JP2014180446A - Gradient magnetic field coil unit and magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gradient magnetic field coil unit and a magnetic resonance imaging apparatus each improved in noise reduction.SOLUTION: The gradient magnetic field coil unit includes: a gradient magnetic field coil; and a cylindrical casing provided with an air column for reducing noise. The gradient magnetic field coil forms a gradient magnetic field in an imaging region. The casing houses the gradient magnetic field coil. The magnetic resonance imaging apparatus is provided with an imaging system and a control system. The imaging system includes the gradient magnetic field coil unit as a constitution element. The control system executes magnetic resonance imaging of a subject by controlling the imaging system.

Description

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

  The MRI apparatus magnetically excites a nuclear spin of a subject placed in a static magnetic field with a radio frequency (RF) signal of Larmor frequency, and generates nuclear magnetic resonance (NMR) generated by this excitation. This is an image diagnostic apparatus that reconstructs an image from a resonance signal.

  In the MRI apparatus, reduction of noise due to vibration of the gradient magnetic field coil is a problem. As a conventional method for quieting the gradient magnetic field coil, there is known a method in which the periphery of the gradient magnetic field coil is sealed to be in a vacuum state. Specifically, a space outside the gradient magnetic field coil formed between the inner cylindrical surface of the static magnetic field magnet and the outer cylindrical surface of the gradient magnetic field coil, and the inner cylindrical surface of the gradient magnetic field coil and the outer cylindrical surface of the bore tube The spaces inside the gradient coil formed between are sealed. And the air propagation sound can be interrupted | blocked and suppressed by making the space around the sealed gradient magnetic field coil into a vacuum state.

JP 2012-157893 A JP-A-10-118043

  It is an object of the present invention to provide a gradient magnetic field coil unit and a magnetic resonance imaging apparatus that can further reduce noise.

A gradient coil unit according to an embodiment of the present invention includes a gradient coil and a cylindrical casing provided with an air column for reducing noise. The gradient magnetic field coil forms a gradient magnetic field in the imaging region. The casing houses the gradient coil.
The magnetic resonance imaging apparatus according to the embodiment of the present invention includes an imaging system and a control system. The imaging system includes the gradient coil unit as a component. The control system executes magnetic resonance imaging of the subject by controlling the imaging system.

The block diagram of the gradient magnetic field coil unit and magnetic resonance imaging apparatus which concern on embodiment of this invention. The side view which shows the structural example of the gradient magnetic field coil unit shown in FIG. The figure which shows the positional relationship of the end surface member of the cylindrical member which forms the air column shown in FIG. 2, and the end surface member of a casing. The figure which shows the example which obstruct | occluded the air column shown in FIG. 2 with the plug. The figure which shows the example which divided | segmented the air column shown in FIG. 2 into several space with the plug. The figure which shows the example which made the cross-sectional area of the cross section of the air column shown in FIG. 1 correspond to the area of the adjacent obstruction | occlusion part. FIG. 3 is a developed sectional view of a casing showing an example in which the opening sides of a plurality of air columns shown in FIG. 2 are staggered. The side view of the gradient magnetic field coil unit which concerns on the 2nd Embodiment of this invention. FIG. 3 is a developed sectional view of a casing showing an example in which a plurality of air columns formed in the gradient coil unit shown in FIG. 2 are connected by a connecting pipe.

  A gradient magnetic field coil unit and a magnetic resonance imaging apparatus according to embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a configuration diagram of a gradient magnetic field coil unit and a magnetic resonance imaging apparatus according to an embodiment of the present invention, and FIG. 2 is a side view showing a structural example of the gradient magnetic field coil unit shown in FIG.

  The magnetic resonance imaging apparatus 1 includes an imaging system 2 and a control system 3. The imaging system 2 includes a static magnetic field magnet 4, a gradient magnetic field coil unit 5, a whole body coil (WBC) 6 and a local RF coil 7 as components. The cylindrical static magnetic field magnet 4, the gradient magnetic field coil unit 5, and the WBC 6 are incorporated in a gantry (mounting base) 8 in a state of being coaxially arranged. Further, a bore tube 9 that forms an imaging region R is provided between the gradient magnetic field coil unit 5 and the WBC 6.

