CN115778353A - Magnetic field free line magnetic particle imaging method based on rotating harmonic diagram - Google Patents
Magnetic field free line magnetic particle imaging method based on rotating harmonic diagram Download PDFInfo
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Abstract
The invention belongs to the technical field of magnetic particle imaging, and particularly relates to a magnetic field free line magnetic particle imaging method, system and equipment based on a rotating harmonic diagram, aiming at solving the problems that the measurement process of a system matrix of the existing magnetic particle imaging method is complex and time-consuming, large in occupied memory and long in calculation time, the system correction efficiency of the magnetic particle imaging equipment is severely limited, and the imaging real-time performance is low. The method comprises the following steps: setting relevant parameters of a magnetic particle imaging device based on magnetic field free lines, starting and operating; constructing system function harmonic graphs of different orders; measuring response signals of a target object to be imaged at 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; a magnetic particle image is reconstructed. According to the invention, the system matrix of other rotation angles is constructed in a mode of rotating the harmonic image, so that the measurement complexity of the system matrix is greatly reduced, and the system correction efficiency of the magnetic particle imaging equipment is improved.
Description
Technical Field
The invention belongs to the technical field of magnetic particle imaging, and particularly relates to a magnetic field free line magnetic particle imaging method, system and device based on a rotating harmonic diagram.
Background
In recent years, the living body noninvasive molecule imaging technology is rapidly developed, and the in-vivo effective observation of various biomolecules is realized. The magnetic particle imaging technology is used for imaging based on the nonlinear magnetization response of the magnetic nanoparticles, has the advantages of high sensitivity, high spatial resolution, no radiation, no background signal interference, no imaging depth limitation and the like, and is expected to be applied to major clinical problems such as deep micro-tumor detection, cardiovascular and cerebrovascular function monitoring and the like.
Magnetic particle imaging techniques use a combination of magnetic fields to detect the concentration profile of magnetic nanoparticle tracers, where the magnetic fields include static and dynamic magnetic fields. The static magnetic field is an inhomogeneous constant magnetic field or gradient magnetic field, and is characterized by comprising one or more low magnetic field regions, and the shape of the magnetic field free point is generally elliptic point-shaped or linear magnetic field free line. The magnetic nano particles are in a non-saturated state in a low-intensity magnetic field region, generate signals when excited by an external magnetic field and are detected by a receiving coil; however, the magnetic field is in a saturated state in a high-intensity magnetic field region, and the excited signal is weak and cannot be detected. The dynamic field is a uniform alternating magnetic field or an excitation magnetic field and is used for driving the low magnetic field area to move in the imaging field of view and exciting the magnetic nano particles to generate a nonlinear characteristic signal. Magnetic particle imaging uses an excitation magnetic field to drive a low magnetic field region to scan a specific track in an imaging field of view, so as to complete spatial encoding of magnetic nanoparticle concentration. Compared with a magnetic field free point, a low magnetic field area of a magnetic field free line is larger, a single scanning coverage range is larger, a signal-to-noise ratio is higher, imaging speed is higher, and the magnetic field free line is widely researched and applied in recent years.
The reconstruction process from signal to image is an important step in magnetic particle imaging, one of the important methods being the system matrix method. Currently, the system matrix method includes the following steps: measuring the signal frequency spectrum of the unit sample at each pixel point in the imaging field of view, constructing a system matrix representing the imaging system in a frequency domain after screening, quantizing the signal of the measured object into an observation vector, establishing a linear equation set, and reconstructing by solving the linear equation set. Magnetic particle imaging systems based on magnetic field free lines can be accurately reconstructed only after the magnetic field free lines or a measured object is rotated to cover all imaging visual fields. Therefore, in the conventional method, a system matrix needs to be measured once when a magnetic field free line or a measured object rotates for a certain angle. The process is complex and time-consuming, occupies a large memory, has long calculation time, seriously limits the system correction efficiency of the magnetic particle imaging equipment, and is difficult to image in real time, so a more efficient magnetic field free line magnetic particle imaging method based on a system matrix is needed.
