WO2013046957A1 - 磁気共鳴イメージング装置 - Google Patents
磁気共鳴イメージング装置 Download PDFInfo
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- WO2013046957A1 WO2013046957A1 PCT/JP2012/070458 JP2012070458W WO2013046957A1 WO 2013046957 A1 WO2013046957 A1 WO 2013046957A1 JP 2012070458 W JP2012070458 W JP 2012070458W WO 2013046957 A1 WO2013046957 A1 WO 2013046957A1
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- magnetic field
- conductor ring
- conductor
- field generator
- gradient magnetic
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/389—Field stabilisation, e.g. by field measurements and control means or indirectly by current stabilisation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3854—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils means for active and/or passive vibration damping or acoustical noise suppression in gradient magnet coil systems
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56518—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to eddy currents, e.g. caused by switching of the gradient magnetic field
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/42—Screening
- G01R33/421—Screening of main or gradient magnetic field
- G01R33/4215—Screening of main or gradient magnetic field of the gradient magnetic field, e.g. using passive or active shielding of the gradient magnetic field
Definitions
- the present invention relates to a magnetic resonance imaging (hereinafter referred to as MRI; Magnetic Resonance Imaging) apparatus including a static magnetic field generator and a gradient magnetic field generator.
- MRI Magnetic Resonance Imaging
- the MRI apparatus obtains a magnetic resonance image (tomographic image) representing the physical properties of the subject placed in the imaging space using the nuclear magnetic resonance phenomenon of the nucleus.
- an MRI apparatus generates a static magnetic field generation apparatus having a static magnetic field generation source that generates a uniform magnetic field (static magnetic field) in an imaging space, and a high-frequency electromagnetic wave for generating nuclear magnetic resonance in a nucleus of a living tissue of a subject.
- a gradient magnetic field generator having a generation source is provided.
- a gradient magnetic field generator superimposes a linear gradient magnetic field in the X, Y, and Z axis directions on a subject placed in a uniform magnetic field according to a desired pulse sequence, and the atomic spin of the subject is changed to Larmor. Excited magnetically at frequency. With this excitation, a magnetic resonance signal is detected, and a magnetic resonance image of the subject, for example, a two-dimensional tomographic image is reconstructed.
- the reason why the vibration is generated in the gradient magnetic field generator and the static magnetic field generator was considered as follows.
- a pulsed current flows through the gradient magnetic field generation source of the gradient magnetic field generator.
- a pulse current flows through the gradient magnetic field generation source arranged in the static magnetic field generated by the static magnetic field generation source. Therefore, the Lorentz force is applied to the gradient magnetic field generation source by coupling of the static magnetic field and the pulse current.
- the gradient magnetic field generator including the gradient magnetic field generation source vibrates. Since the gradient magnetic field generator is attached to a nearby static magnetic field generator by a mounting member such as a bolt, the vibration of the gradient magnetic field generator propagates to the static magnetic field generator via this attachment member, The magnetic field generator also vibrates.
- a magnetic field generated from the gradient magnetic field source and leaking to the static magnetic field source with respect to the gradient magnetic field source is linked with the conductive member constituting the static magnetic field generator, so that the static magnetic field An eddy current is generated in the generator, and the Lorentz force acts on the conductive member of the static magnetic field generator due to the coupling between the eddy current and the static magnetic field, and the static magnetic field generator vibrates.
- a problem to be solved by the present invention is to provide an MRI (magnetic resonance imaging) apparatus capable of reducing vibration while suppressing deterioration of tomographic images.
- the present invention provides each of a pair of arrangement regions that are on both sides of the uniform magnetic field generation region between the static magnetic field generation source and the gradient magnetic field generation source. It is characterized by being an MRI (Magnetic Resonance Imaging) apparatus provided with conductor rings which are arranged and are separated from each other.
- MRI Magnetic Resonance Imaging
- an MRI (magnetic resonance imaging) apparatus capable of reducing vibrations while suppressing deterioration of tomographic images.
- 1 is a perspective view of an MRI (magnetic resonance imaging) apparatus according to a first embodiment of the present invention.
- 1 is a longitudinal sectional view of an MRI apparatus according to a first embodiment of the present invention. It is the schematic of the upper part from the z-axis (center axis) of the longitudinal cross-section of the MRI apparatus which concerns on the 1st Embodiment of this invention. It is the schematic of the upper part from the z-axis of the longitudinal cross-section of the MRI apparatus which concerns on the 2nd Embodiment of this invention. It is the schematic of the upper part from the z-axis of the longitudinal cross-section of the MRI apparatus which concerns on the 3rd Embodiment of this invention.
- FIG. 1 shows a perspective view of an MRI (magnetic resonance imaging) apparatus 1 according to the first embodiment of the present invention.
- the MRI apparatus 1 has a cylindrical static magnetic field generator 2 capable of introducing the subject 10 into the internal imaging space 8 and a nuclear magnetic resonance in an atomic nucleus constituting a living tissue of the introduced subject 10.
- a receiving coil 22 for receiving a signal emitted from the subject 10, a bed 6 on which the subject 10 is loaded, and the like.
- the static magnetic field generator 2 generates a uniform magnetic field 7 (see FIG. 2) in the imaging space 8 in order to orient the spins of atoms constituting the living tissue of the subject 10.
- a shim coil (not shown) is provided on the imaging space 8 side of the static magnetic field generator 2.
- the static magnetic field generator 2 is supported by a vacuum vessel support leg 2f.
- the static magnetic field generator 2 has a cylindrical shape with a z-axis parallel to the horizontal direction as a central axis.
- the gradient magnetic field generator 3 is provided on the imaging space 8 side of the static magnetic field generator 2.
- the gradient magnetic field generator 3 has a cylindrical shape having the same central axis as the static magnetic field generator 2 (with the z axis as the central axis).
- the irradiation coil 4 is provided on the imaging space 8 side of the gradient magnetic field generator 3.
- the irradiation coil 4 has a cylindrical shape having the same central axis as the static magnetic field generator 2 (with the z axis as the central axis).
- the irradiation coil 4 irradiates a high-frequency signal in order to cause nuclear magnetic resonance to occur in atomic nuclei constituting the biological tissue of the subject 10.
- a receiving coil 22 is attached to the bed 6 in order to receive a magnetic resonance signal by nuclear magnetic resonance.
- the conductor ring 5 (5a) is provided on the imaging space 8 side of the static magnetic field generator 2.
- the conductor ring 5 (5 a) is provided on the radially outer side of the gradient magnetic field generator 3.
- the conductor ring 5 (5a) has a cylindrical shape having the same central axis as the static magnetic field generator 2 or the gradient magnetic field generator 3 (having the z axis as the central axis).
- the conductor ring 5 (5a) can be formed of nonmagnetic and conductive copper or aluminum.
- FIG. 2 shows a longitudinal sectional view of the MRI apparatus 1 according to the first embodiment of the present invention.
- the static magnetic field generator 2 includes a plurality of main coils (static magnetic field generation sources) 2a that are superconducting coils, a plurality of shield coils (static magnetic field generation sources) 2b that are superconducting coils, a main coil 2a that is a superconducting coil, and a shield.
