CN115778353B - Magnetic field free line magnetic particle imaging method based on rotation harmonic diagram - Google Patents
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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
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 equipment based on a rotation harmonic diagram.
Background
In recent years, living body noninvasive molecular imaging technology is rapidly developed, and in-vivo effective observation of various biomolecules is realized. The magnetic particle imaging technology is based on the nonlinear magnetization response of magnetic nanoparticles for imaging, 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 the detection of deep micro-tumors, the monitoring of cardiovascular and cerebrovascular functions and other important clinical problems.
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 a non-uniform constant magnetic field, or called gradient magnetic field, and is characterized by comprising one or more low magnetic field regions, typically elliptical punctiform magnetic field free points or linear magnetic field free lines. The magnetic nano particles are in a non-saturated state in a low-strength magnetic field area, generate signals when excited by an external magnetic field, and are detected by a receiving coil; however, the magnetic field is saturated in the high-strength magnetic field region, and the signal is weak and cannot be detected after being excited. The dynamic field is a uniform alternating magnetic field, or excitation magnetic field, used to drive the low magnetic field region to move within the imaging field of view and excite the magnetic nanoparticles to produce nonlinear characteristic signals. The magnetic particle imaging uses an excitation magnetic field to drive a low magnetic field region to scan a specific track in an imaging visual field, so that the spatial coding of the concentration of the magnetic nano particles is completed. The low magnetic field region of the magnetic field free line is larger, the single scan coverage is larger, the signal to noise ratio is higher and the imaging speed is faster than the magnetic field free point, and has been widely studied and applied in recent years.
The reconstruction process from signal to image is an important step in magnetic particle imaging, one important method being the system matrix method. At present, the system matrix method comprises the following steps: measuring signal spectrum of a unit sample at each pixel point in an imaging view field, constructing a system matrix representing an imaging system in a frequency domain after screening, quantifying signals of a 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 require either rotating the magnetic field free lines or rotating the object under test, and accurate reconstruction can only be achieved after covering the entire imaging field of view. Therefore, in the conventional method, the system matrix needs to be measured once every time the free line of the magnetic field or the measured object rotates by a certain angle. The process is complex, 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 real-time imaging is difficult, so that a more efficient magnetic field free line magnetic particle imaging method based on a system matrix is needed.
The reason for measuring the system matrix at all angles in the conventional method is that: after rotation, the magnetic field undergoes slight distortion or deformation. The measurement of the system matrix at each rotation angle is the most accurate measurement and modeling method for the imaging system. However, during rotation, 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 order harmonic response at each pixel within the imaging field of view, and the harmonic plot reflects the spatial response frequency of the system itself. For the free line of the rotating magnetic field, the imaging system rotates by controlling the power-on parameter or mechanically rotating the gradient coil, so that the harmonic diagram in the system matrix can be considered to rotate along with the rotation of the imaging system, but is slightly deformed; for rotating the measured object, the system itself is not changed, but the same rotation process is reflected by converting the coordinate system. In the conventional method, the system matrix between different angles must have highly repetitive information. Based on the above, the invention provides a magnetic field free line magnetic particle imaging method based on a rotation harmonic diagram.
Disclosure of Invention
In order to solve the above problems in the prior art, that is, in order to solve the problems that the existing magnetic particle imaging method based on a system matrix needs to measure a system matrix once every time when a magnetic field free line or an object to be measured rotates by a certain angle, 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 lower, the invention provides a magnetic field free line magnetic particle imaging method based on a rotation harmonic diagram, which is applied to a magnetic particle imaging device based on a magnetic field free line, and comprises the following steps:
Step S100, setting related parameters of the magnetic particle imaging device based on the magnetic field free line, and starting and operating the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
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 line, and setting the moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated 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 line of the magnetic particle imaging device based on the magnetic field free line 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 under 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, combining the observation vector sequences in columns, combining the system matrixes under all rotation angles in columns, and constructing a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
In some preferred embodiments, the signal of each pixel out of the unit sample is measured, and then a system function harmonic diagram with different orders is constructed, and the method is as follows:
measuring time domain signals of unit samples 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 according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free line, and taking the screened harmonic signals as first harmonic signals; and synthesizing first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain a system function harmonic diagram of different orders.