The reason why the system matrix at all angles is measured in the conventional method is that: after rotation, the magnetic field appears slightly distorted or deformed. Therefore, the system matrix under each rotation angle is measured, and the method is the most accurate measurement and modeling method for the imaging system. However, during the rotation process, the system matrix between different angles has high information similarity.
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. For the free line of the rotating magnetic field, the imaging system rotates by controlling the energization parameters or mechanically rotating the gradient coil, and the harmonic diagram in the system matrix also rotates along with the rotation but slightly deforms; for rotating the measured object, the system itself is not changed, but the same rotation process is reflected by converting the coordinate system. Therefore, in the conventional method, highly repetitive information must exist in the system matrix between different angles. Based on the magnetic field free line magnetic particle imaging method, the invention provides a magnetic field free line magnetic particle imaging method based on a rotating harmonic map.
Disclosure of Invention
In order to solve the above problems in the prior art, that is, to solve the problems that the system matrix needs to be measured once when the magnetic field free line or the measured object rotates by a certain angle in the existing magnetic particle imaging method based on the system matrix, the measurement process is complex and time-consuming, the occupied memory is large, the calculation time is long, the system correction efficiency of the magnetic particle imaging device is severely limited, and the imaging real-time performance is low, the invention provides a magnetic field free line magnetic particle imaging method based on a rotation harmonic image, which is applied to a magnetic particle imaging device based on a magnetic field free line, and the method comprises the following steps:
step S100, setting relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and starting and operating the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
step S200, setting the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and setting the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving the unit sample to a specified position according to a set moving path;
step S300, setting a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, and constructing an observation vector sequence;
step S400, rotating the system function harmonic graphs of different orders according to the rotation angles, and constructing a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
step S500, merging the observation vector sequences according to columns, merging system matrixes under each rotation angle according to columns, and constructing a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
In some preferred embodiments, the signal of each pixel output unit sample is measured, and then a harmonic map of system functions of different orders is constructed, wherein the method comprises the following steps:
measuring a time domain signal of a unit sample at each pixel, and obtaining a frequency spectrum through fast Fourier transform;
screening harmonic signals with the signal-to-noise ratio larger than a set signal-to-noise ratio threshold value according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free lines, and taking the screened harmonic signals as first harmonic signals; and synthesizing the first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain system function harmonic graphs of different orders.
In some preferred embodiments, the rotation angle and the rotation sequence are set by:
the initial direction is 0 degrees, stepping rotation is carried out to 180 degrees in an equidistant or unequal interval mode, the moving range of the free line of the magnetic field can be ensured to cover all imaging visual fields, and the rotation is carried out for N angles; where N represents a set number.
In some preferred embodiments, the response signals of the target object to be imaged at each rotation angle are measured and an observation vector sequence is constructed by:
measuring response signals of a target object to be imaged at each rotation angle, constructing observation column vectors at the current rotation angle, and further constructing observation vector sequences at all rotation angles;
the observation column vector is a column vector constructed by extracting the characteristic harmonic of 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 the magnetic field free line.
In some preferred embodiments, the system function harmonic images of different orders are decomposed into a real part harmonic image and an imaginary part harmonic image when being rotated, and the real part harmonic images and the imaginary part harmonic images are synthesized into a complex harmonic image after being rotated;
and after rotating the harmonic images of the system functions of different orders, keeping the size of the image unchanged, using zero filling at the non-pixel point, and rounding at the non-grid pixel point by using an interpolation method.
In some preferred embodiments, a system of linear equations is constructed by:
wherein, the first and the second end of the pipe are connected with each other,
system matrix { A } representing each rotation angle 1, A 2 , ..., A N The system matrixes are merged according to columns,
represents the observation vector sequence b 1 , b 2 , ..., b N All observation vectors in the } are column-wise merged observation vectors,
a discrete vector form representing a target object to be imaged.
