JP2015053982A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic resonance imaging apparatus reducing noise by a reduction in vibration of an RF coil.SOLUTION: A vibration attenuating part 13 formed of an outer layer member 11 disposed on the outer peripheral side of an RF coil 3 composed of an RF bobbin 8 and a circuit part 9, and a vibration damping material 12 bonded to the outer layer member 11 is supported to the RF bobbin 8 via a plurality of outer layer support members 10. The vibration attenuating part 13 has a gap with a circuit part 9 and also a plurality of bores 14. Such a structure enables a reduction in vibration of the RF coil 3 without reducing the bore diameter and without degrading cooling performance of the circuit part 9 of the RF coil 3.

Description

  The present invention relates to a magnetic resonance imaging apparatus using magnetic resonance, and more particularly to a technique for reducing noise generated during imaging.

  The magnetic resonance imaging apparatus obtains a magnetic resonance image representing the physical properties of a subject placed in an imaging space using the nuclear magnetic resonance phenomenon of nuclei. In general, a magnetic resonance imaging apparatus generates a static magnetic field generation system that generates a uniform static magnetic field in an imaging space at the center of a space (bore) where a subject enters, and a high-frequency electromagnetic wave for generating nuclear magnetic resonance. A radio frequency (RF) coil, a receiving coil for detecting a nuclear magnetic resonance signal, a gradient magnetic field coil for generating a gradient magnetic field to give positional information to the nuclear magnetic resonance signal, and the like are provided.

  At the time of imaging, a linear gradient magnetic field is superimposed on the subject placed in a uniform static magnetic field in the three directions of X, Y, and Z according to the desired pulse sequence, and the subject's atomic spin is magnetically excited. Is done. In this way, a pulsed current is passed through the gradient coil during imaging. When a pulse current is passed through a gradient magnetic field coil arranged in a static magnetic field, Lorentz force acts due to the coupling between the static magnetic field and the current, and the gradient magnetic field coil vibrates to generate a vibration radiation sound. This vibration radiation sound is transmitted to the subject, and the subject is exposed to noise. Therefore, by forming a sealed space so as to cover the gradient magnetic field coil, a structure for shielding vibration radiation sound of the gradient magnetic field coil is taken, and noise to the subject is reduced.

  An RF coil and a gantry cover that forms the appearance of the apparatus are arranged on the imaging space side (inner peripheral side) of the gradient magnetic field coil. Conventionally, the gantry cover, the RF coil, and the gradient magnetic field coil are arranged in three layers concentrically from the inner peripheral side to form a sealed space that covers the gradient magnetic field coil with the gantry cover and to form a bore. In recent years, in order to ensure a large bore diameter, it is required to reduce the gap between the gradient coil and the gantry cover. Therefore, the gap between the gradient coil and the gantry cover is reduced by making the RF coil also have a gantry cover function and arranging the RF coil and the gantry cover at the same position. The gantry cover and the RF coil are also called sound insulation members and form a bore and a sealed space that covers the gradient coil.

  The vibration of the gradient magnetic field coil is caused by solid propagation through the support member of the gradient magnetic field coil, and the sound generated by the vibration of the gradient magnetic field coil vibrates the sound insulation member constituting the sealed space by the gas propagation through the air. These propagations vibrate the sound insulation member and generate vibration radiation sound. If the vibration radiated sound from the sound insulation member is large, a sufficient sound insulation effect by the sound insulation member cannot be obtained.

  In recent years, in order to improve the image quality of captured images, the static magnetic field strength and the gradient magnetic field strength are increased. However, the Lorentz force is increased, and the vibration and radiation sound of the gradient magnetic field coil are increased. Therefore, solid propagation and gas propagation to the sound insulation member also increase, and noise also increases. Then, the method of reducing the vibration of sound insulation member itself is examined with the method of reducing these propagation. As a method of reducing the vibration of the sound insulating member itself, there is a method of imparting attenuation to the sound insulating member to dissipate the vibration energy of the sound insulating member. A method of imparting attenuation to such a sound insulation member is disclosed in Patent Document 1.

JP 2002-219113 A

  In Patent Document 1, the vibration energy of the sound insulation member is reduced by attaching the noise attenuation structure, which is a laminated structure of the viscoelastic material on the inner layer and the constraining layer on the outer layer, so as to be integrated with the sound insulation member by adhesion or the like. The noise attenuation structure can dissipate and reduce the vibration of the sound insulation member. However, if the noise attenuating structure is attached to the inner peripheral side of the sound insulating member, the bore diameter is narrowed. Therefore, in order to ensure a large bore diameter, it is attached to the outer peripheral side of the sound insulating member.

