Magnetic particle imaging system and magnetic particle imaging method

Abstract

A gradient magnetic field generating unit (80) comprises a first electromagnet and a second electromagnet, each generating a gradient magnetic field in a study region. The first electromagnet (EM1) comprises a first coil (1A) and a second coil (1B), each for generating a gradient magnetic field, wherein the first coil (1A) and the second coil (1B) are arranged side by side at a distance from each other. The second electromagnet (EM2) faces the first electromagnet (EM1), with the study region located between them, and comprises a third coil (2A) and a fourth coil (2B), each for generating a gradient magnetic field, wherein the third coil (2A) and the fourth coil (2B) are arranged side by side at a distance from each other. The first coil (1A) and the fourth coil (2B) are connected to each other. The second coil (1B) and the third coil (2A) are connected to each other.An imaging unit (10) images magnetic particles exposed to a magnetic field obtained by combining the gradient magnetic fields generated by the first coil (1A), the second coil (1B), the third coil (2A) and the fourth coil (2B).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a magnetic particle imaging system and a magnetic particle imaging method. STATE OF THE ART

[0002] A magnetic particle imaging system is known that includes: a gradient magnetic field generation unit for generating a gradient magnetic field having a weak magnetic field region and a strong magnetic field region in an examination region; and an excited magnetic field generation unit for exciting magnetic particles present in the weak magnetic field region, wherein the magnetic particle imaging system is configured to measure a nonlinear response generated by the excited magnetic particles as a signal. The gradient magnetic field generation unit is an electromagnet, including, for example, a coil and a return yoke made of a substance having a lower magnetic resistance than air.The gradient magnetic field generation unit generates the gradient magnetic field by generating magnetic fields in opposite directions using two electromagnets arranged to face each other. In the weak magnetic field region, a region where the gradient magnetic fields completely cancel each other out, so that they are close to zero, is called the field-free region (FFR). By adjusting the balance between the current amounts flowing through the two electromagnets, the field-free region is sampled to reconstruct the distribution of magnetic particles based on the relationship between the measurement signal and the position of the field-free region. To improve the quality of the reconstructed image, it is necessary to reduce the interval at which the field-free region is sampled and increase the sampling accuracy.Furthermore, in order to obtain a large gradient magnetic field that implements sufficient spatial resolution, it is necessary to apply a high current to the electromagnets in the gradient magnetic field generation unit.

[0003] PTL 1 discloses a magnetic particle imaging (MPI) system including a magnet configured to generate a magnetic field with a field-free line. In the magnet included in a magnetic flux return path, a magnetic flux path located substantially at the center of the field-free line has a first reluctance, and a second magnetic flux path spaced from the center of the field-free line has a second reluctance. LIST OF CITIONSPATENT LITERATURE

[0004] PTL 1: Japanese National Patent Publication No. 2019-523115 SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0005] To implement a magnetic particle imaging system that has high spatial resolution, it is expected that a high current is applied to the electromagnet in the gradient magnetic field generation unit to further accurately sample the field-free region at the smallest possible intervals.

[0006] However, the current supplied to a coil from a power supply pulsates within a current-conduction accuracy range defined by a specific rate of current flowing through the coil. As a result, the position of the field-free region also changes, making it difficult to accurately sample the field-free region with a varying current width that has a magnitude within the current-conduction accuracy range.

[0007] Therefore, an object of the present disclosure is to provide a magnetic particle imaging system and a magnetic particle imaging method that implement high spatial resolution. SOLUTION TO THE PROBLEM

[0008] A magnetic particle imaging system for imaging magnetic particles present in an examination region according to the present disclosure includes a gradient magnetic field generating unit including a first electromagnet and a second electromagnet, each generating a gradient magnetic field in the examination region. The first electromagnet includes a first coil and a second coil, each for generating the gradient magnetic field, wherein the first coil and the second coil are arranged side by side at a distance from each other. The second electromagnet faces the first electromagnet with the examination region therebetween, and includes a third coil and a fourth coil, each for generating the gradient magnetic field, wherein the third coil and the fourth coil are arranged side by side at a distance from each other. The first coil and the fourth coil are connected to each other.The second coil and the third coil are connected to each other. The magnetic particle imaging system further includes an imaging unit for imaging the magnetic particles exposed to a magnetic field obtained by combining the gradient magnetic fields generated by the first coil, the second coil, the third coil, and the fourth coil.

