JP2004237125A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quiet magnetic resonance imaging apparatus suppressing the noise of a whole gantry to an extremely low level by extremely reducing solid-borne vibration from an inclined magnetic field coil and shutting off the air-borne vibration from the inclined magnetic field coil. <P>SOLUTION: This magnetic resonance imaging apparatus is provided with the gantry equipped with a magnet 21 for generating a static magnetic field in an imaging region, leg bodies 22 supporting the magnet 21 on a floor F, the inclined magnetic field coil 23 generating the inclined magnetic field in the imaging region, support bodies 40A and 40B holding the coil 23 in a mechanically non-connected or an approximately non-connected state with the magnet 21 and supporting the coil 24 at another position on the floor F and an anchor 561 rigidly connecting the support bodies 40A and 40B to the floor F. This apparatus is also provided with means 24, 25A, 25B and 50 holding, at least, a part of the inclined magnetic field coil 23 and the support bodies 40A and 40B in a vacuum space. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a magnetic resonance imaging (MRI) apparatus for medical diagnosis and a sound insulation method therefor, and more particularly, to a silent magnetic resonance imaging apparatus capable of significantly suppressing noise generated by driving a gradient magnetic field coil. And a sound insulation method thereof.

  A magnetic resonance imaging device for medical diagnosis is an imaging device based on the magnetic resonance phenomenon of nuclear spins in a subject, and is a non-invasive image of the subject in the absence of X-ray exposure unlike an X-ray device. Can be obtained. Therefore, its usefulness has been demonstrated in clinical settings in recent years.

  In general, a magnetic resonance imaging apparatus for obtaining an MR image includes a gantry for inserting and arranging a subject in a diagnostic space, and an apparatus main body cooperating with the gantry. The gantry is equipped with various types of equipment, such as a magnet such as a superconducting magnet that generates a static magnetic field in the diagnostic space, a gradient coil that generates a linear gradient magnetic field that is superimposed on the static magnetic field, and transmits a high-frequency signal. In addition, an RF coil for receiving the MR signal is indispensable. During imaging, the magnet, the gradient coil, and the RF coil are driven along a desired pulse sequence. That is, according to the pulse sequence, linear gradient magnetic fields in the x, y, and z-axis directions are superimposed on the subject placed in the static magnetic field, and the nuclear spins of the subject are magnetically excited by the high frequency signal of the Larmor frequency. You. A magnetic resonance (MR) signal generated by the excitation is detected, and a two-dimensional tomographic image of the subject is reconstructed based on the signal.

  In such magnetic resonance imaging, in recent years, the need for high-speed imaging to reduce the time required for imaging has become extremely high. In response to this, pulse sequences involving high-speed switching (high-speed inversion) of gradient magnetic field pulses, such as the high-speed EPI method, have been developed, and some have been successfully commercialized. When a gradient magnetic field pulse is generated, an electromagnetic force acts on the gradient magnetic field coil when the pulse rises or reverses. This electromagnetic force causes mechanical distortion in the coil unit, and starts from this, causing vibrations in the entire unit. Due to the vibration of the coil unit, there is a problem that air vibration is generated and noise is generated. In particular, when the gradient magnetic field pulse is reversed at a high speed, the vibration increases, so that the noise increases as the speed increases. This noise may give the subject (patient) lying in the diagnostic space of the gantry a great discomfort or anxiety.

For this reason, several proposals have conventionally been made to eliminate such noise. For example, as shown in Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4 (the above-described first to fourth conventional examples), the entire unit of the gradient magnetic field coil is sealed in a vacuum vessel, This is an attempt to cut off air or vibration or noise due to the vacuum space.
JP-A-59-174746 JP-A-63-246146 JP-A-3-268743 JP-A-6-189932

  However, the above-described conventional noise control method still has the following unsolved problems.

  That is, in the first to fourth conventional examples, the gradient magnetic field coil is simply sealed in a vacuum space, and the containers and covers forming the vacuum space are mechanically connected to the cover and housing of the static magnetic field magnet. In addition, the gradient magnetic field coil itself has a structure in which it is supported by containers and covers of static magnetic field magnets. For this reason, part of the vibration (noise) generated in the gradient magnetic field coil is cut off in the vacuum space, but another part of the vibration propagates to the static magnetic field magnet through the support of the gradient magnetic field coil. Therefore, there is a problem in that the static magnetic field magnet also vibrates due to the vibration generated by the gradient magnetic field coil, and the whole gantry becomes a vibration source, so as to generate a large noise. That is, the conventional measures for vacuum sealing are insufficient for noise suppression.

  The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and when driving a magnetic resonance imaging apparatus, vibration of solid propagation from a gradient magnetic field coil is significantly reduced, and the entire gantry is reduced. It is a first object of the present invention to satisfactorily suppress noise (vibration).

  In addition, the present invention significantly reduces the vibration of solid propagation from the gradient coil when driving the magnetic resonance imaging apparatus, and shuts off the vibration that propagates from the gradient coil to air, thereby reducing the noise (vibration) of the entire gantry. It is a second object of the present invention to provide a silent type magnetic resonance imaging apparatus that suppresses (1) to a very low level.

  In order to achieve the above-described object, the magnetic resonance imaging apparatus of the present invention includes, as one aspect thereof, a static magnetic field generating unit for generating a static magnetic field in an imaging region of a diagnostic space, and a static magnetic field generating unit. A static magnetic field supporting means for supporting at a position on the installation surface, a gradient magnetic field generating means for generating a gradient magnetic field in the imaging region, and the gradient magnetic field generating means is not mechanically coupled to the static magnetic field generating means. Or, a supporting means for a gradient magnetic field, which is maintained in a substantially non-coupled state and supports the gradient magnetic field generating means at a position different from the position on the installation surface, and rigidly couples the support means for the gradient magnetic field to the installation surface. And a gantry provided with a coupling means for reducing noise generated by driving the gradient magnetic field generation means.

