JP2005095479A - Magnetic resonance imaging apparatus and the receiving coil thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the arrangement of a sound insulation member having a simple and space-saving structure for reducing noise of an inclined magnetic field coil in the MRI apparatus. <P>SOLUTION: A sound insulation cover for covering a surrounding area of the inclined magnetic field coil is constituted with different members composed of more than at least two kinds of density for some parts of the surface. Alternatively, an enclosed space storing the inclined magnetic field coil is formed in the MRI apparatus, and a vacuum tank is arranged with the sound insulation member for maintaining vacuum inside the static magnetic field generating part of the inclined magnetic field coil as a wall surface at the static magnetic field generating space of the enclosed space. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as “MRI”) apparatus, and more particularly to a technique for reducing noise generated when a gradient coil is driven.

  In general, an MRI apparatus includes a static magnetic field generating means for generating a uniform static magnetic field in an imaging space, a gradient magnetic field coil for generating a linear gradient magnetic field superimposed on the static magnetic field, and an RF coil for transmitting and receiving a high-frequency electromagnetic field. Yes. During imaging, a linear gradient magnetic field is superimposed on the subject placed in a uniform static magnetic field in the X, Y, and Z directions according to the desired pulse sequence, and the subject's atomic spin is magnetic at a high frequency of the Larmor frequency. Excited. Along with this excitation, a magnetic resonance (MR) signal is detected, and a two-dimensional tomographic image of the subject is reconstructed.

In recent years, there is a growing need for shortening the time required for imaging in such an MRI apparatus. It has been put into practical use.
However, when a pulse current is applied to the gradient magnetic field coil, Lorentz force acts, and the gradient magnetic field coil vibrates due to mechanical distortion and generates noise. Moreover, the vibration and noise increase as the gradient magnetic field pulse is applied and reversed at a higher speed. In other words, the noise generated from the gradient magnetic field coil increases as the imaging speed increases. This noise gives a very uncomfortable feeling to the subject lying in the imaging space.

For this reason, several techniques for reducing the aforementioned vibration and noise have been proposed.
For example, in [Patent Document 1], in a horizontal magnetic field type MRI apparatus, a gradient magnetic field coil is held in an uncoupled or substantially uncoupled state from a static magnetic field generation source, and the static magnetic field generation source is It is rigidly coupled to an installation floor surface different from the installation floor surface, and holds at least a part of the gradient coil and the support in the vacuum space. With this configuration, the vibration that propagates solidly from the gradient coil to the magnet through the gradient coil support means is remarkably reduced, and the vibration that propagates air from the gradient coil is cut off. ).

  Alternatively, in [Patent Document 2], a gradient magnetic field coil is rigidly coupled to a static magnetic field generation source, and the gradient magnetic field coil is covered with a nonmagnetic / nonconductive sound insulation cover, and is constituted by a sound insulation cover and a static magnetic field generation source. A gradient coil is enclosed in a closed space. With this configuration, sound waves generated from the gradient magnetic field coils are reflected by the members constituting the sealed space to reduce radiation to the outside of the sealed space, thereby reducing noise.

Alternatively, [Patent Document 1], [Patent Document 3] and [Patent Document 4] are technologies that utilize vacuum sound insulation, and [Patent Document 3] statically evacuates at least one part of a vacuum housing in a space that can be evacuated. It is formed by at least part of the magnetic field source and at least part of the gradient coil. In [Patent Document 4], the gradient magnetic field coil is covered with a plastic vacuum packing material that has been evacuated in advance. With these configurations, noise is reduced without transmitting vibration due to gas propagation to the external structure.
Japanese Patent Laid-Open No. 10-118043 JP 2001-299719 A Japanese Patent Laid-Open No. 2001-104285 JP 2003-70765 A

  In [Patent Document 1], the vibration of solid propagation is transmitted to the rigidly installed installation floor via the support of the gradient coil, and is reduced by the mass effect of the installation floor. There is a disadvantage that a space for providing the device is required and the apparatus becomes large. Further, since a vacuum space is provided in order to reduce vibration of air propagation from the gradient magnetic field coil, there are technical difficulties in maintaining this vacuum space, and there is a problem that the vacuum vessel is easily deformed. .

