JP2015211766A - Magnetic resonance imaging apparatus and gradient magnetic field coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus which can prevent a static magnetic field from locally getting uneven due to change in temperature of a magnetic SIM (single in-line memory module), and to provide a gradient magnetic field coil.SOLUTION: A magnetic resonance imaging apparatus includes a magnetostatic field magnet, a gradient magnetic field coil, and a SIM tray. The magnetostatic field magnet generates a magnetostatic field at an imaging space where a subject is placed. The gradient magnetic field coil generates a gradient magnetic field at the imaging space. The SIM tray is provided to the gradient magnetic field coil, and has a plurality of SIM pockets which can store a magnetic SIM for correcting unevenness of the magnetostatic field. The SIM tray subjects the magnetic SIM housed in different SIM pockets of a plurality of SIM pockets to thermal bonding.

Description

  Embodiments described herein relate generally to a magnetic resonance imaging apparatus and a gradient magnetic field coil.

  2. Description of the Related Art Conventionally, some magnetic resonance imaging apparatuses include a magnetic shim (for example, an iron shim) for correcting static magnetic field inhomogeneity in an imaging space where a subject is placed. This magnetic shim may generate heat due to the ambient temperature or the like during imaging, and when the temperature changes due to the generated heat, the saturation magnetic flux density changes. As a result, the magnitude of the magnetic flux that converges on the magnetic shim changes, and the uniformity of the static magnetic field may change accordingly. In general, a plurality of magnetic shims are used in a magnetic resonance imaging apparatus. However, since the temperature change of each magnetic shim varies depending on the position at which the magnetic shims are arranged, the static magnetic field may be locally non-uniform. .

JP 2011-15840 A

  The problem to be solved by the present invention is to provide a magnetic resonance imaging apparatus and a gradient magnetic field coil capable of suppressing a static magnetic field from becoming locally non-uniform due to a temperature change of a magnetic material shim.

  A magnetic resonance imaging (MRI) apparatus according to an embodiment includes a static magnetic field magnet, a gradient magnetic field coil, and a shim tray. The static magnetic field magnet generates a static magnetic field in the imaging space where the subject is placed. The gradient magnetic field coil generates a gradient magnetic field in the imaging space. The shim tray has a plurality of shim pockets provided in the gradient magnetic field coil and capable of storing magnetic shims for correcting the non-uniformity of the static magnetic field. The shim tray thermally couples the magnetic shims stored in different shim pockets among the plurality of shim pockets.

FIG. 1 is a diagram illustrating a configuration example of an MRI apparatus according to the first embodiment. FIG. 2 is a perspective view illustrating a configuration example of the gradient magnetic field coil according to the first embodiment. FIG. 3 is a perspective view illustrating a configuration example of the shim tray according to the first embodiment. FIG. 4 is a cross-sectional view illustrating a configuration example of the shim tray according to the first embodiment. FIG. 5 is a cross-sectional view illustrating a configuration example of a shim tray according to the second embodiment. FIG. 6 is a cross-sectional view illustrating a configuration example of a shim tray according to the third embodiment. FIG. 7 is a cross-sectional view illustrating a configuration example of a shim tray according to the fourth embodiment. FIG. 8 is a cross-sectional view illustrating a configuration example of a shim tray according to the fifth embodiment.

  Hereinafter, embodiments of an MRI apparatus and a gradient magnetic field coil will be described in detail based on the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of an MRI apparatus 100 according to the first embodiment. For example, as shown in FIG. 1, the MRI apparatus 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 20, an RF coil 30, a top plate 40, a gradient magnetic field power supply 50, a transmission unit 60, and a reception unit 70. And a sequence control device 80 and a computer system 90.

  The static magnetic field magnet 10 includes a vacuum vessel 11 formed in a substantially cylindrical shape (including one having an elliptical cross section perpendicular to the central axis of the cylinder), and a superconducting coil immersed in a cooling liquid in the vacuum vessel 11. Twelve. The static magnetic field magnet 10 forms an imaging space (bore) in which the subject S is placed inside the cylinder of the static magnetic field magnet 10 and generates a static magnetic field in the imaging space.