In some preferred embodiments, the rotation angle and the rotation sequence are set by:
The initial direction is 0 degrees, the magnetic field is rotated to 180 degrees in a stepping mode in an equidistant or unequal-interval mode, the movement range of the free line of the magnetic field can cover all imaging fields, and the magnetic field is rotated for N angles altogether; 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 under each rotation angle, and constructing an observation column vector under the current rotation angle, so as to construct an observation vector sequence under all rotation angles;
the observation column vector is a column vector constructed according to characteristic harmonic waves used by a system matrix in the initial direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free line, and the characteristic harmonic waves of response signals of a target object to be imaged under a corresponding rotation angle are extracted.
In some preferred embodiments, the system function harmonic graphs of different orders are decomposed into a real part harmonic graph and an imaginary part harmonic graph when rotated, and the real part harmonic graph and the imaginary part harmonic graph are synthesized into a complex harmonic graph after rotation;
and (3) rotating the system function harmonic graphs of different orders, keeping the image size unchanged, using zero filling at non-pixel points, and rounding at non-grid pixel points by using an interpolation method.
In some preferred embodiments, a system of linear equations is constructed by:
wherein,,
representing the system matrix { A } at each rotation angle 1, A 2 , ..., A N Merging system matrix by column, +.>
Representing the sequence of observation vectors { b 1 , b 2 , ..., b N All observation vectors in a } column by columnMerged observation vector, +.>
Representing a discrete vector form of the 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 presented, the system comprising: the system comprises an initialization setting module, a harmonic diagram 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 related parameters of the magnetic particle imaging device based on the magnetic field free line, and start and operate the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
the harmonic diagram 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 line, and set a moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated 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 line of the magnetic particle imaging device based on the magnetic field free line 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 under 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 under all rotation angles in columns, and construct a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by 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; the memory stores instructions executable by the processor for execution by the processor to implement the above-described magnetic field free line magnetic particle imaging method based on a rotational harmonic map.
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-described 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 constructing all system matrixes by only measuring the system matrixes under one angle and constructing the system matrixes of other rotation angles in a mode of rotating a harmonic diagram. The method greatly reduces the complexity of system matrix measurement, reduces the memory resource requirement, improves the system correction efficiency of the magnetic particle imaging equipment, and improves the instantaneity of magnetic particle imaging.
Drawings
Other features, objects and advantages of the present application will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings.
FIG. 1 is a flow chart of a magnetic field free line magnetic particle imaging method based on a rotated harmonic diagram in accordance with one embodiment of the invention;
FIG. 2 is a schematic diagram of a frame of a magnetic field free line magnetic particle imaging method based on a rotational harmonic diagram according to an embodiment of the invention;
FIG. 3 is a schematic illustration of magnetic field free lines of a rotating magnetic particle imaging apparatus or a target object to be imaged in accordance with one embodiment of the present invention;
FIG. 4 is a schematic diagram of a conventional method of an embodiment of the present invention and a process for constructing a system matrix using the method of the present invention;
FIG. 5 is an exemplary plot of harmonic diagrams of system functions rotated two, three, four times in accordance with one embodiment of the present invention;
FIG. 6 is a schematic representation of a magnetic particle image after reconstruction of a standard phantom with a target object in accordance with one embodiment of the present invention;
FIG. 7 is a schematic diagram of a computer system suitable for use in implementing the electronic device of an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The present application is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other.
The magnetic field free line magnetic particle imaging method based on the rotation 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 related parameters of the magnetic particle imaging device based on the magnetic field free line, and starting and operating the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
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 line, and setting the moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated 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 line of the magnetic particle imaging device based on the magnetic field free line 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 under 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, combining the observation vector sequences in columns, combining the system matrixes under all rotation angles in columns, and constructing a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
In order to more clearly describe the magnetic field free line magnetic particle imaging method based on the rotation harmonic diagram, each step in one embodiment of the method of the present invention is described in detail below with reference to the accompanying drawings.
