CN117257311A - Mobile unshielded magnetocardiogram based on giant magneto-impedance sensor - Google Patents

Abstract

The invention discloses a movable unshielded magnetocardiogram system based on giant magneto-impedance technology, which mainly comprises a reference biological magnetic sensor, a biological magnetic sensor array, a data acquisition card, a signal processor, a visual processing and display unit, a system control and self-checking unit, and a structural member consisting of a support column, a cantilever and four pulleys. The reference biological magnetic sensor is arranged at the back heart part of the tested person, and the heart magnetic field signal is collected and used as a reference signal. The biological magnetic sensor array is composed of M x N high-sensitivity Giant Magneto Impedance (GMI) sensors which are made of amorphous linear magnetic materials and are placed in front of the chest of a tested person to collect heart magnetic field signals. The data acquisition unit is responsible for converting the multipath analog signals into digital signals, packaging the digital signals according to channel numbers and transmitting the digital signals to the signal processing unit through a network. The signal processing unit performs various filtering (such as high-pass filtering, low-pass filtering and band-stop filtering), signal alignment, signal period averaging and the like on the signal to improve the signal-to-noise ratio and remove signal fluctuation. And the visualization processing and displaying unit is used for forming a time sequence diagram (a single-channel and multi-channel superposition diagram), a frequency sequence diagram, a magnetic field distribution gradient contour diagram, a magnetic field current direction and polarity arrow diagram and a 3D profile diagram by signals, and displaying the signals through a display. The system control and self-checking unit is responsible for the data flow management of the whole system, including system self-checking (checking whether each module works normally when starting up, and saving the log, uploading fault information), module resetting, starting data flow (detecting, collecting, processing, displaying), establishing, saving, uploading, printing and the like of the patient file. The magnetocardiograph system works in a normal temperature and non-shielding environment. The magnetocardiography system also has structural members such as a supporting column, a cantilever, a chassis, four pulleys and the like, and is convenient for adjusting the measuring position and integrally moving the equipment.

Description

Mobile unshielded magnetocardiogram based on giant magneto-impedance sensor

Technical Field

The invention relates to the technical field of magnetocardiography, in particular to a movable unshielded magnetocardiography based on a giant magneto-impedance sensor.

Background

Currently, for the heart magnetic measurement systems of heart diseases such as myocardial ischemia, myocardial infarction, coronary artery micro-vascular infarction and the like, two generations of products are sequentially developed by heart magnetic detection equipment, and the first generation of products are heart magnetic instruments based on superconducting quantum interference elements (Superconducting Quantum Interference Device, SQUID). The second generation product was a magnetocardiograph based on optically pumped magnetometers (Optical Pump Magnetometer, OPM).

The magnetocardiograph based on superconducting quantum interference element (Superconducting Quantum Interference Device, SQUID) has the advantage of high sensitivity, reaching the femoTesla (fT) level. However, SQUID magnetocardiography equipment is bulky, requires liquid helium or liquid nitrogen for cooling, and also requires a shielding room, and is expensive in equipment and installation and maintenance, so that the SQUID magnetocardiography is introduced only in limited universities and other research institutions.

An magnetocardiogram based on optically pumped magnetometers (Optical Pump Magnetometer, OPM) has the advantage that the sensitivity can be achieved to the sub tesla (pT) level. However, it uses the rare metals rubidium, cesium, heated to 180 degrees with a laser in a vacuum tube, while another laser is used to read the spectrum. Because of the high power consumption of the laser, the shielding chamber is also required, the equipment and the installation and maintenance cost are high, and the shielding chamber needs to work in a zero magnetic field environment, and because of the residual magnetic field in the shielding chamber, a coil needs to be placed in the shielding chamber to counteract the residual magnetic field, and the magnetic field calibration needs to be carried out before each use. Because continuous operation is at high temperatures, another disadvantage arises in that the sensor life is relatively short.

To overcome the drawbacks of the above products, new sensor technologies are needed. In practice, the amplitude of the magnetic field of the heart is measured, mainly in relation to the measured distance, and when the sensor is within 10mm from the chest, the measured magnetic field of the heart has the strongest peak value at the R-wave, between 120 and 500pt, and the peak value of the T-wave is between 20 and 70pt (we mainly care about the R-wave and the T-wave, which are main characterization parameters of the heart beat). The periphery of the SQUID sensor is surrounded by low-temperature gas, so that the distance from the chest of the test object is far, and the tested R wave is within 10 pT. The OPM sensor has large volume and needs to radiate heat, so that the distance from the chest of a test object is long, and the tested R wave is within 40 pT. Therefore, the magnetocardiogram measurement can be realized by a device which is small in volume and works at normal temperature and reaches Pitt (Pico-Tesla) level sensitivity.

