CN117686954A - Magnetic particle imaging method and equipment based on oscillating gradient magnetic field coding - Google Patents
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Abstract
The invention belongs to the technical field of biomedical imaging, in particular relates to a magnetic particle imaging method and equipment based on oscillating gradient magnetic field coding, and aims to solve the problem that magnetic particle imaging is difficult to realize high resolution and high signal to noise ratio simultaneously. The invention comprises the following steps: introducing sine or cosine current to the low-frequency gradient coil to generate an oscillating gradient magnetic field with the gradient strength changing along with time; a uniform high-frequency alternating magnetic field is superimposed on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field; exciting magnetic particles by using a double-frequency nonuniform excitation magnetic field to generate a mixed frequency magnetization response signal; the multichannel receiving coils are utilized to collect time domain signals in parallel; performing Fourier transformation on the time domain signals to obtain frequency signals and extracting intermodulation frequency component signals of the frequency signals; and calculating to obtain the concentration of the magnetic particles by combining the extracted intermodulation frequency component signals and the system matrix, so as to realize magnetic particle imaging. The invention can realize high-resolution and high-sensitivity magnetic particle imaging.
Description
Technical Field
The invention belongs to the technical field of biomedical imaging, and particularly relates to a magnetic particle imaging method and equipment based on oscillating gradient magnetic field coding.
Background
The magnetic particles are superparamagnetic particles, and are widely studied and applied as a novel medical imaging tracer agent in clinical problems such as tumor detection, magnetic particle thermotherapy, targeted drug delivery and the like in recent years. Conventional Magnetic Particle Imaging (MPI) methods rely on a static gradient magnetic field of constant gradient strength for spatial encoding, which can create a stable Field Free Region (FFR) in the center of the field of view. According to the magnetization saturation effect, magnetic particles at the FFR and nearby positions can generate dynamic magnetization response under the excitation of a uniform high-frequency alternating magnetic field, and magnetic particles far away from the FFR are saturated by a strong magnetic field to hardly generate dynamic magnetization response. Therefore, bias magnetic fields in different directions are superimposed on the basis of the static gradient magnetic field and the excitation magnetic field, so that FFR can be moved to perform space scanning, and further space coding is achieved. The above is the basic spatial coding principle of the conventional MPI method, namely that FFR is generated by means of static gradient magnetic fields, and then signals of each spatial position are acquired by moving the FFR.
The conventional MPI spatial coding method has advantages of simple principle and easy implementation, but it is difficult to achieve high resolution and high sensitivity at the same time. This is because a constant gradient strength may cause a contradiction between the spatial resolution and sensitivity of MPI. Theoretically, the larger the gradient strength, the smaller the effective area of the FFR, the more concentrated the acquired magnetic particle signal sources, resulting in higher spatial resolution; at the same time, however, fewer magnetic particle signals can be acquired instantaneously, resulting in a decrease in signal-to-noise ratio and thus an impact on sensitivity. Therefore, in practice, there is a trade-off between spatial resolution and sensitivity, which makes it difficult to achieve both high resolution and high signal-to-noise ratio with conventional MPI, which limits further development of MPI technology in the field of precision diagnostics.
Disclosure of Invention
In order to solve the above problems in the prior art, namely that the traditional MPI is difficult to realize high resolution and high signal to noise ratio at the same time, which limits the further development of MPI technology in the field of accurate diagnosis and treatment, the invention provides a magnetic particle imaging method based on oscillating gradient magnetic field coding, which is applied to magnetic particle imaging equipment; the magnetic particle imaging equipment comprises a low-frequency gradient coil, a high-frequency excitation coil and a multichannel receiving coil; characterized in that the method comprises:
introducing sine or cosine current to the low-frequency gradient coil to enable the low-frequency gradient coil to generate an oscillating gradient magnetic field with gradient strength changing along with time in an imaging view field of the magnetic particle imaging equipment;
current is introduced into the high-frequency excitation coil, and a uniform high-frequency alternating magnetic field is generated; superposing the uniform high-frequency alternating magnetic field on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field;
exciting magnetic particles in an imaging field of the magnetic particle imaging device by using the dual-frequency nonuniform excitation magnetic field to generate a mixed magnetization response component; collecting time domain signals of the mixed magnetization response signals of the magnetic particles along different directions by utilizing the multichannel receiving coil;
performing Fourier transform on the time domain signal to obtain a frequency signal and extracting an intermodulation frequency component signal from the frequency signal; and calculating the concentration of the magnetic particles by combining the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment, so as to realize magnetic particle imaging.
