Electromagnetic device for magnetic particle generation and magnetic particle generation device

Abstract

Electromagnetic device (1) for magnetic particle imaging, comprising the following: - a return yoke (2) with a gap extending in the Y direction and forming a magnetic field space, where the width direction of the magnetic field space is defined as the X direction and the length direction of the magnetic field space is defined as the Y direction; - a gradient magnetic field generation unit (3) formed on the feedback yoke (2) and configured to generate - in the magnetic field space - a gradient magnetic field (HX1) in the X direction and to form - in the magnetic field space - a zero-field region (S1) extending in the Y direction; - an alternating magnetic field generation unit (4) formed on the feedback yoke (2) and configured to generate an alternating magnetic field (HX2) in the magnetic field space; and - a rotation mechanism configured to rotate - when the direction perpendicular to the X-direction and the Y-direction is defined as the Z-direction - the gradient magnetic field (HX1) and the alternating magnetic field (HX2) relative to the subject (6), wherein the Z-direction is the rotation axis (CZ), and wherein the feedback yoke (2) has the following: - an alternating magnetic field yoke (22) configured to correspond to the alternating magnetic field (HX2) and extending in the Y direction; and - a pair of gradient magnetic field yokes (21, 23, 24, 25, 26) which are designed to correspond to the gradient magnetic field (HX1) and which are arranged on the inside of the alternating magnetic field yoke (22) and run in the Y direction so that they are opposite each other.

Description

Technical field

[0001] The present invention relates to an electromagnetic device for use in magnetic particle imaging and a magnetic particle imaging device. State of the art

[0002] Magnetic particle imaging (MPI) has been developed as a method for acquiring a tomographic image of the human body (see, for example, patent literature 1). MPI requires the generation of a magnetic field in a room that is as strong as possible.

[0003] In the MPI described in patent literature 1, a plurality of air-core coils are configured to generate magnetic fields that form a linear zero-field region. Furthermore, in this method, the pairs of air-core coils are controlled such that the zero-field region rotates in the θ-direction while oscillating back and forth in the r-direction, within a two-dimensional polar coordinate system. The "zero-field region," as used here, denotes a region in which the magnetic fields generated by the pairs of air-core coils cancel each other out.

[0004] In the MPI described in patent literature 1, a two-dimensional (2D) tomography image can be acquired with the configuration mentioned above, using a principle similar to X-ray computed tomography (CT), i.e., using a principle of a back-projection method.

[0005] From US patent 8 971 988 B2, an arrangement and a method for influencing and / or detecting magnetic particles in an area of ​​effect are also known, in particular for monitoring intracerebral or intracranial hemorrhages by means of magnetic particle imaging (MPI).

[0006] In addition, reference should be made to the article by Erica E. Mason et al. “Design analysis of an MPI human functional brain scanner”, in: International Journal on Magnetic Particle Imaging, March 23, 2017, 1 - 12. Bibliography Patent literature

[0007] [PTL 1] JP 2013- 502 262 A (see for example Fig. 4 and Fig. 7) Summary of the invention: Technical problem

[0008] In the MPI described in patent literature 1, the majority of air-core coils generate the magnetic fields, as described above. However, the magnetic fields generated by the air-core coils are relatively weak, and consequently, it is difficult to strengthen the magnetic fields generated in the space. Furthermore, as described above, this method requires controlling the air-core coils so that the zero-field region rotates in the θ direction. Therefore, the coil configuration becomes complex, and as a result, satisfactory controllability cannot be achieved.

[0009] The present invention was designed to solve the problem described above. Therefore, it is an object of the invention to provide an electromagnetic device for magnetic particle imaging with which the controllability can be increased while increasing the intensity of a magnetic field generated in a space, and to provide a magnetic particle imaging device comprising the electromagnetic device for magnetic particle imaging. Solution to the problem

[0010] The problem underlying the invention is solved by an electromagnetic device with the features of independent claim 1 or by a magnetic particle imaging device with the features of independent claim 13. Advantageous embodiments of the electromagnetic device according to the invention are specified in dependent claims 2 to 12. Advantageous effects of the invention

[0011] According to the present invention, it is possible to obtain an electromagnetic device for magnetic particle imaging with which the controllability can be increased while increasing the intensity of the magnetic field generated in space, as well as to obtain a magnetic particle imaging device which includes the electromagnetic device for magnetic particle imaging. Brief description of the drawings Fig. Figure 1 is a schematic view illustrating a configuration of an MPI device comprising an electromagnetic device for MPI, according to a first embodiment of the present invention. Fig. Figure 2 is a schematic view to illustrate a subject and a receiving coil to be mounted on the subject, according to Fig. 1. Fig. Figure 3 is a schematic diagram illustrating how magnetic fields in the +X direction and in the -X direction are generated by a gradient magnetic field generating unit according to Fig. 1 will be generated. Fig. Figure 4 is a schematic graph to represent a change along the X-direction of a gradient magnetic field generated by the gradient magnetic field generation unit according to Fig. 1 is generated. Fig. Figure 5 is a schematic graph to represent a change along the X-direction of an alternating magnetic field generated by an alternating magnetic field generation unit according to Fig. 1 is generated. Fig. Figure 6 is a schematic graph illustrating the temporal change of the alternating magnetic field generated by the alternating magnetic field generation unit according to Fig. 1 is generated. Fig. Figure 7 is a schematic graph representing magnetic fields received by magnetic particles moving in a gradient magnetic field according to Fig. There are 4. Fig. Figure 8 is a schematic graph representing an MH curve, which shows the relationship between the magnetic fields generated by the magnetic particles according to Fig. 7 are received, and the magnetization of the magnetic particles is shown. Fig. Figure 9 is a schematic graph to represent the gradient magnetic field according to Fig. 7. Fig. Figure 10 is a schematic graph illustrating a change in the gradient magnetic field that appears when the alternating magnetic field changes according to the gradient magnetic field. Fig. 9 is superimposed. Fig. Figure 11 is a schematic view to schematically illustrate a cross-section along the XZ-plane of a pair of permanent magnets according to Fig. 1. Fig. Figure 12 is a schematic view to illustrate a comparative example for comparison with a return yoke according to Fig. 1. Fig. Figure 13 is a schematic view to illustrate the comparative example for comparison with the return yoke according to Fig. 1. Fig. Figure 14 is a schematic view to schematically illustrate a cross-section along the XZ plane of the feedback yoke, the pair of permanent magnets and a pair of alternating magnetic field generating coils according to Fig. 1. Fig. Figure 15 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke, the pair of permanent magnets and the pair of alternating magnetic field generating coils according to Fig. 1. Fig. Figure 16 is a schematic view to illustrate a comparative example of Fig. 14. Fig. Figure 17 is a schematic view to schematically illustrate a cross-section along the XZ plane of a return yoke, a pair of permanent magnets and a pair of alternating magnetic field generating coils of the electromagnet device according to a second embodiment of the present invention. Fig. Figure 18 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke, the pair of permanent magnets and the pair of alternating magnetic field generating coils of the electromagnet device according to the second embodiment. Fig. Figure 19 is a schematic graph illustrating a distribution in the Z-direction of an alternating magnetic field, which appears in the case where a first protrusion region and a second protrusion region are located at both ends of each gradient magnetic field yoke according to Fig. 18 are trained. Fig. Figure 20 is a schematic view to illustrate another example of the electromagnet device according to the second embodiment. Fig. Figure 21 is a schematic view to schematically illustrate a cross-section along the XZ plane of a feedback yoke and a pair of gradient / alternating magnetic field generating coils of an electromagnet device according to a third embodiment of the present invention. Fig. Figure 22 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke and the pair of gradient / alternating magnetic field generating coils of the electromagnet device according to the third embodiment. Fig. Figure 23 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke and the pair of gradient / alternating magnetic field generating coils of the electromagnet device according to the third embodiment. Fig. Figure 24 is a schematic view to illustrate another example of the electromagnet device according to the third embodiment. Fig. Figure 25 is a schematic view to schematically illustrate a cross-section along the XZ plane of a feedback yoke, an upper gradient magnetic field generating coil, a lower gradient magnetic field generating coil and a pair of alternating magnetic field generating coils of an electromagnet device according to a fourth embodiment of the present invention. Fig. Figure 26 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke, the upper gradient magnetic field generating coil, the lower gradient magnetic field generating coil and the pair of alternating magnetic field generating coils of the electromagnet device according to the fourth embodiment. Fig. Figure 27 is a schematic view to schematically illustrate the cross-section along the XZ plane of the feedback yoke, the upper gradient magnetic field generating coil, the lower gradient magnetic field generating coil and the pair of alternating magnetic field generating coils of the electromagnet device according to the fourth embodiment. Fig. Figure 28 is a schematic view illustrating a configuration of an MPI device comprising an electromagnetic device for MPI, according to a fifth embodiment of the present invention. Description of embodiments