  Among these, preferably, the static magnetic field generating means is constituted by a magnet, and the gradient magnetic field generating means is constituted by a gradient magnetic field coil having an x coil, a y coil and a z coil. For example, the coupling means is a stopper for rigidly coupling the support means to a rigid floor surface formed as the installation surface.

  According to the present invention, a means for maintaining the gradient magnetic field generating means and the static magnetic field generating means in a mechanically non-coupled or substantially non-coupled state and separately supporting the magnetic field generating means on the installation surface, The gantry configuration has a means for rigidly coupling the means to the installation surface, so that the vibration attenuation due to the mass effect of the installation surface such as the floor can be positively used, and solid propagation from the gradient magnetic field coil through the support means for the gradient magnetic field , The noise (vibration) of the gantry as a whole can be suppressed to a very low level and a silent magnetic resonance imaging apparatus can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First Embodiment)
A magnetic resonance imaging apparatus according to a first embodiment will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the magnetic resonance imaging apparatus includes a gantry 11 having a diagnostic space for inserting and arranging a patient for diagnosis, and a bed 12 arranged adjacent to the gantry 11. (See FIG. 2), and a control / processing unit 13 that controls the operations of the gantry 11 and the couch unit 12 and processes the MR reception signal. In addition, the gantry 11 has a structure formed in a central part of the inside thereof so as to penetrate a substantially cylindrical diagnostic space S for inserting and arranging a patient. The axial direction of the cylindrical diagnostic space S is defined as Z, and the X and Y directions orthogonal to the Z direction are defined as illustrated.

  The gantry 11 includes a static magnetic field magnet 21 that generates a static magnetic field in the diagnostic space S defined inside the gantry 11. The magnet 21 is composed of, for example, a superconducting magnet, and has a cylindrical shape having a bore 21br of a predetermined diameter. The magnet 21 is provided with a total of four legs 22... 22 integrally coupled to the outer peripheral surface of the magnet 21 on both sides in the center axis direction (Z-axis direction), and the legs 22. Supported above. The floor F is made of, for example, a concrete material having high rigidity.

  In the bore 21 br of the magnet 21, a structure is provided in which the gradient coil 23 is provided in a vacuum-sealed state. As shown in the drawing, this structure is formed of a non-magnetic material and an inner cylinder 24 having a predetermined length smaller than the bore 21br, and a magnet 21 and an inner cylinder 24 formed of a non-magnetic material at both ends in the Z-axis direction. And the vacuum lids 25A and 25B that close the space between them are configured as main elements.

  The inner cylinder 24 secures the diagnostic space S in the bore 21br of the magnet 21 and holds the RF coil 26 on the inner peripheral surface thereof, and is arranged coaxially with the magnet 21 in the bore 21br. The RF coil 26 uses a whole-body transmission coil here. As shown in FIG. 2, each of the vacuum lids 25A and 25B is a vacuum connecting the flange 30A (30B) to be attached to the side surface 21sd of the magnet 21 and the inner cylinder 24 and the flange 30A (30B) in order to improve the assemblability. And an end plate 31A (31B).

  Each of the flanges 30A and 30B has a base member 30bt integrally formed with a semi-torus-shaped upper portion and a substantially U-shaped lower portion having corners at both lower corners, and an outer peripheral end of the base member 30bt. It is formed by a side member 30sd that is integrally vertically raised, and has an approximately L-shaped cross section in the axial direction. Each of the flanges 30A and 30B has its inner peripheral surface (radial height along the XY plane) of the base member 30bt aligned with that of the inner peripheral surface 21in of the magnet 21 and is installed on the base member 30bt. The magnet 21 is fixed to a side surface 21sd of the magnet 21 via an O-ring 32 as a vacuum seal member by a stopper 33 such as a bolt. The side surface 21sd of the magnet 21 is formed perpendicular to the center axis (Z axis) of the magnet 21. By sliding the position of the base member 30bt in the vertical direction (Y-axis direction) or the horizontal direction (X-axis direction) along the side surface 21sd, the positions of the flanges 30A and 30B can be adjusted and fixed by the stopper 33 at that position. I can do it.

  Each of the vacuum end plates 31A and 31B is fixed to the end of the side member 30sd of the flange 30A (30B) and each end of the inner cylinder 24 by fasteners 34 and 35 such as bolts. O-rings 36 and 37 are interposed on the fixed contact surface as shown in the figure. Of these, the O-rings 36 individually inserted between the vacuum end plates 31A, 31B and the flanges 30A, 30B are capable of position adjustment in a direction orthogonal to the central axis (Z-axis) direction. With the above configuration, a closed space CS is defined in the bore 21br of the magnet 21 by using the inner cylinder 24, the vacuum lids 31A and 31B, and the inner peripheral surface 21in of the magnet 21 as defined bodies. The vertical or horizontal position of the inner cylinder 24 that defines a part of the closed space CS can be changed by finely adjusting the fixed position between the flanges 30A, 30B and the side surface 21sd of the magnet 21. Thereby, the center axis position of the diagnostic space S can be adjusted.

  In this closed space CS, the gradient magnetic field coil 23 is arranged in a state of not contacting the defined body. The gradient magnetic field coil 23 has an x-coil, a y-coil, and a z-coil as its windings, and is formed by laminating and impregnating them on a bobbin, and is formed in a cylindrical shape as a whole. The gradient coil 23 may be a non-shield type or a shield type.

