Magnetic particle imaging device, magnetic particle imaging method, and magnetic particle imaging program

Abstract

An MPI device (1) generates projection data pertaining to magnetization change on the basis of the position of an FFL region (60) in the scanning direction (Y) and the angle in the rotation direction (R) of the FFL region (60); generates, using a system function acquired in advance for each piece of the projection data, corrected projection data by applying sensitivity correction to the projection data; and applies image reconstruction to the corrected projection data to generate a magnetic nanoparticle image. In generating the system function, a control unit (40) forms, in a linear zero magnetic field generation unit (10), the FFL region (60) within a structural body (51), which is a subject including magnetic nanoparticles at a predetermined particle concentration and having a predetermined size; scans, rotates, or scans and rotates the linear zero magnetic field region (60); causes an excited magnetic field application unit (20) to apply an excited magnetic field to a magnetic field region including the FFL region within the structural body (51); causes a detector (30) to detect the magnetization change within the structural body (51); and generates the system function for each piece of the projection data.

Description

[Technical field]

[0001] The present disclosure relates to a magnetic particle imaging device, a magnetic particle imaging method, and a magnetic particle imaging program. [Background technology]

[0002] There has been a proposal for a magnetic particle imaging (also called "Magnetic Particle Imaging (MPI)") device 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 harmonic signals generated from magnetization changes in the magnetic nanoparticles. Patent Document 1 discloses a magnetic particle imaging device that forms a linear zero magnetic field region with a static magnetic field generating coil, causes magnetization changes in the magnetic nanoparticles present in this linear zero magnetic field region, and performs a process of detecting the harmonic signals generated at that time at each position in the scanning direction of the linear zero magnetic field region, thereby imaging the spatial distribution of magnetic nanoparticles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-96960 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above magnetic particle imaging device, it is desirable to detect magnetization changes occurring only in magnetic nanoparticles present within the linear zero magnetic field region. However, in reality, magnetization changes also occur in magnetic nanoparticles around the linear zero magnetic field region due to the influence of local magnetic fields generated in magnetic nanoparticles near (e.g., around) the outside of the linear zero magnetic field region. For this reason, a magnetic nanoparticle image with low spatial resolution is generated.

[0005] An object of the present disclosure is to provide a magnetic particle imaging device, 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 device disclosed herein is a device for generating a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within a subject, and includes 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 applying unit that applies an alternating excitation magnetic field to a magnetic field region including the linear zero magnetic field region, a detection unit that detects magnetization changes of the magnetic nanoparticles generated by the excitation magnetic field, and a control unit, When generating a system function, the control unit causes the linear zero magnetic field generating unit to form the linear zero magnetic field region within a reference structure that is the subject, which contains the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, to scan and rotate the linear zero magnetic field region, causes the excitation magnetic field applying unit to apply the excitation magnetic field to a 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 at multiple angles in a rotation direction that is the direction of the rotation of the linear zero magnetic field region, and causes the detection unit to detect the magnetization change within the structure at multiple angles in a scanning direction that is the direction of the scanning of the linear zero magnetic field region. generating first projection data of the magnetization change based on the position of the magnetization change and the multiple angles in the rotation direction of the linear zero magnetic field region, extracting magnetic particle imaging signals at the multiple angles in the rotation direction from the first projection data, generating first measured magnetic particle imaging signals by removing DC components from the magnetic particle imaging signals at the multiple angles, and calculating the system function as a deconvolution coefficient for each of the first measured magnetic particle imaging signals from the first measured magnetic particle imaging signals acquired from the structure and an ideal magnetic particle imaging signal which is a magnetic signal detected from the structure; The control unit, when generating the magnetic nanoparticle image, causes the linear zero magnetic field generation unit to form the linear zero magnetic field region in an actual imaging target that is the subject, scan and rotate the linear zero magnetic field region in the imaging target, causes the excitation magnetic field application unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region in the imaging target, causes the detection unit to detect the magnetization changes in the imaging target at a plurality of angles in a rotation direction that is the direction of the rotation of the linear zero magnetic field region in the imaging target, generates second projection data of the magnetization changes based on a plurality of positions in a scanning direction that is the direction of the scanning of the linear zero magnetic field region in the imaging target and the plurality of angles in the rotation direction of the linear zero magnetic field region in the imaging target, extracts magnetic particle imaging signals at a plurality of angles in the rotation direction from the second projection data in the imaging target, removes direct current components from the magnetic particle imaging signals in the imaging target at the plurality of angles to generate second measurement magnetic particle imaging signals in the imaging target, and generates second measurement magnetic particle imaging signals in the imaging target. Second measurement magnetic particle imaging signal Using the system function for each Second measurement magnetic particle imaging signal The present invention is characterized in that corrected projection data is generated by performing sensitivity correction on the magnetic nanoparticles, and the magnetic nanoparticle image is generated based on the corrected projection data.

