A stacked high-uniformity magnetic field free-line magnetic particle imaging system and method

Abstract

The present invention belongs to the technical field of magnetic particle imaging, and particularly relates to a stacked high-uniformity magnetic field free-form line magnetic particle imaging system and method, aiming to solve the problem of non-uniform magnetic field free-form lines in existing FFL-MPI, as well as the problems of non-uniform imaging resolution and circular artifacts. The system of the present invention includes: a stacked gradient coil unit composed of N groups of symmetric coil pairs, each group containing n layers of coils with increasing diameters, equipped with a saddle-shaped driving scanning coil and a detection coil; by means of the reverse current mode of adjacent two layers of coils, the magnetic field amplitude is made opposite to the current direction to compensate for the magnetic field non-uniformity and generate a high-uniformity FFL gradient field; the control system precisely collects and processes signals, which are fed back to the imaging unit after analog-to-digital conversion, amplification, and filtering, and are reconstructed into images through imaging algorithms. The present invention solves the problems of uneven resolution and circular artifacts caused by magnetic field non-uniformity, and significantly improves the imaging quality of FFL-MPI devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic particle imaging, and particularly relates to a stacked high-uniformity magnetic field free line magnetic particle imaging system and method. Background Art

[0002] Magnetic Particle Imaging (MPI) is a non-invasive imaging technique that uses superparamagnetic nanoparticles as tracers. When an external high-frequency alternating excitation magnetic field is applied to these particles, they generate specific non-linear magnetic response signals, which can be captured by an MPI device and converted into an image of the particle distribution through an imaging algorithm.

[0003] In an MPI device, a gradient coil module generates a high-intensity static magnetic field, and a drive scan coil module generates a high-frequency dynamic excitation magnetic field. The static magnetic field is used to create a magnetic field free point (FFP) or a magnetic field free line (FFL) and other magnetic field-free regions. Only the magnetic particles in the magnetic field-free region will generate response signals under the drive of the dynamic excitation magnetic field. The magnetic particles outside the magnetic field-free region are already in a saturated state. The farther away from the magnetic field-free region, the stronger the saturated state and the weaker the response signal, and vice versa. Therefore, for an FFL-MPI device, the uniformity of the FFL determines the driving range of the magnetic particles. The particle region driven by a non-uniform FFL expands continuously along the FFL direction, seriously affecting the imaging quality. Therefore, the uniformity of the FFL is crucial for FFL-MPI.

[0004] Due to the non-uniform magnetic field generated by a single coil in a traditional FFL-MPI device, there will be a non-uniform phenomenon where the two sides of the magnetic field free line are wide and the middle is narrow, resulting in problems such as non-uniform imaging resolution and circular artifacts. Summary of the Invention

[0005] To solve the above problems in the prior art, that is, the problem of non-uniform magnetic field free lines in existing FFL-MPI, as well as the problems of non-uniform imaging resolution and circular artifacts, in the first aspect of the present invention, a stacked high-uniformity magnetic field free line magnetic particle imaging system is proposed. The system includes:

[0006] The system includes:

[0007] An imaging and control unit configured to generate a control command for magnetic field change and send it to the signal acquisition and output module; and also configured to perform an imaging algorithm and reconstruct a magnetic particle image based on the received magnetic particle response signal;

[0008] The signal acquisition and output module receives the control command, performs digital-to-analog conversion, and transmits it to the drive scan power amplifier module to amplify the excitation magnetic field current in the control command, and then applies the amplified excitation magnetic field current to the drive scan coil to generate a dynamic excitation magnetic field;

[0009] The signal acquisition and output module transmits the control command after digital-to-analog conversion to the multi-channel gradient power amplifier module to amplify the gradient magnetic field current in the control command, and applies the amplified gradient magnetic field current to the stacked gradient coil unit to generate a static magnetic field, which is superimposed on the dynamic excitation magnetic field to generate an axially highly uniform FFL for scanning and imaging an object to be imaged in the imaging space;

[0010] The signal acquisition and output module receives the magnetic particle response signal processed by the signal processing unit, performs analog-to-digital conversion, and then transmits it to the imaging and control unit; the magnetic particle response signal is collected by the detection coil;

[0011] The stacked gradient coil unit includes four groups of coils, two groups as a pair, and the two coils in each pair are symmetrically arranged and have the same axis; the axes of the two pairs are orthogonal; each group of coils is stacked by n layers of circular ring coils;

[0012] The drive scan coil includes four saddle-shaped coils, which are respectively arranged inside the four groups of coils of the stacked gradient coil unit;

[0013] The detection coil includes four saddle-shaped coils, and the four saddle-shaped coils are respectively arranged in the middle inside the adjacent saddle-shaped coils of the drive scan coil.