  The gradient magnetic field coil 23 is supported on the floor F in the closed space CS by supports 40A and 40B as support means individually provided at both ends in the Z-axis direction. Each of the supports 40A and 40B includes a support member 41 for holding the gradient coil 23 at three points in the closed space CS, two rods 42 and 42 for supporting the support member 41, and the rods 42 and 42. And a base 43 for standing upright. Also, two beams 44, 44 for connecting the bases 43, 43 between both ends in the Z-axis direction are provided. The supports 40A and 40B are preferably formed of aluminum, stainless steel, or a metal obtained by mixing lead and / or brass with them to have high rigidity. Thereby, the vibration transmitted from the gradient magnetic field coil 23 to the supports 40A and 40B can be efficiently transmitted to the floor side.

  Among them, the support member 41 has a shape in which a square rod body is formed in a substantially U-shape. The three-point holding structure receives the position just below the gradient coil 23 at the receiving position.

  At each receiving position of the support member 41, the gradient magnetic field coil 23 is supported by a stopper 46 a (46 b, 46 c) of which the position can be adjusted by screwing in via an elastic member 45 a (45 b, 45 c) such as rubber. Has become. The first elastic member 45c interposed immediately below the gradient coil 23 is supported by a repulsive force, and the second elastic members 45a and 45b interposed directly beside the gradient coil 23 are supported by a repulsive force. The stoppers 46a and 46b that support the horizontal position of the gradient magnetic field coil 23 have the function of adjusting the horizontal position according to the degree of screwing, and the stoppers 46c that support the position directly below the upper and lower positions according to the degree of screwing. It also has the function of adjusting. For this reason, the horizontal and vertical positions of the gradient coil 23 can be adjusted by adjusting the degree of screwing of the stoppers 46a, 46b, 46c.

  Here, at both ends in the Z-axis direction, the first elastic member 45c and the stopper 46c, which are in the position directly below, support the load of the gradient coil 23. For this reason, the elastic constant of the first elastic member 45c immediately below is set to a value sufficiently larger than that of the second elastic members 45a and 45b located just beside. Therefore, the first elastic member 45c directly below reduces the vibration received from the gradient magnetic field coil 23 accompanying supporting the entire load, and reduces the vibration transmitted to the support 40A (40B) through the solid. Has become. Further, the second elastic members 45a and 45b at the sideways position have a sufficiently small elastic constant, so that solid vibration transmitted from the gradient coil 23 to the support 40A (40B) is surely reduced.

  In addition, the support position based on the combination of the first elastic member 45c and the stopper 46c which receives the full load of the gradient magnetic field coil 23 is not necessarily limited to the lowermost portion of the position directly below as shown in the drawing, but may be directly below the position. It may be a lower portion or both side portions appropriately near the position. When such a support position is set to a position in the lateral direction (both side directions) from the position directly below, the gradient magnetic field coil 23 is supported by a shearing force corresponding to the degree of deviation from the position directly below, so that the first elasticity is obtained. It is desirable to adjust the elastic constant of the member 45c accordingly.

  Further, the two rods 42 and 43 have a function of supporting the support member 41 in the vertical direction (Y-axis direction) at predetermined positions on both ends in the lateral direction (X-axis direction). The upper ends of the rods 42, 42 are inserted into holes 41 hl provided in the support member 41 and are fixed with hexagon nuts 47. The hole 41hl provided in the support member 41 is a so-called "dumb hole", and the horizontal and vertical positions can be adjusted by adjusting the height and position when tightening with the hexagon nut 47. This is set for adjusting the position of the gradient coil 23 in the horizontal and vertical directions. The lower ends of the rods 42, 42 extend downward by loosely inserting holes h, h provided below the side members 30sd of the flanges 30A, 30B, and the lower ends thereof are rigidly connected to the base 43 by screwing. .

  The space between the base 43 and the holes h, h of the side member 30sd is hermetically sealed by vacuum bellows 50, 50 as vacuum members having low rigidity. The vacuum bellows 50, 50 and the rods 43, 43 are arranged in a non-contact state. Thus, the closed space CS described above does not communicate with the outside world through the holes h, h, and becomes a completely closed space. The vacuum bellows 50, 50 are made of a member having a small rigidity in order to have a function of suppressing the vibration that goes from the supports 40A, 40B to the vacuum lids 30A, 30B in addition to the sealing function. The vacuum bellows 50 may be replaced with a rubber bellows and a rubber cover.

  As shown in FIG. 2, each of the bases 43 has a step at both ends in the X-axis direction. At the position of this step, each base 43 is rigidly connected to the floor F by anchors 51. are doing. The anchors 51... 51 constitute coupling means for rigidly coupling the support means of the present invention to the installation surface (floor surface). The coupling means typified by the anchors 51... 51 attenuates the vibration propagated from the gradient magnetic field coil 23 via the supports 40A and 40B by utilizing the mass of the floor F which is sufficiently heavier than the gradient magnetic field coil 23 ( (Absorption).

  The beams 44 are connecting members of a predetermined length formed of a highly rigid material such as a metal. Each beam 44 is placed on the floor F surface, and both bases 43, 43 are rigidly connected in the Z-axis direction at both ends in the X-axis direction of the bases 43, 43. Thus, the distance between the two bases 43 in the Z-axis direction can be defined as a set value.

  On the other hand, as shown in FIG. 1, an exhaust means for exhausting air in the closed space CS containing the gradient coil 23 is connected to one vacuum lid 25A. The exhaust means includes a vacuum-resistant hose 55 connected to a predetermined position of the side member 30sd of the flange 30A, and a rotary-type vacuum pump 56 connected to the hose 55, for example. Accordingly, the vacuum pump 56 is driven to obtain a vacuum state of the closed space CS of, for example, about 1.01 × 103 to 102 Ps.