[0007] The magnetic particle imaging method disclosed herein includes a linear zero magnetic field generating 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 applying unit that applies an alternating excitation magnetic field to a magnetic field region including the linear zero magnetic field region, and a detection unit that detects magnetization changes of magnetic nanoparticles generated by the excitation magnetic field, and is executed by a magnetic particle imaging device that generates a magnetic nanoparticle image showing a spatial distribution of the magnetic nanoparticles within an imaging target that is the subject, When generating system functions, The linear zero magnetic field generating unit forms the linear zero magnetic field region within a reference structure that is the subject, the reference structure containing the magnetic nanoparticles at a predetermined particle concentration and having a predetermined size, and scans and rotates the linear zero magnetic field region. The excitation magnetic field applying unit applies the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the structure. The detection unit detects the magnetization change within the structure at a plurality of angles in a rotation direction that is the direction of the rotation of the linear zero magnetic field region. The linear zero magnetic field generating unit detects the magnetization change within the structure at a plurality of angles in a scanning direction that is the direction of the scanning of the linear zero magnetic field region. generating first projection data of the magnetization change based on the multiple angles in the rotation direction of the region; extracting magnetic particle imaging signals at multiple angles in the rotation direction from the first projection data and generating first measured magnetic particle imaging signals by removing DC components from the magnetic particle imaging signals at the multiple angles; and calculating the system function as a deconvolution coefficient for each of the first measured magnetic particle imaging signals from the first measured magnetic particle imaging signals acquired from the structure and an ideal magnetic particle imaging signal which is a magnetic signal detected from the structure, When generating the magnetic nanoparticle image, A step of forming the linear zero magnetic field region in the actual imaging target which is the subject, by the linear zero magnetic field generating unit, and scanning and rotating the linear zero magnetic field region in the imaging target; a step of causing the excitation magnetic field application unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region in the imaging target; a step of causing the detection unit to detect the magnetization changes in the imaging target at a plurality of angles in a rotational direction that is the direction of the rotation of the linear zero magnetic field region in the imaging target; a step of generating second projection data of the magnetization changes based on a plurality of positions in a scanning direction that is the direction of the scan of the linear zero magnetic field region in the imaging target and the plurality of angles in the rotational direction of the linear zero magnetic field region in the imaging target; a step of extracting magnetic particle imaging signals at a plurality of angles in the rotational direction from the second projection data in the imaging target, and removing direct current components from the magnetic particle imaging signals in the imaging target at the plurality of angles to generate second measurement magnetic particle imaging signals in the imaging target; Second measurement magnetic particle imaging signal Using the system function for each Second measurement magnetic particle imaging signal generating corrected projection data by performing sensitivity correction on the magnetic nanoparticles; and generating the magnetic nanoparticle image based on the corrected projection data. Effect of the Invention

[0008] By using the magnetic particle imaging device, magnetic particle imaging method, and magnetic particle imaging program of the present disclosure, it is possible to generate magnetic nanoparticle images with high spatial resolution. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a schematic configuration of a magnetic particle imaging device according to an embodiment. [Diagram 2] 1 is a perspective view showing a schematic structure of a main part of an MPI device according to an embodiment, and a human being as a subject to be imaged. [Diagram 3] FIG. 1 is a perspective view showing a schematic configuration of a main part of an MPI device according to an embodiment, and a cylindrical body as a structural body. [Figure 4]FIG. 1 shows magnetic nanoparticles of known concentration, a linear zero magnetic field region, a magnetic response signal which is a measured magnetic signal, and a known magnetic response signal. [Diagram 5] FIG. 1 is a diagram showing the relationship between the system function, the spatial distribution of magnetic nanoparticles, and the magnetic signal (measurement vector). [Figure 6] FIG. 2 is a diagram illustrating an example of a hardware configuration of an MPI device according to an embodiment. [Figure 7] 11 is a flowchart showing an example of a process for generating a magnetic nanoparticle image by an MPI device according to an embodiment. [Figure 8] 1 is a flowchart illustrating an example of a generation process of a system function of an MPI apparatus according to an embodiment. [Figure 9] Figure 9(A) shows an example of projection data on the scanning position-angle coordinate system, while Figure 9(B) shows a waveform showing the intensity of the measured MPI signal at a certain angle and a signal obtained by subjecting the measured MPI signal to fast Fourier transform (FFT). [Figure 10] Fig. 10(A) shows the signal in Fig. 9(B). Fig. 10(B) shows a waveform showing the intensity of the signal obtained by removing the DC component from the measured MPI signal in Fig. 10(A) and a signal obtained by FFT processing the measured MPI signal from which the DC component has been removed. [Figure 11] Fig. 11(A) shows the signal in Fig. 10(B). Fig. 11(B) shows the waveform of the measured MPI signal, which is a magnetic signal detected from a cylindrical object, which is a standard imaging target, and the signal obtained by FFT processing of this measured MPI signal. Fig. 11(C) shows the deconvolution coefficients calculated from Fig. 11(A) and (B) and the coefficients obtained by FFT processing of the deconvolution coefficients. [Figure 12] Fig. 12(A) shows the signal in Fig. 10(B). Fig. 12(B) shows the coefficients in Fig. 11(C). Fig. 12(C) shows a waveform showing the intensity of the noise-removed MPI signal, which is the corrected MPI signal, and a signal obtained by FFT processing the noise-removed MPI signal. [Figure 13] Fig. 13(A) shows the corrected projection data, and Fig. 13(B) shows the original uncorrected projection data. [Figure 14]Figure 14(A) shows a magnetic nanoparticle image created by performing image reconstruction on the corrected projection data, and Figure 14(B) shows a magnetic nanoparticle image based on the original uncorrected projection data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an MPI device, an MPI method, and an MPI program according to embodiments will be described with reference to the drawings. The following embodiments are merely examples, and the embodiments can be appropriately combined and each embodiment can be appropriately modified.