  In [Patent Document 2], the gradient magnetic field coil is fixed to the static magnetic field generating means by rigid coupling, the fixed support member is minimized, the sealed space is formed only by the sound insulation cover, and the sound insulation structure is simplified. The problem of the first known example is overcome. However, in the second known example, in order to maintain the linear characteristics of the gradient coil, a non-magnetic / non-conductive material must be selected as a sound insulation cover facing the imaging space among the shielding materials covering the gradient coil. I do not get. Nonmagnetic and nonconductive materials include glass, GFRP (glass fiber reinforced resin), FRP (fiber reinforced resin), etc., all of which have a density of 1 to 2.5 × 103 [kg / m3] and zinc・ The density of non-magnetic metals such as copper and lead is less than 9 to 11 × 103 [kg / m3]. Therefore, it can be understood from the equation (1) described later that the sound insulation performance of the nonmagnetic / nonconductive material is lower than that of the nonmagnetic metal. For this reason, in [Patent Document 2], it is necessary to increase the thickness of the sound insulation cover in order to improve the sound insulation performance. However, increasing the plate thickness leads to narrowing of the imaging space, and gives a sense of blockage and pressure to the subject in the imaging space.

  In [Patent Document 2], the gradient magnetic field coil is rigidly fixed to the static magnetic field generating means. At this time, if the static magnetic field generating means includes a heavy object such as an iron magnetic shield, it is possible to sufficiently expect the vibration reduction effect due to the mass effect. In recent years, however, active shield type superconducting magnets that do not have a magnetic shield have increased with the reduction in weight and magnetic field of magnets. In these superconducting magnets, the vacuum vessel surrounds the superconducting coil. When the gradient magnetic field coil is rigidly fixed to the vacuum vessel as in [Patent Document 2], the vibration of the gradient magnetic field coil propagates to the vacuum vessel. However, a lightweight vacuum vessel is insufficient in the vibration reduction effect due to the mass effect and generates noise.

In [Patent Document 1], since the gradient magnetic field coil needs to be hermetically arranged in a vacuum atmosphere or the like, its hermetic structure is complicated, and hermetic seals are particularly used for drawing out current leads for coil energization and cooling pipes. The assembly structure becomes complicated, such as by using the In addition, evacuation is always necessary after the device is assembled, and the work is particularly complicated when the gradient magnetic field coil is attached and detached at the installation site of a medical institution or the like. In addition, in the case of an open type MRI apparatus, the gradient magnetic field coil is often a flat plate, and if the surroundings are in a vacuum atmosphere, the pressure deformation of the surrounding structural members tends to be large, which adversely affects the magnetic field performance. End up. [Patent Document 3] always requires evacuation. In the example of the open-type MRI apparatus in [Patent Document 4], the vacuum pack is arranged on the entire surface including the upper and lower surfaces and the peripheral surface of the container accommodating the gradient magnetic field coil, and the outer periphery thereof is less likely to be deformed than the vacuum pack. Since it is reinforced with reinforced price ticks, the container for accommodating the gradient coil becomes thick. As a side effect, the imaging space is narrowed, giving the subject a feeling of obstruction and pressure.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems, and a noise insulation member having a simple and space-saving structure is arranged so as to cover the gradient magnetic field coil, thereby reducing the noise of the gradient magnetic field coil. That is.

In order to solve the above problems, the present invention is configured as follows.
According to the first embodiment, the static magnetic field generating means having a uniform static magnetic field space, the gradient magnetic field coil disposed on the static magnetic field region surface side of the static magnetic field generating means, and the periphery of the gradient magnetic field coil are sealed In a magnetic resonance imaging apparatus having a sound insulation cover that
The surface with the sound insulation cover is formed of at least two kinds of members having different densities.

  Further, according to the second embodiment, in the MRI apparatus of the first embodiment, the sound insulating cover disposed on the facing surface side is a flat plate formed of a first material that is nonmagnetic and nonconductive. A member made of a second material having a density different from that of the first material is interspersed in the shaped member. This second material is preferably a metal.

  According to the third embodiment, in the MRI apparatus of the second embodiment, the sound insulation cover disposed on the facing surface side is made of the composite metal material.

  According to the fourth embodiment, in the MRI apparatus according to the first embodiment, a part of the static magnetic field generating means is part of a structure for sealing the gradient magnetic field coil.

  Further, according to the fifth embodiment, in the MRI apparatus of the first embodiment, the gradient magnetic field coil is coupled and fixed to the static magnetic field generating means, and a weight is attached to the outer periphery of the static magnetic field generating means .

According to the sixth embodiment, in the MRI apparatus of the first embodiment, the RF coil is a part of a sound insulation cover, and a weight is attached on the surface of the RF coil.
Further, according to the seventh embodiment, in the MRI apparatus of the first embodiment, the static magnetic field generating means oppose each other across the static magnetic field region.

