suitable for an analog dynamic signal system. The low-noise program-controlled current source designed by the invention is provided with an input screen, is convenient for constant current output and waveform output, and is convenient to operate and use.

3) Helmholtz coil array

The Helmholtz coil is a device for manufacturing a small-range uniform magnetic field, and has the advantages of large uniform area, wide use space and simple and convenient operation. The magnetic field can be combined in one dimension, two dimensions and three dimensions, and can provide alternating current and direct current magnetic fields, and the current and the magnetic field have good linear relation. Helmholtz coils are widely used in various subjects such as electronics, biology, medical treatment, aerospace and the like, and have the following main purposes: the method comprises the steps of generating a standard magnetic field, offsetting and compensating the earth magnetic field, simulating the geomagnetic environment, judging the magnetic shielding effect, simulating the electromagnetic interference, calibrating a Hall probe and various magnetometers, researching the biological magnetic field and the like. The helmholtz coil is composed of a pair of identical circular conductor coils. The central axes of the two circular coils of radius R are both coaxial with the Z axis. The distance h between the two circular coils is equal to the radius R of the two circular coils. The two circular coils have the same number of turns, each conductor coil carries the same-direction current I, and the current value and the magnetic field intensity have good linear relation. As shown in fig. 4, the magnetic field lines at the planar surface in the center of the helmholtz coil are distributed. The magnetic field between the two coils is approximately uniform. The invention fully utilizes the characteristic that Helmholtz coils generate uniform magnetic fields, and utilizes the Helmholtz coil array 2 to simulate the magnetic field in the vertical direction of the heart.

The heart magnetic field simulation system based on the Helmholtz coil array is mainly realized as follows:

firstly, actually collecting a magnetic field signal in the vertical direction of the heart on a human body by utilizing an SERF atomic magnetometer to serve as an original signal, carrying out Fourier transform on the original signal, analyzing the frequency spectrum component of the original signal, and then synthesizing the required magnetic field signal in the vertical direction of the heart by utilizing the obtained frequency spectrum component. When the method is used for conveniently simulating the generation of the magnetic field in the vertical direction of the heart, the duration and the amplitude of each wave group can be adjusted.

And secondly, because the probes used by the SERF atomic magnetometer are multi-channel, designing a Helmholtz coil array to meet the requirement of using the multi-channel SERF atomic magnetometer.

And thirdly, designing a low-noise current source to generate the current required by the Helmholtz coil, and considering that the cardiac magnetic field signal is a dynamic analog signal and is convenient to operate, designing a low-noise program-controlled current source taking the MCU as the master control. The low-noise program-controlled current source used by the invention consists of the following parts: the battery pack power supply part comprises a power module, an AD module, a DA module, a power amplifier module, an MCU control module, a human-computer interaction module and the like.

And fourthly, designing a PCB (printed Circuit Board) to integrate the system, and then putting the Helmholtz coil array 2 into a magnetic shielding barrel (room) 1 to test the performance of the whole system by utilizing an SERF (serial enhanced reactor) atomic magnetometer.

The Helmholtz coil array-based heart magnetic field simulation system provided by the invention has the advantages that:

(1) the invention can synthesize the magnetic field signal in the vertical direction of the heart by carrying out frequency spectrum processing on the original signal obtained by utilizing the SERF atomic magnetometer. Meanwhile, the magnetic field in the vertical direction of the heart generated by the simulation of the invention can also adjust the duration and amplitude of each wave group.

(2) The Helmholtz coil array used in the invention can simulate the magnetic field in the vertical direction of the heart, can adapt to the use requirements of the multichannel SERF atomic magnetometer, and has the advantage of realizing the multichannel SERF atomic magnetometer measurement.

(3) The low-noise programmable current source can generate the current required for generating the pT-level magnetic field and has the advantage of having extremely small noise influence on the heart magnetic field.

Drawings

Fig. 1 is a system block diagram of a heart magnetic field simulation system based on a helmholtz coil array according to the present invention;

in the figure: 1 magnetic shielding barrel (room), 2 Helmholtz coil array and 3 low-noise program-controlled current source;

FIG. 2 is a Helmholtz coil array simulation modeling diagram;

FIG. 3 is a Helmholtz coil layout;

FIG. 4 is a cross-sectional view of the magnetic field generated by the Helmholtz coil;

FIG. 5 is a design flow chart of the present invention.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

The invention provides a Helmholtz coil array-based system for simulating a cardiac magnetic field, which is convenient for calibrating a probe of an SERF atomic magnetometer, verifying the integrity of MCG signals and testing the accuracy of disease diagnosis of the SERF atomic magnetometer. Meanwhile, when the SERF atomic magnetometer is researched, the problem that a human body needs to repeatedly carry out experiments is solved by using the method.

