Magnet for magnetic particle imaging device

Abstract

A magnet (100, 300, 400) for a magnetic particle imaging device comprises a pair of first direct-current coils (10), a pair of second direct-current coils (20), and a pair of alternating-current coils (30). The pair of first direct-current coils are opposed to each other in a first direction (DR1). The pair of second direct-current coils are opposed to each other in a second direction (DR2) perpendicular to the first direction or in a third direction (DR3) perpendicular to the first direction and the second direction. The pair of alternating-current coils are opposed to each other in the first direction or in the second direction. Each of the pair of second direct-current coils has a pair of first linear parts (22). Each of the pair of first linear parts extends along the same direction as the direction in which the pair of alternating-current coils are opposed to each other.

Description

Magnets for magnetic particle imaging devices

[0001] The present disclosure relates to magnets for magnetic particle imaging devices.

[0002] Japanese Patent Laid-Open Publication No. 2022-126838 (Patent Document 1) describes a magnet for a magnetic particle imaging (MPI) device. The magnet for a magnetic particle imaging device described in Patent Document 1 has a pair of DC coils and a pair of AC coils.

[0003] The pair of DC coils are arranged opposite each other in a first direction. The direction perpendicular to the first direction is defined as a second direction, and the direction perpendicular to the first and second directions is defined as a third direction. The pair of DC coils generate a zero magnetic field region (FFL: Field Free Line) between the pair of DC coils. In the zero magnetic field region, the magnetic field component along the third direction is zero. The zero magnetic field region extends along the third direction. The pair of AC coils are arranged opposite each other in the first direction. The pair of AC coils move the position of the zero magnetic field region in the first direction.

[0004] At the position where the ends of the pair of DC coils in the third direction face each other, a magnetic field is generated along the third direction. Due to the generation of such a magnetic field, the length of the zero magnetic field region in the third direction becomes smaller. In order to extend the length of the zero magnetic field region in the third direction, the magnet for a magnetic particle imaging device described in Patent Document 1 uses a circular correction coil.

[0005] Japanese Patent Application Laid-Open No. 2022-126838

[0006] In the magnet for a magnetic particle imaging device described in Patent Document 1, when the position of the zero magnetic field region in the first direction is moved by a pair of AC coils, the correction by the circular correction coil becomes insufficient, and the length of the zero magnetic field region in the third direction becomes small. As a result, in a magnetic particle imaging device using the magnet for a magnetic particle imaging device described in Patent Document 1, the edges of the image of the magnetic particles to be observed may be cut off.

[0007] The present disclosure has been made in consideration of the above-mentioned problems of the prior art. More specifically, the present disclosure provides a magnet for a magnetic particle imaging device that can prevent the zero magnetic field region from becoming shorter when the zero magnetic field region is moved.

[0008] The magnet for a magnetic particle imaging device of the present disclosure comprises a pair of first DC coils, a pair of second DC coils, and a pair of AC coils. The pair of first DC coils are arranged to face each other in a first direction. The pair of second DC coils are arranged to face each other in a second direction perpendicular to the first direction or in a third direction perpendicular to the first and second directions. The pair of AC coils are arranged to face each other in the first direction or the second direction. Each of the pair of second DC coils has a pair of first straight portions. Each of the pair of first straight portions extends along the same direction as the direction in which the pair of AC coils are arranged to face each other.

[0009] According to the magnet for a magnetic particle imaging device of the present disclosure, it is possible to prevent the zero magnetic field region from becoming shorter when the zero magnetic field region is moved.

[0010] 1 is a perspective view of a magnet 100 for a magnetic particle imaging device. FIG. 2 is a schematic first cross-sectional view of the magnet 100 for a magnetic particle imaging device. FIG. 3 is a schematic third cross-sectional view of the magnet 100 for a magnetic particle imaging device. FIG. 4 is a perspective view of a magnet 200 for a magnetic particle imaging device. FIG. 5 is a schematic first cross-sectional view of the magnet 200 for a magnetic particle imaging device. FIG. 6 is a schematic second cross-sectional view of the magnet 200 for a magnetic particle imaging device. FIG. 7 is a schematic third cross-sectional view of the magnet 200 for a magnetic particle imaging device. FIG. 8 is a graph showing the relationship between position in a first direction DR1 and magnetic fields 14, 23, and 51. FIG. 9 is a perspective view of a magnet 300 for a magnetic particle imaging device. FIG. 10 is a side view of a magnet 400 for a magnetic particle imaging device. FIG. 11 is a plan view of a magnet 400 for a magnetic particle imaging device.

[0011] Embodiment 1 A magnet for a magnetic particle imaging apparatus according to embodiment 1 will be described below. The magnet for a magnetic particle imaging apparatus according to embodiment 1 is designated as a magnet 100 for a magnetic particle imaging apparatus.

[0012] (Configuration of the magnet 100 for magnetic particle imaging apparatus) The configuration of the magnet 100 for magnetic particle imaging apparatus will be described below.

[0013] Fig. 1 is a perspective view of a magnet 100 for a magnetic particle imaging apparatus. As shown in Fig. 1, the magnet 100 for a magnetic particle imaging apparatus has a pair of first DC coils 10, a pair of second DC coils 20, and a pair of AC coils 30.

