Magnetic particle imaging apparatus, magnetic particle imaging method, and magnetic particle imaging program
The magnetic particle imaging apparatus corrects for external magnetic field interference by scanning and rotating a linear zero magnetic field region, enabling high spatial resolution magnetic nanoparticle imaging.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2025-04-30
- Publication Date
- 2026-05-29
Smart Images
Figure 0007867594000001 
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Abstract
Description
Technical Field
[0005]
[0001] The present disclosure relates to a magnetic particle imaging apparatus, a magnetic particle imaging method, and a magnetic particle imaging program.
Background Art
[0002] There has been a proposal for a magnetic particle imaging (also referred to as "Magnetic Particle Imaging (MPI)") apparatus that injects magnetic nanoparticles as a contrast agent into an imaging target and images the spatial distribution of the magnetic nanoparticles in the imaging target based on a harmonic signal generated from the magnetization change of the magnetic nanoparticles. Patent Document 1 discloses a magnetic particle imaging apparatus that forms a linear zero magnetic field region with a static magnetic field generation coil, causes a magnetization change in the magnetic nanoparticles existing in this linear zero magnetic field region, and detects the harmonic signal generated at that time at each position in the scanning direction of the linear zero magnetic field region to image the spatial distribution of the magnetic nanoparticles.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the above magnetic particle imaging apparatus, it is desirable to detect only the magnetization change generated by the magnetic nanoparticles existing in the linear zero magnetic field region. However, in reality, it is affected by the local magnetic field generated by the magnetic nanoparticles near the outside (for example, the periphery) of the linear zero magnetic field region, and the magnetization change also occurs in the magnetic nanoparticles around the linear zero magnetic field region. Therefore, a magnetic nanoparticle image with low spatial resolution is generated.
[0005] This disclosure aims to provide a magnetic particle imaging apparatus, a magnetic particle imaging method, and a magnetic particle imaging program that enable the generation of magnetic nanoparticle images with high spatial resolution. [Means for solving the problem]
[0006] The magnetic particle imaging apparatus of this disclosure is an apparatus for generating a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles in a subject, comprising: a linear zero magnetic field generation unit that forms a linear zero magnetic field region in the subject and moves the linear zero magnetic field region in a predetermined direction; an excitation magnetic field application unit that applies an alternating current excitation magnetic field to a magnetic field region including the linear zero magnetic field region; a detection unit that detects the magnetization change of the magnetic nanoparticles generated by the excitation magnetic field; and a control unit. When generating the magnetic nanoparticle image, the control unit causes the linear zero magnetic field generation unit to form the linear zero magnetic field region within the imaging target as the subject, scan or rotate the linear zero magnetic field region, or scan and rotate it, causes the excitation magnetic field application unit to apply the excitation magnetic field, causes the detection unit to detect the magnetization change, generates projection data of the magnetization change based on the position of the linear zero magnetic field region in the scanning direction and the angle of the linear zero magnetic field region in the rotation direction, generates corrected projection data by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each projection data, and generates the magnetic nanoparticle image based on the corrected projection data. The control unit, when generating the system function, is characterized in that it causes the linear zero magnetic field generation unit to form the linear zero magnetic field region within the structure which is the subject, which contains the magnetic nanoparticles of a predetermined particle concentration and has a predetermined size, scans or rotates or scans and rotates the linear zero magnetic field region, causes the excitation magnetic field application unit to apply the excitation magnetic field to the magnetic field region including the linear zero magnetic field region within the structure, causes the detection unit to detect the magnetization change within the structure, and generates the system function for each projection data based on the magnetization change within the structure.