- the cooling container 2e that houses and cools the coil 2b together with the refrigerant, the radiation shield plate 2d that covers the cooling container 2e and shields the radiant heat radiated from the vacuum container 2c, and the cooling container 2e and the radiation shield plate 2d are housed in a vacuum environment.
- a vacuum vessel 2c for heat insulation a vacuum vessel support leg 2f (see FIG. 1) for supporting the vacuum vessel 2c on the installation floor, and a load support for adiabatic support of the cooling vessel 2e and the radiation shield plate 2d in the vacuum vessel 2c. (Not shown).
- the plurality of main coils (static magnetic field generation sources) 2a have a ring shape with the z axis as a common central axis.
- a plurality of main coils 2a are arranged in the z-axis direction (four in the example of FIG. 2).
- the plurality of main coils 2 a generate a static magnetic field that becomes a uniform magnetic field 7 in the imaging space (space) 8.
- the plurality of main coils 2a generate a static magnetic field in addition to the imaging space 8, and particularly generate a leakage magnetic field at a position farther than the main coil 2a with respect to the z axis.
- the plurality of shield coils (static magnetic field generation sources) 2b can reduce the magnitude of this leakage magnetic field.
- the plurality of shield coils 2b have a ring shape having the z-axis as a common central axis.
- a plurality of shield coils 2b are arranged in the z-axis direction (two (a pair) in the example of FIG. 2).
- the plurality of shield coils 2b are disposed in the vicinity of a pair of main coils 2a disposed at both ends of the plurality of shield coils 2b arranged in the z-axis direction.
- the plurality of shield coils 2b are arranged farther from the z-axis than the pair of main coils 2a arranged at both ends in the z-axis direction.
- the gradient magnetic field generator 3 is omitted in FIG. 2 and described as one, but actually has a plurality of main coils (gradient magnetic field generation sources) 3a.
- main coils gradient magnetic field generation sources
- one gradient magnetic field generation device 3 is omitted in FIG. 2 and is actually described, it actually includes a plurality of shield coils (gradient magnetic field generation sources) 3b.
- the gradient magnetic field generator 3 has the resin 3c which fixes the main coil 3a and the shield coil 3b mutually.
- the main coil (gradient magnetic field generation source) 3a has a cylindrical shape with the z axis as the central axis.
- the main coil 3 a generates a gradient magnetic field 9 that is superimposed on the uniform magnetic field 7 in the imaging space 8.
- the main coil 3 a generates a leakage magnetic field other than the imaging space 8.
- the shield coil (gradient magnetic field generation source) 3b can reduce the magnitude of this leakage magnetic field.
- the shield coil 3b has a cylindrical shape with the z axis as the central axis.
- the shield coil 3b is disposed farther than the main coil 3a with respect to the z axis.
- the shield coil 3b is disposed on the static magnetic field generator 2 side with respect to the main coil 3a.
- the gradient magnetic field generator 3 is attached to the vacuum vessel 2c via an attachment member (not shown).
- the conductor ring 5 is provided between the static magnetic field generation source 2a of the static magnetic field generation device 2 and the gradient magnetic field generation source 3a of the gradient magnetic field generation device 3. Is arranged.
- the conductor ring 5 (5a, 5b) is provided on the opposite side of the imaging space 8 in which the gradient magnetic field 9 is generated with the gradient magnetic field generation source 3a interposed therebetween.
- the conductor ring 5 (5a, 5b) generates the uniform magnetic field 7 on the imaging space 8 side of the region where the gradient magnetic field generating device 3 is arranged in the z-axis direction (the magnetic field direction of the uniform magnetic field 7).
- the pair of conductor rings 5a (5) and 5b (5) are separated from each other.
- the conductor ring 5 (5a, 5b) is mechanically coupled to the gradient magnetic field generator 3.
- the electrical resistivity (sheet resistance) per plate thickness of the conductor ring 5 (5a, 5b) is that of the outer wall of the vacuum vessel 2c (radiation shield plate 2d, cooling vessel 2e) of the static magnetic field generator 2 and the gradient magnetic field generator 3.
- the resistivity of the conductor of the conductor ring 5 is the resistance of members such as the outer wall of the vacuum container 2c (radiation shield plate 2d, cooling container 2e) of the static magnetic field generator 2 and the gradient magnetic field generator 3. It is desirable to be lower than the rate.
- the conductor rings 5 (5a, 5b) are arranged in the vicinity of the pair of main coils 2a arranged at both ends of the main coils 2a arranged in the z-axis direction.
- the conductor ring 5 (5a, 5b) is disposed at a position where the ends of the main coil 3a and the shield coil 3b of the gradient magnetic field generation source are disposed in the z-axis direction.
- the conductor rings 5 are arranged at positions where the main coil 2a at both ends of the static magnetic field generator and the outer ends of the shield coil 2b in the z-axis direction are arranged in the z-axis direction.
- the outer end of the conductor ring 5 (5a, 5b) in the z-axis direction may reach the outer end of the gradient magnetic field generator 3 in the z-axis direction, but does not protrude.
- the conductor ring 5a and the conductor ring 5b are arranged spatially separated in the z-axis direction (direction of the uniform magnetic field 7). Further, each of the conductor ring 5a and the conductor ring 5b is preferably formed of a continuous body in a circumferential direction with respect to the z-axis.
- the conductor ring 5a and the conductor ring 5b may be exposed on the surface of the gradient magnetic field generator 3, or may be embedded in the resin 3c between the surface of the gradient magnetic field generator 3 and the shield coil 3b.
- a uniform magnetic field 7 is generated in the imaging space 8 by the static magnetic field generator 2, but at the same time, a static magnetic field is also generated in a region where the gradient magnetic field generator 3 is disposed.
- a pulsed current flows through the main coil 3a and the shield coil 3b arranged in the static magnetic field.
- a pulsed Lorentz force acts on the main coil 3a and the shield coil 3b due to the coupling between the static magnetic field and the pulsed current, and the gradient magnetic field generator 3 vibrates.
- the vibration of the gradient magnetic field generator 3 propagates to the vacuum vessel 2c via an attachment member that attaches the gradient magnetic field generator 3 to the static magnetic field generator 2, and radiates from the vacuum vessel 2c via the load support.
- each member of the static magnetic field generator 2 vibrates.
- a leakage magnetic field generated from the main coil 3a and the shield coil 3b of the gradient magnetic field generator 3 and leaked to the main coil 2a and the shield coil 2b side of the static magnetic field generator 2 becomes a vacuum vessel (outer wall) 2c or a radiation shield.
- the eddy current is induced in the conductive member such as the plate 2d and the cooling container 2e, and these eddy currents are coupled with the static magnetic field so that the Lorentz force acts on the conductive member (outer wall).
- the conductive member (outer wall) vibrates.
- the conductor ring 5 (5a, 5b) vibrates with the vibration of the gradient magnetic field generator 3.
- the relative distance between the conductor ring 5 (5a, 5b) and the main coil 2a and the shield coil 2b of the static magnetic field generator 2 is changed by the vibration.
- the magnetic flux linked to the conductor ring 5 (5a, 5b) changes, and an eddy current is induced in the conductor ring 5 (5a, 5b).
- the frequency of vibration is relatively low, the effect of vibration damping due to eddy current heat generation is significant.