[0014] One of the pair of first DC coils 10 may be referred to as a first DC coil 10a, and the other of the pair of first DC coils 10 may be referred to as a first DC coil 10b. Furthermore, one of the pair of second DC coils 20 may be referred to as a second DC coil 20a, and the other of the pair of second DC coils 20 may be referred to as a second DC coil 20b. Furthermore, one of the pair of AC coils 30 may be referred to as an AC coil 30a, and the other of the pair of AC coils 30 may be referred to as an AC coil 30b.

[0015] The pair of first DC coils 10 are arranged facing each other with a gap in between in the first direction DR1. That is, the first direction DR1 is the direction in which the pair of first DC coils 10 are arranged facing each other. The second direction DR2 is a direction perpendicular to the first direction DR1, and the third direction DR3 is a direction perpendicular to the first direction DR1 and the second direction DR2.

[0016] The first DC coil 10 has a pair of straight portions 11 and a pair of straight portions 12. The pair of straight portions 11 are arranged facing each other with a gap in the second direction DR2. The straight portions 11 extend along the third direction DR3. One of the pair of straight portions 11 may be referred to as straight portion 11a, and the other of the pair of straight portions 11 may be referred to as straight portion 11b. The pair of straight portions 12 are arranged facing each other with a gap in the third direction DR3. The straight portions 12 extend along the second direction DR2. One of the pair of straight portions 12 may be referred to as straight portion 12a, and the other of the pair of straight portions 12 may be referred to as straight portion 12b.

[0017] The straight line portions 11a and 11b of the first DC coil 10a are arranged opposite to and spaced apart from the straight line portions 11a and 11b of the first DC coil 10b, respectively. The straight line portions 12a and 12b of the first DC coil 10a are arranged opposite to and spaced apart from the straight line portions 12a and 12b of the first DC coil 10b, respectively.

[0018] The direction of current flowing through the first DC coil 10a is opposite to the direction of current flowing through the first DC coil 10b. That is, the direction of current flowing through the straight portion 11a of the first DC coil 10a is opposite to the direction of current flowing through the straight portion 11a of the first DC coil 10b, the direction of current flowing through the straight portion 11b of the first DC coil 10a is opposite to the direction of current flowing through the straight portion 11b of the first DC coil 10b, the direction of current flowing through the straight portion 12a of the first DC coil 10a is opposite to the direction of current flowing through the straight portion 12a of the first DC coil 10b, and the direction of current flowing through the straight portion 12b of the first DC coil 10a is opposite to the direction of current flowing through the straight portion 12b of the first DC coil 10b. The current flowing through the first DC coil 10 is supplied from a DC power source (not shown).

[0019] FIG. 2 is a schematic first cross-sectional view of the magnet 100 for a magnetic particle imaging device. In FIG. 2, the pair of second DC coils 20 and the pair of AC coils 30 are omitted, and the generated magnetic fields are indicated by dotted lines. FIG. 2 also shows a cross section perpendicular to the second direction DR2. In the pair of first DC coils 10, a magnetic field as shown in FIG. 2 is generated due to the direction of the current as described above. More specifically, the pair of first DC coils 10 generate a zero magnetic field region 13 between the pair of first DC coils 10. In the zero magnetic field region 13, the magnetic field component along the third direction DR3 is zero. The zero magnetic field region 13 extends in the third direction DR3. When no current flows through the pair of AC coils 30, the zero magnetic field region 13 is located at the midpoint MP of the pair of first DC coils 10 in the first direction DR1.

[0020] Furthermore, the pair of first DC coils 10 generate a magnetic field 14 at a position where one end of the first DC coil 10a in the third direction DR3 faces one end of the first DC coil 10b in the third direction DR3, and at a position where the other end of the first DC coil 10a in the third direction DR3 faces the other end of the first DC coil 10b in the third direction DR3. The direction of the magnetic field 14 is along the third direction DR3.

[0021] The first DC coil 10 has a first length and a second length. The first length is the length of the first DC coil 10 in the second direction DR2. The second length is the length of the first DC coil 10 in the third direction DR3. The second length is preferably longer than the first length. In other words, the longitudinal direction of the first DC coil 10 is preferably aligned with the third direction DR3. From another perspective, the length of the straight portion 11 is preferably longer than the length of the straight portion 12.

[0022] 1 , the pair of second DC coils 20 are disposed, for example, facing each other with a gap in between in the third direction DR3. Note that one of the pair of second DC coils 20 may be referred to as second DC coil 20a, and the other of the pair of second DC coils 20 may be referred to as second DC coil 20b.

[0023] The second DC coil 20 has a pair of straight portions 21 and a pair of straight portions 22. The pair of straight portions 21 are arranged facing each other with a gap in the first direction DR1. The straight portions 21 extend along the second direction DR2. One of the pair of straight portions 21 may be referred to as straight portion 21a, and the other of the pair of straight portions 21 may be referred to as straight portion 21b. The pair of straight portions 22 are arranged facing each other with a gap in the second direction DR2. The straight portions 22 extend along the first direction DR1. One of the pair of straight portions 22 may be referred to as straight portion 22a, and the other of the pair of straight portions 22 may be referred to as straight portion 22b. The shape and ampere-turns of the second DC coil 20 are different from those of the first DC coil 10, for example. Note that an ampere-turn is the product of the coil current per turn and the number of turns.