[0009] A magnetic particle imaging method for imaging magnetic particles present in an examination region according to the present disclosure includes: generating, by a first electromagnet and a second electromagnet, a gradient magnetic field in the examination region. The first electromagnet includes a first coil and a second coil arranged side by side at a distance from each other. The second electromagnet faces the first electromagnet with the examination region therebetween and includes a third coil and a fourth coil, the third coil and the fourth coil being arranged side by side at a distance from each other.The magnetic particle imaging method further includes: causing a first current to flow through the first coil and the fourth coil, and causing a second current to flow through the second coil and the third coil; and imaging the magnetic particles exposed to a magnetic field obtained by combining gradient magnetic fields generated by the first coil, the second coil, the third coil, and the fourth coil. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0010] In the present disclosure, the first coil and the fourth coil are connected to each other, and the second coil and the third coil are connected to each other, or the first current is caused to flow through the first coil and the fourth coil, and the second current is caused to flow through the second coil and the third coil. Therefore, the present disclosure enables high spatial resolution to be realized. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing magnetic particle imaging in a reference example. Fig. 2 is an illustration of a magnetic particle imaging system according to a first embodiment when viewed in one direction. Fig. 3 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in the same direction as in Fig. 2. Fig. Fig. 4(a) is a diagram showing a direction and a magnitude of a gradient magnetic field A generated by a first coil 1A, Fig. Fig. 4(b) is a diagram showing a direction and a magnitude of a gradient magnetic field B generated by a fourth coil 2B, and Fig. 4(c) is a diagram showing a direction and a magnitude of a combined magnetic field obtained by combining the gradient magnetic field A and the gradient magnetic field B. Fig. 5 is a diagram showing a direction and a magnitude of a magnetic field obtained by combining gradient magnetic fields A, B, C, and D. Fig. 6 is a flowchart illustrating a procedure of a magnetic particle imaging method in the first embodiment. Fig. 7 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in yet another direction. Fig. 8 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in yet another direction. Fig. Figure 9 is a diagram showing a refrigerant flow when the magnetic particle imaging system is viewed in one direction. Fig. 10 is a diagram showing a portion through which the refrigerant flows when the magnetic particle imaging system is viewed in a different direction. Fig. 11 is a diagram showing a cross section along a line XI-XI in Fig. 13 shows. Fig. 12 is an illustration of a magnetic particle imaging system according to a second embodiment when viewed in a different direction. Fig. 13 is a diagram of a magnetic particle imaging system according to a modification of the second embodiment when viewed in one direction. Fig. 14 is a diagram showing a cross section along a line XIV-XIV in Fig. 13 shows. DESCRIPTION OF EMBODIMENTS

[0011] Embodiments are described below with reference to the accompanying drawings. First embodiment (reference example)

[0012] Fig. 1 is a diagram showing magnetic particle imaging in a reference example.

[0013] A magnetic particle imaging system includes: a first electromagnet EM1 consisting of a coil 1 and a return yoke 3; and an electromagnet EM2 consisting of a coil 2 and a return yoke 4. The first electromagnet EM1 and the second electromagnet EM2 are arranged to face each other to generate opposing magnetic fields toward an examination region.

[0014] To obtain a large gradient magnetic field with the smallest possible current as in a commonly used electromagnet, coils 1 and 2 are connected to separate power supplies V1 and V2, respectively, and a field-free region FFR is sampled by adjusting the current balance.

[0015] As described above, due to the pulsation caused by the characteristics of the power supplies, the power supplies V1 and V2 are supplied with a safety margin of ± (A% reading + B% rated) with respect to the input target current value. The first term in the safety margin represents an error related to the reading value, and the second term in the safety margin represents an error of a constant value that is independent of the input. When a current different from the specified current is applied, the field-free region FFR should exist at a different position from the assumed position, and thus the field-free region FFR cannot be sampled with high accuracy.

[0016] Fig. 2 is a diagram of a magnetic particle imaging system according to the first embodiment when viewed in one direction. Fig. 3 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in the same direction as in Fig. 2. The Fig. 2 and Fig. 3 show representations when viewed in a Z-direction. Fig. 3 shows part of the configuration in Fig. 2 not.

[0017] The magnetic particle imaging system includes a gradient magnetic field generating unit 80, an imaging unit 10, a first power supply VI, a second power supply V2, a rotation mechanism 20, a receiving coil RC, and an excitation coil EC.

[0018] The gradient magnetic field generation unit 80 includes a first electromagnet EM1 and a second magnet EM2, each of which generates a gradient magnetic field in the examination region.

