Magnetic induction tomography device and method for stroke based on magnetic nanoparticles

Abstract

This invention relates to the field of medical imaging, specifically to a magnetic induction tomography method for stroke based on magnetic nanoparticles, comprising the following steps: 1) a signal source outputs a reference voltage signal and an excitation voltage signal with the same frequency and phase; 2) obtaining the complex signal of each coil pair combination in the empty field state; 3) intravenously injecting a magnetic nanoparticle contrast agent into the stroke patient; 4) obtaining the complex signal of each coil pair combination in the object field state; 5) calculating the real part data of the imaging signal of each coil pair combination; 6) obtaining the sensitivity matrix data corresponding to the detection area in numerical simulation software; 7) obtaining the distribution image of magnetic nanoparticles in the patient's brain tissue using the conjugate gradient algorithm. This invention, through improvements to the principle, device, and method of magnetic induction tomography, achieves tracer static imaging of stroke, meets the need for rapid stroke detection, and greatly improves the success rate of patient treatment.

Description

Technical Field

[0001] This invention relates to the field of medical imaging, specifically to a magnetic induction tomography device and method for stroke based on magnetic nanoparticles. Background Technology

[0002] Magnetic induction tomography (MIT), also known as eddy current imaging, has unique advantages such as being non-contact, non-invasive, portable, and low-cost. The basic principle of MIT detection is Faraday's theory of electromagnetic induction, and its basic detection process is as follows:

[0003] First, an alternating magnetic field is applied to the stroke imaging detection area. Then, induced eddy currents are formed inside the electromagnetically sensitive material within the sensing area, thereby generating a secondary magnetic field. Finally, magnetic field detectors arranged outside the stroke imaging detection area are used to collect MIT data. After the data is processed, the MIT image can be obtained using an image reconstruction algorithm.

[0004] However, due to the very low conductivity of brain tissue and the very weak alternating magnetic field it generates, the current MIT imaging technology has very low sensitivity for stroke. It can only achieve time-varying imaging and cannot achieve static imaging, thus failing to meet the clinical needs for rapid imaging detection of stroke.

[0005] Stroke is characterized by high incidence, high disability rate, high mortality rate, and high recurrence rate. Once it occurs, approximately 1.9 million brain cells die every minute, leading to serious complications such as paralysis, speech disorders, dysphagia, cognitive impairment, and depression, severely impacting the patient's quality of life and placing a huge burden on families and society. Early detection and early treatment are crucial for improving the success rate of stroke treatment and postoperative outcomes, especially the first 4.5 hours after onset, which is the golden period for rescue. If rapid static imaging of the stroke can be achieved within this golden period, the success rate of patient treatment will be greatly improved. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a magnetic induction tomography imaging device and method for stroke based on magnetic nanoparticles. After improving the magnetic induction tomography imaging device, magnetic nanoparticles are used as contrast agents. By utilizing the high sensitivity of the magnetization response characteristics of magnetic nanoparticles, static imaging of stroke can be achieved, meeting the needs of rapid stroke detection and greatly improving the success rate of patient treatment.

[0007] The objective of this invention is achieved by the following scheme: a magnetic induction tomography imaging device for stroke based on magnetic nanoparticles, comprising a signal source, a power amplifier, an analog switch, a computer, multiple relays, and at least eight receiving coils, each receiving coil being evenly spaced and arranged in a ring around the center of the detection area; further comprising at least eight excitation coils for generating an excitation magnetic field to magnetize the magnetic nanoparticles, each excitation coil being evenly spaced and arranged in a ring around the center of the detection area, and located outside the receiving coils;

[0008] The number of relays is the same as the number of excitation coils. One end of the normally open contact group of each relay is connected in parallel to the signal output terminal of the power amplifier, and the other end is connected to one end of the corresponding excitation coil. The other end of each excitation coil is connected in series with capacitor C and resistor R to ground, forming an RLC series resonant circuit.

[0009] The analog switch is a multi-channel analog switch, with each receiving coil connected to a corresponding signal input terminal of the multi-channel analog switch. The signal output terminal of the multi-channel analog switch is connected to the acquisition signal input terminal of the computer. The reference signal input terminal of the computer is connected to the reference signal output terminal of the signal source, and the excitation signal output terminal of the signal source is connected to the signal input terminal of the power amplifier.