[0011] In Figs. 1 to 4, the coordinate axes of an XYZ orthogonal coordinate system are shown to facilitate understanding of the relationship between the figures. The Z axis is the longitudinal coordinate axis of the linear zero magnetic field (also called "Free Field Line (FFL)") region. The Y axis is the coordinate axis of 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 axis and the Y axis. In Figs. 2 and 3, the R direction indicates the rotation direction of the FFL region. In Figs. 2 and 3, the central axis of rotation in the R direction is the X direction axis. In the figures, the same or corresponding configurations are given the same symbols.

[0012] <<Configuration of MPI device>> FIG. 1 is a diagram showing a schematic configuration of an MPI device 1 according to an embodiment. The MPI device 1 is a device that generates (also called "reconstructs") a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles within an imaging target 50 as a subject. The MPI device 1 is also a device that can implement an MPI method according to an embodiment. The MPI device 1 is also a device that can execute an MPI program according to an embodiment.

[0013] FIG. 2 is a perspective view that shows a schematic structure of the main parts of the MPI device 1 and an imaging target 50. The imaging target 50 is, for example, a human being to whom magnetic nanoparticles have been administered. The imaging target 50 may be something other than a human being (for example, an animal, a plant, etc.). The magnetic nanoparticles are magnetic particles containing a magnetic material and having a diameter in the nanometer range. The magnetic nanoparticles are formed, for example, so as to have the property of gathering at an affected area (for example, specific cells in the brain, organs, etc.) after being administered to a human being. As an example of the magnetic nanoparticles, for example, "Resovist (registered trademark)" (generic name: Ferucarbotran), which is a hydrophilic colloidal liquid of superparamagnetic iron oxide coated with carboxydextran, is known.

[0014] As shown in Figure 1, the MPI device 1 includes a linear zero magnetic field generating 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 that serves as a magnetization change detection unit that detects (i.e., measures) magnetization changes in magnetic nanoparticles, and a control unit 40 that controls the entire device.

[0015] The linear zero magnetic field generating unit 10 forms an FFL region 60 in the subject and moves the FFL region 60 in a predetermined direction. For example, the linear zero magnetic field generating unit 10 forms an FFL region 60 in 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 generating unit 10 has a linear zero magnetic field generating coil 11 as a first linear zero magnetic field generating unit and a linear zero magnetic field generating coil 12 as a second linear zero magnetic field generating unit. The linear zero magnetic field generating coils 11 and 12 are arranged on opposite sides of the imaging target 50 as the subject. The linear zero magnetic field generating coils 11 and 12 are magnetic field generating coils, and are supplied with power by linear zero magnetic field power supplies 13 and 14.

[0016] The linear zero magnetic field generating unit 10 linearly moves the FFL region 60 by a predetermined moving distance in the scanning direction (for example, the Y direction in Figs. 1 to 3). For example, the linear zero magnetic field generating 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 magnetic field power supplies 13 and 14. The movement of the FFL region 60 may also be performed by the movement of the imaging target 50, or the movement of the linear zero magnetic field generating unit 10, or the movement of the imaging target 50 and the linear zero magnetic field generating unit 10.

[0017] Furthermore, the linear zero magnetic field generating unit 10 can rotate the FFL region 60 by a predetermined rotation angle. The linear zero magnetic field generating 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 magnetic field power supplies 13 and 14. The rotation of the FFL region 60 may also be performed by rotating the linear zero magnetic field generating coils 11 and 12 in the R direction and the -R direction, or by rotating the imaging target 50 in the R direction and the -R direction.