[0012] An electromagnetic device for magnetic particle imaging and a magnetic particle imaging apparatus according to exemplary embodiments of the present invention are now described with reference to the drawings. In the description of the drawings, identical or similar components are assigned the same reference numerals, and their further description is omitted. First embodiment

[0013] Fig. Figure 1 is a schematic view illustrating a configuration of an MPI device comprising an electromagnetic device 1 for MPI, according to a first embodiment for carrying out the present invention. Fig. Figure 2 is a schematic view to illustrate a subject 6 and a receiving coil 7 to be mounted on the subject 6, according to Fig. 1.

[0014] The MPI device, which is in Fig. As illustrated in Figure 1, the electromagnetic device 1 for the MPI (hereinafter referred to as the "electromagnetic device") and the receiving coil 7, which is to be mounted on the subject 6, comprise: a feedback yoke 2, a gradient magnetic field generating unit 3, an alternating magnetic field generating unit 4, a rotation mechanism, and a movement mechanism.

[0015] In the embodiments, the lateral direction of the magnetic field space is defined as the X-direction, the longitudinal direction of the magnetic field space is defined as the Y-direction, and the direction perpendicular to the X-direction and the Y-direction is defined as the Z-direction. Furthermore, in the embodiments, as a specific example for subject 6, it is assumed that subject 6 is a human body.

[0016] The feedback yoke 2 forms a gap and has a magnetic field space that extends in the Y direction. In other words, the feedback yoke 2 has a gap for forming the magnetic field space that extends in the Y direction. The feedback yoke 2 is formed, for example, using a laminated steel plate or another iron plate that is resistant to eddy currents.

[0017] The gradient magnetic field generation unit 3 is formed on the feedback yoke 2. The gradient magnetic field generation unit 3 is configured such that it generates a gradient magnetic field HX1 in the X-direction in the magnetic field space of the feedback yoke 2, which changes primarily along the X-direction, and that it further forms a zero-field region S1 in the magnetic field space, which extends in the Y-direction.

[0018] More precisely: The gradient magnetic field generation unit 3 is configured to generate magnetic fields in the +X direction and in the -X direction to produce the gradient magnetic field HX1. The zero-field region S1 is configured to extend in the Y direction near the center of the magnetic field space when the magnetic fields in the +X direction and in the -X direction generated by the gradient magnetic field generation unit 3 cancel each other out near the center of the magnetic field space. Fig. Figure 1 shows a zero-field line CY that passes through the center of the zero-field region S1 and runs in the Y direction.

[0019] As a specific configuration of the gradient magnetic field generation unit 3, the gradient magnetic field generation unit 3 is, for example, as in Fig. 1 illustrated - formed from a pair of rectangular permanent magnets 31 formed on the inside, i.e. on the sides of the gap of the return yoke 2 and running in the Y direction such that they are opposite each other.

[0020] The alternating magnetic field generation unit 4 is formed on the feedback yoke 2. The alternating magnetic field generation unit 4 is configured such that it generates an alternating magnetic field HX2 in the X-direction in the magnetic field space of the feedback yoke 2, which is spatially uniform and changes over time.

[0021] As a specific configuration of the alternating magnetic field generation unit 4, the alternating magnetic field generation unit 4 is, for example, as in Fig. Figure 1 illustrates this – formed from a pair of ring-shaped alternating magnetic field generating coils 41, which are located on the inside of the feedback yoke 2 and extend in the Y direction such that they are opposite each other. A power source is connected to the pair of alternating magnetic field generating coils 41 and is configured to supply energy to the pair of alternating magnetic field generating coils 41.

[0022] The rotation mechanism is configured to rotate the gradient magnetic field HX1, generated by the gradient magnetic field generation unit 3, and the alternating magnetic field HX2, generated by the alternating magnetic field generation unit 4, relative to the subject 6, with the Z-direction being the axis of rotation. As the gradient magnetic field HX1 and the alternating magnetic field HX2 rotate as described above, the zero-field region S1 will also rotate, with the Z-direction being the axis of rotation.

[0023] As a specific configuration of the rotation mechanism, the rotation mechanism is configured to rotate, for example, the return yoke 2 with respect to the stationary subject 6. In other words, the rotation mechanism is configured to—as in Fig. Figure 1 illustrates how the feedback yoke 2 rotates, with the central axis of the feedback yoke 2 in the Z-direction being the rotation axis CZ, thus causing the gradient magnetic field HX1 and the alternating magnetic field HX2 to rotate. The rotation axis CZ is perpendicular to each of the zero-field region S1 and the zero-field line CY, and it corresponds to a body axis of subject 6.

[0024] When the feedback yoke 2 is rotated, the gradient magnetic field generation unit 3 and the alternating magnetic field generation unit 4, which are formed on the feedback yoke 2, are also rotated, and as a result, the gradient magnetic field HX1 and the alternating magnetic field HX2 are rotated. The rotation mechanism is formed, for example, using a motor 5.

[0025] The movement mechanism is configured to rotate the gradient magnetic field HX1, generated by the gradient magnetic field generation unit 3, and the alternating magnetic field HX2, generated by the alternating magnetic field generation unit 4, in the Z-direction relative to subject 6. When the gradient magnetic field HX1 and the alternating magnetic field HX2 are moved as described above, the zero-field region S1 is also moved in the Z-direction.

[0026] As a specific configuration of the movement mechanism, the movement mechanism is configured to move, for example, the return yoke 2 relative to the stationary subject 6. In other words, the movement mechanism is configured to—as in Fig. Figure 1 illustrates - the return yoke 2 is moved in the Z direction, i.e. in the upward-downward direction of the drawing plane, so that the gradient magnetic field HX1 and the alternating magnetic field HX2 are moved in the Z direction.

[0027] When the return yoke 2 is moved, the gradient magnetic field generation unit 3 and the alternating magnetic field generation unit 4, which are formed on the return yoke 2, are also moved, and as a result, the gradient magnetic field HX1 and the alternating magnetic field HX2 are moved. A rack and pinion drive system, for example, is used as a drive system for the movement mechanism.

[0028] The receiving coil 7, for example, is - as in Fig. Figure 2 illustrates this – formed from a pair of saddle-shaped coils. The receiving coil 7 is configured to detect the magnetization in the X-direction of magnetic particles present in the subject 6, which is located in the magnetic field space of the feedback yoke 2.

[0029] Next, an example of the gradient magnetic field HX1, generated by the gradient magnetic field generation unit 3, will be given with reference to Fig. 3 and Fig. 4 described. Fig. Figure 3 is a schematic diagram illustrating how the magnetic fields in the +X direction and in the -X direction are generated by the gradient magnetic field generating unit 3 according to Fig. 1 will be generated. Fig. Figure 4 is a schematic graph to represent a change along the X-direction of the gradient magnetic field HX1, which is generated by the gradient magnetic field generation unit 3 according to Fig. 1 is generated.