  Among the gantry cover and the RF coil that are sound insulation members, an outer periphery of the RF coil includes an element such as a capacitor and a coil circuit portion made of copper foil. Since this circuit portion is provided, it is difficult to attach the noise attenuating structure to the RF coil by bonding or the like. In addition, since the circuit unit generates heat during photographing, the adhesion of the noise attenuation structure to the circuit unit decreases the cooling performance of the circuit unit. In particular, the heat generation of the circuit unit is increasing with the improvement of the imaging performance, and it is difficult to attach the noise attenuation structure to the circuit unit in order to ensure the reliability of the circuit unit. Although a noise attenuation structure can be attached in addition to the circuit portion, since the range is small, a sufficient attenuation imparting effect cannot be obtained.

  Accordingly, an object of the present invention is to provide a magnetic resonance imaging apparatus that reduces the vibration of the RF coil without reducing the bore diameter and without reducing the cooling performance of the RF coil circuit unit in order to solve the above problems. It is to provide.

  In order to achieve the above object, in the present invention, a static magnetic field generation system for generating a static magnetic field in an imaging space, a gradient magnetic field generation system for generating a gradient magnetic field in the imaging space, and a radio frequency (RF) electromagnetic wave An RF coil having a circuit unit for irradiating the substrate and an RF bobbin for supporting the circuit unit, and a vibration damping unit disposed between the gradient magnetic field generation system and the RF coil. Provided is a magnetic resonance imaging apparatus which is made of a vibrating material and is configured such that an outer layer member is supported by an RF bobbin with a circuit portion and a gap by a plurality of outer layer support members.

  A vibration attenuating part for applying attenuation to the RF coil can be provided between the RF coil and the gradient magnetic field coil, and the vibration attenuating part has a gap with the circuit part of the RF coil, thereby reducing the bore diameter of the magnetic resonance imaging apparatus. Without reducing the cooling performance of the circuit unit, the vibration of the RF coil can be reduced.

1 is a diagram illustrating a cross-sectional view in the body axis direction of a subject of a magnetic resonance imaging apparatus according to Example 1. FIG. 1 is a cross-sectional view perpendicular to a body axis of a magnetic resonance imaging apparatus according to a first embodiment. FIG. 3 is a diagram illustrating a cross-sectional view in the body axis direction of the gradient coil and the RF coil of the magnetic resonance imaging apparatus according to the first embodiment. FIG. 3 is a cross-sectional view perpendicular to the body axes of the gradient magnetic field coil and the RF coil of the magnetic resonance imaging apparatus according to the first embodiment. It is a figure which shows an example of the whole structure of the magnetic resonance imaging apparatus which concerns on an Example.

  Hereinafter, a mode for carrying out the present invention will be described with reference to the drawings. First, referring to FIG. 5, a general configuration example of a magnetic resonance imaging (MRI) apparatus to which the present invention is applied will be described. I will explain.

  The MRI apparatus obtains a tomographic image of a subject using a nuclear magnetic resonance (NMR) phenomenon. As shown in FIG. 5, a static magnetic field generation system 22, a gradient magnetic field generation system 23, , A transmission system 25, a reception system 26, a signal processing system 27, a sequencer 24, and a central processing unit (hereinafter referred to as CPU) 28 that is a processing unit.

  The static magnetic field generation system 22 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 21 when the vertical magnetic field method is used, and in the body axis direction when the horizontal magnetic field method is used. Therefore, a permanent magnet type, normal conducting type or superconducting type static magnetic field generating source is arranged around the subject 21.

  The gradient magnetic field generation system 23 includes a gradient magnetic field coil 29 wound in the three-axis directions of X, Y, and Z, which is a coordinate system (stationary coordinate system) of the MRI apparatus, and a gradient magnetic field power source 30 that drives each gradient magnetic field coil. The gradient magnetic fields Gx, Gy, and Gz are applied in the X, Y, and Z triaxial directions by driving the gradient magnetic field power supply 30 of each coil in accordance with a command from the sequencer 24 described later. At the time of imaging, a slice direction gradient magnetic field pulse (Gs) is applied in a direction orthogonal to the slice plane (imaging cross section) to set a slice plane for the subject 21, and the remaining planes orthogonal to the slice plane and orthogonal to each other are set. A phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in two directions, and information on the position in each direction is encoded in the echo signal.