[0018] The excitation magnetic field application unit 20 has an excitation magnetic field generating coil 21 that applies an AC excitation magnetic field to the 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, a ring-shaped coil wound in the R direction.

[0019] The detection unit 30 detects magnetization changes caused by the excitation magnetic field of the magnetic nanoparticles contained in the FFL region 60 (more precisely, detects harmonic signals caused by the magnetization changes as magnetic response signals). The detection unit 30 has, for example, one or more magnetic field detectors (e.g., coils for magnetic field detection). The detection signal output from the detection unit 30 may be amplified by an amplifier circuit. The one or more magnetic field detectors may be semiconductor elements for magnetic field detection (e.g., Hall elements, etc.).

[0020] The control unit 40 controls the overall operation of the MPI device 1. When generating a magnetic nanoparticle image, the control unit 40 causes the linear zero magnetic field generating unit 10 to form an FFL region 60 in the imaging target 50, to scan, or rotate, or scan and rotate the FFL region 60, causes the excitation magnetic field applying unit 20 to apply an excitation magnetic field, and causes the detection unit 30 to detect magnetization changes. 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 magnetization changes 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 previously acquired for each projection data. Furthermore, the control unit 40 generates a magnetic nanoparticle image (for example, FIG. 14(A) described later) based on the corrected projection data (for example, FIG. 13(A) described later).

[0021] FIG. 3 is a perspective view that shows a schematic structure of the main parts of the MPI device 1 according to the embodiment and a structure 51 as a subject. The structure 51 is, for example, a cylindrical body. However, the structure 51 is not limited to a cylindrical body. 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 generating unit 10 to form an FFL region 60 in the structure 51, which is a reference subject containing magnetic nanoparticles at a predetermined particle concentration and having a predetermined size, to scan, rotate, or scan and rotate the FFL region 60, causes the excitation magnetic field applying unit 20 to apply an excitation magnetic field to a magnetic field region including the FFL region 60 in the structure 51, causes the detection unit 30 to detect magnetization changes in the structure 51, and generates a system function for each projection data based on the magnetization changes in 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] FIG. 4 is a diagram showing magnetic nanoparticles of known concentration, the FFL region 60, a measured magnetic response signal, and a known magnetic response signal. All 8×4 circles shown in FIG. 4 indicate magnetic nanoparticles of known concentration. FIG. 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 the FFL region 60 and its surroundings, and has a waveform similar to a triangular waveform, and that the ideal known magnetic response characteristic (the sum of magnetic signals generated only in the FFL region 60) is a rectangular waveform shown by a dashed line. By exciting the magnetic nanoparticles having magnetization, the magnetic signal corresponding to the magnetization change (i.e., the change in magnetization of the magnetic nano signal) is directly detected by the detection unit 30 from the magnetic nanoparticles within the field of view (FOV) of the detection unit 30.

[0023] 5 is a diagram showing the relationship between the system function S, the spatial distribution c of the magnetic nanoparticles in the FFL region 60, and the measured magnetic response signal u (i.e., the measurement vector). As shown in FIG. 5, the measured magnetic response signal u is a signal obtained by convolving the spatial distribution c of the magnetic nanoparticles in the FFL region 60 with the system function S, which indicates the detection sensitivity (i.e., the magnetic properties).

[0024] FIG. 6 is a diagram showing an example of a hardware configuration of an MPI device 1 according to an embodiment. As shown in FIG. 6, a control unit 40 of the MPI device 1 has, for example, 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 a 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 a part of an external device capable of communicating with the MPI device 1. The storage device 70 may be, for example, a storage device of a server capable of communicating 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 (e.g., an MPI program that executes the MPI method according to the embodiment) stored in a memory 42. The processor 41 may be any of a processing device, an arithmetic device, a microprocessor, a microcomputer, and a DSP (Digital Signal Processor).

[0026] Where the processing circuitry is dedicated hardware, the processing circuitry 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 any combination thereof.

[0027] When the processing circuit is the processor 41, the MPI program is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 42. The processor 41 realizes the functions of each part by reading and executing the MPI program stored in the memory 42.

[0028] The MPI device 1 may be partially realized by dedicated hardware and partially realized by software or firmware. In this way, the processing circuit can realize each function by hardware, software, firmware, or any combination of these.

[0029] <<Operation when generating magnetic nanoparticle images>> Next, we will explain the operation of the MPI device 1 when generating a magnetic nanoparticle image. The operation of the MPI device 1 when generating a magnetic nanoparticle image differs from that described in Patent Document 1 in that a system function is used to perform correction processing of the projection data.

[0030] Fig. 7 is a flowchart showing an example of a process for generating a magnetic nanoparticle image by the MPI device 1. Fig. 7 shows an example in which the MPI device 1 changes both the position of the FFL region 60 in the scanning direction and the angle of the FFL region 60. However, the MPI device 1 may change only the position of the FFL region 60 in the scanning direction, or may change only the angle of the FFL region 60.