[0030] As per Fig. As can be seen in Figure 3, the zero-field region S1, which extends in the Y direction, spreads out in the X direction around the zero-field line CY. In a region S2, which is distinct from the zero-field region S1, the intensity of the magnetic field in the +X direction continues to increase in the +X direction, and the intensity of the magnetic field in the -X direction continues to increase in the -X direction. As shown in Figure 3, the zero-field region S1, which extends in the Y direction, spreads out in the X direction around the zero-field line CY. Fig. As can be seen in Figure 4, the gradient magnetic field HX1 also changes mainly along the X-direction.

[0031] If the gradient magnetic field generating unit 3 is formed from the pair of permanent magnets 31 described above, then, if the length in the Y-direction of each permanent magnet 31 is longer than a gap in the X-direction of the pair of permanent magnets 31, the gradient magnetic field HX1 can be obtained, which is uniform in the Y-direction. In this case, the zero-field region S1 is also uniform in the Y-direction.

[0032] Next, an example of the alternating magnetic field HX2, generated by the alternating magnetic field generation unit 4, will be given with reference to Fig. 5 and Fig. 6 described. Fig. Figure 5 is a schematic graph to represent a change along the X-direction of the alternating magnetic field HX2, which is generated by the alternating magnetic field generation unit 4 according to Fig. 1 is generated. Fig. Figure 6 is a schematic graph to represent a change over time of the alternating magnetic field HX2, which is generated by the alternating magnetic field generation unit 4 according to Fig. 1 is generated.

[0033] As per Fig. 5 and Fig. As can be seen in Figure 6, the alternating magnetic field HX2 is uniform along the X-direction, and it changes over time in the form of a sine wave or cosine wave.

[0034] When the receiving coil 7 is used in the MPI device, it is preferred that the frequency of the alternating magnetic field HX2 ranges from approximately 1 kHz to approximately 20 kHz, with regard to the sensitivity of the receiving coil 7.

[0035] The first embodiment describes, by way of example, the case in which the alternating magnetic field generation unit 4 is configured to generate an alternating magnetic field in the X-direction, i.e., the alternating magnetic field HX2, but the present invention is not limited thereto. More precisely: The alternating magnetic field generation unit 4 can be configured to generate—instead of the alternating magnetic field HX2—an alternating magnetic field that is perpendicular to the gradient magnetic field HX1, i.e., an alternating magnetic field in the Y-direction or Z-direction.

[0036] Next, the principle of MPI will be described. Here, (1) a signal of the magnetic particles that can be obtained along the zero-field region S1, first described, and (2) A method for acquiring a 2D tomography image is then described.

[0037] The aforementioned element (1) is referred to Fig. 7 and Fig. 8 described. Fig. Figure 7 is a schematic graph representing the magnetic fields received by the magnetic particles in the gradient magnetic field HX1 according to Fig. There are 4. Fig. Figure 8 is a schematic graph representing an MH curve, which shows the relationship between the magnetic fields generated by the magnetic particles according to Fig. 7 are received, and the magnetization of the magnetic particles is shown.

[0038] A case is assumed in which the magnetic particles present in subject 6 are located along the zero-field region S1, which runs in the Y direction, as shown in Fig. 3 and Fig. Figure 4 describes this by way of example. In this case, the magnetic field in the zero-field region S1 is zero, and consequently, the magnetic particles can move freely. If, in this state, the alternating magnetic field HX2 is applied to the subject 6, the magnetic moment of the magnetic particles oscillates in the direction of the alternating magnetic field HX2. If the receiving coil 7 is located near the magnetic particles, the receiving coil 7 receives a variation in magnetic flux accompanied by the oscillation of the magnetic moment, and as a result, a voltage is generated in the receiving coil 7.

[0039] As in Fig. As shown in Figure 7, the gradient magnetic field HX1 increases linearly in the +X direction. Furthermore, the magnetic field received by magnetic particles located at position A, in the X direction of the zero-field region S1, is a magnetic field aH, and the magnetic field aH is zero. Additionally, the magnetic field received by magnetic particles located at position B, in the X direction of region S2, which is different from the zero-field region S1, is a magnetic field bH.

[0040] If the alternating magnetic field HX2 is not applied to the magnetic particles, as in Fig. As shown in Figure 8, the magnetization of the magnetic particles receiving the magnetic field aH is zero, and the magnetization of the magnetic particles receiving the magnetic field bH is the magnetization bM.

[0041] When the alternating magnetic field HX2 is applied to the magnetic particles, the magnetization of the magnetic particles receiving the magnetic field aH, to which the alternating magnetic field HX2 is superimposed, changes, accompanied by a change in the time course of the alternating magnetic field HX2 according to the MH curve shown in Fig. Figure 8 is shown. Similarly, the magnetization of the magnetic particles receiving a magnetic field obtained from the alternating magnetic field HX2 superimposed on the magnetic field bH changes in accordance with the change over time of the alternating magnetic field HX2 according to the MH curve.

[0042] When the alternating magnetic field HX2 is applied to the magnetic particles, as described above and as in Fig. As shown in Figure 8, the magnetization is in an unsaturated state and changes non-linearly for the magnetic particles receiving the magnetic field aH, while the magnetization is in a saturated state for the magnetic particles bH, regardless of the alternating magnetic field HX2. The term "saturated state," as used here, denotes a state in which the strength of the magnetization of the magnetic particles does not change, and the term "unsaturated state" denotes a state in which the strength of the magnetization of the magnetic particles changes.

[0043] Even when the alternating magnetic field HX2 is applied to the magnetic particles receiving the magnetic field bH, the magnetization of the magnetic particles remains saturated. In this case, a voltage with the same frequency component as that of the alternating magnetic field HX2 is generated in the receiving coil 7. In other words, a voltage with only a first-order component is generated in the receiving coil 7.

[0044] On the other hand, when the alternating magnetic field HX2 is applied to the magnetic particles receiving the magnetic field aH, the magnetization of the magnetic particles transitions from a saturated to an unsaturated state. Therefore, the magnetization of the magnetic particles changes non-linearly according to the MH curve, and consequently, the magnetic flux density, i.e., the magnetic flux corresponding to the magnetization described above, changes non-linearly without proportionality to the alternating magnetic field HX2. In this case, a voltage is generated in the receiving coil 7, which has a frequency component obtained by combining the same frequency component as that of the alternating magnetic field HX2 with a harmonic component of the third or higher order.

[0045] As described above, the following applies: When the alternating magnetic field HX2 is applied to the magnetic particles located in the zero-field region S1, a voltage containing the third-order or higher harmonic component is generated in the receiving coil 7. Conversely, when the alternating magnetic field HX2 is applied to the magnetic particles located in region S2, which is different from the zero-field region S1, a voltage containing only the first-order component is generated in the receiving coil 7.

[0046] If the voltage of the harmonic component of the third or higher order, generated in the receiving coil 7, is observed, then the magnetization of the magnetic particles located in the zero-field region S1 can be detected. In other words, the receiving coil 7 can detect—as accumulated magnetization—the magnetization of the magnetic particles along the zero-field region S1.

[0047] The alternating magnetic field HX2 links the receiving coil 7, and consequently, the voltage of the first-order component caused by the linking of the alternating magnetic field HX2 is generated in the receiving coil 7. Therefore, the voltage of the first-order component generated in the receiving coil 7 is not observed. The voltage of the third- or higher-order harmonic component generated in the receiving coil 7 can be observed, for example, using a lock-in amplifier, or it can be observed, for example, by Fourier transformation of a voltage signal.

[0048] The element (2) mentioned above will now be referred to Fig. 9 and Fig. 10 described. Fig. Figure 9 is a schematic graph representing the gradient magnetic field HX1 according to Fig. 7. Fig. Figure 10 is a schematic graph illustrating a change in the gradient magnetic field HX1 that appears when the alternating magnetic field HX2 changes according to the gradient magnetic field HX1. Fig. 9 is superimposed.

