CN115778353B - Magnetic field free line magnetic particle imaging method based on rotation harmonic diagram - Google Patents

Abstract

The invention belongs to the technical field of magnetic particle imaging, in particular relates to a magnetic field free line magnetic particle imaging method, a magnetic field free line magnetic particle imaging system and magnetic field free line magnetic particle imaging equipment based on a rotation harmonic diagram, and aims to solve the problems that a measuring process of a system matrix of the existing magnetic particle imaging method is complex, time consuming, large in occupied memory and long in calculation time, system correction efficiency of the magnetic particle imaging equipment is severely limited, and imaging instantaneity is low. The method comprises the following steps: setting related parameters of a magnetic particle imaging device based on a magnetic field free line, and starting and operating the magnetic particle imaging device; constructing system function harmonic graphs of different orders; measuring response signals of a target object to be imaged under each rotation angle and constructing an observation vector sequence; rotating the system function harmonic graphs of different orders to construct a system matrix under each rotation angle; reconstructing a magnetic particle image. The invention constructs the system matrix with other rotation angles by rotating the harmonic diagram, greatly reduces the complexity of system matrix measurement and improves the system correction efficiency of the magnetic particle imaging equipment.

Description

Free-line Magnetic Particle Imaging Method Based on Rotational Harmonic Map

technical field

The invention belongs to the technical field of magnetic particle imaging, and in particular relates to a magnetic particle imaging method, system and equipment based on a rotating harmonic diagram of a magnetic field free line.

Background technique

In recent years, the rapid development of in vivo non-invasive molecular imaging technology has realized the effective observation of various biomolecules in vivo. Magnetic particle imaging technology is based on the nonlinear magnetization response of magnetic nanoparticles for imaging. It has the advantages of high sensitivity, high spatial resolution, no radiation, no background signal interference, and no limitation of imaging depth. It is expected to be applied to deep micro-tumor detection, heart and brain Major clinical issues such as vascular function monitoring.

Magnetic particle imaging uses a combination of magnetic fields, both static and dynamic, to probe the concentration distribution of magnetic nanoparticle tracers. The static magnetic field is an inhomogeneous constant magnetic field, or called a gradient magnetic field. Its prominent feature is that it contains one or more low magnetic field regions, and its shape is usually an elliptical point-shaped free point of the magnetic field or a linear free line of the magnetic field. Magnetic nanoparticles are in a non-saturated state in the low-intensity magnetic field region, and generate signals when excited by an external magnetic field, and are detected by the receiving coil; but in a saturated state in the high-intensity magnetic field region, the signal is weak after being excited and cannot be detected. The dynamic field is a uniform alternating magnetic field, or called an excitation magnetic field, which is used to drive the low magnetic field region to move within the imaging field of view and to excite magnetic nanoparticles to generate nonlinear characteristic signals. Magnetic particle imaging uses an excitation magnetic field to drive a low magnetic field region to scan a specific trajectory within the imaging field of view to complete the spatial encoding of the concentration of magnetic nanoparticles. Compared with the magnetic field free point, the low magnetic field area of the magnetic field free line is larger, the single scan covers a larger area, the signal-to-noise ratio is higher, and the imaging speed is faster. It has been widely studied and applied in recent years.

The reconstruction process from signal to image is an important step in magnetic particle imaging, and one of the important methods is the system matrix method. At present, the steps of the system matrix method are: measure the signal spectrum of the unit sample at each pixel in the imaging field of view, construct a system matrix representing the imaging system in the frequency domain after screening, quantify the signal of the measured object into an observation vector, and establish A system of linear equations, reconstructed by solving a system of linear equations. The magnetic particle imaging system based on the free line of the magnetic field needs to rotate the free line of the magnetic field or the measured object to cover the entire imaging field of view before accurate reconstruction can be performed. Therefore, in the traditional method, the system matrix needs to be measured once every time the free line of the magnetic field or the measured object is rotated at a certain angle. This process is complex, time-consuming, takes up a lot of memory, and takes a long time to calculate, which severely limits the system calibration efficiency of magnetic particle imaging equipment, and it is difficult to perform real-time imaging. Therefore, a more efficient magnetic particle imaging method based on system matrix free lines of magnetic field is needed.

The reason for measuring the system matrix at all angles in the traditional method is that after rotation, the magnetic field is slightly distorted or deformed. Therefore, measuring the system matrix at each rotation angle is the most accurate measurement and modeling method for the imaging system. However, during the rotation process, there is a high degree of information similarity in the system matrix between different angles.