[0031] First, the control unit 40 controls the linear zero magnetic field generating unit 10 to form an FFL region 60 within the imaging target 50 (shown in FIG. 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 FIG. 2.

[0032] Next, the control unit 40 controls the linear zero magnetic field generating unit 10 to set the angle of the FFL region 60 to an initial angle (step ST12). The initial angle is, for example, a predetermined angle in the R direction in FIG.

[0033] Next, the control unit 40 controls the excitation magnetic field applying unit 20 to excite the magnetic nanoparticles in the FFL region 60, and causes the detection unit 30 to detect a change in magnetization (step ST13).

[0034] Next, the control unit 40 judges whether or not detection has been completed for all the predetermined angles in the R direction of the FFL region 60 at the current position in the scanning direction. If there is an angle for which detection has not been completed (NO in step ST14), the control unit 40 returns the process to step ST12, controls the linear zero magnetic field generating unit 10 to rotate the FFL region 60 by a certain rotation angle to set the next angle (i.e., one of the predetermined angles), and returns to the process of step ST14 through the process of step ST13. If there is no angle for which detection has not been completed at the current position in the scanning direction, that is, if detection has been completed for all angles (YES in step ST14), the control unit 40 advances the process to step ST15.

[0035] In step ST15, the control unit 40 judges whether or not detection (i.e., the processing of steps ST12 to ST14) has been completed for all of the multiple predetermined positions in the Y direction of the FFL region 60. If there are any positions for which detection has not been completed (NO in step ST15), the control unit 40 returns the processing to step ST11, controls the linear zero magnetic field generating unit 10 to move the FFL region 60 in the Y direction by a certain distance to set the next position (i.e., one of the multiple predetermined positions), and returns to the processing of step ST15 via the processing of steps ST12 to ST14. If there are no positions for which detection has not been completed, that is, if detection has been completed for all positions (YES in step ST15), the control unit 40 advances the processing 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 (e.g., 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 in a direction along the FFL region 60 onto the magnetic field detector of the detection unit 30. Therefore, the projection position is a position corresponding to the position of the FFL region 60 in the scanning direction. The projection position is also called the scan position. The projection angle is an angle corresponding to the rotation angle of the FFL region 60 in the R direction.

[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. The control unit 40 may also select a system function from the storage device 70, estimate a system function other than the selected system function by interpolation for 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] <<Behavior when creating system functions>> Fig. 8 is a flowchart showing an example of a generation process of a system function of the MPI device 1. Fig. 8 shows an example in which the MPI device 1 changes both the position of the FFL region 60 in the scanning direction and the angle of the FFL region 60. However, the MPI device 1 may change only the position of the FFL region 60 in the scanning direction, or may change only the angle of the FFL region 60.

[0040] In generating the system function, first, the control unit 40 controls the linear zero magnetic field generating unit 10 to generate the FFL region 60 in the structure 51 (FIG. 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 FIG. 3.

[0041] Next, the control unit 40 controls the linear zero magnetic field generating unit 10 to set the angle of the FFL region 60 to an initial angle (step ST22). The initial angle is, for example, a predetermined angle in the R direction in FIG.

[0042] Next, the control unit 40 controls the excitation magnetic field applying unit 20 to excite the magnetic nanoparticles in the FFL region 60, and causes the detection unit 30 to detect a change in magnetization (step ST23).

[0043] Next, the control unit 40 judges whether or not 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 is an angle for which detection has not been completed at the current scanning direction position (NO in step ST24), the control unit 40 returns the process to step ST22, controls the linear zero magnetic field generating unit 10 to rotate the FFL region 60 by a certain rotation angle to set the next angle (i.e., one of the predetermined angles), and returns to the process of step ST24 via the process of step ST23. If there is no angle for which detection has not been completed at the current scanning direction position, that is, if detection has been completed for all angles (YES in step ST24), the control unit 40 advances the process to step ST25.

[0044] In step ST25, the control unit 40 judges whether or not detection (i.e., the processing of steps ST22 to ST24) has been completed for all of the predetermined scanning direction positions in the Y direction of the FFL region 60. If there is a scanning direction position for which detection has not been completed (NO in step ST25), the control unit 40 returns the processing to step ST21, controls the linear zero magnetic field generating unit 10 to move the FFL region 60 in the Y direction by a certain distance to set the next scanning direction position (i.e., one of the predetermined scanning direction positions), and returns to the processing of step ST25 through the processing of steps ST22 to ST24. If there is no scanning direction position for which detection has not been completed, that is, if detection has been completed for all scanning direction positions (YES in step ST25), the control unit 40 advances the processing 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 onto the detection unit 30).