  The gradient magnetic field coil 20 is formed in a substantially cylindrical shape (including one in which a cross section perpendicular to the central axis of the cylinder is an ellipse), and is disposed inside the static magnetic field magnet 10. The gradient magnetic field coil 20 generates a gradient magnetic field in an imaging space where the subject S is placed by a current supplied from the gradient magnetic field power supply 50. For example, the gradient magnetic field coil 20 includes a main coil 21 that generates gradient magnetic fields along the X-axis, Y-axis, and Z-axis directions in the imaging space, and a shield coil 22 that cancels the leakage magnetic field of the main coil 21. . Here, a shim tray insertion guide 23 is formed between the main coil 21 and the shield coil 22. The shim tray insertion guide 23 is inserted with a shim tray 24 containing an iron shim 25 for correcting the non-uniformity of the static magnetic field in the imaging space. The configuration of the gradient coil 20 will be described in detail later.

  The RF coil 30 is formed in a substantially cylindrical shape (including one in which a cross section perpendicular to the central axis of the cylinder is an ellipse), and is disposed inside the gradient coil 20. The RF coil 30 receives the RF pulse supplied from the transmission unit 60 and generates a high-frequency magnetic field in the imaging space where the subject S is placed. The RF coil 30 receives a magnetic resonance signal emitted from the subject S when the hydrogen nuclei are excited by the high-frequency magnetic field.

  The top plate 40 is provided on a bed (not shown) so as to be movable in the horizontal direction, and the subject S is placed and moved to the imaging space during imaging. The gradient magnetic field power supply 50 supplies a current to the gradient magnetic field coil 20 based on an instruction from the sequence controller 80.

  The transmission unit 60 supplies an RF pulse to the RF coil 30 based on an instruction from the sequence control device 80. The receiving unit 70 receives the magnetic resonance signal received by the RF coil 30, and transmits raw data obtained by digitizing the received magnetic resonance signal to the sequence control device 80.

  The sequence control device 80 scans the subject S by driving the gradient magnetic field power supply 50, the transmission unit 60, and the reception unit 70, respectively, under the control of the computer system 90. Then, when the raw data is transmitted from the receiving unit 70 as a result of the scanning, the sequence control device 80 transmits the raw data to the computer system 90.

  The computer system 90 controls the entire MRI apparatus 100. Specifically, the computer system 90 includes an input unit that accepts various inputs from the operator, a sequence control unit that causes the sequence control device 80 to execute a scan based on an imaging condition input from the operator, and the sequence control device 80. An image reconstruction unit that reconstructs an image based on raw data transmitted from the storage unit, a storage unit that stores the reconstructed image, a display unit that displays various information such as the reconstructed image, and instructions from the operator Based on the main control unit for controlling the operation of each functional unit.

  FIG. 2 is a perspective view showing a configuration example of the gradient magnetic field coil 20 according to the first embodiment. For example, as shown in FIG. 2, the gradient magnetic field coil 20 includes a main coil 21 formed in a substantially cylindrical shape, and a shield coil 22 disposed outside the main coil 21. A plurality of shim tray insertion guides 23 are formed between the main coil 21 and the shield coil 22.

  The shim tray insertion guide 23 is a through hole that forms openings on both end faces of the gradient magnetic field coil 20, and is formed over the entire length in the longitudinal direction of the gradient magnetic field coil 20. For example, the shim tray insertion guides 23 are formed at equal intervals in the circumferential direction so as to be parallel to each other in a region sandwiched between the main coil 21 and the shield coil 22. A shim tray 24 is inserted into each shim tray insertion guide 23.

  The shim tray 24 is formed in a substantially rod shape with resin. A predetermined number of iron shims 25 are stored in the shim tray 24. For example, the shim tray 24 has a length excluding both ends of the gradient magnetic field coil 20. The shim tray 24 is inserted into each shim tray insertion guide 23 and fixed to the center of the gradient magnetic field coil 20. Although not shown in FIG. 2, for example, a plurality of cooling pipes for cooling the gradient magnetic field coil 20 are spirally embedded in the gradient magnetic field coil 20 along the cylindrical shape.