In a second aspect of the present invention, a magnetic field free line magnetic particle imaging system based on a rotational harmonic map is provided, the system comprising: the device comprises an initialization setting module, a harmonic image construction module, an observation vector construction module, a system matrix construction module and an image reconstruction module;
the initialization setting module is configured to set relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and start and operate the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
the harmonic map construction module is configured to set the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and set the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving a unit sample to a specified position according to a set moving path;
the observation vector construction module is configured to set a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals 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 graphs of different orders according to the rotation angles, and construct a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
the image reconstruction module is configured to combine the observation vector sequences in columns, combine the system matrixes at each rotation angle in columns, and construct a linear equation set after combination; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
In a third aspect of the present invention, an electronic device is provided, including: at least one processor; and a memory communicatively coupled to at least one of the processors; wherein the memory stores instructions executable by the processor for execution by the processor to implement the method of magnetic field free line magnetic particle imaging based on a rotated harmonic map as described above.
In a fourth aspect of the present invention, a computer-readable storage medium is provided, which stores computer instructions for execution by the computer to implement the above-mentioned magnetic field free line magnetic particle imaging method based on a rotational harmonic map.
The invention has the beneficial effects that:
the invention provides a method for measuring a system matrix at one angle only, and constructing the system matrix at other rotation angles by rotating a harmonic diagram, thereby completing the construction of all system matrices. The method can greatly reduce the complexity of system matrix measurement, simultaneously reduce the requirement of memory resources, improve the system correction efficiency of the magnetic particle imaging equipment and improve the real-time property of magnetic particle imaging.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the following detailed description of non-limiting embodiments thereof, made with reference to the accompanying drawings.
FIG. 1 is a schematic flow chart of a magnetic field free line magnetic particle imaging method based on a rotational harmonic map according to an embodiment of the present invention;
FIG. 2 is a block diagram of a magnetic field free line magnetic particle imaging method based on a rotational harmonic map according to an embodiment of the present invention;
FIG. 3 is a schematic illustration of a free line of magnetic field or target object to be imaged of a rotating magnetic particle imaging apparatus of one embodiment of the present invention;
FIG. 4 is a schematic diagram of a system matrix constructed by the conventional method and the method of the present invention according to an embodiment of the present invention;
FIG. 5 is an exemplary plot of a harmonic plot of a system function of the second, third, and fourth rotation of one embodiment of the present invention;
FIG. 6 is a schematic diagram of a reconstructed magnetic particle image of a master phantom and a target object according to an embodiment of the invention;
fig. 7 is a schematic structural diagram of a computer system suitable for implementing an electronic device according to an embodiment of the present application.
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The present application will be described in further detail with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not restrictive of the invention. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The magnetic field free line magnetic particle imaging method based on the rotating harmonic diagram is applied to a magnetic particle imaging device based on magnetic field free lines; as shown in fig. 1, the method includes:
step S100, setting relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and starting and operating the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
step S200, setting the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and setting the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free lines, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving the unit sample to a specified position according to a set moving path;
step S300, setting a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, and constructing an observation vector sequence;
step S400, rotating system function harmonic graphs of different orders according to the rotation angles, and constructing a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
step S500, merging the observation vector sequences according to columns, merging system matrixes under each rotation angle according to columns, and constructing a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
In order to more clearly explain the magnetic field free line magnetic particle imaging method based on the rotating harmonic diagram, the steps in one embodiment of the method are described in detail below with reference to the accompanying drawings.
Step S100, setting relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and starting and operating the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and the frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
in this embodiment, the related parameters of the magnetic particle imaging apparatus based on the free lines of the magnetic field are initialized, and the related parameters include the radius of the imaging field, the gradient of the selected magnetic field, the amplitude and frequency of the excitation magnetic field, the digital sampling frequency and time, and the size of the unit sample. After initialization, the magnetic particle imaging device based on the magnetic field free lines is started and operated.
Step S200, setting the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and setting the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving the unit sample to a specified position according to a set moving path;
in this embodiment, the system matrix measuring device is preferably configured as a three-axis translation stage or a mechanical arm, and can move a unit sample (the invention preferably uses a point sample (called delta phantom in the paper, temporarily without standard Chinese translation (specific reference: top C, gungor A. Tomographic Field Free Linear imaging With Open-side Scanner Configuration [ J ]. IEEE transactions on medical imaging, 2020, 39 (12): 4164-4173.)) to a designated position according to a set path, usually in the shape of a pixel or voxel, with Magnetic nanoparticles in the cavity and cubic particle cavities inside).