  According to the MRI apparatus of the first to seventh embodiments described above, by covering the gradient coil by increasing the mass of the sound insulation member while maintaining a simple and space-saving structure, the mass effect of the gradient coil can be increased. Noise can be reduced.

  In the above embodiment, the weight of the sound insulation cover is increased by interspersing weights on the sound insulation cover to increase the sound insulation effect of the sound insulation cover. The present invention further includes the following configuration in which a sound insulation member having a vacuum chamber is disposed so as to cover the gradient magnetic field coil, and noise from the gradient magnetic field coil is blocked using the sound insulation effect of vacuum.

According to the eighth embodiment, a pair of static magnetic field generating means arranged opposite to each other across the uniform static magnetic field space and having a substantially flat facing surface, and the uniform static magnetic field space side of the static static magnetic field generating means on the uniform static magnetic field space side. In a magnetic resonance imaging apparatus having a pair of gradient magnetic field coils and RF coils having a substantially flat shape arranged opposite to each other across a magnetic field space,
Forming a sealed space for accommodating the gradient coil on the static magnetic field space side of the static magnetic field generating means;
A side surface of the static magnetic field generating means in the sealed space is used as a wall surface of the static magnetic field generating means, and a sound insulating member having an internal vacuum maintained at least partially on the static magnetic field space side of the gradient coil.

  Further, according to the ninth embodiment, in the MRI apparatus of the eighth embodiment, the sound insulating member has a structure in which a vacuum tank having a flat shape is sealed in a vacuum, and the assembly of the apparatus is performed. And evacuation is unnecessary during operation.

  According to the tenth embodiment, in the MRI apparatus of the ninth embodiment, the flat vacuum chamber is arranged on the surface on the opposite surface side of the gradient coil.

  According to the eleventh embodiment, in the MRI apparatus of the ninth embodiment, the flat vacuum chamber is provided on the surface of the RF coil on the side opposite to the surface.

  Further, according to the twelfth embodiment, in the MRI apparatus of the ninth embodiment, the flat vacuum chamber has a structure in which the periphery of two glass plates is bonded and the gap is vacuum sealed And

  According to the thirteenth embodiment, in the MRI apparatus of the ninth embodiment, the outer shape of the flat vacuum chamber is a disk shape.

  According to the fourteenth embodiment, in the MRI apparatus of the ninth embodiment, the outer shape of the flat vacuum chamber is rectangular and is attached to a disk-shaped RF coil or gradient magnetic field coil.

  According to the fifteenth embodiment, in the MRI apparatus of the ninth embodiment, the flat vacuum chamber is arranged on the radiographic space side of the RF coil.

  According to the sixteenth embodiment, in the MRI apparatus of the ninth embodiment, the flat vacuum chamber is arranged on both surfaces of the gradient magnetic field coil or the RF coil.

  According to the MRI apparatus of the above eighth to sixteenth embodiments, the gradient magnetic field coil is provided by arranging the sound insulation member having a simple and space-saving structure in which the inside is maintained in a vacuum so as to cover the gradient magnetic field coil. It is possible to reduce noise from the device structure that is generated by air propagation of the membrane vibration.

  According to the present invention, the noise of the gradient coil can be reduced by arranging the sound insulation member having a simple and space-saving structure so as to cover the gradient coil.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.
First, an outline of the MRI apparatus according to the present invention will be described. FIG. 1 shows a basic configuration of a vertical magnetic field type MRI apparatus which is an embodiment of the MRI apparatus. FIG. 1 is a cross-sectional view showing an arrangement of a static magnetic field generation source 1, a gradient magnetic field coil (hereinafter referred to as GC) 2, an RF coil 12, and a sound insulation cover 3. An example in which a superconducting magnet using a superconducting coil is adopted as a static magnetic field generation source will be described. However, a normal conducting magnet using a permanent magnet or a normal conducting coil can be used as a static magnetic field generation source.

  In FIG. 1, the MRI apparatus has a pair of a static magnetic field generation source 1 and a static magnetic field generation source 1 that are arranged to face each other in the vertical direction across a uniform static magnetic field region 7 (imaging space), with a predetermined interval. Two supporting columns 8 to be supported and a pair of RF coils 12 and GC2 disposed to face the inside of the static magnetic field generating source 1 are provided.