Step S100, setting related parameters of the magnetic particle imaging device based on the magnetic field free line, and starting and operating the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
In this embodiment, the parameters related to the magnetic particle imaging apparatus based on the free line of the magnetic field are initialized, including the imaging field radius, the selected magnetic field gradient, the excitation field amplitude and frequency, the digital sampling frequency and time, and the unit sample size. After initialization, the magnetic particle imaging device based on the free line of the magnetic field 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 line, and setting the moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated position according to a set moving path;
in this embodiment, the system matrix measuring device is preferably configured as a three-axis displacement table or a mechanical arm, and is capable of moving a unit sample (a dot sample (referred to as delta phasom in the paper, or a standard chinese translation is not used in the paper) (specifically referred to as Top C, gungor a. Tomographic Field Free Line Magnetic ParticleImaging With an Open-Sided Scanner Configuration J. IEEE transactions onmedical imaging, 2020, 39 (12): 4164-4173)) to a specified position according to a set path, wherein the unit sample is usually in the shape of a pixel or voxel, and magnetic nanoparticles are contained in a cavity, and a cubic particle cavity is contained therein.
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 line, and setting a moving path of a unit sample by combining the imaging field radius; then the system matrix a in this 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 system function; the method comprises the following 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 according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free line, and taking the screened harmonic signals as first harmonic signals; and synthesizing first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain a system function harmonic diagram of different orders. The system function harmonic diagram is all particle harmonic signals which can be detected under the condition of the current magnetic particle imaging device with the signal to noise ratio, the same harmonic at each pixel or voxel in the imaging visual field of the magnetic particle imaging device based on the magnetic field free line is synthesized into each order system function harmonic diagram, the harmonic information is complex, and the harmonic diagram can be decomposed into a real part harmonic diagram and an imaginary part harmonic diagram; the unit sample is a carrier liquid cavity which is used in testing the system matrix, is filled with unit concentration magnetic nano particles and has the same size as the highest resolution of imaging of the magnetic particle imaging device based on the magnetic field free line.
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 line of the magnetic particle imaging device based on the magnetic field free line 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 under each rotation angle and constructing an observation vector sequence;
in this embodiment, the initial direction is preferably 0 °, and the magnetic field free line is rotated to 180 ° in steps in an equidistant or non-equidistant manner, so as to ensure that the movement range of the magnetic field free line can cover the whole imaging field (i.e. the requirement of the rotation sequence), and the magnetic field free line is rotated N angles altogether; in this embodiment, N represents a set number, and in this embodiment, the number is 9 or more, and in other embodiments, the number may be set according to actual situations.
Rotating the magnetic field free line of the magnetic particle imaging device based on the magnetic field free line 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 under each rotation angle and constructing an observation vector sequence, wherein the method comprises the following steps:
rotating the magnetic field free line of the magnetic particle imaging device or the target object to be imaged based on the magnetic field free line according to the rotation angles and the rotation sequence, measuring response signals of the target object to be imaged under each rotation angle, constructing an observation column vector under the current rotation angle, and further constructing an observation vector sequence under all rotation angles; the observation column vector is a column vector constructed according to characteristic harmonic waves used by a system matrix in the initial direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free line, and the characteristic harmonic waves of response signals of a target object to be imaged under a corresponding rotation angle are extracted.
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;
in the embodiment, when the system function harmonic graphs of different orders are rotated, the system function harmonic graphs are decomposed into a real part harmonic graph and an imaginary part harmonic graph, and the real part harmonic graph and the imaginary part harmonic graph are synthesized into a complex harmonic graph after rotation;
and (3) rotating the system function harmonic graphs of different orders, keeping the image size unchanged, using zero filling at non-pixel points, and rounding at non-grid pixel points by using an interpolation method.
The system matrix at each rotation angle is denoted as { A ] 1, A 2 , ..., A N }。
Step S500, combining the observation vector sequences in columns, combining the system matrixes under all rotation angles in columns, and constructing a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
In this embodiment, a system of linear equations is constructed by:
wherein,,
representing the system matrix { A } at each rotation angle 1, A 2 , ..., A N Merging system matrix by column, +.>
Representing the sequence of observation vectors { b 1 , b 2 , ..., b N All observation vectors in the sequence are combined observation vector, < >>
Representing a discrete vector form of the target object to be imaged.
