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

Abstract

To generate a magnetic nanoparticle image with the high spatial resolution.SOLUTION: An MPI apparatus (1) generates projection data of magnetization changes on the basis of a position in a scanning direction (Y) and an angle in a rotation direction (R) of an FFL region (60), performs sensitivity correction using a system function for each projection data to generate corrected projection data, and performs image reconstruction for the same to generate a magnetic nanoparticle image. A control unit (40), during generation of the system function, causes a linear zero magnetic field generation unit (10) to form the FFL region (60) within a structure (51) that contains magnetic nanoparticles at a predetermined particle concentration and has a predetermined size, scan or rotate, or scan and rotate the FFL region (60), causes an excitation magnetic field application unit (20) to apply an excitation magnetic field to a magnetic field region including the FFL region within the structure (51), and causes a detector (30) to detect magnetization changes within the structure (51) to generate the system function for each projection data.SELECTED DRAWING: Figure 1

Description

Technical Field

[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 object to be imaged and images the spatial distribution of the magnetic nanoparticles in the object to be imaged 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 performs a process of detecting 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 within the linear zero magnetic field region. However, in reality, it is affected by the local magnetic field generated by the magnetic nanoparticles in the vicinity (for example, the periphery) outside the linear zero magnetic field region, and the magnetization change also occurs in the magnetic nanoparticles around the linear zero magnetic field region. For this reason, a magnetic nanoparticle image with low spatial resolution is generated.

[0005] The present 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 Problems

[0006] The magnetic particle imaging apparatus of the present disclosure is an apparatus that generates a magnetic nanoparticle image showing the spatial distribution of magnetic nanoparticles in a subject, and includes 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 excitation magnetic field to a magnetic field region including the linear zero magnetic field region, a detection unit that detects a 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 forms the linear zero magnetic field region in an imaging target as the subject by the linear zero magnetic field generation unit, 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, causes the detection unit to detect the magnetization change, generates projection data of the magnetization change based on the position in the scanning direction of the linear zero magnetic field region and the angle in the rotation direction of the linear zero magnetic field region, generates corrected projection data by performing sensitivity correction on the projection data using a system function acquired in advance for each of the projection data, and generates the magnetic nanoparticle image based on the corrected projection data. When generating the system function, the control unit forms the linear zero magnetic field region in a structure that is the subject containing the magnetic nanoparticles with a predetermined particle concentration and having a predetermined size by the linear zero magnetic field generation unit, 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 a magnetic field region including the linear zero magnetic field region in the structure, causes the detection unit to detect the magnetization change in the structure, and generates the system function for each of the projection data based on the magnetization change in the structure.

[0007] The magnetic particle imaging method of the present disclosure forms a linear zero magnetic field region in a subject, and includes a linear zero magnetic field generation unit that scans and moves the linear zero magnetic field region in a predetermined scanning direction and 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, and a detection unit that detects a magnetization change of magnetic nanoparticles generated by the excitation magnetic field. The method is executed by a magnetic particle imaging apparatus that generates a magnetic nanoparticle image showing a spatial distribution of magnetic nanoparticles in an imaging target as the subject, and when generating the magnetic nanoparticle image, the method includes: causing the linear zero magnetic field generation unit to form the linear zero magnetic field region in the imaging target, and scan, or rotate, or scan and rotate the linear zero magnetic field region; causing the excitation magnetic field application unit to apply the excitation magnetic field; causing the detection unit to detect the magnetization change; generating projection data of the magnetization change based on a position in the scanning direction of the linear zero magnetic field region and an angle in the rotation direction of the linear zero magnetic field region; generating corrected projection data by performing sensitivity correction on the projection data using a system function 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 includes: causing the linear zero magnetic field generation unit to form the linear zero magnetic field region in a structure that is the subject and includes the magnetic nanoparticles with a predetermined particle concentration and has a predetermined size, and scan, or rotate, or scan and rotate the linear zero magnetic field region; 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 structure; causing the detection unit to detect the magnetization change in the structure; and generating the system function for each of the projection data based on the magnetization change in the structure.

Advantages of the Invention

[0008] By using the magnetic particle imaging apparatus, magnetic particle imaging method, and magnetic particle imaging program of the present disclosure, a magnetic nanoparticle image with high spatial resolution can be generated.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the MPI device, MPI method, and MPI program according to the embodiments will be described with reference to the drawings. The following embodiments are merely examples, and it is possible to appropriately combine the embodiments and appropriately modify each embodiment.