Analyzing the magnetic particle imaging process, the system matrix expresses the harmonic response of each order at each pixel in the imaging field of view, and the harmonic map reflects the spatial response frequency of the system itself. For the free line of the rotating magnetic field, the imaging system itself is rotated by controlling the electrification parameters or mechanically rotating the gradient coil, and it can be considered that the harmonic diagram in the system matrix also rotates with it, but with a slight deformation; for the rotating measured object, the system itself does not Unchanged, but the same rotation is reflected by transforming the coordinate system. Therefore, in the traditional method, there must be highly repetitive information in the system matrix between different angles. Based on this, the present invention proposes a method for magnetic particle imaging of free lines of magnetic field based on rotation harmonic diagram.

Contents of the invention

In order to solve the above problems in the prior art, that is, in order to solve the existing magnetic particle imaging method based on the system matrix, the system matrix needs to be measured once every time the free magnetic field line or the measured object is rotated at a certain angle, and the measurement process is complicated and time-consuming. It takes up a lot of memory and takes a long time to calculate, which seriously limits the system correction efficiency of magnetic particle imaging equipment, and the real-time performance of imaging is low. A magnetic particle imaging device based on free lines of a magnetic field, the method comprising:

Step S100, setting the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, starting and running the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selected magnetic field gradient, excitation magnetic field Amplitude and frequency, digital sampling frequency and time, unit sample size;

Step S200, setting the position and direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field, and combining the imaging field of view radius, setting the moving path of the unit sample; moving the unit sample according to the set moving path, Measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free lines of the magnetic field, and then construct system function harmonic diagrams of different orders; A device for moving samples to designated locations;

Step S300, taking the direction of the system matrix measuring device as the initial direction, setting the rotation angle and the rotation sequence; rotating the magnetic field free lines of the magnetic particle imaging device based on the magnetic field free lines or The target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence;

Step S400, according to the rotation angle, rotate the harmonic diagram of the system function of different orders, and construct the system matrix under each rotation angle based on the rotated harmonic diagram of the system function of different orders;

Step S500, combining the observation vector sequence by column, merging the system matrices under each rotation angle by column, and constructing a linear equation system after merging; solving the linear equation system to obtain the corresponding Reconstructed magnetic particle image.

In some preferred embodiments, the signal of each pixel out of the unit sample is measured, and then the harmonic diagram of the system function of different orders is constructed, and the method is as follows:

Measure the time-domain signal of the unit sample at each pixel, and obtain the frequency spectrum through fast Fourier transform;

According to the signal-to-noise ratio of the magnetic particle imaging device based on the free line of magnetic field, filter the harmonic signal whose signal-to-noise ratio is greater than the set signal-to-noise ratio threshold, and use the filtered harmonic signal as the first harmonic signal; based on the said Spectrum, the first harmonic signals of the same order at each pixel are synthesized to obtain system function harmonic diagrams of different orders.

In some preferred implementations, the rotation angle and rotation sequence are set, and the method is as follows:

Taking the initial direction as 0°, stepping and rotating to 180° according to equal intervals or unequal intervals, ensuring that the range of motion of the free line of the magnetic field can cover the entire imaging field of view, and rotate N angles in total; where N represents the set number .

In some preferred embodiments, the response signal of the target object to be imaged at each rotation angle is measured and the observation vector sequence is constructed, the method is:

Measure the response signal of the target object to be imaged at each rotation angle and construct the observation column vector at the current rotation angle, and then construct the observation vector sequence at all rotation angles;

The observation column vector is the characteristic harmonic used to extract the response signal of the target object to be imaged at the corresponding rotation angle according to the characteristic harmonic used by the system matrix in the initial direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field Column vector of wave builds.

In some preferred embodiments, when rotating the harmonic diagram of the system function of different orders, it is decomposed into a real part harmonic diagram and an imaginary part harmonic diagram, and synthesized into a complex harmonic diagram after rotation;

Keep the size of the image unchanged after rotating the harmonic diagram of the system function of different orders, use zero padding at the non-grid pixel points, and use the interpolation method to round the non-grid pixel points.

In some preferred embodiments, construct linear equation system, its method is:

; ; ;

in, Represents the system matrix {A _1, A ₂ , ..., A _N } at each rotation angle to merge the system matrix by column, Represents the observation vector after all the observation vectors in the observation vector sequence {b ₁ , b ₂ , ..., b _N } are merged by columns, A discrete vector form representing the target object to be imaged.