[0046] In step ST27, the control unit 40 generates a system function indicating the detection sensitivity for each combination of position and angle in the scanning direction, and in step ST28, stores a system function set including a plurality of system functions in the storage device 70.

[0047] <Processing to generate images from projection data> The process of generating a reconstructed image from projection data will be described with reference to FIGS. 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. The multiple angles are, for example, angles in the rotation direction indicated by R. FIG. 9(A) shows an example of projection data projected onto a scan position-angle coordinate system. The scan positions correspond to the positions of multiple magnetic field detectors (or detection elements) of the detection unit 30. In FIG. 9(A), the brighter the area, the stronger the intensity of the measured MPI signal, which is a measured magnetic response signal, i.e., the larger the amplitude. FIG. 9(B) shows a waveform (Original Signal) showing the intensity of the measured MPI signal at a certain angle in FIG. 9(A) and a signal (Original Signal FFT) obtained by subjecting the measured MPI signal to fast Fourier transform (FFT) processing.

[0049] Next, the control unit 40 removes the DC component from the signal in Fig. 9(B). Fig. 10(A) shows the signal in Fig. 9(B). Fig. 10(B) shows a waveform (Signal without DC) indicating the intensity of a signal obtained by removing the DC component from the measured MPI signal in Fig. 10(A), and a signal (Signal without DC FFT) obtained by FFT processing the measured MPI signal from which the DC component has been removed.

[0050] Next, the control unit 40 calculates the deconvolution coefficient S(f) as a system function from the signal in FIG. 10(B) and the ideal MPI signal. FIG. 11(A) shows the signal in FIG. 10(B). FIG. 11(B) shows the waveform of the ideal MPI signal m(x), which is a magnetic signal detected from the cylindrical body that is the reference structure 51, and the signal M(f) obtained by FFT processing of this ideal MPI signal. FIG. 11(C) shows the deconvolution coefficient s(t) calculated from FIGS. 11(A) and (B) and the deconvolution coefficient FFT S(f) obtained by FFT processing of the deconvolution coefficient s(t). Here, f indicates frequency, t indicates time, and x indicates position in the scanning direction (or the position of the magnetic field detector).

[0051] Next, the control unit 40 calculates the noise-removed MPI signal m(x) and its Fourier transformed signal M(f) from the signal in Fig. 10(B) and the deconvolution coefficients (i.e., system functions) in Fig. 11(C). Fig. 12(A) shows the signal in Fig. 10(B). Fig. 12(B) shows the deconvolution coefficients in Fig. 11(C). Fig. 12(C) shows a waveform indicating the intensity of the noise-removed MPI signal m(x) as a corrected MPI signal, and M(f) which is a signal obtained by FFT processing of the noise-removed MPI signal.

[0052] By the processing shown in Figures 9(A) and (B) to Figures 12(A) to (C), a noise-removed MPI signal shown in Figure 12(C) can be generated from a signal based on the original projection data shown in Figure 9(B).

[0053] Effects of the embodiment FIG. 13(A) shows corrected projection data generated by the control unit 40 of the MPI device 1 according to the embodiment. FIG. 13(B) shows the original projection data (comparative example) that has not been corrected. As shown in FIG. 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 range where magnetic nanoparticles exist (white area) and the range where magnetic nanoparticles do not exist (black area). In this way, by using the MPI device 1 according to the embodiment, it is possible to generate a magnetic nanoparticle image with high spatial resolution.

[0054] FIG. 14(A) shows a magnetic nanoparticle image created by performing image reconstruction on the corrected projection data of the MPI device 1 according to the embodiment. FIG. 14(B) shows a magnetic nanoparticle image (comparative example) based on the original projection data that has not been corrected. As shown in FIG. 14(B), when an image is reconstructed using uncorrected projection data, the boundary between the range where magnetic nanoparticles exist (white area) and the range where magnetic nanoparticles do not exist (black area) becomes unclear. In addition, in FIG. 14(B), the large outer circle is an artifact. In contrast, as shown in FIG. 14(A), the corrected projection data generated by the MPI device 1 according to the embodiment has a clear circular boundary between the range where magnetic nanoparticles exist (white area) and the range where magnetic nanoparticles do not exist (black area). In this way, by using the MPI device 1 according to the embodiment, a magnetic nanoparticle image with high spatial resolution can be generated. [Explanation of symbols]

[0055] 1 MPI device, 10 linear zero magnetic field generating unit, 11, 12 linear zero magnetic field generating coil, 13, 14 linear zero magnetic field power supply, 20 excitation magnetic field application unit, 21 excitation magnetic field generating coil, 22 excitation magnetic field power supply, 30 detection unit, 40 control unit, 50 imaging subject (subject), 51 structure (subject), 60 FFL area, 70 storage device, R rotation direction.