[0011] In FIGS. 1 to 4, for ease of understanding the relationship between the figures, the coordinate axes of the XYZ orthogonal coordinate system are shown. The Z-axis is the longitudinal coordinate axis of the linear zero magnetic field (also referred to as "Free Field Line (FFL)") region. The Y-axis is the coordinate axis in the scanning direction (Y direction) of the FFL region orthogonal to the Z-axis. The X-axis is the coordinate axis in the direction orthogonal 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 the rotation in the R direction is the axis in the X direction. In the figures, the same or corresponding components 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 the main part of the MPI device 1 and the imaging target 50. The imaging target 50 is, for example, a human being in whom magnetic nanoparticles have been administered into the body. 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 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 being. As the magnetic nanoparticles, for example, “Resovist (registered trademark)” (generic name: Ferucarbotran), which is a hydrophilic colloid 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, 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 includes 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 each other with the imaging target 50 as the subject interposed therebetween. The linear zero magnetic field generation 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 generation 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 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 orthogonal to the longitudinal direction (Z direction) of the FFL region 60. The movement of the FFL region 60 is executed, for example, by controlling the linear zero magnetic field power supplies 13 and 14. Further, the movement of the FFL region 60 may be executed by the movement of the imaging target 50, or the movement of the linear zero magnetic field generation unit 10, or the movement of the imaging target 50 and the linear zero magnetic field generation unit 10.

[0017] Also, the linear zero magnetic field generation unit 10 can rotate the FFL region 60 by a predetermined rotation angle. The linear zero magnetic 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 executed, for example, by controlling the linear zero magnetic field power supplies 13 and 14. Further, the rotation of the FFL region 60 may be executed by the rotation of the linear zero magnetic field generation coils 11 and 12 in the R direction and the -R direction, or the rotation of the imaging target 50 in the R direction and the -R direction.

[0018] The excitation magnetic field application unit 20 includes an excitation magnetic field generation coil 21 that applies an alternating 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 generation coil 21. As shown in FIGS. 1 to 3, the excitation magnetic field generation coil 21 is, for example, an annular coil wound in the R direction.

[0019] The detection unit 30 detects the magnetization change generated by the excitation magnetic field of the magnetic nanoparticles contained in the FFL region 60 (more precisely, detects the harmonic signal generated by the magnetization change as a magnetic response signal). The detection unit 30 has, for example, one or a plurality of magnetic field detectors (for example, magnetic field detection coils). The detection signal output from the detection unit 30 may be amplified by an amplifier circuit. The one or a plurality of magnetic field detectors may be semiconductor elements for magnetic field detection (for example, 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 generation unit 10 to form the FFL region 60 in the imaging target 50, scan, or rotate, or scan and rotate the FFL region 60, causes the excitation magnetic field application unit 20 to apply an excitation magnetic field, and causes the detection unit 30 to detect the magnetization change. Further, the control unit 40 changes the position in the scanning direction (Y direction) of the FFL region 60 and the angle in the rotation direction R of the FFL region 60, generates projection data of the magnetization change based on the position in the scanning direction of the FFL region 60 and the angle of the FFL region 60, and performs sensitivity correction on the projection data using a system function acquired in advance for each projection data to generate corrected projection data. Further, 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 schematically showing the structure of the main part of the MPI device 1 according to the embodiment and the structure of the structure 51 as a subject. The structure 51 is, for example, a cylinder. However, the structure 51 is not limited to a cylinder. The system function used for generating the corrected projection data is generated in advance. When generating the system function, the control unit 40 forms an FFL region 60 in the structure 51, which is a reference subject containing magnetic nanoparticles with a predetermined particle concentration and having a predetermined size, in the linear zero magnetic field generation unit 10, scans or rotates or scans and rotates the FFL region 60, applies an excitation magnetic field to the magnetic field region including the FFL region 60 in the structure 51 in the excitation magnetic field application unit 20, causes the detection unit 30 to detect the magnetization change in the structure 51, and generates a system function for each projection data based on the magnetization change in the structure 51. The system function is generated based on the detection sensitivity at each position in the scanning direction and each angle in the rotation direction.