[0010] Preferably, each excitation coil is provided with a magnetic core, each excitation coil is wound on the corresponding magnetic core, and the extension line of the center line of each magnetic core passes through the center point of the detection area.

[0011] Preferably, the ratio of the coil length to the coil diameter of the excitation coil is 5:1 to 10:1.

[0012] Preferably, the ratio of the coil length to the coil diameter of the receiving coil is 0.1:1 to 0.3:1, and the number of turns of each receiving coil is greater than 500 turns.

[0013] Preferably, the ratio of the diameters of the excitation coil and the receiving coil is 2:1 to 5:1.

[0014] Preferably, the frequency of the excitation magnetic field of the excitation coil is 1 to 10 kHz.

[0015] The method for magnetic induction tomography of stroke using the device described in this invention includes the following steps:

[0016] 1) The signal source outputs a reference voltage signal and an excitation voltage signal, wherein the reference voltage signal and the excitation voltage signal have the same frequency and phase, and the frequency of the excitation voltage signal is 1 to 10 kHz;

[0017] 2) Energize one excitation coil, then energize each receiving coil in sequence, and pair them with the excitation coil in sequence to form different coil pairing combinations;

[0018] After confirming that the detection area is in an empty field state, the computer sequentially collects the voltage signals output by the receiving coils in each coil pairing combination, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the empty field complex signal of each coil pairing combination.

[0019] The remaining excitation coils are paired with each receiving coil in sequence according to the above method to obtain the remaining coil pairing combinations of the empty field complex signal;

[0020] 3) After intravenous injection of magnetic nanoparticle contrast agent into a stroke patient, the patient's head is placed in the detection area to change the detection area from an empty field state to a material field state.

[0021] 4) After confirming that the detection area is in the object field state, the computer sequentially collects the voltage signals output by the receiving coils in all coil pairings, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the object field complex signal of each coil pairing.

[0022] 5) Calculate the real part of the imaging signal for each coil pairing combination according to the following formula:

[0023] R n =Real((B n -A n ) / A n ) n∈N+

[0024] In the formula, R n B represents the real part of the imaging signal for the nth coil pairing combination. n Let A be the complex signal of the object field in the nth coil pairing combination. n The complex signal in the empty field for the nth coil pairing combination;

[0025] 6) Obtain the sensitivity matrix data corresponding to the detection area in the numerical simulation software;

[0026] 7) Based on the sensitivity matrix data and the real part data of the imaging signals of each coil pairing combination, the distribution image of magnetic nanoparticles in the patient's brain tissue is obtained using the conjugate gradient algorithm.

[0027] The beneficial effects of this invention are as follows:

[0028] The detection area is the stroke imaging detection area. At least 8 receiving coils and 8 excitation coils are arranged in a ring around the center of the detection area, and each excitation coil is located outside the receiving coil. They are used to generate an excitation magnetic field to magnetize magnetic nanoparticles. The receiving coils are used to sense the alternating magnetic field and output the corresponding voltage signal to the computer.

[0029] The number of relays is the same as the number of excitation coils. One end of the normally open contact group of each relay is connected in parallel to the signal output terminal of the power amplifier, and the other end is connected to one end of the corresponding excitation coil. The other end of each excitation coil is connected in series with capacitor C and resistor R to ground, forming an RLC series resonant circuit.

[0030] When the normally open contact group of the relay corresponding to any excitation coil is closed, the excitation coil is energized, that is, the excitation coil is connected to the power amplifier and forms an RLC series resonant circuit with capacitor C and resistor R in series. At this time, the normally open contact groups of the other relays are open, causing the other excitation coils to be disconnected from the circuit.

[0031] When the circuit resonates, the inductive reactance of the coil is canceled out, which greatly reduces the load impedance of the power amplifier, increases the excitation current of the excitation coil, and increases the magnetic field strength generated by the excitation coil. This allows the magnetic nanoparticles in the stroke imaging detection area to be better magnetized. After being magnetized, the magnetic nanoparticles generate a magnetization magnetic field in the same direction as the excitation magnetic field. The magnetization field strength is proportional to the concentration of magnetic nanoparticles in the stroke imaging detection area.