  On the other hand, the local RF coil 7 is disposed at a position corresponding to the imaging region of the subject O. In the illustrated example, a local RF coil 7 for spine is provided on the top plate 11 of the bed 10 as an RF coil for reception. Further, as required, a desired transmission or transmission / reception RF coil such as a head coil can be provided.

  The control system 3 is a system for executing MR imaging of the subject O by controlling the imaging system 2. For that purpose, a gradient magnetic field power source for supplying current to the gradient coil unit 5, a transmitter for applying an RF signal to an RF coil for transmission such as WBC6, a receiver for receiving an MR signal from an RF coil for reception, and a pulse sequence The control system 3 includes components such as a sequencer that controls the control device according to the above and a computer that generates MR image data by image reconstruction processing for MR signals.

  The gradient magnetic field coil unit 5 is configured by housing the gradient magnetic field coil 12 in a hollow and cylindrical casing 13. In the illustrated example, a cylindrical shield coil 14 is further provided outside the cylindrical gradient coil 12. That is, the gradient magnetic field coil 12 and the shield coil 14 are accommodated in the casing 13. The gradient magnetic field coil 12 provided with the shield coil 14 is called an active shield gradient coil (ASGC). In ASGC, the gradient coil 12 is also referred to as a main coil. In addition, a cooling system or the like may be provided in the casing 13 in addition to the gradient magnetic field coil 12 and the shield coil 14.

  The gradient magnetic field coil 12 is a coil for forming a gradient magnetic field in the imaging region R. In the imaging region R, a coordinate system having an X axis, a Y axis, and a Z axis orthogonal to each other with the center of the static magnetic field as the origin is defined. Accordingly, the gradient magnetic field coil 12 is configured by overlapping a cylindrical X-axis coil, a Y-axis coil, and a Z-axis coil. The shield coil 14 is a coil that generates a magnetic field that cancels a leakage magnetic field from the gradient magnetic field coil 12 that is a main coil. Therefore, the uniformity of the static magnetic field in the imaging region R can be improved by driving the shield coil 14.

  The casing 13 is configured by closing the cylindrical outer cylinder member 15 constituting the outer wall of the gradient magnetic field coil unit 5 and the cylindrical inner cylinder member 16 constituting the inner wall with end face members 17 at both ends. Can do. Thereby, a cylindrical gap is formed in the casing 13.

  Furthermore, the casing 13 can be provided with a through hole 18 in the longitudinal direction. The through hole 18 can be formed using the cylindrical member 19. The cylindrical member 19 that forms the through-hole 18 is provided at a position that does not interfere with stored items in the casing 13 such as the gradient coil 12 and the shield coil 14. Therefore, in the illustrated example, a plurality of cylindrical members 19 and through holes 18 are provided between the gradient magnetic field coil 12 and the shield coil 14.

  A part of the through hole 18 can be used for installing the iron shim 20. The iron shim 20 can be stored in a nonmagnetic and nonconductive shim tray 21 and inserted into the through hole 18 of the casing 13. For example, if a plurality of block-shaped iron shims 20 are housed in a rectangular tube-shaped shim tray 21, the iron shims 20 can be easily installed. In addition, once the shim tray 21 inserted into the through hole 18 of the casing 13 is easily taken out, the number of iron shims 20 in the shim tray 21 can be increased or decreased.

  A part of the through hole 18 is also used as an air column 22 for reducing noise. Therefore, even if the shim tray 21 is inserted into the through hole 18, a gap is still formed inside the through hole 18. That is, the casing 13 has a structure in which the air column 22 is formed as a gap adjacent to the iron shim 20 installed in the through hole 18.

  In order to divide the through hole 18 into a region for installing the iron shim 20 and a region for the air column 22, as shown in the figure, a partition plate 23 having the radial direction of the gradient coil unit 5 as the thickness direction. May be provided in the through hole 18. In this case, it can be said that the gap for installing the iron shim 20 and the air column 22 are provided adjacent to each other in the radial direction of the gradient coil unit 5. However, an arbitrary structure can be adopted to fix the shim tray 21 in the through hole 18. For example, a fixing member such as an L-shaped metal fitting may be attached in the through hole 18 and the shim tray 21 may be fixed in the through hole 18 by the fixing member.