  The sequencer 24 is a means for controlling to repeatedly apply a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence, and is operated under the control of the CPU 28. Various commands necessary for image data collection are sent to the transmission system 25, the gradient magnetic field generation system 23, and the reception system 26. The sequencer 24 and the CPU 28 can be collectively referred to as a control unit.

  The transmission system 25 irradiates the subject 21 with an RF pulse in order to cause nuclear magnetic resonance to occur in the nuclear spins of the atoms constituting the living tissue of the subject 21, and the high frequency oscillator 31, the modulator 32, It consists of a high frequency amplifier 33 and a high frequency coil (RF coil) 34a on the transmission side. The high-frequency pulse output from the high-frequency oscillator 31 is amplitude-modulated by the modulator 32 at a timing according to a command from the sequencer 24, and the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 33 and placed close to the subject 21. By supplying the RF coil 34a, the subject 21 is irradiated with the RF pulse.

  The reception system 26 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 21 as a reception signal. The reception side RF coil 34b and the signal amplifier 35 are used as the reception signal. And a quadrature phase detector 36 and an analog / digital (A / D) converter 37. The NMR signal of the response of the subject 21 induced by the electromagnetic wave irradiated from the RF coil 34a on the transmission side is detected by the RF coil 34b arranged in the vicinity of the subject 21 and amplified by the signal amplifier 35. Thereafter, the signals are divided into two orthogonal signals by the quadrature phase detector 36 at a timing according to a command from the sequencer 24, converted into digital quantities by the A / D converter 37, and sent to the signal processing system 27.

  The signal processing system 27 performs various data processing and display and storage of processing results. The signal processing system 27 includes an external storage device such as an optical disk 39 and a magnetic disk 38, and a display 40 including a liquid crystal display (LCD). When data from the receiving system 26 is input to the CPU 28, the CPU 28 constituting the control unit executes processing such as signal processing and image reconstruction, and displays the tomographic image of the subject 21 as a result on the display 40. At the same time, it is recorded on the magnetic disk 38 of the external storage device.

  The operation unit 45 inputs various control information of the MRI apparatus and control information of processing performed by the signal processing system 27 and includes a trackball or mouse 43 and a keyboard 44. The operation unit 45 is disposed in the vicinity of the display 40, and is used by the operator to interactively control various processes of the MRI apparatus through the operation unit 45 while looking at the display 40.

  In the MRI apparatus shown in FIG. 5, the RF coil 34a and the gradient magnetic field coil 29 on the transmission side are tested in the static magnetic field space of the static magnetic field generating system 22 into which the subject 21 is inserted if the vertical magnetic field method is used. If it is a horizontal magnetic field system, it is installed facing the person 21 so as to surround the subject 21. The RF coil 34b on the reception side is installed so as to face or surround the subject 21.

  At present, the radionuclide to be imaged by the MRI apparatus is a hydrogen nucleus (proton) which is a main constituent material of the subject as widely used clinically. By imaging information related to the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. can be imaged two-dimensionally or three-dimensionally. .

  As Example 1, an example of a horizontal magnetic field type MRI apparatus using a superconducting magnet that generates a uniform static magnetic field in the horizontal direction using a superconducting coil as a static magnetic field magnet will be described. 1 and 2 are cross-sectional views of the main part of the MRI apparatus according to the first embodiment. FIG. 1 is a cross-sectional view in the body axis direction of the subject 1 and FIG. 2 is perpendicular to the body axis of the subject 1. In addition, it is sectional drawing of a direction, In FIG. 2, the subject abbreviate | omitted illustration.

  The MRI apparatus according to the present embodiment causes nuclear magnetic resonance (NMR) to occur in the superconducting magnet 2 disposed so as to cover the subject 1 and the hydrogen nuclei (protons) constituting the living tissue of the subject 1. An RF coil 3 that emits a high-frequency signal, a receiving coil (not shown) for receiving a signal emitted from the subject 1, and position information for each signal emitted from the subject The gradient magnetic field coil 4, a gantry cover 5 disposed so as to cover the superconducting magnet and the gradient magnetic field coil, and a bed (not shown) on which the subject is mounted are configured. 1 and FIG. 2 correspond to the static magnetic field generation system 22, the RF coil 34a, the RF coil 34b, and the gradient magnetic field coil 29 in FIG. Yes.