And then solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
When solving the linear equation set, a regularized iterative solving algorithm is preferably used, specifically: an objective function was established using the L2 norm and iteratively solved using the kaczmarz algorithm. The technical method in the paper comprises the following steps: an objective function is established using the L1 norm and the TV norm, and the solution is iterated using the ADMM algorithm.
In addition, in order to further verify the effectiveness of the method of the present invention, the following is exemplified.
In this embodiment, the magnetic particle imaging device based on the magnetic field free line preferably adopts an open magnetic field free line magnetic particle imaging system, wherein the radius of the imaging field of view is set to 20 mm, and the magnetic particle imaging mode based on the magnetic field free line is shown in fig. 3 to be a rotating magnetic field free line or a rotating object to be measured. Selecting magnetic field H SF The gradient is set to be 1T/m, and a driving magnetic field uses a high-frequency low-amplitude sine alternating magnetic field H DF Focusing magnetic field H FF Magnetic field h=h of composite magnetic particle imaging system using low frequency high amplitude sinusoidal alternating magnetic field SF +H DF +H FF 。
Wherein the amplitude of the driving magnetic field is A DF =8mt, frequency f DF =2500 hz, i.e
The amplitude of the focusing magnetic field is A FF =14mt, frequency f DF =20 hz, i.e
The sampling rate in the digital sampling process is 1 megahertz and the sampling time is 1 second. The three-axis displacement table is used as a measuring device for measuring a system matrix, the size of the system matrix is set to 20 rows and 20 columns, and the size of each pixel is 2 mm.
The test uses particles as superparamagnetic nano-iron oxide particles, and the particle model can be roughly understood as the particles described by the adiabatic langevin model:
wherein->
For the nature of the particle itself and for measuring environmental parameters.
Then, the displacement table is fixed firstly, the magnetic particle imaging device is properly far away from the displacement table, the direction of the detection rod of the current displacement table is taken as the initial direction, namely 0 degrees, a test sample (namely a target object to be imaged) is moved according to a track of a first row and a later row when a system matrix is measured, a unit sample is set to be a liquid carrying cavity with the concentration of the test particle stock solution, and the magnetic particle imaging device based on a magnetic field free line is started.
The signal of the unit sample at each pixel is measured, a frequency spectrum diagram is obtained by using fast Fourier transform, 2, 3, 4, 5, 6 and 7-order harmonic waves are selected as particle signals according to the imaging device signal to noise ratio, and the fundamental frequency signals are eliminated in consideration of direct feed-through interference. After the signals of all pixel points in the image field are tested, harmonic graphs of 2, 3, 4, 5, 6 and 7-order particle signals are respectively built.
The shapp-logan head model was used as a standard test simulator, and the rotation sequence was set to be clockwise, 3.6 ° step angle, and rotated 50 degrees in total, as shown in (a) of fig. 6. Rotating the shepp-logan head model in rotation order, measuring the signal of the particle response at each angle, and building the observation vector { b ] using 2, 3, 4, 5, 6, 7 order harmonics 1 , b 2 , ..., b N }。
And (3) 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, as shown in (b) of fig. 4, so as to obtain the system function harmonic graphs under all angles. The conventional method builds a systematic demonstration as shown in fig. 4 (a).
The (a), (b) and (c) in fig. 5 are harmonic diagrams of the particle signals 2, 3 and 4 at the initial angle, 36 ° rotation and 72 ° (i.e., rotation angle 1, rotation angle 2, rotation angle 3, and the same applies in fig. 4). Establishing each order harmonic diagram as a system matrix { A } under a corresponding angle 1, A 2 , ..., A N }。
All the system matrixes are combined into a system matrix A according to columns, all the observation vectors are combined into an observation vector b according to columns, an imaging system linear equation set of an object to be measured is established, a regularization kaczmarz method is used for solving the linear equation set, a regularization parameter is set to be 0.001, and the iteration times are set to be 1000 times, so that x is obtained. Finally, x is rearranged into an image of the target object to be imaged, as shown in (b) of fig. 6.