[0032] The analog switch is a multi-channel analog switch, with each receiving coil connected to a corresponding signal input terminal of the multi-channel analog switch. The signal output terminal of the multi-channel analog switch is connected to the acquisition signal input terminal of the computer. The reference signal input terminal of the computer is connected to the reference signal output terminal of the signal source, and the excitation signal output terminal of the signal source is connected to the signal input terminal of the power amplifier.

[0033] By acquiring the output signals of the receiving coils in each coil pairing combination under the empty field and object field conditions in the stroke imaging detection area, the relative perturbation of the magnetization field strength generated by the magnetization of magnetic nanoparticles to the excitation magnetic field strength generated by the excitation coil is calculated, and the distribution image of magnetic nanoparticles in the patient's brain tissue is obtained.

[0034] This invention uses the real part data of the relative complex signal under the state of the air field and the object field in the stroke imaging detection area to represent the relative perturbation of the magnetization field strength generated by the magnetization of magnetic nanoparticles on the excitation magnetic field strength generated by the excitation coil and to perform imaging, which is different from the traditional magnetic induction tomography method that uses "magnetic induction phase shift" imaging.

[0035] The advantages of this invention are as follows:

[0036] ① This invention achieves a magnetic field strength in the excitation coil that is significantly higher than that of traditional magnetic induction tomography systems, reaching the saturation magnetization field of magnetic nanoparticles and greatly improving the detection sensitivity of magnetic nanoparticles: Each excitation coil is equipped with a magnetic core, and each excitation coil is wound on a corresponding magnetic core. The ratio of the coil length to the coil diameter of the excitation coil is 5:1 to 10:1. The ratio of the coil length to the coil diameter of the receiving coil is 0.1:1 to 0.3:1, and the number of turns of each receiving coil is greater than 500 turns. The ratio of the coil diameters of the excitation coil and the receiving coil is 2:1 to 5:1.

[0037] ② The excitation magnetic field frequency of the excitation coil is 1-10KHz, which will not generate eddy currents in the patient's brain tissue. Unlike traditional magnetic induction tomography, it does not belong to eddy current detection. Therefore, it will not image normal brain tissue outside the stroke site in the patient's skull. This invention only generates a magnetization effect on magnetic nanoparticles and uses the magnetization magnetic field generated by the magnetic nanoparticles to image the disturbance of the excitation magnetic field. Therefore, normal brain tissue outside the stroke site in the patient's skull will not interfere with the magnetic nanoparticle imaging, thus improving the sensitivity of stroke imaging. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the circuit structure of the magnetic induction tomography device for stroke based on magnetic nanoparticles described in this invention.

[0039] Figure 2 This is a schematic diagram showing the positional distribution of the excitation coil and receiving coil around the stroke imaging detection area in an embodiment of the present invention;

[0040] Figure 3 This is a flowchart of the magnetic induction tomography device for stroke used in this invention;

[0041] Figure 4 This is a schematic diagram of magnetic nanoparticle imaging in an embodiment of the present invention. Detailed Implementation

[0042] like Figures 1 to 2 As shown, a magnetic induction tomography (MRI) device for stroke based on magnetic nanoparticles includes a signal source, a power amplifier, an analog switch, a computer, multiple relays, and at least eight receiving coils. The receiving coils are evenly spaced and arranged in a ring around the center of the detection area. The device also includes at least eight excitation coils for generating an excitation magnetic field to magnetize the magnetic nanoparticles. The excitation coils are evenly spaced and arranged in a ring around the center of the detection area, located outside the receiving coils. Each excitation coil has a magnetic core, and each excitation coil is wound on a corresponding magnetic core. The extension of the center line of each magnetic core passes through the center point of the detection area.

[0043] The ratio of the length to the diameter of the excitation coil is 5:1 to 10:1. The ratio of the length to the diameter of the receiving coil is 0.1:1 to 0.3:1, and each receiving coil has more than 500 turns. The ratio of the diameters of the excitation coil and the receiving coil is 2:1 to 5:1.

[0044] In this embodiment, the magnetic cores are all manganese-zinc ferrite cores, the number of excitation coils and receiving coils are 8 each, and the detection area is a circular area.

[0045] The excitation coil has a length of 120mm, a diameter of 25mm, and 120 turns.

[0046] The receiving coil has a length of 2.7 mm, a diameter of 12 mm, and 2500 turns.