  A superconducting magnet 2 that functions as a static magnetic field generation system includes a ring-shaped superconducting coil that is arranged in the body axis direction of the subject so as to cover the subject 1, a cooling container that houses the superconducting coil, and radiant heat. A radiation shield plate that shields the vacuum vessel, a vacuum vessel that stores them in a vacuum environment, a vacuum vessel support leg that supports the floor where the vacuum vessel is installed, and a load support that supports the cooling vessel and the radiation shield plate in the vacuum vessel. Consists of body etc. 1 and 2 show only the vacuum vessel 6 and the vacuum vessel support leg 7 which are members on the outer surface side of the superconducting magnet.

  As is clear from FIGS. 1 and 2, the vacuum vessel 6 has a hollow cylindrical shape, a cylindrical vacuum vessel inner cylinder surface 6a on the inner peripheral side of the vacuum vessel 6, and a cylindrical shape on the outer peripheral side of the vacuum vessel. It consists of a vacuum vessel outer cylinder surface 6b and a disk-like vacuum vessel side surface 6c on the side surface of the vacuum vessel. In addition, since the vacuum vessel 6 requires a vacuum strength, it is generally a structure in which a stainless steel member is welded and is supported by a vacuum vessel support leg 7 provided on the lower side of the vacuum vessel outer cylindrical surface 6b.

  A gradient magnetic field coil 4 constituting a gradient magnetic field generating system that forms a gradient magnetic field in a static magnetic field in order to give position information of a magnetic resonance signal is disposed on the inner peripheral side of the vacuum vessel inner cylindrical surface 6a. The gradient magnetic field coil 4 is a solid cylindrical shape in which a conductor that generates a gradient magnetic field in three directions of the X direction, the Y direction, and the Z direction is molded with resin, and a gradient magnetic field coil mounting member (not shown) is interposed therebetween. Attached to the vacuum vessel 6.

  The RF coil 3 that irradiates a high-frequency signal to cause nuclear magnetic resonance (NMR) to the atomic nuclei constituting the living tissue of the subject is disposed on the inner peripheral side of the gradient magnetic field coil 4. The RF coil 3 includes a coil circuit unit that radiates high-frequency electromagnetic waves and an RF bobbin that supports the circuit unit. The RF bobbin is a cylindrical bobbin made of a non-magnetic and non-metallic material, for example, a fiber reinforced resin, in order to avoid affecting the magnetic resonance image, and is vacuumed through an RF coil mounting member (not shown). Attached to the container.

  In the configuration of the present embodiment, the RF coil 3, the gradient magnetic field coil 4, and the vacuum vessel 6 are arranged concentrically in the order of the RF coil 3, the gradient magnetic field coil 4, and the vacuum vessel 6 from the subject side. Here, the gantry cover 5 is disposed so as to cover the gradient magnetic field coil 4 and the vacuum vessel 6 from the viewpoint of design and safety. In some cases, the gantry cover 5 is disposed so as to cover up to the RF coil 3, but in this embodiment, the RF coil 3 also serves as a part of the gantry cover 5 in order to secure a large bore diameter by space saving. . The gantry cover 5 has a hollow cylindrical shape, and a cylindrical gantry cover outer cylindrical surface 5b on the outer peripheral side of the cylindrical gantry cover inner cylindrical surface 5a on the inner peripheral side of the gradient magnetic field coil 4 and a vacuum vessel outer cylindrical surface 6b. The gantry cover side surface 5c on the side surface of the apparatus.

  As with the RF coil 3, the gantry cover 5 is made of a non-magnetic and non-metallic material such as a fiber reinforced resin in order to avoid affecting the magnetic resonance image. Since it is installed mainly from the viewpoint of design, the thickness of the gantry cover 5 is about 2 to 5 mm, which is small enough to have a minimum strength that can maintain the cover shape. Attachment to the vacuum vessel 6 is carried out at a plurality of locations with gantry cover attachment members such as bolts (not shown) in order to ensure the installation accuracy of the gantry cover 5.

  The gantry cover is composed of a plurality of members, but is not necessarily divided into an inner cylinder surface, an outer cylinder surface, and a side surface, and is divided in consideration of design and installation workability. From the viewpoint of design, the inner peripheral diameter of the gantry cover inner cylinder surface 5a and the RF coil 3 is the same, and the gantry cover inner cylinder surface 5a and the RF coil 3 are installed so as not to cause a gap. The dimensions of the MRI apparatus are defined by the gantry cover.