[0007] The magnetic particle imaging method of the present disclosure is a method performed by a magnetic particle imaging apparatus that generates a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within an object to be imaged, and comprises: a linear zero magnetic field generation unit that forms a linear zero magnetic field region within an object, scans the linear zero magnetic field region in a predetermined scanning direction and moves it in a predetermined direction; an excitation magnetic field application unit that applies an alternating current excitation magnetic field to a magnetic field region including the linear zero magnetic field region; and a detection unit that detects the magnetization change of magnetic nanoparticles generated by the excitation magnetic field, and generates a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within an object to be imaged as an object, the object being imaged. When generating the magnetic nanoparticle image, the process includes: forming a linear zero magnetic field region within the imaging target in the linear zero magnetic field generation unit, scanning or rotating the linear zero magnetic field region, or scanning and rotating the linear zero magnetic field region; applying the excitation magnetic field to the excitation magnetic field application unit; detecting the magnetization change in the detection unit; generating projection data of the magnetization change based on the position of the linear zero magnetic field region in the scanning direction and the angle of the linear zero magnetic field region in the rotation direction; generating corrected projection data by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each of the projection data; and generating the magnetic nanoparticle image based on the corrected projection data. When generating the system function, the method is characterized by comprising the steps of: forming a linear zero magnetic field region within a structure which is the subject containing magnetic nanoparticles of a predetermined particle concentration and having a predetermined size in the linear zero magnetic field generation unit, and scanning or rotating or scanning and rotating the linear zero magnetic field region; applying the excitation magnetic field application unit to the magnetic field region including the linear zero magnetic field region within the structure; detecting the magnetization change within the structure in the detection unit; and generating the system function for each projection data based on the magnetization change within the structure. [Effects of the Invention]
[0008] By using the magnetic particle imaging apparatus, magnetic particle imaging method, and magnetic particle imaging program of this disclosure, it is possible to generate magnetic nanoparticle images with high spatial resolution. [Brief explanation of the drawing]
[0009] [Figure 1] This figure schematically shows the configuration of a magnetic particle imaging apparatus according to an embodiment. [Figure 2] This is a perspective view schematically showing the structure of the main parts of the MPI device according to the embodiment and a human being, which is the subject of imaging. [Figure 3] This is a schematic perspective view showing the structure of the main parts of the MPI device according to the embodiment, and the cylindrical body as a structural element. [Figure 4] This figure shows magnetic nanoparticles of known concentration, a linear zero-magnetic-field region, a measured magnetic response signal, and a known magnetic response signal. [Figure 5] This figure shows the relationship between the system function, the spatial distribution of magnetic nanoparticles, and the magnetic signal (measurement vector). [Figure 6] This figure shows an example of the hardware configuration of an MPI device according to the embodiment. [Figure 7] This flowchart shows an example of the magnetic nanoparticle image generation process of the MPI device according to the embodiment. [Figure 8] This flowchart shows an example of the system function generation process for an MPI device according to the embodiment. [Figure 9] Figure 9(A) shows an example of projection data on scan position and angular coordinates. Figure 9(B) shows a waveform indicating the intensity of the measured MPI signal at a certain angle and a signal obtained by processing the measured MPI signal with a Fast Fourier Transform (FFT). [Figure 10] Figure 10(A) shows the signal from Figure 9(B). Figure 10(B) shows the waveform indicating the intensity of the signal obtained by removing the DC component from the measured MPI signal in Figure 10(A), and the signal obtained by performing FFT processing on the measured MPI signal from which the DC component has been removed. [Figure 11]Figure 11(A) shows the signal from Figure 10(B). Figure 11(B) shows the waveform of the measured MPI signal, which is a magnetic signal detected from a cylindrical object that is the standard imaging target, and the signal obtained by processing this measured MPI signal with FFT. Figure 11(C) shows the inverse convolution coefficients calculated from Figures 11(A) and (B) and the coefficients obtained by processing them with FFT. [Figure 12] Figure 12(A) shows the signal in Figure 10(B). Figure 12(B) shows the coefficients in Figure 11(C). Figure 12(C) shows the waveform indicating the intensity of the denoised MPI signal, which is the corrected MPI signal, and the signal obtained by processing the denoised MPI signal with FFT. [Figure 13] Figure 13(A) shows the corrected projection data. Figure 13(B) shows the original, uncorrected projection data. [Figure 14] Figure 14(A) shows an image of magnetic nanoparticles created by image reconstruction on corrected projection data. Figure 14(B) shows an image of magnetic nanoparticles based on the original, uncorrected projection data. [Modes for carrying out the invention]
[0010] The following describes an MPI device, MPI method, and MPI program according to an embodiment, with reference to the drawings. The following embodiment is merely an example, and it is possible to combine the embodiments as appropriate and modify each embodiment as appropriate.
[0011] Figures 1-4 show the coordinate axes of the XYZ Cartesian coordinate system to facilitate understanding of the relationships between the figures. The Z axis is the longitudinal axis of the linear zero magnetic field (also called "Free Field Line (FFL)") region. The Y axis is the coordinate axis in the scanning direction (Y direction) of the FFL region, perpendicular to the Z axis. The X axis is the coordinate axis perpendicular to both the Z and Y axes. In Figures 2 and 3, the R direction indicates the rotation direction of the FFL region. In Figures 2 and 3, the central axis of rotation in the R direction is the X direction axis. Note that identical or corresponding components in the figures are denoted by the same reference numerals.
