WO2023093697A1

WO2023093697A1 - Dynamic active field stabilization method, system and device for liquid-helium-free superconducting magnet

Info

Publication number: WO2023093697A1
Application number: PCT/CN2022/133397
Authority: WO
Inventors: 梁平; 陈超锋; 王先建; 罗佐; 李超; 周企佳
Original assignee: 鑫高益医疗设备股份有限公司
Priority date: 2021-11-24
Filing date: 2022-11-22
Publication date: 2023-06-01
Also published as: CN114388217A

Abstract

The present application relates to a dynamic active field stabilization method, system and device for a liquid-helium-free superconducting magnet. The method comprises the following steps: collecting operation fixed frequency information of a compressor (S1); obtaining an analog signal sync according to the operation fixed frequency information of the compressor (S2); generating a dynamic current I(t) according to the analog signal sync (S3); and synchronously applying the dynamic current I(t) to the liquid-helium-free magnet, to dynamically compensate for the magnetic field generated by the liquid-helium-free magnet (S4), such that the strength of the magnetic field B0 generated by the liquid-helium-free magnet is kept stable. The dynamic active field stabilization system for a liquid-helium-free superconducting magnet comprises a signal acquisition module (41), a synchronous measurement module (42), a current synchronous compensation module (51), and a parameter measurement module (44). A device for the dynamic active field stabilization system for a liquid-helium-free superconducting magnet comprises a 4K cold head (1), a liquid-helium-free magnet (2), a liquid helium compressor (3), a signal processor (4), and a shimming power supply (5). According to the present application, appropriate dynamic current is actively applied to a shimming coil, such that the stability of the magnetic field of the liquid-helium-free magnet is improved.

Description

A dynamic active field stabilization method, system and device for a liquid helium-free superconducting magnet

technical field

The present application relates to the field of magnetic resonance technology, in particular to a method, system and device for dynamic and active field stabilization of a liquid helium superconducting magnet.

Background technique

In the magnetic resonance system, the main magnet is the core of the whole system. The uniform and stable static magnetic field generated by the main magnet is the basis of the imaging of the magnetic resonance system, and this performance determines the imaging quality of the magnetic resonance system. Poor magnetic field uniformity will blur and distort the image. The performance evaluation index of the main magnet is mainly the magnetic field strength, uniformity and stability of the main magnet.

At present, liquid helium-free superconducting magnets mainly adopt conduction cooling technology. In a vacuum environment, key components such as liquid helium-free superconducting coils, superconducting switches, and superconducting joints are directly cooled by the cold head of the refrigerator and the conduction cooling network with extremely uniform temperature distribution. Keep the temperature of the liquid-free helium magnet constant.

For the above-mentioned related technologies, due to the reciprocating motion of the cold head of the refrigerator, and the periodic vibration caused by it, the slight fluctuation of the magnet temperature, etc., will cause the periodic fluctuation of the main magnetic field of the magnet, resulting in a decrease in the stability of the main magnet. Since the magnetic field will affect the phase of the magnetic resonance echo signal, magnetic resonance imaging has very high requirements on the stability of the magnetic field, and small dynamic fluctuations will seriously affect the quality of magnetic resonance imaging.

Contents of the invention

In order to reduce the magnetic field fluctuation of the magnet, the present application provides a method, system and device for dynamic and active field stabilization of a liquid helium-free superconducting magnet.

A dynamic and active field stabilization method for a liquid-helium-free superconducting magnet provided by this application adopts the following technical scheme:

A method for dynamic and active field stabilization of a liquid helium-free superconducting magnet, comprising the following steps:

Collect compressor operation fixed frequency information;

According to the fixed frequency information of compressor operation, the analog signal sync is obtained;

According to the analog signal sync, a dynamic current I(t) is generated;

The dynamic current I(t) is synchronously applied to the helium-free magnet to dynamically compensate the magnetic field generated by the helium-free magnet, so that the intensity of the magnetic field B0 generated by the helium-free magnet remains stable.