  The static magnetic field generation source 1 includes a superconducting coil group 9 for generating a vertical static magnetic field in the uniform static magnetic field region 7, and a cryocontainer for cooling and holding the superconducting coil group 9 at a temperature at which predetermined superconducting characteristics can be obtained. It consists of ten. The cryocontainer 10 includes a refrigerant container (not shown) that contains a refrigerant such as liquid helium that immerses the superconducting coil group 9, a heat shield (not shown) that contains the refrigerant container and prevents heat radiation, It is outside and includes the entire superconducting magnet including the heat shield, and is composed of a vacuum vessel (not shown) for preventing heat convection. The opposing surface 11 of the static magnetic field generation source 1, that is, the opposing surface 11 of the cryocontainer 10 is substantially parallel.

  The superconducting coil group 9 is enclosed in a cylindrical cryocontainer 10 and is installed vertically symmetrically across the uniform static magnetic field region 7 in the center of the superconducting magnet. The upper and lower cryocontainers 10 are predetermined by the support 8 between them. The distance is maintained and maintained. The support 8 functions to mechanically support the upper and lower cryocontainers 10, but may have a function of thermally connecting the refrigerant containers in the upper and lower cryocontainers 10 as necessary. Further, the number of support columns 8 is not necessarily limited to the two shown in FIG. 1, and can be four or one, for example.

  As described above, a pair of the static magnetic field generation sources 1 composed of the cryocontainer 10 containing the superconducting coil 9 is supported by the support column 8 and arranged so as to face each other in the vertical direction. Then, a substantially flat GC2 that generates a gradient magnetic field and a substantially flat RF coil 12 that generates a high-frequency magnetic field are vertically symmetrical with respect to the center plane of a uniform static magnetic field region 7 formed between both static magnetic field generation sources 1. And it arrange | positions on the surface by the side of the uniform static magnetic field space 7 of the static magnetic field generation source 1. FIG. These arrangement orders are the sound insulation cover 3, the RF coil 12, GC2, and the static magnetic field generation source 1 in order from the center plane. In FIG. 1, GC2 is covered with a sound insulation cover 3 (in FIG. 1, including the RF coil 12), thereby confining the GC2 within the sealed space to reduce noise.

  The RF coil 12 applies a high-frequency magnetic field to the subject to induce a nuclear magnetic resonance (hereinafter referred to as NMR) phenomenon, and then transmits an NMR signal emitted from the subject by another RF coil or the same RF coil 12. To detect. When detecting the NMR signal, position information is given to the NMR signal detected by applying a gradient magnetic field to the subject by the GC 2. An image is reconstructed from the obtained NMR signal and displayed.

  Next, a first embodiment in which the present invention is applied to the MRI apparatus will be described. In this embodiment, the GC is rigidly fixed to the static magnetic field generation source 1, and a weight is scattered on the sound insulation cover 3 covering the periphery of the GC to increase its mass (weight), thereby enhancing the sound insulation effect of the sound insulation cover 3. FIG. 2 shows a schematic sectional view of the first configuration example. In this first configuration example, the GC is rigidly fixed to the static magnetic field generation source 1, and the vibration of the GC is attenuated by the mass effect of the static magnetic field generation source 1. Therefore, it is desirable that the static magnetic field generation source 1 has a mass that can attenuate the vibration of the GC due to its mass effect. In addition, a sound insulation cover with dotted weights is arranged so as to cover the periphery of the GC.

In general, the transmission loss TL [dB] representing the sound insulation performance of the sound insulation material is represented by the following equation (1).
TL = 18 ・ log (f ・ ρ ・ t) −44 (1)
Here, f: frequency of sound [Hz], ρ: material density of the shielding material [kg / m 3], and t: thickness of the shielding material [m]. Therefore, from formula (1), it can be understood that as the shielding material, the higher the density and thickness, the higher the sound insulation performance, and the higher the mass effect, the better (ρ · t). That is, increasing the mass of the sound insulation cover by interspersing weights contributes to the improvement of the sound insulation performance.

  FIG. 3 shows a configuration example of a sound insulation cover with a weight disposed on the opposite surface side of the GC. A non-magnetic and non-metallic member is used as the flat plate-like sound insulating member 4 as a base. For example, plate glass and FRP (glass fiber resin) are suitable. On the other hand, as the weight member 5, a member having a sufficiently higher density than the base member is used. For example, a nonmagnetic metal / nonmagnetic alloy member such as zinc / copper / lead or brass (zinc / copper) is suitable.

  It is desirable that the weight member is not loosened. For example, a through hole may be provided in the sound insulating member of the base, a screw may be cut in the through hole, and the weight member may be tightened as a screw. Furthermore, it can be fixed so as not to loosen by using bolt fastening or an adhesive material in the through hole. Or it is good also as a structure stuck on the surface of the dent provided in the sound insulation member of a base, or the sound insulation member of a base, without making it a through-hole.