[0019] In magnetic particle imaging, a varying magnetic field generated by the excitation coil causes a change in the magnetization of magnetic particles contained within a subject. This change in magnetization causes an induced voltage or current in the receiving coil RC, and this induced voltage or current is then measured as a signal. The gradient magnetic fields generated by the first electromagnet EM1 and the second electromagnet EM2 create a field-free region (FFR), and the magnetic particles present near the field-free region (FFR) in the examination region contribute to the signal. The field-free region (FFR) is scanned to obtain the relationship between its position and signal intensity. Image reconstruction is then performed based on this relationship to generate the magnetic particle distribution pattern.The field-free region FFR is referred to as a point-like field-free region FFP or a linear field-free region FFL depending on its shape. In the present embodiment, the field-free region FFR is not limited to such a point-like field-free region FFP or a linear field-free region FFL.

[0020] The first electromagnet EM1 includes a first coil 1A, a second coil 1B, and a first return yoke 3. The first return yoke 3 is connected to the first coil 1A and the second coil 1B. The second magnet EM2 includes a third coil 2A, a fourth coil 2B, and a second return yoke 4. The second return yoke 4 is connected to the third coil 2A and the fourth coil 2B.

[0021] The first electromagnet EM1 includes a first return yoke 3, and the second electromagnet EM2 includes a second return yoke 4, so that the gradient magnetic field can be generated efficiently. Since a magnetic circuit is mainly formed by the first return yoke 3 and the second return yoke 4, a first number of turns N1 of each of the first coil 1A and the third coil 2A must be different from a second number of turns N2 of each of the second coil 1B and the fourth coil 2B. When the first number of turns N1 and the second number of turns N2 are the same, the presence of the first return yoke 3 and the second return yoke 4 causes the first coil 1A and the fourth coil 2B to generate magnetic fields in opposite directions of substantially the same magnitude for the examination region.Therefore, the field-free region FFR cannot be sensed even if the current flowing through each coil is changed.

[0022] The first electromagnet EM1 and the second electromagnet EM2 are arranged facing each other in a first direction (a Y direction), with the examination region between them. The first electromagnet EM1 and the second electromagnet EM2 each generate a magnetic field. A strong magnetic field gradient can be efficiently generated by the first return yoke 3 and the second return yoke 4.

[0023] The magnetic field from the first electromagnet EM1 and the magnetic field from the second electromagnet EM2 substantially cancel each other out midway between the first electromagnet EM1 and the second electromagnet EM2 to create a field-free region FFR in which a magnetic field is locally zero.

[0024] The excitation coil EC generates a high-frequency magnetic field in the examination region. The receiving coil RC detects a change in the corresponding magnetic flux in the examination region.

[0025] By causing a current to flow through the excitation coil EC, a high-frequency magnetic field is applied to a region where magnetic particles are distributed. In the region distant from the field-free region FFR, magnetic saturation occurs due to a static magnetic field. Therefore, even when such a high-frequency magnetic field is applied, only a small magnetization change occurs in the magnetic particles present in the region. Near the field-free region FFR, magnetic saturation does not occur due to a small magnetic field, and the application of a high-frequency magnetic field causes a significant magnetization change in the magnetic particles present in the region. This magnetization change causes a change in the magnetic flux associated with the receiving coil RC. This change in the magnetic flux is represented as a change in the voltage induced in the receiving coil RC.The magnitude of the voltage change depends on the amount of magnetic particles present in the field-free region FFR. In other words, the voltage induced in the receiving coil RC changes according to the amount of magnetic particles present in the field-free region FFR.

[0026] By changing the balance between the currents applied to the first electromagnet EM1 and the second electromagnet EM2, the field-free region FFR is gradually displaced. While the rotation mechanism 20 gradually performs a rotational scan of the field-free region FFR in the subject into which the magnetic particles are injected, the imaging unit 10 measures the change in the voltage induced in the receiving coil RC to acquire signal intensity data corresponding to the spatial position of the field-free region. Based on the data, the imaging unit 10 maps the spatial distribution of the magnetic particles within the subject.