[0012] 《Configuration of MPI Device》 FIG. 1 is a diagram schematically showing the configuration of an MPI device 1 according to an embodiment. The MPI device 1 is a device that generates (also referred to as "reconstructs") a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within an imaging target 50 as a subject. Further, the MPI device 1 is a device capable of implementing the MPI method according to the embodiment. Further, the MPI device 1 is a device capable of executing the MPI program according to the embodiment.
[0013] FIG. 2 is a perspective view schematically showing the structure of a main part of the MPI device 1 and the imaging target 50. The imaging target 50 is, for example, a human in whom magnetic nanoparticles have been administered into the body. The imaging target 50 may be something other than a human (for example, an animal, a plant, etc.). The magnetic nanoparticles are magnetic particles having a diameter in the nanometer range containing a magnetic substance. The magnetic nanoparticles are formed, for example, to have the property of gathering at an affected part (for example, specific cells in the brain, organs, etc.) after being administered to a human. As the magnetic nanoparticles, for example, "Resovist (registered trademark)" (generic name: Ferucarbotran), which is a hydrophilic colloidal solution of superparamagnetic iron oxide coated with carboxydextran, is known.
[0014] As shown in FIG. 1, the MPI device 1 includes a linear zero magnetic field generation unit 10 that forms an FFL region 60, an excitation magnetic field application unit 20 that applies an alternating excitation magnetic field, a detection unit 30 as a magnetization change detection unit that detects (that is, measures) the magnetization change of the magnetic nanoparticles, and a control unit 40 that controls the entire device.
[0015] The linear zero magnetic field generation unit 10 forms an FFL region 60 within the subject and moves the FFL region 60 in a predetermined direction. For example, the linear zero magnetic field generation unit 10 forms an FFL region 60 within the subject and scans the FFL region 60 in a predetermined scanning direction (Y direction), or rotates the FFL region 60 in a predetermined rotation direction (R direction), or scans the FFL region 60 in a predetermined scanning direction (Y direction) and rotates it in a predetermined rotation direction (R direction). The linear zero magnetic field generation unit 10 has a linear zero magnetic field generation coil 11 as a first linear zero magnetic field generation unit and a linear zero magnetic field generation coil 12 as a second linear zero magnetic field generation unit. The linear zero magnetic field generation coils 11 and 12 are arranged on opposite sides of the imaging target 50, which is the subject. The linear zero magnetic field generation coils 11 and 12 are magnetic field generating coils and are powered by linear zero magnetic field power supplies 13 and 14.
[0016] The linear zero-field generation unit 10 moves the FFL region 60 linearly by a predetermined distance in the scanning direction (for example, the Y direction in Figures 1-3). For example, the linear zero-field generation unit 10 sequentially moves the position of the FFL region 60 to each of a plurality of predetermined positions in the scanning direction. The scanning direction is, for example, the Y direction perpendicular to the longitudinal direction (Z direction) of the FFL region 60. The movement of the FFL region 60 is performed, for example, by controlling the linear zero-field power supplies 13 and 14. Alternatively, the movement of the FFL region 60 may be performed by moving the imaging target 50, moving the linear zero-field generation unit 10, or moving the imaging target 50 and the linear zero-field generation unit 10 together.
[0017] Furthermore, the linear zero-field generation unit 10 can rotate the FFL region 60 by predetermined rotation angles. The linear zero-field generation unit 10 rotates the FFL region 60, for example, in the R direction parallel to the YZ plane. The rotation of the FFL region 60 is performed, for example, by controlling the linear zero-field power supplies 13 and 14. Alternatively, the rotation of the FFL region 60 may be performed by rotating the linear zero-field generation coils 11 and 12 in the R and -R directions, or by rotating the imaging target 50 in the R and -R directions.
[0018] The excitation magnetic field application unit 20 includes an excitation magnetic field generating coil 21 that applies an alternating current excitation magnetic field to a magnetic field region including the FFL region 60, and an excitation magnetic field power supply 22 that supplies power to the excitation magnetic field generating coil 21. As shown in Figures 1 to 3, the excitation magnetic field generating coil 21 is, for example, an annular coil wound in the R direction.
[0019] The detection unit 30 detects the magnetization change of magnetic nanoparticles contained within the FFL region 60 caused by the excitation magnetic field (more precisely, it detects the harmonic signals generated by the magnetization change as a magnetic response signal). The detection unit 30 has, for example, one or more magnetic field detectors (e.g., magnetic field detection coils). The detection signal output from the detection unit 30 may be amplified by an amplification circuit. One or more magnetic field detectors may be semiconductor elements for magnetic field detection (e.g., Hall elements).
