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

Abstract

The invention belongs to the technical field of magnetic particle imaging, particularly relates to a stacked high-uniformity magnetic field free line magnetic particle imaging system and method, and aims to solve the problems that magnetic field free lines in an existing FFL-MPI are not uniform, imaging resolution is not uniform, and circumferential artifacts exist. The system comprises a laminated gradient coil unit composed of N groups of symmetrical coil pairs, each group comprising n layers of coils with increasing diameters, and a saddle-shaped driving scanning coil and a detection coil; through a reverse current mode of two adjacent layers of coils, the magnetic field amplitude is opposite to the current direction, the non-uniformity of the magnetic field is compensated, and a high-uniformity FFL gradient field is generated; the control system accurately collects and processes signals, the signals are fed back to the imaging unit after analog-to-digital conversion, amplification and filtering, and imaging is reconstructed through an imaging algorithm. According to the invention, the problems of non-uniform resolution and circumferential artifacts caused by non-uniform magnetic field are solved, and the imaging quality of FFL-MPI equipment is remarkably improved.

Description

Technical Field

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

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

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

[0004] The traditional FFL-MPI device has an uneven magnetic field generated by a single coil, which causes the magnetic field free line to be wide on both sides and narrow in the middle, resulting in problems such as uneven imaging resolution and circular artifacts. Summary of the invention

[0005] In order to solve the above-mentioned problems in the prior art, namely, the problem of non-uniform magnetic field free lines in the existing FFL-MPI, and the problem of non-uniform imaging resolution and circumferential artifacts, the first aspect of the present invention proposes a stacked high-uniform magnetic field free line magnetic particle imaging system, the system comprising: 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 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.

[0006] In some preferred embodiments, the magnetic fields generated by the two coils in each pair of the stacked gradient coil unit 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.

[0007] In some preferred embodiments, 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 to reverse current modes and controlling the current ratio.

[0008] In some preferred embodiments, the saddle coils in the drive scanning coil and the detection coil are coils wound by litz wire.

[0009] In some preferred embodiments, the signal processing unit processes compensation, filtering, and amplification.

[0010] In some preferred embodiments, the diameters of the n layers of annular coils in each group of coils increase from the inside to the outside.

[0011] In some preferred embodiments, the current passed through each set of coils is a sinusoidal alternating current, that is: 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.

[0012] In some preferred embodiments, the ,in, is the current proportionality coefficient, Indicates Group The amplitude of the layer current.

[0013] In some preferred embodiments, the current control ratio of two adjacent layers of coils in each group of coils of the stacked gradient coil unit 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.

[0014] The second invention of the present invention provides a stacked high uniformity magnetic field free line magnetic particle imaging method. Based on the stacked high uniformity magnetic field free line magnetic particle imaging system, 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.

[0015] Beneficial effects of the present invention: 1. Optimization of stacked gradient coils: The stacked gradient coils are composed of N groups of symmetrical coil pairs, each group of coils is composed of n layers of coils stacked together. The optimal solution for each group of coils is that the diameter of each layer of coils increases gradually from bottom to top, and a driving scanning coil is arranged in a matching manner, specifically a saddle-shaped coil, which is arranged in the aperture direction. The detection coil is arranged in the driving scanning coil, and the N groups of saddle-shaped coils are arranged vertically in the radial plane; 2. Reverse current mode setting: Each layer of coils is independently and synchronously controlled according to the control command, and is configured so that the magnetic field amplitude of each group of coils is the same and the direction is opposite. This is achieved by setting the two 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 inhomogeneity of the magnetic field of the adjacent layer, thereby generating a high-uniformity FFL gradient field and achieving uniform distribution and optimization of the overall magnetic field. 3. Precise control and imaging: The control commands of the imaging and control unit are converted into digital signals through the signal acquisition and output module, amplified by the power amplifier, and stacked gradient coils and scanning coils are applied. The signal processing unit amplifies and filters the particle signals detected by the detection coils, and the digital-to-analog conversion is fed 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 command to solve the problem of uneven free lines of the magnetic field, as well as the problem of uneven resolution and circular artifacts in the imaging. The overall quality of the imaging is further improved through the precise sampling feedback of the particle signal and the reconstruction of the imaging algorithm. In summary, the stacked gradient coil and its control system of the present invention achieve uniform distribution and optimization of the overall magnetic field through optimized design and precise control, thereby improving the overall quality of magnetic resonance imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 It is a block diagram of a stacked high-uniform magnetic field free-line magnetic particle imaging system of the present invention.

[0017] Figure 2 This is a four-layer structure example of the stacked gradient coil of the present invention. 。

[0018] Figure 3 It is a side cross-sectional view of a four-layer structure example of the stacked gradient coil of the present invention.