[0027] The first coil 1A and the second coil 1B are spaced apart from each other in a first direction (a Y direction). The first coil 1A and the second coil 1B each generate a first gradient magnetic field in the first direction in the examination region. The third coil 2A and the fourth coil 2B are spaced apart from each other in the first direction (the Y direction). The third coil 2A and the fourth coil 2B each generate a second gradient magnetic field in a second direction in the examination region. The central axes of the first coil 1A, the second coil 1B, the third coil 2A, and the fourth coil 2B coincide with each other or substantially coincide with each other and extend in the first direction (the Y direction).A central portion C1 of the first return yoke 3 and a central portion C2 of the second return yoke 4 are arranged around and extend along the central axes of the first coil 1A, the second coil 1B, the third coil 2A and the fourth coil 2B.

[0028] The imaging unit 10 includes a control unit 11 and a storage unit 12. The storage unit 12 stores the signal intensity at each position in the field-free region FER. The control unit 11 reconstructs an image (images an image) representing the signal intensity stored in the storage unit 12. The imaging unit 10 may include a memory and a processor that executes a program stored in the memory.

[0029] The first power supply V1 is connected to the first coil 1A and the fourth coil 2B, which are connected in series. The first power supply V1 causes a first current to flow through the first coil 1A and the fourth coil 2B. The magnitude of the first current is variable, and the first power supply V1 is subjected to constant current control.

[0030] The second power supply V2 is connected to the second coil 1B and the third coil 2A, which are connected in series. The second power supply V2 causes a second current to flow through the second coil 1B and the third coil 2A. The magnitude of the second current is variable, and the second power supply V2 is subjected to constant current control.

[0031] The magnitude of each of the currents output by the first power supply V1 and the second power supply V2 can be controlled by a control circuit (not shown).

[0032] The first coil 1A and the third coil 2A each have the first number of turns N1. The second coil 1B and the fourth coil 2B each have the second number of turns N2.

[0033] The first number of turns N1 is greater than the second number of turns N2. In the electromagnet EM1, which includes the first coil 1A and the second coil 1B spaced apart in a Y-axis direction (a direction in which these coils face each other), and the electromagnet EM2, which includes the third coil 2A and the fourth coil 2B spaced apart in the Y-axis direction (a direction in which these coils face each other), the portions of the magnetic fields generated by the first coil 1A and the third coil 2A located on the side farther from the examination region do not contribute to the examination region and form force paths within the return yokes 3 and 4. In other words, in the first coil 1A and the third coil 2A, only a small contribution is made to the amount of scanning of the field-free region FFR according to the current change.Therefore, the first number of turns N1 of each of the first coil 1A and the third coil 2A is set to be larger than the second number of turns N2 of each of the second coil 1B and the fourth coil 2B to make it possible to reduce the amount of scanning of the field-free region FFR according to the current change.

[0034] The first electromagnet EM1 and the second electromagnet EM2 face each other in the first direction (the Y direction) with the examination region therebetween. The first coil 1A and the second coil 1B are spaced apart from each other in the first direction (the Y direction). The third coil 2A and the fourth coil 2B are spaced apart from each other in the first direction (the Y direction). The first coil 1A is arranged at a position farther from the examination region than the second coil 1B. The third coil 2A is arranged at a position farther from the examination region than the fourth coil 2B.

[0035] When the first current from the first power supply V1 increases, the second current from the second power supply V2 decreases by the same amount as the first current increases. When the first current from the first power supply V1 decreases, the second current from the second power supply V2 increases by the same amount as the first current decreases. This makes it possible to scan the field-free region FFR while maintaining the magnitude of the gradient of the gradient magnetic field as much as possible, and thereby suppress the occurrence of artifacts during imaging. If the second current increases when the first current increases, or if the second current decreases when the first current decreases, only the magnitude of the magnetic field gradient changes, and the field-free region FFR cannot be scanned.

[0036] Fig. 4(a) is a diagram showing the direction and magnitude of a gradient magnetic field A generated by the first coil 1A. Fig. 4(b) is a diagram showing the direction and magnitude of a gradient magnetic field B generated by the fourth coil 2B. Fig. Figure 4(c) is a diagram showing the direction and magnitude of a combined magnetic field obtained by combining the gradient magnetic fields A and B. The figures show that the gradient magnetic fields A and B cancel each other.

[0037] Similarly, a gradient magnetic field C generated by the second coil 1B and a gradient magnetic field D generated by the third coil 2A cancel each other out.

[0038] Fig. 5 is a diagram showing the direction and magnitude of a magnetic field obtained by combining the gradient magnetic fields A, B, C, and D.