In a preferred embodiment, the alternating frequency of the uniform high-frequency alternating magnetic fieldOscillation frequency greater than the oscillating gradient magnetic field>。
In a preferred embodiment, the oscillating gradient magnetic field is:
；
；
；
；
wherein,representing an oscillating gradient magnetic field>Representing space vector>Time of presentation->、/>、Respectively representing the gradient strength of the oscillating gradient magnetic field along the x, y and z directions; />、/>、/>Respectively represent peak gradient intensity of the oscillating gradient magnetic field along x, y and z directions, +.>Represents oscillation frequency, t represents time
In a preferred embodiment, the dual-frequency inhomogeneous excitation magnetic field is:
；
；
wherein,representing a dual-frequency inhomogeneous excitation field, +.>Indicating the magnitude of a uniform high frequency alternating magnetic field,representing the oscillating gradient magnetic field at different positions +.>Magnetic field amplitude at>Indicates the alternating frequency of the uniform high-frequency alternating magnetic field,/->Represents the oscillation frequency +.>Representing space vector>，/>，/>Representing the vector of the oscillating gradient magnetic field in the x, y, z direction, < >>、/>、/>Respectively represent peak gradient intensities of the oscillating gradient magnetic field along x, y, z directions, x, y, z representing space vector +.>Is defined by the coordinates of (a).
In a preferred embodiment, the time domain signal fourier expansion of the mixed magnetization response signal corresponding to the mixed magnetization response is:
；
wherein,representing the frequency signal; />Indicating a frequency of +.>Fourier coefficients of intermodulation frequency components of a time domain signal of the magnetization response signal; />；/>The method comprises the steps of carrying out a first treatment on the surface of the t represents time, < >>Representing the alternating frequency of a uniform high-frequency alternating magnetic field; />Representing the oscillation frequency of the oscillating gradient magnetic field; i represents an imaginary unit.
In a preferred embodiment, the three-dimensional multi-channel coil acquires the time domain signals of the mixed magnetization response signals of the magnetic particles along different directions in parallel, wherein each acquisition time isInteger multiples of (2); />Representing the oscillation frequency of the oscillating gradient magnetic field.
In a preferred embodiment, the frequency signal is frequency extracted by the method comprising:
extraction frequencyAs an extracted intermodulation frequency component signal.
In a preferred embodiment, the method of achieving magnetic particle imaging is: firstly, obtaining an imaging equation based on the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment; the imaging equation is:
；
wherein,representing the extracted intermodulation frequency component signals; />Representing a system matrix; />Represent the firstThe magnetic particle concentration at each position, L is the total number of pixels after discretization of the imaging field of view, +.>Representing a spatial position index number;
by measuring the extracted intermodulation frequency component signal each timeAnd a system matrix of said magnetic particle imaging device>Inversion calculation of the concentration of the magnetic particles>；/>The oscillating gradient magnetic field is spatially->A location of the site;
and then based on theMagnetic particle imaging was performed.
In a second aspect of the present invention, a magnetic particle imaging apparatus based on oscillating gradient magnetic field encoding is provided, and a magnetic particle imaging method based on the oscillating gradient magnetic field encoding is provided, where the system includes:
an oscillating gradient magnetic field generator comprising one or more pairs of low frequency gradient coils and an alternating current source; the oscillating gradient magnetic field generator is used for generating an oscillating gradient magnetic field with gradient strength changing along with time and three direction components in an imaging view field of the magnetic particle imaging device;
the uniform high-frequency magnetic field generator comprises a single-channel or multi-channel high-frequency excitation coil and a high-frequency alternating current source; the uniform high-frequency magnetic field generator is used for generating a uniform high-frequency alternating magnetic field in an imaging view field of the magnetic particle imaging device; the uniform high-frequency alternating magnetic field is overlapped on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field; the dual-frequency nonuniform excitation magnetic field excites magnetic particles in an imaging view field of the magnetic particle imaging device to generate a mixed frequency magnetization response signal;
the multichannel magnetic induction receiver comprises a multichannel receiving coil and an amplifying and filtering circuit; the multichannel magnetic induction receiver is used for collecting time domain signals of mixed frequency magnetization response signals of magnetic particles along different directions in parallel;
a digital signal processing unit for performing fourier transform on the time domain signal and extracting intermodulation frequency component signals;
and the image reconstruction unit is used for carrying out image reconstruction by combining the extracted intermodulation frequency component signals and the system matrix of the magnetic particle imaging equipment.