[0019] Figure 4 It is a comparison diagram of the magnetic field uniformity distribution simulation of the traditional FFL magnet and the stacked gradient coil of the present invention.

[0020] Figure 5 It is a flow chart of a stacked high-uniform magnetic field free-line magnetic particle imaging method of the present invention.

[0021] Figure 1 Among them, 1. Imaging and control unit; 2. Signal acquisition and output module; 3. Drive scanning power amplifier module; 4. Multi-channel gradient power amplifier module; 5. Signal processing unit; 6. Stacked gradient coil unit; 7. Drive scanning coil; 8. Detection coil. DETAILED DESCRIPTION

[0022] The present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the relevant invention are shown in the accompanying drawings.

[0023] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] In order to more clearly explain the stacked high uniformity magnetic field free line magnetic particle imaging system of the present invention, the following is combined with Figures 1 to 5 Each step in the embodiment of the present invention is described in detail.

[0025] A stacked high uniformity magnetic field free line magnetic particle imaging system according to the first embodiment of the present invention is shown in FIG. Figure 1 , the system comprises: The imaging and control unit 1 is configured to generate a control command for a magnetic field change and send it to the signal acquisition and output module 2, and is also configured to execute an imaging algorithm based on the received magnetic particle response signal to perform magnetic particle image reconstruction; Signal acquisition and output module 2, with a high sampling frequency computing unit (generally ), configured as: Receive the control command of the imaging and control unit 1, perform digital-to-analog conversion, and transmit the control command after digital-to-analog conversion to the drive scanning 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 scanning coil 7 to generate a dynamic excitation magnetic field; The signal acquisition and output module 2 is further configured to: transmit the control command after digital-to-analog conversion 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; The signal acquisition and output module 2 receives the magnetic particle response signal processed by the signal processing unit 5 and transmits it to the imaging and control unit 1 after performing analog-to-digital conversion. The magnetic particle response signal is acquired by the detection coil 8, and the acquired signal is transmitted to the imaging and control unit 1 after performing analog-to-digital conversion, and image reconstruction is performed according to a predetermined reconstruction algorithm; In this embodiment, the signal processing unit 5 processes including compensation, filtering, and amplification; In this embodiment, the stacked gradient coil unit 6 includes four groups of coils, two groups form a pair, the two groups of coils in each pair are symmetrically arranged, and the axes are the same; the two pairs of axes are orthogonal; each group of coils is formed by stacking n layers of circular ring coils, and the diameters of the n layers of circular ring coils in each group of coils increase from the inside to the outside; the four groups of coils of the stacked gradient coil unit are wound by litz wire, pure copper wire or hollow copper tube coils; The driving scanning coil 7 generates a dynamic excitation magnetic field, including four saddle-shaped coils, which are respectively arranged inside the four groups of coils of the stacked gradient coil unit 6 and arranged in a circumferential direction (x direction in the figure), and the saddle-shaped coils are all coils wound by litz wires; The detection coil 8 is used to detect or collect radial component signals of magnetic particle magnetization, that is, magnetic particle response signals, and includes four saddle-shaped coils, all of which are coils wound by litz wire. It is explained here that the four saddle-shaped coils of the detection coil 8 are smaller in size than the four saddle-shaped coils of the drive scanning coil 7. The specific size and shape can be adjusted according to actual needs and are not limited here. The position (the four saddle-shaped coils of the detection coil 8) is arranged in the drive scanning coil 7, specifically, respectively arranged in the middle of the inner side of the adjacent saddle-shaped coils of the drive scanning coil 7, that is, two groups form a pair, and the two groups of coils in each pair are symmetrically arranged with the same axis; the two pairs of axes are orthogonal, and the four saddle-shaped coils of the detection coil 8 are 45 degrees apart from the four saddle-shaped coils of the drive scanning coil 7 in the radial circumferential direction to ensure the uniformity and symmetry of the detection coil 8, and the axis of the detection coil 8 is consistent with the axis of the drive scanning coil 7 and the stacked gradient coil unit 6; In this embodiment, the magnetic fields generated by the two coils in each pair of the stacked gradient coil unit 6 have the same amplitude and opposite phases; The magnetic field amplitudes of the two adjacent layers in each group of coils are the same and the phases are opposite, which is achieved by setting the two adjacent layers of coils in reverse current mode and controlling the ratio. Specifically, in each group of coils, the first layer and the second layer are set in reverse current mode, and the magnetic field generated by the first layer is used to compensate for the inhomogeneity of the magnetic field generated by the second layer. Similarly, the third and fourth layers are in reverse current mode, and the current ratio 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 (magnetic field conversion efficiency), Adjust parameters for uniformity; And by observing the uniformity of FFL, the k uniformity adjustment parameter can be adjusted to achieve active control of FFL uniformity; In this embodiment, see Figure 2 , taking a four-group, four-layer stacked gradient coil structure as an example, a detailed description is given: 611~614, 621~624, 631~634, 641~644 are four groups of coils. The magnetic field generated by the four groups of coils is recorded as , in each group The layer coil is recorded as The magnetic field generated is recorded as , the coil groups 611~614 and 631~634 are symmetrically distributed and have the same magnetic field amplitude but opposite directions, that is, ; 621~624 and 641~644 coil groups are symmetrically distributed and have the same magnetic field amplitude but opposite directions, that is, ; The four coils work together to produce the FFL in the x-axis direction; After the FFL is generated, the FFL needs to be moved and scanned for encoding space. Each set of coils is fed with the gradient magnetic field current in the control command, that is, the sinusoidal alternating current, namely That is, each group of coils in each layer is independently controlled synchronously, and the current is controlled according to Independent control, where for: ,in, 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, is the uniformity adjustment parameter; Group, The amplitude of the layer current is , and there is , in, is the current proportionality coefficient, Indicates Group The amplitude of the layer 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 Initial phase of layer current; Correspondingly, the driving scanning coil 7 is composed of four groups of saddle-shaped coils, which are arranged in the aperture direction (x direction in the figure) and are wound by litz wires. The winding axes of the four groups of saddle-shaped coils are consistent with the axes of the four groups of gradient coils. The magnetic field generated by the driving scanning coil is superimposed on the magnetic field generated by the above-mentioned gradient coils, and the FFL is rapidly excited in a direction perpendicular to the FFL to drive the particles to generate response signals. Correspondingly, the detection coil 8 is arranged in the drive scanning coil 7, which is four groups of saddle-shaped coils arranged vertically in the radial plane. The axis of the coil pair is consistent with the axis of the surrounding drive scanning coil and gradient coil, and is used to detect the radial component signal of the magnetization of the magnetic particles. After filtering and amplification by the signal processing unit 5, it is input to the imaging and control unit 1 via the signal acquisition module 2 and image reconstruction is performed according to a predetermined reconstruction algorithm.