[0020] The control unit 40 controls the overall operation of the MPI device 1. When generating a magnetic nanoparticle image, the control unit 40 instructs the linear zero magnetic field generation unit 10 to form an FFL region 60 within the imaging target 50, scans or rotates or scans and rotates the FFL region 60, applies an excitation magnetic field to the excitation magnetic field application unit 20, and causes the detection unit 30 to detect the magnetization change. Furthermore, the control unit 40 changes the position of the FFL region 60 in the scanning direction (Y direction) and the angle of the rotation direction R of the FFL region 60, generates projection data of the magnetization change based on the position of the FFL region 60 in the scanning direction and the angle of the FFL region 60, and generates corrected projection data by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each projection data. Furthermore, the control unit 40 generates a magnetic nanoparticle image (for example, Figure 14(A) described later) based on the corrected projection data (for example, Figure 13(A) described later).
[0021] Figure 3 is a schematic perspective view showing the structure of the main part of the MPI device 1 according to the embodiment and the structure 51 as the subject. The structure 51 is, for example, a cylinder. However, the structure 51 is not limited to a cylinder. The system function used to generate the corrected projection data is generated in advance. When generating the system function, the control unit 40 causes the linear zero magnetic field generation unit 10 to form an FFL region 60 within the structure 51, which is a reference subject containing magnetic nanoparticles of a predetermined particle concentration and having a predetermined size, to scan or rotate the FFL region 60, or scan and rotate it, to cause the excitation magnetic field application unit 20 to apply an excitation magnetic field to the magnetic field region including the FFL region 60 within the structure 51, to cause the detection unit 30 to detect the magnetization change within the structure 51, and generates a system function for each projection data based on the magnetization change within the structure 51. The system function is generated based on the detection sensitivity of each position in the scanning direction and each angle in the rotation direction.
[0022] Figure 4 shows magnetic nanoparticles of known concentration, the FFL region 60, the measured magnetic response signal, and a known magnetic response signal. All 8x4 circles shown in Figure 4 represent magnetic nanoparticles of known concentration. Figure 4 shows that the FFL region 60 moves in the Y direction, the measured magnetic response signal is the sum of magnetic signals generated in and around the FFL region 60 and has a waveform similar to a triangular waveform, and the ideal known magnetic response characteristic (sum of magnetic signals generated only in the FFL region 60) is a rectangular waveform shown by a dashed line. By exciting magnetized magnetic nanoparticles, the detection unit 30 directly detects a magnetic signal corresponding to the change in magnetization (i.e., the change in magnetization of the magnetic nanoparticles) from the magnetic nanoparticles within the field of view (FOV) of the detection unit 30.
[0023] Figure 5 shows the relationship between the system function S, the spatial distribution c of magnetic nanoparticles in the FFL region 60, and the measured magnetic response signal u (i.e., the measurement vector). As shown in Figure 5, the measured magnetic response signal u is obtained by convolving the system function S, which represents the detection sensitivity (i.e., magnetic properties), onto the spatial distribution c of magnetic nanoparticles in the FFL region 60.
[0024] Figure 6 shows an example of the hardware configuration of the MPI device 1 according to an embodiment. As shown in Figure 6, the control unit 40 of the MPI device 1 has a processor 41 such as a CPU (Central Processing Unit) and a memory 42 which is a volatile storage device. The control unit 40 may be a computer. The memory 42 is a semiconductor memory such as RAM (Random Access Memory). The MPI device 1 also has a storage device 70 such as a hard disk drive (HDD) or a solid state drive (SSD). The storage device 70 may be part of an external device that can communicate with the MPI device 1. The storage device 70 may be, for example, the storage device of a server that can communicate via a network.
[0025] Each function of the MPI device 1 is realized by a processing circuit. The processing circuit may be dedicated hardware or a processor 41 that executes a program stored in memory 42 (for example, an MPI program that executes the MPI method according to the embodiment). The processor 41 may be a processing unit, arithmetic unit, microprocessor, microcomputer, or DSP (Digital Signal Processor).
[0026] When the processing circuit is dedicated hardware, the processing circuit may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination of any of these.
[0027] When the processing circuit is a processor 41, the MPI program is implemented by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in memory 42. The processor 41 implements the functions of each part by reading and executing the MPI program stored in memory 42.