[0014] In some preferred embodiments, the magnetic fields generated by the two coils in each pair in the stacked gradient coil unit have the same amplitude and opposite phases;

[0015] The magnetic fields of adjacent two layers in each group of coils have the same amplitude and opposite phases.

[0016] In some preferred embodiments, the magnetic fields having the same amplitude and opposite phases are achieved by setting the adjacent two layers of coils in each group to a reverse current mode and controlling the current ratio.

[0017] In some preferred embodiments, the saddle-shaped coils in the drive scan coil and the detection coil are both coils wound by litz wire.

[0018] In some preferred embodiments, the processing by the signal processing unit includes compensation, filtering, and amplification.

[0019] In some preferred embodiments, the diameters of the n layers of circular ring coils in each group of coils increase sequentially from the inside to the outside.

[0020] In some preferred embodiments, the current passed through each group of coils is a sinusoidal alternating current, that is:

[0021]

[0022] wherein, represents the change of the current of the th layer of the th group with time; represents the amplitude of the current of the th layer of the th group; represents the frequency of the alternating current, represents the initial phase of the current of the th

[0023] In some preferred embodiments, the , where is the current proportionality coefficient, represents the amplitude of the current of the th layer of the

[0024] In some preferred embodiments, the current control ratio between adjacent two layers of coils in each group of the stacked gradient coil unit is:

[0025] ;

[0026] ;

[0027] wherein, is the current of the th layer of the th group, is the current of the th , , and are in a reverse current mode, is the current proportionality coefficient, is the conversion efficiency of the th layer, is the uniformity adjustment parameter.

[0028] The second invention of the present invention proposes a stacked high-uniformity magnetic field free-line magnetic particle imaging method, based on the described stacked high-uniformity magnetic field free-line magnetic particle imaging system, the method includes the following steps:

[0029] Step 1: Use the imaging and control unit to generate a control command for magnetic field variation, and send the control command to the signal acquisition and output module;

[0030] Step 2: In the signal acquisition and output module, perform digital-to-analog conversion on the received control command; transmit the digitally-analog converted control command to the drive scan power amplifier module and the multi-channel gradient power amplifier module;

[0031] Step 3: In the drive scan power amplifier module, amplify the excitation magnetic field current in the control command; apply the amplified excitation magnetic field current to the drive scan coil to generate a dynamic excitation magnetic field; in the multi-channel gradient power amplifier module, amplify the gradient magnetic field current in the control command; apply the amplified gradient magnetic field current to the stacked gradient coil unit to generate a static magnetic field; the static magnetic field is superimposed on the dynamic excitation magnetic field to generate an axially highly uniform FFL for scanning the object to be imaged in the imaging space;

[0032] Step 4: Use the detection coil to collect the response signal of the magnetic particles in the object to be imaged; transmit the collected magnetic particle response signal to the signal processing unit for processing; after processing, enter the signal acquisition and output module to perform analog-to-digital conversion on the processed magnetic particle response signal; transmit the analog-to-digital converted signal to the imaging and control unit;

[0033] Step 5: In the imaging and control unit, execute an imaging algorithm based on the received magnetic particle response signal to perform magnetic particle image reconstruction.

[0034] Advantages of the present invention:

[0035] 1. Optimization of the stacked gradient coil: The stacked gradient coil is composed of N groups of symmetric coil pairs, each group of coils is composed of n layers of coil laminations. A more optimal solution for each group of coils is that the diameter of each layer of coil gradually increases from bottom to top. A drive scan coil is correspondingly arranged, specifically a saddle-shaped coil, which is arranged around the aperture direction. The detection coil is arranged inside the drive scan coil, and N groups of saddle-shaped coils are vertically arranged in the radial plane;

[0036] 2. Setting of the reverse current mode: Each layer of coil is independently and synchronously controlled according to the control command, and is configured such that the magnetic field amplitudes of each group and each layer of coils are the same and the directions are opposite. Specifically, it is achieved by setting adjacent layers of coils to the reverse current mode and controlling the ratio. In this way, the magnetic field generated by each layer is used to compensate for the non-uniformity of the magnetic field of the adjacent layer, thereby generating a highly uniform FFL gradient field and realizing the uniform distribution and optimization of the overall magnetic field;