The giant magneto-impedance (GMI) sensor based on amorphous wire magnetic material has higher sensitivity, and the GMI magnetometer adopting the digital full-bridge peak-to-peak voltage detection circuit can even reach pT resolution. By MI coaxial detection, a differential mode is added in a peak-to-peak voltage detection circuit, and the GMI gradiometer can be further developed. This eliminates the background magnetic field, thereby eliminating the need for expensive shielding chambers or enclosures. GMI consumes very little power and therefore can operate at room temperature without refrigeration. The GMI gradiometer has low material cost, simple circuit and small volume, and is suitable for large-scale popularization in medical treatment.

Disclosure of Invention

The invention discloses a movable unshielded magnetocardiogram based on a giant magneto-impedance sensor, which mainly comprises a reference biological magnetic sensor unit, a biological magnetic sensor array, a data acquisition unit, a signal processing unit, a visual processing and displaying unit, a system control and self-checking unit, support columns, a cantilever, a chassis, four pulleys and other structural members. The reference biological magnetic sensor is arranged at the back heart part of the tested person, and the heart magnetic field signal is collected and used as a reference signal. The biological magnetic sensor array is composed of M x N giant magneto-impedance (GMI) sensors based on the Pitt (pT) level sensitivity of amorphous linear magnetic materials, and is placed in front of the chest of a tested person to collect heart magnetic field signals. The data acquisition unit is responsible for converting the multipath analog signals from the sensor into digital signals and then transmitting the digital signals to the signal processing unit through a network. The signal processing unit performs various filtering (such as high-pass filtering, low-pass filtering and band-stop filtering), signal alignment, signal period averaging and the like on the signal to improve the signal-to-noise ratio and remove signal fluctuation. And the visual processing unit is used for forming a time sequence diagram (a single-channel and multi-channel superposition diagram), a frequency sequence diagram, a magnetic field distribution gradient contour diagram, a magnetic field current direction and polarity arrow diagram and a 3D heart outline diagram by signals and displaying the signals on a display. The system control and self-checking unit is responsible for the data flow management of the whole system, including system self-checking (checking whether each module works normally when starting up, and saving the log, uploading fault information), module resetting, starting data flow (such as detection, collection, processing and display), establishing, saving, uploading and printing of patient files, etc. The magnetocardiography system also has structural members such as a supporting column, a cantilever, a chassis, four pulleys and the like, and is convenient for adjusting the measuring position and integrally moving the equipment.

Further, in the invention, the reference biological magnetic sensor is placed at the heart position of the back of the tested person, the detected signal amplitude is much higher than the detected signal of the sensor array, and the detected signal is used as the reference signal, so that the signal of the subsequent signal processing unit is aligned, and the filtering operation is performed.

Further, in the present invention, the bio-magnetic sensor array is composed of m×n giant magneto-impedance (GMI) sensors based on the picot (pT) level sensitivity of amorphous wires, which is a key to the success and failure of the system, and the signal RMS noise must be controlled within 10pT to effectively detect the T wave of the heart pulse current (its peak value is about 30 pT). Meanwhile, differential processing is needed to eliminate the uniform magnetic field (such as the earth magnetic field of about 45 uT) of the environment, so that the equipment can realize an unshielded chamber and an unshielded cover.

Furthermore, in the invention, the data acquisition unit is responsible for converting the multipath analog signals from the sensor into digital signals, synchronous acquisition is realized through the control of the FPGA, and the acquired data are packaged and transmitted to the signal processing unit through a network after being numbered.

Further, in the present invention, the signal processing and display unit performs various filtering (such as high-pass filtering, low-pass filtering and band-stop filtering), signal alignment, signal period averaging, etc. on the signal to improve the signal-to-noise ratio and remove signal fluctuations. The high-pass filtering mainly filters out noise below 0.1 Hz. The low pass filtering mainly filters out noise above 100 Hz. The band reject filter or notch filter is to filter out mains frequency noise at 50Hz (china, europe) or 60Hz (united states, japan). Empirical mode decomposition (Empirical Mode Decomposition, EMD) can correct for large fluctuations in the signal caused by chest breathing. In order to improve the signal-to-noise ratio, signal cycle average and other operations can be adopted, the signal needs to be aligned with a reference signal before cycle average, namely the peak value of the QRS is found, and the signal-to-noise ratio SNR can be improved by 200% by adopting cumulative average of 10-30 cycles.