In the second aspect of the present invention, a magnetic field free-line magnetic particle imaging system based on a rotating harmonic diagram is proposed. The system includes: an initialization setting module, a harmonic diagram building module, an observation vector building module, a system matrix building module, an image rebuild module;

The initialization setting module is configured to set the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, start and run the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selection Magnetic field gradient, excitation magnetic field amplitude and frequency, digital sampling frequency and time, unit sample size;

The harmonic diagram construction module is configured to set the position and direction of the system matrix measurement device in the magnetic particle imaging device based on free lines of magnetic field, and combine the imaging field of view radius to set the moving path of the unit sample; according to the setting Move the unit sample according to the moving path, measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free line of magnetic field, and then construct the harmonic diagram of the system function of different orders; the system matrix measurement device is A device that moves a unit sample to a designated location according to a set movement path;

The observation vector construction module is configured to take the direction of the system matrix measurement device as the initial direction, set the rotation angle and the rotation sequence; rotate the magnetic particle imaging based on the free line of the magnetic field according to the rotation angle and the rotation sequence The free line of the magnetic field of the device or the target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence;

The system matrix construction module is configured to rotate the system function harmonic diagrams of different orders according to the rotation angle, and construct the system matrix at each rotation angle based on the rotated system function harmonic diagrams of different orders;

The image reconstruction module is configured to combine the observation vector sequence by column, and combine the system matrices under each rotation angle by column. After the combination, construct a linear equation system; solve the linear equation system to obtain The imaged target object corresponds to the reconstructed magnetic particle image.

In a third aspect of the present invention, an electronic device is proposed, including: at least one processor; and a memory connected to at least one processor in communication; wherein, the memory stores instructions executable by the processor , the instructions are used to be executed by the processor to implement the above method for magnetic particle imaging of free lines of magnetic field based on rotational harmonic diagrams.

According to the fourth aspect of the present invention, a computer-readable storage medium is proposed, the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to realize the above-mentioned rotating harmonic diagram-based Magnetic field free-line magnetic particle imaging method.

Beneficial effects of the present invention:

The present invention proposes to measure the system matrix at only one angle, and construct the system matrix of other rotation angles by rotating the harmonic diagram, and then complete the construction of all system matrices. This method will greatly reduce the complexity of system matrix measurement, reduce memory resource requirements, improve the system calibration efficiency of magnetic particle imaging equipment, and improve the real-time performance of magnetic particle imaging.

Description of drawings

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.

Fig. 1 is a schematic flow chart of a method for magnetic particle imaging of free lines of magnetic field based on a rotating harmonic diagram according to an embodiment of the present invention;

FIG. 2 is a schematic framework diagram of a magnetic particle imaging method based on a rotating harmonic diagram of a magnetic field free line according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of the free lines of the magnetic field or the target object to be imaged in the rotating magnetic particle imaging device according to an embodiment of the present invention;

Fig. 4 is a schematic diagram of the process of constructing a system matrix in a traditional method of an embodiment of the present invention and the method of the present invention;

Fig. 5 is an example diagram of the harmonic diagram of the second, third and fourth system functions of rotation in an embodiment of the present invention;

Fig. 6 is a schematic diagram of a standard phantom and a reconstructed magnetic particle image of a target object according to an embodiment of the present invention;

Fig. 7 is a schematic structural diagram of a computer system suitable for realizing the electronic device of the embodiment of the present application according to an embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain related inventions, rather than to limit the invention. It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

A method of magnetic particle imaging based on free lines of magnetic field based on rotational harmonic diagrams in the first embodiment of the present invention is applied to a magnetic particle imaging device based on free lines of magnetic field; as shown in FIG. 1 , the method includes:

Step S100, setting the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, starting and running the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selected magnetic field gradient, excitation magnetic field Amplitude and frequency, digital sampling frequency and time, unit sample size;

Step S200, setting the position and direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field, and combining the imaging field of view radius, setting the moving path of the unit sample; moving the unit sample according to the set moving path, Measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free lines of the magnetic field, and then construct system function harmonic diagrams of different orders; A device for moving samples to designated locations;

Step S300, taking the direction of the system matrix measuring device as the initial direction, setting the rotation angle and the rotation sequence; rotating the magnetic field free lines of the magnetic particle imaging device based on the magnetic field free lines or The target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence;

Step S400, according to the rotation angle, rotate the harmonic diagram of the system function of different orders, and construct the system matrix under each rotation angle based on the rotated harmonic diagram of the system function of different orders;

Step S500, combining the observation vector sequence by column, merging the system matrices under each rotation angle by column, and constructing a linear equation system after merging; solving the linear equation system to obtain the corresponding Reconstructed magnetic particle image.

In order to more clearly describe a magnetic particle imaging method for free lines of magnetic field based on rotational harmonic diagrams of the present invention, the steps in an embodiment of the method of the present invention will be described in detail below in conjunction with the accompanying drawings.