By adopting the above technical scheme, since the periodic change of the magnetic field is generated by the periodic movement of the piston of the liquid helium compressor, the analog signal sync is obtained according to the fixed frequency information of the compressor operation by collecting the fixed frequency information of the compressor operation. The analog signal sync applies a dynamic current I(t) to the liquid-free helium magnet, so that the liquid-free helium magnet generates a compensation magnetic field that is complementary to the fluctuation of the original magnetic field. The two magnetic fields are superimposed to eliminate the fluctuation of the magnetic field to a certain extent and form a stable New magnetic field for better quality magnetic resonance imaging.

Preferably, after the dynamic current I(t) is synchronously applied to the liquid-free helium magnet to dynamically compensate the magnetic field generated by the liquid-free helium magnet, the following steps are also included:

The modification signal is received, and the current intensity and phase of the dynamic current I(t) are adjusted to further stabilize the magnetic field.

By adopting the above technical scheme, due to the difference of each liquid-free magnet, personnel can adjust the current intensity and phase of the dynamic current I(t), so that the generated compensation magnetic field fits the actual magnetic field change, so that the actual magnetic field Further stabilization.

Preferably, according to the analog signal sync, the following steps are included in generating the dynamic current I(t):

According to the analog signal sync, the shimming power supply is controlled to generate a dynamic current I(t)=I ₀ *sin(ωt+Φ+Φ ₀ );

Among them, ω and Φ are synchronized with the analog signal sync, so that the cycle of ω and sync is the same, and the phase of Φ and sync is the same, Φ ₀ is the phase variable, and I ₀ is the current intensity variable.

By adopting the above technical scheme, since the magnetic field generated by the current is proportional to the intensity of the current, personnel can adjust the intensity and phase of the current to change the intensity and time-varying phase of the generated compensation magnetic field to make it fit the actual liquid-free helium The magnetic field of the magnet changes, making the compensated magnetic field more stable.

The present application also provides a dynamic active field stabilization system for a liquid helium-free superconducting magnet.

The signal acquisition module is used to collect the fixed frequency information of compressor operation;

The synchronous measurement module is used to obtain the cycle information and phase information of the current liquid helium compressor operation according to the fixed frequency information of the compressor operation;

The signal generation module outputs the analog signal sync according to the period information and the phase information; and,

The current synchronous compensation module is used to generate a dynamic current I(t) according to the analog signal sync and apply the dynamic current I(t) to the liquid-free helium magnet synchronously to dynamically compensate the magnetic field generated by the liquid-free helium magnet, so that no The strength of the magnetic field B0 generated by the liquid helium magnet remains stable.

Preferably, it also includes:

The parameter determination module is used to receive the modification signal and adjust the current intensity and phase of the dynamic current I(t), so as to further stabilize the magnetic field B0.

The present application also provides a dynamic active field stabilization device for a liquid helium-free superconducting magnet.

A dynamic active field stabilization device for a liquid helium-free superconducting magnet, including a 4K cold head, a liquid helium-free magnet, and a liquid helium compressor. The liquid helium compressor cools the liquid-helium magnet through a 4K cold head, and is characterized in that : It also includes a signal processor and a shimming power supply, the liquid helium compressor is provided with a running frequency detection sensor, and the running frequency detection sensor is used to detect the fixed frequency information of the compressor running to output a detection signal, and the signal processor Coupled with the operating frequency detection sensor to obtain an analog signal sync according to the detection signal, the signal processor is coupled with the shim power supply to control the output dynamic current I(t) of the shim power supply, and the output of the shim power supply is coupled The end is coupled with the shim coil arranged in the liquid-free helium magnet.

By adopting the above technical scheme, the detection signal is output by the operating frequency detection sensor to the signal processor, and the signal processor processes the detection signal to obtain an analog signal sync, and then the shim power supply is controlled by the analog signal sync to output a corresponding dynamic current I( t), the dynamic current I(t) is input to the liquid-free helium magnet, and a corresponding magnetic field is generated to compensate the original magnetic field of the liquid-free helium magnet to obtain a stable magnetic field.

Preferably, a first filter is provided between the shim power supply and the shim coil in the liquid helium-free magnet.

By adopting the above technical solution, the setting of the first filter can filter out the interference signal between the output terminal of the shimming power supply and the liquid-free magnet, so that the dynamic current I(t) is more stable.