[0024] The straight line portions 21a and 21b of the second DC coil 20a are arranged opposite to and spaced apart from the straight line portions 21a and 21b of the second DC coil 20b. The straight line portions 22a and 22b of the second DC coil 20a are arranged opposite to and spaced apart from the straight line portions 22a and 22b of the second DC coil 20b. Note that the straight line portion 21a is closer to the first DC coil 10a than the straight line portion 21b in the first direction DR1.

[0025] The direction of current flowing through the second DC coil 20a is opposite to the direction of current flowing through the second DC coil 20b. That is, the direction of current flowing through the straight portion 21a of the second DC coil 20a is opposite to the direction of current flowing through the straight portion 21a of the second DC coil 20b, the direction of current flowing through the straight portion 21b of the second DC coil 20a is opposite to the direction of current flowing through the straight portion 21b of the second DC coil 20b, the direction of current flowing through the straight portion 22a of the second DC coil 20a is opposite to the direction of current flowing through the straight portion 22a of the second DC coil 20b, and the direction of current flowing through the straight portion 22b of the second DC coil 20a is opposite to the direction of current flowing through the straight portion 22b of the second DC coil 20b. The current flowing through the second DC coil 20a is supplied from a DC power source (not shown).

[0026] The second DC coil 20 has a third length and a fourth length. The third length is the length of the second DC coil 20 in the first direction DR1. The fourth length is the length of the second DC coil 20 in the second direction DR2. The third length is preferably longer than the fourth length. In other words, the longitudinal direction of the second DC coil 20 is preferably aligned with the first direction DR1. From another perspective, the length of the straight portion 22 is preferably longer than the length of the straight portion 21.

[0027] FIG. 3 is a schematic second cross-sectional view of the magnet 100 for a magnetic particle imaging device. In FIG. 3 , the pair of first DC coils 10 and the pair of AC coils 30 are omitted, and the generated magnetic fields are indicated by dotted lines. FIG. 3 also shows a cross section perpendicular to the first direction DR1. As shown in FIG. 3 , the pair of second DC coils 20 generate a magnetic field 23 at a position where one end of the first DC coil 10a in the third direction DR3 faces one end of the first DC coil 10b in the third direction DR3, and at a position where the other end of the first DC coil 10a in the third direction DR3 faces the other end of the first DC coil 10b in the third direction DR3. The direction of the magnetic field 23 is along the third direction DR3, which is opposite to the direction of the magnetic field 14.

[0028] From another perspective, the direction of the current flowing through the straight portion 21 a of the second DC coil 20 a is opposite to the direction of the current flowing through the straight portion 12 a of the first DC coil 10 a, the direction of the current flowing through the straight portion 21 b of the second DC coil 20 a is opposite to the direction of the current flowing through the straight portion 12 a of the first DC coil 10 b, the direction of the current flowing through the straight portion 21 a of the second DC coil 20 b is opposite to the direction of the current flowing through the straight portion 12 b of the first DC coil 10 a, and the direction of the current flowing through the straight portion 21 b of the second DC coil 20 b is opposite to the direction of the current flowing through the straight portion 12 b of the first DC coil 10 b.

[0029] 1 , the pair of AC coils 30 are disposed facing each other with a gap in between in the first direction DR1. One of the pair of AC coils 30 may be referred to as AC coil 30a, and the other of the pair of AC coils 30 may be referred to as AC coil 30b. The pair of AC coils 30 are disposed between the pair of first DC coils 10. The AC coil 30a is closer to the first DC coil 10a than the AC coil 30b.

[0030] The AC coil 30 has a pair of straight portions 31 and a pair of straight portions 32. The pair of straight portions 31 are arranged facing each other with a gap in the second direction DR2. The straight portions 31 extend along the third direction DR3. One of the pair of straight portions 31 may be referred to as straight portion 31a, and the other of the pair of straight portions 31 may be referred to as straight portion 31b. The pair of straight portions 32 are arranged facing each other with a gap in the third direction DR3. The straight portions 32 extend along the second direction DR2. One of the pair of straight portions 32 may be referred to as straight portion 32a, and the other of the pair of straight portions 32 may be referred to as straight portion 32b.

[0031] The straight line portions 31a and 31b of the AC coil 30a are arranged opposite to and spaced apart from the straight line portions 31a and 31b of the AC coil 30b, respectively. The straight line portions 32a and 32b of the AC coil 30a are arranged opposite to and spaced apart from the straight line portions 32a and 32b of the AC coil 30b, respectively.

[0032] The direction of current flowing through the AC coil 30a is the same as the direction of current flowing through the AC coil 30b. That is, the direction of current flowing through the straight portion 31a of the AC coil 30a is the same as the direction of current flowing through the straight portion 31a of the AC coil 30b, the direction of current flowing through the straight portion 31b of the AC coil 30a is the same as the direction of current flowing through the straight portion 31b of the AC coil 30b, the direction of current flowing through the straight portion 32a of the AC coil 30a is the same as the direction of current flowing through the straight portion 32a of the AC coil 30b, and the direction of current flowing through the straight portion 32b of the AC coil 30a is the same as the direction of current flowing through the straight portion 32b of the AC coil 30b. The current flowing through the AC coil 30 is supplied from an AC power source (not shown). When a current flows through the pair of AC coils 30, the zero magnetic field region 13 moves along the first direction DR1.

[0033] Figure 4 is a schematic third cross-sectional view of the magnet 100 for magnetic particle imaging devices. The pair of second DC coils 20 are omitted from Figure 4. Figure 4 also shows a cross section perpendicular to the second direction DR2. As shown in Figure 4, the magnet 100 for magnetic particle imaging devices may further have an iron core 40.