In a preferred embodiment, if the oscillating gradient magnetic field generator comprises a pair of low frequency gradient coils, the multichannel magnetic induction receiver comprises three sets of independent channel and axially mutually orthogonal receiving coils;
the two low-frequency gradient coils are annular electromagnetic coils and are respectively used as a first coil and a second coil; the high-frequency excitation coil is a cylindrical coil and is used as a third coil; the receiving coils parallel to the high-frequency excitation coil in the receiving coils of the three groups of independent channels are cylindrical coils and serve as fourth coils, and the other two groups of coils are annular electromagnetic coils and serve as fifth coils and sixth coils and seventh coils and eighth coils respectively;
the first coil and the second coil are coaxially and symmetrically arranged at two sides of the third coil; the axis of the third coil is perpendicular to the axes of the first coil and the second coil;
the third coil and the fourth coil are coaxial, and the axis is perpendicular to the first plane; the first plane is a plane in which axes of the first coil and the second coil are located;
the third coil radius is greater than the fourth coil radius.
The invention has the beneficial effects that:
(1) The invention relates to a magnetic particle imaging method based on oscillating gradient magnetic field coding, which adopts an oscillating gradient magnetic field and a uniform high-frequency alternating magnetic field to excite magnetic particles simultaneously to generate a mixing response signal related to a space position. Because the gradient strength changes with time, the signal to noise ratio of the method is not limited by the specific gradient strength, so that the method has higher sensitivity. Meanwhile, the magnetic particle response signals under the excitation of the frequency mixing have richer intermodulation frequency components, and higher spatial resolution can be realized through image reconstruction;
(2) The method can solve the contradiction between resolution and sensitivity caused by the static gradient magnetic field in the traditional magnetic particle imaging method, and is hopeful to realize the magnetic particle imaging with high resolution and high sensitivity at the same time. Meanwhile, the FFR position is moved without an additional magnetic field, so that compared with the traditional method, the FFR position moving method has lower hardware complexity and lower power consumption;
(3) The invention simultaneously excites magnetic particles by combining a low-frequency oscillation gradient magnetic field and a high-frequency uniform high-frequency alternating magnetic field, and the magnetic particles can generate mixing signals under the excitation of magnetic fields with more than two frequencies according to the nonlinear magnetization response characteristics of the magnetic particles. The frequency components of the mixed signal are more abundant, and sideband harmonic components are generated besides the integral frequency multiplication harmonic components of the high-frequency alternating magnetic field frequency in the traditional MPI. Because the magnetic field vectors of the low-frequency oscillation gradient magnetic field in different positions in space are different and identical, sideband harmonic components generated by magnetic particles in different positions are also different and identical. And simultaneously, the spatial resolution is further improved by utilizing the integer frequency harmonic component and the sideband harmonic component for image reconstruction.
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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, in which:
FIG. 1 is a flow chart of a magnetic particle imaging method based on oscillating gradient magnetic field encoding in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of a magnetic particle imaging apparatus based on oscillating gradient magnetic field encoding in accordance with an embodiment of the present invention;
FIG. 3 is a top view of a magnetic particle imaging apparatus based on oscillating gradient magnetic field encoding in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram of a computer system for a server implementing embodiments of the methods, systems, and apparatus of the present application.
Detailed Description
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, for convenience of description, only the portions related to the present invention are shown in the drawings.