  When the gap for installing the iron shim 20 and the air column 22 are adjacent to each other in the radial direction of the gradient coil unit 5, the installation position of the iron shim 20 is set to the static magnetic field magnet 4 side, and the air column 22 is set to the bore side. It is desirable from the viewpoint of effectively exhibiting the action of the iron shim 20. That is, the structure of the casing 13 is preferably a structure in which the installation position of the iron shim 20 is the static magnetic field magnet 4 and the air column 22 is formed on the bore side.

  Among the through holes 18, the shape of the space for installing the iron shim 20 is matched with the shape of the shim tray 21. Therefore, if the cross section of the shim tray 21 is rectangular, the cross section of the gap for the iron shim 20 is also rectangular. On the other hand, the shape of the air column 22 is a shape suitable for reducing noise generated from the gradient coil unit 5.

  Noise generated from the gradient coil unit 5 is suppressed by the resonance phenomenon of the air column 22. Therefore, the resonance frequency of the air column 22 is adjusted so that the noise is sufficiently reduced. Specifically, a sound wave having a frequency equivalent to the frequency of the sound radiated from the gradient magnetic field coil unit 5 and having a phase opposite to the phase of the sound radiated from the gradient magnetic field coil unit 5 is generated by the air column 22. The resonance frequency of the air column 22 is adjusted to occur. Thereby, the noise of the specific frequency radiated | emitted from the casing 13 of the gradient magnetic field coil unit 5 can be canceled. That is, noise can be suppressed by interference of sound waves generated by air column vibration.

  As shown in the figure, when the air column 22 is provided as a part of the through hole 18, the open tube having both ends opened through the casing 13 in the longitudinal direction and the partition plate 23 as a part of the inner surface is the casing 13. Will be formed. That is, the casing 13 has an air column 22 that is open at both ends.

The resonance frequency fm of the open tube is expressed by the equation (1) as is well known.
fm = mv / (2L) (1)
In Equation (1), m is a natural number, v is the speed of sound, and L is the length of the air column 22. As shown in Expression (1), by appropriately determining the length L of the air column 22, the resonance frequency of the air column 22 can be matched with the frequency of the sound radiated from the gradient coil unit 5. Therefore, the position of the end portion of the cylindrical member 19 that forms the air column 22 does not necessarily need to match the position of the end surface member 17 of the casing 13.

  FIG. 3 is a diagram showing a positional relationship between one end of the cylindrical member 19 forming the air column 22 shown in FIG. 2 and the end surface member 17 of the casing 13.

  3A shows an example of a structure in which at least one end of the cylindrical member 19 forming the air column 22 protrudes from the end face of the casing 13 that houses the gradient coil 12, and FIG. FIG. 3C shows an example of a structure in which the position of at least one end of the cylindrical member 19 forming the column 22 is matched with the position of the end surface of the casing 13 that houses the gradient coil 12, and FIG. FIG. 3 is a diagram showing an example of a structure in which at least one end of a cylindrical member 19 is inside the end face of a casing 13 that houses a gradient magnetic field coil 12.

  As shown in FIG. 3A, one or both open ends of the cylindrical member 19 forming the air column 22 can be opened to the outside of the casing 13. In the example shown in FIG. 3 (A), the end of the cylindrical member 19 is inserted into the gap provided in the casing 13 so as to protrude. However, the cylindrical member 19 may be a part of the casing 13 by forming a protruding portion penetrating the end surface of the casing 13.

  Further, as shown in FIG. 3B, the position of one or both open ends of the cylindrical member 19 forming the air column 22 can be matched with the position of the end face of the casing 13. In the example shown in FIG. 3B, the cylindrical member 19 is a part of the casing 13. However, as in the example shown in FIG. 3A, a gap may be provided in the casing 13 and the cylindrical member 19 may be inserted as another member.

  Alternatively, as shown in FIG. 3C, one open end of the cylindrical member 19 forming the air column 22 can be disposed inside the casing 13. Of course, one open end of the cylindrical member 19 may be opened to the outside of the casing 13, and the other open end may be opened inside the casing 13.

  The shim tray 21 can be inserted into and removed from the cylindrical member 19 as long as at least one open end of the cylindrical member 19 communicates with the outside of the casing 13. For this reason, the length of the cylindrical member 19 can be adjusted flexibly.

  Further, in order to adjust the resonance frequency of the air column 22, the air column 22 can be closed with a plug 24 made of a non-magnetic material. That is, a plug 24 for adjusting the resonance frequency of the air column 22 by closing the air column 22 can be provided in the casing 13. When one open end of the air column 22 is closed with the plug 24, the air column 22 is closed.