Firstly, setting the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and setting the moving path of a unit sample by combining the imaging view field radius; then, the system matrix A in the direction (i.e., the initial direction of the system matrix measuring device) is measured 1 As a system reference, constructing a harmonic diagram of each order of system function; the method comprises the following specific steps:
moving the unit sample according to a set moving path, measuring a time domain signal of the unit sample at each pixel, and obtaining a frequency spectrum through fast Fourier transform;
screening harmonic signals with the signal-to-noise ratio larger than a set signal-to-noise ratio threshold value according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free lines, and taking the screened harmonic signals as first harmonic signals; and synthesizing the first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain system function harmonic graphs of different orders. The system function harmonic image is all particle harmonic signals which can be detected under the condition of the signal-to-noise ratio of the current magnetic particle imaging device, the same harmonic waves at each pixel or voxel in the imaging field of the magnetic particle imaging device based on the magnetic field free line are synthesized into the system function harmonic image of each order, the harmonic information is complex, and the harmonic image can be decomposed into a real part harmonic image and an imaginary part harmonic image; the unit sample is a liquid carrying cavity which is used in a system matrix testing process, is filled with magnetic nano particles with unit concentration and has the same size as the highest resolution imaged by the magnetic particle imaging device based on the magnetic field free lines.
Step S300, setting a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, and constructing an observation vector sequence;
in this embodiment, it is preferable that the initial direction is 0 °, the magnetic field is rotated to 180 ° in a step-by-step manner with equal or unequal intervals, and the movement range of the free line of the magnetic field is ensured to cover the entire imaging field of view (i.e. the requirement of the rotation sequence), and the magnetic field is rotated by N angles altogether; where N represents a set number, in this embodiment, equal to or greater than 9, and in other embodiments, may be set according to actual conditions.
Rotating the magnetic field free lines or the target object to be imaged of the magnetic particle imaging device based on the magnetic field free lines according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged under each rotation angle and constructing an observation vector sequence, wherein the method comprises the following steps of:
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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, constructing an observation column vector at the current rotation angle, and further constructing an observation vector sequence at all rotation angles; the observation column vector is a column vector constructed by extracting the characteristic harmonic of 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 the magnetic field free line.
Step S400, rotating system function harmonic graphs of different orders according to the rotation angles, and constructing a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
in this embodiment, when the system function harmonic images of different orders are rotated, the system function harmonic images are decomposed into a real part harmonic image and an imaginary part harmonic image, and the real part harmonic images and the imaginary part harmonic images are synthesized into a complex harmonic image after being rotated;
and after rotating the harmonic images of the system functions of different orders, keeping the size of the image unchanged, using zero filling at the non-pixel point, and rounding at the non-grid pixel point by using an interpolation method.
The system matrix at each rotation angle is represented as { A } 1, A 2 , ..., A N }。
Step S500, merging the observation vector sequences according to columns, merging the system matrixes under each rotation angle according to columns, and constructing a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
In this embodiment, a linear equation system is constructed by:
wherein the content of the first and second substances,
system matrix { A } representing each rotation angle 1, A 2 , ..., A N The system matrixes are merged according to columns,
represents the observation vector sequence b 1 , b 2 , ..., b N All observation vectors in the tree are combined according to columns,
a discrete vector form representing a target object to be imaged.
And then, solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
When solving the linear equation set, a regularized iterative solution algorithm is preferably used, and specifically: the L2 norm is used to build the objective function, which is solved iteratively using the kaczmarz algorithm. The technical method in the paper is as follows: an objective function is established by using the L1 norm and the TV norm, and an ADMM algorithm is used for iterative solution.
In addition, in order to further verify the effectiveness of the method of the present invention, the following examples are given.