Further, in the invention, the signal is formed into a time sequence diagram (single-channel and multi-channel superposition diagram), a frequency sequence diagram, a magnetic field distribution gradient contour diagram, a magnetic field current density and polarity arrow diagram and a 3D heart contour diagram by a visualization processing unit. The time series plot is used to measure ST time intervals and ST elevation. The frequency sequence diagram shows the heart cycle. The magnetic field distribution gradient contour map is used to observe whether the cardiac magnetic field is multipolar or bipolar. The magnetic field current density and the polar arrow diagram are used to observe the angle by which the polar arrow rotates when the T peak is observed at the R peak. The above figures are important means for doctors to judge the nature and location of heart rhythm abnormality, myocardial infarction, coronary microvascular infarction and the like.

Further, in the present invention, the system control and self-checking unit is responsible for data flow management of the whole system, including system self-checking, module resetting, starting data flow (e.g. detection, acquisition, processing, display), patient file creation, storage, uploading, printing, etc.

Furthermore, in the invention, the self-checking functional module of the system control and self-checking unit is used as a maintenance measure, and when the system is started, whether each module works normally is checked, a log is stored, and fault information is uploaded.

Furthermore, in the invention, the GMI sensor has low power consumption, no need of refrigeration and heat dissipation, and the signal acquisition unit and the processing unit have low power consumption and small volume, so that the magnetocardiogram system has small whole volume, low power consumption and convenient movement.

Drawings

Fig. 1 is a system block diagram, which is composed of a reference sensor unit (100), a biological magnetic sensor array (200), a data acquisition card (300), a signal processing unit (400), a visualization processing and display unit (500), a system control and self-checking unit (700), a system power supply (800), a support, a cantilever, a pulley, a chassis and other structural units (600).

Fig. 2 is a sensor array showing the internal composition of a bio-magnetic sensor array (200) consisting of M x N bio-magnetic sensors, the sensors being bio-magnetic sensors of GMI type pT-level sensitivity.

Fig. 3 shows a signal acquisition unit (200) consisting of a channel ADC (201, 202, 203, 204) and an FPGA unit (205). The FPGA unit (205) receives the back-end control command, controls the analog-to-digital conversion of the multiple paths of ADC (201, 202, 203, 204), transmits the analog-to-digital conversion to the FPGA unit (205) through the SPI bus, and the FPGA packages data and transmits the data to the back-end through the Ethernet.

Fig. 4 is a signal processing block diagram showing a signal processing unit (400) consisting of a high pass filter (401), a low pass filter (402), a notch filter (403), a classical modal decomposition (404), and an average filter (405).

Fig. 5 is a magnetic field sequence diagram (multi-channel stack) and magnetic field gradient map, which shows a magnetocardiogram signal time sequence diagram (single-channel and multi-channel stack) and magnetic field map gradient map.

Fig. 6R/T is a graph showing the magnetic field map gradient at the R-pulse peak and the magnetic field map gradient at the T-pulse peak of the magnetocardiogram signal.

Fig. 7 is a diagram of an example of human body detection, which is composed of a main case, a reference sensor, a sensor array, a display terminal, an operation table, and support columns and cantilevers, etc. of the whole apparatus. The person to be tested is laid on a non-ferromagnetic bed to be tested. The reference sensor is placed at the heart site on the back of the subject.

Description of the embodiments

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.

Fig. 7 is a human body detection implementation example, and the whole device is composed of a main case, a reference sensor, a sensor array, a display terminal, an operation table, a support column, a cantilever, and the like. The detected person lies on a non-ferromagnetic bed to be detected, and the sensor array can move in three planes (XY plane/XZ plane/YZ plane) of XYZ space coordinates through controlling a mechanical component, so that three degrees of freedom are provided. Four pulleys are arranged below the main case, and the equipment can be pushed to work in different rooms. The whole environment does not need a shielding room or a shielding shell.