- the eddy current induced in the conductor ring 5 (5a, 5b) is coupled with the magnetic field generated by the static magnetic field generation source (main coil 2a, shield coil 2b) to form the conductor ring 5 (
- the Lorentz force acting on 5a, 5b) acts in the direction to cancel the vibration of the conductor ring 5 (5a, 5b).
- the electromagnetic ring which tries to maintain the positional relationship between the conductor ring 5 (5a, 5b) and the static magnetic field generation source (main coil 2a, shield coil 2b). Reaction force acts.
- the vibration of the conductor ring 5 (5a, 5b) is suppressed by the static magnetic field.
- the vibration of the gradient magnetic field generator 3 mechanically coupled to the conductor ring 5 (5a, 5b) (relative position invariant) is also suppressed.
- the rigidity of the gradient magnetic field generator 3 can be increased by mechanically coupling the conductor ring 5 (5a, 5b) to the gradient magnetic field generator 3 (relative position invariant). This increases the effect of mechanically reducing the vibration of the gradient magnetic field generator 3.
- the vibration propagation to the static magnetic field generator 2 is also reduced, and the vibration of the static magnetic field generator 2 is also suppressed.
- the above-mentioned electromagnetic vibration suppressing effect is obtained more strongly as the change in the linkage flux when the conductor ring 5 (5a, 5b) vibrates is larger.
- the main coil 2a of the static magnetic field generation source in the MRI apparatus 1 is provided with the imaging space 8 in order to make the imaging space 8 in which the uniform magnetic field 7 is generated as wide as possible. It is arranged so that the magnetomotive force becomes larger at positions farther away from the main coil 2a, that is, at both ends in the z-axis direction (direction of the uniform magnetic field 7).
- the conductor ring 5 (5a, 5b) is disposed in the vicinity of the main coil 2a at both ends in the z-axis direction (the direction of the uniform magnetic field 7), that is, in the z-axis direction, on both outer sides of the imaging space
- the said vibration suppression effect can be obtained effectively.
- a leakage magnetic field leaking from the gradient magnetic field generator 3 to the static magnetic field generator 2 is shielded, and an eddy current is generated in a conductive member constituting the static magnetic field generator 2. Decreases and Lorentz force decreases. This also reduces the vibration of the static magnetic field generator 2.
- the leakage magnetic field of the gradient magnetic field generator 3 tends to increase near both ends of the gradient magnetic field generator 3 in the z-axis direction. In this vicinity, the magnetomotive force of the main coil 2a of the static magnetic field generation source is also large.
- the tomographic image may be deteriorated due to an error magnetic field due to the eddy current when the tomographic image is taken.
- the distance between the imaging space 8 and the conductor rings 5 (5a, 5b) is increased by disposing the conductor ring 5 (5a, 5b) in the arrangement region R away from the imaging space 8.
- the influence of the error magnetic field due to the eddy current can be reduced.
- a reduction in eddy current generated in the static magnetic field generator 2 due to the leakage magnetic field shielding effect of the conductor ring 5 (5a, 5b) also acts as a reduction effect of the error magnetic field.
- the conductor ring 5 As described above, according to the conductor ring 5 (5a, 5b), it is possible to obtain a vibration suppressing effect while reducing the influence of the error magnetic field on the imaging space 8 by the eddy current generated in the conductor ring 5 (5a, 5b). Can do. Further, since the conductor ring 5 (5a, 5b) is installed in the arrangement region R, a mechanical space such as a vibration damping material or a sound absorbing material is used by using a space where the conductor ring 5 (5a, 5b) is not installed. Installation of vibration suppression means, installation of members such as coils included in the gradient magnetic field generator 3, and the static magnetic field generation source (main coil 2a, shield coil 2b) inside the static magnetic field generator 2 are brought closer to the imaging space 8 side.
- FIG. 4 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the second embodiment of the present invention.
- the MRI apparatus 1 of the second embodiment is different from the MRI apparatus 1 of the first embodiment in that a plurality of conductor rings 5 are arranged in each of the pair of arrangement regions R.
- a plurality (three in the example of FIG. 4) of conductor rings 5a 1 , 5a 2 , 5a 3 are provided in one of the pair of arrangement regions R.
- a plurality of (three in the example of FIG. 4) conductor rings 5b 1 , 5b 2 , 5b 3 are provided on the other of the pair of arrangement regions R.
- the plurality of conductor rings 5a 1 , 5a 2 , 5a 3 have a ring shape with the z-axis as a common central axis.
- the plurality of conductor rings 5a 1 , 5a 2 , 5a 3 are arranged in the z-axis direction.
- the width in the z-axis direction of the plurality of conductor rings 5a 1 , 5a 2 , 5a 3 is desirably wider as the distance from the imaging space 8 in the z-axis direction becomes larger ((width of the conductor ring 5a 1 )> (conductor) Width of ring 5a 2 )> (width of conductor ring 5a 3 )).
- the plurality of conductor rings 5b 1 , 5b 2 , 5b 3 have a ring shape with the z axis as a common central axis.
- the plurality of conductor rings 5b 1 , 5b 2 , 5b 3 are arranged in the z-axis direction.
- the width in the z-axis direction of the plurality of conductor rings 5b 1 , 5b 2 , 5b 3 is desirably wider as the distance from the imaging space 8 in the z-axis direction becomes larger ((width of the conductor ring 5b 1 )> (conductor) Width of ring 5b 2 )> (width of conductor ring 5b 3 )).
- the plurality of conductor rings 5a 1 , 5a 2 , 5a 3 and the plurality of conductor rings 5b 1 , 5b 2 , 5b 3 eddy currents can be generated in a wider range, so that electromagnetic vibration is suppressed. The effect can be further enhanced. Moreover, the mechanical vibration suppression effect of the gradient magnetic field generator 3 can also be obtained as in the first embodiment. Furthermore, when the conductor ring 5a and the conductor ring 5b of the first embodiment are divided into a plurality of conductor rings 5a 1 , 5a 2 , 5a 3 and a plurality of conductor rings 5b 1 , 5b 2 , 5b 3. Considering this, the size of the eddy current generated can be reduced, and the heat generation efficiency can be increased because eddy current heat generation is dispersed.
- FIG. 5 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the third embodiment of the present invention.
- the MRI apparatus 1 of the third embodiment is different from the MRI apparatus 1 of the first embodiment in that the conductor ring 5 (5a, 5b) is mechanically connected to the static magnetic field generator 2 (vacuum vessel 2c). It is a point connected to (relative position invariant).
- the conductor ring 5 (5a, 5b) is provided on the opposite side of the imaging space 8 where the uniform magnetic field 7 (see FIG. 2) is generated with the static magnetic field generation source 2a interposed therebetween.
- the use of the conductor ring 5 (5a, 5b) having a resistance lower than that of the material of the vacuum vessel 2c enhances the magnetic coupling and has a great vibration suppressing effect. Can be obtained.
- the installation of the conductor ring 5 (5a, 5b) provides a mechanical vibration suppressing effect of the vacuum vessel 2c.
- the installation of the conductor ring 5 (5a, 5b) provides the vibration suppression effect by shielding the leakage magnetic field from the gradient magnetic field generator 3 as in the first embodiment.