  Further, as shown in FIG. 2, a mechanism for supplying power to the gradient magnetic field coil 23 and supplying a cooling medium is provided via a vacuum lid 26B of the gantry 11 on the side opposite to the bed 12. The vacuum lid 26B includes the flange 30B and the vacuum end plate 31B as described above. At a predetermined position of the side member 30sd of the flange 30B, as shown in the figure, a vacuum-resistant vibration insulating terminal 60 for preventing a discharge phenomenon is hermetically attached, and an external power supply line 61 and an internal power supply line 62 are connected via the terminal 60. Are connected to each other. The terminal 60 functions as a relay that relays power from a non-vacuum room to the vacuum space CS. The external power supply line 61 is connected to a gradient magnetic field power supply (not shown) provided in the control / processing unit 13. The internal power supply line 62 is disposed in a closed space CS, that is, a vacuum space, is connected to the winding of the gradient magnetic field coil 23, and supplies a pulse voltage of, for example, about ± 2000 V supplied through the external power supply line 61 to the winding. It has become. The internal power supply line 62 is also made of a flexible, vacuum-resistant wire that can be easily bent in order to reduce solid propagation of vibration from the gradient coil 23.

  As shown, a vacuum-resistant two-port coupler 64 is hermetically attached to another predetermined position of the side member 30sd of the flange 30B. The coupler 64 functions as a relay body that allows a cooling medium (for example, water) for cooling the gradient coil 23 to flow between the room and the vacuum space CS. Two outer tubes 65, 65 and two inner tubes 66, 66 are connected via a coupler 64 for each traffic path. The outer tubes 65 are connected to a cooling medium supply source such as a faucet. Flexible vacuum-resistant tubes are used for the inner tubes 66, 66, so that solid propagation of vibration from the gradient coil 23 can be reliably reduced.

  The other end of each of the inner tubes 66 is connected to an inlet and an outlet of a cooling tube (not shown) spirally wound, for example, inside the gradient coil 23. For this reason, the cooling medium supplied via one outer tube 65 reaches the cooling tube from one inner tube 66, circulates through the cooling tube, and again passes through the other inner tube 66 and the other outer tube 65. It is returned to the cooling medium supply. Thus, the heat generated by driving the gradient coil 23 is forcibly removed.

  Furthermore, a bed 12 is provided for inserting and arranging a patient in the diagnostic opening S of the gantry 11. The couch section 12 has a couch 67 placed at a position facing the diagnostic space S as shown in FIG. The bed 67 has a top 67t that can slide in the Z-axis direction, and the patient lies on his / her back on the top 67t. When the top 67t slides, it gradually enters the diagnostic space S. In the present embodiment, a top rail 68 is provided to support the entering top 67t in a sliding state. As shown, the top plate rail 68 is formed of a substantially U-shaped plate having a predetermined width and formed of a non-magnetic material. The slide portion of the top plate rail 68 is inserted into the diagnostic space S, and is fixed on the floor F without contact with the inner cylinder 24 and the vacuum lids 25A and 25B. That is, the top plate rail 68 is mechanically separated and installed independently of the gantry 11, and has a structure in which the sliding portion of the horizontal portion guides and supports the rollers of the top plate 67t. In the case of the conventional apparatus, such a top rail is fixed to a part of the diagnostic opening.

  Further, as shown in FIG. 1, the control / processing unit 13 includes a console provided with an input device and a display, a control cabinet as a control center, a gradient magnetic field power supply under the control of the control cabinet, a high frequency amplifier, a reception amplifier, A static magnetic field power supply is provided. Thus, the gantry 11 is driven to acquire an MR signal in accordance with a desired pulse sequence.

  An iron shim or a shim coil for shimming a static magnetic field can be provided at a desired position of the gantry structure shown in FIGS. 1 and 2 if necessary.

  Next, the function and effect of the first embodiment will be described.

  First, the vacuum pump 56 is operated to evacuate the closed space CS surrounding the gradient magnetic field coil 23, and a vacuum state of a predetermined value is created in the closed space CS. Further, a current is supplied to the magnet 21 from the static magnetic field power supply, and a static magnetic field is generated in the diagnostic space S including the imaging region. In this state, the subject lying on the top 67t is inserted into the diagnostic space S. At this time, the top plate 67t is guided and supported by the top plate rail 68 unique to this embodiment. Next, if necessary, a shimming process is performed, and after a necessary preparation such as installation of a receiving coil and positioning on a slice surface is performed, diagnosis is started. That is, a control command is issued from the control / processing unit 13 to each element of the gantry according to a desired pulse sequence, and an MR signal from the subject is received. Image data is reconstructed based on the MR signal.

  In the drive state based on this pulse sequence, a pulse current that rises and falls sharply is supplied to the gradient coil 23. In particular, when the pulse sequence is a sequence for high-speed imaging, the polarity of the pulse current is reversed at high speed. Since the gradient magnetic field coil 23 is placed in a static magnetic field, an electromagnetic force is generated each time a pulse current that changes at a high speed flows through the gradient magnetic field coil 23, and mechanical bending, that is, vibration occurs due to the electromagnetic force. Since the magnitude of the electromagnetic force varies in a complicated manner depending on the positions of the x coil, the y coil, the z coil, etc., the gradient magnetic field coil 23 normally vibrates in a complicated mode.

  Even if the gradient magnetic field coil 23 vibrates, in the case of the present embodiment, since the gradient magnetic field coil 23 is placed in the vacuum space, the air around it does not vibrate. That is, the air propagation of the vibration as indicated by the arrow A1 in FIG. 3 is reliably eliminated / suppressed, and the vibration transmitted to the outside is significantly reduced.

  On the other hand, the vibration of the gradient magnetic field coil 23 propagates through the supports 40A and 40B, and tends to leak to the outside. However, since various vibration absorbing or suppressing measures are taken as described above for this solid propagation as well, the leaked vibration is extremely small.

  First, vibrations are absorbed as much as possible by the elastic members 45a, 45b, 45c at both ends in the Z-axis direction which support the gradient magnetic field coil 23 from directly beneath and directly below, and the transmission of vibrations to the supports 40A, 40B is suppressed. . Vibrations not removed by these elastic members propagate to the supports 40A and 40B.