  As an example of this configuration example, a case where plate glass (density: about 2 [g / cm3]) is used as the sound insulation member of the base and copper (density: about 8 [g / cm3]) is used as the weight member will be described. When a sound insulation cover material with a weight with a ratio of plate glass to copper of 2: 1 is used, the thickness is constant and the weight can be doubled compared to a sound insulation cover material made of a single plate glass. Therefore, from the above-mentioned formula (1), it is understood that the sound insulation cover material with a weight is superior in sound insulation performance by 6 dB even though the thickness is the same as that of the sound insulation cover material made of a single plate glass. In other words, the same sound insulation performance can be obtained even with half the plate thickness. Furthermore, since this configuration can further expand the imaging space, there is an effect that an effect of increasing the sense of security of the subject can be obtained.

  Next, a second configuration example based on the first embodiment will be described. In this second configuration example, a concave portion 20 is provided on the facing surface side of the superconducting magnet that is a static magnetic field generation source, and the GC2 and the RF coil 12 are housed in the concave portion 20 and covered with a sound insulation cover with a weight. The figure is shown in FIG. The GC2 and the RF coil 12 are fixed to the superconducting magnet via the GC support 21 and the RF coil support 22, respectively. At this time, since the sound insulation cover generally has a higher sound insulation performance in a higher frequency band, it is desirable that the GC2 and the RF coil 12 be rigidly fixed to the superconducting magnet. The sound insulation cover 3 with the weight is disposed only on the facing surface of the GC 2 and the RF coil 12.

  On the other hand, on the side surface and back surface of the GC2, the inner surface of the recess 20 of the superconducting magnet is used as a sound insulation cover. In general, a superconducting magnet uses a stainless cryocontainer 10 for housing a superconducting coil. In order to improve the sound insulation performance, the thickness of the inner surface (stainless steel) of the recess 20 of the superconducting magnet may be increased.

  Further, if the entire surface or a part of the recess 20 of the superconducting magnet is configured using a member having a density higher than that of the material of the cryocontainer 10 (stainless steel), the thickness of the recess 20 can be reduced to widen the space. Since the sound insulation effect can be maintained and improved, a storage space for the GC2 and the RF coil 12 or a wiring space can be secured.

  If it is not easy to fix the weight member by bolt fastening using a through hole in the cryo container recess 20 or the use of a screw member, the weight member may be bonded and fixed on the inner surface of the recess 20.

Next, a third configuration example based on the first embodiment will be described. This third configuration example is a configuration in which weights are scattered on the surface of a cryocontainer of a superconducting magnet, and a schematic sectional view thereof is shown in FIG. For example, stainless steel or lead is suitable as the weight member 5 in this configuration example. When GC2 is rigidly fixed to the cryocontainer 10, the vibration of GC2 is transmitted to the cryocontainer 10 via the GC support 21. The vibration transmitted to the cryocontainer 10 is attenuated by the mass effect of the superconducting magnet including the cryocontainer 10 to which the mass is increased by adding the weight member 5, but may not be completely attenuated. Further, there is a case where it vibrates with a unique vibration mode corresponding to the structure (shape / weight) of the superconducting magnet. In these cases, vibration analysis using a computer simulation or the like is performed in advance, and a weight is placed on the cryocontainer 10 at a position where the antinodes of vibrations. The same effect as increasing can be obtained. Thereby, the vibration transmitted to the cryocontainer 10 can be attenuated. With this configuration, vibration and noise can be further suppressed with respect to vibration and noise in a certain frequency band in addition to the mass effect.
If it is not easy to fix the weight member by fastening bolts using screw holes or using screw members on the cryocontainer surface, the weight member may be adhered and fixed on the cryocontainer surface.

  Next, a fourth configuration example based on the first embodiment will be described. This fourth configuration example is a configuration in which an RF coil and a sound insulation cover with a weight are integrated, and FIG. 6 shows a schematic cross-sectional view thereof. The RF coil 12 and the sound insulation cover 3 with a weight are integrated so as not to be separated by vibration using bolt fastening or an adhesive. FIG. 7 shows an example of a method for fixing the sound insulation cover (including the RF coil 12) 3. A step 23 is provided at the end of the cryocontainer recess 20 that also serves as a part of the sound insulation cover 3. Using this step 23 portion, the sound insulation cover 3 with a weight is fixed by fastening bolts 24 or an adhesive or the like, and the cryocontainer recess 20 is tightly sealed so that there is no gap or play. Furthermore, the joint surface may be sealed with lead tape or the like. In addition, a damping material such as rubber may be used at the joint between the soundproof cover 3 with the weight and the fixing member. By using the damping material, it is possible to obtain an effect of suppressing the vibration transmitted from the GC 2 to the cryocontainer 10 from being transmitted to the soundproof cover 3 with the weight.