- the thermal conductivity of the vacuum vessel 2c is higher than that of the gradient magnetic field generator 3, the heat radiation characteristics of the conductor ring 5 (5a, 5b) that generates heat by eddy current heat generation can be improved.
- FIG. 6 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to a modification of the third embodiment of the present invention.
- the MRI apparatus 1 of the modified example of the third embodiment is different from the MRI apparatus 1 of the third embodiment in that the conductor ring 5 (5a, 5b) is located on the vacuum side of the vacuum container 2c. 2c is mechanically (relative position invariant). According to this, the radiated sound accompanying the vibration of the conductor ring 5 (5a, 5b) does not propagate in the air, and the noise can be reduced.
- the conductor ring 5 (5a, 5b) can be accommodated in the vacuum vessel 2c, the space for accommodating the subject 10 surrounded by the static magnetic field generator 2 is expanded, and the MRI apparatus 1 having a higher degree of openness can be provided. It becomes.
- FIG. 7 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the fourth embodiment of the present invention.
- the MRI apparatus 1 of the fourth embodiment is different from the MRI apparatus 1 of the second embodiment (FIG. 4) in that the conductor rings 5 (5a 1 , 5a 2 , 5a 3 , 5b 1 , 5b 2 , 5b 3 ) is mechanically (relatively invariant) coupled to the static magnetic field generator 2 (vacuum vessel 2c). According to this, the effect in 1st, 2nd and 3rd embodiment can be acquired.
- FIG. 8 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to a modification of the fourth embodiment of the present invention.
- the MRI apparatus 1 of the modification of the fourth embodiment is different from the MRI apparatus 1 of the fourth embodiment in that the conductor rings 5 (5a 1 , 5a 2 , 5a 3 , 5b 1 , 5b 2 , 5b 3 ) is that the vacuum side of the vacuum vessel 2c is mechanically (relatively invariant) coupled to the vacuum vessel 2c. According to this, the effect in the modification of 1st, 2nd embodiment and 3rd Embodiment can be acquired.
- FIG. 9 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the fifth embodiment of the present invention.
- the MRI apparatus 1 of the fifth embodiment differs from the MRI apparatus 1 of the first embodiment in that the conductor ring 5 (5a, 5b (see the first embodiment, FIG. 3)) is a gradient magnetic field.
- the first conductor ring 5 (5ai, 5bi) that is mechanically (relatively invariant) coupled to the generator 3 and the static magnetic field generator 2 (vacuum vessel 2c) are mechanically (relatively invariant) coupled,
- the first conductor ring 5ai (5) and the second conductor ring 5ao (5) are close to each other, do not mechanically support each other, and are electrically insulated from each other.
- first conductor ring 5bi (5) and the second conductor ring 5bo (5) face each other in close proximity, do not mechanically support each other, and are electrically insulated from each other.
- This vibration suppressing effect is obtained when the second conductor ring 5 (5ao, 5bo) on the static magnetic field generator 2 side is provided on the imaging space 8 side of the vacuum vessel 2c, and the first conductor ring 5 (5ai, 5bi) and the second conductor ring 5 (5ao, 5bo) are shortened, and thus become stronger.
- FIG. 10 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the modification of the fifth embodiment of the present invention.
- the MRI apparatus 1 of the modification of the fifth embodiment is different from the MRI apparatus 1 of the fifth embodiment in that the second conductor ring 5 (5ao, 5bo) is on the vacuum side of the vacuum vessel 2c. The point is that it is mechanically (relatively invariant) coupled to the vacuum vessel 2c. Also by this, the effect in the modification of 1st Embodiment, 3rd Embodiment, and 5th Embodiment can be acquired.
- FIG. 11 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the sixth embodiment of the present invention.
- the MRI apparatus 1 of the sixth embodiment is different from the MRI apparatus 1 of the fifth embodiment in that the first conductor ring 5 (5ai, 5bi (fifth embodiment, see FIG. 9)) A plurality of points are arranged in each of the pair of arrangement regions R.
- a plurality of second conductor rings 5 (5ao, 5bo (see the fifth embodiment, FIG. 9)) are arranged in each of the pair of arrangement regions R.
- first conductor rings 5ai 1 , 5ai 2 , 5ai 3 are provided in one of the pair of arrangement regions R.
- Plural (three in the example of FIG. 11) first conductor rings 5bi 1 , 5bi 2 , 5bi 3 are provided on the other of the pair of arrangement regions R.
- the plurality of first conductor rings 5ai 1 , 5ai 2 , 5ai 3 have a ring shape with the z-axis as a common central axis.
- the plurality of first conductor rings 5ai 1 , 5ai 2 , 5ai 3 are arranged in the z-axis direction.
- the width in the z-axis direction of the plurality of first conductor rings 5ai 1 , 5ai 2 , 5ai 3 is desirably wider as the distance from the imaging space 8 is increased in the z-axis direction ((width of the first conductor ring 5ai 1 )> (Width of first conductor ring 5ai 2 )> (width of first conductor ring 5ai 3 )).
- the plurality of first conductor rings 5bi 1 , 5bi 2 , 5bi 3 have a ring shape with the z axis as a common central axis.
- the plurality of first conductor rings 5bi 1 , 5bi 2 , 5bi 3 are arranged in the z-axis direction.
- the width in the z-axis direction of the plurality of first conductor rings 5bi 1 , 5bi 2 , 5bi 3 is desirably wider as the distance from the imaging space 8 is increased in the z-axis direction ((width of the first conductor ring 5bi 1 )> (Width of first conductor ring 5bi 2 )> (width of first conductor ring 5bi 3 )).
- eddy currents can be generated in a wider range.
- the suppression effect can be further enhanced.
- the effect in 1st, 2nd, 4th, and 5th embodiment can be acquired.
- a plurality (three in the example of FIG. 11) of second conductor rings 5ao 1 , 5ao 2 , and 5ao 3 are provided in one of the pair of arrangement regions R.
- Plural (three in the example of FIG. 11) second conductor rings 5 bo 1 , 5 bo 2 , 5 bo 3 are provided on the other of the pair of arrangement regions R.
- the plurality of second conductor rings 5ao 1 , 5ao 2 , 5ao 3 have a ring shape with the z-axis as a common central axis.
- the plurality of second conductor rings 5ao 1 , 5ao 2 , 5ao 3 are arranged in the z-axis direction.
- the width of the plurality of second conductor rings 5ao 1 , 5ao 2 , 5ao 3 in the z-axis direction becomes wider as the distance from the imaging space 8 increases in the z-axis direction ((width of the second conductor ring 5ao 1 )> (Width of second conductor ring 5ao 2 )> (width of second conductor ring 5ao 3 )).
- the plurality of second conductor rings 5bo 1 , 5bo 2 , 5bo 3 have a ring shape with the z axis as a common central axis.
- the plurality of second conductor rings 5bo 1 , 5bo 2 , 5bo 3 are arranged in the z-axis direction. It is desirable that the width of the plurality of second conductor rings 5bo 1 , 5bo 2 , 5bo 3 in the z-axis direction becomes wider as the distance from the imaging space 8 increases in the z-axis direction ((width of the second conductor ring 5bo 1 )> (Width of second conductor ring 5bo 2 )> (width of second conductor ring 5bo 3 )).