[0022] FIG. 4 is a diagram showing magnetic nanoparticles with a known concentration, the FFL region 60, the measured magnetic response signal, and the known magnetic response signal. All of the 8×4 round marks shown in FIG. 4 indicate magnetic nanoparticles with a known concentration. FIG. 4 shows that the FFL region 60 moves in the Y direction, the measured magnetic response signal is the sum of the magnetic signals generated in the FFL region 60 and its surroundings and is a waveform similar to a triangular wave, and the ideal known magnetic response characteristic (the sum of the magnetic signals generated only in the FFL region 60) is a rectangular wave indicated by a broken line. By exciting the magnetic nanoparticles with magnetization, a magnetic signal corresponding to the magnetization change (that is, the change in the magnetization of the magnetic nanoparticles) is directly detected by the detection unit 30 from the magnetic nanoparticles within the field of view (FOV) of the detection unit 30.

[0023] FIG. 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 (that is, 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 indicating the detection sensitivity (that is, the magnetic characteristics).

[0024] FIG. 6 is a diagram showing an example of the hardware configuration of the MPI device 1 according to the embodiment. As shown in FIG. 6, the 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). Further, the MPI device 1 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 that can communicate with the MPI device 1. The storage device 70 may be, for example, a 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 (for example, an MPI program that causes the MPI method according to the embodiment to be executed) stored in the 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] When the processing circuit is dedicated hardware, the processing circuit is, 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 the processor 41, the MPI program is implemented by software, firmware, or a combination of software and firmware. The software and firmware are described 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] Note that part of the MPI device 1 may be realized by dedicated hardware and part by software or firmware. In this way, the processing circuit can realize each function by hardware, software, firmware, or any combination thereof.

[0029] 《Operation during Generation of Magnetic Nanoparticle Image》 Next, the operation during the generation of the magnetic nanoparticle image by the MPI device 1 will be described. The operation during the generation of the magnetic nanoparticle image by the MPI device 1 is different from that described in Patent Document 1 in that correction processing of projection data is performed using a system function.

[0030] FIG. 7 is a flowchart showing an example of the generation process of the magnetic nanoparticle image by the MPI device 1. FIG. 7 shows an example in which the MPI device 1 changes both the position in the scanning direction of the FFL region 60 and the angle of the FFL region 60. However, the MPI device 1 may change only the position in the scanning direction of the FFL region 60, or may change 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 the FFL region 60 in the imaging target 50 (shown in FIG. 2) and sets the position in the scanning direction of the FFL region 60 to the 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 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 FIG. 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 and cause the detection unit 30 to detect the magnetization change (step ST13).

[0034] 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 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 generation unit 10 to rotate the FFL region 60 by a certain rotation angle to set it to the next angle (that is, one of the predetermined angles), and after going through the process of step ST13, returns to the process of step ST14. 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 determines whether detection (that is, the processes of steps ST12 to ST14) has been completed for all of the plurality of predetermined positions in the Y direction of the FFL region 60. If there is a position for which detection has not been completed (NO in step ST15), the control unit 40 returns the process to step ST11, controls the linear zero magnetic field generation unit 10 to move the FFL region 60 in the Y direction by a certain distance to set it to the next position (that is, one of the plurality of predetermined positions), and after going through the processes of steps ST12 to ST14, returns to the process of step ST15. If there is no position 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 process 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 with respect to the detection unit 30). Here, the projection data is data obtained by performing projection processing on the detection data in the direction along the FFL region 60 with respect to the magnetic field detector of the detection unit 30. Therefore, the projection position is a position corresponding to the position in the scanning direction of the FFL region 60. The projection position is also called the scan position. Further, the projection angle is an 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. Further, the control unit 40 selects a system function from the storage device 70, and estimates a system function other than the selected system function by interpolation for the position in the scanning direction or the rotation angle in the linear zero magnetic field region, or both, using the selected system function, and may 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 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 generation of system function》 FIG. 8 is a flowchart showing an example of the generation process of the system function of the MPI device 1. FIG. 8 shows an example in which the MPI device 1 changes both the position in the scanning direction of the FFL region 60 and the angle of the FFL region 60. However, the MPI device 1 may change only the position in the scanning direction of the FFL region 60, or may change only the angle of the FFL region 60.

[0040] In generating system functions, first, the control unit 40 controls the linear zero magnetic field generation unit 10 to generate an FFL region 60 in the structure 51 (Fig. 3) and sets the position in the scanning direction of the FFL region 60 to the 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 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 Fig. 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 and cause the detection unit 30 to detect the magnetization change (step ST23).