Step S100, setting the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, starting and running the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selected magnetic field gradient, excitation magnetic field Amplitude and frequency, digital sampling frequency and time, unit sample size;

In this embodiment, the related parameters of the magnetic particle imaging device based on free lines of magnetic field are first initialized, and the related parameters include imaging field of view radius, selected magnetic field gradient, excitation magnetic field amplitude and frequency, digital sampling frequency and time, and unit sample size. After initialization, turn on and run the magnetic particle imaging device based on free lines of magnetic field.

Step S200, setting the position and direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field, and combining the imaging field of view radius, setting the moving path of the unit sample; moving the unit sample according to the set moving path, Measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free lines of the magnetic field, and then construct system function harmonic diagrams of different orders; A device for moving samples to designated locations;

In this embodiment, the system matrix measurement device is preferably set as a three-axis translation platform or a mechanical arm, which can move the unit sample (the present invention preferably uses a point sample (called delta phantom in the paper, not available yet) according to the set path. Standard Chinese translation (specific references: Top C , Gungor A . Tomographic Field Free LineMagnetic Particle Imaging With an Open-Sided Scanner Configuration[J]. IEEEtransactions on medical imaging, 2020, 39(12):4164-4173.)) Usually its The shape is the shape of a pixel or a voxel, the cavity is filled with magnetic nanoparticles, and the interior is a cubic particle cavity) to move to a specified position.

First set the position and direction of the system matrix measurement device in the magnetic particle imaging device based on free lines of magnetic field, and combine the imaging field of view radius to set the moving path of the unit sample; then measure the direction (that is, the system matrix measurement device) The system matrix A ₁ of the initial direction) is used as the system benchmark, and the harmonic diagram of the system function of each order is constructed; the details are as follows:

Move the unit sample according to the set moving path, measure the time-domain signal of the unit sample at each pixel, and obtain the spectrum through fast Fourier transform;

According to the signal-to-noise ratio of the magnetic particle imaging device based on the free line of magnetic field, filter the harmonic signal whose signal-to-noise ratio is greater than the set signal-to-noise ratio threshold, and use the filtered harmonic signal as the first harmonic signal; based on the said Spectrum, the first harmonic signals of the same order at each pixel are synthesized to obtain system function harmonic diagrams of different orders. That is, the system function harmonic diagram is all the particle harmonic signals that can be detected under the condition of the signal-to-noise ratio of the current magnetic particle imaging device. The same harmonics are synthesized into harmonic diagrams of system functions of each order, and the harmonic information is complex numbers, and the harmonic diagrams can be decomposed into real part harmonic diagrams and imaginary part harmonic diagrams; the unit sample is the equipped unit used when testing the system matrix The liquid-carrying cavity with the same concentration of magnetic nanoparticles and the same size as the highest resolution imaging device of the magnetic particle imaging device based on free lines of magnetic field.

Step S300, taking the direction of the system matrix measuring device as the initial direction, setting the rotation angle and the rotation sequence; rotating the magnetic field free lines of the magnetic particle imaging device based on the magnetic field free lines or The target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence;

In this embodiment, it is preferable to take the initial direction as 0°, and step and rotate to 180° according to equal or unequal intervals, so as to ensure that the range of motion of the free lines of the magnetic field can cover the entire imaging field of view (that is, the requirement of the rotation sequence) , a total of N angles are rotated; wherein, N represents the set number, in this embodiment, it is greater than or equal to 9, and in other embodiments, it can be set according to the actual situation.

Rotate the free lines of the magnetic field or the target object to be imaged of the magnetic particle imaging device based on the free line of magnetic field according to the rotation angle and the rotation sequence, measure the response signals of the target object to be imaged at each rotation angle and construct an observation vector sequence, its methods are:

Rotate the free lines of the magnetic field or the target object to be imaged of the magnetic particle imaging device based on the free line of magnetic field according to the rotation angle and the rotation sequence, measure the response signal of the target object to be imaged at each rotation angle and construct the current rotation The observation column vector under the angle, and then construct the observation vector sequence under all rotation angles; The observation column vector is the feature used according to the system matrix under the initial direction of the system matrix measurement device in the magnetic particle imaging device based on free lines of magnetic field The harmonic extraction is a column vector constructed by the characteristic harmonics of the response signal of the target object to be imaged corresponding to the rotation angle.

Step S400, according to the rotation angle, rotate the harmonic diagram of the system function of different orders, and construct the system matrix under each rotation angle based on the rotated harmonic diagram of the system function of different orders;

In this embodiment, when the system function harmonic diagrams of different orders are rotated, they are decomposed into real part harmonic diagrams and imaginary part harmonic diagrams, and synthesized into complex harmonic diagrams after rotation;

Keep the size of the image unchanged after rotating the harmonic diagram of the system function of different orders, use zero padding at the non-grid pixel points, and use the interpolation method to round the non-grid pixel points.