- the plurality of second conductor rings 5ao 1 , 5ao 2 , 5ao 3 and the plurality of second conductor rings 5bo 1 , 5bo 2 , 5bo 3 can generate eddy currents in a wider range, The suppression effect can be further enhanced.
- first conductor ring 5ai 1 and the second conductor ring 5ao 1 are close to each other and face each other.
- the first conductor ring 5ai 2 and the second conductor ring 5ao 2 are close to each other and face each other.
- the first conductor ring 5ai 3 and the second conductor ring 5ao 3 are close to each other and face each other.
- the first conductor ring 5bi 1 and the second conductor ring 5bo 1 are close to each other and face each other.
- a first conductor ring 5bi 2 and the second conductor ring 5Bo 2 are opposed in close proximity.
- the first conductor ring 5bi 3 and the second conductor ring 5bo 3 are close to each other and face each other.
- FIG. 12 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to a modification of the sixth embodiment of the present invention.
- the MRI apparatus 1 of the modified example of the sixth embodiment is different from the MRI apparatus 1 of the sixth embodiment in that the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 5bo 3 ) is mechanically (relatively invariant) coupled to the vacuum vessel 2c on the vacuum side of the vacuum vessel 2c. Also by this, the effect in 1st, 2nd, 4th, 5th, and 6th embodiment can be acquired.
- FIG. 13 shows a schematic diagram of a portion above the z axis of the longitudinal section of the MRI apparatus 1 according to the seventh embodiment of the present invention.
- the MRI apparatus 1 of the seventh embodiment is different from the MRI apparatus 1 of the fifth embodiment in that the conductor ring 5 (5a, 5b) is further different from the first conductor ring 5 (5ai, 5bi).
- the third conductor ring 5 (5am, 5bo) disposed between the second conductor rings 5 (5ao, 5bo) and insulated from the first conductor ring 5 (5ai, 5bi) and the second conductor ring 5 (5ao, 5bo). 5 bm).
- the third conductor ring 5 (5am, 5bm) can be supported on, for example, the ceiling, wall, or floor of the room where the MRI apparatus 1 is installed.
- the third conductor ring 5am (5) and the first conductor ring 5ai (5) face each other closely, do not mechanically support each other, and are electrically insulated from each other.
- the third conductor ring 5am (5) and the second conductor ring 5ao (5) are close to each other, do not mechanically support each other, and are electrically insulated from each other.
- the third conductor ring 5bm (5) and the first conductor ring 5bi (5) face each other close to each other, do not mechanically support each other, and are electrically insulated from each other.
- the third conductor ring 5bm (5) and the second conductor ring 5bo (5) face each other in close proximity, do not mechanically support each other, and are electrically insulated from each other.
- the width in the z-axis direction of the third conductor ring 5 (5am, 5bm) is the width in the z-axis direction of the first conductor ring 5 (5ai, 5bi) and the z-axis direction of the second conductor ring 5 (5ao, 5bo).
- FIG. 14 the schematic of the upper part from the z-axis of the longitudinal cross-section of the MRI apparatus 1 which concerns on the modification of the 7th Embodiment of this invention is shown.
- the MRI apparatus 1 of the modified example of the seventh embodiment is different from the MRI apparatus 1 of the seventh embodiment in that the second conductor ring 5 (5ao, 5bo) is on the vacuum side of the vacuum vessel 2c. The point is that it is mechanically (relatively invariant) coupled to the vacuum vessel 2c. Also by this, an effect similar to the effect in the fifth embodiment can be obtained.
- FIG. 15 is a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the eighth embodiment of the present invention.
- conductor ring 5 is further first conductor ring 5 (5ai 1, 5ai 2 5ai 3 , 5bi 1 , 5bi 2 , 5bi 3 ) and the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 , 5bo 3 ) and the first conductor ring 5 ( 5ai 1 , 5ai 2 , 5ai 3 , 5bi 1 , 5bi 2 , 5bi 3 ) and the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 , 5bo 3 ) and the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo
- the third conductor rings 5am 1 , 5am 2 , 5am 3 (5) and the first conductor rings 5ai 1 , 5ai 2 , 5ai 3 (5) are close to each other and do not mechanically support each other, In addition, they are electrically insulated from each other.
- the third conductor rings 5am 1 , 5am 2 , 5am 3 (5) and the second conductor rings 5ao 1 , 5ao 2 , 5ao 3 (5) are close to each other and mechanically supported by each other. And are electrically insulated from each other.
- the third conductor rings 5bm 1 , 5bm 2 , 5bm 3 (5) and the first conductor rings 5bi 1 , 5bi 2 , 5bi 3 (5) are close to each other and do not mechanically support each other, In addition, they are electrically insulated from each other.
- the third conductor rings 5bm 1 , 5bm 2 , 5bm 3 (5) and the second conductor rings 5bo 1 , 5bo 2 , 5bo 3 (5) are close to each other and mechanically supported by each other. And are electrically insulated from each other.
- the width of the third conductor ring 5 (5am 1 , 5bm 1 ) in the z-axis direction is equal to the width of the first conductor ring 5 (5ai 1 , 5bi 1 ) in the z-axis direction and the second conductor ring 5 (5ao 1 , 5bo).
- the third conductive ring 5 (5am 3, 5BM 3 )
- FIG. 16 is a schematic view of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the modification of the eighth embodiment of the present invention.
- the MRI apparatus 1 according to the modification of the eighth embodiment is different from the MRI apparatus 1 of the eighth embodiment in that the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 5bo 3 ) is mechanically (relatively invariant) coupled to the vacuum vessel 2c on the vacuum side of the vacuum vessel 2c. Also by this, the same effect as the effect in the eighth embodiment can be obtained.
- FIG. 17 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the ninth embodiment of the present invention.
- the MRI apparatus 1 of the ninth embodiment is different from the MRI apparatus 1 of the seventh embodiment in that it is between the first conductor ring 5 (5ai, 5bi) and the second conductor ring 5 (5ao, 5bo). This is the point that the elastic body 11 is provided.
- An elastic body 11 is provided between the first conductor ring 5 (5ai, 5bi) and the third conductor ring 5 (5am, 5bm).
- An elastic body 11 is also provided between the second conductor ring 5 (5ao, 5bo) and the third conductor ring 5 (5am, 5bm).
- the elastic body 11 is not limited to the spring material as shown in FIG. 17 and may be a rubber material.
- a rubber material is filled between the first conductor ring 5 (5ai, 5bi), the second conductor ring 5 (5ao, 5bo), and the third conductor ring 5 (5am, 5bm), and the first conductor ring 5 (5ai). 5bi), the second conductor ring 5 (5ao, 5bo) and the third conductor ring 5 (5am, 5bm) may be bonded together and integrated.
- FIG. 18 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the tenth embodiment of the present invention.
- the MRI apparatus 1 of the tenth embodiment is different from the MRI apparatus 1 of the eighth embodiment in that the first conductor ring 5 (5ai 1 , 5ai 2 , 5ai 3 , 5bi 1 , 5bi 2 , 5bi 3 ) And the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 , 5bo 3 ).
- the first conductor ring 5 (5ai 1, 5ai 2, 5ai 3, 5bi 1, 5bi 2, 5bi 3) and the third conductor ring 5 (5am 1, 5am 2, 5am 3, 5bm 1, 5bm 2, 5bm 3)
- An elastic body 11 is provided therebetween.