[0034] Although the example in which the pair of AC coils 30 are arranged opposite each other in the first direction DR1 has been described above, the pair of AC coils 30 may be arranged opposite each other in the second direction DR2. In this case, when a current flows through the pair of AC coils 30, the zero magnetic field region 13 moves along the second direction DR2.

[0035] <Modification 2> In the above, an example has been described in which the first DC coil 10 has both a pair of straight portions 11 and a pair of straight portions 12, but the first DC coil 10 does not have to have any straight portions. That is, the first DC coil 10 may be a circular coil. Furthermore, the first DC coil 10 may have only either the pair of straight portions 11 or the pair of straight portions 12.

[0036] <Modification 3> In the above, an example has been described in which the second DC coil 20 has both the pair of straight portions 21 and the pair of straight portions 22, but the second DC coil 20 may have only the pair of straight portions 22, and not the pair of straight portions 21. Note that when the pair of AC coils 30 are arranged opposite each other in the second direction DR2 as in Modification 1, the second DC coil 20 may have only the pair of straight portions 21, and not the pair of straight portions 22.

[0037] (Effects of the magnet 100 for magnetic particle imaging devices) The effects of the magnet 100 for magnetic particle imaging devices will be explained below in comparison with a magnet for magnetic particle imaging devices according to a comparative example. The magnet for magnetic particle imaging devices according to the comparative example will be referred to as magnet 200 for magnetic particle imaging devices.

[0038] Figure 5 is a perspective view of the magnet 200 for a magnetic particle imaging device. As shown in Figure 5, the magnet 200 for a magnetic particle imaging device has a pair of DC circular coils 50 instead of the pair of second DC coils 20. The pair of DC circular coils 50 are arranged opposite each other with a gap in between in the second direction DR2, similar to the pair of second DC coils 20. Except for this point, the configuration of the magnet 200 for a magnetic particle imaging device is the same as the configuration of the magnet 100 for a magnetic particle imaging device.

[0039] FIG. 6 is a schematic first cross-sectional view of the magnet 200 for magnetic particle imaging devices. In FIG. 6, the pair of first DC coils 10 and the pair of AC coils 30 are omitted, and the generated magnetic fields are indicated by dotted lines. FIG. 6 also shows a cross section passing through the midpoint MP and perpendicular to the first direction DR1. As shown in FIG. 6, in the magnet 200 for magnetic particle imaging devices, the pair of DC circular coils 50 generate magnetic fields 51 at a position where one end of the first DC coil 10a in the third direction DR3 faces one end of the first DC coil 10b in the third direction DR3, and at a position where the other end of the first DC coil 10a in the third direction DR3 faces the other end of the first DC coil 10b in the third direction DR3. The direction of the magnetic field 51 is along the third direction DR3, which is opposite to the direction of the magnetic field 14.

[0040] Figure 7 is a second schematic cross-sectional view of the magnet 200 for magnetic particle imaging devices. In Figure 7, the pair of AC coils 30 and the pair of DC circular coils 50 are omitted, and the generated magnetic fields are indicated by dotted lines. Figure 7 also shows a cross section perpendicular to the second direction DR2. As shown in Figure 7, in the magnet 200 for magnetic particle imaging devices, the magnetic field 51 cancels out the magnetic field 14, causing the zero magnetic field region 13 to extend along the third direction DR3 (see dotted lines).

[0041] FIG. 8 is a schematic third cross-sectional view of the magnet 200 for a magnetic particle imaging device. In FIG. 8 , the pair of first DC coils 10 and the pair of AC coils 30 are omitted, and the generated magnetic fields are indicated by dotted lines. FIG. 8 also shows a cross section passing through a position shifted from the midpoint MP and perpendicular to the first direction DR1. As shown in FIG. 8 , due to the circular shape of the DC circular coil 50, the magnetic field 51 fluctuates along the first direction DR1. Therefore, when the pair of AC coils 30 are energized and the position of the zero magnetic field region 13 moves along the first direction DR1, the magnetic field 14 cannot be sufficiently canceled out by the magnetic field 51, and the length of the zero magnetic field region 13 in the third direction DR3 is shortened.

[0042] On the other hand, in the magnet 100 for magnetic particle imaging devices, the second DC coil 20 has a pair of straight portions 22. The pair of straight portions 22 extend along the first direction DR1, i.e., the direction in which the pair of AC coils 30 move the zero magnetic field region 13 (the direction in which the pair of AC coils 30 face each other). Therefore, in the second DC coil 20, fluctuations in the magnetic field 23 along the first direction DR1 are smaller than fluctuations in the magnetic field 51 along the first direction DR1. As a result, in the magnet 100 for magnetic particle imaging devices, even if current is passed through the pair of AC coils 30 and the position of the zero magnetic field region 13 moves along the first direction DR1, the magnetic field 14 can be sufficiently canceled out by the magnetic field 23, and the length of the zero magnetic field region 13 in the third direction DR3 can be maintained.