Preferably, a second filter is provided on the liquid helium tube between the liquid helium compressor and the 4K cold head.

By adopting the above technical solution, the second filter is used to filter out the interference signal on the liquid helium tube, so as to prevent it from interfering with the magnetic field of the liquid helium-free magnet.

In summary, the present application includes at least one of the following beneficial technical effects:

1. This application can effectively suppress the periodic fluctuation of the magnetic field of the liquid-free helium magnet by actively applying a suitable dynamic current to the shim coil, and improve the stability of the magnetic field of the liquid-free helium magnet;

2. This application adjusts the intensity and phase of the dynamic current so that it can adapt to the actual situation of the periodic fluctuation of the magnetic field of the liquid-free helium magnet, so as to achieve the best compensation effect and improve the scope of application of the application.

Description of drawings

Fig. 1 is a flow chart of a dynamic active field stabilization method for a liquid helium-free superconducting magnet according to an embodiment of the present application.

Fig. 2 is a structure diagram of a liquid helium-free superconducting magnet dynamic active field stabilization system according to an embodiment of the present application.

Fig. 3 is a first structural diagram of a liquid helium-free superconducting magnet dynamic active field stabilization device according to an embodiment of the present application.

Fig. 4 is a cross-sectional view of a liquid-helium-free magnet of a liquid-helium-free superconducting magnet dynamic active field stabilization device according to an embodiment of the present application.

Fig. 5 is a second structural diagram of a liquid helium-free superconducting magnet dynamic active field stabilization device according to an embodiment of the present application.

Explanation of reference signs: 1. 4K cold head; 2. Liquid-free helium magnet; 21. Vacuum container; 22. Shielding layer; 23. Shimming coil; 24. Gradient coil; 25. Inner cavity; 26. Magnetic field detector; 3. Liquid helium compressor; 31. Operating frequency detection sensor; 4. Signal processor; 41. Signal acquisition module; 42. Synchronous measurement module; 43. Signal generation module; 44. Parameter determination module; 5. Shimming power supply; 51. Current synchronous compensation module; 6. Filter board; 61. First filter; 62. Second filter.

Detailed ways

The embodiment of the present application discloses a method for dynamic and active field stabilization of a liquid helium-free superconducting magnet.

Referring to Fig. 1, a method for dynamic active field stabilization of a liquid-free superconducting magnet is characterized in that it comprises the following steps:

S1: Collect information about the fixed frequency of compressor operation;

Specifically, according to the operating frequency detection sensor distributed on the liquid helium compressor 3, the operating state of the liquid helium compressor 3 is collected in real time. For example, due to the periodic movement of the liquid helium compressor 3 piston, the housing of the liquid helium compressor 3 will Continuous periodic vibration, by installing an acceleration sensor on the shell of the liquid helium compressor 3, the output signal of the acceleration sensor is collected as the fixed frequency information of the compressor operation. The fixed frequency information of the compressor operation is generally around 1Hz.

In other embodiments, the rotation angle value of the motor output shaft of the liquid helium compressor 3 can also be collected, and the fixed frequency information of compressor operation can be obtained according to the change of the rotation angle value.

S2: According to the fixed frequency information of compressor operation, the analog signal sync is obtained;

Specifically, after obtaining the compressor running fixed frequency information, the analog signal sync is obtained through the signal generation module according to the compressor running fixed frequency information; for example, the compressor running fixed frequency information is acceleration information, which follows the liquid helium compressor 3 The shell vibrates and changes periodically. When the acceleration sensor is at the highest point, the acceleration is 0, and then the acceleration is also 0 when it falls to the lowest point. Calculate the interval time of three consecutive compressor running fixed frequency information with a value of 0 to get In addition, according to the acceleration direction before the fixed frequency information of the compressor running with a value of 0, it can be obtained whether the acquisition phase of the fixed frequency information of the compressor is a peak or a trough, and thus the phase information of the compressor running fixed frequency information can be obtained , and then simulate the signal sync according to the period information and phase information, so that the period and phase of the analog signal sync are respectively the same as the period information and phase information. The signal generation module can be a PC or other intelligent processors.