[0047] The diameter of the coil is the outer diameter of the coil.

[0048] The number of relays is the same as the number of excitation coils. One end of the normally open contact group of each relay is connected in parallel to the signal output terminal of the power amplifier, and the other end is connected to one end of the corresponding excitation coil. The other end of each excitation coil is connected in series with capacitor C and resistor R to ground, forming an RLC series resonant circuit.

[0049] The capacitance C is determined by "making the RLC series resonant circuit resonate at the frequency of the magnetic field generated by the excitation coil". In this embodiment, the capacitance C is 4.7uF, the resistance R is 1 ohm, and the signal frequency output by the signal source is 3KHz. The above capacitance value is just enough to make the RLC series resonant circuit resonate when the excitation magnetic field frequency of the excitation coil is 3KHz, so as to eliminate the high inductive reactance of the excitation coil, meet the load requirements of the power amplifier, and improve the excitation magnetic field strength generated by the excitation coil.

[0050] The analog switch is a multi-channel analog switch, with each receiving coil connected to a corresponding signal input terminal of the multi-channel analog switch. The signal output terminal of the multi-channel analog switch is connected to the acquisition signal input terminal of the computer. The reference signal input terminal of the computer is connected to the reference signal output terminal of the signal source, and the excitation signal output terminal of the signal source is connected to the signal input terminal of the power amplifier. The reference voltage signal output by the signal source has the same frequency and phase as the excitation voltage signal, and the frequency of the excitation voltage signal is 1–10 kHz.

[0051] In this embodiment, the frequency of the reference voltage signal and the excitation voltage signal output by the signal source is 3KHz. Therefore, the excitation magnetic field frequency of each excitation coil is the same, which is 3KHz.

[0052] The multiplexer is an ADG1407, which can output any one of the eight differential input channel signals from the common differential output terminal of the ADG1407.

[0053] The computer is equipped with a data acquisition card, which includes at least two signal acquisition channels and has a sampling frequency greater than 100KHz and a bit depth greater than 14 bits, such as a commercial PCI-5122 data acquisition card.

[0054] The signal source has a dual-channel signal output function with a bandwidth greater than 10KHz, such as the commercially available signal source AFG3252.

[0055] The power amplifier is commercially available and has an output current greater than 2A and a bandwidth greater than 10KHz, such as the LYB-5040 power amplifier.

[0056] Both ends of each receiving coil are connected to the corresponding differential signal input terminals on the ADG1407. The common differential output terminal of the ADG1407 is connected to the acquisition signal input terminal of the PCI-5122 data acquisition card. The reference signal input terminal of the PCI-5122 data acquisition card is connected to the reference signal output terminal of the signal source AFG3252. The excitation signal output terminal of the signal source AFG3252 is connected to the signal input terminal of the power amplifier LYB-5040, enabling the computer to synchronously acquire the voltage signal output by the receiving coil and the reference voltage signal output by the signal source AFG3252.

[0057] like Figure 3 As shown, the method for achieving static imaging of stroke using the magnetic induction tomography device for stroke described in this embodiment includes the following steps:

[0058] 1) The signal source outputs a reference voltage signal and an excitation voltage signal. The reference voltage signal and the excitation voltage signal have the same frequency and phase. The frequency of the excitation voltage signal is 1 to 10 kHz. The output current intensity of the power amplifier is adjusted so that the magnetic field intensity generated by the excitation coil reaches the saturation magnetization intensity of the magnetic nanoparticles.

[0059] In this embodiment, both the reference voltage signal and the excitation voltage signal are sinusoidal signals with the same frequency and phase, both with an amplitude of 1VPP and a frequency of 3KHz. The power amplifier is in constant current output mode and the output current is set to 2A.

[0060] 2) Energize one excitation coil, then energize each receiving coil in sequence, and pair them with the excitation coil in sequence to form different coil pairing combinations;

[0061] After confirming that the detection area is in an empty field state, the computer sequentially collects the voltage signals output by the receiving coils in each coil pairing combination, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the empty field complex signal of each coil pairing combination.