[0026] It should be noted that the stacked high uniformity magnetic field free line magnetic particle imaging system provided in the above embodiment is only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the modules or steps in the embodiments of the present invention can be decomposed or combined. For example, the modules in the above embodiment can be combined into one module, or further divided 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 the modules or steps, and are not regarded as improper limitations of the present invention.

[0027] The second embodiment of the present invention, see Figure 5 , a stacked high uniformity magnetic field free line magnetic particle imaging method, the method comprising 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.

[0028] In summary, the gradient magnetic field current is controlled by the imaging and control unit 1 according to the individual control strategy of each group and each layer of coils. The signal is generated, outputted through the signal acquisition and output module 2, and amplified and provided by the multi-channel gradient power amplifier module 4; the excitation magnetic field current for driving the scanning coil 7 is generated by the imaging and control unit 1, outputted through the signal output module 2, and amplified and provided 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 inputted by the signal acquisition and output module 2 to the imaging and control unit 1 for algorithm reconstruction.

[0029] Figure 4 This 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. Through further calibration, the gradient can be made more uniform along the axial direction.

[0030] Although the various steps in the above embodiment are described in the above-mentioned order, those skilled in the art can understand that in order to achieve the effect 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 reverse order. These simple changes are within the scope of protection of the present invention.

[0031] Those skilled in the art should be able to appreciate that the modules and method steps of each example described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, computer software, or a combination of the two, and the programs corresponding to the software modules and method steps can be placed in random access memory (RAM), memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disks, removable disks, CD-ROMs, or any other form of storage medium known in the technical field. In order to clearly illustrate the interchangeability of electronic hardware and software, the composition and steps of each example have been generally described in the above description according to the function. Whether these functions are performed in 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.

[0032] The terms "first", "second", etc. are used to distinguish similar objects rather than to describe or indicate a particular order or sequence.

[0033] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that includes a list of elements includes not only those elements but also other elements not expressly listed, or also includes elements inherent to such process, method, article, or apparatus / device.

[0034] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand 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 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 system according to claim 1, characterized in that: The diameters of the n layers of annular coils in each group of coils increase sequentially from the inside to the outside.

7. A stacked high uniformity magnetic field free line magnetic particle imaging method according to claim 6, 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.

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

9. The stacked high uniformity magnetic field free line magnetic particle imaging method according to claim 7, 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.

10. 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 9, 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