[0039] It is assumed that the amount of movement of the field-free region FFR with respect to a current change in the reference example in which the power supply is not shared by the two coils facing each other is 10 mm / A. When the power supplies V1 and V2 are shared by the two coils 1A and 2B facing each other, or by the coils 1B and 2A facing each other, as in the present embodiment, the magnetic fields cancel each other out at a certain rate. Thus, the amount of movement of the field-free region FFR with respect to a current change is, for example, 5 mm / A. In other words, in the present embodiment, the amount of current required to move the field-free region FFR by the same distance increases.On the other hand, the error magnitude of the position of the field-free region FFR with respect to an error of the current resulting from the safety degrees of the power supplies V1 and V2 becomes small, thus enabling more accurate sensing than in the reference example.

[0040] Fig. 6 is a flowchart illustrating a procedure of a magnetic particle imaging method in the first embodiment.

[0041] In step S101, the first electromagnet EM1 and the second electromagnet EM2 each generate a gradient magnetic field in the examination region.

[0042] In step S102, the first power supply V1 causes the first current to flow through the first coil 1A and the fourth coil 2B, and the second power supply V2 causes the second current to flow through the second coil 1B and the third coil 2A. In this case, as the first current from the first power supply V1 increases, the second current from the second power supply V2 decreases by the same amount as the first current increases. As the first current from the first power supply V1 decreases, the second current from the second power supply V2 increases by the same amount as the first current decreases.

[0043] In step S103, the imaging unit 10 images the magnetic particles exposed to a magnetic field obtained by combining the gradient magnetic fields generated by the first coil 1A, the second coil 1B, the third coil 2A, and the fourth coil 2B.

[0044] Fig. 7 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in yet another direction. Fig. 7 shows a representation when viewed in an X-direction. Fig. 8 is a diagram of the magnetic particle imaging system according to the first embodiment when viewed in yet another direction. Fig. Figure 8 shows a representation when viewed in the Y direction.

[0045] The magnetic particle imaging system includes first spacers SP1A and SP1B, second spacers SP2A and SP2B, third spacers SP3A and SP3B, fourth spacers SP4A and SP4B, fifth spacers SP5A and SP5B, and sixth spacers SP6A and SP6B.

[0046] First spacers SP1A and SP1B are provided to maintain a distance between the middle section C1 (see Fig. 3) of the first return yoke 3 and each of the first coil 1A and second coil 1B in the direction perpendicular to the center axes of the first coil 1A and second coil 1B (in the radial direction of each of the first coil 1A and second coil 1B). The second spacers SP2A and SP2B are provided to maintain a distance between the center portion C2 (see Fig. 3) of the second return yoke 4 and each of the third coil 2A and the fourth coil 2B in the direction perpendicular to the center axes of the third coil 2A and the fourth coil 2B (in the radial direction of each of the third coil 2A and the fourth coil 2B) constant. When the relative positions between the return yokes 3, 4 and the coils 1A, 1B, 2A, 2B change, the gradient magnetic fields become unstable. Thus, the first spacers SP1A, SP1B and the second spacers SP2A, SP2B are provided to keep the distance from the return yokes 3 and 4 to the coils 1A, 1B and 2A, 2B constant.

[0047] The third spacers SP3A and SP3B are provided to maintain a constant distance in the direction in which the first coil 1A and the second coil 1B are spaced from each other (in the Y-axis direction). The fourth spacers SP4A and SP4B are provided to maintain a constant distance in the direction in which the third coil 2A and the fourth coil 2B are spaced from each other (in the Y-axis direction). The fifth spacers SP5A and SP5B are provided to maintain a constant distance in the direction in which the first coil 1A and the first return yoke 3 are spaced from each other (in the Y-axis direction). The sixth spacers SP6A and SP6B are provided to maintain a constant distance in the direction in which the third coil 2A and the second return yoke 4 are spaced from each other (in the Y-axis direction).If these spacers are not provided, a repulsive force is generated between the electromagnets EM1 and EM2 facing each other, so that the positions of the coils 1A, 1B, 2A and 2B change.

[0048] In the present embodiment, the coils are connected between the facing electromagnets, and the magnetic fields generated by these electromagnets cancel each other out at a certain rate, reducing the scanning range of the field-free region FFR relative to the current change in the power supply connected to the coils. Thus, to achieve the same scanning range as in the conventional case, it is necessary to cause more electric power to flow through each coil than in the conventional case, resulting in increased heat generation in each coil.Therefore, the third spacers SP3A and SP3B, the fourth spacers SP4A and SP4B, the fifth spacers SP5A and SP5B, and the sixth spacers SP6A and SP6B are used to ensure flow paths through which the heat generated by the coils 1A, 1B, 2A, and 2B is released, and thereby the densities of the currents flowing through the coils 1A, 1B, 2A, and 2B, respectively, can be increased, so that the cross-sectional areas of the coils 1A, 1B, 2A, and 2B can be reduced.