[0037] 3. Precise control and imaging: The control commands of the imaging and control unit are converted from analog to digital by the signal acquisition and output module, amplified by the power amplifier, applied to the stacked gradient coils and the driving scan coils. The signal processing unit amplifies and filters the particle signals detected by the detection coils, performs digital-to-analog conversion and then feeds back to the imaging and control unit. The imaging algorithm reconstructs the image. In this way, the magnetic field is precisely controlled through the control commands to solve the problem of uneven magnetic field free lines, as well as the problems of uneven imaging resolution and circular artifacts. Through the precise sampling feedback of the particle signals and the reconstruction of the imaging algorithm, the overall quality of the imaging is further improved;

[0038] In summary, through optimized design and precise control, the stacked gradient coils and its control system of the present invention achieve uniform distribution and optimization of the overall magnetic field, and improve the overall quality of magnetic resonance imaging. Brief Description of the Drawings

[0039] Other features, objectives and advantages of this application will become more obvious by reading the detailed description of the non-restrictive embodiments with reference to the following drawings:

[0040] Figure 1 is a block diagram of a stacked high-uniformity magnetic field free line magnetic particle imaging system of the present invention.

[0041] Figure 2 is an example diagram of a four-layer structure of the stacked gradient coils of the present invention 。

[0042] Figure 3 is a side cross-sectional view of an example of a four-layer structure of the stacked gradient coils of the present invention.

[0043] Figure 4 is a simulation comparison diagram of the magnetic field uniformity distribution between the traditional FFL magnet and the stacked gradient coils of the present invention.

[0044] Figure 5 is a flowchart of a method for stacked high-uniformity magnetic field free line magnetic particle imaging of the present invention.

[0045] Figure 1 Among them, 1. Imaging and control unit; 2. Signal acquisition and output module; 3. Driving scan power amplifier module; 4. Multi-channel gradient power amplifier module; 5. Signal processing unit; 6. Stacked gradient coil unit; 7. Driving scan coil; 8. Detection coil. Detailed Embodiments

[0046] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related invention, rather than limiting the invention. Additionally, it should be noted that for ease of description, only parts related to the relevant invention are shown in the drawings.

[0047] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and embodiments.

[0048] To more clearly illustrate a stacked high-uniformity magnetic field free-line magnetic particle imaging system of the present invention, the following will be combined with Figures 1 to 5 to elaborate on each step in the embodiments of the present invention.

[0049] A stacked high-uniformity magnetic field free-line magnetic particle imaging system according to the first embodiment of the present invention, see Figure 1 , the system includes:

[0050] An imaging and control unit 1, configured to generate a control command for magnetic field change and send it to the signal acquisition and output module 2, and also configured to execute an imaging algorithm based on the received magnetic particle response signal to perform magnetic particle image reconstruction;

[0051] The signal acquisition and output module 2 has a computing unit with a high sampling frequency (generally ), and is configured to:

[0052] Receive the control command of the imaging and control unit 1, perform digital-to-analog conversion, and transmit the digitally converted control command to the drive scan power amplifier module 3 to amplify the excitation magnetic field current in the control command, and then apply the amplified excitation magnetic field current to the drive scan coil 7 to generate a dynamic excitation magnetic field;

[0053] The signal acquisition and output module 2 is further configured to: transmit the digitally converted control command to the multi-channel gradient power amplifier module 4 to amplify the gradient magnetic field current in the control command, and apply the amplified gradient magnetic field current to the stacked gradient coil unit 6 to generate a static magnetic field, and superimpose it with the dynamic excitation magnetic field to generate an axially highly uniform FFL to scan the object to be imaged in the imaging space;

[0054] The signal acquisition and output module 2 receives the magnetic particle response signal processed by the signal processing unit 5, performs analog-to-digital conversion, and then transmits it to the imaging and control unit 1. The magnetic particle response signal is collected by the detection coil 8, and the collected signal is subjected to analog-to-digital conversion and then transmitted to the imaging and control unit 1, and image reconstruction is performed according to a predetermined reconstruction algorithm;

[0055] In this embodiment, the signal processing unit 5 performs processing including compensation, filtering, and amplification;

[0056] In this embodiment, the stacked gradient coil unit 6 includes four sets of coils. Two sets form a pair, and the two sets of coils in each pair are symmetrically arranged and have the same axis; the axes of the two pairs are orthogonal; each set of coils is formed by stacking n layers of circular ring-shaped coils, and the diameters of the n layers of circular ring-shaped coils in each set of coils increase sequentially from the inside to the outside; the four sets of coils of the stacked gradient coil unit are wound with litz wire, pure copper wire, or hollow copper tube coils;