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 present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
The invention provides a magnetic particle imaging method of oscillating gradient magnetic field coding, which is applied to magnetic particle imaging equipment; the magnetic particle imaging equipment comprises a low-frequency gradient coil, a high-frequency excitation coil and a multichannel receiving coil; the method comprises the following steps: introducing sine or cosine current to the low-frequency gradient coil to enable the low-frequency gradient coil to generate an oscillating gradient magnetic field with gradient strength changing along with time in an imaging view field of the magnetic particle imaging equipment;
current is introduced into the high-frequency excitation coil, and a uniform high-frequency alternating magnetic field is generated; superposing the uniform high-frequency alternating magnetic field on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field;
exciting magnetic particles in an imaging field of the magnetic particle imaging device by using the dual-frequency nonuniform excitation magnetic field to generate a mixed magnetization response component; collecting time domain signals of the mixed magnetization response signals of the magnetic particles along different directions by utilizing the multichannel receiving coil;
performing Fourier transform on the time domain signal to obtain a frequency signal and extracting an intermodulation frequency component signal from the frequency signal; and calculating the concentration of the magnetic particles by combining the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment, so as to realize magnetic particle imaging.
In order to more clearly describe the magnetic particle imaging method based on the oscillating gradient magnetic field encoding of the present invention, each step in the embodiment of the present invention will be described in detail with reference to fig. 1.
The magnetic particle imaging method based on the oscillating gradient magnetic field coding of the first embodiment of the invention comprises the following steps in detail:
introducing sine or cosine current to the low-frequency gradient coil to enable the low-frequency gradient coil to generate an oscillating gradient magnetic field with gradient strength changing along with time in an imaging view field of the magnetic particle imaging equipment; the oscillating gradient magnetic field is:
；
；
；
；
wherein,representing an oscillating gradient magnetic field>Representing space vector>Time of presentation->、/>、Respectively representing the gradient strength of the oscillating gradient magnetic field along the x, y and z directions; />、/>、/>Respectively represent the edge of the oscillating gradient magnetic fieldPeak gradient intensity in x, y, z direction, x, y, z represents space vector +.>Is defined by the coordinates of (a).
Current is introduced into the high-frequency excitation coil, and a uniform high-frequency alternating magnetic field is generated; superposing the uniform high-frequency alternating magnetic field on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field;
the uniform high-frequency alternating magnetic field can be unidirectional or multi-directional, and fig. 2 shows an example of unidirectional uniform high-frequency alternating magnetic field, wherein the uniform high-frequency alternating magnetic field is generated by the high-frequency excitation coil in fig. 2, and the frequency of the supplied alternating current is far greater than the oscillation frequency of the oscillating gradient magnetic field. The alternating frequency of the uniform high-frequency alternating magnetic fieldOscillation frequency greater than the oscillating gradient magnetic field>。
The dual-frequency non-uniform excitation magnetic field is as follows:
；
；
wherein,representing a dual-frequency inhomogeneous excitation field, +.>Indicating the magnitude of a uniform high frequency alternating magnetic field,representing the oscillating gradient magnetic field at different positions +.>Magnetic field amplitude at>Indicates the alternating frequency of the uniform high-frequency alternating magnetic field,/->Represents the oscillation frequency +.>Representing space vector>，/>，/>Representing the vector of the oscillating gradient magnetic field in the x, y, z direction, < >>、/>、/>Respectively represent peak gradient intensities of the oscillating gradient magnetic field along x, y, z directions, x, y, z representing space vector +.>Is defined by the coordinates of (a).
Exciting magnetic particles in an imaging field of the magnetic particle imaging device by using the dual-frequency nonuniform excitation magnetic field to generate a mixed magnetization response component; collecting time domain signals of the mixed magnetization response signals of the magnetic particles along different directions by utilizing the multichannel receiving coil;
the high-frequency alternating magnetic field and the oscillating gradient magnetic field excite the magnetic nano particles in the imaging area at the same time, and the excitation magnetic field contains two frequency components, so that the magnetic nano particles generate mixed magnetization response.
The mixed magnetization response is derived from the nonlinear response characteristics of the magnetic nanoparticles, such as the magnetic nanoparticle magnetization response M (H) shown in fig. 2. When magnetic fields of two or more frequencies excite magnetic nanoparticles simultaneously, the signal generated by the magnetic nanoparticles contains not only components of two excitation frequencies but also frequency components generated by intermodulation of the two frequencies due to the nonlinear magnetization response characteristic shown in fig. 2.
The time domain signal fourier expansion of the mixed magnetization response signal corresponding to the mixed magnetization response is:
；
wherein,representing the frequency signal; />Indicating a frequency of +.>Fourier coefficients of intermodulation frequency components of a time domain signal of the magnetization response signal; />；/>t represents time, < >>Representing the alternating frequency of a uniform high-frequency alternating magnetic field; />Representing the oscillation frequency of the oscillating gradient magnetic field; i represents imaginary units, ">Representing the oscillating gradient magnetic field at different positions +.>At the magnitude of the magnetic field. />The larger the fourier coefficients of the larger n harmonic components in the mixed magnetization response signal of the magnetic particles at the larger positions.