  FIG. 3 is a perspective view illustrating a configuration example of the shim tray 24 according to the first embodiment. For example, as shown in FIG. 3, the shim tray 24 includes an elongated box-shaped tray body 24a and a lid 24b. The tray main body 24a has a plurality of shim pockets 24d that are continuously formed in the longitudinal direction and each of which can accommodate a magnetic shim 24c. The magnetic shims 24c are magnetic members formed in a thin plate shape, and are stored in the shim pockets 24d where necessary in order to correct the non-uniformity of the static magnetic field in the imaging space. For example, the magnetic shim 24c is made of iron, permendur, sendust, or the like.

  The configuration of the MRI apparatus 100 according to this embodiment has been described above. Under such a configuration, in the MRI apparatus 100 according to the present embodiment, the shim tray 24 thermally couples the magnetic shims 24c housed in different shim pockets of the plurality of shim pockets 24d.

  Conventionally, a magnetic shim may generate heat during imaging due to the ambient temperature of the gradient magnetic field coil or the eddy current loss of the magnetic shim itself. When the temperature changes due to heat generation, the saturation magnetic flux density changes. To do. As a result, the magnitude of the magnetic flux that converges on the magnetic shim changes, and the uniformity of the static magnetic field may change accordingly. In general, a plurality of magnetic shims are used in a magnetic resonance imaging apparatus. However, since the temperature change of each magnetic shim varies depending on the position at which the magnetic shims are arranged, the static magnetic field may be locally non-uniform. .

  On the other hand, in the MRI apparatus according to this embodiment, the magnetic shims 24c housed in different shim pockets are thermally coupled by the shim tray 24, so that the temperature of each magnetic shim 24c is made uniform. Thereby, it can suppress that a static magnetic field becomes locally non-uniform | heterogenous by the temperature change of the magnetic body shim 24c. Below, the structural example of the shim tray 24 which concerns on this embodiment is demonstrated.

  FIG. 4 is a cross-sectional view illustrating a configuration example of the shim tray 24 according to the first embodiment. FIG. 4 shows a cross section that passes through substantially the center of the shim tray 24 and is parallel to the longitudinal direction and the thickness direction of the shim tray 24. As shown in FIG. 4, the shim tray 24 includes an elongated box-shaped tray main body 24a and a lid 24b.

  The tray body 24a has a plurality of shim pockets 24d formed continuously in the longitudinal direction. In each shim pocket 24d, as many magnetic shims 24c as necessary for correcting the non-uniformity of the static magnetic field in the imaging space are stacked and stored. As a result of storing the required number of magnetic shims 24c in each shim pocket 24d, the magnetic shims 24c may be stored in all the shim pockets 24d, but the magnetic shims 24d may be stored in some of the shim pockets 24d. There is a case where no 24c is stored.

  The lid 24b is fixed to the tray body 24a so as to cover the plurality of shim pockets 24d. In each shim pocket 24d, a spacer 24e having an appropriate thickness is disposed between the laminated magnetic body shim 24c and the lid body 24b. The spacer 24e is positioned by pressing the magnetic shim 24c against the bottom of the shim pocket 24d when the lid 24b is fixed so that the magnetic shim 24c does not move in the shim pocket 24d.

  The shim tray 24 has a heat conducting member 24f provided across a plurality of shim pockets 24d. The heat conducting member 24f directly contacts the magnetic material shim 24c accommodated in the different shim pockets 24d directly or through another heat conducting member to thermally couple the magnetic material shims. As a result, even when a specific magnetic shim 24c generates a large amount of heat, the heat is dispersed to other magnetic shims 24c via the heat conducting member 24f, and the temperature of each magnetic shim 24c is made uniform. Is done.

  Here, the heat conducting member 24f is provided at the bottom of the shim pocket 24d. For example, the heat conducting member 24f is a plate-like or sheet-like member formed of a material having thermal conductivity, and is embedded in a resin that forms the bottom of the tray body 24a.

  More specifically, for example, the heat conducting member 24f is provided at least on the bottom surface of each shim pocket 24d so as to directly contact the magnetic shim 24c when the magnetic shim 24c is accommodated in each shim pocket 24d. It is embedded so that a part is exposed. Here, the range in which the heat conducting member 24f is exposed at the bottom surface of the shim pocket 24d may be the entire bottom surface of the shim pocket 24d or a part of the bottom surface of the shim pocket 24d. In addition, the heat conducting member 24f does not directly contact the magnetic shim 24c, but via a thermally conductive spacer inserted between the bottom surface of the shim pocket 24d and the magnetic shim 24c. You may contact the magnetic body shim 24c indirectly.