[0057] The driving scan coil 7, which generates a dynamic excitation magnetic field, includes four saddle-shaped coils, which are respectively arranged inside the four sets of coils of the stacked gradient coil unit 6 and are arranged in a surrounding manner in the aperture direction (legend x direction). The saddle-shaped coils are all coils wound with litz wire;

[0058] The detection coil 8, which is used to detect or collect the radial component signal of the magnetization of magnetic particles, that is, the magnetic particle response signal, includes four saddle-shaped coils. The saddle-shaped coils are all coils wound with litz wire. Here, it should be noted that the sizes of the four saddle-shaped coils of the detection coil 8 are smaller than those of the four saddle-shaped coils of the driving scan coil 7. The specific sizes and shapes can be adjusted according to actual needs and are not limited here. Its position (the four saddle-shaped coils of the detection coil 8) is arranged inside the driving scan coil 7, specifically at the middle position between the adjacent saddle-shaped coils of the driving scan coil 7, that is, two sets form a pair, and the two sets of coils in each pair are symmetrically arranged and have the same axis; the axes of the two pairs are orthogonal, and the four saddle-shaped coils of the detection coil 8 are separated by 45 degrees from the four saddle-shaped coils of the driving scan coil 7 in the radial circumferential direction to ensure the uniformity and symmetry of the detection coil 8. The axis of the detection coil 8 is consistent with the axes of the driving scan coil 7 and the stacked gradient coil unit 6;

[0059] In this embodiment, the magnetic field amplitudes generated by the two sets of coils in each pair of the stacked gradient coil unit 6 are the same and the phases are opposite;

[0060] The magnetic field amplitudes of adjacent two layers in each set of coils are the same and the phases are opposite, which is achieved by setting the adjacent two layers of coils in a reverse current mode and controlling the ratio. Specifically, in each set of coils, the first layer and the second layer are set in a reverse current mode. The magnetic field generated by the first layer is used to compensate for the non-uniformity of the magnetic field generated by the second layer, and so on for the third layer and the fourth layer, which are in a reverse current mode. The current ratio is:

[0061] ;

[0062] ;

[0063] Wherein, is the layer current of the th group, is the layer current of the th group, , , and are in a reverse current mode, is the current proportionality coefficient, is the conversion efficiency (magnetic field conversion efficiency) of the th layer; is the uniformity adjustment parameter;

[0064] And the active control of the FFL uniformity can be achieved by observing the uniformity of the FFL and adjusting the k uniformity adjustment parameter;

[0065] In this embodiment, referring to Figure 2 , taking a four-group and four-layer stacked gradient coil structure as an example, a detailed description is as follows:

[0066] 611~614, 621~624, 631~634, 641~644 are four groups of coils, and the magnetic fields generated by the four groups of coils are denoted as , and the th layer coil in each group is denoted as , and the magnetic field generated is denoted as . The 611~614 and 631~634 coil groups are symmetrically distributed and have the same magnetic field amplitude but opposite directions, that is, ; the 621~624 and 641~644 coil groups are symmetrically distributed and have the same magnetic field amplitude but opposite directions, that is, ; the four groups of coils act together to generate the FFL in the x-axis direction;

[0067] After generating the FFL, in order to encode the space, the FFL needs to be moved and scanned. Each group of coils is passed through the gradient magnetic field current in the control command, that is, a sinusoidal alternating current, that is, That is, each layer of each group of coils is independently and synchronously controlled, and the current is in accordance with Independently controlled, where is: , where is the th layer current of the th group, is the th layer current of the th group, , , and are in a reverse current mode, is the current proportionality coefficient, is the conversion efficiency of the layer, is the uniformity adjustment parameter; the th group, the amplitude of the layer current is , and there is where is the current proportionality coefficient, represents the amplitude of the layer current of the ， In the formula, represents the current of the layer of the th group changing with time ; represents the amplitude of the layer current of the th group; represents the frequency of the alternating current, represents the initial phase of the

[0068] layer current of the

[0069] Correspondingly, the drive scan coil 7 is composed of four groups of saddle-shaped coils, which are arranged around the aperture direction (legend x direction) and wound by litz wire. The central axes of the four groups of saddle-shaped coils are consistent with the central axes of the 4 groups of gradient coils. The magnetic field generated by the drive scan coil is superimposed on the magnetic field generated by the above gradient coils to quickly excite the FFL along the direction perpendicular to the FFL to drive the particles to generate response signals;

[0070] It should be noted that the above-described stacked high-uniformity magnetic field free-line magnetic particle imaging system provided by the above embodiments is only illustrated by the division of the above functional modules. In practical applications, the above functions can be allocated to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be further decomposed or combined. For example, the modules in the above embodiments can be combined into one module, or further split into multiple sub-modules to complete all or part of the functions described above. The names of the modules and steps involved in the embodiments of the present invention are only for distinguishing each module or step, and are not regarded as improper limitations of the present invention.