  Next, a fifth configuration example based on the first embodiment will be described. This fifth configuration example is a configuration example using a metal composite resin material as a sound insulation cover, and a schematic sectional view thereof is shown in FIG. In this configuration example, by adopting an impregnation structure in which the sound insulation cover 3 is impregnated with a resin mixed with fine metal powder, the weight member can be fixed without looseness. Further, since the weight members can be scattered more finely, the influence of eddy currents and the like that deteriorate the linear characteristics of the GC can be minimized. However, since the higher frequency electromagnetic wave is more easily absorbed by the metal, the metal composite resin is selected so as not to affect the high frequency electromagnetic wave transmitted and received by the RF coil 12. For example, iron, copper, or lead is suitable as the metal powder. In addition, if the resin is made of glass, the same effect can be obtained with metal glass.

  The first embodiment of the present invention has been described so far by increasing the mass of the sound insulation cover by increasing the mass by interspersing the weight insulation member with the sound insulation cover. In the first embodiment, the vertical magnetic field type MRI apparatus has been described as an example, but the present invention can be similarly applied to a tunnel type horizontal magnetic field method.

  Next, a second embodiment of the present invention will be described in which a sound insulating member having a vacuum chamber is disposed so as to cover the GC, and the noise from the GC is blocked using the sound insulating effect of the vacuum.

  First, a sixth configuration example based on this embodiment will be described. In this sixth configuration example, a flat vacuum chamber 53 is arranged in contact with the RF coil 12, and a schematic cross-sectional view of a region related to the vacuum chamber 53 is shown in FIG. GC2 is fixed to the surface of the static magnetic field generation source 1 by bolts 51. The flat vacuum chamber 53 is attached on the surface of the RF coil 12 on the static magnetic field generation source side so as to be in contact with the RF coil 12. For example, as a structure that also serves as the base (substrate) of the RF coil 12, both can be bonded and bonded. Then, it is fixed to the static magnetic field generation source 1 via the fixing bolt 52.

  In this configuration example, the bolt 52 that fixes the vacuum chamber 53 and the RF coil 12 passes through the inside of the GC 2, but a gap is provided between the GC 2 and the fixing bolt 52, and the vibration of the GC 2 causes the bolt 52 to vibrate. The structure is difficult to propagate to the vacuum chamber 53 and the RF coil 12 via the. Further, in order to prevent the noise of GC2 from leaking to the outside, it is preferable to arrange the GC2 so as to be sealed inside the recess of the static magnetic field generation source 1 as shown in FIG.

  FIG. 10 shows a cross-sectional structure of the flat vacuum chamber 53. The vacuum chamber 53 is configured by fixing two glasses 54 in parallel with each other with a narrow gap therebetween. The surroundings are sealed with a vacuum seal 55, and a vacuum atmosphere is created by exhausting the internal gap between the two pieces of glass. In addition, although an exhaust port exists in the edge part of a glass surface, it seals after exhausting. Therefore, it is not necessary to always exhaust the inside, and the operating cost can be greatly reduced. Further, since the periphery of the gradient magnetic field coil is not in contact with the vacuum atmosphere, the gradient magnetic field coil and the surrounding structure for housing it do not require a structural member that can withstand the vacuum pressure. Therefore, compared with the structure which arrange | positions a gradient magnetic field coil in a vacuum, the manufacturing cost of a gradient magnetic field coil and its periphery can be reduced.

  Here, when the inside is in a vacuum state, atmospheric pressure acts in the direction of crushing the gap due to atmospheric pressure, and therefore a spacer 56 for preventing deformation is disposed in the gap. In this configuration example, for example, the glass has a thickness of 2 mm, a gap of 0.5 mm, and a nylon wire having a diameter of 0.5 mm can be placed inside.

  Further, as an additional effect of this configuration example, the heat generation of GC2 is insulated by the flat vacuum chamber 53, so that the thermal influence on the RF coil 12 portion becomes smaller than in the conventional case. Also, by constructing the vacuum chamber 53 with a glass plate, the rigidity is higher than the glass fiber reinforced plastic that is the material of the base (substrate) of the RF coil 12, and as a result, the vibration of the RF coil 12 and the examinee The deformation of the RF coil 12 due to the load on the placed table is also reduced.