[0049] As described above, the prior art described in patent literature 1 is as follows: In a two-dimensional polar coordinate system, each pair of air-core coils is controlled such that the linear zero-field region rotates in the θ-direction while moving back and forth in the r-direction. As a result, as in X-ray computed tomography, an accumulated magnetization distribution in the R-direction is obtained, and a 2D tomographic image is generated using the principle of a back-projection method.

[0050] As per Fig. As can be seen in Figure 10, the following applies in this embodiment: With the alternating magnetic field HX2 superimposed on the gradient magnetic field HX1, the zero-field region S1 moves in the X-direction. In other words: If the alternating magnetic field HX2 is not superimposed on the gradient magnetic field HX1, as in Figure 10, the following applies: Fig. As shown in Figure 9, the zero-field region S1 is located at position A.

[0051] As in Fig. As shown in Figure 10, the following applies in contrast: When a positive alternating magnetic field HX2 is superimposed on the gradient magnetic field HX1, the zero-field region S1 moves in the -X direction relative to position A. When a negative alternating magnetic field HX2 is superimposed on the gradient magnetic field HX1, the zero-field region S1 moves in the +X direction relative to position A.

[0052] As described above, when the alternating magnetic field HX2 is superimposed on the gradient magnetic field HX1, the zero-field region S1 is moved in the X-direction. The rotation mechanism also rotates the zero-field region S1, with the Z-direction being the axis of rotation. In other words, in the first embodiment—in contrast to the prior art described in patent literature 1—the linear zero-field region can be rotated while moving back and forth without the use of multiple pairs of air-core coils.

[0053] In this embodiment, the alternating magnetic field generation unit 4 can be formed from at least one pair of ring-shaped coils, as described above, and consequently, the controllability is improved with a simpler structure compared to the prior art described in patent literature 1. Furthermore, by forming the feedback yoke 2 from iron, a stronger magnetic field can be obtained.

[0054] Furthermore, if the linear zero-field region is merely rotated while moving back and forth, only a 2D image can be obtained. In the first embodiment, the zero-field region S1 is moved in the Z-direction by means of the movement mechanism, and consequently a 3D image can be obtained.

[0055] Next, the configuration of the return yoke 2 in this embodiment will be described with reference to Fig. 11 to Fig. 16 described.

[0056] First, the zero-field region S1, which is generated by the gradient magnetic field generation unit 3, is described with reference to Fig. 11 described. Fig. Figure 11 is a schematic view to schematically illustrate a cross-section along the XZ-plane of a pair of permanent magnets 31 according to Fig. 1. Fig. Figure 11 shows magnetic flux lines FL generated by the permanent magnets 31.

[0057] As in Fig. As illustrated in Figure 11, the pair of permanent magnets 31 is arranged such that N poles face each other across a gap in the X-direction. The magnetic flux lines FL generated by the permanent magnets 31 are initially a large number of lines, but in Fig. Figure 11 is representative and shows only a single line.

[0058] In the XZ plane, which is in Fig. As shown in Figure 11, the following applies: If the center of the gap is X = Z = 0, the magnetic fields generated by the N poles of the pair of permanent magnets 31 collide and repel each other at position X = 0, and the zero-field region S1 is formed near the position of X = 0 and Z = 0. For example, if the pair of permanent magnets 31 is longer in the Y-direction than the gap, the zero-field region S1 is such that it extends in the Y-direction.

[0059] Next, a comparative example will be given for comparison with the return yoke 2 in the first embodiment with reference to Fig. 12 and Fig. 13 described. Fig. 12 and Fig. Figure 13 shows schematic views to illustrate the comparative example for comparison with the return yoke 2 according to Fig. 1.

[0060] Fig. Figure 12 shows magnetic paths P1 generated by the permanent magnets 31, and Fig. Figure 13 shows magnetic paths P2 generated by the alternating magnetic field generating coils 41. As in Fig. 12 and Fig. As illustrated in Figure 13, a pair of yokes 20 are used as a comparative example instead of the return yoke 2, which run in the Y direction and are opposite each other.

[0061] As in Fig. As illustrated in Figure 12, the pair of permanent magnets 31 is individually arranged on the pair of Jochen magnets 20. In this case, the number of magnetic paths P1 passing through a core with large µ is large, and as a result, the gradient magnetic field HX1 generated by the permanent magnets 31 is strong.

[0062] As in Fig. As illustrated in Figure 13, the pair of alternating magnetic field generating coils 41 is individually arranged to surround the pair of Jochen 20. In this case, most of the magnetic paths P2 exist in an air region with high magnetic resistance, and as a result, the alternating magnetic field HX2 generated by the alternating magnetic field generating coils 41 is weak.

[0063] In order to increase the intensities of the gradient magnetic field HX1 and the alternating magnetic field HX2, it is therefore necessary to design a configuration of the feedback yoke 2 to optimize the specifications of the magnetic paths P1 and the magnetic paths P2.

[0064] Next, the configuration of the return yoke 2 in this embodiment will be described with reference to Fig. 14 and Fig. 15 described. Fig. 14 and Fig. Figure 15 shows schematic views illustrating a cross-section along the XZ plane of the feedback yoke 2, the pair of permanent magnets 31 and the pair of alternating magnetic field generating coils 41 according to Fig. 1.

[0065] Fig. Figure 14 shows magnetic paths P1 generated by the permanent magnets 31, and Fig. Figure 15 shows magnetic paths P2 generated by the alternating magnetic field generating coils 41.

[0066] As in Fig. 14 and Fig. As shown in Figure 15, the feedback yoke 2 has an alternating magnetic field yoke 22, configured to correspond to the alternating magnetic field HX2 and extending in the Y direction, and a pair of gradient magnetic field yokes 21, configured to correspond to the gradient magnetic field HX1, arranged on the inside of the alternating magnetic field yoke 22 and extending in the Y direction so that they are opposite each other. The pair of gradient magnetic field yokes 21 each have a rectangular cross-sectional shape, and the alternating magnetic field yoke 22 has a U-shaped cross-sectional shape.

[0067] The pair of permanent magnets 31 is arranged on the inside of the alternating magnetic field yoke 22, and they run in the Y direction so that they are opposite each other. The pair of permanent magnets 31 each has a rectangular cross-sectional shape, and they are arranged individually on the pair of gradient magnetic field yokes 21.

[0068] The pair of alternating magnetic field generating coils 41 is arranged on the inside of the alternating magnetic field yoke 22, and they run in the Y direction so that they are opposite each other. The pair of alternating magnetic field generating coils 41 is arranged individually so that it surrounds the pair of gradient magnetic field yokes 21.

[0069] As in Fig. As shown in Figure 14, the magnetic paths P1, generated by the permanent magnets 31, pass through the alternating magnetic field generating coils 41, thus minimizing the energy, since the alternating magnetic field generating coils 41 can be assumed to have µ = 1. As shown in Fig. As illustrated in Figure 15, most of the magnetic paths P2 generated by the alternating magnetic field generating coils 41 pass through the alternating magnetic field yoke 22, and consequently the alternating magnetic field generating coils 41 can generate a strong magnetic field, compared to the comparison example according to Fig. 13.

[0070] As can be seen from the comparative example in Fig. As can be seen in Figure 16, it is important that the gradient magnetic field yokes 21 are arranged on the inside of the alternating magnetic field yoke 22. Fig. Figure 16 is a schematic view to illustrate a comparative example of Fig. 14. Fig. Figure 16 shows magnetic paths P1 generated by the permanent magnets 31.

[0071] As in Fig. As illustrated in Figure 16, the following applies: If the gradient magnetic field yokes 21 are arranged on the outside of the alternating magnetic field yoke 22, the magnetic paths P1 generated by the permanent magnets 31 pass through the alternating magnetic field yoke 22, and consequently the permanent magnets 31 cannot generate the gradient magnetic field HX1.

[0072] As in Fig. As illustrated in Figure 14, the first embodiment therefore assumes the configuration in which the gradient magnetic field yokes 21 are arranged on the inside of the alternating magnetic field yoke 22, and with such a configuration the specifications of the magnetic paths P1 and the magnetic paths P2 can be optimized.