[0062] The remaining excitation coils are paired with each receiving coil in sequence according to the above method to obtain the remaining coil pairing combinations of the empty field complex signal;

[0063] The complex signals of the empty field are used to form a set of complex signals of the empty field using all the paired combinations of coils. The mathematical expression of this set of complex signals of the empty field is as follows:

[0064] A = {A1, A2, A3, ..., A...} n} n∈N+

[0065] In the formula, A1 is the complex signal of the first coil pairing combination, A2 is the complex signal of the second coil pairing combination, A3 is the complex signal of the third coil pairing combination, and A... n The complex signal in the empty field for the nth coil pairing combination;

[0066] In this embodiment, the Fourier transform algorithm is the FFT algorithm, i.e., Fast Fourier Transform.

[0067] 3) Stroke patients are given intravenous injection of magnetic nanoparticle contrast agents. After the magnetic nanoparticles accumulate in the patient's brain tissue, the patient's head is placed in the detection area to change the detection area from an empty field state to a material field state.

[0068] In this embodiment, the empty field state refers to the state in which no patient's head is placed in the stroke imaging detection area. In this state, only air exists in the stroke imaging detection area.

[0069] The aforementioned object-field state refers to the state in which the patient's head is placed within the stroke imaging detection area. In this state, not only does the stroke imaging detection area contain air, but the patient's head is also present. Magnetic nanoparticles within the patient's brain tissue can be magnetized within the stroke imaging detection area.

[0070] First, the magnetic nanoparticles in the patient's brain tissue are magnetized using an extremely low-frequency alternating magnetic field generated by an improved magnetic induction tomography device for stroke. Then, by detecting the disturbance of the excitation magnetic field by the magnetizing magnetic field, a highly sensitive static imaging of the distribution of magnetic nanoparticles is achieved, thereby realizing static imaging of the stroke site. Since the eddy currents generated in the brain tissue by the extremely low-frequency excitation magnetic field are very small, this imaging method will not image brain tissue outside the stroke site in the patient's brain.

[0071] 4) After confirming that the stroke imaging detection area is in a state of object field, the computer sequentially acquires the voltage signals output by the receiving coils in all coil pairings, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the object field complex signal of each coil pairing, forming a set of object field complex signals. The mathematical expression of this set of object field complex signals is as follows:

[0072] B = {B1, B2, B3, ..., B} n} n∈N+

[0073] In the formula, B1 is the complex object-field signal of the first coil pairing combination, B2 is the complex object-field signal of the second coil pairing combination, B3 is the complex object-field signal of the third coil pairing combination, and B... n The complex signal of the object field for the nth coil pairing combination;

[0074] 5) Calculate the real part data of the imaging signal for each coil pairing combination according to the following formula to form the real part data set of the imaging signal:

[0075] R n =Real((B n -A n ) / A n ) n∈N+

[0076] In the formula, R n B represents the real part of the imaging signal for the nth coil pairing combination. n Let A be the complex signal of the object field in the nth coil pairing combination. n The complex signal in the empty field for the nth coil pairing combination;

[0077] R n This represents the relative perturbation of the magnetic field strength generated by the magnetization of magnetic nanoparticles to the excitation magnetic field strength generated by the excitation coil, and is proportional to the concentration of magnetic nanoparticles.

[0078] The mathematical expression for the real part dataset of the imaging is as follows:

[0079] R ={ R 1, R 2, R 3, ..., R n} n∈N+

[0080] In the formula, R 1 represents the real part of the imaging signal of the first coil pairing combination. R 2 represents the real part of the imaging signal from the second coil pairing combination. R3 represents the real part of the imaging signal of the third coil pairing combination. R n This represents the real part of the imaging signal for the nth coil pairing combination.

[0081] 6) In numerical simulation software, the sensitivity matrix data corresponding to the detection area is obtained according to the coil arrangement of the magnetic induction tomography device for stroke.

[0082] In this embodiment, the numerical simulation software is COMSOL Multiphysics 5.6. A coil arrangement model of the stroke magnetic induction tomography imaging device is established in COMSOL Multiphysics 5.6 at a 1:1 scale. Then, the sensitivity matrix data of the stroke imaging detection area of ​​the device is obtained through simulation.

[0083] 7) Based on the sensitivity matrix data and the real part data of the imaging signals of each coil pairing combination, the distribution image of magnetic nanoparticles in the patient's brain tissue was obtained using the conjugate gradient algorithm:

[0084] The computer imports the sensitivity matrix data of the stroke imaging detection area and the real part data of the imaging signal of 64 pairs of coils in the real part data of the imaging into MATLAB, and uses the conjugate gradient algorithm to obtain the distribution image of magnetic nanoparticles in the patient's brain tissue.