Fig. 2 shows the internal composition of a bio-magnetic sensor array (200) consisting of M x N bio-magnetic sensor (201) units, the sensor being a GMI type pT-level sensitive bio-magnetic sensor. To eliminate the ambient uniform magnetic field (e.g., the earth's magnetic field around 45 uT), achieve an unshielded chamber and an unshielded enclosure, we select a magnetic gradiometer type of biological magnetic sensor (201). The parameters of m×n can be selected from common types of 4*6, 5*6, 6×6,6×8, 8×8, 12×8, etc., and the sensors are uniformly placed within a range of 20cm×20 cm.

The reference sensor is the same type as the sensors in the sensor array.

Fig. 3 shows a signal acquisition unit (300) consisting of a channel ADC (301, 302, 303, 304, 305) and an FPGA unit (306). The FPGA selects ZYNQ7020 of Xilinx, an ARM processor is contained in the FPGA, and the embedded real-time operating system supports multithreading by using FreeRTOS. The ADC is an 8-channel 24-bit analog-to-digital converter, selected from ADS131M08 from TI. A maximum of 12 ADS131M08 is required to collect sensor parameters, forming 96 (12 x 8) channels.

Fig. 4 shows a signal processing unit (400) consisting of a high pass filter (401), a low pass filter (402), a notch filter (403), a classical modal decomposition (404), and an average filter (405). The signal processor performs various filtering (such as high pass filtering, low pass filtering and band reject filtering), signal alignment, signal period averaging, etc. on the signal to improve the signal-to-noise ratio and remove signal fluctuations. The high-pass filtering mainly filters out noise below 0.1 Hz. The low pass filtering mainly filters out noise above 100 Hz. Band reject filtering or notch filtering is to filter out 50Hz (china, europe) or 60Hz (united states, japan) mains frequency noise. Empirical mode decomposition (Empirical Mode Decomposition, EMD) can correct for large fluctuations in the signal caused by chest breathing. In order to improve the signal-to-noise ratio, signal cycle average and other operations can be adopted, the signal and the reference signal need to be aligned before cycle average, namely the peak value of the QRS is found, and the signal-to-noise ratio SNR can be improved by 200% by adopting cumulative average of 30-30 cycles. The algorithm units such as signal processing and the like can be realized at the PC end, and the quick and convenient deployment can be realized by adopting Python or C language programming.

Fig. 5 shows a time series diagram (single-channel and multi-channel superimposed diagram) of the magnetocardiogram signal and a magnetic field map gradient diagram, and fig. 6 shows a magnetic field map gradient diagram at the peak of the R pulse and a magnetic field map gradient diagram at the peak of the T pulse. The magnetic field mapping gradient map and the polar arrow map are used for observing the angle of rotation of the polar arrow and whether the magnetic field mapping gradient map and the polar arrow map are multiple poles when the T peak is observed at the R peak, so that whether cardiovascular diseases such as arrhythmia, myocardial infarction, coronary microvascular infarction and the like can be judged.

Claims (9)

1. A mobile unshielded magnetocardiogram system based on a giant magneto-impedance sensor, comprising: the system comprises a reference biological magnetic sensor, a biological magnetic sensor array, a data acquisition and signal processing unit, a visual processing and display unit, a system control and self-checking unit, a support column, a cantilever, a chassis and a structural member consisting of four pulleys, wherein the reference biological magnetic sensor, the biological magnetic sensor array, the data acquisition and signal processing unit, the visual processing and display unit and the system control and self-checking unit work in an unshielded environment at normal temperature.

2. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein said reference biological magnetic sensor is a giant magneto-impedance (GMI) sensor fabricated based on amorphous wire magnetic material.

3. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein said biological magnetic sensor array is composed of M x N giant magneto-impedance (GMI) sensors fabricated based on amorphous wire magnetic material, M x N being 4*6, 5*6, 6 x 6,6 x 8, 8 x 8, 12 x 8.

4. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein said data acquisition and signal processing unit is responsible for converting multiple analog signals into digital signals and filtering the signals.

5. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein said visualization processing and display unit maps the signals into a time series plot, a frequency series plot, a magnetic field distribution gradient contour plot, a magnetic field current direction and polarity arrow plot, a 3D contour plot, and displays them on a display.

6. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system according to claim 1, wherein said system control and self-test unit is responsible for data flow management of the whole system, including system self-test, module reset, start data flow (detection, acquisition, processing, display).

7. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein the support column, cantilever, chassis and four pulleys are assembled together as a mechanical structure of the device.

8. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein the system operates without an expensive shielded room or a shielded housing.

9. The giant magneto-impedance sensor-based mobile unshielded magnetocardiography system of claim 1, wherein the system operates at room temperature without refrigeration.