S3: Generate a dynamic current I(t) according to the analog signal sync;

Specifically, the signal generation module outputs the analog signal sync to the shimming power supply, and controls the shimming power supply to generate a dynamic current I(t)=I ₀ *sin(ωt+Φ+Φ ₀ );

S4: synchronously applying the dynamic current I(t) to the liquid-free helium magnet 2 to dynamically compensate the magnetic field generated by the liquid-free helium magnet 2;

Specifically, the dynamic current I(t) is synchronously applied to the shimming coils in the liquid-free helium magnet 2, so that the shimming coils generate corresponding magnetic fields, so that when the temperature of the piston of the liquid helium compressor 3 periodically moves When changing, when the original magnetic field generated by the liquid-free helium magnet 2 fluctuates periodically, the dynamic current I(t) is synchronously applied to the shim coil so that the compensation magnetic field generated by the shim coil is complementary to the original magnetic field of the liquid-free helium magnet 2 , to offset the periodic fluctuation of the original magnetic field, so that the magnetic field remains stable. For example: the periodic fluctuation of the original magnetic field is B0(t), the compensation magnetic field generated by the dynamic current I(t) is B'0(t), and B0(t)+B'0(t)=B0 is a constant value.

S5: receiving a modification signal, adjusting the current intensity and phase of the dynamic current I(t), so as to further stabilize the magnetic field.

Concrete: Since each non-liquid helium magnet 2 will have a magnetic field fluctuation, and due to the difference of each non-liquid helium magnet 2, the amplitude of the periodic fluctuation of the magnetic field will also be different, so in the application of this method , it needs to be debugged according to the actual situation, and the debugging method is as follows:

Through the method of MRI imaging, the compensated B0 magnetic field is measured, the measurement results are manually evaluated by personnel, and the current is further fed back and corrected according to the evaluation results. The specific process is fine-tuned by the personnel through the parameter determination module. Dynamic current I(t) The I ₀ , Φ ₀ are realized. This process needs to be repeated several times until the image of the magnetic field B0 generated by the MRI system reaches a constant state.

The implementation principle of a liquid helium-free superconducting magnet dynamic active field stabilization method in the embodiment of the present application is as follows: the operating frequency of the liquid helium compressor 3 is converted into a sine wave containing amplitude and phase information, and then the amplitude of the sine wave And the phase is adjusted to form an analog signal sync, when the analog signal sync is input to the shim power supply to form a dynamic current I(t), the fluctuating magnetic field generated by the dynamic current I(t) through the shim coil can be compared with the original liquid helium magnet 2 The phases of the magnetic fields are complementary, and the superposition of the two forms a constant magnetic field B0, which makes the quality of the magnetic resonance imaging higher.

In order to realize the above method, the embodiment of the present application also discloses a liquid helium-free superconducting magnet dynamic active field stabilization system.

With reference to Fig. 2, a kind of liquid helium superconducting magnet dynamic active stabilization system, comprises signal acquisition module 41, synchronous measurement module 42, current synchronous compensation module 51 and parameter measurement module 44, signal acquisition module 41, synchronous measurement module 42, Both the current synchronous compensation module 51 and the parameter measurement module 44 are PC terminals. in:

Signal collection module 41, used for collecting compressor operation fixed frequency information;

The synchronous measurement module 42 is used to obtain the cycle information and phase information of the current operation of the liquid helium compressor 3 according to the compressor operation fixed frequency information;

The signal generation module 43 outputs the analog signal sync according to the period information and the phase information;

The current synchronous compensation module 51 is used to generate a dynamic current I(t) according to the analog signal sync and apply the dynamic current I(t) to the liquid-free helium magnet 2 synchronously to dynamically compensate the magnetic field generated by the liquid-free helium magnet 2 , so that the strength of the magnetic field generated by the liquid-free helium magnet 2 remains stable;

And, the parameter measurement module 44 is used to receive the modification signal, and the control signal generation module 43 modifies the amplitude and phase of the analog signal sync to adjust the current intensity and phase of the dynamic current I(t), so as to further stabilize the magnetic field.

The embodiment of the present application also discloses a device for a liquid helium-free superconducting magnet dynamic active field stabilization method.