  Further, for example, the heat conducting member 24f is formed of a material having higher heat conductivity than the material forming the shim tray 24. As such a material, for example, copper can be used. In general, since the resin forming the shim tray 24 has low thermal conductivity, the magnetic shim 24c accommodated in each shim pocket 24d is thermally insulated when the heat conducting member 24f is not provided. Become. Therefore, by forming the heat conducting member 24f with a material having higher heat conductivity than the shim tray 24, heat can be conducted between the magnetic shims 24c accommodated in the shim pockets 24d.

  Further, for example, the heat conducting member 24 f may be formed of a material having a larger heat capacity than the material forming the shim tray 24. As such a material, for example, aluminum can be used. The heat conducting member 24f may generate heat depending on the ambient temperature as in the case of the magnetic shim, and may disturb the uniformity of the static magnetic field. On the other hand, by forming the heat conducting member 24f with a material having a larger heat capacity than the shim tray 24, it is possible to suppress the temperature rise of the temperature of the heat conducting member 24f. As a result, the temperature change of the heat conducting member 24 can be suppressed, and the variation in the uniformity of the static magnetic field due to the heat generated by the heat conducting member 24 can be suppressed.

  Although the first embodiment has been described above, the MRI apparatus 100 described in the above embodiment is implemented by appropriately changing the configuration of the shim tray 24 without changing the basic configuration shown in FIGS. Is possible. Hereinafter, another embodiment related to the MRI apparatus 100 will be described focusing on the configuration of the shim tray. In each embodiment described below, components having the same structure or function as the components described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

(Second Embodiment)
FIG. 5 is a cross-sectional view illustrating a configuration example of the shim tray 124 according to the second embodiment. FIG. 5 shows a cross section that passes through substantially the center of the shim tray 124 and is parallel to the longitudinal direction and the thickness direction of the shim tray 124. The shim tray 124 according to the present embodiment has substantially the same configuration as the shim tray 24 described in the first embodiment, but the configuration of the heat conducting member is different from that of the first embodiment.

  As shown in FIG. 5, the shim tray 124 includes a heat conducting member 124 f provided across a plurality of shim pockets 24 d, similarly to the shim tray 24 described in the first embodiment.

  Here, in the present embodiment, the heat conducting member 124f is formed by joining the first heat conducting member 124fa and the second heat conducting member 124fb. The first heat conducting member 124fa is formed of a material having higher heat conductivity than the material forming the shim tray 124. As such a material, for example, copper can be used. The second heat conducting member 124fb is formed of a material having a larger heat capacity than the material forming the shim tray 124. As such a material, for example, aluminum can be used. The first heat conducting member 124fa is provided at a position where the first heat conducting member 124fa is in direct contact with the magnetic shim 24c housed in a different shim pocket or indirectly through another heat conducting member.

  For example, the first heat conducting member 124fa and the second heat conducting member 124fb are plate-like or sheet-like members each made of a material having thermal conductivity, and are stacked in the tray body. It is embedded in the resin that forms the bottom of 24a. Here, for example, the first heat conducting member 124fa is disposed at least on the bottom surface of each shim pocket 24d so as to directly contact the magnetic shim 24c when the magnetic shim 24c is stored in each shim pocket 24d. It is embedded so that a part is exposed. The range where the first heat conducting member 124fa is exposed at the bottom surface of the shim pocket 24d may be the entire bottom surface of the shim pocket 24d or a part of the bottom surface of the shim pocket 24d. The first heat conducting member 124fa is not directly in contact with the magnetic shim 24c, but is provided with a thermally conductive spacer inserted between the bottom surface of the shim pocket 24d and the magnetic shim 24c. The magnetic material shim 24c may be indirectly contacted. The second heat conducting member 124fb is embedded in close contact with the back surface of the first heat conducting member 124fa when the shim pocket 24d side of the first heat conducting member 124fa is the front side.

(Third embodiment)
FIG. 6 is a cross-sectional view illustrating a configuration example of a shim tray 224 according to the third embodiment. FIG. 6 shows a cross section passing through the bottom surface of the shim pocket 24 d in the shim tray 224. Note that the shim tray 224 according to this embodiment has substantially the same configuration as the shim tray 24 described in the first embodiment, but the shape of the heat conducting member is different from that of the first embodiment.