  By forming a closed space that covers the gradient magnetic field coil 4 that is a vibration source with the RF coil 3 and the gantry cover 5, the RF coil 3 and the gantry cover 5 serve as a sound insulating member. In order to reduce the sound insulation effect, the leakage sound from the gap in the closed space is sealed so that the gap between the RF coil 3 and the inner cylindrical surface 5a of the gantry cover and the members constituting the gantry cover is sealed so that no leakage sound is generated. The

  A subject is mounted on a bed and inserted into a cylindrical space (bore) constituted by the RF coil 3 and the gantry cover 5. If the cross-sectional diameter (bore diameter) of the bore is small, the subject may feel a blockage or the like, and may be affected psychologically and physically, which may hinder the examination. Further, accessibility is not good when the examiner installs a receiving coil (not shown) on the subject. Therefore, securing a large bore diameter is one of the factors that increase the added value of the product.

  An example of another detailed configuration of the RF coil 3 installed on the inner diameter side of the gradient magnetic field coil 4 of the MRI apparatus of the first embodiment will be described with reference to FIGS. 3 and 4. In other words, FIGS. 3 and 4 show only the gradient magnetic field coil 4 and the RF coil 3 portion of FIGS. 1 and 2.

  The RF coil 3 according to this embodiment includes an RF bobbin 8 and a circuit unit 9, and the circuit unit 9 is disposed on the outer peripheral side of the RF bobbin 8. The circuit unit 9 is made of an element such as a capacitor or copper foil, and irradiates a high-frequency electromagnetic wave. The circuit unit 9 needs to be arranged at a predetermined interval from the gradient magnetic field coil 4 from the viewpoint of electrical insulation from the gradient magnetic field coil 4 and irradiation performance. In addition to the predetermined interval, the interval between the RF coil 3 and the gradient coil 4 is determined in consideration of the self-weight deflection of the RF coil 3 and the installation accuracy, and the interval is about 10 to 30 mm. By reducing this interval, a large bore diameter is ensured. Since the RF bobbin 8 installs the circuit unit 9 at a predetermined position, the RF bobbin 8 needs to have sufficient rigidity and thickness to ensure installation accuracy. On the other hand, in order to ensure a large bore diameter, the thickness of the RF bobbin 8 should be small. Therefore, the thickness of the RF bobbin 8 is a plate thickness that can ensure a minimum rigidity, and is about 3 to 10 mm. 3 and 4, the RF bobbin 8 is a simple cylinder, but the rigidity of the RF bobbin may be improved by providing a ring-shaped rib around the RF bobbin 8.

  Then, a thin plate-like outer layer member 11 is supported on the RF bobbin 8 by a plurality of outer layer support members 10 provided on the RF bobbin 8, and a damping material 12 is attached to the outer peripheral side of the outer layer member 11, so that the outer layer member 11. And a vibration attenuating portion 13 made of the damping material 12 is provided. In order to avoid affecting the magnetic resonance image, the material of the outer layer member 11 and the outer layer support member 10 is made of a nonmagnetic and nonmetallic material, for example, a fiber reinforced resin, like the RF bobbin 8. A damping material 12 made of a polymer damping material or the like is also used that does not affect the magnetic resonance image.

  3 and 4, the outer layer member 11 is shown as one cylindrical member having a cylindrical shape. However, the outer layer member 11 may be divided into a plurality of portions in the axial direction, the circumferential direction, or both directions of the cylindrical member. When the outer layer member 11 is divided into a plurality in the circumferential direction, it may be an arc-shaped member or a plate-shaped member. Here, the axial direction of the cylindrical member is the same direction as the body axis direction of the subject. The outer layer member 11 may not be disposed on the entire surface so as to cover the RF bobbin 8, and when the outer layer member 11 is divided into a plurality of members, there may be a gap between the disposed members. The outer layer member 11 has a thickness smaller than that of the RF bobbin 8 and is about 1 to 3 mm. The damping material 12 may be divided and disposed in the same manner as the outer layer member, and the thickness of the damping material 12 is preferably equal to or greater than the plate thickness of the outer layer member 11. The vibration attenuating unit 13 of the present embodiment described above has a thickness that can be disposed between the RF coil 3 and the gradient magnetic field coil 4, and has a gap between the circuit unit 9 and the gradient magnetic field coil 4.