When the multichannel receiving coil parallelly collects time domain signals of the mixed magnetization response signals of the magnetic particles along different directions, the collecting time of each time isInteger multiples of (2); />Representing the oscillation frequency of the oscillating gradient magnetic field. The frequency signal is subjected to frequency extraction, and the method comprises the following steps: the extraction frequency is->As an extracted intermodulation frequency component signal.
The multichannel receiving coil can be a three-dimensional multichannel coil, the three-dimensional multichannel coil is utilized to collect time domain signals of mixed frequency magnetization response signals of magnetic nano particles along different directions in parallel, and the collection time of each time isInteger multiples of (2). As shown in fig. 2, the time domain signals of the X, Y, Z receive channels are different from each other.
Because the oscillating gradient magnetic field contains magnetic field components in three directions, magnetic nanoparticles can be excited to generate magnetization response components in three directions, and therefore, a three-dimensional multichannel coil is adopted to receive signals, and further, rapid three-dimensional space coding is realized.
Performing Fourier transform on the time domain signal to obtain a frequency signal and extracting the frequency signal; and calculating the concentration of the magnetic particles by combining the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment, so as to realize magnetic particle imaging.
The method for realizing magnetic particle imaging comprises the following steps:
firstly, obtaining an imaging equation based on the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment; the imaging equation is:
；
wherein,representing the extracted intermodulation frequency component signals; />Representing a system matrix; />Represent the firstThe magnetic particle concentration at each position, L is the total number of pixels after discretization of the imaging field of view, +.>Representing a spatial position index number; />The oscillating gradient magnetic field is spatially->A location of the site;
by measuring the extracted intermodulation frequency component signal each timeAnd a system matrix of said magnetic particle imaging device>Inversion calculation of the concentration of the magnetic particles>；
Then based onThe saidMagnetic particle imaging was performed.
Although the steps are described in the above-described sequential order in the above-described embodiments, it will be appreciated by those skilled in the art that in order to achieve the effects of the present embodiments, the steps need not be performed in such order, and may be performed simultaneously (in parallel) or in reverse order, and such simple variations are within the scope of the present invention.
A second embodiment of the present invention provides a magnetic particle imaging apparatus based on oscillating gradient magnetic field encoding, and a magnetic particle imaging method based on the oscillating gradient magnetic field encoding, where the system includes:
an oscillating gradient magnetic field generator comprising one or more pairs of low frequency gradient coils and an alternating current source; the oscillating gradient magnetic field generator is used for generating an oscillating gradient magnetic field with the gradient strength changing along with time in an imaging view field of the magnetic particle imaging device; when the oscillating gradient magnetic field generator comprises a plurality of pairs of low frequency gradient coils, different pairs of low frequency gradient coils are axially mutually orthogonal.
The uniform high-frequency magnetic field generator comprises a single-channel or multi-channel high-frequency excitation coil and a high-frequency alternating current source; the uniform high-frequency magnetic field generator is used for generating a uniform high-frequency alternating magnetic field in an imaging view field of the magnetic particle imaging device; the uniform high-frequency alternating magnetic field is overlapped on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field; the dual-frequency nonuniform excitation magnetic field excites magnetic particles in an imaging field of view of the magnetic particle imaging device to generate mixed magnetization response components;
the multichannel magnetic induction receiver comprises a multichannel receiving coil and an amplifying and filtering circuit; the multichannel magnetic induction receiver is used for collecting time domain signals of mixed frequency magnetization response signals of magnetic particles along different directions in parallel; the amplifying and filtering circuit is used for reducing the frequency in the time domain signal to be less thanAnd is greater than->Is filtered out;
a digital signal processing unit for performing fourier transform on the time domain signal and extracting intermodulation frequency component signals;
and the image reconstruction unit is used for carrying out image reconstruction by combining the extracted intermodulation frequency component signals and the system matrix of the magnetic particle imaging equipment.