[0028] Furthermore, the MPI device 1 may be partially implemented with dedicated hardware and partially implemented with software or firmware. In this way, the processing circuit can implement each function using hardware, software, firmware, or any combination of these.
[0029] Operation during the generation of magnetic nanoparticle images Next, we will explain the operation of the MPI device 1 when generating magnetic nanoparticle images. The operation of the MPI device 1 when generating magnetic nanoparticle images differs from that described in Patent Document 1 in that it uses a system function to perform correction processing on the projection data.
[0030] Figure 7 is a flowchart illustrating an example of the magnetic nanoparticle image generation process of the MPI device 1. Figure 7 shows an example in which the MPI device 1 changes both the scanning direction position and the angle of the FFL region 60. However, the MPI device 1 may change only the scanning direction position of the FFL region 60, or only the angle of the FFL region 60.
[0031] First, the control unit 40 controls the linear zero magnetic field generation unit 10 to form an FFL region 60 within the imaging target 50 (shown in Figure 2), and sets the position of the FFL region 60 in the scanning direction to an initial position (step ST11). The initial position is, for example, a predetermined position in the Y direction in Figure 2.
[0032] Next, the control unit 40 controls the linear zero magnetic field generation unit 10 to set the angle of the FFL region 60 to the initial angle (step ST12). The initial angle is, for example, a predetermined angle in the R direction in Figure 2.
[0033] Next, the control unit 40 controls the excitation magnetic field application unit 20 to excite the magnetic nanoparticles in the FFL region 60, causing the detection unit 30 to detect the change in magnetization (step ST13).
[0034] Next, the control unit 40 determines whether detection has been completed for all predetermined angles in the R direction of the FFL region 60 at the current scanning direction position. If there are angles that have not been detected (NO in step ST14), the control unit 40 returns to step ST12, controls the linear zero magnetic field generation unit 10 to rotate the FFL region 60 by a certain rotation angle to set it to the next angle (i.e., one of the predetermined angles), proceeds to step ST13, and returns to step ST14. If there are no angles that have not been detected at the current scanning direction position, i.e., detection has been completed for all angles (YES in step ST14), the control unit 40 proceeds to step ST15.
[0035] In step ST15, the control unit 40 determines whether detection (i.e., processing in steps ST12 to ST14) has been completed for all of the predetermined positions in the Y direction of the FFL region 60. If there are positions where detection is not yet complete (NO in step ST15), the control unit 40 returns to step ST11, controls the linear zero magnetic field generation unit 10 to move the FFL region 60 a certain distance in the Y direction to set it to the next position (i.e., one of the predetermined positions), goes through the processing in steps ST12 to ST14, and returns to the processing in step ST15. If there are no positions where detection is not yet complete, i.e., detection has been completed for all positions (YES in step ST15), the control unit 40 proceeds to step ST16.
[0036] In step ST16, the control unit 40 generates projection data of the magnetization change based on the position and angle of the magnetization change (for example, the projection position and projection angle of the projection data relative to the detection unit 30). Here, the projection data is data obtained by projecting the detection data onto the magnetic field detector of the detection unit 30 in a direction along the FFL region 60. Therefore, the projection position is the position corresponding to the position in the scanning direction of the FFL region 60. The projection position is also called the scan position. The projection angle is the angle corresponding to the rotation angle in the R direction of the FFL region 60.
[0037] In step ST17, the control unit 40 selects a system function for each projection position and projection angle from the storage device 70, performs sensitivity correction on the projection data using the selected system function, and generates corrected projection data. Alternatively, the control unit 40 may select a system function from the storage device 70, estimate a system function other than the selected system function by interpolation on the position in the scanning direction or the angle in the rotation direction of the linear zero magnetic field region, or both, using the selected system function, and perform sensitivity correction on the projection data using the selected system function and the estimated system function to generate corrected projection data. In this case, the number of system functions to be acquired in advance can be reduced.
[0038] In step ST18, the control unit 40 generates a magnetic nanoparticle image based on the corrected projection data.
[0039] 《Operation during the generation of system functions》 Figure 8 is a flowchart illustrating an example of the system function generation process of the MPI device 1. Figure 8 shows an example in which the MPI device 1 changes both the scanning direction position and the angle of the FFL region 60. However, the MPI device 1 may change only the scanning direction position of the FFL region 60, or only the angle of the FFL region 60.
[0040] In generating the system function, first, the control unit 40 controls the linear zero-field generation unit 10 to generate an FFL region 60 within the structure 51 (Figure 3), and sets the position of the FFL region 60 in the scanning direction to an initial position (step ST21). The initial position is, for example, a predetermined position in the Y direction in Figure 3.