  As shown in FIG. 6, the shim tray 224 includes a heat conducting member 224f provided across a plurality of shim pockets 24d, similar to the shim tray 24 described in the first embodiment.

  Here, in this embodiment, at least one slit is formed in the heat conducting member 224f. The slit here is, for example, an elongated rectangular hole formed along the surface of the heat conducting member 224f, and is formed so as to penetrate from the front surface to the back surface of the heat conducting member 224f. As described above, when the heat conductive member 224f is formed of a conductive material, an induced current is generated when the gradient magnetic field is switched, which may cause eddy currents in the MRI apparatus 100. On the other hand, by providing a slit in the heat conducting member 224f, the flow of the organic current generated in the heat conducting member 224f can be divided, and the generation of eddy current can be suppressed. Further, heat generation of the heat conducting member 224f due to eddy current loss can be suppressed.

  For example, as shown in FIG. 6, two slits 224h along the longitudinal direction of the shim tray 224 are formed in the position of each shim pocket 24d in the heat conducting member 224f. For example, as shown in FIG. 6, two slits 224i along the short direction of the shim tray 224 are formed in the heat conducting member 224f at a position between adjacent shim pockets 24d. By forming the slits in this manner, for example, the eddy current divided for each position of the shim pocket 24d in the longitudinal direction of the shim tray 224 by the slit 224i formed between the shim pockets 24d is The slit 224h formed at the position of the shim pocket 24d is divided in the short direction of the shim tray 224.

  Note that the number, position, and shape of the slits formed in the heat conducting member 224f are not necessarily limited to those shown in FIG. The number, position, and shape of the slits are determined as appropriate so that the induced current generated in the heat conducting member 224f can be efficiently divided. Further, how eddy current is generated in the heat conducting member 224f varies depending on the position where the shim tray 224 is disposed. Therefore, for example, the number, position, and shape of the slits formed in the heat conducting member 224f may be determined according to the position where the shim tray 224 is disposed in the gradient coil 20.

(Fourth embodiment)
FIG. 7 is a cross-sectional view illustrating a configuration example of a shim tray 324 according to the fourth embodiment. FIG. 7 shows a cross section that passes through substantially the center of the shim tray 324 and is parallel to the longitudinal direction and the thickness direction of the shim tray 324. The shim tray 324 according to the present embodiment has substantially the same configuration as the shim tray 24 described in the first embodiment, but the position where the heat conducting member is arranged is different from that of the first embodiment.

  As shown in FIG. 7, the shim tray 324 includes an elongated box-shaped tray body 324a and a lid 324b, similar to the shim tray 24 described in the first embodiment. The shim tray 324 includes a heat conducting member 324f provided across the plurality of shim pockets 24d. The heat conducting member 324f directly contacts the magnetic material shim 24c accommodated in the different shim pockets 24d or indirectly through another heat conducting member to thermally couple the magnetic material shims. As a result, even when a specific magnetic shim 24c generates a large amount of heat, the heat is dispersed to other magnetic shims 24c via the heat conducting member 324f, and the temperature of each magnetic shim 24c is made uniform. Is done.

  Here, in the present embodiment, the heat conducting member 324f is provided on the lid 324b that covers the shim pocket 24d. In each shim pocket 24d, a spacer 324e having an appropriate thickness is disposed between the laminated magnetic body shim 24c and the lid 324b. The spacer 324e is positioned by pressing the magnetic shim 24c against the bottom of the shim pocket 324 when the lid 324b is fixed so that the magnetic shim 24c does not move in the shim pocket 24d.

  Here, in this embodiment, the spacer 324e is formed of a material having thermal conductivity. Thereby, the heat conducting member 324f provided on the lid 324b indirectly contacts the magnetic shim 24c stored in the shim pocket 24d via the spacer 324. Further, for example, by arranging a spacer having an appropriate thickness between the bottom surface of the shim pocket 24d and the magnetic material shim 24c, the heat conducting member 324f provided on the lid 324b and the magnetic material shim 24c are directly connected. You may make it contact.