The resonance frequency fn of the closed tube is expressed by equation (2) as is well known.
fn = (2n-1) v / (4L) (2)
In equation (1), n is a natural number, v is the speed of sound, and L is the length of the air column 22. Therefore, in the case of a closed tube as well as in the case of an open tube, by appropriately determining the length L of the air column 22, the resonance frequency of the air column 22 is set to the frequency of the sound radiated from the gradient magnetic field coil unit 5. Can be adapted to Of course, the closed end of the air column 22 can also be arranged inside and outside the casing 13 as shown in FIG.

  FIG. 4 is a view showing an example in which the air column 22 shown in FIG.

  As shown in FIG. 4A, the air column 22 can be closed by plugging one end of the air column 22 open at both ends with a plug 24. When the plug 24 is used, the length of the air column 22 can be changed without changing the length of the cylindrical member 19 itself constituting the air column 22. That is, as shown in FIG. 4B, the length of the air column 22 formed by the closed tube can be changed by adjusting the thickness of the plug 24 and the installation position of the plug 24 with respect to the tubular member 19.

  As a specific example, if the length of the air column 22 is 1200 mm by adjusting the position of the plug 24 packed in the air column 22 when the natural frequency of the gradient coil unit 5 is 500 Hz, The resonance frequencies in can be 72 Hz, 216 Hz, 360 Hz, 504 Hz,.

  As described above, the shim tray 21 can be put in and out as long as at least one end of the cylindrical member 19 is open. Therefore, one end of the cylindrical member 19 may be closed with the plug 24 so that one end of the air column 22 is covered. In other words, not only the through-hole 18 but also a hole having at least one end opened in the casing 13, and a part of the hole is used for installing the iron shim 20, while the remaining part of the hole is used for noise reduction. It can be used as the air column 22.

  Further, the casing 13 may be provided with a structure that partitions the air column 22 into a plurality of spaces by the plug 24. In this case, the cylindrical member 19 is a hole that opens at both ends but does not penetrate.

  FIG. 5 is a diagram showing an example in which the air column 22 shown in FIG. 2 is divided into a plurality of spaces by the plug 24.

  As shown in FIG. 5A, if one plug 24 is provided as a partition plate for the air column 22, two closed tubes and the air column 22 can be formed in the casing 13. Even in this case, the resonance frequency of each air column 22 can be easily adjusted by appropriately determining the thickness of the plug 24. On the other hand, by providing two plugs 24 as partition plates as shown in FIG. 5B, the lengths of the two closed tubes opened at both end faces of the casing 13 can be changed. As shown in FIGS. 5 (A) and 5 (B), the installation of the plug 24 can forcibly create a sonic node at the installation position of the plug 24.

  In this way, the length of the air column 22 is adjusted by the length of the cylindrical member 19 and the installation of the plug 24, and the resonance frequency of the air column 22 can be adjusted to the main frequency of noise generated from the gradient coil unit 5. it can. The frequency of noise generated from the gradient coil unit 5 can be actually measured at the time of installation or the like. Accordingly, for example, when the gradient coil unit 5 is installed on the gantry 8 or periodically inspected, the plug 24 is arranged so that the noise is actually generated and the plug 24 is disposed at a position where the generated noise is further reduced. The position of 24 may be changed. Note that the noise frequency can be estimated by simulation.

  Regarding the cross section of the air column 22 as well, it is desirable to appropriately determine the air propagation sound radiated from the air column 22 to be a sound wave that can satisfactorily cancel the noise. For example, it is appropriate that the cross section of the air column 22 has a certain cross-sectional shape such as a circle or a polygon. That is, it is desirable to form the same air column 22 in the casing 13 regardless of the position in the longitudinal direction in the cross-sectional shape at the position where it is not closed.

  Further, the air column 22 can be formed adjacent to the gap for installing the shim tray 21 as described above. The gaps for the shim tray 21 are typically provided at a plurality of positions at equal intervals on the circumference when viewed from the end face side of the casing 13 that houses the gradient coil 12. Therefore, it is effective to arrange the air column 22 at a plurality of positions in accordance with the position of the gap of the shim tray 21. That is, when viewed from the end face side of the casing 13 that houses the gradient magnetic field coil 12, it is preferable to arrange the plurality of air columns 22 at positions that are equidistant on the circumference. In this case, the plurality of air columns 22 are arranged at equal angles around the central axis of the gradient coil unit 5.