[0041] Next, the control unit 40 controls the linear zero magnetic field generation unit 10 to set the angle of the FFL region 60 to the initial angle (step ST22). The initial angle is, for example, a predetermined angle in the R direction in Figure 3.
[0042] Next, the control unit 40 controls the excitation magnetic field application unit 20 to excite the magnetic nanoparticles in the FFL region 60, causing the detection unit 30 to detect the change in magnetization (step ST23).
[0043] Next, the control unit 40 determines whether detection has been completed for all of the predetermined angles in the R direction of the FFL region 60 at the current scanning direction position. If there are angles that have not been detected at the current scanning direction position (NO in step ST24), the control unit 40 returns to step ST22, controls the linear zero magnetic field generation unit 10 to rotate the FFL region 60 by a certain rotation angle to set it to the next angle (i.e., one of the predetermined angles), proceeds to step ST23, and returns to step ST24. If there are no angles that have not been detected at the current scanning direction position, i.e., detection has been completed for all angles (YES in step ST24), the control unit 40 proceeds to step ST25.
[0044] In step ST25, the control unit 40 determines whether detection (i.e., processing in steps ST22 to ST24) has been completed for all of the predetermined positions in the Y direction of the FFL region 60. If there are positions in the scanning direction for which detection has not been completed (NO in step ST25), the control unit 40 returns to step ST21, controls the linear zero magnetic field generation unit 10 to move the FFL region 60 by a certain distance in the Y direction to set it to the next scanning direction position (i.e., one of the predetermined positions in the scanning direction), and returns to step ST25 after processing in steps ST22 to ST24. If there are no positions in the scanning direction for which detection has not been completed, that is, if detection has been completed for all positions in the scanning direction (YES in step ST25), the control unit 40 proceeds to step ST26.
[0045] In step ST26, the control unit 40 generates projection data of the magnetization change based on the position and angle of the magnetization change (for example, the projection position and projection angle of the projection data relative to the detection unit 30).
[0046] In step ST27, the control unit 40 generates a system function that indicates the detection sensitivity for each combination of position and angle in the scanning direction, and in step ST28, the system function set containing the multiple system functions is stored in the storage device 70.
[0047] 《Process for generating images from projection data》 The process of generating reconstructed images from projection data will be explained with reference to Figures 9(A) and (B) through 14(A) and (B).
[0048] First, the control unit 40 extracts MPI signals at multiple angles from the projection data. These multiple angles are, for example, rotational angles indicated by R. Figure 9(A) shows an example of projection data projected onto a scan position-angle coordinate system. The scan position corresponds to the positions of the multiple magnetic field detectors (or detection elements) of the detection unit 30. In Figure 9(A), the brighter the area, the stronger the intensity of the measured MPI signal, which is the measured magnetic response signal, i.e., the larger the amplitude. Figure 9(B) shows the waveform (Original Signal) indicating the intensity of the measured MPI signal at a certain angle in Figure 9(A), and the signal obtained by processing the measured MPI signal with a Fast Fourier Transform (FFT) (Original Signal FFT).
[0049] Next, the control unit 40 removes the DC component from the signal in Figure 9(B). Figure 10(A) shows the signal in Figure 9(B). Figure 10(B) shows the waveform (Signal without DC) indicating the intensity of the signal obtained by removing the DC component from the measured MPI signal in Figure 10(A), and the signal (Signal without DC FFT) obtained by performing FFT processing on the measured MPI signal from which the DC component has been removed.
[0050] Next, the control unit 40 calculates the inverse convolution coefficient S(f) as a system function from the signal in Figure 10(B) and the ideal MPI signal. Figure 11(A) shows the signal in Figure 10(B). Figure 11(B) shows the waveform of the ideal MPI signal m(x), which is the magnetic signal detected from the cylindrical body that is the reference structure 51, and the signal M(f) obtained by processing this ideal MPI signal with FFT. Figure 11(C) shows the inverse convolution coefficient s(t) calculated from Figures 11(A) and (B), and the inverse convolution coefficient FFT S(f) obtained by processing it with FFT. Here, f is the frequency, t is the time, and x is the position in the scanning direction (or the position of the magnetic field detector).
[0051] Next, the control unit 40 calculates the denoised MPI signal m(x) and the Fourier transformed signal M(f) from the signal in Figure 10(B) and the inverse convolution coefficients (i.e., the system function) in Figure 11(C). Figure 12(A) shows the signal in Figure 10(B). Figure 12(B) shows the inverse convolution coefficients in Figure 11(C). Figure 12(C) shows the waveform indicating the intensity of the denoised MPI signal m(x) as a corrected MPI signal and the signal M(f) obtained by processing the denoised MPI signal with FFT.