[0043] Next, the control unit 40 determines whether detection has been completed for all of a plurality of 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 at the current position in the scanning direction (NO in step ST24), the control unit 40 returns the process 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 (that is, one of the plurality of predetermined angles), and after passing through the process of step ST23, returns to the process of step ST24. 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 ST24), the control unit 40 advances the process to step ST25.

[0044] In step ST25, the control unit 40 determines whether the detection (i.e., the processes of steps ST22 to ST24) has been completed for all of a plurality of predetermined scanning direction positions in the Y direction of the FFL region 60. If there is a scanning direction position where the detection is not completed (NO in step ST25), the control unit 40 returns the process to step ST21, controls the linear zero magnetic field generation unit 10, moves 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 plurality of predetermined scanning direction positions), and after going through the processes of steps ST22 to ST24, returns to the process of step ST25. If there is no scanning direction position where the detection is not completed, that is, if the detection has been completed for all scanning direction positions (YES in step ST25), the control unit 40 advances the process 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 with respect to the detection unit 30).

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

[0047] 《Process of Generating an Image from Projection Data》 With reference to FIGS. 9(A) and (B) to FIGS. 14(A) and (B), the process of generating a reconstructed image from the projection data will be described.

[0048] First, the control unit 40 extracts MPI signals at a plurality of angles from the projection data. The plurality of angles are, for example, angles in the rotational direction indicated by R. FIG. 9(A) shows an example of the projection data projected on the scanning position - angle coordinates. The scanning position corresponds to the positions of a plurality of magnetic field detectors (or detection elements) of the detection unit 30. In FIG. 9(A), the brighter the part, the stronger the intensity of the measured MPI signal, which is the measured magnetic response signal, that is, the larger the amplitude. FIG. 9(B) shows the waveform (Original Signal) of the intensity of the measured MPI signal at a certain angle in FIG. 9(A) and the signal (Original Signal FFT) obtained by performing fast Fourier transform (FFT) processing on the measured MPI signal.

[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 the waveform (Signal without DC) of the intensity of the signal obtained by removing the DC component from the measured MPI signal in FIG. 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 deconvolution coefficient S(f) as the 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 the magnetic signal detected from the cylindrical body that is the reference structure 51, and the signal M(f) obtained by performing FFT processing on 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, which is S(f), obtained by performing FFT processing on it. Here, f represents frequency, t represents time, and x represents the 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 the signal M(f) obtained by Fourier-transforming it from the signal in FIG. 10(B) and the inverse convolution coefficient (i.e., system function) in FIG. 11(C). FIG. 12(A) shows the signal in FIG. 10(B). FIG. 12(B) shows the inverse convolution coefficient in FIG. 11(C). FIG. 12(C) shows the waveform indicating the intensity of the noise-removed MPI signal m(x) as the corrected MPI signal and the signal M(f) obtained by subjecting the noise-removed MPI signal to FFT processing.

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

[0053] 《Effects of the Embodiment》 FIG. 13(A) shows the corrected projection data generated by the control unit 40 of the MPI apparatus 1 according to the embodiment. FIG. 13(B) shows the original uncorrected projection data (comparative example). As shown in FIG. 13(A), in the corrected projection data generated by the control unit 40 of the MPI apparatus 1 according to the embodiment, the boundary between the range where magnetic nanoparticles exist (white region) and the range where magnetic nanoparticles do not exist (black region) is in a clear straight line. Thus, by using the MPI apparatus 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 apparatus 1 according to the embodiment. FIG. 14(B) shows a magnetic nanoparticle image (comparative example) based on the original uncorrected projection data. As shown in FIG. 14(B), when an image is reconstructed using the uncorrected projection data, the boundary between the region where magnetic nanoparticles exist (white region) and the region where magnetic nanoparticles do not exist (black region) becomes unclear. In FIG. 14(B), the large outer circle is an artifact. On the other hand, as shown in FIG. 14(A), the corrected projection data generated by the MPI apparatus 1 according to the embodiment has a clear circular shape for the boundary between the region where magnetic nanoparticles exist (white region) and the region where magnetic nanoparticles do not exist (black region). Thus, by using the MPI apparatus 1 according to the embodiment, a magnetic nanoparticle image with high spatial resolution can be generated.