[0049] Fig. Figure 9 is a diagram showing a refrigerant flow when the magnetic particle imaging system is viewed in one direction. Fig. 9 shows a representation when viewed in the X direction. Fig. 10 is a diagram showing a portion through which the refrigerant flows when the magnetic particle imaging system is viewed in a different direction. Fig. 10 shows a representation when viewed in the Z-direction. In Fig. 10 represents a section (FC) surrounded by a dashed line, a section through which refrigerant flows.

[0050] The cooling mechanisms 15 and 16 cause the refrigerant to flow through the spaces formed by the third spacers SP3A, SP3B, the fourth spacers SP4A, SP4B, the fifth spacers SP5A, SP5B and the sixth spacers SP6A, SP6B.

[0051] This allows coils 1A, 1B, 2A, and 2B to be cooled more efficiently than in the case of natural convection of the refrigerant caused by a temperature change or a pressure difference. As a result, the clearances (the flow paths) provided by spacers SP3A, SP3B and spacers SP4A, SP4B can be reduced in size, allowing the size of electromagnets EM1 and EM2 to be reduced. Furthermore, the densities of the currents flowing through coils 1A, 1B, 2A, and 2B, respectively, can be increased, allowing the cross-sectional areas of coils 1A, 1B, 2A, and 2B to be reduced.

[0052] By configuring the first coil 1A and the second coil 1B to be spaced apart in the direction in which these coils face each other (the Y-axis direction), and the third coil 2A and the fourth coil 2B to be spaced apart in the direction in which these coils face each other (the Y-axis direction), the area of ​​the portion where each of these coils is cooled can be increased compared to the case where these coils are spaced apart in the radial direction thereof. Furthermore, since the flow path of the refrigerant is not complicated, the heat generated by these coils can be efficiently released.

[0053] According to the present embodiment, the electromagnets, each including two or more split coils, are arranged to face each other, and the coils between the electromagnets facing each other are connected to each other so that the magnetic fields generated by the electromagnets can cancel each other out at a certain rate. As a result, the amount of sampling of the field-free region FFR with respect to the current change in the power supply connected to each coil decreases. Therefore, the positional deviation of the field-free region FFR caused by the current pulsation in the power supply can be reduced, and thus the field-free region FFR can be accurately sampled at fine intervals while applying a high current.

[0054] The present embodiment is the same as Patent Application Publication 1 in that "the field-free region FFR is formed by a structure in which electromagnets, each having a coil and a return yoke, face each other, and the field-free region FFR is sensed by changing the amount of current flowing through each coil." However, the present embodiment differs from Patent Application Publication 1 in that "in a structure in which electromagnets, each having divided coils having a different number of turns, face each other, the same current is caused to flow through the coils having a different number of turns and connected between the facing electromagnets."In PTL 1, since the coils between the facing electromagnets are not connected to each other, there is no effect of enabling accurate sensing of the field-free region FFR at fine intervals while applying a high current as in the present embodiment.

[0055] In the present embodiment, the first coil 1A and the fourth coil 2B, which are connected to the first power supply V1, face each other and therefore generate magnetic fields in opposite directions. Furthermore, since the number of turns of the first coil 1A and the fourth coil 2B differs, the magnetic fields generated by these coils cancel each other out at a certain rate. This increases the amount of current required to scan the field-free region FFR by the same amount. Furthermore, the scanning amount of the field-free region FFR decreases with respect to the current change in the first power supply V1. Regarding the above-described point, the same also applies to the second coil 1B and the third coil 2A, which are connected to the second power supply V2.Therefore, according to the present embodiment, the positional deviation of the field-free region FFR caused by the pulsation of the current in the power supply can be reduced, and thus the field-free region FFR can be accurately sampled at fine intervals while a high current is applied. Second embodiment

[0056] Fig. 11 is a diagram showing a cross section along a line XI-XI in Fig. 13 shows. Fig. 11 shows a representation when viewed in the X-direction. Fig. 12 is a diagram of a magnetic particle imaging system according to the second embodiment when viewed in a different direction. Fig. 12 shows a representation when viewed in the Y-direction. In Fig. 12, FC represents a section through which refrigerant flows.