As shown in fig. 1, a system architecture diagram of a heart magnetic field simulation system based on a helmholtz coil array is provided, which mainly includes: a magnetic shielding barrel (room) 1, a Helmholtz coil array 2 and a low-noise program-controlled current source 3. The Helmholtz coil array 2 is arranged inside the magnetic shielding barrel (room) 1 and used for generating a magnetic field in the vertical direction of the heart. The low-noise program-controlled current source 3 is arranged outside the shielding barrel (room) 1 and is used for generating current signals required by the magnetocardiogram. The Helmholtz coil array 2 is connected with a low-noise programmable current source 3 through a lead. The synthesized magnetocardiogram signal is input into a Micro Controller Unit (MCU) of a program-controlled current source, and then output to the Helmholtz coil array 2 through the program-controlled current source to generate a magnetic field simulating the vertical direction of the heart. In the invention, the magnetic shielding barrel (room) represents a magnetic shielding barrel or a magnetic shielding room.

(1) Magnetic shielding barrel (room) 1

The simulation of the magnetic field in the vertical direction of the heart and the system test are both carried out in the magnetic shielding barrel (room) 1. The strength of the cardiac magnetic field is in the pT order, while the earth has a magnetic field of about 60 μ T, so the generation of the cardiac magnetic field, the measurement of the cardiac magnetic field and the system test need to be carried out in a magnetic shielding environment. The magnetic shielding barrel (room) 1 is used for shielding a geomagnetic field and an environmental magnetic field, and the remanence of an internal working area needs to be within 20nT so as to provide a working environment for the SERF atomic magnetometer. The inner layer of the magnetic shielding barrel 1 is an epoxy or aluminum layer, the outer layer is an aluminum layer, the middle layer is three layers of permalloy with high magnetic permeability, one end is at the bottom, the other end is a movable cover, and the magnetic shielding barrel has extremely high magnetic permeability and good plasticity to a weak magnetic field.

(2) Helmholtz coil array

The Helmholtz coil is a device for manufacturing a small-range uniform magnetic field, and has the advantages of large uniform area, wide use space and simple and convenient operation. The magnetic field can be combined in one dimension, two dimensions and three dimensions, and can provide alternating current and direct current magnetic fields, and the current and the magnetic field have good linear relation. Helmholtz coils are widely used in various subjects such as electronics, biology, medical treatment, aerospace and the like, and have the following main purposes: the method comprises the steps of generating a standard magnetic field, offsetting and compensating the earth magnetic field, simulating the geomagnetic environment, judging the magnetic shielding effect, simulating the electromagnetic interference, calibrating a Hall probe and various magnetometers, researching the biological magnetic field and the like. As shown in fig. 3, the helmholtz coil is composed of a pair of identical circular conductor coils. The central axes of the two circular coils of radius R are both coaxial with the Z axis. The two circular coils have a distance h-R. The two circular coils have the same number of turns, each conductor coil carries the same-direction current I, and the current value and the magnetic field value have good linear relation.

As shown in fig. 4, the magnetic field lines at the planar surface in the center of the helmholtz coil are distributed. The magnetic field between the two coils is approximately uniform. The invention fully utilizes the characteristic that Helmholtz coils generate uniform magnetic fields, and utilizes the Helmholtz coil array 2 to simulate the magnetic field in the vertical direction of the heart. Because the probes used by the SERF atomic magnetometer are multi-channel, the helmholtz coil array 2 is designed to meet the requirements for use of a multi-channel SERF atomic magnetometer.

The Helmholtz coil array 2 is arranged in a magnetic shielding barrel (room) 1, and the array is arranged in a 4 multiplied by 4 mode to simulate the vertical magnetic field of the heart.

(3) Low-noise program-controlled current source

Because the cardiac magnetic field signal is different from a normal sinusoidal signal or other simple signal, the input of the cardiac magnetic field signal is facilitated by using a programmed current source. Meanwhile, because the magnitude of the intensity of the cardiac magnetic field is in the pT magnitude, a low-noise programmed current source is needed to prevent noise from influencing the output magnetic field. The low-noise programmable current source 3 is adopted, so that the influence of extra output impedance caused by designing the Helmholtz coil array 2 and the input lead of the Helmholtz coil array 2 is avoided. The low-noise program-controlled current source 3 used by the invention has continuous and adjustable functions, has a large output range, can realize constant current output and arbitrary waveform output, and is suitable for an analog dynamic signal system. The low-noise program-controlled current source 3 designed by the invention is provided with an input screen, is convenient for constant current output and waveform output, and is convenient to operate and use. Considering that the heart magnetic field signal is a dynamic analog signal and is convenient to operate, a low-noise program-controlled current source 3 taking MCU as a master control is designed.