[0052] The processes shown in Figures 9(A) and (B) through 12(A) to (C) allow for the generation of a denoised MPI signal, as shown in Figure 12(C), from the signal based on the original projection data shown in Figure 9(B).
[0053] Effects of the Embodiment Figure 13(A) shows corrected projection data generated by the control unit 40 of the MPI device 1 according to the embodiment. Figure 13(B) shows the original projection data without correction (comparative example). As shown in Figure 13(A), the corrected projection data generated by the control unit 40 of the MPI device 1 according to the embodiment has a clear linear boundary between the area where magnetic nanoparticles are present (white area) and the area where magnetic nanoparticles are not present (black area). Thus, by using the MPI device 1 according to the embodiment, it is possible to generate magnetic nanoparticle images with high spatial resolution.
[0054] Figure 14(A) shows a magnetic nanoparticle image created by image reconstruction on corrected projection data from the MPI device 1 according to the embodiment. Figure 14(B) shows a magnetic nanoparticle image based on the original, uncorrected projection data (comparative example). As shown in Figure 14(B), when an image is reconstructed using uncorrected projection data, the boundary between the area where magnetic nanoparticles exist (white area) and the area where magnetic nanoparticles do not exist (black area) becomes unclear. Note that the large outer circle in Figure 14(B) is an artifact. In contrast, as shown in Figure 14(A), the corrected projection data generated by the MPI device 1 according to the embodiment has a clear circular boundary between the area where magnetic nanoparticles exist (white area) and the area where magnetic nanoparticles do not exist (black area). Thus, by using the MPI device 1 according to the embodiment, it is possible to generate a magnetic nanoparticle image with high spatial resolution. [Explanation of Symbols]
[0055] 1 MPI device, 10 Linear zero field generation unit, 11, 12 Linear zero field generation coils, 13, 14 Power supply for linear zero field, 20 Excitation field application unit, 21 Excitation field generation coil, 22 Power supply for excitation field, 30 Detection unit, 40 Control unit, 50 Image target (subject), 51 Structure (subject), 60 FFL area, 70 Storage device, R Rotation direction.
Claims
1. A magnetic particle imaging device that generates a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within a subject, A linear zero magnetic field generating unit that forms a linear zero magnetic field region within the subject and moves the linear zero magnetic field region in a predetermined direction, An excitation magnetic field application unit that applies an alternating current excitation magnetic field to a magnetic field region including the linear zero magnetic field region, A detection unit for detecting the change in magnetization of the magnetic nanoparticles generated by the excitation magnetic field, Control unit and It has, When the control unit generates the magnetic nanoparticle image, The linear zero magnetic field generation unit forms the linear zero magnetic field region within the image target as the subject, and scans or rotates or scans and rotates the linear zero magnetic field region. The excitation magnetic field is applied to the excitation magnetic field application unit, The detection unit is instructed to detect the magnetization change. Projection data of the magnetization change is generated based on the position of the linear zero magnetic field region in the scanning direction and the angle of the linear zero magnetic field region in the rotation direction. Corrected projection data is generated by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each of the aforementioned projection data. Based on the corrected projection data, the magnetic nanoparticle image is generated. When the control unit generates the system function, The linear zero magnetic field generating unit forms the linear zero magnetic field region within the structure which is the subject, which contains the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, and scans or rotates the linear zero magnetic field region, or scans and rotates it. The excitation magnetic field application unit is used to apply the excitation magnetic field to a magnetic field region within the structure that includes the linear zero magnetic field region. The detection unit is instructed to detect the change in magnetization within the structure. The system function is generated for each projection data based on the magnetization change within the structure. A magnetic particle imaging apparatus characterized by the following features.
2. The magnetic particle imaging apparatus according to claim 1, characterized in that the linear zero magnetic field generation unit moves the linear zero magnetic field region in a linear fashion by a predetermined distance in the scanning direction during scanning.
3. The magnetic particle imaging apparatus according to claim 1 or 2, characterized in that the scanning direction is perpendicular to the longitudinal direction of the linear zero magnetic field region.
4. The magnetic particle imaging apparatus according to any one of claims 1 to 3, characterized in that the linear zero magnetic field generating unit rotates the linear zero magnetic field region by a predetermined rotation angle during the rotation.