- the second conductor ring 5 (5ao 1, 5ao 2, 5ao 3, 5bo 1, 5bo 2, 5bo 3) and the third conductor ring 5 (5am 1, 5am 2, 5am 3, 5bm 1, 5bm 2, 5bm 3)
- An elastic body 11 is also provided therebetween.
- the third conductor ring 5 (5am 1, 5am 2, 5am 3, 5bm 1, 5bm 2, 5bm 3) , without support from the outside, the first conductor ring 5 (5ai 1, 5ai 2, 5ai 3 5bi 1 , 5bi 2 , 5bi 3 ) and the second conductor ring 5 (5ao 1 , 5ao 2 , 5ao 3 , 5bo 1 , 5bo 2 , 5bo 3 ). Then, the same effect as in the eighth embodiment can be obtained.
- FIG. 19 shows a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the eleventh embodiment of the present invention.
- the MRI apparatus 1 of the eleventh embodiment is different from the MRI apparatus 1 of the fifth embodiment in that the first conductor ring 5ai that is mechanically (relatively invariant) coupled to the gradient magnetic field generator 3.
- 5bi 1 (5ai, 5bi (fifth embodiment, see FIG.
- the second conductor rings 5ao 2 and 5bo 2 (5ao and 5bo (see the fifth embodiment, FIG. 9)) insulated from 5bi 1 (5ai and 5bi) are not opposed to each other. For this reason, the first conductor rings 5ai 1 , 5bi 1 (5ai, 5bi) face each other close to the static magnetic field generator 2 (vacuum vessel 2c).
- the second conductor rings 5ao 2 and 5bo 2 (5ao and 5bo) face each other in the vicinity of the gradient magnetic field generator 3.
- the leakage magnetic field shielding effect demonstrated in 1st Embodiment can be exhibited more efficiently. Further, since the first conductor rings 5ai 1 and 5bi 1 and the second conductor rings 5ao 2 and 5bo 2 are not opposed to each other, the interval between the static magnetic field generator 2 and the gradient magnetic field generator 3 can be reduced. .
- the width of the first conductor rings 5ai 1 and 5bi 1 in the z-axis direction is preferably larger than the width of the second conductor rings 5ao 2 and 5bo 2 in the z-axis direction.
- FIG. 20 is a schematic diagram of a portion above the z-axis of the longitudinal section of the MRI apparatus 1 according to the twelfth embodiment of the present invention.
- the MRI apparatus 1 of the twelfth embodiment is different from the MRI apparatus 1 of the eleventh embodiment in that the first conductor rings 5ai 1 , 5ai 3 , 5bi 1 , 5bi 3 are in a pair of arrangement regions R.
- Each is a plurality of points.
- a plurality of second conductor rings 5ao 2 and 5bo 2 may be arranged in each of the pair of arrangement regions R.
- the first conductor rings 5ai 1 , 5ai 3 , 5bi 1 , 5bi 3 and the second conductor rings 5ao 2 , 5bo 2 are alternately arranged in the z-axis direction.
- the width of the plurality of conductor rings 5ai 1 , 5ai 3 , 5bi 1 , 5bi 3 , 5ao 2 , 5bo 2 in the z-axis direction is preferably wider as the distance from the imaging space 8 is increased in the z-axis direction ((first 1 conductor ring 5ai 1 width)> (second conductor ring 5ao 2 width)> (first conductor ring 5ai 3 width), (first conductor ring 5bi 1 width)> (second conductor ring 5bo 2 width) Width)> (width of the first conductor ring 5bi 3 )).
- first 1 conductor ring 5ai 1 width >
- superconducting coils are taken up as the static magnetic field generation sources 2a and 2b, but the present invention is not limited to this.
- a normal conducting coil or a permanent magnet may be used as the static magnetic field generating sources 2a and 2b.
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Abstract
Description
図1に、本発明の第1の実施形態に係るMRI(磁気共鳴イメージング)装置1の斜視図を示す。MRI装置1は、被検体10を内部の撮像空間8に導入可能な円筒形状の静磁場発生装置2と、導入された被検体10の生体組織を構成する原子核に核磁気共鳴を起こさせるために高周波信号を照射する照射コイル4と、被検体10から発せられる各々の信号に位置情報を与えるための傾斜磁場発生装置3と、傾斜磁場発生装置3の径方向外側に設けられる導体リング5(5a)と、被検体10から発せられる信号を受信するための受信コイル22と、被検体10を積載する寝台6等で構成されている。
図4に、本発明の第2の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第2の実施形態のMRI装置1が、第1の実施形態のMRI装置1と異なっている点は、導体リング5が、一対の配置領域R内それぞれに複数配置されている点である。具体的には、一対の配置領域Rの一方に、複数(図4の例では3つ)の導体リング5a1、5a2、5a3が、設けられている。一対の配置領域Rの他方に、複数(図4の例では3つ)の導体リング5b1、5b2、5b3が、設けられている。複数の導体リング5a1、5a2、5a3は、z軸を互いに共通する中心軸とするリング形状をしている。複数の導体リング5a1、5a2、5a3は、z軸方向に配列されている。複数の導体リング5a1、5a2、5a3のz軸方向の幅は、z軸方向に撮像空間8から離れる程、広くなっているのが望ましい((導体リング5a1の幅)>(導体リング5a2の幅)>(導体リング5a3の幅))。同様に、複数の導体リング5b1、5b2、5b3は、z軸を互いに共通する中心軸とするリング形状をしている。複数の導体リング5b1、5b2、5b3は、z軸方向に配列されている。複数の導体リング5b1、5b2、5b3のz軸方向の幅は、z軸方向に撮像空間8から離れる程、広くなっているのが望ましい((導体リング5b1の幅)>(導体リング5b2の幅)>(導体リング5b3の幅))。複数の導体リング5a1、5a2、5a3と、複数の導体リング5b1、5b2、5b3とによれば、より広範囲に渦電流を発生させることができるので、電磁気的な振動の抑制効果を一層高めることができる。また、第1の実施形態と同様に、傾斜磁場発生装置3の機械的な振動抑制効果も得られる。更に、第1の実施形態の導体リング5aと導体リング5bを、複数の複数の導体リング5a1、5a2、5a3と、複数の導体リング5b1、5b2、5b3とに分割したと考えれば、発生させる渦電流の渦の大きさを小さくすることができ、渦電流発熱が分散するので放熱の効率を高めることができる。