  Once the vibration propagates to the supports 40A, 40B, it is actively guided downward by the rigidly connected support member 41, rod 42 and base 43 (see arrow A2 in FIG. 3). Most of the vibrations guided as described above are transmitted to the floor F because the base 43 is rigidly connected to the floor F by the anchors 51. Since the mass of the floor F is very large, the vibration is reliably damped by the mass effect of the floor.

  When vibration passes through the supports 40A and 40B, there is also a route indicated by an arrow A3 in FIG. 3 as a vibration transmission path. However, in the present embodiment, since the vacuum bellows 50 is used as a member that connects the supports 40A and 40B and the vacuum lids 25A and 25B to maintain the closed space CS in a vacuum state, vibration transmitted to the vacuum lids 25A and 25B is not generated. Significantly reduced. For this reason, even if the supports 40A and 40B vibrate, the vibration is hardly transmitted to the inner cylinder 24 and the portion connected to the inner cylinder 24, or at least the static magnetic field magnet 21. That is, a portion that vibrates in response to the vibration of the supports 40A and 40B is almost eliminated.

  Further, except for a part of the base 43, almost all outer surfaces of the supports 40A and 40B are surrounded by a vacuum space (closed space CS). For this reason, similarly to the above-described gradient coil 23, the amount of vibration that propagates through the air and leaks to the outside is very small.

Thus, according to the gantry configuration of the present embodiment,
(1) In particular, air propagation (that is, noise) of vibrations generated in the gradient magnetic field coil itself and the supports 40A and 40B, which have large vibrations, is largely cut off by generating a vacuum space.
(2) Such vibrations are eliminated as much as possible by an elastic member interposed between the supports 40 and 40B and the gradient magnetic field coil 23,
(3) The remaining vibration is positively released to the floor F via the supports 40 and 40B and is attenuated by the mass effect of the floor to reduce noise, and
(4) The magnet is supported by individual support of the gradient magnetic field coil 23, the magnet 21, and the top rail 68, flexibility of the power supply line and the cooling tube, and suppression of vibration by the floor F and the vacuum bellows 50. Almost all of the vibration transmitted to the top rail and the top rail can be eliminated, and the vibration object can be reduced to reduce noise. At this time, there is also an effect of reducing vibration in the middle of the fixed propagation path that is routed farther to the floor side. Therefore, even in the same driving state, a high-speed pulse sequence is used as compared with various gantry configurations described in the related art and a gantry configuration in which the gradient coil and the static magnetic field magnet are simply mechanically separately supported. However, vibration and noise caused by the vibration of the gradient magnetic field coil itself can be significantly reduced, and anxiety and discomfort given to the patient due to the noise (vibration) can be satisfactorily eliminated.

  In addition, in the case of the gantry configuration of the present embodiment, as described above, the functions of adjusting the center axis position of the diagnostic space S and adjusting the position of the gradient magnetic field coil 23 are interposed everywhere as described above. There is also an advantage that it becomes easier.

  In the present invention, in the gantry configuration described above, a vacuum space is not created around the gradient magnetic field coil and the support, but the magnet 21 and the gradient magnetic field coil 24 are separately supported as described above, and the support 40A, It is possible to adopt a structure in which 40B is rigidly connected to the floor F with the anchors 51... 51, which also makes it possible to reduce the mass effect of the floor compared with a conventional structure in which the magnet and the gradient coil are only separately supported. As a result, the overall noise can be reduced.

  In the above-described gantry configuration, an elastic body may be interposed between the base 43 and the floor F so as to further absorb the vibration propagating through the fixed body. In this case, the anchors 51,..., 51 may be used, or may not be used in some cases. Even if the anchors 51,..., 51 are not used, the fixed propagation path from the gradient magnetic field coil 23 to the magnet 21, the inner cylinder 24, etc., is detoured to the floor side via the supports 40A, 40B, so that it is longer. Therefore, the vibration transmitted to the magnet 21 and the inner cylinder 24 becomes dull, and the noise (vibration) can be similarly reduced by the damping effect in the middle.

  Further, in the above-described configuration, the mounting position of the power line terminal and / or the cooling tube coupler as the relay may be air-tightly mounted on a part of the support, for example, the base, instead of the above-described vacuum lid. Good. In this case, the power supply line and the cooling tube form, for example, a routing path extending to the gradient coil through the base, the rod, and the support member.

  Further, as a cooling structure for cooling the gradient magnetic field coil 23, for example, as shown in Japanese Patent Application Laid-Open No. 6-189932, a number of cooling pipes are arranged in parallel, spirally wound and solidified with a resin to form a cylinder. It may be.

(Second embodiment)
A magnetic resonance imaging apparatus according to a second embodiment will be described with reference to FIGS. In the following description, the same or similar components as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. (The same applies to embodiments described later.)
The magnetic resonance imaging apparatus of the present embodiment aims to achieve a remarkable noise reduction as compared with the related art and to simplify the configuration required for the noise reduction as much as possible.

  4 and 5 show the configuration of only the gantry 11 of the magnetic resonance imaging apparatus. This gantry 11 is formed substantially in the same manner as that of the first embodiment, but differs in the configuration of the vacuum lid.

  The gantry 11 has vacuum lids 70A and 70B at both ends in the Z-axis direction for sealing the space between the inner cylinder 24 and the static magnetic field magnet 21. Each of the vacuum lids 70A and 70B includes a flange 71A (71B) and a vacuum end plate 72A (72A), similarly to the first embodiment. Each of the flanges 71A and 71B further includes a base member 71bt and a side member 71sd integrally formed in an L-shaped axial cross section. The base member 71bt is airtightly attached to the side surface 21sd of the magnet 21, and the side member 71sd is It is airtightly coupled to the vacuum end plate 72A (72B).