In the embodiment, the magnetic particle imaging apparatus based on the free magnetic field lines preferably employs an open magnetic free line magnetic particle imaging system, wherein the size radius of the imaging field is set to be 20 mm, and the magnetic particle imaging manner based on the free magnetic field lines is shown as a rotating magnetic free line or a rotating object to be measured in fig. 3. Selection field H SF The gradient is set to be 1T/m, and the driving magnetic field uses a high-frequency low-amplitude sine alternating magnetic field H DF Focusing magnetic field H FF Synthesizing a magnetic field H = H of the magnetic particle imaging system by using a low-frequency high-amplitude sine alternating magnetic field SF +H DF +H FF 。
Wherein the amplitude of the driving magnetic field is A DF Frequency of f =8mT DF =2500 Hz, i.e.
The amplitude of the focusing magnetic field is A FF Frequency f =14mT DF =20 Hz, i.e.
In the digital sampling process, the sampling rate is 1 MHz, and the sampling time is 1 second. The three-axis displacement table is used as a measuring device of a measuring system matrix, the size of the measuring system matrix is set to be 20 rows and 20 columns, and each pixel is 2 millimeters in size.
The test uses particles that are superparamagnetic nano-iron oxide particles, and the particle model can be roughly understood as a particle described by the adiabatic langevin model:
in which
The particle properties and the measured environmental parameters.
Then, fixing the displacement table, appropriately keeping the magnetic particle imaging device away from the displacement table, taking the direction of a detection rod of the current displacement table as an initial direction, namely 0 degrees, moving a test sample (namely a target object to be imaged) according to a track of a first column and a second row during measurement of a system matrix, setting a unit sample as a carrier liquid cavity with a 2 mm cubic volume and the concentration of a stock solution of the test particles, and starting the magnetic particle imaging device based on a free line of a magnetic field.
Measuring the signal of a unit sample at each pixel, obtaining a spectrogram by using fast Fourier transform, selecting 2, 3, 4, 5, 6 and 7 orders of harmonics as particle signals according to the signal-to-noise ratio of an imaging device, and eliminating fundamental frequency signals by considering direct feed-through interference. After testing the signals of all pixel points in the image visual field, respectively establishing harmonic images of 2, 3, 4, 5, 6 and 7-order particle signals.
With the shepp-logan head model as a standard test phantom, as shown in fig. 6 (a), the rotation sequence was set clockwise, 3.6 ° step angle, and rotated by 50 angles in total. Rotating the shepp-logan head model in a rotation sequence, measuring the signal of the particle response at each angle, and establishing an observation vector { b ] by using harmonics of orders 2, 3, 4, 5, 6 and 7 1 , b 2 , ..., b N }。
And (c) rotating the system function harmonic graphs of each order established according to the system matrix under the initial angle according to the same rotation angle sequence, and obtaining the system function harmonic graphs under all angles as shown in (b) in fig. 4. The conventional method constructs a system as shown in fig. 4 (a).
As shown in fig. 5, (a), (b), and (c) are harmonic graphs of order 2, 3, and 4 of the particle signals at an initial angle, rotated by 36 °, and rotated by 72 ° (i.e., rotated by 1, 2, and 3, and the same in fig. 4). Establishing each order harmonic image as a system matrix { A ] under a corresponding angle 1, A 2 , ..., A N }。
And combining all the system matrixes into a system matrix A according to columns, combining all the observation vectors into an observation vector b according to columns, establishing an imaging system linear equation set of the object to be measured, solving the linear equation set by using a regularization kaczmarz method, setting regularization parameters to be 0.001, and setting iteration times to be 1000 times to obtain x. Finally, x is rearranged into an image of the target object to be imaged, as shown in (b) of fig. 6.