図5に、本発明の第3の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第3の実施形態のMRI装置1が、第1の実施形態のMRI装置1と異なっている点は、導体リング5(5a、5b)が、静磁場発生装置2(真空容器2c)に機械的(相対位置不変)に結合している点である。導体リング5(5a、5b)は、静磁場発生源2aを挟んで均一磁場7(図2参照)が発生する撮像空間8の反対側に設けられている。断層画像の撮影時、傾斜磁場発生装置3に電流が通電されると、傾斜磁場発生装置3から発生し静磁場発生装置2側に漏れる漏れ磁場によって真空容器2cに渦電流が誘導され、ローレンツ力により真空容器2cに振動が発生する。真空容器2cが振動すると、導体リング5(5a、5b)も共に振動して静磁場発生源のメインコイル2aとシールドコイル2bとの相対距離が変化することで、振動を抑制する方向にローレンツ力が導体リング5(5a、5b)に作用し、導体リング5(5a、5b)と真空容器2cの振動が抑制される。真空容器2cを構成する材料が電気導体である場合は、その真空容器2cの材料よりも低抵抗の導体リング5(5a、5b)を用いることで、磁気的な結合が強まり、大きな振動抑制効果を得ることができる。また、導体リング5(5a、5b)の設置により、第1の実施形態とは異なり、真空容器2cの機械的な振動抑制効果が得られる。また、導体リング5(5a、5b)の設置により、第1の実施形態と同様に、傾斜磁場発生装置3からの漏れ磁場遮蔽による振動抑制効果が得られる。更に、傾斜磁場発生装置3より真空容器2cの方が熱伝導率が高い場合、渦電流発熱によって発熱する導体リング5(5a、5b)の放熱特性を向上させることができる。
図6に、本発明の第3の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第3の実施形態の変形例のMRI装置1が、第3の実施形態のMRI装置1と異なっている点は、導体リング5(5a、5b)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによれば、導体リング5(5a、5b)の振動に伴う放射音が空気伝播せず、騒音を小さくできる。また、真空容器2c内に導体リング5(5a、5b)が収納できるので、静磁場発生装置2によって囲まれる被検体10が収容される空間が広がり、より開放度の高いMRI装置1が提供可能となる。
図7に、本発明の第4の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第4の実施形態のMRI装置1が、第2の実施形態(図4)のMRI装置1と異なっている点は、導体リング5(5a1、5a2、5a3、5b1、5b2、5b3)が、静磁場発生装置2(真空容器2c)に機械的(相対位置不変)に結合している点である。これによれば、第1と第2と第3の実施形態における効果を得ることができる。
図8に、本発明の第4の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第4の実施形態の変形例のMRI装置1が、第4の実施形態のMRI装置1と異なっている点は、導体リング5(5a1、5a2、5a3、5b1、5b2、5b3)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによれば、第1と第2の実施形態と第3の実施形態の変形例における効果を得ることができる。
図9に、本発明の第5の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第5の実施形態のMRI装置1が、第1の実施形態のMRI装置1と異なっている点は、導体リング5(5a、5b(第1の実施形態、図3参照))が、傾斜磁場発生装置3に機械的(相対位置不変)に結合している第1導体リング5(5ai、5bi)と、静磁場発生装置2(真空容器2c)に機械的(相対位置不変)に結合し、第1導体リング5(5ai、5bi)に対向するように配置され、第1導体リング5(5ai、5bi)から絶縁されている第2導体リング5(5ao、5bo)とを有している点である。第1導体リング5ai(5)と第2導体リング5ao(5)とは、近接して対向し、且つ、互いに機械的に支持せず、且つ、互いに電気的に絶縁されている。同様に、第1導体リング5bi(5)と第2導体リング5bo(5)とは、近接して対向し、且つ、互いに機械的に支持せず、且つ、互いに電気的に絶縁されている。第1導体リング5(5ai、5bi)のz軸方向の幅は、第2導体リング5(5ao、5bo)のz軸方向の幅に略等しくなっている。なお、(第1導体リング5aiの幅)=(第2導体リング5aoの幅)、(第1導体リング5biの幅)=(第2導体リング5boの幅)である。
図10に、本発明の第5の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第5の実施形態の変形例のMRI装置1が、第5の実施形態のMRI装置1と異なっている点は、第2導体リング5(5ao、5bo)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによっても、第1の実施形態と第3の実施形態の変形例と第5の実施形態とにおける効果を得ることができる。
図11に、本発明の第6の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第6の実施形態のMRI装置1が、第5の実施形態のMRI装置1と異なっている点は、第1導体リング5(5ai、5bi(第5の実施形態、図9参照))が、一対の配置領域R内それぞれに複数配置されている点である。また、第2導体リング5(5ao、5bo(第5の実施形態、図9参照))が、一対の配置領域R内それぞれに複数配置されている点である。
図12に、本発明の第6の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第6の実施形態の変形例のMRI装置1が、第6の実施形態のMRI装置1と異なっている点は、第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによっても、第1と第2と第4と第5と第6の実施形態における効果を得ることができる。
図13に、本発明の第7の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第7の実施形態のMRI装置1が、第5の実施形態のMRI装置1と異なっている点は、導体リング5(5a、5b)が、さらに、第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)の間に配置され、第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)から絶縁されている第3導体リング5(5am、5bm)を有している点である。これによれば、導体リングの数を増やすことで、導体リング間の間隔を狭めることができ、第5の実施形態で記した振動抑制効果を一層強く得ることができる。なお、第3導体リング5(5am、5bm)は、例えば、MRI装置1が設置される部屋の天井や壁、床に支持させることができる。
図14に、本発明の第7の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第7の実施形態の変形例のMRI装置1が、第7の実施形態のMRI装置1と異なっている点は、第2導体リング5(5ao、5bo)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによっても、第5の実施形態における効果と同様な効果を得ることができる。
図15に、本発明の第8の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第8の実施形態のMRI装置1が、第6の実施形態のMRI装置1と異なっている点は、導体リング5(5a、5b)が、さらに、第1導体リング5(5ai1、5ai2、5ai3、5bi1、5bi2、5bi3)と第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)の間に配置され、第1導体リング5(5ai1、5ai2、5ai3、5bi1、5bi2、5bi3)と第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)から絶縁されている第3導体リング5(5am1、5am2、5am3、5bm1、5bm2、5bm3)を有している点である。これによれば、導体リングの数を増やすことで、導体リング間の間隔を狭めることができ、第5の実施形態で記した振動抑制効果を一層強く得ることができる。
図16に、本発明の第8の実施形態の変形例に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第8の実施形態の変形例のMRI装置1が、第8の実施形態のMRI装置1と異なっている点は、第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)が、真空容器2cの真空側において、真空容器2cに機械的(相対位置不変)に結合している点である。これによっても、8の実施形態における効果と同様の効果を得ることができる。