[0071] In the second embodiment of the present invention, refer to Figure 5 , a stacked high-uniformity magnetic field free-line magnetic particle imaging method, the method comprising the following steps:

[0072] Step 1, generating a control command for magnetic field change by using the imaging and control unit, and sending the control command to the signal acquisition and output module;

[0073] Step 2, in the signal acquisition and output module, performing digital-to-analog conversion on the received control command; transmitting the digitally-analog converted control command to the drive scan power amplifier module and the multi-channel gradient power amplifier module;

[0074] Step 3, in the drive scan power amplifier module, amplifying the excitation magnetic field current in the control command; applying the amplified excitation magnetic field current to the drive scan coil to generate a dynamic excitation magnetic field; in the multi-channel gradient power amplifier module, amplifying the gradient magnetic field current in the control command; applying the amplified gradient magnetic field current to the stacked gradient coil unit to generate a static magnetic field; the static magnetic field is superimposed on the dynamic excitation magnetic field to generate an axially high-uniformity FFL for scanning an object to be imaged in the imaging space;

[0075] Step 4, using the detection coil to collect the response signal of the magnetic particles in the object to be imaged; transmitting the collected magnetic particle response signal to the signal processing unit for processing; after processing, entering the signal acquisition and output module, performing analog-to-digital conversion on the processed magnetic particle response signal; transmitting the analog-to-digital converted signal to the imaging and control unit;

[0076] Step 5, in the imaging and control unit, performing an imaging algorithm based on the received magnetic particle response signal to perform magnetic particle image reconstruction.

[0077] In summary, the gradient magnetic field current is independently controlled by the imaging and control unit 1 according to the individual control strategy for each group and each layer in accordance with It is generated, output through the signal acquisition and output module 2, and provided after being amplified by the multi-channel gradient power amplifier module 4; the exciting magnetic field current for driving the scanning coil 7 is generated by the imaging and control unit 1, output through the signal output module 2, and provided after being amplified by the driving scanning power amplifier module 3; the signal received by the detection coil 8 is filtered and amplified by the signal processing unit 5, and then input into the imaging and control unit 1 through the signal acquisition and output module 2 for algorithm reconstruction.

[0078] Figure 4 It is a simulation comparison diagram of the magnetic field uniformity distribution of the traditional FFL magnet and the stacked magnet in the present invention: the left figure is the gradient magnetic field generated by the traditional FFL magnet. It can be seen that the gradient first increases and then decreases along the axial direction, and the change is obvious; the right figure is the gradient magnetic field generated by the stacked magnet of the present invention. It can be seen that the gradient is almost unchanged along the axial direction, and through further calibration, the gradient can be made more uniform along the axial direction.

[0079] Although each step was described in the above order in the above embodiments, those skilled in the art can understand that in order to achieve the effects of this embodiment, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are all within the protection scope of the present invention.

[0080] Those skilled in the art should be able to realize that the modules and method steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. The programs corresponding to the software modules and method steps can be placed in a random access memory (RAM), memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, register, hard disk, removable disk, CD-ROM, or any other form of storage medium well-known in the technical field. To clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in the form of electronic hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0081] Terms such as "first" and "second" are used to distinguish similar objects, rather than to describe or represent a specific order or sequence.

[0082] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to those process, method, article, or apparatus / device.