A second embodiment of the present invention is a magnetic field free line magnetic particle imaging system based on a rotation harmonic diagram, as shown in fig. 2, comprising: an initialization setting module 100, a harmonic diagram 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 related parameters of the magnetic particle imaging device, and turn on and operate the magnetic particle imaging device based on magnetic field free lines; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
the harmonic diagram construction module 200 is configured to set a position and a direction of a system matrix measurement device in the magnetic particle imaging device based on the magnetic field free line, and set a movement path of a unit sample in combination with the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated position according to a set moving path;
The observation vector construction module 300 is configured to set a rotation angle and a rotation sequence by taking a direction of the system matrix measurement device as an initial direction; rotating the magnetic field free line of the magnetic particle imaging device based on the magnetic field free line 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 under each rotation angle and constructing an observation vector sequence;
the system matrix construction module 400 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 500 is configured to combine the observation vector sequences in columns, combine the system matrices at each rotation angle in columns, and construct a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
It will be clear to those skilled in the art that, for convenience and brevity of description, specific working processes and related descriptions of the above-described system may refer to corresponding processes in the foregoing method embodiments, which are not repeated herein.
It should be noted that, in the magnetic field free line magnetic particle imaging system based on the rotation harmonic diagram provided in the foregoing embodiment, only the division of the foregoing functional modules is illustrated, in practical application, the foregoing functional allocation may be performed by different functional modules according to needs, that is, the modules or steps in the foregoing 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 a plurality of sub-modules, so as to complete all or part of the functions described above. The names of the modules and steps related to the embodiments of the present invention are merely for distinguishing the respective modules or steps, and are not to be construed as unduly limiting the present invention.
An electronic device of 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 magnetic field free line magnetic particle imaging method based on a rotational harmonic map as described in the claims.
A fourth embodiment of the present invention is a computer-readable storage medium storing computer instructions for execution by the computer to implement the above-described magnetic field free line magnetic particle imaging method based on a rotation harmonic diagram.
It will be clear to those skilled in the art that, for convenience and brevity of description, specific working processes of the electronic device, the computer readable storage medium 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, which are not described herein again.
Reference is now made to FIG. 7, which is a block diagram illustrating a computer system suitable for use in implementing embodiments of the methods, systems, and apparatus of the present application. The server illustrated in fig. 7 is merely an example, and should not be construed as limiting the functionality and scope of use of the embodiments herein.
As shown in fig. 7, the computer system includes a central processing unit (CPU, central Processing Unit) 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, random Access Memory) 703. In the RAM703, various programs and data required for the system operation are also stored. The CPU701, ROM702, and RAM703 are connected to each other through a bus 704. An Input/Output (I/O) interface 705 is also connected to bus 704.
The following components are connected to the I/O interface 705: an input section 706 including a keyboard, a mouse, and the like; an output portion 707 including a Cathode Ray Tube (CRT), a liquid crystal display (LCD, liquid Crystal Display), and the like, a speaker, and the like; a storage section 708 including a hard disk or 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. The 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 therefrom is mounted into the storage section 708 as necessary.
In particular, according to embodiments of the present disclosure, the processes described above with reference to 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 shown in the flowcharts. In such an embodiment, the computer program may be downloaded and installed from a network via the communication portion 709, and/or installed from the removable medium 711. The computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof, a more specific example of a computer-readable storage medium may include, but is not limited to, an electrical connection having one or more wires, a portable computer disk, 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 disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof A program for use by or in connection with an instruction execution system, apparatus, or device is propagated or transmitted. 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 of the present application may be written in one or more programming languages, including an object oriented programming language such as Java, smalltalk, C ++ 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 kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computer (for example, through the Internet using an Internet service provider).
The flowcharts 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 objects and not for describing a particular sequential or chronological order.
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/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/apparatus.
Thus far, the technical solution of the present invention has 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 protection of the present invention is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present invention, and such modifications and substitutions will fall within the scope of the present invention.
Claims (9)
1. A magnetic field free line magnetic particle imaging method based on a rotation harmonic diagram, which is applied to a magnetic field free line-based magnetic particle imaging device, and is characterized in that the method comprises the following steps:
Step S100, setting related parameters of the magnetic particle imaging device based on the magnetic field free line, and starting and operating the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
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 line, and setting the moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated 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 line of the magnetic particle imaging device based on the magnetic field free line 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 under 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, combining the observation vector sequences in columns, combining the system matrixes under all rotation angles in columns, and constructing a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by the target object to be imaged.