図17に、本発明の第9の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第9の実施形態のMRI装置1が、第7の実施形態のMRI装置1と異なっている点は、第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)の間に弾性体11が設けられている点である。第1導体リング5(5ai、5bi)と第3導体リング5(5am、5bm)の間に弾性体11が設けられている。第2導体リング5(5ao、5bo)と第3導体リング5(5am、5bm)の間にも弾性体11が設けられている。これによって、第3導体リング5(5am、5bm)は、外部から支持することなく、第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)によって、柔に支持することができる。そして、第7の実施形態と同様の効果を得ることができる。なお、弾性体11としては、図17に示したような、ばね材に限られず、ゴム材であってもよい。第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)と第3導体リング5(5am、5bm)の間に、ゴム材を充填して、第1導体リング5(5ai、5bi)と第2導体リング5(5ao、5bo)と第3導体リング5(5am、5bm)を互いに接着し、一体化してもよい。もちろん、ばね材を用いて一体化してもよい。
図18に、本発明の第10の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第10の実施形態のMRI装置1が、第8の実施形態のMRI装置1と異なっている点は、第1導体リング5(5ai1、5ai2、5ai3、5bi1、5bi2、5bi3)と第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)の間に弾性体11が設けられている点である。第1導体リング5(5ai1、5ai2、5ai3、5bi1、5bi2、5bi3)と第3導体リング5(5am1、5am2、5am3、5bm1、5bm2、5bm3)の間に弾性体11が設けられている。第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)と第3導体リング5(5am1、5am2、5am3、5bm1、5bm2、5bm3)の間にも弾性体11が設けられている。これによって、第3導体リング5(5am1、5am2、5am3、5bm1、5bm2、5bm3)は、外部から支持することなく、第1導体リング5(5ai1、5ai2、5ai3、5bi1、5bi2、5bi3)と第2導体リング5(5ao1、5ao2、5ao3、5bo1、5bo2、5bo3)によって、柔に支持することができる。そして、第8の実施形態と同様の効果を得ることができる。
図19に、本発明の第11の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第11の実施形態のMRI装置1が、第5の実施形態のMRI装置1と異なっている点は、傾斜磁場発生装置3に機械的(相対位置不変)に結合している第1導体リング5ai1、5bi1(5ai、5bi(第5の実施形態、図9参照))と、静磁場発生装置2(真空容器2c)に機械的(相対位置不変)に結合し、第1導体リング5ai1、5bi1(5ai、5bi)から絶縁されている第2導体リング5ao2、5bo2(5ao、5bo(第5の実施形態、図9参照))とが、対向していない点である。このため、第1導体リング5ai1、5bi1(5ai、5bi)は、静磁場発生装置2(真空容器2c)に近接して対向している。第2導体リング5ao2、5bo2(5ao、5bo)は、傾斜磁場発生装置3に近接して対向している。これによれば、第1の実施形態で説明した漏れ磁場遮蔽効果をより効率的に発揮することができる。また、第1導体リング5ai1、5bi1と、第2導体リング5ao2、5bo2とが、対向していないので、静磁場発生装置2と傾斜磁場発生装置3の間隔を狭くすることができる。なお、第1導体リング5ai1、5bi1のz軸方向の幅は、第2導体リング5ao2、5bo2のz軸方向の幅より広くなっているのが望ましい。即ち、(第1導体リング5ai1の幅)>(第2導体リング5ao2の幅)、(第1導体リング5bi1の幅)>(第2導体リング5bo2の幅))であることが望ましい。
図20に、本発明の第12の実施形態に係るMRI装置1の縦断面のz軸より上方部分の概略図を示す。第12の実施形態のMRI装置1が、第11の実施形態のMRI装置1と異なっている点は、第1導体リング5ai1、5ai3、5bi1、5bi3が、一対の配置領域R内それぞれに、複数配置されている点である。これに限らず、第2導体リング5ao2、5bo2が、一対の配置領域R内それぞれに、複数配置されていてもよい。第1導体リング5ai1、5ai3、5bi1、5bi3と、第2導体リング5ao2、5bo2とは、z軸方向に、交互に配置されている。複数の導体リング5ai1、5ai3、5bi1、5bi3、5ao2、5bo2のz軸方向の幅は、z軸方向に撮像空間8から離れる程、広くなっているのが望ましい((第1導体リング5ai1の幅)>(第2導体リング5ao2の幅)>(第1導体リング5ai3の幅)、(第1導体リング5bi1の幅)>(第2導体リング5bo2の幅)>(第1導体リング5bi3の幅))。これによれば、より広範囲に渦電流を発生させることができるので、振動の抑制効果を一層高めることができる。
2 静磁場発生装置
2a 静磁場発生源(メインコイル)
2b 静磁場発生源(シールドコイル)
2c 真空容器(静磁場発生装置の外壁)
2d 輻射シールド板
2e 冷却容器
2f 真空容器支持脚
3 傾斜磁場発生装置
3a 傾斜磁場発生源(メインコイル)
3b 傾斜磁場発生源(シールドコイル)
3c レジン
4 照射コイル
5、5a、5b 導体リング
5ai(1、2、3)、5bi(1、2、3) 第1導体リング
5ao(1、2、3)、5bo(1、2、3) 第2導体リング
5am(1、2、3)、5bm(1、2、3) 第3導体リング
6 寝台
7 均一磁場
8 撮像空間
9 傾斜磁場
10 被検体
11 弾性体
22 受信コイル
R 配置領域
Claims (11)
- 空間に均一磁場を発生させる静磁場発生源を有する静磁場発生装置と、
前記均一磁場に傾斜磁場を重畳させる傾斜磁場発生源を有する傾斜磁場発生装置と、
前記静磁場発生源と前記傾斜磁場発生源との間で、前記均一磁場の発生する領域の均一磁場方向両側である一対の配置領域内のそれぞれに配置され互いに離れて対をなす導体リングとを備えたことを特徴とする磁気共鳴イメージング装置。 - 前記導体リングが、一対の前記配置領域内それぞれに複数配置されていることを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。
- 前記導体リングが、前記傾斜磁場発生装置に機械的に結合していることを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。
- 前記導体リングが、前記静磁場発生装置に機械的に結合していることを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。
- 前記導体リングは、
前記傾斜磁場発生装置に機械的に結合している第1導体リングと、
前記静磁場発生装置に機械的に結合し、前記第1導体リングに対向するように配置され、前記第1導体リングから絶縁されている第2導体リングとを有することを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。 - 前記導体リングは、
前記第1導体リングと前記第2導体リングの間に配置され、前記第1導体リングと前記第2導体リングから絶縁されている第3導体リングを有することを特徴とする請求の範囲第5項に記載の磁気共鳴イメージング装置。 - 前記第1導体リングと前記第2導体リングの間に設けられた弾性体を有することを特徴とする請求の範囲第5項に記載の磁気共鳴イメージング装置。
- 前記導体リングは、
前記傾斜磁場発生装置に機械的に結合し、前記静磁場発生装置に対向するように配置されている第1導体リングと、
前記静磁場発生装置に機械的に結合し、前記傾斜磁場発生装置に対向するが前記第1導体リングに対向しないように配置され、前記第1導体リングから絶縁されている第2導体リングとを有することを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。 - 前記導体リングの板厚あたりの電気抵抗率は、前記静磁場発生装置と前記傾斜磁場発生装置の外壁の板厚あたりの電気抵抗率より低いことを特徴とする請求の範囲第1項に記載の磁気共鳴イメージング装置。
- 空間に傾斜磁場を発生させる傾斜磁場発生源と、
前記傾斜磁場発生源を挟んで前記傾斜磁場が発生する前記空間の反対側に設けられ、前記傾斜磁場の発生する領域の前記傾斜磁場の磁場方向両側である一対の配置領域内のそれぞれに配置され互いに離れて対をなす導体リングとを備えたことを特徴とする傾斜磁場発生装置。 - 空間に均一磁場を発生させる静磁場発生源と、
前記静磁場発生源を挟んで前記均一磁場が発生する前記空間の反対側に設けられ、前記均一磁場の発生する領域の前記均一磁場の磁場方向両側である一対の配置領域内のそれぞれに配置され互いに離れて対をなす導体リングとを備えたことを特徴とする静磁場発生装置。
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JPWO2013046957A1 (ja) | 2015-03-26 |
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