  The vacuum end plate 72A (72B), the base member 71bt, and the side member 71sd are formed longer in the hem direction (vertical Y-axis direction) than the members of the first embodiment, and their ends are bent or bent inward. End portions are provided, and the end portions are air-tightly fixed on the base 43 by inserting a vacuum seal member therebetween. Thus, the closed space CS including the portion above the base 43 of each of the supports 40A and 40B and the gradient coil 24 can be sealed. In the case of the present embodiment, the vacuum bellows used for connecting the vacuum lid and the support used in the first embodiment becomes unnecessary.

  Other configurations are the same as or equivalent to the device of the first embodiment.

  For this reason, although vibrations propagated through the solids from the supports 40A, 40B to the vacuum lids 70A, 70B remain, the vibrations are absorbed by the elastic members of the supports 40A, 40B, and are rigidly connected to the floor F of the supports 40A, 40B. The absorption due to the mass effect of the accompanying floor is greatly effective. Thereby, the vibration-producing portions, such as the gradient magnetic field coil 23 and the supports 40A and 40B, having particularly large vibrations are preferentially damped, so that the noise caused by the vibration of the gradient magnetic field coil 23 is significantly reduced as compared with the related art. The structure can be simplified by omitting the vacuum bellows.

(Modification 1)
A modification of the second embodiment will be described with reference to FIGS. The gantry of the magnetic resonance imaging apparatus according to this modification is such that the support means for the gradient magnetic field coil and the static magnetic field magnet are formed in common.

  As shown in FIGS. 6 and 7, a support 40A for supporting the gradient magnetic field coil 23 is provided (the same support is provided at the opposite end in the Z-axis direction). The support 40A is mounted on two rails 75, 75 via elastic bodies 74, 74 individually. The two rail bodies 75 are fixed on the floor F. At this time, it is desirable that the rail bodies 75 are rigidly connected to the floor F. These two rail bodies 75, 75 also support the static magnetic field magnet 21 at the same time.

  The opening between the inner cylinder 24 and the inner peripheral surface 21in of the magnet 21 is hermetically sealed using a vacuum lid 76 having a substantially U-shaped cross section in the axial direction and with vacuum sealing members 77 and 78 interposed therebetween. I have. The above-described vacuum bellows 50 are mounted in a gap between the vacuum lid 76 and the base 43 of the support 40A.

  With this configuration, the solid propagation path of the vibration from the gradient magnetic field coil 23 to the magnet 21 is once turned to the floor side by the insertion of the support body 40A, so that it is far more detoured than before. Therefore, not only the sound insulation effect of the vacuum space CS but also the vibration damping effect due to the detour of the solid propagation path is added, so that the noise can be significantly reduced as compared with the related art. In the case of the conventional device in which the gradient magnetic field coil is supported on the inner peripheral surface or side surface of the static magnetic field magnet, since the gradient magnetic field coil 23 is connected to the magnet 21 through an extremely short path, the vibration of the gradient magnetic field coil is almost directly applied to the magnet. There is a disadvantage that the vibration is transmitted and the vibration of the magnet is also added to the noise source. However, even with a gantry having a relatively simple supporting structure, it is possible to provide a silent magnetic resonance imaging apparatus that eliminates such inconveniences. When the rail body is rigidly connected to the floor F, as described above, the vibration damping due to the mass effect of the floor also acts, thereby further improving the quietness.

  The same effect as described above can be obtained by the configuration in which the elastic body 74 is interposed between the rail body 75 and the floor F.

(Third embodiment)
A magnetic resonance imaging apparatus according to a third embodiment will be described with reference to FIGS.

  The magnetic resonance imaging apparatus according to the present embodiment aims to obtain a further noise reduction effect than that of the first embodiment. In order to achieve this object, the gantry 11 shown in FIGS. 8 and 9 has another noise reduction mechanism added to that of the first embodiment.

  The main body of the gantry 11 is configured the same as in FIGS. In addition, at both ends in the Z-axis direction, a sound absorbing material (sound insulating material) 80 is attached to the entire outside of the base 43 of the vacuum lid 25A (25B) and the support 40A (40B). As the sound absorbing material, for example, a urethane material, a sponge material, or the like is used. The thickness is also appropriately selected. Therefore, the portions of the vacuum lids 25A, 25B, the vacuum bellows 50,... 50, and the bases 43, 43 exposed to the atmosphere are completely covered with the sound absorbing material 80. Therefore, noise (vibration) slightly leaking to the outside through these exposed portions is reliably absorbed.

  In the floor F, a groove 81 is formed at a predetermined depth to separate the grounded portions of the supports 40A and 40B and the grounded portion of the static magnetic field magnet 21. For this reason, both grounding portions are separated in distance, and the path length between them becomes more detour as shown by arrow A4 in the figure. Therefore, the vibration propagates through the supports 40A and 40B through the solid and propagates to the floor F. The vibration is absorbed by the mass effect of the floor F, and even if there is a vibration component that cannot be completely absorbed, the vibration component propagates farther. It is transmitted to the magnet 21 only through the path A4. While passing through the distant propagation path A4, the vibration is further attenuated, and eventually, most of the vibration is absorbed by the floor F and is not transmitted to the magnet 21.

  As described above, in addition to the configuration of the first embodiment, a mechanism for suppressing vibration propagation to the atmosphere and vibration propagation to the static magnetic field magnet more finely is provided. In the case of the first embodiment as well, it can be suppressed more reliably.

  Note that the attachment of the sound absorbing material and the formation of the floor groove can be favorably performed also on the gantry of the second embodiment (FIGS. 4 and 5).

  Also, a sound absorbing material or an elastic body for absorbing vibration may be embedded in the groove formed in the floor without leaving the air as described above. Further, the entire portion of the floor where the static magnetic field magnets are installed may be configured as a vibration-isolating floor independent of that of the support.

(Fourth embodiment)
A magnetic resonance imaging apparatus according to a fourth embodiment will be described with reference to FIG.