[0043] Fig. 9 is a graph showing the relationship between position in the first direction DR1 and magnetic field 14, magnetic field 23, and magnetic field 51. The horizontal axis in Fig. 9 represents position in the first direction DR1. Note that the value (X) on the horizontal axis in Fig. 9 is in meters, with positive values ​​representing positions closer to first DC coil 10b than midpoint MP and negative values ​​representing positions closer to first DC coil 10a than midpoint MP. The vertical axis in Fig. 9 represents the normalized strength of magnetic field 14, magnetic field 23, and magnetic field 51, normalized such that the magnetic field strength at X = 0 m is 1.

[0044] 9, magnetic field 51 rapidly becomes weaker than magnetic field 23 as the absolute value of X, i.e., the distance from midpoint MP in first direction DR1, increases. Therefore, in magnet 200 for magnetic particle imaging devices, magnetic field 51 cannot sufficiently cancel out magnetic field 14 at X = 0.1 m, and the length of zero magnetic field region 13 in third direction DR3 decreases.

[0045] On the other hand, the degree to which magnetic field 23 weakens with distance from midpoint MP in first direction DR1 is gentler than magnetic field 51. Therefore, in magnet 100 for magnetic particle imaging devices, if the imaging region is within the range of X = ±0.1 m, magnetic field 51 can sufficiently cancel out magnetic field 14 at X = 0.1 m, and the length of zero magnetic field region 13 in third direction DR3 can be maintained.

[0046] At X=0.1 m, the pair of second DC coils 20 preferably generate a magnetic field 23 such that the magnetic flux density along the third direction DR3 at a position where one end of the first DC coil 10a in the third direction DR3 faces one end of the first DC coil 10b in the third direction DR3 (where the other end of the first DC coil 10a in the third direction DR3 faces the other end of the first DC coil 10b in the third direction DR3) is 10 Gauss or less or 1 Gauss or less. At X=0.1 m, the length in the third direction DR3 of the region where the magnetic flux density along the third direction DR3 is 10 Gauss or less (or 1 Gauss or less), i.e., the region that can be regarded as a substantially zero magnetic field region 13, is preferably 0.3 or more times the first length. Such a region is a region where an image of magnetic particles can be acquired.

[0047] The current flowing through the first DC coil 10 and the current flowing through the second DC coil 20 are preferably determined as follows: The magnitude of the gradient magnetic field generated by the first DC coil 10 is G, and the gradient magnetic field generated by the first DC coil 10 per unit current is C. １ The gradient magnetic field per unit current generated by the second DC coil 20 is C ２ and the current flowing through the first DC coil 10 is I １ and the current flowing through the second DC coil 20 is I ２ and the magnetic field 14 per unit current is B ｚ１ and the magnetic field 23 per unit current is B ｚ２ In the magnet 100 for magnetic particle imaging apparatus, the second DC coil 20 does not generate a gradient magnetic field, so C ２ is 0. Therefore, G, C １ and I １ Between them, C １ ×I １ = G (Equation 1) holds. １ , I ２ , B ｚ１ and B ｚ２ Between ｚ１ ×I １ +B ｚ２ ×I ２= 0 (Equation 2). If the desired G (usually about 1 T / m) is determined, I can be calculated from Equation 1. １ = G / C １ By I １ is determined, and the first term of Equation 2 is also determined. ２ I ２ =B ｚ１ ×I １ / B ｚ２ It is decided.

[0048] In the magnet 100 for a magnetic particle imaging device, the second length is greater than the first length (the straight portion 11 is longer than the straight portion 12), so that the zero magnetic field region 13 can be extended along the third direction DR3.

[0049] Embodiment 2. A magnet for a magnetic particle imaging device according to embodiment 2 will be described. The magnet for a magnetic particle imaging device according to embodiment 2 is referred to as magnet for a magnetic particle imaging device 300. Here, differences from magnet for a magnetic particle imaging device 100 will be mainly described, and overlapping explanations will not be repeated.

[0050] (Configuration of the magnet 300 for magnetic particle imaging apparatus) The configuration of the magnet 300 for magnetic particle imaging apparatus will be described below.

[0051] Figure 10 is a perspective view of a magnet 300 for a magnetic particle imaging apparatus. As shown in Figure 10, the magnet 300 for a magnetic particle imaging apparatus has a pair of first DC coils 10, a pair of second DC coils 20, and a pair of AC coils 30. In these respects, the configuration of the magnet 300 for a magnetic particle imaging apparatus is common to the configuration of the magnet 100 for a magnetic particle imaging apparatus.

[0052] In the magnet 300 for a magnetic particle imaging device, a pair of second DC coils 20 are arranged facing each other with a gap in the second direction DR2. In the magnet 300 for a magnetic particle imaging device, each of the pair of straight portions 21 extends along the third direction DR3. If the shape of the first DC coil 10 is the same as the shape of the second DC coil 20, the ampere-turns of the second DC coil 20 will be the same as the ampere-turns of the first DC coil 10. In these respects, the configuration of the magnet 300 for a magnetic particle imaging device differs from the configuration of the magnet 100 for a magnetic particle imaging device. Note that in the magnet 100 for a magnetic particle imaging device, the second DC coil 20 does not generate a gradient magnetic field, but in the magnet 300 for a magnetic particle imaging device, the second DC coil 20 generates a gradient magnetic field.