  Further, when both ends of each air column 22 are open, the gradient magnetic field coil 12 in which each area of the cross section of the plurality of air columns 22 becomes two closed surfaces adjacent to both sides of each air column 22 is provided. The casing 13 can be provided with a structure that is equivalent to one area of the end face for storage.

  FIG. 6 is a diagram showing an example in which the cross-sectional area of the cross section of the air column 22 shown in FIG.

  As shown in FIG. 6, an end face of the casing 13 that houses the gradient coil 12 exists between the adjacent air columns 22. Therefore, the area Sclose of the closed portion formed between the air columns 22 adjacent in the circumferential direction and the cross-sectional area Sopen of the air column 22 opened in the radial direction adjacent to the gap for insertion of the shim tray 21 are made equal. can do. As a result, the noise radiated from the end face of the casing 13 can be canceled by the radiated sound having the same intensity generated from the air column 22.

  As another example, the sides closing the air column 22 can be staggered so that the directions of the closed tubes adjacent on the circumference are opposite to each other.

  FIG. 7 is a sectional development view of the casing 13 showing an example in which the opening sides of the plurality of air columns 22 shown in FIG. 2 are staggered.

  In FIG. 7, the horizontal axis indicates the axial direction (Z-axis direction) of the gradient magnetic field coil unit 5, and the vertical axis linearly indicates the circumferential direction (C-axis direction) along the arrangement positions of the plurality of air columns 22. Is. As shown in FIG. 7, a plurality of closed tubes can be formed in the casing 13 by closing each end of the plurality of air columns 22 with a plug 24. Further, the casing 13 is formed with a structure in which the closed ends of the two adjacent air columns 22 are opposite to each other so that the phases of the air propagation sound radiated from the two adjacent air columns 22 are opposite to each other. Can do. That is, only one side of the plurality of air columns 22 is closed by the plug 24, and one of the two adjacent air columns 22 is closed by the plug 24 on the bed 10 side, and the other is closed by the plug 24 on the anti-bed side. be able to.

  When the air column 22 is configured in this way, when two adjacent air columns 22 resonate, antinodes and nodes of sound waves appear alternately. That is, the sound wave becomes a node on the inner surface of the plug 24, and the sound wave becomes an antinode at the end of the air column 22 on the side where the plug 24 is not attached. Accordingly, the phases of all the sound waves having an odd multiple of the fundamental frequency generated from the two adjacent air columns 22 are opposite to each other. That is, two adjacent air columns 22 generate a sound wave having a fundamental frequency opposite to each other, a sound wave having a triple frequency, a sound wave having a frequency of 5 times, and a sound wave having a frequency of 7 times or more.

  For this reason, the sound waves having phases opposite to each other cancel each other out by interference, and noise at the resonance frequency generated by the resonance of the air column 22 can be reduced. As a result, the diffracted sound synthesized at the end face of the gradient coil unit 5 can be reduced.

  In addition to the above, as a feature of the air column 22 other than the shape, a sound absorbing material may be provided on the surface of the casing 13 on which the air column 22 is formed. If a sound absorbing material is provided on the inner surface of the air column 22, noise radiated from the inner surface of the air column 22 can also be removed.

  Furthermore, a noise reduction technique by forming a vacuum region can be used in combination. In the example shown in FIG. 1, the space between the outer cylindrical member 15 of the gradient magnetic field coil unit 5 and the inner cylindrical member of the static magnetic field magnet 4 is sealed by two sealing members 25 such as ring-shaped packings. Similarly, the space between the inner cylindrical member 16 and the bore tube 9 of the gradient magnetic field coil unit 5 is sealed by two ring-shaped sealing members 26. And the outer surface side and inner surface side of the gradient magnetic field coil unit 5 are each made into a vacuum state. For this reason, the noise emitted from the outer surface and the inner surface of the gradient magnetic field coil unit 5 is suppressed by the vacuum mechanism, while the noise emitted from both ends of the gradient magnetic field coil unit 5 that is not sealed is the air column 22. Can be suppressed.