Referring to Fig. 3 and Fig. 4, a kind of device of liquid helium superconducting magnet dynamic active field stabilization method, comprises 4K cold head 1, liquid helium magnet 2, liquid helium compressor 3, signal processor 4, filter plate 6 and The shimming power supply 5 and the liquid helium compressor 3 are connected to the 4K cold head 1 through the liquid helium tube, and the liquid helium compressor 3 cools down the shim coil 23 in the liquid helium-free magnet 2 through the 4K cold head 1 .

The liquid-free helium magnet 2 includes a vacuum container 21, a shielding layer 22, a shim coil 23, and a gradient coil 24. The vacuum container 21 is provided with an inner cavity 25, and the shim coil 23 and the gradient coil 24 are fixedly connected to the vacuum container 21 and are all located in the inner chamber. In the chamber 25, the gradient coil 24 is used to generate the original magnetic field, the inner chamber 25 is used to communicate with the 4K cold head 1 to form an ultra-low temperature environment, and the shielding layer 22 is arranged on the inner wall of the inner chamber 25 to block low temperature. A magnetic field detector 26 is fixedly installed on the liquid-free helium magnet 2 , and the magnetic field detector 26 is coupled with the signal processor 4 .

Referring to Fig. 3 and Fig. 5, the signal processor 4 is an intelligent processing device, which can be a PC or other intelligent devices. The signal processor 4 includes a signal acquisition module 41 , a synchronous measurement module 42 , a current synchronous compensation module 51 and a parameter determination module 44 . The signal acquisition module 41 , the synchronous measurement module 42 , the current synchronous compensation module 51 and the parameter determination module 44 are system modules inside the signal processor 4 .

An operating frequency detection sensor 31 is fixedly installed in the liquid helium compressor 3 , and the operating frequency detection sensor 31 is used to detect information on a fixed operating frequency of the compressor to output a detection signal. In this embodiment, the operating frequency detection sensor 31 is an acceleration sensor, and the acceleration sensor is fixed on the shell of the liquid helium compressor 3. The liquid helium compressor 3 in the present embodiment drives the piston rod to reciprocate periodically through the output shaft of the motor, so that The surface of the liquid helium compressor 3 shell vibrates slightly, causing the acceleration sensor to move up and down, and the position and acceleration of the acceleration sensor will change periodically. The frequency of this vibration is the same as the frequency of the piston movement of the liquid helium compressor 3, so the signal processor 4. It is possible to detect the periodic change of the signal to obtain the period and phase of the operation of the liquid helium compressor 3 . In other embodiments, the operating frequency detection sensor 31 can also use an angle sensor. By detecting the rotation angle of the output shaft of the motor output shaft of the liquid helium compressor 3, the signal processor 4 also obtains the fixed frequency of the operation of the liquid helium compressor 3 .

The signal processor 4 is coupled with the operating frequency detection sensor 31 to receive the detection signal and obtain the operating cycle and phase of the liquid helium compressor 3 according to the detection signal, and generate an analog signal sync according to the operating cycle and phase of the liquid helium compressor 3 . The input end of the shim power supply 5 is coupled to the signal processor 4, the shim power supply 5 is a multi-stage shim power supply 5, and the shim power supply 5 includes a current synchronous compensation module 51 for outputting a dynamic current after receiving an analog signal sync I(t), the output end of the shim power supply 5 is coupled to the shim coil 23 to apply the dynamic current I(t) to the shim coil 23 in the liquid-free helium magnet 2 to generate a compensation magnetic field.

A first filter 61 and a second filter 62 are fixedly installed on the filter plate 6, and the first filter 61 is coupled on the electrical connection point between the output end of the shim power supply 5 and the shim coil 23 to filter out the The interference signal in the line makes the transmission of the dynamic current I(t) more stable, the liquid helium is transmitted between the liquid helium compressor 3 and the 4K cold head and the gas helium is recovered through the liquid helium tube, and the second filter 62 is installed in the liquid helium The liquid helium tube between the compressor 3 and the 4K cold head 1 is used to filter out the interference signal on the liquid helium tube to prevent the interference signal from affecting the magnetic field generated by the liquid helium magnet 2, so that the liquid helium magnet does not The operation is more stable.