[0057] The magnetic particle imaging system in the second embodiment differs from the magnetic particle imaging system in the first embodiment in the positions of the coils 1A, 1B, 2A, and 2B. In the magnetic particle imaging system in the first embodiment, in the direction (the Y-axis direction) in which the first electromagnet EM1 and the second electromagnet EM2 face each other, the first coil 1A is spaced from the second coil 1B, and the third coil 2A is spaced from the fourth coil 2B.

[0058] In the magnetic particle imaging system in the second embodiment, the first coil 1A is spaced from the second coil 1B in the radial direction (on an XZ plane) of the first coil 1A and the second coil 1B, and the third coil 2A is spaced from the fourth coil 2B in the radial direction (on the XZ plane) of the third coil 2A and the fourth coil 2B.

[0059] In the second embodiment, the coil thickness in the direction in which the electromagnets EM1 and EM2 face each other (in the Y-axis direction) is relatively large, which increases the mechanical strength of the coils 1A, 1B, 2A and 2B against the repulsive force generated by the electromagnets EM1 and EM2, so that the coils 1A, 1B, 2A and 2B are less likely to break.

[0060] A seventh spacer SP7 is provided to serve as a frame around which the first coil 1A and the second coil 1B are wound, and to fix the positions of the first coil 1A and the second coil 1B. The seventh spacer SP7 has a vent hole through which the heat generated by the first coil 1A and the second coil 1B is dissipated.

[0061] An eighth spacer SP8 is provided to serve as a frame around which the third coil 2A and fourth coil 2B are wound and to fix the positions of the third coil 2A and fourth coil 2B. The eighth spacer SP8 has a vent hole through which the heat generated by the third coil 2A and fourth coil 2B is dissipated. Modification of the second embodiment

[0062] Fig. 13 is a diagram of a magnetic particle imaging system according to a modification of the second embodiment when viewed in one direction.

[0063] Fig. 13 shows a representation when viewed in the Z direction. Fig. 14 is a diagram showing a cross section along a line XIV-XIV in Fig. 13 shows.

[0064] A ninth spacer SP9 is provided to fix the position of the second coil 1B. A tenth spacer SP10 is provided to fix the position of the fourth coil 2B.

[0065] The cooling mechanisms 17 and 18 cause the refrigerant to flow through the space between the first coil 1A and the second coil 1B, the space between the second coil 1B and the ninth spacer SP9, the space between the third coil 2A and the fourth coil 2B, and the space between the fourth coil 2B and the tenth spacer SP10. In the present modification, the refrigerant flows in the direction (the Y-axis direction) in which the first electromagnet EM1 and the second electromagnet EM2 face each other. Modification (yoke)

[0066] The first electromagnet EM1 may not have a first return yoke 3, and the second electromagnet EM2 may not have a second return yoke 4. If the first electromagnet EM1 does not have a first return yoke 3 and the second electromagnet EM2 does not have a second return yoke 4, the first number of turns N1 may be equal to or different from the second number of turns N2.

[0067] This is because the contribution of the first coil 1A and the fourth coil 2B, which are connected to the first power supply V1, to the examination region also depends on the distance between the examination region and each of the first coil 1A and the fourth coil 2B. Thus, the FFR can be sensed by changing the current flowing through each coil, even if the first coil 1A and the fourth coil 2B have the same number of turns. The same applies to the second coil 1B and the third coil 2A.

[0068] It is to be understood that the embodiments disclosed in this specification are illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims rather than the above description, and is intended to include any modifications that are within the meaning and scope equivalent to the terms of the claims. LIST OF REFERENCE SYMBOLS

[0069] 1, 1A, 1B, 2, 2A, 2B coil, 3, 4 return yoke, 10 imaging unit, 11 control unit, 12 storage unit, 15, 16, 17, 18 cooling mechanism, 20 rotation mechanism, 80 gradient magnetic field generation unit, EC excitation coil, EM1, EM2 electromagnet, FFR field-free region, RC receiving coil, SP1B, SP1A, SP2A, SP2B, SP3A, SP3B, SP4A, SP4B, SP5B, SP5A, SP6A, SP6B, SP7, SP8, SP9, SP10 spacer, V1, V2 power supply. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2019-523115

[0004]