  Of course, the vacuum mechanism may be omitted, and noise generated from the gradient coil unit 5 by only the air column 22 may be suppressed. That is, the silent mechanism using the air column 22 can be used as an alternative mechanism of the silent mechanism using vacuum.

  That is, in the gradient magnetic field coil unit 5 and the magnetic resonance imaging apparatus 1 as described above, the air column 22 is provided in the casing 13 of the gradient magnetic field coil 12 so that the noise of the gradient magnetic field coil unit 5 is reduced by the resonance phenomenon of the air column 22. It is a thing.

  For this reason, according to the gradient magnetic field coil unit 5 and the magnetic resonance imaging apparatus 1, it is possible to reduce the diffracted sound into the bore generated from the end face of the gradient magnetic field coil unit 5. In particular, when a silent mechanism using a vacuum is provided in the gradient magnetic field coil unit 5, it is possible to reduce the noise generated from the both end surfaces without sealing the both end surfaces of the gradient magnetic field coil unit 5 to a vacuum state. Become.

  In other words, the adoption of the silent mechanism using the air column 22 makes it possible to open both ends of the gradient magnetic field coil unit 5 to the atmosphere without sealing the whole including both end faces. That is, only the outer surface side of the inner cylinder member 16 and the outer surface side of the outer cylinder member 15 of the gradient magnetic field coil unit 5 need to be in a vacuum state.

  When both ends of the gradient coil unit 5 are opened to the atmosphere, the diffracted sound from the end face of the gradient coil unit 5 into the bore becomes dominant with respect to the noise in the bore. Therefore, diffracted sound from the end face of the gradient coil unit 5 into the bore can be reduced by resonance of the air column 22. For this reason, noise can be suppressed without providing a large-scale and expensive vacuum mechanism. In addition, the installation workability of the gradient coil unit 5 including the vacuum mechanism can be improved.

  On the contrary, the silent technology using the air column 22 can be used as an alternative technology of the silent mechanism using vacuum. In this case, the structure of the gradient coil unit 5 can be simplified and the manufacturing cost can be reduced. In addition, workability can be improved compared to the case where a vacuum mechanism is provided.

  Moreover, in the silent technology using the air column 22, the frequency of noise to be suppressed can be flexibly adjusted. For this reason, it is possible to reduce noise having a low frequency of 1000 Hz or less, which is difficult to suppress with the sound absorbing material.

(Second Embodiment)
FIG. 8 is a side view of the gradient coil unit according to the second embodiment of the present invention.

  The second embodiment is different from the first embodiment in that the air column 22 is provided in the casing 13 of the gradient magnetic field coil unit 5A as an independent hole separately from the gap for inserting the shim tray 21. Since other configurations and operations are substantially the same, only the gradient coil unit 5A is illustrated, and the same components are denoted by the same reference numerals and description thereof is omitted.

  A plurality of holes for installing the iron shim 20 are provided in the casing 13 of the gradient coil unit 5A along the circumference. The casing 13 has a structure in which an air column 22 is formed as another hole between a plurality of holes for installing the iron shim 20. Also in this case, the desired air column 22 can be closed at a desired position by the plug 24 as in the first embodiment. Further, a silent mechanism using a vacuum may be used together, or a silent mechanism using a vacuum may be omitted.

  For this reason, according to the gradient magnetic field coil unit 5A in 2nd Embodiment, the effect similar to the gradient magnetic field coil unit 5 in 1st Embodiment can be acquired. In particular, in the gradient magnetic field coil unit 5A in the second embodiment, a place for providing the air column 22 can be easily secured when the casing 13 is thin.

(Other embodiments)
Although specific embodiments have been described above, the described embodiments are merely examples, and do not limit the scope of the invention. The novel methods and apparatus described herein can be implemented in a variety of other ways. Various omissions, substitutions, and changes can be made in the method and apparatus described herein without departing from the spirit of the invention. The appended claims and their equivalents include such various forms and modifications as are encompassed by the scope and spirit of the invention.

  For example, any air column 22 among a plurality of air columns 22 formed as holes in the casing 13 constituting the gradient coil units 5, 5A can be connected by a connecting pipe. Thereby, the length of the air column 22 can be made significantly longer than the length of the casing 13. In this case, the casing 13 is formed with a plurality of air columns 22 in which at least two air columns 22 are connected to each other by a connecting pipe.