As shown in fig. 2, if the oscillating gradient magnetic field generator includes a pair of low-frequency gradient coils, the multi-channel magnetic induction receiver includes three independent channels and is in a scenario of receiving coils with axial directions orthogonal to each other, a schematic diagram of a magnetic particle imaging device based on oscillating gradient magnetic field encoding;
the two low-frequency gradient coils are annular electromagnetic coils and are respectively used as a first coil and a second coil; the high-frequency excitation coil is a cylindrical coil and is used as a third coil; the receiving coils parallel to the high-frequency excitation coil in the receiving coils of the three groups of independent channels are cylindrical coils and serve as fourth coils, and the other two groups of coils are annular electromagnetic coils and serve as fifth coils and sixth coils and seventh coils and eighth coils respectively;
the first coil and the second coil are coaxially and symmetrically arranged at two sides of the third coil; the axis of the third coil is perpendicular to the axes of the first coil and the second coil;
the third coil and the fourth coil are coaxial, and the axis is perpendicular to the first plane; the first plane is a plane in which axes of the first coil and the second coil are located;
the third coil radius is greater than the fourth coil radius.
It will be clear to those skilled in the art that, for convenience and brevity of description, the specific working process of the system described above and the related description may refer to the corresponding process in the foregoing method embodiment, which is not repeated here.
It should be noted that, in the magnetic particle imaging apparatus based on the oscillating gradient magnetic field encoding 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 multiple 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.
Referring to fig. 3, which is a top view of a magnetic particle imaging apparatus based on an oscillating gradient magnetic field encoding in an embodiment of the present invention, 1 and 2 in fig. 3 respectively represent electromagnetic low-frequency gradient coils in an oscillating gradient magnetic field generator, and an oscillating gradient magnetic field can be generated in an imaging field of view under the power supply of a low-frequency ac power supply. In fig. 3, 3 shows a magnetic field transmitting coil in a uniform high-frequency magnetic field generator, and a uniform high-frequency alternating magnetic field can be generated in an imaging field of view by an oscillating gradient magnetic field under the power supply of a high-frequency alternating current power supply, wherein the magnetic field transmitting coil is shown as a single-channel magnetic field transmitting coil along the x direction in the axial direction, and a multi-channel magnetic field transmitting coil along the y and z directions can be additionally added. In fig. 3, 4 represents a receiving coil along the x direction, 5 and 6 represents a receiving coil along the y direction, 7 and 8 represent a receiving coil along the z direction, and the receiving coils in the three directions form a multichannel receiving coil together, are used for collecting dynamic magnetization vector signals of magnetic nano particles along different directions, and are transmitted to a digital signal processing unit through an amplifying and filtering circuit. The digital signal processing unit is responsible for carrying out Fourier transform on the acquired time domain signals to frequency signals, then carrying out frequency selection, and selecting the needed intermodulation frequency component signals. The image reconstruction unit is used for carrying out image reconstruction by combining the selected intermodulation frequency component signals and a system matrix which is measured in advance.
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 particle imaging method based on oscillating gradient magnetic field encoding described above.
A fourth embodiment of the present invention is a computer-readable storage medium storing computer instructions for execution by the computer to implement the magnetic particle imaging method based on oscillating gradient magnetic field encoding described above.
It will be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working process of the storage device and the processing device described above and the related description may refer to the corresponding process in the foregoing method embodiment, which is not repeated herein.
Those of skill in the art will appreciate that the various illustrative modules, method steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the program(s) corresponding to the software modules, method steps, may be embodied in Random Access Memory (RAM), memory, read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. To clearly illustrate this interchangeability of electronic hardware and software, various illustrative components and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as electronic hardware or software depends upon the particular application and design constraints imposed on the solution. Those skilled in the art may implement the described functionality using different approaches for each particular application, but such implementation is not intended to be limiting.
Referring now to FIG. 4, there is shown a block diagram of a computer system for a server implementing embodiments of the methods, systems, and apparatus of the present application. The server illustrated in fig. 4 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. 4, the computer system includes a central processing unit (CPU, central Processing Unit) 401, which can perform various appropriate actions and processes according to a program stored in a Read Only Memory (ROM) 402 or a program loaded from a storage section 408 into a random access Memory (RAM, random Access Memory) 403. In the RAM403, various programs and data required for the system operation are also stored. The CPU 401, ROM 402, and RAM403 are connected to each other by a bus 404. An Input/Output (I/O) interface 405 is also connected to bus 404.