Claims

1. 1. A magnetic particle imaging apparatus for generating a magnetic nanoparticle image showing a spatial distribution of magnetic nanoparticles within a subject, comprising: 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 excitation magnetic field to a magnetic field region including the linear zero magnetic field region; A detection unit that detects a change in magnetization of the magnetic nanoparticles caused by the excitation magnetic field; A control unit; having When generating a system function, the control unit The linear zero magnetic field generating unit forms the linear zero magnetic field region within a reference structure that is the subject and includes the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, and scans and rotates the linear zero magnetic field region; The excitation magnetic field applying unit applies the excitation magnetic field to a magnetic field region including the linear zero magnetic field region in the structure; causing the detector to detect the magnetization change in the structure at a plurality of angles in a rotational direction that is the direction of the rotation of the linear zero magnetic field region; generating first projection data of the magnetization change based on a plurality of positions in a scanning direction, which is a direction of the scanning of the linear zero magnetic field region, and the plurality of angles in the rotation direction of the linear zero magnetic field region; extracting magnetic particle imaging signals at a plurality of angles in the rotation direction from the first projection data, and removing direct current components from the magnetic particle imaging signals at the plurality of angles to generate a first measurement magnetic particle imaging signal; calculating the system function as a deconvolution coefficient for each of the first measurement magnetic particle imaging signals from the first measurement magnetic particle imaging signal acquired from the structure and an ideal magnetic particle imaging signal that is a magnetic signal detected from the structure; When generating the magnetic nanoparticle image, the control unit The linear zero magnetic field generating unit forms the linear zero magnetic field region within the actual imaging target which is the subject, and scans and rotates the linear zero magnetic field region within the imaging target; causing the excitation magnetic field applying unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the imaging subject; causing the detector to detect the magnetization changes in the imaging target at a plurality of angles in a rotational direction that is a direction of the rotation of the linear zero magnetic field region in the imaging target; generating second projection data of the magnetization change based on a plurality of positions in a scanning direction, the scanning direction being a direction of the linear magnetic field zero region within the imaging subject, and the plurality of angles in the rotation direction of the linear magnetic field zero region within the imaging subject; extracting magnetic particle imaging signals at a plurality of angles in the rotational direction from the second projection data within the imaging target, and removing direct current components from the magnetic particle imaging signals within the imaging target at the plurality of angles to generate second measurement magnetic particle imaging signals within the imaging target; generating corrected projection data by performing a sensitivity correction on the second measurement magnetic particle imaging signal in the imaging target using the system function for each of the second measurement magnetic particle imaging signals in the imaging target; generating the magnetic nanoparticle image based on the corrected projection data A magnetic particle imaging device comprising:

2. 2. The magnetic particle imaging apparatus according to claim 1, wherein the linear zero magnetic field generating unit linearly moves the linear zero magnetic field region in the scanning direction by a predetermined moving distance during the scanning.

3. 3. A magnetic particle imaging apparatus according to claim 1, wherein the scanning direction is a direction perpendicular to the longitudinal direction of the linear zero magnetic field region.

4. 4. The magnetic particle imaging apparatus according to claim 1, wherein the linear zero magnetic field generating unit rotates the linear zero magnetic field region by a predetermined rotation angle during the rotation.

5. When generating the system functions, the control unit generates a system function indicating detection sensitivity for each combination of the position and the angle, and stores a system function set including a plurality of the system functions in a storage device.

5. A magnetic particle imaging apparatus according to claim 1, wherein the first and second electrodes are arranged in a first plane.

6. The control unit, when generating the magnetic nanoparticle image, selects the system function from the storage device, performs sensitivity correction on the second measurement magnetic particle imaging signal using the selected system function, and generates the corrected projection data.

6. A magnetic particle imaging apparatus according to claim 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 second measurement magnetic particle imaging signal using the selected system function and the estimated system function, and generates the corrected projection data.

6. A magnetic particle imaging apparatus according to claim 5.

8. The system further includes a storage device for storing the set of system functions. A magnetic particle imaging apparatus according to any one of claims 5 to 7.