  FIG. 9 is a cross-sectional development view of the casing 13 showing an example in which a plurality of air columns 22 formed in the gradient coil unit 5 shown in FIG.

  9, the horizontal axis indicates the axial direction (Z-axis direction) of the gradient magnetic field coil units 5 and 5A, and the vertical axis linearly indicates the circumferential direction (C-axis direction) along the arrangement position of the plurality of air columns 22. It is shown. As shown in FIG. 9, for example, the open ends of two adjacent air columns 22 can be connected to each other by a connecting pipe 30. In this case, a plurality of U-shaped air columns 22 that are open at both ends are formed in the casing 13. Also in this case, similarly to the example shown in FIG. 7, the connecting pipe 30 is placed on the bed 10 so that the opening side of the U-shaped air column 22 is opposite to each other between the adjacent U-shaped air columns 22. It can be provided alternately on the side and the counter bed side.

DESCRIPTION OF SYMBOLS 1 Magnetic resonance imaging apparatus 2 Imaging system 3 Control system 4 Static magnetic field magnet 5, 5A Gradient magnetic field coil unit 6 Whole body coil (WBC)
7 Local RF coil 8 Gantry (frame)
9 Bore tube 10 Bed 11 Top plate 12 Gradient magnetic field coil 13 Casing 14 Shield coil 15 Outer cylinder member 16 Inner cylinder member 17 End face member 18 Through hole 19 Cylindrical member 20 Iron shim 21 Shim tray 22 Air column 23 Partition plate 24 Plug 25 26 Sealing member 30 Connecting pipe R Imaging region O Subject

Claims (15)

A gradient coil for forming a gradient magnetic field in the imaging region;
A cylindrical casing that houses the gradient magnetic field coil and is provided with an air column for reducing noise;
A gradient magnetic field coil unit.   The gradient magnetic field coil unit according to claim 1, wherein the casing has a structure in which the air column is formed as another hole between a plurality of holes for installing an iron shim.   The gradient magnetic field coil unit according to claim 1, wherein the casing has a structure in which the air column is formed as a gap adjacent to an iron shim installed in a hole.   The gradient magnetic field coil unit according to claim 3, wherein the casing has a structure in which the installation position of the iron shim is on the magnet side and the air column is formed on the bore side.   The gradient magnetic field coil unit according to any one of claims 1 to 4, wherein the casing includes an air column having both ends open.   The gradient coil unit according to any one of claims 1 to 4, wherein the casing includes a plug for adjusting a resonance frequency of the air column by closing the air column.   The gradient magnetic field coil unit according to claim 6, wherein the casing has a structure in which the air column is partitioned into a plurality of spaces by the plug.   The casing has closed ends of the two air columns so that one end of each of the plurality of air columns is closed with the plug, and the phases of the air-propagating sounds radiated from the two adjacent air columns are opposite to each other. The gradient magnetic field coil unit according to claim 6, which has a structure in which the sides are opposite to each other.   The casing has a structure in which at least one end of a cylindrical member forming the air column protrudes from an end face that houses the gradient magnetic field coil or a structure that is inside the end face that houses the gradient coil. The gradient magnetic field coil unit of any one of thru | or 8.   The inclination according to any one of claims 1 to 9, wherein the casing has a plurality of the air columns at positions at equal intervals on a circumference when viewed from an end face side that houses the gradient magnetic field coil. Magnetic field coil unit.   11. The gradient magnetic field coil unit according to claim 1, wherein the casing has the same air column in a cross-sectional shape at a position where the casing is not closed regardless of a position in the longitudinal direction.   The gradient coil unit according to any one of claims 1 to 11, wherein a sound absorbing material is provided on a surface of the casing forming the air column.   The casing has a plurality of air columns, and each of the cross-sectional areas of the plurality of air columns has an end surface for storing the gradient magnetic field coils that are two closed surfaces adjacent to both sides of each air column. 6. The gradient coil unit according to claim 5, wherein the gradient coil unit has a structure equivalent to one area.   The gradient coil unit according to any one of claims 1 to 4, wherein the casing has a plurality of air columns in which at least two air columns are connected to each other by a connecting pipe. An imaging system including the gradient coil unit according to any one of claims 1 to 14 as a component;
A control system for performing magnetic resonance imaging of a subject by controlling the imaging system;
A magnetic resonance imaging apparatus comprising:

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