[0053] In addition, since the magnetic field 23 is in the opposite direction to the magnetic field 14 in the magnet 300 for magnetic particle imaging apparatus, the direction of the current flowing through the straight portion 21 a of the second DC coil 20 a is the same as the direction of the current flowing through the straight portion 11 a of the first DC coil 10 a, the direction of the current flowing through the straight portion 21 b of the second DC coil 20 a is the same as the direction of the current flowing through the straight portion 11 a of the first DC coil 10 b, the direction of the current flowing through the straight portion 21 a of the second DC coil 20 b is the same as the direction of the current flowing through the straight portion 11 b of the first DC coil 10 a, and the direction of the current flowing through the straight portion 21 b of the second DC coil 20 b is the same as the direction of the current flowing through the straight portion 11 b of the first DC coil 10 b.

[0054] In the magnet 300 for magnetic particle imaging apparatus, the shape of the first DC coil 10 may differ from the shape of the second DC coil 20 due to the placement of other AC coils or other reasons. In this case, the magnitude of the gradient magnetic field generated by the first DC coil 10 and the magnitude of the gradient magnetic field generated by the second DC coil 20 will differ, and the magnitude of the magnetic field 14 and the magnitude of the magnetic field 23 will also differ. For this reason, it is preferable that the current flowing through the first DC coil 10 and the current flowing through the second DC coil 20 be determined as follows.

[0055] The magnitude of the gradient magnetic field generated by the first DC coil 10 is G, and the gradient magnetic field generated by the first DC coil 10 per unit current is C. １The gradient magnetic field per unit current generated by the second DC coil 20 is C ２ and the current flowing through the first DC coil 10 is I １ and the current flowing through the second DC coil 20 is I ２ and the magnetic field 14 per unit current is B ｚ１ and the magnetic field 23 per unit current is B ｚ２ Between these parameters, C １ ×I １ +C ２ ×I ２ =G (Formula 1), B ｚ１ ×I １ +B ｚ２ ×I ２ = 0 (Equation 2). Once a desired G (usually about 1 T / m) is determined, the current flowing through the first DC coil 10 (i.e., I １ ) and the current flowing through the second DC coil 20 (i.e., I ２ ) is obtained.

[0056] (Effects of the Magnet 300 for Magnetic Particle Imaging Apparatus) The effects of the magnet 300 for magnetic particle imaging apparatus will be described below.

[0057] In the magnet 300 for a magnetic particle imaging device, a pair of second DC coils 20 generate a magnetic field 23 to cancel out the magnetic field 14, and the fluctuation of the magnetic field 23 along the first direction DR1 is small, so that even when a pair of AC coils 30 moves the zero magnetic field region 13 along the first direction DR1, the length of the zero magnetic field region 13 in the third direction DR3 can be maintained.

[0058] Embodiment 3. A magnet for a magnetic particle imaging device according to embodiment 3 will be described. The magnet for a magnetic particle imaging device according to embodiment 2 will be referred to as magnet for a magnetic particle imaging device 400. Here, differences from magnet for a magnetic particle imaging device 300 will be mainly described, and overlapping explanations will not be repeated.

[0059] (Configuration of the magnet 400 for magnetic particle imaging apparatus) The configuration of the magnet 400 for magnetic particle imaging apparatus will be described below.

[0060] Fig. 11 is a side view of the magnet 400 for a magnetic particle imaging device. Fig. 11 shows a side view taken along the third direction DR3. Fig. 12 is a plan view of the magnet 400 for a magnetic particle imaging device. As shown in Figs. 11 and 12, the magnet 400 for a magnetic particle imaging device has a pair of first DC coils 10, a pair of second DC coils 20, and a pair of AC coils 30. In these respects, the configuration of the magnet 400 for a magnetic particle imaging device is common to the configuration of the magnet 300 for a magnetic particle imaging device.

[0061] In the magnet 400 for a magnetic particle imaging apparatus, the second DC coil 20 is divided into at least two split DC coils, and the AC coil 30 is divided into at least two split AC coils. In the example shown in Fig. 11, the second DC coil 20 is divided into a first split DC coil 24 and a second split DC coil 25, and the AC coil 30 is divided into a first split AC coil 33 and a second split AC coil 34.

[0062] The first divided DC coil 24 of the second DC coil 20a and the first divided DC coil 24 of the second DC coil 20b are arranged opposite each other with a gap in the second direction DR2. The first divided DC coil 24 of the second DC coil 20a and the first divided DC coil 24 of the second DC coil 20b are arranged between the second divided DC coil 25 of the second DC coil 20a and the second divided DC coil 25 of the second DC coil 20b. The length of the second divided DC coil 25 in the first direction DR1 is greater than the length of the first divided DC coil 24 in the first direction DR1.

[0063] The first split AC coil 33 of the AC coil 30a and the first split AC coil 33 of the AC coil 30b are arranged opposite to each other with a gap in the first direction DR1. The first DC coil 10 is arranged between the first split AC coil 33 and the second split AC coil 34. From another perspective, the first split AC coil 33 is located inside the first DC coil 10, and the second split AC coil 34 is located outside the first DC coil 10. The first split DC coil 24 is located between the first split AC coil 33 of the AC coil 30a and the first split AC coil 33 of the AC coil 30b.

[0064] The coil width of the second divided AC coil 34 is preferably larger than the coil width of the first divided AC coil 33. In these respects, the configuration of the magnet 400 for magnetic particle imaging devices differs from the configuration of the magnet 300 for magnetic particle imaging devices.