2. The method for imaging magnetic free line magnetic particles based on the rotation harmonic diagram according to claim 1, wherein the method for measuring the signal of the unit sample at each pixel in the imaging field of view of the magnetic free line magnetic particle imaging device to construct the system function harmonic diagram with different orders is as follows:
measuring time domain signals of unit samples 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 according to the signal-to-noise ratio of the magnetic particle imaging device based on the magnetic field free line, and taking the screened harmonic signals as first harmonic signals; and synthesizing first harmonic signals of the same order at each pixel based on the frequency spectrum to obtain a system function harmonic diagram of different orders.
3. The method for imaging free line magnetic particles of a magnetic field based on a rotation harmonic diagram according to claim 2, wherein the rotation angle and the rotation sequence are set, and the method is as follows:
the initial direction is 0 degrees, the magnetic field is rotated to 180 degrees in a stepping mode in an equidistant or unequal-interval mode, the movement range of the free line of the magnetic field can cover all imaging fields, and the magnetic field is rotated for N angles altogether; where N represents a set number.
4. A method of magnetic field free line magnetic particle imaging based on a rotational harmonic map as claimed in claim 3, wherein the response signals of the target object to be imaged at each rotational angle are measured and an observation vector sequence is constructed, the method comprising:
measuring response signals of a target object to be imaged under each rotation angle, and constructing an observation column vector under the current rotation angle, so as to construct an observation vector sequence under all rotation angles;
the observation column vector is a column vector constructed according to characteristic harmonic waves used by a system matrix in the initial direction of a system matrix measuring device in the magnetic particle imaging device based on the magnetic field free line, and the characteristic harmonic waves of response signals of a target object to be imaged under a corresponding rotation angle are extracted.
5. The method for imaging free line magnetic particles of a magnetic field based on a rotation harmonic diagram according to claim 1, wherein the free line magnetic particles are decomposed into a real harmonic diagram and an imaginary harmonic diagram when the system function harmonic diagrams of different orders are rotated, and the real harmonic diagram and the imaginary harmonic diagram are synthesized into a complex harmonic diagram after rotation;
and (3) rotating the system function harmonic graphs of different orders, keeping the image size unchanged, using zero filling at non-pixel points, and rounding at non-grid pixel points by using an interpolation method.
6. The method for imaging free line magnetic particles of a magnetic field based on a rotation harmonic diagram according to claim 1, wherein a system of linear equations is constructed by:
；/>
；/>
the method comprises the steps of carrying out a first treatment on the surface of the Wherein (1)>
Representing the system matrix { A } at each rotation angle 1, A 2 , ..., A N Merging system matrix by column, +.>
Representing the sequence of observation vectors { b 1 , b 2 , ..., b N All observation vectors in the sequence are combined observation vector, < >>
Representing a discrete vector form of the target object to be imaged.
7. A magnetic field free line magnetic particle imaging system based on a rotational harmonic map, based on the magnetic field free line magnetic particle imaging method based on a rotational harmonic map according to any of claims 1-6, characterized in that the system comprises: the system comprises an initialization setting module, a harmonic diagram 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 related parameters of the magnetic particle imaging device based on the magnetic field free line, and start and operate the magnetic particle imaging device based on the magnetic field free line; the related parameters comprise the imaging field radius size, the selected magnetic field gradient, the excitation magnetic field amplitude and frequency, the digital sampling frequency and time and the unit sample size;
the harmonic diagram 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 line, and set a moving path of a unit sample by combining the imaging field radius; moving the unit sample according to a set moving path, measuring signals of the unit sample at each pixel in an imaging visual field range of the magnetic particle imaging device based on the magnetic field free line, and further constructing system function harmonic diagrams of different orders; the system matrix measuring device is used for moving the unit sample to a designated 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 line of the magnetic particle imaging device based on the magnetic field free line 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 under 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 under all rotation angles in columns, and construct a linear equation set after combining; and solving the linear equation set to obtain a magnetic particle image which is correspondingly reconstructed by 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 rotational harmonic diagram based magnetic field free line magnetic particle imaging method of any of claims 1-6.
9. A computer readable storage medium storing computer instructions for execution by the computer to implement the rotational harmonic map-based magnetic field free line magnetic particle imaging method of any of claims 1-6.
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