  For example, the heat conductive member 324f is a material having a higher thermal conductivity than the material forming the shim tray 324, or the material forming the shim tray 324, like the heat conductive member 24f described in the first embodiment. It is made of a material having a larger heat capacity than

  Further, for example, the heat conduction member 324f is a first heat conduction made of a material having higher heat conductivity than the material forming the shim tray 324, similarly to the heat conduction member 124f described in the second embodiment. The member may be formed by bonding a second heat conductive member formed of a material having higher heat conductivity than the material forming the shim tray 324. In this case, the first heat conducting member and the second heat conducting member are embedded in the resin forming the lid body 324b in a state where the first heat conducting member and the second heat conducting member are laminated. Here, the first heat conducting member is embedded on the side of the lid 324b facing the tray main body 324a and the shim pocket 24d. The second heat conducting member is embedded in close contact with the back surface of the first heat conducting member when the shim pocket 24d side of the first heat conducting member is the front side.

  In addition, as in the third embodiment, at least one slit may be formed in the heat conducting member 324f.

  In the first to fourth embodiments described above, in the shim tray, the example in which the heat conduction member is provided on the bottom of the shim pocket or the lid has been described. However, the position where the heat conduction member is provided is not limited thereto. I can't. For example, the heat conducting member may be provided on a side portion along the longitudinal direction of the shim tray. In that case, at least a part of the heat conducting member is formed on the inner side surface of each shim pocket so that the magnetic shim is directly brought into contact with the shim pocket when the magnetic shim is stored in each shim pocket. Embedded to be exposed. In addition, the heat conducting member does not directly contact the magnetic shim, but indirectly through a spacer having thermal conductivity inserted between the inner side surface of the shim pocket and the magnetic shim. The magnetic material shim may be contacted.

  In the first to fourth embodiments described above, for example, the heat conducting member is made of a nonmagnetic material. As such a material, for example, copper or aluminum can be used. When the heat conducting member is formed of a magnetic material, it may cause the uniformity of the static magnetic field adjusted by the magnetic material shim. On the other hand, by forming the heat conducting member from a non-magnetic material, it is possible to prevent the heat conducting member from disturbing the uniformity of the static magnetic field.

  Moreover, in the 1st-4th embodiment mentioned above, a heat conductive member is formed with a nonelectroconductive material, for example. As such a material, for example, copper or aluminum can be used. Since the heat conducting member is provided in the gradient magnetic field coil together with the shim tray, if it is formed of a conductive material, an induced current is generated when the gradient magnetic field is switched, which may cause eddy currents in the MRI apparatus. On the other hand, by forming the heat conducting member from a non-conductive material, it is possible to prevent the heat conducting member from causing eddy current.

(Fifth embodiment)
FIG. 8 is a diagram showing a configuration of a shim tray 424 according to the fifth embodiment. FIG. 8 shows a cross section that passes through substantially the center of the shim tray 424 and is parallel to the longitudinal direction and the thickness direction of the shim tray 424. The shim tray 424 according to the present embodiment has substantially the same shape as the shim tray 24 described in the first embodiment. However, at least a part of the shim tray 424 has heat conductivity instead of having a heat conducting member. This is different from the first embodiment.

  As shown in FIG. 8, the shim tray 424 includes an elongated box-shaped tray body 424a and a lid 424b, similar to the shim tray 24 described in the first embodiment.

  Here, in this embodiment, the shim tray 424 is formed of a material having at least a part of the portion straddling the plurality of shim pockets 24d. For example, each of the tray main body 424a and the lid body 424b is formed of a material having thermal conductivity. For example, the tray body 424a and the lid body 424b are formed of a resin mixed with fine powder having thermal conductivity such as copper. As a result, even when a specific magnetic shim 24c generates a large amount of heat, the heat is dispersed to other magnetic shims 24c via the tray body 424a and the lid 424b, and the temperature of each magnetic shim 24c. Is made uniform.

  Further, for example, both the tray main body 424a and the lid 424b are not necessarily formed of a material having thermal conductivity, and any one of them may be formed of a material having thermal conductivity. In this case, for example, when the tray body 424a is formed of a material having thermal conductivity, the bottom surface of the shim pocket 24d and the magnetic material shim 24c are brought into direct contact. For example, when the lid 424b is formed of a material having thermal conductivity, a spacer having thermal conductivity is provided between the lid 424b and the magnetic shim 24c, as in the fourth embodiment. By inserting, the lid 424b is indirectly brought into contact with the magnetic shim 24c.