[0065] Similar to the second DC coil 20, each of the first and second divided DC coils 24 and 25 has a pair of straight line portions that are spaced apart and face each other in the first direction DR1 and extend along the third direction DR3, and a pair of other straight line portions that are spaced apart and face each other in the third direction DR3 and extend along the first direction DR1. Similar to the AC coil 30, each of the first and second divided AC coils 33 and 34 has a pair of straight line portions that are spaced apart and face each other in the second direction DR2 and extend along the third direction DR3, and a pair of other straight line portions that are spaced apart and face each other in the third direction DR3 and extend along the second direction DR2.

[0066] (Effects of the Magnet 400 for Magnetic Particle Imaging Apparatus) The effects of the magnet 400 for magnetic particle imaging apparatus will be described below.

[0067] For example, when the AC coil 30 is located outside the first DC coil 10, the distance between the midpoint MP in the first direction DR1 and the AC coil 30 becomes large, requiring a large number of ampere turns for the AC coil 30. On the other hand, when the AC coil is located inside the first DC coil 10, the distance between the midpoint MP in the first direction DR1 and the first DC coil 10 becomes large, requiring a large number of ampere turns for the first DC coil 10. In other words, the ampere turns of either the first DC coil 10 or the AC coil 30 may be designed to be extremely large.

[0068] The magnet 400 for magnetic particle imaging devices makes it easy to adjust the ampere-turns of the first DC coil 10 and the AC coil 30. More specifically, in the magnet 400 for magnetic particle imaging devices, the first divided AC coil 33 is located near the midpoint MP, so that a large magnetic field can be generated even if the first divided AC coil 33 has a small number of ampere-turns, and the total number of ampere-turns of the first divided AC coil 33 and the second divided AC coil 34 can be made small.

[0069] Furthermore, in the magnet 400 for magnetic particle imaging devices, the first DC coil 10 is located between the first divided AC coil 33 and the second divided AC coil 34, which makes it possible to suppress an increase in the distance between the first DC coil 10 and the midpoint MP, i.e., to suppress an increase in the ampere-turns of the first DC coil 10. In this way, in the magnet 400 for magnetic particle imaging devices, it is easy to adjust the ampere-turns of the first DC coil 10 and the AC coil 30 so that the ampere-turns of either the first DC coil 10 or the AC coil 30 do not become extremely large.

[0070] Although the above describes an example in which the AC coil 30 is divided, it is also possible to divide the first DC coil 10 without dividing the AC coil 30, and place the AC coil 30 between the divided DC coils that make up the first DC coil 10. Furthermore, although the above describes an example in which a pair of AC coils 30 are arranged opposite each other in the first direction DR1, when a pair of AC coils 30 are arranged opposite each other in the second direction DR2, it is also possible to place the second DC coil 20 between the first divided AC coil 33 and the second divided AC coil 34.

[0071] [Additional Notes] The above embodiments include the following configurations.

[0072] <Supplementary Note 1> A magnet for a magnetic particle imaging device, comprising: a pair of first DC coils; a pair of second DC coils; and a pair of AC coils, wherein the pair of first DC coils are arranged opposite each other in a first direction, the pair of second DC coils are arranged opposite each other in a second direction perpendicular to the first direction or a third direction perpendicular to the first direction and the second direction, the pair of AC coils are arranged opposite each other in the first direction or the second direction, each of the pair of second DC coils has a pair of first straight portions, and each of the pair of first straight portions extends along the same direction as the direction in which the pair of AC coils are arranged opposite each other.

[0073] <Supplementary Note 2> A magnet for a magnetic particle imaging device as described in Supplementary Note 1, wherein each of the pair of first DC coils has a pair of second straight portions, each of the pair of second straight portions extends along the third direction, and each of the pair of first DC coils has a first length that is a length in the second direction and a second length that is a length in the third direction and is greater than the first length.

[0074] <Supplementary Note 3> The magnet for a magnetic particle imaging apparatus according to Supplementary Note 1, wherein each of the pair of first DC coils has the same shape and the same ampere-turns as each of the pair of second DC coils.

[0075] <Supplementary Note 4> The magnet for a magnetic particle imaging apparatus according to Supplementary Note 1, wherein each of the pair of first DC coils has a different shape and ampere-turns than each of the pair of second DC coils.

[0076] <Supplementary Note 5> A magnet for a magnetic particle imaging device according to any one of Supplementary Note 1 to Supplementary Note 4, wherein, in a cross section perpendicular to the direction in which the pair of AC coils are arranged opposite to each other, the pair of first DC coils are configured to generate a first magnetic field along the third direction at a position where ends of each of the pair of first DC coils in the third direction face each other, and the pair of second DC coils are configured to generate a second magnetic field in a direction opposite to the first magnetic field at the position so that, in the cross section, the magnetic flux density in the direction along the third direction at the position is 10 gauss or less.

[0077] <Appendix 6> A magnet for a magnetic particle imaging device as described in Appendix 5, wherein the length in the third direction of a region in the cross section where the magnetic flux density in the direction along the third direction is 10 Gauss or less is 0.3 times or more the width in the third direction of the pair of first DC coils.

[0078] <Supplementary Note 7> The magnet for a magnetic particle imaging device according to any one of Supplementary Note 1 to Supplementary Note 6, wherein each of the pair of AC coils has at least a first split AC coil and a second split AC coil, the first split AC coil of one of the pair of AC coils and the first split AC coil of the other of the pair of AC coils are arranged opposite each other in the first direction and are located between the pair of first DC coils, one of the pair of first DC coils is located between the first split AC coil of one of the pair of AC coils and the second split AC coil of one of the pair of AC coils, and the other of the pair of first DC coils is located between the first split AC coil of the other of the pair of AC coils and the second split AC coil of the other of the pair of AC coils.