  Next, a seventh configuration example based on the second embodiment will be described. This seventh configuration example has the same basic arrangement as the sixth configuration example, but the GC2 is not directly fixed on the container wall of the static magnetic field generation source 1, but is fixed on the container wall via the vibration absorbing material 60, In addition, the container wall of the static magnetic field generation source 1 and the vacuum chamber 53 are not in direct contact with each other with the vibration absorbing material 61 interposed therebetween, and a sealed space is formed in the concave portion 20 of the static magnetic field generation source 1 so that the GC 2 FIG. 11 is a schematic cross-sectional view showing a configuration example housed in the housing. Since the vibration absorbing materials 60 and 61 are arranged in the path through which the vibration of the GC 2 propagates to the RF coil 12, in addition to the sound insulation effect of the vacuum chamber 53, the silent effect is superior to the sixth configuration example of FIG.

  Next, an eighth configuration example based on the second embodiment will be described. The eighth configuration example is different from the sixth configuration example in the container structure of the static magnetic field generation source 1, and the static magnetic field generation source 1 has no recess for accommodating GC2 and the like, and the surface on the imaging space side is flat. FIG. 12 shows a schematic cross-sectional view of a configuration example in which a flat vacuum chamber 53 is disposed in the magnetic field generation source 1.

  If the GC2 is not sealed as described above, the sound insulation effect is small by simply attaching the flat glass vacuum chamber 53 to the RF coil 12. Therefore, as shown in FIG. 12, a closed space is formed in the gap between the vacuum chamber 53 and the static magnetic field generation source 1 by using the sound absorbing material 71 or the like to accommodate the GC 2 therein. Thereby, a sealed space is formed, and the use of the vibration absorbing material 71 can reduce the vibration of the static magnetic field generating source 1 from being propagated to the RF coil 12 and the vacuum chamber 53 as a solid. Others are the same as the sixth configuration example.

  Next, a ninth configuration example based on the second embodiment will be described. This ninth configuration example is a configuration example when the shape of the vacuum chamber is a rectangle other than a circle, for example, and a top view thereof is shown in FIG. In the above configuration examples 6 to 8, the shape of the flat vacuum chamber 53 is a circular flat plate adapted to the shape of the static magnetic field generation source 1 and the RF coil 12, but as in this configuration example, a rectangular flat plate vacuum chamber It is also possible to use 53. As a result, the entire surface of the RF coil 12 cannot be covered, but a sound insulation effect can be exhibited in the portion covered with the vacuum chamber 53.

  For example, as shown in FIG. 14, by disposing the vacuum chamber 53 so as to cover a large area on the back surface of the RF coil 12, the effect is reduced, but noise reduction can be realized. Moreover, if it is the rectangular vacuum chamber 53, the vacuum heat insulation glass generally marketed can also be used and this invention can be applied easily.

  FIG. 15 is a schematic view of the wiring lead portion of the gradient magnetic field coil in the ninth configuration example. As explained in the ninth configuration example, since there is no restriction that the entire surface of the RF coil 12 is covered with the vacuum chamber 53, a region where the vacuum chamber 53 is not partially provided can be provided. The part 55 can be easily provided. Note that these cables can be drawn out of the static magnetic field generation source 1 through the inside of the static magnetic field generation source 1 instead of the imaging space side.

  Next, a tenth configuration example based on the second embodiment will be described. This tenth configuration example is a configuration example in which a flat vacuum chamber 53 is arranged on the surface of GC2, and a schematic sectional view thereof is shown in FIG. In this case, since the vacuum chamber 53 itself vibrates, its sound insulation effect is small, but the external propagation of the membrane vibration of GC2 can be reduced, and in addition, the bending rigidity of the GC2 surface can be increased. Noise can be reduced.

  Next, an eleventh configuration example based on the second embodiment will be described. This eleventh configuration example is a configuration example in which a flat vacuum chamber 53 is arranged on the surface of the RF coil 12, and a schematic sectional view thereof is shown in FIG. This configuration example can also exhibit a sound insulation effect.

  In the above description of the second embodiment, the example in which the vacuum chamber 53 is disposed only on one side of the GC2 or the RF coil 12 has been described, but the vacuum chamber 53 may be disposed on one or both surfaces of the GC2 or the RF coil 12. Good.