[0073] As described above, according to the first embodiment, the following applies: The electromagnetic device for MPI is configured such that—if the latitude direction of the magnetic field space is defined as the X-direction and the longitude direction of the magnetic field space is defined as the Y-direction—the gradient magnetic field is generated in the X-direction within the magnetic field space inside the feedback yoke, thus generating the zero-field region in the magnetic field space, which extends in the Y-direction, and thus generating the alternating magnetic field in the magnetic field space. Furthermore, the electromagnetic device for MPI is configured such that the gradient magnetic field and the alternating magnetic field are rotated relative to the subject, with the Z-direction being the axis of rotation.

[0074] As a result, the controllability of the electromagnetic device can be increased, while the intensity of the magnetic field generated in the magnetic field space is also increased. Furthermore, the electromagnetic device adopts a system in which the feedback yoke rotates, causing the gradient magnetic field and the alternating magnetic field to rotate relative to the stationary subject. This simplifies the coil configuration and simultaneously enhances controllability. Additionally, the feedback yoke is used in the electromagnetic device, and consequently, a strong magnetic field can be generated in the magnetic field space. Second embodiment

[0075] In the second embodiment of the present invention, an electromagnet device 1 is described which has gradient magnetic field yokes 23 having a different configuration than the gradient magnetic field yokes 21, compared to the first embodiment described above. In the second embodiment, the description of similarities to the first embodiment described above is omitted, and the main focus is on the differences.

[0076] Fig. 17 and Fig. Figure 18 are schematic views to schematically illustrate the cross-section along the XZ plane of a return yoke 2, a pair of permanent magnets 31 and a pair of alternating magnetic field generating coils 41 of the electromagnet device 1 according to the second embodiment.

[0077] Fig. Figure 17 shows magnetic paths P1 generated by the permanent magnets 31, and Fig. Figure 18 shows magnetic paths P2 generated by the alternating magnetic field generating coils 41.

[0078] As in Fig. 17 and Fig. As illustrated in Figure 18, a pair of gradient magnetic field yokes 23 extend in the Y-direction so that they are opposite each other, and each has a cross-sectional shape in the form of a square U. Each of the pair of gradient magnetic field yokes 23 has a base region 23a extending in the Y-direction, a first projection region 23b extending in the X-direction from one end of the base region 23a, and a second projection region 23c extending in the X-direction from the other end of the base region 23a. The pair of permanent magnets 31 is individually arranged on the base region 23a of the pair of gradient magnetic field yokes 23.

[0079] In contrast to the gradient magnetic field yokes 21 in the first embodiment described above, the first projection area 23b and the second projection area 23c are formed at both ends of the gradient magnetic field yokes 23. In this case, the magnetic paths P1 generated by the permanent magnets 31 pass through iron, which has a lower magnetic resistance than air, for the first projection area 23b and the second projection area 23c.

[0080] More precisely: As in Fig. As shown in Figure 17, an air region of each magnetic path P1 has the following areas: a magnetic path between Pa and Pb, a magnetic path between Pb and Pc, and a magnetic path between Pc and Pd. In this case, the magnetic path P1 does not pass through the air region, which has a high magnetic resistivity, specifically for a magnetic path between Pd and Pe, compared to the configuration mentioned above. Fig. 14. In other words, the magnetic path P1 passes through iron, which has the low magnetic resistance, for the magnetic path between Pd and Pe.

[0081] Therefore, the magnetic resistance of the permanent magnets 31 is reduced. As a result, the magnetic fluxes corresponding to the magnetic fields P1 increase, and the gradient magnetic field HX1 becomes stronger. As described above, the permanent magnets 31, together with the first protrusion area 23b and the second protrusion area 23c, can generate the stronger gradient magnetic field HX1.

[0082] Furthermore, the first protrusion area 23b and the second protrusion area 23c provide a good effect for the alternating magnetic field HX2, in addition to the gradient magnetic field HX1. More precisely: As in Fig. As illustrated in Figure 18, a magnetic path P2, generated by the alternating magnetic field generating coils 41, passes through the first protrusion area 23b, another magnetic path P2 passes through the second protrusion area 23c, and yet another magnetic path P2 passes through the base area 23a.

[0083] The distributions of the alternating magnetic field HX2, which appear in the case where the first projection area 23b and the second projection area 23c are formed, and in the case where the first projection area 23b and the second projection area 23c are not formed, are shown below with reference to Fig. 19 described. Fig. Figure 19 is a schematic graph illustrating a distribution in the Z-direction of the alternating magnetic field HX2, which is shown in the case where the first protrusion region 23b and the second protrusion region 23c are located at both ends of each gradient magnetic field yoke 23 according to Fig. 18 are trained.

[0084] Fig. Figure 19 shows, as a comparative example, the distribution in the Z-direction of the alternating magnetic field HX2, which is shown in the case in which the first projection area 23b and the second projection area 23c are not at both ends of each gradient magnetic field yoke 23 according to Fig. 18 are trained.

[0085] In the event that the first projection area 23b and the second projection area 23c are not formed, the alternating magnetic field HX2 spreads outwards from the vicinity of both end regions in the Z-direction of the gradient magnetic field yokes 21, as shown in Fig. 15 as described and shown above. In this case, the distribution in the Z-direction of the alternating magnetic field HX2 is a convex distribution, as in Fig. 19 shown.

[0086] In contrast, when the first protrusion region 23b and the second protrusion region 23c are formed, the number of magnetic paths P2 passing through the protrusion regions is large compared to the number of magnetic paths P2 passing through the base region 23a, and consequently, some of the outward-scattering alternating magnetic field HX2 can be canceled out. In this case, the Z-direction distribution of the alternating magnetic field HX2 becomes flatter in a uniform region, as shown in Fig. 19 shown.

[0087] As described above, the uniform alternating magnetic field HX2 can be easily obtained along the Z-direction by providing the first projection area 23b and the second projection area 23c. A more uniform alternating magnetic field HX2 can be generated by appropriately adjusting the length in the X-direction and the length in the Z-direction of each of the first projection area 23b and the second projection area 23c.

[0088] Next, another example of the configuration of the gradient magnetic field yokes 23 in this embodiment will be given with reference to Fig. 20 described. Fig. Figure 20 is a schematic view to illustrate the further example of the electromagnet device 1 according to the second embodiment. Fig. Figure 20 is a schematic view illustrating a cross-section along the XZ plane of the feedback yoke 2, the pair of permanent magnets 31 and the pair of alternating magnetic field generating coils 41 in the other example of the electromagnet device 1.

[0089] In the gradient magnetic field yoke configuration 23 mentioned above, the first projection region 23b and the second projection region 23c are formed at both ends of the base region 23a. In contrast, in a configuration of the gradient magnetic field yokes 24, which are described in Fig. As shown in Figure 20, a first projection area 24a and a second projection area 24b are formed on each inner surface of the alternating magnetic field yoke 22.

[0090] More precisely, the following applies, as in Fig. Figure 20 shows: Each of the pair of gradient magnetic field yokes 24 has the first projection area 24a, which projects in the X direction from the inside of the alternating magnetic field yoke 22, and the second projection area 24b, which projects in the X direction from the inside of the alternating magnetic field yoke 22, so that they are separated in the Z direction from the first projection area 24a.

[0091] In the pair of permanent magnets 31, these are arranged individually on the inner surfaces of the alternating magnetic field yoke 22, which are opposite each other, between the first projection area 24a and the second projection area 24b of each of the pair of gradient magnetic field yokes 24.

[0092] As described above, in this embodiment, the shape of each of the pair of gradient magnetic field yokes in the electromagnet device for the MPI is specifically provided, compared to the configuration in the first embodiment as described above, so that stronger gradient magnetic fields and alternating magnetic fields can be generated, and so that the alternating magnetic field can be generated with a more uniform distribution in the Z direction. Third embodiment

[0093] In a third embodiment for carrying out the present invention, an electromagnetic device 1 is described which differs from the first embodiment described above, specifically in the configuration of the feedback yoke 2, the gradient magnetic field generation unit 3, and the alternating magnetic field generation unit 4. In the third embodiment, the description of similarities to the first and second embodiments described above is omitted, and the main focus is on describing the differences compared to the first and second embodiments described above.