The following components are connected to the I/O interface 405: an input section 406 including a keyboard, a mouse, and the like; an output portion 407 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 408 including a hard disk or the like; and a communication section 409 including a network interface card such as a LAN (local area network ) card, a modem, or the like. The communication section 409 performs communication processing via a network such as the internet. The drive 410 is also connected to the I/O interface 405 as needed. A removable medium 411 such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is installed on the drive 410 as needed, so that a computer program read therefrom is installed into the storage section 408 as needed.
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 409 and/or installed from the removable medium 411. The above-described functions defined in the method of the present application are performed when the computer program is executed by a Central Processing Unit (CPU) 401. It should be noted that the computer readable medium described in the present application may be a computer readable signal medium or a computer readable storage medium, or any combination of the two. The computer readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a combination of any of the foregoing. More specific examples of the 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. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. In the present application, however, a computer-readable signal medium may include a data signal propagated in baseband or as part of a carrier wave, with computer-readable program code embodied therein. Such a propagated data signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination of the foregoing. A computer readable signal medium may also be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an 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 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 be within the scope of the present invention.
Claims (10)
1. A magnetic particle imaging method based on oscillating gradient magnetic field coding is applied to magnetic particle imaging equipment; the magnetic particle imaging equipment comprises a low-frequency gradient coil, a high-frequency excitation coil and a multichannel receiving coil; characterized in that the method comprises:
introducing sine or cosine current to the low-frequency gradient coil to enable the low-frequency gradient coil to generate an oscillating gradient magnetic field with gradient strength continuously changing along with time and three direction components in an imaging view field of the magnetic particle imaging equipment;
current is introduced into the high-frequency excitation coil, and a uniform high-frequency alternating magnetic field is generated; superposing the uniform high-frequency alternating magnetic field on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field;
exciting magnetic particles in an imaging field of the magnetic particle imaging device by using the double-frequency nonuniform excitation magnetic field to generate mixed magnetization response signals in three directions; the multichannel receiving coil is utilized to collect time domain signals of the mixed magnetization response signals of the magnetic particles along different directions simultaneously;
performing Fourier transform on the time domain signal to obtain a frequency signal and extracting an intermodulation frequency component signal from the frequency signal; and calculating the concentration of the magnetic particles by combining the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment, so as to realize magnetic particle imaging.
2. The method for magnetic particle imaging based on oscillating gradient magnetic field encoding according to claim 1, wherein the alternating frequency of the uniform high-frequency alternating magnetic fieldOscillation frequency greater than the oscillating gradient magnetic field>。
3. The method of magnetic particle imaging based on oscillating gradient magnetic field encoding of claim 1, wherein the oscillating gradient magnetic field is:
；
；
；
；
wherein,representing an oscillating gradient magnetic field>Representing space vector>Time of presentation->、/>、/>Respectively represent oscillating laddersGradient strength of the gradient magnetic field along the x, y and z directions; />、/>、/>Respectively represent peak gradient intensity of the oscillating gradient magnetic field along x, y and z directions, +.>The oscillation frequency is represented, and t is time.
4. The method of magnetic particle imaging based on oscillating gradient magnetic field encoding of claim 1, wherein the dual-frequency inhomogeneous excitation magnetic field is:
；
；
wherein,representing a dual-frequency inhomogeneous excitation field, +.>Representing the magnitude of a uniform high-frequency alternating magnetic field,/->Representing the oscillating gradient magnetic field at different positions +.>Magnetic field amplitude at>Indicating the alternating frequency of the uniform high-frequency alternating magnetic field,represents the oscillation frequency +.>Representing space vector>，/>，/>Representing the vector of the oscillating gradient magnetic field in the x, y, z direction, < >>、/>、/>Respectively represent peak gradient intensity of the oscillating gradient magnetic field along x, y and z directions, and x, y and z represent space vectorsIs defined by the coordinates of (a).
5. The method for magnetic particle imaging based on oscillating gradient magnetic field encoding according to claim 2, wherein,
the fourier expansion of the time domain signal of the mixed magnetization response signal is:
；
wherein,representing the frequency signal; />Indicating a frequency of +.>Fourier coefficients of intermodulation frequency components of a time domain signal of the magnetization response signal; />；/>t represents time, < >>Representing the alternating frequency of a uniform high-frequency alternating magnetic field; />Representing the oscillation frequency of the oscillating gradient magnetic field; i represents imaginary units, ">Representing the oscillating gradient magnetic field at different positions +.>Magnetic field amplitude at>Representing the space vector.