9. A magnetic particle imaging method, which is executed by a magnetic particle imaging device that has a linear zero magnetic field generating 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 applying unit that applies an alternating excitation magnetic field to a magnetic field region including the linear zero magnetic field region, and a detection unit that detects a magnetization change of magnetic nanoparticles generated by the excitation magnetic field, and generates a magnetic nanoparticle image showing a spatial distribution of the magnetic nanoparticles within an imaging target that is the subject, When generating system functions, A step of forming the linear zero magnetic field region in a reference structure that is the subject and includes the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size in the linear zero magnetic field generating unit, and scanning and rotating the linear zero magnetic field region; A step of causing the excitation magnetic field application unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the structure; causing the detector to detect the magnetization change in the structure at a plurality of angles in a rotational direction that is the direction of the rotation of the linear zero magnetic field region; generating first projection data of the magnetization change based on a plurality of positions in a scanning direction, which is a direction of the scanning of the linear zero magnetic field region, and the plurality of angles in the rotation direction of the linear zero magnetic field region; extracting magnetic particle imaging signals at a plurality of angles in the rotation direction from the first projection data, and removing direct current components from the magnetic particle imaging signals at the plurality of angles to generate a first measurement magnetic particle imaging signal; calculating the system function as a deconvolution coefficient for each of the first measured magnetic particle imaging signals from the first measured magnetic particle imaging signals acquired from the structure and an ideal magnetic particle imaging signal that is a magnetic signal detected from the structure; When generating the magnetic nanoparticle image, A step of forming the linear zero magnetic field region in the actual imaging target which is the subject, by the linear zero magnetic field generating unit, and scanning and rotating the linear zero magnetic field region in the imaging target; A step of causing the excitation magnetic field applying unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the imaging subject; causing the detector to detect the magnetization changes in the imaging subject at a plurality of angles in a rotational direction that is a direction of the rotation of the linear zero magnetic field region in the imaging subject; generating second projection data of the magnetization change based on a plurality of positions in a scanning direction, the scanning direction being a direction of the linear magnetic field zero region within the imaging subject, and the plurality of angles in the rotation direction of the linear magnetic field zero region within the imaging subject; extracting magnetic particle imaging signals at a plurality of angles in the rotation direction from the second projection data of the imaging target, and removing direct current components from the magnetic particle imaging signals of the imaging target at the plurality of angles to generate second measurement magnetic particle imaging signals of the imaging target; generating corrected projection data by performing a sensitivity correction on the second measurement magnetic particle imaging signals in the imaging target using the system function for each of the second measurement magnetic particle imaging signals in the imaging target; generating the magnetic nanoparticle image based on the corrected projection data. A method for magnetic particle imaging comprising:

10. A magnetic particle imaging program executed by a magnetic particle imaging device that has a linear zero magnetic field generating 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 applying unit that applies an alternating excitation magnetic field to a magnetic field region including the linear zero magnetic field region, and a detection unit that detects magnetization changes of magnetic nanoparticles generated by the excitation magnetic field, and that generates a magnetic nanoparticle image showing a spatial distribution of the magnetic nanoparticles within an imaging target that is the subject, When generating a system function, the magnetic particle imaging device A step of forming the linear zero magnetic field region in a reference structure that is the subject and includes the magnetic nanoparticles at a predetermined particle concentration and has a predetermined size in the linear zero magnetic field generating unit, and scanning and rotating the linear zero magnetic field region; A step of causing the excitation magnetic field application unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the structure; causing the detector to detect the magnetization change in the structure at a plurality of angles in a rotational direction that is the direction of the rotation of the linear zero magnetic field region; generating first projection data of the magnetization change based on a plurality of positions in a scanning direction, which is a direction of the scanning of the linear zero magnetic field region, and the plurality of angles in the rotation direction of the linear zero magnetic field region; extracting magnetic particle imaging signals at a plurality of angles in the rotation direction from the first projection data, and removing direct current components from the magnetic particle imaging signals at the plurality of angles to generate a first measurement magnetic particle imaging signal; calculating the system function as a deconvolution coefficient for each of the first measured magnetic particle imaging signals from the first measured magnetic particle imaging signals acquired from the structure and an ideal magnetic particle imaging signal that is a magnetic signal detected from the structure; When generating the magnetic nanoparticle image, the magnetic particle imaging device A step of forming the linear zero magnetic field region in the actual imaging target which is the subject, by the linear zero magnetic field generating unit, and scanning and rotating the linear zero magnetic field region in the imaging target; A step of causing the excitation magnetic field applying unit to apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region within the imaging subject; causing the detector to detect the magnetization changes in the imaging subject at a plurality of angles in a rotational direction that is a direction of the rotation of the linear zero magnetic field region in the imaging subject; generating second projection data of the magnetization change based on a plurality of positions in a scanning direction, the scanning direction being a direction of the linear magnetic field zero region within the imaging subject, and the plurality of angles in the rotation direction of the linear magnetic field zero region within the imaging subject; extracting magnetic particle imaging signals at a plurality of angles in the rotation direction from the second projection data of the imaging target, and removing direct current components from the magnetic particle imaging signals of the imaging target at the plurality of angles to generate second measurement magnetic particle imaging signals of the imaging target; generating corrected projection data by performing a sensitivity correction on the second measurement magnetic particle imaging signals in the imaging target using the system function for each of the second measurement magnetic particle imaging signals in the imaging target; generating the magnetic nanoparticle image based on the corrected projection data. A magnetic particle imaging program comprising:

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