[0094] Fig. 21 to Fig. Figure 23 are schematic views to schematically illustrate a cross-section along the XZ plane of a feedback yoke 2 and a pair of gradient / alternating magnetic field generating coils 81 of the electromagnet device 1 according to the third embodiment.

[0095] Fig. Figure 22 shows magnetic paths P1 generated by the gradient / alternating magnetic field generating coils 81, which are configured to generate a gradient magnetic field and an alternating magnetic field simultaneously, and Fig. Figure 23 shows magnetic paths P2 generated by the gradient / alternating magnetic field generating coils 81.

[0096] In the first and second embodiments described above, a system is assumed in which the gradient magnetic field HX1 is generated by the permanent magnets, and in which the alternating magnetic field HX2 is generated by the coils. In contrast, this embodiment assumes a system in which the gradient magnetic field HX1 and the alternating magnetic field HX2 are generated simultaneously by the coils and without the use of the permanent magnets.

[0097] As in Fig. 21 to Fig. As shown in Figure 23, the electromagnetic device 1 has a gradient / alternating magnetic field generating unit 8 instead of the gradient magnetic field generating unit 3 and the alternating magnetic field generating unit 4, which is configured to generate the gradient magnetic field HX1 and the alternating magnetic field HX2 in the magnetic field space of the feedback yoke 2.

[0098] The gradient / alternating magnetic field generation unit 8 is formed from the pair of gradient / alternating magnetic field generation coils 81 which are arranged on the inside of the alternating magnetic field yoke 22 and which run in the Y direction so that they are opposite to each other.

[0099] A pair of gradient magnetic field yokes 25 extends in the Y direction so that they are opposite each other, and each has a cross-sectional shape in the form of an E. Each of the pair of gradient magnetic field yokes 25 has a base region 25a extending in the Y direction, a first projection region 25b extending in the X direction from one end of the base region 25a, a second projection region 25c extending in the X direction from the other end of the base region 25a, and a third projection region 25d extending in the X direction from the center of the base region 25a.

[0100] The pair of gradient / alternating magnetic field generating coils 81 is arranged such that they are individually inserted into the third projection areas 25d of the pair of gradient magnetic field yokes 25. A pair of energy sources 82 and 83 is individually connected to the pair of gradient / alternating magnetic field generating coils 81. The energy source 82 is configured to energize one of the gradient / alternating magnetic field generating coils 81, and the energy source 83 is configured to energize the other of the gradient / alternating magnetic field generating coils 81.

[0101] It is necessary for the pair of energy sources 82 and 83 to send electric currents II in the same direction through the pair of gradient / alternating magnetic field generating coils 81 to generate the alternating magnetic field HX2. It is also necessary for the pair of energy sources 82 and 83 to send electric currents I2 in opposite directions through the pair of gradient / alternating magnetic field generating coils 81 to generate the gradient magnetic field HX1.

[0102] Therefore, the total current I caused to flow through one of the gradient / alternating magnetic field generating coils 81 by the energy source 82, and the total current I' caused to flow through the other of the gradient / alternating magnetic field generating coils 81 by the energy source 83, are expressed by the following relations. I=I1+I2I'=I1−I2

[0103] As described above, the electric current caused to flow through one of the gradient / alternating magnetic field generating coils 81 by the energy source 82 and the electric current I' caused to flow through the other of the gradient / alternating magnetic field generating coils 81 by the energy source 83 are different from each other. As a result, the alternating magnetic field HX2 is generated by the current components with the same sign as the electric current I and the electric current I', i.e., the electric currents I1, and the gradient magnetic field HX1 is generated by the current components with opposite signs as the electric current I and the electric current I', i.e., the electric currents I2.

[0104] As in Fig. As illustrated in Figure 22, the pair of gradient / alternating magnetic field generating coils 81 generates the gradient magnetic field HX1 through the current components with opposite signs, i.e., the electric currents I2, which is accompanied by the generation of the magnetic paths P1. In this case, the magnetic paths P1 pass through the gradient magnetic field yokes 25, as in the first and second embodiments described above.

[0105] As in Fig. As illustrated in Figure 23, the pair of gradient / alternating magnetic field generating coils 81 generates the alternating magnetic field HX2 through the current components of the same sign, i.e., the electric currents I1, which is accompanied by the generation of the magnetic paths P2. In this case, the magnetic paths P2 pass through the alternating magnetic field yokes 22, as in the first and second embodiments described above.

[0106] If the yoke is not saturated, the magnetic paths overlap. The magnetic field distribution can be manipulated by appropriately adjusting the length in the X direction and the length in the Z direction of each of the first projection area 25b and the second projection area 25c.

[0107] Next, another example of the configuration of the electromagnetic device 1 according to the third embodiment will be given with reference to Fig. 24 described. Fig. Figure 24 is a schematic view to illustrate the further example of the electromagnet device 1 according to the third embodiment of the present invention. Fig. Figure 24 is a schematic view illustrating a cross-section along the XZ plane of the feedback yoke 2, a pair of gradient magnetic field generating coils 32 and a pair of ring-shaped alternating magnetic field generating coils 42 in the other example of the electromagnet device 1.

[0108] As in Fig. As shown in Figure 24, the following applies: the gradient magnetic field generation unit 3 is formed from the pair of gradient magnetic field generation coils 32, which are arranged on the inside of the alternating magnetic field yoke 22 and which run in the Y direction so that they are opposite to each other. The alternating magnetic field generation unit 4 is formed from the pair of annular alternating magnetic field generation coils 42, which are arranged on the inside of the alternating magnetic field yoke 22 and which run in the Y direction so that they are opposite to each other.

[0109] A pair of gradient magnetic field yokes 26 extends in the Y direction so that they are opposite each other, and they each have a cross-sectional shape in the form of an E. Each of the pair of gradient magnetic field yokes 26 has a base region 26a extending in the Y direction, a first projection region 26b projecting in the X direction from one end of the base region 26a, a second projection region 26c projecting in the X direction from another end of the base region 26a, and a third projection region 26d projecting in the X direction from the center of the base region 26a.

[0110] The pair of gradient magnetic field generating coils 32 is arranged such that they are individually inserted into the third projection regions 26d of the pair of gradient magnetic field yokes 26. The pair of alternating magnetic field generating coils 42 is individually arranged such that it surrounds the pair of gradient magnetic field yokes 26.

[0111] The pair of gradient magnetic field generating coils 32 is connected in parallel, and a power source 33, which is a DC power source, is also connected in parallel to the pair of gradient magnetic field generating coils 32. The power source 33 is configured to supply energy to the pair of gradient magnetic field generating coils 32. The pair of gradient magnetic field generating coils 32 is configured to have opposite polarities, and consequently, they can generate the gradient magnetic field HX1 when supplied with energy by the power source 33.

[0112] The pair of alternating magnetic field generating coils 42 is connected in parallel to each other, and an AC power source 43 is also connected in parallel to the pair of alternating magnetic field generating coils 42. The pair of alternating magnetic field generating coils 42 is configured such that the electric currents flow through them in the same direction, and consequently, they can generate the alternating magnetic field HX2 when energized by the power source 43.

[0113] As described above, according to the third embodiment, even when the gradient magnetic field is generated using coils instead of permanent magnets, similar effects to those of the first and second embodiments described above can be achieved, in contrast to the configurations of the first and second embodiments described above. Fourth embodiment

[0114] In a fourth embodiment of the present invention, an electromagnetic device 1 is described which adopts a system in which the gradient magnetic field HX1 and the alternating magnetic field HX2 are simultaneously generated by means of coils, and which has a configuration that differs from that described in the third embodiment described above. In the fourth embodiment, the description of similarities to the first to third embodiments described above is omitted, and the differences compared to the first to third embodiments described above are mainly described.