The figure which shows the schematic cross section of the MRI apparatus concerning this invention. FIG. 2 is a diagram showing a schematic cross section of a first configuration example according to the first embodiment of the present invention. A state in which the gradient magnetic field coil is rigidly fixed to a static magnetic field generation source and covered with a sound insulation cover with a weight is shown. The figure which shows the sound-insulation cover with a weight arrange | positioned in the opposing surface of the gradient magnetic field coil in the 1st Embodiment of this invention. FIG. 3 is a diagram showing a schematic cross section of a second configuration example according to the first embodiment of the present invention. The state where the GC is housed in the recess of the static magnetic field generation source is shown. FIG. 5 is a diagram showing a schematic cross section of a third configuration example according to the first embodiment of the present invention. A mode that the weight member was scattered on the cryocontainer surface of a superconducting magnet is shown. FIG. 5 is a diagram showing a schematic cross section of a fourth configuration example according to the first embodiment of the present invention. The state where the RF coil and the sound insulation cover are integrated is shown. The figure which shows the example of fixation of a sound insulation cover (an RF coil is included). FIG. 6 is a diagram showing a schematic cross section of a fifth configuration example according to the first embodiment of the present invention. A state in which a metal composite resin material is used for the sound insulation cover is shown. FIG. 10 is a diagram showing a schematic cross section of a sixth configuration example according to the second embodiment of the present invention. A mode that the flat vacuum chamber was arrange | positioned in contact with RF coil is shown. The figure which shows the cross-section of the flat vacuum tank in the 2nd Embodiment of this invention. FIG. 20 is a diagram showing a schematic cross-section of a seventh configuration example in the second embodiment of the present invention. A state in which the container wall of the static magnetic field generation source and the vacuum chamber are brought into contact with each other with a vibration absorbing material interposed therebetween is shown. The figure which shows the schematic cross section of the 8th structural example in the 2nd Embodiment of this invention. A mode that the flat vacuum chamber is arrange | positioned to the static magnetic field generation source without a recessed part is shown. The figure which shows the schematic cross section of the 9th structural example in the 2nd Embodiment of this invention. A state in which a rectangular vacuum chamber is arranged is shown. The figure which shows a mode that the rectangular vacuum chamber was arrange | positioned on the back surface of RF coil. The figure which shows the outline of the wiring extraction part of a gradient magnetic field coil in the 9th structural example in the 2nd Embodiment of this invention. The figure which shows the schematic cross section of the 10th structural example in the 2nd Embodiment of this invention. A state in which the flat vacuum chamber 53 is arranged on the surface of the gradient magnetic field coil is shown. The figure which shows the schematic cross section of the 11th structural example in the 2nd Embodiment of this invention. A mode that the flat vacuum chamber is arrange | positioned on the surface of RF coil is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Static magnetic field magnet 2 ... Gradient magnetic field coil 3 ... Sound insulation cover 4 ... Base (board | substrate) of a flat plate-shaped sound insulation member
DESCRIPTION OF SYMBOLS 5 ... Weight member 7 ... Imaging | photography space 8 ... Support | pillar 10 ... Cryo container 12 ... RF coil 51 ... GC fixing bolt 52 ... RF fixing bolt 53 ... Flat vacuum tank 54 ... Plate glass 55 ... Wiring material 56 ... Spacer 60, 61 ... Damping material 71 ... Sound insulation material

Claims (2)

Magnetism comprising a static magnetic field generating means having a uniform static magnetic field space, a gradient magnetic field coil disposed on the surface of the static magnetic field region of the static magnetic field generating means, and a sound insulation cover for sealing the periphery of the gradient magnetic field coil. In a resonance imaging apparatus,
A magnetic resonance imaging apparatus, wherein a surface having the sound insulation cover is formed of at least two kinds of members having different densities. A pair of static magnetic field generating means arranged opposite to each other across the uniform static magnetic field space and having a substantially flat opposing surface, and arranged opposite to each other with the uniform static magnetic field space on the side of the uniform static magnetic field space of the static static magnetic field generating means In a magnetic resonance imaging apparatus having a pair of gradient magnetic field coils and RF coils having a substantially flat shape,
Forming a sealed space for accommodating the gradient coil on the static magnetic field space side of the static magnetic field generating means;
A side surface of the static magnetic field generating means in the sealed space is used as a wall surface of the static magnetic field generating means, and at least a part of the sound insulation member having a vacuum inside is disposed on the static magnetic field space side of the gradient magnetic field coil. Magnetic resonance imaging apparatus.

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