Claims

[1] A magnetic particle imaging system for imaging magnetic particles present in a region of interest, the magnetic particle imaging system comprising: a gradient magnetic field generating unit including a first electromagnet and a second electromagnet, each generating a gradient magnetic field in the examination region, wherein the first electromagnet includes a first coil and a second coil each for generating the gradient magnetic field, wherein the first coil and the second coil are arranged side by side at a distance from each other, the second electromagnet faces the first electromagnet, with the examination region therebetween, and includes a third coil and a fourth coil each for generating the gradient magnetic field, the third coil and the fourth coil being arranged side by side at a distance from each other, the first coil and the fourth coil are connected to each other, the second coil and the third coil are connected to each other and the magnetic particle imaging system further comprises: an imaging unit for imaging the magnetic particles exposed to a magnetic field obtained by combining the gradient magnetic fields generated by the first coil, the second coil, the third coil, and the fourth coil. [2] Magnetic particle imaging system according to claim 1, wherein the first electromagnet includes a first return yoke connected to the first coil and the second coil, the second electromagnet includes a second return yoke connected to the third coil and the fourth coil, the first coil and the third coil each have a first number of turns and the second coil and the fourth coil each have a second number of turns that is different from the first number of turns. [3] The magnetic particle imaging system of claim 2, further comprising: a first spacer for keeping constant a distance between the first return yoke and each of the first coil and the second coil, the distance being a distance in a radial direction from each of the first coil and the second coil; and a second spacer for keeping constant a distance between the second return yoke and each of the third coil and the fourth coil, the distance being a distance in a radial direction from each of the third coil and the fourth coil. [4] Magnetic particle imaging system according to one of claims 1 to 3, wherein causing a first current to flow through the first coil and the fourth coil, causing a second current to flow through the second coil and the third coil, when the first current increases, the second current decreases by an amount equal to an amount by which the first current increases, and when the first current decreases, the second current increases by an amount equal to an amount by which the first current decreases. [5] Magnetic particle imaging system according to one of claims 1 to 4, wherein the first electromagnet and the second electromagnet face each other in a first direction, with the examination region lying therebetween, and the first direction extends as follows: in a direction in which the first coil and the second coil are spaced apart from each other, and in a direction in which the third coil and the fourth coil are spaced apart from each other. [6] Magnetic particle imaging system according to claim 5, wherein the first coil is arranged at a position further away from the examination region than the second coil, the third coil is arranged at a position further away from the examination region than the fourth coil, and the first number of turns is greater than the second number of turns. [7] Magnetic particle imaging system according to one of claims 1 to 6, further comprising: a third spacer for keeping constant a distance in a direction in which the first coil and the second coil are spaced from each other; a fourth spacer for keeping a distance constant in a direction in which the third coil and the fourth coil are spaced from each other; a fifth spacer for keeping a distance constant in a direction in which the first coil and the first return yoke are spaced from each other; and a sixth spacer for keeping a distance constant in a direction in which the third coil and the second return yoke are spaced from each other. [8] The magnetic particle imaging system according to claim 7, further comprising a cooling mechanism for causing coolant to flow into a space formed by each of the third spacer, the fourth spacer, the fifth spacer, and the sixth spacer. [9] Magnetic particle imaging system according to one of claims 1 to 4, wherein the first electromagnet and the second electromagnet face each other in a first direction, with the examination region lying therebetween, the first coil and the second coil are spaced apart from each other in a plane perpendicular to the first direction and the third coil and the fourth coil are spaced apart from each other in a plane perpendicular to the first direction. [10] A magnetic particle imaging method for imaging magnetic particles present in a region of interest, the magnetic particle imaging method comprising: Generating, by a first electromagnet and a second electromagnet, a gradient magnetic field in the examination region, wherein the first electromagnet includes a first coil and a second coil arranged side by side at a distance from each other, and wherein the second electromagnet faces the first electromagnet with the examination region therebetween, and includes a third coil and a fourth coil, the third coil and the fourth coil being arranged side by side at a distance from each other; Causing a first current to flow through the first coil and the fourth coil, and causing a second current to flow through the second coil and the third coil; and Imaging the magnetic particles exposed to a magnetic field obtained by combining gradient magnetic fields generated by the first coil, the second coil, the third coil, and the fourth coil. [11] The magnetic particle imaging method according to claim 10, wherein causing the first current and the second current to flow includes: when the first current increases, decreasing the second current by an amount equal to an amount by which the first current increases; and if the first current decreases, increase the second current by an amount equal to an amount by which the first current decreases.

Images