[0083] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easily understood by those skilled in the art that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A stacked high uniformity magnetic field free line magnetic particle imaging system, characterized in that: The system includes: An imaging and control unit, configured to generate a control command for magnetic field change and send it to the signal acquisition and output module; and further configured to execute an imaging algorithm based on the received magnetic particle response signal to perform magnetic particle image reconstruction; The signal acquisition and output module receives the control command, performs digital-to-analog conversion, and transmits the control command to the drive scanning power amplifier module to amplify the excitation magnetic field current in the control command, and then applies the amplified excitation magnetic field current to the drive scanning coil to generate a dynamic excitation magnetic field; The signal acquisition and output module transmits the control command after digital-to-analog conversion to the multi-channel gradient power amplifier module to amplify the gradient magnetic field current in the control command, and applies the amplified gradient magnetic field current to the stacked gradient coil unit to generate a static magnetic field, which is superimposed with the dynamic excitation magnetic field to generate an axially highly uniform FFL to scan the object to be imaged in the imaging space; The signal acquisition and output module receives the magnetic particle response signal processed by the signal processing unit and transmits it to the imaging and control unit after performing analog-to-digital conversion; the magnetic particle response signal is collected by the detection coil; The stacked gradient coil unit comprises four groups of coils, two groups forming a pair, the two groups of coils in each pair being symmetrically arranged with the same axis; the two pairs of axes being orthogonal; each group of coils being formed by stacking n layers of annular coils; The diameters of the n layers of annular coils in each group of coils increase from the inside to the outside; The drive scanning coil comprises four saddle-shaped coils, which are respectively arranged on the inner sides of the four groups of coils of the stacked gradient coil unit; The detection coil comprises four saddle-shaped coils, and the four saddle-shaped coils are respectively arranged in the middle of the inner side of the saddle-shaped coils adjacent to the driving scanning coil.

2. The stacked high uniformity magnetic field free line magnetic particle imaging system according to claim 1, characterized in that: The magnetic fields generated by the two coils in each pair of the stacked gradient coil units have the same amplitude and opposite phases; The magnetic field amplitudes of two adjacent layers in each group of coils are the same and the phases are opposite.

3. The stacked high uniformity magnetic field free line magnetic particle imaging system according to claim 2, characterized in that: The magnetic field amplitudes are the same and the phases are opposite, which is achieved by setting two adjacent layers of coils in each group of coils in reverse current mode and controlling the current ratio.

4. The stacked high uniformity magnetic field free line magnetic particle imaging system according to claim 1, characterized in that: The saddle-shaped coils in the driving scanning coil and the detecting coil are coils wound by litz wire.

5. The stacked high uniformity magnetic field free line magnetic particle imaging system according to claim 1, characterized in that: The signal processing unit processes including compensation, filtering and amplification.

6. The stacked high uniformity magnetic field free line magnetic particle imaging method according to claim 1, characterized in that: A current is passed through each set of coils, and the current is a sinusoidal alternating current: ； In the formula, Indicates Group The current of the layer changes with time changes; Indicates Group The amplitude of the layer current; Indicates the frequency of alternating current, Indicates Group The initial phase of the layer current.

7. A stacked high uniformity magnetic field free line magnetic particle imaging method according to claim 6, characterized in that: Said for: ,in, is the current proportionality coefficient, Indicates Group The amplitude of the layer current.

8. The stacked high uniformity magnetic field free line magnetic particle imaging method according to claim 6, characterized in that: The current control ratio of the two adjacent layers of coils in each group of coils is: ； ； In the formula, For the Group Sheet current, For the Group Sheet current, , , and In between is the reverse current mode, is the current proportionality coefficient, For the The conversion efficiency of the layer, Adjust the parameters for uniformity.

9. A stacked high uniformity magnetic field free line magnetic particle imaging method, based on a stacked high uniformity magnetic field free line magnetic particle imaging system according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: Step 1, using the imaging and control unit to generate a control command for magnetic field change, and sending the control command to the signal acquisition and output module; Step 2: In the signal acquisition and output module, the received control command is converted into digital-to-analog format; the control command after the digital-to-analog conversion is transmitted to the drive scanning power amplifier module and the multi-channel gradient power amplifier module; Step 3, in the drive scanning power amplifier module, amplify the excitation magnetic field current in the control command; apply the amplified excitation magnetic field current to the drive scanning coil to generate a dynamic excitation magnetic field; in the multi-channel gradient power amplifier module, amplify the gradient magnetic field current in the control command; apply the amplified gradient magnetic field current to the stacked gradient coil unit to generate a static magnetic field; the static magnetic field is superimposed on the dynamic excitation magnetic field to generate an FFL with high axial uniformity for scanning the object to be imaged in the imaging space; Step 4, using the detection coil to collect the response signal of the magnetic particles in the object to be imaged; transmitting the collected magnetic particle response signal to the signal processing unit for processing; after processing, entering the signal acquisition and output module, performing analog-to-digital conversion on the processed magnetic particle response signal; transmitting the analog-to-digital converted signal to the imaging and control unit; Step 5: In the imaging and control unit, an imaging algorithm is executed based on the received magnetic particle response signal to perform magnetic particle image reconstruction.

Images