  As shown in the figure, the gantry 11 of this magnetic resonance imaging apparatus extends a skirt portion of a vacuum lid 70A composed of a flange and a vacuum end plate, and extends the extended end portion around a lower end side portion of a base 43 of a support 40A. It is airtightly bound. This is the same for the vacuum lids at both ends in the Z-axis direction.

  As a result, the closed space CS evacuated to vacuum includes not only the gradient coil 23 but also all of the supports 40A and 40B at both ends. Accordingly, it is not necessary to use the above-described vacuum bellows or the like, and the entire portion that vibrates most can be accommodated in the vacuum space, and a large sound insulation effect can be obtained. At the same time, a vibration absorption effect in which the support is rigidly connected to the floor can be obtained, and a magnetic resonance imaging apparatus excellent in quietness can be provided.

(Fifth embodiment)
A magnetic resonance imaging apparatus according to a fifth embodiment will be described with reference to FIG. In the present embodiment, particularly, the above-described coupling mechanism between the vacuum lid and the inner cylinder is further enhanced. FIG. 11 shows only such a coupling mechanism at one end of the gantry in the Z-axis direction.

  As shown in FIG. 11, the gantry of the magnetic resonance imaging apparatus according to the present embodiment includes a vacuum lid 90 that seals a gap between the inner peripheral surface 21in of the static magnetic field magnet 21 and the inner cylinder 24. The vacuum lid 90 has a flange 91 and a vacuum end plate 92. The flange 91 is composed of a base member 91bt that is air-tightly attached to the side surface 21sd of the magnet 21 and a side member 91sd integrated with the base member 91, and has an L-shaped cross section in the Z-axis direction. The base member 91bt is airtightly attached to the side surface 21sd by the stopper 94 with the vacuum seal member 93 interposed.

  A step portion 91dn is formed integrally with a tip portion of the side member 91sd. The outer peripheral end of the vacuum end plate 92 is airtightly attached to the step portion 91dn by a stopper 96 with a vacuum seal member 95 interposed therebetween. The inner peripheral end of the vacuum end plate 92 is in contact with the end taper 24tp of the inner cylinder 24 via a vacuum seal member 97 having a relatively small elastic constant, and is fastened by a stopper 98. This fastening is mainly performed by sealing with a vacuum seal member 97, and the weight support of the inner cylinder 24 is left to a support mechanism described later. The vacuum seal member 97 used for the end taper 24tp can cooperate with the tapered surface of the vacuum end plate 92 even when the vacuum end plate 92 moves within a predetermined range in the Z-axis direction to absorb the movement and seal. have. As a result, even when the length of the magnet 21 in the direction of the central axis (Z axis) varies during manufacturing, a good sealing effect can be obtained regardless of the variation.

  Further, a plate-shaped locking portion 99 is protruded near the end taper 24tp of the inner cylinder 24. The locking portion 99 and the step portion 91dn are opposed to each other, and an inner cylinder suspension mechanism 100 capable of adjusting the position in the vertical direction (Y-axis direction) is provided between the locking portion 99 and the step portion 91dn. The inner cylinder suspension mechanism 100 includes an upper suspension body 100a having one end attached to the stepped portion 91dn and capable of adjusting the vertical position by rotation, and a torus having the other end of the upper suspension body 100a penetrated and locked. Elastic member 100b, a lower suspension 100c having one end locked to the outer peripheral side of the elastic member 100b, and a connector 100d for connecting the other end of the lower suspension 100c to the locking portion 99. And

  For this reason, the elastic member 100b supports almost the entire weight of the inner cylinder 24 from the vacuum lid 90, that is, the magnet 21, by the shearing force. At this time, since the elastic member 100b is interposed, the solid vibration transmitted from the magnet 21 to the inner cylinder 24 can be reduced. Further, since most of the weight of the inner cylinder 24 is supported by the inner cylinder suspending mechanism 100, the elastic constant of the vacuum seal member 97 can be reduced as described above. The fixed propagation of the vibration reaching the cylinder 24 can be reduced. Further, in the case of such a configuration, the elastic constant of the elastic member 100b for supporting the inner cylinder may be a value sufficiently smaller than that of the above-mentioned first elastic member 45c which receives the weight of the gradient magnetic field coil of FIG. That is, very little solid-borne vibration through the inner cylinder suspension mechanism 100 is required.

  As described above, since the vibration is not transmitted from the magnet 21 to the inner cylinder 24 as much as possible, not only the vibration coming around due to the vibration of the gradient magnetic field coil 23 but also the vibration originating from the driving of the magnet 21 itself. Is also reliably suppressed. Therefore, the vibration of the inner cylinder 24 that is exposed because the sound absorbing material or the like is structurally difficult to apply can be suppressed, and the generation of noise can be prevented.

(Modification 2)
A modification will be described with reference to FIG. FIG. 3 shows an example of drawing a power supply line into the gradient coil 23. A relay terminal 110 having vibration insulation and vacuum resistance is attached to a flange 30B of the vacuum lid 25B by interposing a flexible elastic material 110a. The power supply line 111 is drawn into the vacuum space CS via the relay terminal 110. The power supply line 111 has a structure of an inner electric wire 111a in which at least a bendable core wire (for example, a mesh conductor) is covered with an electrical insulating material in the vacuum space CS.

  Since the inner wire 111a is connected to the gradient coil 23, the vibration that propagates from the gradient coil 23 to the vacuum lid 25B via the inner wire 111a is greatly reduced. Further, the elastic material 110a of the relay terminal 110 makes such vibration propagation suppression more remarkable. In addition, since the inner electric wire 111a is covered with an electrical insulating material, a discharge phenomenon can be reliably prevented.