Description of Reference Numerals

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

Claims

1. A magnetic particle imaging 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 configured to form a linear zero magnetic field region in the subject and move the linear zero magnetic field region in a predetermined direction; an excitation magnetic field application unit configured to apply an alternating excitation magnetic field to a magnetic field region including the linear zero magnetic field region; a detection unit configured to detect a magnetization change of the magnetic nanoparticles generated by the excitation magnetic field; a control unit; wherein 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 an imaging target as the subject, and scan, or rotate, or scan and rotate the linear zero magnetic field region; 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 a position in the scanning direction of the linear zero magnetic field region and an angle in the rotation direction of the linear zero magnetic field region; generates corrected projection data by performing sensitivity correction on the projection data using a system function acquired in advance for each of the projection data; generates the magnetic nanoparticle image based on the corrected projection data; when generating the system function, the control unit causes the linear zero magnetic field generation unit to form the linear zero magnetic field region in a structure that is the subject containing the magnetic nanoparticles with a predetermined particle concentration and having a predetermined size, and scan, or rotate, or scan and rotate the linear zero magnetic field region; 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 within the structure; causes the detection unit to detect the magnetization change within the structure; generates the system function for each of the projection data based on the magnetization change within the structure. A magnetic particle imaging apparatus characterized by the above.

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

3. The magnetic particle imaging apparatus according to claim 1 or 2, wherein the scanning direction is a direction orthogonal 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, wherein the linear zero magnetic field generation unit rotates the linear zero magnetic field region by a predetermined rotation angle during the rotation.

5. When generating the system function, the control unit generates a system function indicating the detection sensitivity at each combination of the position and the angle, and stores a set of system functions including the plurality of system functions in a storage device. The magnetic particle imaging apparatus according to any one of claims 1 to 4, characterized in that.

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 claim 5, characterized in that.

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, and 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 claim 5, characterized in that.

8. Further comprising the storage device for storing the set of system functions The magnetic particle imaging apparatus according to any one of claims 5 to 7, characterized in that.

9. A magnetic particle imaging method executed by a magnetic particle imaging apparatus having a linear zero magnetic field generation unit that forms a linear zero magnetic field region in a 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, 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 magnetic nanoparticles in an imaging target as the subject, wherein: When generating the magnetic nanoparticle image, forming the linear zero magnetic field region in the imaging target in the linear zero magnetic field generation unit, and scanning, or rotating, or scanning and rotating the linear zero magnetic field region; causing the excitation magnetic field application unit to apply the excitation magnetic field; causing the detection unit to detect the magnetization change; 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 acquired in advance for each of the projection data; generating the magnetic nanoparticle image based on the corrected projection data, and having When generating the system function, causing the linear zero magnetic field generation unit to form the linear zero magnetic field region in a structure that is the subject containing the magnetic nanoparticles with a predetermined particle concentration and having a predetermined size, and scanning, or rotating, or scanning and rotating the linear zero magnetic field region; 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 structure; causing the detection unit to detect the magnetization change in the structure; generating the system function for each of the projection data based on the magnetization change in the structure, and having A magnetic particle imaging method characterized by the above.

10. A magnetic particle imaging program executed by a magnetic particle imaging apparatus having a linear zero magnetic field generation unit that forms a linear zero magnetic field region in a 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, 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 magnetic nanoparticles in an imaging target that is the subject, When generating the magnetic nanoparticle image, the magnetic particle imaging apparatus is caused to cause the linear zero magnetic field generation unit to form the linear zero magnetic field region in the imaging target, and scan, or rotate, or scan and rotate the linear zero magnetic field region; cause the excitation magnetic field application unit to apply the excitation magnetic field; cause the detection unit to detect the magnetization change; generate 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 acquired in advance for each of the projection data; Generating the magnetic nanoparticle image based on the corrected projection data; and causing the above steps to be executed, When generating the system function, the magnetic particle imaging apparatus is caused to form the linear zero magnetic field region in a structure that is the subject containing the magnetic nanoparticles having a predetermined particle concentration and having a predetermined size in the linear zero magnetic field generation unit, and scan, or rotate, or scan and rotate the linear zero magnetic field region; apply the excitation magnetic field to a magnetic field region including the linear zero magnetic field region in the structure in the excitation magnetic field application unit; detect the magnetization change in the structure in the detection unit; generate the system function for each of the projection data based on the magnetization change in the structure; and cause the above steps to be executed A magnetic particle imaging program characterized by the above.

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