[0085] like Figure 4 As shown, each test container contained 0.4 ml of magnetic nanoparticle solution. Figure A shows the magnetic nanoparticle distribution in the container at detection area A, Figure B shows the magnetic nanoparticle distribution in the container at location B, Figure C shows the magnetic nanoparticle distribution in the containers at detection areas C1 and C2, and Figure D shows the magnetic nanoparticle distribution in the containers at detection areas D1 and D2.

[0086] Therefore, this invention introduces magnetic nanoparticles as a contrast agent into the traditional magnetic induction tomography method according to the above method. First, the magnetic nanoparticles in the patient's brain tissue are magnetized by the extremely low frequency alternating magnetic field generated by the improved stroke magnetic induction tomography device. Then, by detecting the disturbance of the excitation magnetic field by the magnetization magnetic field, highly sensitive static imaging of stroke is achieved.

[0087] The imaging method of this invention does not respond to the patient's brain tissue, but only to the magnetic nanoparticles in the brain tissue. The imaging sensitivity is much higher than that of traditional magnetic induction tomography, which can fully meet the needs of rapid static imaging of stroke and greatly improve the success rate of patient treatment.

[0088] It is worth noting that all coil pairings were obtained in the following manner:

[0089] First, control the normally open contact group of any one relay to close, so that the excitation coil is energized, that is, the excitation coil is connected to the power amplifier, and forms an RLC series resonant circuit with capacitor C and resistor R in series. At this time, the normally open contact groups of the other relays are opened, so that the other excitation coils are disconnected from the circuit.

[0090] Then, the multi-channel analog switch selects any receiving coil to connect to the computer. The coil pairing combination is the selected excitation coil and receiving coil at this time. That is, a coil pairing combination consists of an excitation coil and a receiving coil.

[0091] Since there are 8 excitation coils and 8 receiving coils in this embodiment, according to the principle of permutation and combination, it can be calculated that there are 64 different coil pair combinations that can be formed by combining 8 excitation coils and 8 receiving coils.

[0092] Different coil pairing combinations are obtained by controlling the on / off states of relays and multiplexed analog switches in this manner: First, the excitation voltage signal from the signal source AFG3252 is amplified by the power amplifier LYB-5040 to drive the excitation coil of the currently connected circuit to generate an excitation magnetic field. Then, each receiving coil is sequentially connected to the circuit and the computer. The computer acquires the voltage signal output from the receiving coil through the data acquisition card PCI-5122 and performs a Fourier transform. Next, the excitation coil of the currently connected circuit is disconnected, and another excitation coil is selected to connect to the circuit. The above method is repeated to acquire the voltage signal output from the receiving coil in the remaining coil pairing combinations and perform a Fourier transform.

[0093] In this embodiment, the voltage signals emitted by the receiving coils in the 64 pairs of coil pairs are collected sequentially in the empty field and the object field, respectively, in the manner described above. For each voltage signal output by the receiving coil in a coil pair, it is subjected to Fourier transform together with the reference voltage signal to obtain the complex signal corresponding to the coil pair. This process continues until all the complex signals corresponding to the 64 pairs of coil pairs have been collected.