The system matrix under each rotation angle is expressed as {A _1, A ₂ , ..., A _N }.

Step S500, combining the observation vector sequence by column, merging the system matrices under each rotation angle by column, and constructing a linear equation system after merging; solving the linear equation system to obtain the corresponding Reconstructed magnetic particle image.

In this embodiment, construct linear equation system, its method is:

; ; ;

in, Represents the system matrix {A _1, A ₂ , ..., A _N } at each rotation angle to merge the system matrix by column, Represents the observation vector after all the observation vectors in the observation vector sequence {b ₁ , b ₂ , ..., b _N } are merged by columns, A discrete vector form representing the target object to be imaged.

Then, the linear equations are solved to obtain a reconstructed magnetic particle image corresponding to the target object to be imaged.

Among them, when solving the linear equation system, it is preferable to use a regularized iterative solution algorithm, specifically: use the L2 norm to establish an objective function, and use the kaczmarz algorithm to iteratively solve it. The technical method in the paper: use the L1 norm and TV norm to establish the objective function, and use the ADMM algorithm to iteratively solve it.

In addition, in order to further verify the effectiveness of the method of the present invention, an example is given below.

In this embodiment, the magnetic particle imaging device based on free lines of magnetic field preferably adopts an open free line of magnetic field magnetic particle imaging system, wherein the radius of the imaging field of view is set to 20 mm, and the magnetic particle imaging method based on free lines of magnetic field is shown in Figure 3 Free line of rotating magnetic field or rotating object to be measured. Select the magnetic field H _SF gradient to be set to 1T/m, the driving magnetic field uses a high-frequency low-amplitude sinusoidal alternating magnetic field H _DF , the focusing magnetic field H _FF uses a low-frequency high-amplitude sinusoidal alternating magnetic field, and the synthetic magnetic particle imaging system magnetic field H=H _SF +H _DF + H _FF .

Among them, the amplitude of the driving magnetic field is A _DF =8mT, and the frequency is f _DF =2500 Hz, namely

(1)

The amplitude of the focusing magnetic field is A _FF =14mT, and the frequency is f _DF =20 Hz, namely

(2)

The sampling rate in the digital sampling process is 1 MHz, and the sampling time is 1 second. A three-axis translation stage is used as the measurement device for the measurement system matrix. The size of the test system matrix is set to 20 rows and 20 columns, and the size of each pixel is 2 mm.

The particles used in the test are superparamagnetic nano-iron oxide particles, and the particle model can be roughly understood as the particles described by the adiabatic Langevin model: ,in For the properties of the particle itself and the measurement of environmental parameters.

Then fix the translation stage first, move the magnetic particle imaging device away from the translation platform appropriately, and take the direction of the detection rod of the current translation platform as the initial direction, that is, 0°. When measuring the system matrix, move the test sample (that is, The target object), the unit sample is set to a 2 mm cubic liquid-carrying cavity filled with the concentration of the test particle stock solution, and the magnetic particle imaging device based on the free line of the magnetic field is turned on.

Measure the signal of the unit sample at each pixel, use the fast Fourier transform to obtain the spectrogram, select the 2nd, 3rd, 4th, 5th, 6th, and 7th order harmonics as the particle signal according to the signal-to-noise ratio of the imaging device, and take into account the fundamental frequency signal Direct feedthrough interference is excluded. After testing the signals of all pixels in the field of view, the harmonic diagrams of the 2nd, 3rd, 4th, 5th, 6th, and 7th order particle signals are respectively established.

Taking the shepp-logan head model as the standard test phantom, as shown in (a) in Figure 6, the rotation sequence is set to clockwise, with a step angle of 3.6°, and a total of 50 angles are rotated. Rotate the shepp-logan head model according to the rotation sequence, measure the signal of the particle response at each angle, and use the 2, 3, 4, 5, 6, 7 order harmonics to establish the observation vector {b ₁ , b ₂ , ..., b _N }.

According to the same order of rotation angles, the system function harmonic diagrams of each order established according to the system matrix at the initial angle are rotated, as shown in (b) in Figure 4, and the system function harmonic diagrams at all angles are obtained. The traditional method of building a system proof, as shown in (a) in Figure 4.

(a), (b), and (c) in Figure 5 are particles with initial angles, 36° rotation, and 72° rotation (that is, rotation angle 1, rotation angle 2, and rotation angle 3, the same as in Figure 4) Signal 2, 3, 4 order harmonic diagram. The harmonic diagram of each order is established as the system matrix {A _1, A ₂ , ..., A _N } under the corresponding angle.