[0115] Fig. 25 to Fig. Figure 27 are schematic views to schematically illustrate the cross-section along the XZ plane of the feedback yoke 2, an upper gradient magnetic field generating coil 34, a lower gradient magnetic field generating coil 35 and a pair of alternating magnetic field generating coils 44 of the electromagnet device 1 according to the fourth embodiment.

[0116] Fig. 25 shows subject 6. It also shows Fig. 26 magnetic paths P1, which are generated by the upper gradient magnetic field generating coil 34 and the lower gradient magnetic field generating coil 35, and Fig. Figure 27 shows magnetic paths P2 generated by the pair of alternating magnetic field generating coils 44.

[0117] As in Fig. 25 to Fig. As illustrated in Figure 27, the feedback yoke 2 has an alternating magnetic field yoke 22 configured to correspond to the alternating magnetic field HX2, as well as an upper gradient magnetic field yoke 27 and a pair of lower gradient magnetic field yokes 28 configured to correspond to the gradient magnetic field HX1. The alternating magnetic field yoke 22 has a square U-shaped cross-section, the upper gradient magnetic field yoke 27 has a rectangular cross-section, and the pair of lower gradient magnetic field yokes 28 each have a rectangular cross-section.

[0118] The alternating magnetic field yoke 22 extends in the Y direction. The upper gradient magnetic field yoke 27 is located on the inside of the alternating magnetic field yoke 22, and also extends in an upper region in the Z direction, and it extends in the Y direction. The pair of lower gradient magnetic field yokes 28 are located on the inside of the alternating magnetic field yoke 22, and also extend in a lower region in the Z direction, and they extend in the Y direction so that they are opposite each other. The pair of lower gradient magnetic field yokes 28 are located on the lower side of the upper gradient magnetic field yoke 27.

[0119] The gradient magnetic field generation unit 3 is formed from an annular upper gradient magnetic field generation coil 34, which is arranged on the inside of the alternating magnetic field yoke 22 and which runs in the Y direction, and an annular lower gradient magnetic field generation coil 35, which is arranged on the outside of the alternating magnetic field yoke 22 and runs in the Y direction.

[0120] The upper gradient magnetic field generating coil 34 is arranged around the upper gradient magnetic field yoke 27. The lower gradient magnetic field generating coil 35 is arranged on the underside of the upper gradient magnetic field generating coil 34. The upper gradient magnetic field generating coil 34 and the lower gradient magnetic field generating coil 35 are configured such that electric currents flow through them in opposite directions. Therefore, the upper gradient magnetic field generating coil 34 and the lower gradient magnetic field generating coil 35 can generate the gradient magnetic field HX1 when energized. In the configuration of the fourth embodiment, the upper gradient magnetic field yoke 27 is configured in addition to the configurations in the first to third embodiments described above, and consequently, a stronger gradient magnetic field HX1 can be generated.

[0121] The alternating magnetic field generation unit 4 is formed from the pair of alternating magnetic field generation coils 44, which are arranged on the inside of the alternating magnetic field yoke 22 and which run in the Y direction, so that they are opposite to each other.

[0122] The pair of alternating magnetic field generating coils 44 is individually arranged to surround the pair of lower gradient magnetic field yokes 28. The pair of alternating magnetic field generating coils 44 is configured so that the electric currents flow through it in the same direction. Therefore, the pair of alternating magnetic field generating coils 44 can generate the alternating magnetic field HX2 when energized.

[0123] In the event that the head and other parts of the subject 6 enter the return yoke 2, it is necessary that the gap width W1 between the pair of lower gradient magnetic field yokes 28 be wide. Furthermore, a human body is generally wider at the shoulders than at the head. Therefore, the electromagnet device 1 is configured such that the lower gradient magnetic field generating coil 35 is located on the outside of the alternating magnetic field yoke 22, and consequently, the inner width W2 of the lower gradient magnetic field generating coil 35 is wider than the gap width W1 between the pair of lower gradient magnetic field yokes 28.

[0124] With this configuration, i.e. the configuration in which the pair of lower gradient magnetic field yokes 28 and the lower gradient magnetic field generating coil 35 are arranged such that the inner width W2 is wider than the gap width W1, a space can be provided into which the shoulders can enter, which are wider than the head.

[0125] As in Fig. As illustrated in Figure 26, the upper gradient magnetic field generating coil 34 and the lower gradient magnetic field generating coil 35 generate the gradient magnetic field HX1, which is accompanied by the generation of the magnetic paths P1. As shown in Fig. 27 illustrates that the pair of alternating magnetic field generating coils 44 also generates the alternating magnetic field HX2, which is accompanied by the generation of the magnetic paths P2.

[0126] As described above, according to the fourth embodiment, in contrast to the configurations in the first and second embodiments described above, the following applies: The system in which the gradient magnetic field and the alternating magnetic field are generated simultaneously by the coils is used, and effects similar to those of the first and second embodiments described above can be achieved, even with the configuration that differs from that of the third embodiment described above. Fifth embodiment

[0127] In a fifth embodiment of the present invention, an electromagnetic device 1 is described which differs from the first to fourth embodiments described above, specifically in the configuration of the rotation mechanism and the movement mechanism. In the fifth embodiment, the description of similarities to the first to fourth embodiments described above is omitted, and the focus is primarily on the differences compared to the first to fourth embodiments described above.

[0128] Fig. Figure 28 is a schematic view illustrating a configuration of an MPI device comprising the electromagnetic device 1 for the MPI according to the fifth embodiment.

[0129] In the first embodiment described above, the following applies: To rotate the gradient magnetic field HX1 and the alternating magnetic field HX2 relative to the subject 6, a system is used in which the feedback yoke 2 is rotated, with the central axis in the Z-direction of the feedback yoke 2 being the axis of rotation CZ. Furthermore, to rotate the gradient magnetic field HX1 and the alternating magnetic field HX2 relative to the subject 6, a system is used in which the feedback yoke 2 is moved in the Z-direction.

[0130] In contrast, the fifth embodiment is configured as follows: To rotate the gradient magnetic field HX1 and the alternating magnetic field HX2 relative to the subject 6, a system is used in which the subject 6 is rotated, with the body axis of the subject 6, which corresponds to the central axis in the Z-direction of the return yoke 2, being the axis of rotation CZ. Furthermore, to move the gradient magnetic field HX1 and the alternating magnetic field HX2 relative to the subject 6, a system is used in which the subject 6 is moved in the Z-direction.

[0131] More precisely: To rotate Subject 6, the rotation mechanism is configured to rotate a placement area on which Subject 6 is placed, with the rotation axis CZ being the axis of rotation. To move Subject 6, the movement mechanism is also configured to move the placement area on which Subject 6 is to be placed in the Z direction. If Subject 6 is a human body, the placement area would be, for example, a chair on which the person can sit.

[0132] As described above, the rotation mechanism is configured to rotate subject 6 relative to the stationary return yoke 2. Furthermore, the movement mechanism is configured to rotate subject 6 relative to the stationary return yoke 2.