[0094] For example, first connect the excitation coil T1 to the circuit (at this time, the other excitation coils are not connected to the circuit), then connect the receiving coil S1 to the circuit (at this time, the other receiving coils are not connected to the circuit), and obtain the complex signals corresponding to the coil pairing combinations formed by the excitation coil T1 and the receiving coil S1. Then disconnect the receiving coil S1 from the circuit and connect the receiving coil S2 to the circuit, and obtain the complex signals corresponding to the coil pairing combinations formed by the excitation coil T1 and the receiving coil S2, and so on, until the complex signals corresponding to the coil pairing combinations formed by the excitation coil T1 and the receiving coils S1 to S8 are collected. Then disconnect the excitation coil T1 and connect the excitation coil T2 to the circuit, and so on, until all the complex signals corresponding to these 64 pairs of coil pairing combinations are collected.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A magnetic induction tomography (MRI) device for stroke based on magnetic nanoparticles, characterized in that, It includes a signal source, a power amplifier, an analog switch, a computer, multiple relays, and at least eight receiving coils, which are evenly spaced and arranged in a ring around the center of the detection area; it also includes at least eight excitation coils for generating an excitation magnetic field to magnetize magnetic nanoparticles, which are evenly spaced and arranged in a ring around the center of the detection area, and located outside the receiving coils. The number of relays is the same as the number of excitation coils. One end of the normally open contact group of each relay is connected in parallel to the signal output terminal of the power amplifier, and the other end is connected to one end of the corresponding excitation coil. The other end of each excitation coil is connected in series with capacitor C and resistor R to ground, forming an RLC series resonant circuit. Each excitation coil in the RLC series resonant circuit is equipped with a magnetic core, and each excitation coil is wound on the corresponding magnetic core. The extension line of the center line of each magnetic core passes through the center point of the detection area. The frequency of the excitation magnetic field of each excitation coil is 1 to 10 kHz, so that when the RLC series resonant circuit resonates, the magnetic field strength generated by the excitation coil reaches the saturation magnetization field strength of the magnetic nanoparticles, while avoiding eddy current interference in brain tissue. The analog switch is a multi-channel analog switch, with each receiving coil connected to a corresponding signal input terminal of the multi-channel analog switch. The signal output terminal of the multi-channel analog switch is connected to the acquisition signal input terminal of the computer. The reference signal input terminal of the computer is connected to the reference signal output terminal of the signal source. The excitation signal output terminal of the signal source is connected to the signal input terminal of the power amplifier. The real part data of the relative complex signals under the air field and object field conditions in the detection area are used to represent the relative perturbation of the magnetization field strength generated by the magnetization of the magnetic nanoparticles on the excitation magnetic field strength generated by the excitation coil, and imaging is performed.

2. The magnetic induction tomography device for stroke based on magnetic nanoparticles according to claim 1, characterized in that, The ratio of the coil length to the coil diameter of the excitation coil is 5:1 to 10:

1.

3. The magnetic induction tomography device for stroke based on magnetic nanoparticles according to claim 1, characterized in that, The ratio of the coil length to the coil diameter of the receiving coil is 0.1:1 to 0.3:1, and the number of turns of each receiving coil is greater than 500.

4. The magnetic induction tomography device for stroke based on magnetic nanoparticles according to claim 1, characterized in that, The ratio of the diameters of the excitation coil and the receiving coil is 2:1 to 5:

1.

5. A method for magnetic induction tomography of stroke using the device described in claim 1, characterized in that, Includes the following steps: 1) The signal source outputs a reference voltage signal and an excitation voltage signal, wherein the reference voltage signal and the excitation voltage signal have the same frequency and phase, and the frequency of the excitation voltage signal is 1 to 10 kHz; 2) Energize one excitation coil, then energize each receiving coil in sequence, and pair them with the excitation coil in sequence to form different coil pairing combinations; After confirming that the detection area is in an empty field state, the computer sequentially collects the voltage signals output by the receiving coils in each coil pairing combination, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the empty field complex signal of each coil pairing combination. The remaining excitation coils are paired with each receiving coil in sequence according to the above method to obtain the remaining coil pairing combinations of the empty field complex signal; 3) After intravenous injection of magnetic nanoparticle contrast agent into a stroke patient, the patient's head is placed in the detection area to change the detection area from an empty field state to a material field state. 4) After confirming that the detection area is in the object field state, the computer sequentially collects the voltage signals output by the receiving coils in all coil pairings, and performs Fourier transform on each voltage signal and the reference voltage signal to obtain the object field complex signal of each coil pairing. 5) Calculate the real part of the imaging signal for each coil pairing combination according to the following formula: R n =Real((B n- A n ) / A n ) n∈N+ In the formula, R n B represents the real part of the imaging signal for the nth coil pairing combination. n Let A be the complex signal of the object field in the nth coil pairing combination. n The complex signal in the empty field for the nth coil pairing combination; 6) Obtain the sensitivity matrix data corresponding to the detection area in the numerical simulation software; 7) Based on the sensitivity matrix data and the real part data of the imaging signals of each coil pairing combination, the distribution image of magnetic nanoparticles in the patient's brain tissue is obtained using the conjugate gradient algorithm.

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