A magnetic field free line magnetic particle imaging system based on a rotational harmonic map according to a second embodiment of the present invention, as shown in fig. 2, includes: the system comprises an initialization setting module 100, a harmonic map construction module 200, an observation vector construction module 300, a system matrix construction module 400 and an image reconstruction module 500;
the initialization setting module 100 is configured to set relevant parameters of the magnetic particle imaging apparatus, and start and operate the magnetic particle imaging apparatus based on the magnetic field free line; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and the frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
the harmonic map construction module 200 is configured to set the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and set the moving path of the unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving the unit sample to a specified position according to a set moving path;
the observation vector constructing module 300 is configured to set a rotation angle and a rotation order with the direction of the system matrix measuring apparatus as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, and constructing an observation vector sequence;
the system matrix constructing module 400 is configured to rotate the system function harmonic graphs of different orders according to the rotation angles, and construct a system matrix at each rotation angle based on the rotated system function harmonic graphs of different orders;
the image reconstruction module 500 is configured to merge the observation vector sequences in columns, merge the system matrices at each rotation angle in columns, and construct a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
It can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working process and related description of the system described above may refer to the corresponding process in the foregoing method embodiment, and details are not described herein again.
It should be noted that, the magnetic field free line magnetic particle imaging system based on the rotational harmonic map provided in the foregoing embodiment is only illustrated by dividing the above functional modules, and in practical applications, the above functions may be allocated to different functional modules according to needs, that is, the modules or steps in the embodiment of the present invention are further decomposed or combined, for example, the modules in the foregoing embodiment may be combined into one module, or may be further split into multiple sub-modules, so as to complete all or part of the above described functions. 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 to be construed as unduly limiting the present invention.
An electronic device according to a third embodiment of the present invention includes at least one processor; and a memory communicatively coupled to at least one of the processors; wherein the memory stores instructions executable by the processor for execution by the processor to implement the method of claim-based magnetic field free line magnetic particle imaging.
A computer-readable storage medium of a fourth embodiment of the present invention stores computer instructions for execution by the computer to implement the above-mentioned magnetic field free line magnetic particle imaging method based on a rotational harmonic map.
It can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes and related descriptions of the electronic device and the computer-readable storage medium described above may refer to corresponding processes in the foregoing method examples, and are not described herein again.
Referring now to FIG. 7, there is illustrated a block diagram of a computer system suitable for use as a server in implementing embodiments of the method, system, and apparatus of the present application. The server shown in fig. 7 is only an example, and should not bring any limitation to the functions and the scope of use of the embodiments of the present application.
As shown in fig. 7, the computer system includes a Central Processing Unit (CPU) 701, which can perform various appropriate actions and processes according to a program stored in a Read Only Memory (ROM) 702 or a program loaded from a storage section 708 into a Random Access Memory (RAM) 703. In the RAM703, various programs and data necessary for system operation are also stored. The CPU701, the ROM702, and the RAM703 are connected to each other via a bus 704. An Input/Output (I/O) interface 705 is also connected to the bus 704.
The following components are connected to the I/O interface 705: an input portion 706 including a keyboard, a mouse, and the like; an output section 707 including a Cathode Ray Tube (CRT), a Liquid Crystal Display (LCD), and a speaker; a storage section 708 including a hard disk and the like; and a communication section 709 including a Network interface card such as a LAN (Local Area Network) card, a modem, or the like. 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, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is mounted on the drive 710 as necessary, so that a computer program read out therefrom is mounted 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 may be implemented as computer software programs. For example, embodiments of the present disclosure include a computer program product comprising a computer program embodied on a computer-readable medium, the computer program comprising program code for performing the method illustrated by the flow chart. In such an embodiment, the computer program may be downloaded and installed from a network through the communication section 709, and/or installed from the removable medium 711. More specific examples of a computer readable storage medium may include, but are not limited to, an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing Propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to: wireless, wire, fiber optic cable, RF, etc., or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present application may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, smalltalk, C + + or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. 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 the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).
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 the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). 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 the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing or implying a particular order or sequence.
The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.