Merge all system matrices into system matrix A by columns, merge all observation vectors into observation vector b by columns, establish the linear equations of the imaging system of the object to be measured, and use the regularized kaczmarz method to solve the linear equations, and set the regularization parameters is 0.001, the number of iterations is set to 1000, and x is obtained. Finally, x is rearranged into the image of the target object to be imaged, as shown in (b) in Fig. 6 .

A magnetic field free-line magnetic particle imaging system based on a rotating harmonic diagram according to the second embodiment of the present invention, as shown in FIG. 2 , the system includes: an initialization setting module 100, a harmonic diagram construction module 200, and an observation vector construction module 300 , system matrix construction module 400, image reconstruction module 500;

The initialization setting module 100 is configured to set the relevant parameters of the magnetic particle imaging device, start and run the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selection of magnetic field gradient, excitation Magnetic field amplitude and frequency, digital sampling frequency and time, unit sample size;

The harmonic diagram construction module 200 is configured to set the position and direction of the system matrix measurement device in the magnetic particle imaging device based on free lines of magnetic field, and combine the imaging field of view radius to set the movement path of the unit sample; according to the design Move the unit sample with a predetermined moving path, measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free line of magnetic field, and then construct the harmonic diagram of the system function of different orders; the system matrix measurement device It is a device that moves the unit sample to a designated position according to a set movement path;

The observation vector construction module 300 is configured to take the direction of the system matrix measuring device as the initial direction, set the rotation angle and the rotation sequence; rotate the magnetic particles based on the free lines of the magnetic field according to the rotation angle and the rotation sequence The magnetic field free line of the imaging device or the target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence;

The system matrix construction module 400 is configured to rotate the system function harmonic diagrams of different orders according to the rotation angle, and construct the system matrix at each rotation angle based on the rotated system function harmonic diagrams of different orders;

The image reconstruction module 500 is configured to combine the observation vector sequence by column, combine the system matrices under each rotation angle by column, and construct a linear equation system after the combination; solve the linear equation system to obtain The target object to be imaged corresponds to the reconstructed magnetic particle image.

Those skilled in the technical field can clearly understand that for the convenience and brevity of the description, the specific working process and relevant descriptions of the above-described system can refer to the corresponding process in the foregoing method embodiments, and will not be repeated here.

It should be noted that the magnetic field free line magnetic particle imaging system based on the rotating harmonic diagram provided in the above embodiment is only illustrated by the division of the above functional modules. In practical applications, the above functions can be allocated by different functional modules, that is, to decompose or combine the modules or steps in the embodiments of the present invention. For example, the modules in the above embodiments can be combined into one module, or can be further split into multiple sub-modules to complete the above-described full or partial functionality. The names of the modules and steps involved in the embodiments of the present invention are only used to distinguish each module or step, and are not regarded as improperly limiting the present invention.

An electronic device according to the third embodiment of the present invention includes at least one processor; and a memory communicatively connected to at least one of the processors; wherein, the memory stores instructions executable by the processor, and the instructions It is used to be executed by the processor to realize the magnetic particle imaging method based on the rotational harmonic diagram of the above-mentioned claims.

A computer-readable storage medium according to the fourth embodiment of the present invention, the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to realize the above-mentioned magnetic field freedom based on the rotation harmonic diagram Line Magnetic Particle Imaging Methods.

Those skilled in the technical field can clearly understand that for the convenience and brevity of the description, the specific working process and related instructions of the electronic device and the computer-readable storage medium described above can refer to the corresponding process in the aforementioned method example. This will not be repeated here.

Referring now to FIG. 7 , it shows a schematic structural diagram of a server computer system suitable for implementing the method, system, and device embodiments of the present application. The server shown in FIG. 7 is only an example, and should not limit the functions and scope of use of this embodiment of the present application.

As shown in Figure 7, the computer system includes a central processing unit (CPU, Central Processing Unit) 701, which can be stored in a program in a read-only memory (ROM, Read Only Memory) 702 or loaded into a random access memory from a storage section 708 (RAM, Random Access Memory) 703 to execute various appropriate actions and processing. In RAM 703, various programs and data necessary for system operation are also stored. The CPU 701 , ROM 702 , and RAM 703 are connected to each other via a bus 704 . An input/output (I/O, Input/Output) interface 705 is also connected to the bus 704 .