[0079] <Supplementary Note 8> The magnet for a magnetic particle imaging device according to Supplementary Note 7, wherein the coil width of the second divided AC coil is larger than the coil width of the first divided AC coil.

[0080] <Supplementary Note 9> The magnet for a magnetic particle imaging device according to Supplementary Note 7 or Supplementary Note 8, wherein each of the pair of second DC coils has at least a first split DC coil and a second split DC coil, the second split DC coil of one of the pair of second DC coils and the second split DC coil of the other of the pair of second DC coils are arranged opposite each other with the first split DC coil of one of the pair of second DC coils and the first split DC coil of the other of the pair of second DC coils interposed therebetween, and the first split DC coil of one of the pair of second DC coils and the first split DC coil of the other of the pair of second DC coils are located between the first split AC coil of one of the pair of AC coils and the first split AC coil of the other of the pair of AC coils.

[0081] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The basic scope of the present disclosure is defined by the claims, not by the above-described embodiments, and it is intended to include all modifications within the meaning and scope of the claims.

[0082] 10, 10a, 10b First DC coil, 11, 11a, 11b, 12, 12a, 12b Straight portion, 13 Zero magnetic field region, 14 Magnetic field, 20, 20a, 20b Second DC coil, 21, 21a, 21b, 22, 22a, 22b Straight portion, 23 Magnetic field, 24 First divided DC coil, 25 Second divided DC coil, 30, 30a, 30b AC coil, 31, 31a, 31b, 32, 32a, 32b Straight portion, 33 First divided AC coil, 34 Second divided AC coil, 40 Iron core, 50 DC circular coil, 51 Magnetic field, 100, 200, 300, 400 Magnet for magnetic particle imaging device, DR1 First direction, DR2 Second direction, DR3 Third direction, MP Midpoint.

Claims

1. A magnet for a magnetic particle imaging device comprising: a pair of first DC coils, a pair of second DC coils, and a pair of AC coils, wherein the pair of first DC coils are arranged opposite each other in a first direction, the pair of second DC coils are arranged opposite each other in a second direction perpendicular to the first direction or a third direction perpendicular to the first direction and the second direction, the pair of AC coils are arranged opposite each other in the first direction or the second direction, each of the pair of second DC coils has a pair of first straight portions, and each of the pair of first straight portions extends along the same direction as the direction in which the pair of AC coils are arranged opposite each other.

2. A magnet for a magnetic particle imaging device as described in claim 1, wherein each of the pair of first DC coils has a pair of second straight portions, each of the pair of second straight portions extends along the third direction, and each of the pair of first DC coils has a first length which is a length in the second direction and a second length which is a length in the third direction and is greater than the first length.

3. A magnet for a magnetic particle imaging device as claimed in claim 1, wherein each of said pair of first DC coils has the same shape and the same ampere-turns as each of said pair of second DC coils.

4. A magnet for a magnetic particle imaging device as claimed in claim 1, wherein each of said pair of first DC coils has a different shape and ampere-turns than each of said pair of second DC coils.

5. A magnet for a magnetic particle imaging device as described in any one of claims 1 to 4, wherein, in a cross section perpendicular to the direction in which the pair of AC coils are arranged opposite to each other, the pair of first DC coils are configured to generate a first magnetic field along the third direction at a position where ends of each of the pair of first DC coils in the third direction face each other, and the pair of second DC coils are configured to generate a second magnetic field in a direction opposite to the first magnetic field at the position so that the magnetic flux density in the direction along the third direction at the position in the cross section is 10 Gauss or less.

6. A magnet for a magnetic particle imaging device as described in claim 5, wherein the length in the third direction of the region in the cross section where the magnetic flux density in the direction along the third direction is 10 Gauss or less is 0.3 times or more the width in the third direction of the pair of first DC coils.

7. A magnet for a magnetic particle imaging device as described in any one of claims 1 to 6, wherein each of the pair of AC coils has at least a first split AC coil and a second split AC coil, the first split AC coil of one of the pair of AC coils and the first split AC coil of the other of the pair of AC coils are arranged opposite each other in the first direction and are between the pair of first DC coils, one of the pair of first DC coils is between the first split AC coil of one of the pair of AC coils and the second split AC coil of one of the pair of AC coils, and the other of the pair of first DC coils is between the first split AC coil of the other of the pair of AC coils and the second split AC coil of the other of the pair of AC coils.

8. A magnet for a magnetic particle imaging device as set forth in claim 7, wherein the coil width of said second split AC coil is greater than the coil width of said first split AC coil.

9. A magnet for a magnetic particle imaging device as described in claim 7 or claim 8, wherein each of the pair of second DC coils has at least a first split DC coil and a second split DC coil, the second split DC coil of one of the pair of second DC coils and the second split DC coil of the other of the pair of second DC coils are arranged opposite each other with the first split DC coil of one of the pair of second DC coils and the first split DC coil of the other of the pair of second DC coils interposed therebetween, and the first split DC coil of one of the pair of second DC coils and the first split DC coil of the other of the pair of second DC coils are located between the first split AC coil of one of the pair of AC coils and the first split AC coil of the other of the pair of AC coils.

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