5. When the control unit generates the system function, it generates a system function that indicates the detection sensitivity for each combination of position and angle, and stores a set of system functions including a plurality of the system functions in the storage device. A magnetic particle imaging apparatus according to any one of claims 1 to 4.
6. When generating the magnetic nanoparticle image, the control unit selects the system function from the storage device, performs sensitivity correction on the projection data using the selected system function, and generates the corrected projection data. The magnetic particle imaging apparatus according to feature 5.
7. When generating the magnetic nanoparticle image, the control unit selects the system function from the storage device, estimates a system function other than the selected system function by interpolation using the selected system function, performs sensitivity correction on the projection data using the selected system function and the estimated system function, and generates the corrected projection data. The magnetic particle imaging apparatus according to feature 5.
8. The storage device further comprises the storage device for storing the aforementioned system function set. A magnetic particle imaging apparatus according to any one of claims 5 to 7.
9. A magnetic particle imaging method is performed by a magnetic particle imaging apparatus that generates a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within an imaging target, which is the subject, and comprises: a linear zero magnetic field generation unit that forms a linear zero magnetic field region within a subject and moves the linear zero magnetic field region in a predetermined direction; an excitation magnetic field application unit that applies an alternating current excitation magnetic field to a magnetic field region including the linear zero magnetic field region; and a detection unit that detects the change in magnetization of magnetic nanoparticles generated by the excitation magnetic field, the apparatus generating a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within the imaging target, which is the subject, When generating the magnetic nanoparticle image, The linear zero magnetic field generation unit is used to form the linear zero magnetic field region within the imaging target, and the linear zero magnetic field region is scanned, rotated, or scanned and rotated. The steps include applying the excitation magnetic field to the excitation magnetic field application unit, The step of causing the detection unit to detect the change in magnetization, A step of generating projection data of the magnetization change based on the position of the linear zero magnetic field region in the scanning direction and the angle of the linear zero magnetic field region in the rotation direction, The steps include generating corrected projection data by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each of the aforementioned projection data, The step of generating the magnetic nanoparticle image based on the corrected projection data is included. When generating the function of the aforementioned system, The linear zero magnetic field generating unit forms the linear zero magnetic field region within the structure which is the subject, which contains the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, and the linear zero magnetic field region is scanned, rotated, or scanned and rotated. The steps include: applying the excitation magnetic field to the excitation magnetic field application unit to a magnetic field region within the structure that includes the linear zero magnetic field region; The step of causing the detection unit to detect the change in magnetization within the structure, The step of generating the system function for each projection data based on the magnetization change within the structure is also included. A magnetic particle imaging method characterized by the following features.
10. A magnetic particle imaging program is performed by a magnetic particle imaging apparatus that generates a magnetic particle image showing the spatial distribution of magnetic nanoparticles within an imaging target, which is the subject, and comprises: a linear zero magnetic field generation unit that forms a linear zero magnetic field region within a subject and moves the linear zero magnetic field region in a predetermined direction; an excitation magnetic field application unit that applies an alternating current excitation magnetic field to a magnetic field region including the linear zero magnetic field region; and a detection unit that detects the change in magnetization of magnetic nanoparticles generated by the excitation magnetic field, the apparatus having these components, When generating the magnetic nanoparticle image, the magnetic particle imaging apparatus is used. The linear zero magnetic field generation unit is used to form the linear zero magnetic field region within the imaging target, and the linear zero magnetic field region is scanned, rotated, or scanned and rotated. The steps include applying the excitation magnetic field to the excitation magnetic field application unit, The step of causing the detection unit to detect the change in magnetization, A step of generating projection data of the magnetization change based on the position of the linear zero magnetic field region in the scanning direction and the angle of the linear zero magnetic field region in the rotation direction, The steps include generating corrected projection data by performing sensitivity correction on the projection data using a system function that has been acquired in advance for each of the aforementioned projection data, The step of generating the magnetic nanoparticle image based on the corrected projection data is performed, When generating the aforementioned system function, the magnetic particle imaging apparatus is used. The linear zero magnetic field generating unit forms the linear zero magnetic field region within the structure which is the subject, which contains the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, and the linear zero magnetic field region is scanned, rotated, or scanned and rotated. The steps include: applying the excitation magnetic field to the excitation magnetic field application unit to a magnetic field region within the structure that includes the linear zero magnetic field region; The step of causing the detection unit to detect the change in magnetization within the structure, The procedure involves generating the system function for each projection data based on the magnetization change within the structure. A magnetic particle imaging program characterized by the following features.