6. The method of magnetic particle imaging based on oscillating gradient magnetic field encoding of claim 5, wherein said multichannel receiver coil acquires time domain signals of mixed magnetization response signals of said magnetic particles in different directions in parallel, each acquisition timeThe space isInteger multiples of (2); />Representing the oscillation frequency of the oscillating gradient magnetic field.
7. The method of magnetic particle imaging based on oscillating gradient magnetic field encoding of claim 6, wherein intermodulation frequency component signals are extracted from the frequency signals by:
extraction frequencyAs an extracted intermodulation frequency component signal.
8. The method for imaging magnetic particles based on oscillating gradient magnetic field encoding according to claim 6, wherein the method for realizing magnetic particle imaging is as follows:
firstly, obtaining an imaging equation based on the extracted intermodulation frequency component signals and a system matrix of the magnetic particle imaging equipment; the imaging equation is:
；
wherein,representing the extracted intermodulation frequency component signals; />Representing a system matrix; />Indicate->The magnetic particle concentration at each position, L is the total number of pixels after discretization of the imaging field of view, +.>Representing a spatial position index number; />The oscillating gradient magnetic field is spatially->A location of the site;
by measuring the extracted intermodulation frequency component signal each timeAnd a system matrix of the magnetic particle imaging deviceInversion calculation of the concentration of the magnetic particles>；
And then based on theMagnetic particle imaging was performed.
9. A magnetic particle imaging apparatus based on oscillating gradient magnetic field encoding, a magnetic particle imaging method based on oscillating gradient magnetic field encoding according to any of the preceding claims 1-7, characterized in that the system comprises:
an oscillating gradient magnetic field generator comprising one or more pairs of low frequency gradient coils and an alternating current source; the oscillating gradient magnetic field generator is used for generating an oscillating gradient magnetic field with gradient strength changing along with time and three direction components in an imaging view field of the magnetic particle imaging device;
the uniform high-frequency magnetic field generator comprises a single-channel or multi-channel high-frequency excitation coil and a high-frequency alternating current source; the uniform high-frequency magnetic field generator is used for generating a uniform high-frequency alternating magnetic field in an imaging view field of the magnetic particle imaging device; the uniform high-frequency alternating magnetic field is overlapped on the oscillating gradient magnetic field to form a double-frequency nonuniform excitation magnetic field; the dual-frequency nonuniform excitation magnetic field excites magnetic particles in an imaging view field of the magnetic particle imaging device to generate a mixed frequency magnetization response signal;
the multichannel magnetic induction receiver comprises a multichannel receiving coil and an amplifying and filtering circuit; the multichannel magnetic induction receiver is used for collecting time domain signals of mixed frequency magnetization response signals of magnetic particles along different directions in parallel;
a digital signal processing unit for performing fourier transform on the time domain signal and extracting intermodulation frequency component signals;
and the image reconstruction unit is used for carrying out image reconstruction by combining the extracted intermodulation frequency component signals and the system matrix of the magnetic particle imaging equipment.
10. A magnetic particle imaging device based on oscillating gradient magnetic field encoding, wherein if the oscillating gradient magnetic field generator comprises a pair of low frequency gradient coils, the multichannel magnetic induction receiver comprises three groups of independent-channel receiving coils which are mutually orthogonal in axial direction;
the two low-frequency gradient coils are annular electromagnetic coils and are respectively used as a first coil and a second coil; the high-frequency excitation coil is a cylindrical coil and is used as a third coil; the receiving coils parallel to the high-frequency excitation coil in the receiving coils of the three groups of independent channels are cylindrical coils and serve as fourth coils, and the other two groups of coils are annular electromagnetic coils and serve as fifth coils and sixth coils and seventh coils and eighth coils respectively;
the first coil and the second coil are coaxially and symmetrically arranged at two sides of the third coil; the axis of the third coil is perpendicular to the axes of the first coil and the second coil;
the third coil and the fourth coil are coaxial, and the axis is perpendicular to the first plane; the first plane is a plane in which axes of the first coil and the second coil are located;
the third coil radius is greater than the fourth coil radius.
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