  In the first to fifth embodiments described above, the example in which the shim tray is an integrated one having a plurality of shim pockets formed continuously in the longitudinal direction has been described. Not limited. For example, the shim tray may be configured to be divided into a plurality of sub-trays each having one or a plurality of shim pockets. Each sub-tray is connected in the longitudinal direction and used as one shim tray.

  In this case, the heat conducting member is also divided for each sub-tray. That is, each sub-tray is configured to have a heat conducting member individually. And when each subtray is connected, the heat conductive member which each subtray has is connected between adjacent subtrays, and functions similarly to the heat conductive member demonstrated in 1st-5th embodiment.

  According to each embodiment mentioned above, since the magnetic body shim 24c accommodated in a different shim pocket is thermally coupled, the temperature of each magnetic body shim 24c is equalized. As a result, the temperature of the specific magnetic material shim 24c does not change, but the temperature of the entire heat-coupled magnetic material shim 24c is made uniform, which alleviates non-uniformity of the static magnetic field at a specific position. it can. Further, by thermally coupling the magnetic material shim 24c, even when the temperature of the specific magnetic material shim 24c generates heat, the heat is dispersed in the other magnetic material shims 24c. Temperature rise can be suppressed. Moreover, since the temperature change of the whole magnetic body shim 24c is suppressed by suppressing the temperature rise of the whole magnetic body shim 24c, the fluctuation | variation of the uniformity of a static magnetic field can be suppressed.

  According to at least one embodiment described above, it is possible to prevent the static magnetic field from becoming locally non-uniform due to a temperature change of the magnetic material shim.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 100 Magnetic Resonance Imaging (MRI) apparatus 10 Static magnetic field magnet 20 Gradient magnetic field coil 24 Shim tray

Claims (11)

A static magnetic field magnet that generates a static magnetic field in the imaging space where the subject is placed;
A gradient coil for generating a gradient magnetic field in the imaging space;
A shim tray having a plurality of shim pockets provided in the gradient magnetic field coil and capable of storing a magnetic shim for correcting non-uniformity of the static magnetic field;
The magnetic resonance imaging apparatus, wherein the shim tray thermally couples magnetic shims stored in different shim pockets among the plurality of shim pockets. The shim tray has a heat conducting member provided across the plurality of shim pockets,
The heat conducting member is in direct contact with the magnetic material shim accommodated in the different shim pockets or indirectly through another heat conducting member to thermally couple each magnetic material shim. Item 2. The magnetic resonance imaging apparatus according to Item 1.   The magnetic resonance imaging apparatus according to claim 2, wherein the heat conductive member is formed of a material having higher heat conductivity than a material forming the shim tray.   The magnetic resonance imaging apparatus according to claim 2, wherein the heat conducting member is formed of a material having a larger heat capacity than a material forming the shim tray. The heat conducting member is formed of a first heat conducting member made of a material having a higher thermal conductivity than the material forming the shim tray and a material having a larger heat capacity than the material forming the shim tray. Formed by joining the second heat conducting member,
The said 1st heat conductive member is provided in the position which contacts the magnetic body shim accommodated in the said different shim pocket directly or indirectly through another heat conductive member. The magnetic resonance imaging apparatus described.   The magnetic resonance imaging apparatus according to claim 2, wherein at least one slit is formed in the heat conducting member.   The magnetic resonance imaging apparatus according to claim 2, wherein the heat conducting member is provided at a bottom portion of the shim pocket.   The magnetic resonance imaging apparatus according to claim 2, wherein the heat conducting member is provided on a lid that covers the shim pocket.   The magnetic resonance imaging apparatus according to claim 2, wherein the heat conducting member is made of a nonmagnetic material.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the shim tray is formed of a material having thermal conductivity at least part of a portion straddling the plurality of shim pockets. A shim tray having a plurality of shim pockets capable of storing magnetic shims for correcting the non-uniformity of a static magnetic field in an imaging space where a subject is placed;
The gradient magnetic field coil, wherein the shim tray thermally couples magnetic shims stored in different shim pockets of the plurality of shim pockets.

Images