The low-noise program-controlled current source 3 is arranged outside the magnetic shielding barrel (room) 1 and used for providing current required by the Helmholtz coil array 2, outputting a synthesized magnetocardiogram signal, meeting the requirements of noise level and precision level and providing a human-computer interaction interface for convenient operation.

As shown in fig. 5, the design flow chart of the present invention is as follows:

firstly, a magnetic field signal in the vertical direction of a heart is actually acquired on a human body by utilizing a SERF atomic magnetometer to serve as original magnetocardiogram data, then, the original magnetocardiogram data needs to be processed firstly, the magnetocardiogram signals are mainly concentrated between 0.03Hz and 45Hz, a Butterworth low-pass digital filter is written firstly to filter a high-frequency noise part, and parameters of the low-pass filter are designed as follows, wherein the passband cut-off frequency is 45Hz, the stopband cut-off frequency is 60Hz, the passband attenuation is 0dB, and the stopband attenuation is 20 dB. Then, a Gaussian window function zero-phase shift filter is programmed to filter low-frequency drift interference and 50Hz power frequency interference, and the signals processed in the processing process can be regarded as relatively pure magnetocardiogram signals. Fourier transform is carried out on the signals to respectively obtain amplitude information (FFTAmplitude (f)) and corresponding phase information (FFTPhase (f)), the two kinds of information are stored (only the information below 60Hz is reserved), and the signals are synthesized by a Fourier series mode to output the required heart vertical direction magnetic field signals. The following is the synthesis formula:

when the method is used for conveniently simulating the generation of the magnetic field in the vertical direction of the heart, the duration and the amplitude of each wave group can be adjusted.

The second step of design and simulation of geometric parameters of the coil array is as follows:

(1) the coil form is selected to be Helmholtz coils, the number of turns of the upper and lower groups of coils is 1, namely, the coils are single-wire coils, as shown in FIG. 3;

(2) the wire diameter is set to 1mm and the coil radius R is set to 2cm, so h-R-2 cm;

(3) the distance between the central axes of two adjacent coils is set to be 5 cm.

The coil power supply straight wire adopts the mode of the adjacent design, namely the current inflow end power supply wire and the current outflow end power supply wire are tightly attached, so that the purpose of the design is to enable the magnetic fields of the power supply wires to be mutually offset, thereby reducing the influence on the magnetic fields of the coils to the minimum, the coil material is filled with copper, and the solution domain material is filled with air. In order to improve the calculation precision, the finite element meshing size is selected as 'refining'. According to simulation results, under the above design parameters, the magnetic field in the range of the cylinder with the radius of 1cm and the height of 1cm at the central part of the coil can be regarded as uniform magnetic field, and the simulation modeling diagram of the Helmholtz coil array is shown in FIG. 2.

And (3) magnetic field numerical calculation: the theoretical calculation formula of the Helmholtz coil magnetic field is as follows:

through practical verification, the magnetic field after theoretical calculation is better in accordance with the simulation result.

And thirdly, designing a low-noise program-controlled current source 3, wherein the low-noise program-controlled current source comprises a battery pack power supply part, a power supply module, an AD module, a DA module, a power amplifier module, an MCU control module, a man-machine interaction module and the like, wherein the battery pack power supply part is used for designing the low-noise program-controlled current source 3. The simulation system can meet the requirement of generating a current value required by meeting the requirement of simulating a cardiac magnetic field, has the advantage of a simulation dynamic signal system, simulates and generates a cardiac magnetic signal in the vertical direction of the heart, can also adjust the duration and amplitude of each wave group, and simultaneously meets the requirements of generating the low noise and high precision of the cardiac magnetic field by the low-noise program-controlled current source 3. Meanwhile, the method also comprises the program design of the program-controlled current source, including the program design of human-computer interaction serial port communication and the program design of DAC module SPI communication, wherein the hardware SPI or the software simulation SPI can be adopted.

And fourthly, integrating and testing, designing and processing a PCB (printed Circuit Board) to the designed low-noise program-controlled current source 3 and the Helmholtz coil array 2, then testing inside the magnetic shielding barrel (room) 1, writing the synthesized magnetocardiogram signal into the low-noise program-controlled current source, and testing through an SERF (serial enhanced microwave filter) atomic magnetometer.

Those skilled in the art will appreciate that the invention may be practiced without these specific details.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and the preferred embodiments are not exhaustive and do not limit the invention to the precise embodiments described. Various modifications and improvements of the technical solution of the present invention may be made by those skilled in the art without departing from the spirit of the present invention, and the technical solution of the present invention is to be covered by the protection scope defined by the claims.