The following components are connected to the I/O interface 705: an input section 706 including a keyboard, a mouse, etc.; an output section 707 including a cathode ray tube (CRT, Cathode Ray Tube), a liquid crystal display (LCD, Liquid Crystal Display) etc., and a speaker ; a storage section 708 comprising a hard disk, etc.; and a communication section 709 comprising network interface cards such as LAN (Local Area Network, Local Area Network) cards, modems, etc. The communication section 709 performs communication processing via a network such as the Internet. A drive 710 is also connected to the I/O interface 705 as needed. A removable medium 711 such as a magnetic disk, optical disk, magneto-optical disk, semiconductor memory, etc. is mounted on the drive 710 as necessary so that a computer program read therefrom is installed into the storage section 708 as necessary.

In particular, according to an embodiment of the present disclosure, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present disclosure include a computer program product, which includes a computer program carried on a computer-readable medium, where the computer program includes program codes for executing the methods shown in the flowcharts. In such an embodiment, the computer program may be downloaded and installed from a network via communication portion 709 and/or installed from removable media 711 . When the computer program is executed by the central processing unit (CPU701), the above-mentioned functions defined in the method of the present application are executed. It should be noted that the computer-readable medium mentioned above in the present application can be a computer-readable signal medium or a computer-readable storage medium Or any combination of the above two. Computer-readable storage media can be, for example—but not limited to—electric, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or devices, or any combination of the above. Computer More specific examples of readable storage media may include, but are not limited to, electrical connections with one or more wires, portable computer diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable Read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination of the above. In this application, the computer-readable storage medium can be Is any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, device, or device. In this application, a computer-readable signal medium can be included in the baseband or propagated as part of a carrier wave A data signal, which carries computer-readable program code. This propagated data signal can take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. Computer-readable signal media can also Any computer-readable medium, other than a computer-readable storage medium, that can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device. Contained on a computer-readable medium Program code may be transmitted using any suitable medium, including but not limited to: wireless, wire, optical fiber cable, RF, etc., or any suitable combination of the above.

Computer program code for performing the operations of the present application may be written in one or more programming languages or combinations thereof, including object-oriented programming languages—such as Java, Smalltalk, C++, and conventional Procedural Programming Language - such as "C" or a similar programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In cases involving a remote computer, the remote computer can be connected to the user computer through any kind of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computer (such as through an Internet service provider). Internet connection).

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present application. In this regard, each block in a flowchart or block diagram may represent a module, program segment, or portion of code that contains one or more logical functions for implementing specified executable instructions. It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or they may sometimes be executed in the reverse order, depending upon the functionality involved. It should also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by a dedicated hardware-based system that performs the specified functions or operations , or may be implemented by a combination of dedicated hardware and computer instructions.

The terms "first", "second", etc. are used to distinguish similar items, and are not used to describe or represent a specific order or sequence.

The term "comprising" or any other similar term is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus/apparatus comprising a set of elements includes not only those elements but also other elements not expressly listed, or Also included are elements inherent in these processes, methods, articles, or devices/devices.

So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings, but those skilled in the art will easily understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims (9)