[0133] As described above, according to the fifth embodiment, in contrast to the configurations of the first to fourth embodiments described above, the following applies: A configuration is used in which the feedback yoke is held stationary and in which the subject is rotated such that the gradient magnetic field and the alternating magnetic field rotate relative to the subject. In this way, a configuration is used in which the subject, which is lighter than the feedback yoke, is rotated instead of the feedback yoke, and consequently a simpler configuration of the electromagnet device can be achieved. Reference symbol list 1 Electromagnetic device for MPI 2 Return yoke 20 yoke 21 Gradient magnetic field yoke 22 Alternating magnetic field yoke 23 Gradient magnetic field yoke 23a Basic area 23b first lead area 23c second lead area 24 Gradient magnetic field yoke 24a first advantage area 24b second lead area 25 Gradient magnetic field yoke 25a Basic area 25b first lead area 25c second lead area 25d third advantage area 26 Gradient magnetic field yoke 26a Basic area 26b first lead area 26c second lead area 26d third advantage area 27 upper gradient magnetic field yoke 28 lower gradient magnetic field yoke 3 Gradient magnetic field generation unit 31 Permanent magnet 32 Gradient magnetic field generating coil 33 Energy source 34 upper gradient magnetic field generating coil 35 lower gradient magnetic field generating coil 4 alternating magnetic field generation unit 41 Alternating magnetic field generating coil 42 Alternating magnetic field generating coil 43 Energy source 44 Alternating magnetic field generating coil 5 engine 6 Subject 7 Receiving coil 8 Gradient / alternating magnetic field generation unit 81 Gradient / alternating magnetic field generating coil 82 Energy source

Claims

[1] Electromagnetic device (1) for magnetic particle imaging, comprising: - a return yoke (2) with a gap extending in the Y direction and forming a magnetic field space, where the width direction of the magnetic field space is defined as the X direction and the length direction of the magnetic field space is defined as the Y direction; - a gradient magnetic field generation unit (3) formed on the feedback yoke (2) and configured to generate - in the magnetic field space - a gradient magnetic field (HX1) in the X direction and to form - in the magnetic field space - a zero-field region (S1) extending in the Y direction; - an alternating magnetic field generation unit (4) formed on the feedback yoke (2) and configured to generate an alternating magnetic field (HX2) in the magnetic field space; and - a rotation mechanism configured to rotate - when the direction perpendicular to the X-direction and the Y-direction is defined as the Z-direction - the gradient magnetic field (HX1) and the alternating magnetic field (HX2) relative to the subject (6), wherein the Z-direction is the rotation axis (CZ), and wherein the feedback yoke (2) has the following: - an alternating magnetic field yoke (22) configured to correspond to the alternating magnetic field (HX2) and extending in the Y direction; and - a pair of gradient magnetic field yokes (21, 23, 24, 25, 26) which are designed to correspond to the gradient magnetic field (HX1) and which are arranged on the inside of the alternating magnetic field yoke (22) and run in the Y direction so that they are opposite each other. [2] Electromagnetic device (1) for magnetic particle imaging according to claim 1, further comprising a movement mechanism configured to move the gradient magnetic field (HX1) and the alternating magnetic field (HX2) in the Z direction relative to the subject (6). [3] Electromagnetic device (1) for magnetic particle imaging according to claim 2, wherein the rotation mechanism is configured to rotate the return yoke (2), and wherein the movement mechanism is configured to move the return yoke (2). [4] Electromagnetic device (1) for magnetic particle imaging according to claim 2, wherein the rotation mechanism is configured to rotate the subject (6), and wherein the movement mechanism is configured to move the subject (6). [5] Electromagnetic device (1) for magnetic particle imaging according to one of the preceding claims, wherein the alternating magnetic field generating unit (4) is formed from a pair of alternating magnetic field generating coils (41, 42, 44) which are arranged on the inside of the alternating magnetic field yoke (22) and run in the Y direction so that they are opposite each other, and wherein the gradient magnetic field generating unit (3) is formed from a pair of permanent magnets (31) arranged on the inside of the alternating magnetic field yoke (22) and running in the Y direction so that they are opposite each other. [6] Electromagnetic device (1) for magnetic particle imaging according to claim 5, wherein the pair of permanent magnets (31) is individually arranged on the pair of gradient magnetic field yokes (21). [7] Electromagnetic device (1) for magnetic particle imaging according to claim 5, wherein each of the pair of gradient magnetic field yokes (23) comprises the following: - a base area (23a) extending in the Y direction; - a first proximal area (23b) extending in the X direction from one end of the base area (23a); and - a second projection area (23c) extending in the X direction from the other end of the base area (23a); and wherein the pair of permanent magnets (31) are individually arranged on the base areas (23a) of the pair of gradient magnetic field yokes (23). [8] Electromagnetic device (1) for magnetic particle imaging according to claim 5, wherein each of the pair of gradient magnetic field yokes (24) comprises the following: - a first projection area (24a) extending in the X direction from the inside of the alternating magnetic field yoke (22); and - a second projection area (24b) extending in the X direction from the inside of the alternating magnetic field yoke (22) so that it is separated in the Z direction from the first projection area (24a), and wherein the pair of permanent magnets (31) are arranged individually on the inner surfaces of the alternating magnetic field yoke (22) opposite each other, between the first projection area (24a) and the second projection area (24b) each of the pair of gradient magnetic field yokes (24). [9] Electromagnetic device (1) for magnetic particle imaging according to one of the preceding claims, which furthermore has a gradient / alternating magnetic field generation unit (8) instead of the gradient magnetic field generation unit (3) and the alternating magnetic field generation unit (4), which is configured to generate the gradient magnetic field (HX1) and the alternating magnetic field (HX2) in the magnetic field space, wherein the gradient / alternating magnetic field generation unit (8) is formed from a pair of gradient / alternating magnetic field generation coils (81) arranged on the inside of the alternating magnetic field yoke (22) and running in the Y direction so that they are opposite each other, wherein each of the pair of gradient magnetic field yokes (25) has the following: - a base area (25a) extending in the Y direction; - a first projection area (25b) extending in the X direction from one end of the base area (25a); and a second protrusion area (25c) extending in the X direction from the other end of the base area (25a); and - a third projection area (25d) extending in the X direction from the center of the base area (25a), wherein the pair of gradient / alternating magnetic field generating coils (81) are arranged such that they are individually inserted into the third projection areas (25d) of the pair of gradient magnetic field yokes (25). [10] Electromagnetic device (1) for magnetic particle imaging according to any one of claims 1 to 8, wherein the alternating magnetic field generating unit (4) is formed from a pair of alternating magnetic field generating coils (42) which are arranged on the inside of the alternating magnetic field yoke (22) and run in the Y direction so that they are opposite each other, wherein the gradient magnetic field generation unit (3) is formed from a pair of gradient magnetic field generation coils (32) arranged on the inside of the alternating magnetic field yoke (22) and running in the Y direction so that they are opposite each other, wherein each of the pair of gradient magnetic field yokes (32) has the following: - a base area (26a) extending in the Y direction; - a first proximal area (26b) extending in the X direction from one end of the base area (26a); - a second projection area (26c) extending in the X direction from the other end of the base area (26a); and - a third projection area (26d) extending in the X direction from the center of the base area (26a), wherein the pair of gradient magnetic field generating coils (32) are arranged such that they are individually inserted into the third projection areas (26d) of the pair of gradient magnetic field yokes (26). [11] Electromagnetic device (1) for magnetic particle imaging according to any one of claims 1 to 4, wherein the return yoke (2) has the following features: - a pair of lower gradient magnetic field yokes (28) configured to correspond to the gradient magnetic field (HX1), and arranged on the inside of the alternating magnetic field yoke (22) and on a bottom side of the upper gradient magnetic field yoke (27) and extending in the Y direction so that they are opposite each other, wherein the alternating magnetic field generating unit (4) is formed from a pair of alternating magnetic field generating coils (44) arranged on the inside of the alternating magnetic field yoke (22) and extending in the Y direction so that they are opposite each other, and wherein the gradient magnetic field generating unit (3) is formed from the following: - an upper gradient magnetic field generating coil (34) arranged on the inside of the alternating magnetic field yoke (22) and extending in the Y direction; and - a lower gradient magnetic field generating coil (35) located on the outside of the alternating magnetic field yoke (22) and a lower side of the upper gradient magnetic field generating coil (34) and extending in the Y direction. [12] Electromagnetic device (1) for magnetic particle imaging according to claim 11, wherein the lower gradient magnetic field generating coil (35) has an inner width (W2) which is wider than the gap width (W1) between the pair of lower gradient magnetic field yokes (28). [13] Magnetic particle imaging device comprising an electromagnetic device for magnetic particle imaging according to any one of claims 1 to 12.

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