(Modification 3)
Another modification will be described with reference to FIG. FIG. 3 shows an example in which a cooling tube is drawn into the gradient coil 23. A two-port coupler 113 having vibration insulation and vacuum resistance is attached to the flange 30B of the vacuum lid 25B with a flexible elastic material 113a interposed therebetween. The tubes 114 and 115 move between the vacuum space CS and the outside via the coupler 113. Therefore, the vibration propagating from the gradient magnetic field coil 23 to the vacuum lid 25B via the tubes 114 and 115 is appropriately reduced due to the elastic member 113a of the coupler 113.

(Modification 4)
FIG. 14 shows another modification. The gantry 11 shown in the figure has the same components as those of FIG. However, instead of the floor F described above, a ceiling C is used as a mounting surface of the supports 40A and 40B that support the gradient magnetic field coil 23. That is, the static magnetic field magnet 21 is installed on the floor F as before, but the gradient magnetic field coil 23 is supported (suspended) on the ceiling C via the supports 40A and 40B. The ceiling C is also formed with high rigidity, and supports 40A and 40B are rigidly connected to the ceiling C by anchors 51.

  For this reason, the vibration damping effect by the mass effect of the ceiling C can be obtained, and the floors F (magnet installation) and the ceiling C (gradient magnetic field coil installation), which have very little influence on the vibration characteristics, are provided as installation surfaces. , The solid-state propagation of vibration between the installation surfaces can be almost completely blocked, and a silent gantry with significantly reduced noise can be provided.

FIG. 1 is a partially broken front view showing a configuration of a gantry of a magnetic resonance imaging apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view along line II-II in FIG. 1 illustrating a configuration of the gantry. The figure explaining the solid-state propagation path of the vibration which passes through a support body. FIG. 6 is a partially broken front view showing a configuration of a gantry of a magnetic resonance imaging apparatus according to a second embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the configuration of the gantry, taken along line VV in FIG. 4. FIG. 9 is a partially broken front view showing a configuration of a gantry of the magnetic resonance imaging apparatus according to the first modification. FIG. 7 is a schematic cross-sectional view along line VII-VII in FIG. 6 illustrating a configuration of the gantry. FIG. 9 is a partially broken front view showing a configuration of a gantry of a magnetic resonance imaging apparatus according to a third embodiment of the present invention. FIG. 9 is a schematic cross-sectional view along line IX-IX in FIG. 8 showing a configuration of the gantry. FIG. 14 is a partially broken front view showing a configuration of a gantry of a magnetic resonance imaging apparatus according to a fourth embodiment of the present invention. FIG. 14 is a partially cutaway front view showing a configuration of a gantry of a magnetic resonance imaging apparatus according to a fifth embodiment of the present invention. FIG. 10 is a partial cross-sectional view illustrating a situation where a power supply line is drawn into a gantry according to a second modification. FIG. 13 is a partial cross-sectional view illustrating a supply state of a cooling medium tube to a gantry according to a third modification. FIG. 14 is a partial cross-sectional view showing support using both a floor and a ceiling of a gantry according to Modification Example 4.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 11 Gantry 12 Bed part 21 Magnet 22 Leg (support means for static magnetic fields)
23 Gradient magnetic field coil 24 Inner cylinder (defined body / vacuum space forming means)
25A, 25B, 70A, 70B, 76, 90 Vacuum lid (lid / definer / vacuum space forming means)
30A, 30B, 71A, 71B, 91 Flange (defined body / vacuum space forming means)
31A, 31B, 72A, 72B, 92 Vacuum end plate (defining body / vacuum space forming means)
36 O-rings 40A, 40B support (support means for gradient magnetic field)
41 support member 42 rod 43 base 44 beam (combined body)
45c First elastic members 45a, 45b Second elastic members 46a, 46b, 46c Stopper 47 Hexagon nut 50 Vacuum bellows (blocker / definer / vacuum space forming means)
51 anchor (joining means)
55 vacuum resistant hose (pump means / vacuum space forming means)
56 vacuum pump (pump means / vacuum space forming means)
60,110 terminal (relay)
61 External power line 62 Internal power line 65, 113 Coupler (relay body)
65 External tube 66 Internal tube 67t Top plate 68 Top plate rail 74 Elastic body 75 Rail body 80 Sound absorbing material 81 Groove 97 Vacuum seal member 100 Inner cylinder suspension mechanism (suspension mechanism)
100a, 100c Upper and lower suspension members (support members)
100b Elastic member 111a Internal electric wires 114, 115 Cooling tube S Diagnosis space F Floor (installation surface)
C Ceiling (installation surface)
CS closed space h hole

Claims (4)

A static magnetic field generating means for generating a static magnetic field in the imaging area of the diagnostic space, a static magnetic field supporting means for supporting the static magnetic field generating means at a position on the installation surface, and a gradient magnetic field in the imaging area For the gradient magnetic field generating means, the gradient magnetic field generating means and the static magnetic field generating means are mechanically uncoupled or substantially uncoupled from each other, and the gradient magnetic field generating means is located at the position on the installation surface. Has a gantry provided with a supporting means for the gradient magnetic field supporting at another different position, and a coupling means for rigidly coupling the supporting means for the gradient magnetic field to the installation surface, and with the driving of the gradient magnetic field generating means. A magnetic resonance imaging apparatus characterized in that generated noise is suppressed. 2. The magnetic resonance imaging apparatus according to claim 1, wherein said static magnetic field generating means comprises a magnet, and said gradient magnetic field generating means comprises a gradient magnetic field coil having an x coil, a y coil and a z coil. 3. The magnetic resonance imaging apparatus according to claim 2, further comprising: a vacuum space forming means having at least a defining body defining a closed space around the gradient magnetic field coil and a pump means for exhausting the closed space. The magnetic resonance imaging apparatus according to claim 2, wherein the coupling unit is a stopper that rigidly couples the gradient magnetic field support unit to a rigid floor surface formed as the installation surface.

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