1. A method for magnetic particle imaging based on free lines of magnetic field based on rotational harmonic diagrams, applied to a magnetic particle imaging device based on free lines of magnetic field, characterized in that the method comprises: Step S100, setting the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, starting and running the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selected magnetic field gradient, excitation magnetic field Amplitude and frequency, digital sampling frequency and time, unit sample size; Step S200, setting the position and direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field, and combining the imaging field of view radius, setting the moving path of the unit sample; moving the unit sample according to the set moving path, Measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free lines of the magnetic field, and then construct system function harmonic diagrams of different orders; A device for moving samples to designated locations; Step S300, taking the direction of the system matrix measuring device as the initial direction, setting the rotation angle and the rotation sequence; rotating the magnetic field free lines of the magnetic particle imaging device based on the magnetic field free lines or The target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence; Step S400, according to the rotation angle, rotate the harmonic diagram of the system function of different orders, and construct the system matrix under each rotation angle based on the rotated harmonic diagram of the system function of different orders; Step S500, combining the observation vector sequence by column, merging the system matrices under each rotation angle by column, and constructing a linear equation system after merging; solving the linear equation system to obtain the corresponding Reconstructed magnetic particle image. 2. the magnetic particle imaging method based on the free line of magnetic field free line according to claim 1, is characterized in that, measure the unit sample at each pixel place in the magnetic particle imaging device imaging field of view based on the free line of magnetic field Signal, and then construct the harmonic diagram of the system function of different order, the method is as follows: Measure the time-domain signal of the unit sample at each pixel, and obtain the frequency spectrum through fast Fourier transform; According to the signal-to-noise ratio of the magnetic particle imaging device based on the free line of magnetic field, filter the harmonic signal whose signal-to-noise ratio is greater than the set signal-to-noise ratio threshold, and use the filtered harmonic signal as the first harmonic signal; based on the said Spectrum, the first harmonic signals of the same order at each pixel are synthesized to obtain system function harmonic diagrams of different orders. 3. the magnetic field free line magnetic particle imaging method based on rotating harmonic diagram according to claim 2, is characterized in that, setting rotation angle and rotation order, its method is: Taking the initial direction as 0°, stepping and rotating to 180° according to equal intervals or unequal intervals, ensuring that the range of motion of the free line of the magnetic field can cover the entire imaging field of view, and rotate N angles in total; where N represents the set number . 4. the magnetic field free line magnetic particle imaging method based on rotating harmonic diagram according to claim 3, it is characterized in that, measure the response signal of the target object to be imaged under each rotation angle and construct observation vector sequence, its method is: Measure the response signal of the target object to be imaged at each rotation angle and construct the observation column vector at the current rotation angle, and then construct the observation vector sequence at all rotation angles; The observation column vector is the characteristic harmonic used to extract the response signal of the target object to be imaged at the corresponding rotation angle according to the characteristic harmonic used by the system matrix in the initial direction of the system matrix measuring device in the magnetic particle imaging device based on free lines of magnetic field Column vector of wave builds. 5. the magnetic field free line magnetic particle imaging method based on rotating harmonic diagram according to claim 1, is characterized in that, when rotating the system function harmonic diagram of different orders, it is decomposed into real part harmonic diagram, imaginary part harmonic graph, synthesized into a complex harmonic graph after rotation; Keep the size of the image unchanged after rotating the harmonic diagram of the system function of different orders, use zero padding at the non-grid pixel points, and use the interpolation method to round the non-grid pixel points. 6. the magnetic field free line magnetic particle imaging method based on rotating harmonic diagram according to claim 1, is characterized in that, constructs linear equations, its method is: ; ; ;in, Represents the system matrix {A _1, A ₂ , ..., A _N } at each rotation angle to merge the system matrix by column, Represents the observation vector after all the observation vectors in the observation vector sequence {b ₁ , b ₂ ,..., b _N } are merged by columns, A discrete vector form representing the target object to be imaged. 7. A magnetic field free-line magnetic particle imaging system based on a rotational harmonic diagram, based on the magnetic field free-line magnetic particle imaging method based on a rotational harmonic diagram according to any one of claims 1-6, characterized in that the system Including: initialization setting module, harmonic diagram building module, observation vector building module, system matrix building module, image reconstruction module; The initialization setting module is configured to set the relevant parameters of the magnetic particle imaging device based on free lines of magnetic field, start and run the magnetic particle imaging device based on free lines of magnetic field; the relevant parameters include imaging field of view radius, selection Magnetic field gradient, excitation magnetic field amplitude and frequency, digital sampling frequency and time, unit sample size; The harmonic diagram construction module is configured to set the position and direction of the system matrix measurement device in the magnetic particle imaging device based on free lines of magnetic field, and combine the imaging field of view radius to set the moving path of the unit sample; according to the setting Move the unit sample according to the moving path, measure the signal of the unit sample at each pixel within the imaging field of view of the magnetic particle imaging device based on the free line of magnetic field, and then construct the harmonic diagram of the system function of different orders; the system matrix measurement device is A device that moves a unit sample to a designated location according to a set movement path; The observation vector construction module is configured to take the direction of the system matrix measurement device as the initial direction, set the rotation angle and the rotation sequence; rotate the magnetic particle imaging based on the free line of the magnetic field according to the rotation angle and the rotation sequence The free line of the magnetic field of the device or the target object to be imaged, measuring the response signal of the target object to be imaged at each rotation angle and constructing an observation vector sequence; The system matrix construction module is configured to rotate the system function harmonic diagrams of different orders according to the rotation angle, and construct the system matrix at each rotation angle based on the rotated system function harmonic diagrams of different orders; The image reconstruction module is configured to combine the observation vector sequence by column, and combine the system matrices under each rotation angle by column. After the combination, construct a linear equation system; solve the linear equation system to obtain The imaged target object corresponds to the reconstructed magnetic particle image. 8. An electronic device, characterized in that it comprises: at least one processor; and memory communicatively coupled to at least one of said processors; Wherein, the memory stores instructions that can be executed by the processor, and the instructions are used to be executed by the processor to realize the free line of magnetic field based on the rotating harmonic diagram according to any one of claims 1-6. Magnetic Particle Imaging Methods. 9. A computer-readable storage medium, characterized in that the computer-readable storage medium stores computer instructions, and the computer instructions are used to be executed by the computer to implement the method described in any one of claims 1-6. Free-line magnetic particle imaging method for magnetic field based on rotational harmonic map.

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