All of the above are preferred embodiments of the application, and are not intended to limit the protection scope of the application. Therefore, all equivalent changes made according to the structure, shape, and principle of the application should be covered by the protection scope of the application. Inside.

Claims

A method for dynamic active field stabilization of a liquid-helium-free superconducting magnet, characterized in that it comprises the following steps:

Collect compressor operation fixed frequency information;

According to the fixed frequency information of compressor operation, the analog signal sync is obtained;

According to the analog signal sync, a dynamic current I(t) is generated;
The dynamic current I(t) is synchronously applied to the liquid-free helium magnet (2) to dynamically compensate the magnetic field generated by the liquid-free helium magnet (2), so that the intensity of the magnetic field B0 generated by the liquid-free helium magnet (2) remains stable .
A dynamic active field stabilization method for a liquid-free helium superconducting magnet according to claim 1, characterized in that: the dynamic current I(t) is synchronously applied to the liquid-free helium magnet (2) to stabilize the liquid-helium-free magnet (2) After the generated magnetic field is dynamically compensated, the following steps are also included:

The modification signal is received, and the current intensity and phase of the dynamic current I(t) are adjusted to further stabilize the magnetic field B0.
The dynamic active field stabilization method for a liquid-free superconducting magnet according to claim 2, characterized in that, according to the analog signal sync, generating the dynamic current I (t) comprises the following steps:

According to the analog signal sync, the shimming power supply is controlled to generate a dynamic current I(t)=I 0 *sin(ωt+Φ+Φ 0 );

Among them, ω and Φ are synchronized with the analog signal sync, so that the cycle of ω and sync is the same, and the phase of Φ and sync is the same, Φ 0 is the phase variable, and I 0 is the current intensity variable.
A system based on the liquid helium-free superconducting magnet dynamic active field stabilization method described in any one of claims 1-3, characterized in that it includes:

A signal collection module (41), used for collecting information on a fixed frequency of operation of the compressor;

The synchronous measurement module (42) is used to obtain the cycle information and phase information of the current operation of the liquid helium compressor (3) according to the fixed frequency information of the operation of the compressor;

The signal generating module (43) outputs the analog signal sync according to the period information and the phase information; and,

The current synchronous compensation module (51) is used to generate a dynamic current I(t) according to the analog signal sync and apply the dynamic current I(t) to the liquid-free helium magnet (2) synchronously to adjust the liquid-helium-free magnet (2) The generated magnetic field is dynamically compensated so that the intensity of the magnetic field B0 generated by the liquid-free helium magnet (2) remains stable.
A liquid-helium-free superconducting magnet dynamic active field stabilization system according to claim 4, further comprising:

The parameter determination module (44) is used to receive the modification signal and adjust the current intensity and phase of the dynamic current I(t), so as to further stabilize the magnetic field B0.
A device based on the liquid helium-free superconducting magnet dynamic active field stabilization method described in any one of claims 1-3, comprising a 4K cold head (1), a liquid helium-free magnet (2), and a liquid helium compressor (3) , the liquid helium compressor (3) cools the liquid helium-free magnet (2) through a 4K cold head (1), and is characterized in that: it also includes a signal processor (4) and a shimming power supply (5), the The liquid helium compressor (3) is provided with a running frequency detection sensor (31), and the running frequency detection sensor (31) is used to detect the fixed frequency information of the compressor running to output a detection signal, and the signal processor (4) and The operating frequency detection sensor (31) is coupled to obtain an analog signal sync according to the detection signal, and the signal processor (4) is coupled to the shim power supply (5) to control the shim power supply (5) to output a dynamic current I(t ), the output end of the shim power supply (5) is coupled with the shim coil (23) arranged in the liquid-free helium magnet (2).
A dynamic active field stabilization device for a liquid-free helium superconducting magnet according to claim 6, characterized in that: the shim power supply (5) and the shim coil (23) in the liquid-free helium magnet (2) A first filter (61) is arranged between them.
A liquid helium-free superconducting magnet dynamic active field stabilization device according to claim 6, characterized in that: the liquid helium tube between the liquid helium compressor (3) and the 4K cold head (1) is provided with Second filter (62).