Claims (9)
1. A magnetic field free line magnetic particle imaging method based on a rotating harmonic map is applied to a magnetic particle imaging device based on magnetic field free lines, and is characterized by comprising the following steps:
step S100, setting relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and starting and operating the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
step S200, setting the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and setting the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free lines, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving the unit sample to a specified position according to a set moving path;
step S300, setting a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged at each rotation angle, and constructing an observation vector sequence;
step S400, rotating the system function harmonic graphs of different orders according to the rotation angles, and constructing a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
step S500, merging the observation vector sequences according to columns, merging system matrixes under each rotation angle according to columns, and constructing a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
2. The magnetic field free line magnetic particle imaging method based on the rotational harmonic map as claimed in claim 1, wherein the signal of unit sample at each pixel within the imaging field of view of the magnetic field free line magnetic particle imaging apparatus is measured to construct the system function harmonic map of different orders by:
measuring a time domain signal of a unit sample at each pixel, and obtaining a frequency spectrum through fast Fourier transform;
screening harmonic signals with the signal-to-noise ratio larger than a set signal-to-noise ratio threshold value according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free lines, and taking the screened harmonic signals as first harmonic signals; and synthesizing the first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain system function harmonic graphs of different orders.
3. The method according to claim 2, wherein the rotation angle and the rotation sequence are set by:
the initial direction is 0 degrees, stepping rotation is carried out to 180 degrees in an equidistant or unequal interval mode, the moving range of the free line of the magnetic field can be ensured to cover all imaging visual fields, and the rotation is carried out for N angles; where N represents the set number.
4. The magnetic field free line magnetic particle imaging method based on the rotating harmonic map of claim 3, wherein the response signal of the target object to be imaged at each rotation angle is measured and an observation vector sequence is constructed by the method comprising:
measuring response signals of a target object to be imaged at each rotation angle, constructing observation column vectors at the current rotation angle, and further constructing observation vector sequences at all rotation angles;
the observation column vector is a column vector constructed by extracting the characteristic harmonic of 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 the magnetic field free line.
5. The magnetic field free line magnetic particle imaging method based on the rotated harmonic image as claimed in claim 1, wherein the system function harmonic images of different orders are decomposed into a real part harmonic image and an imaginary part harmonic image when rotated, and the real part harmonic image and the imaginary part harmonic image are synthesized into a complex harmonic image after being rotated;
and after rotating the harmonic images of the system functions of different orders, keeping the size of the image unchanged, using zero filling at the non-pixel point, and rounding at the non-grid pixel point by using an interpolation method.
6. The magnetic field free line magnetic particle imaging method based on the rotational harmonic map of claim 1, wherein a system of linear equations is constructed by:
7. A magnetic field free line magnetic particle imaging system based on a rotational harmonic map, the system comprising: the device comprises an initialization setting module, a harmonic image construction module, an observation vector construction module, a system matrix construction module and an image reconstruction module;
the initialization setting module is configured to set relevant parameters of the magnetic particle imaging device based on the magnetic field free lines, and start and operate the magnetic particle imaging device based on the magnetic field free lines; the related parameters comprise the radius of an imaging visual field, the gradient of a selection magnetic field, the amplitude and frequency of an excitation magnetic field, the digital sampling frequency and time and the size of a unit sample;
the harmonic map construction module is configured to set the position and the direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free lines, and set the moving path of a unit sample by combining the imaging view field radius; moving the unit sample according to a set moving path, measuring the signal of the unit sample at each pixel in the imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic graphs of different orders; the system matrix measuring device is a device for moving a unit sample to a specified position according to a set moving path;
the observation vector construction module is configured to set a rotation angle and a rotation sequence by taking the direction of the system matrix measuring device as an initial direction; 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 according to the rotation angles and the rotation sequence, measuring response signals 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 graphs of different orders according to the rotation angles, and construct a system matrix under each rotation angle based on the rotated system function harmonic graphs of different orders;
the image reconstruction module is configured to merge the observation vector sequences in columns, merge the system matrixes at each rotation angle in columns, and construct a linear equation set after merging; and solving the linear equation set to obtain a magnetic particle image which is reconstructed correspondingly to the target object to be imaged.
8. An electronic device, comprising:
at least one processor; and a memory communicatively coupled to at least one of the processors;
wherein the memory stores instructions executable by the processor for execution by the processor to implement the method of magnetic field free line magnetic particle imaging based on rotational harmonic maps of any of claims 1-6.
9. A computer-readable storage medium storing computer instructions for execution by the computer to implement the method of rotating harmonic map-based magnetic field free line magnetic particle imaging according to any one of claims 1 to 6.
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