  The outer layer support member 10 has a columnar shape or a rib shape, and is disposed at a position where there is no circuit portion, and rigidly supports the outer layer member 11. Attachment of the outer layer support member 10 to the RF bobbin 8 and attachment of the outer layer member 11 to the outer layer support member 10 are performed by adhesion or the like. The arrangement of the outer layer support member 10 is selected so that the outer layer member 11 does not contact the circuit portion 9 or the gradient magnetic field coil 4 due to deformation. 3 and 4, the outer layer support member 10 is disposed at three locations in the axial direction and at four locations in the circumferential direction, but this is not restrictive.

  Now, as shown in FIG. 3, the vibration damping part 13 of the present embodiment has a plurality of perforations 14. The shape of the perforations 14 is circular or slit-shaped. The perforations 14 are provided at positions that do not affect the support of the vibration damping unit 13. When the vibration attenuating unit 13 is divided and arranged, a slit may be formed by a gap between the divided vibration attenuating units 13.

  In addition, although not shown in FIGS. 1 to 4, the MRI apparatus of the present embodiment is similar to the configuration shown in FIG. 5. Needless to say, an image reconstructing function for obtaining a magnetic resonance image based on a nuclear magnetic resonance signal is provided with a control unit for controlling the whole.

  Next, the operation of the MRI apparatus according to the present embodiment described above will be described below. At the time of imaging, a pulse-like current flows through the gradient magnetic field coil 4 arranged in the static magnetic field, the static magnetic field and the current are coupled, Lorentz force acts, and the gradient magnetic field coil 4 vibrates. The vibration of the gradient magnetic field coil 4 propagates to the RF coil 3 and the gantry cover 5 via a support member for the gradient magnetic field coil 4 (not shown). Further, vibration radiation sound is generated by the vibration of the gradient coil 4. The vibration radiation sound of the gradient magnetic field coil 4 propagates to the RF coil 3 and the gantry cover 5 through air. Vibrations of the RF coil 8 and the gantry cover 5 are generated by solid state propagation, which is propagation through this member, and gas propagation, which is propagation through air, to generate vibration radiation sound of the RF coil 3 and the gantry cover 5, It propagates to the subject 1 through and becomes noise. In particular, for the subject, since the contribution of the radiated sound due to the vibration of the RF coil 3 in the vicinity of the subject is large, it is important to reduce the vibration of the RF coil 3.

  In the MRI apparatus configured as described above, the vibration energy of the RF coil 3, mainly the RF bobbin 8 generated by solid propagation and gas propagation, is propagated to the vibration damping unit 13 via the outer layer support member 10. Dissipated by the vibration damping unit 13. Therefore, RF coil vibration is reduced and vibration radiation sound from the RF coil 3 is reduced.

  Vibration damping is very effective at resonance. Since the outer layer member 11 has a thin plate structure and supports only a part of the outer layer member 11, the outer layer member 11 has a number of natural modes and is likely to cause resonance. Therefore, vibration attenuation at the vibration attenuation unit 13 can be performed effectively. Moreover, since the rigidity of the outer layer member 11 of the vibration attenuation unit 13 is reduced by providing the perforation 14 in the vibration attenuation unit 13, the vibration attenuation unit 13 has more eigenmodes.

  Further, by providing the vibration attenuating unit 13 between the RF coil 8 and the gradient magnetic field coil 4, the vibration attenuating unit 13 receives and dissipates the acoustic energy that is the gas propagation, and dissipates the gas to the RF coil 8. As a result, the vibration of the RF coil 8 is also reduced.

  Furthermore, the perforation 14 provided in the vibration damping unit 13 can obtain a large acoustic energy damping effect at a specific frequency. The frequency can be adjusted by the size and the number of the perforations 14, and, for example, a large noise reduction effect can be obtained by setting the resonance frequency of the gradient magnetic field coil 4 or the resonance frequency of the bore, which is a factor that increases noise. it can. Further, by providing the perforations 14 having a plurality of dimensions by changing the diameter and length, acoustic attenuation corresponding to a plurality of frequencies can be obtained.

  As a specific example of the perforation 14, for example, the distance between the circuit portion 9 of the RF coil 3 and the outer layer member 11 of the vibration attenuation portion 13 is 5 mm, the thickness of the vibration attenuation portion 13 is 5 mm, and the opening ratio is 0. .04, if the diameter of the perforations 14 is 25 mm, the resonance frequency is 970 Hz. In this way, by appropriately setting parameters such as the vibration attenuating portion 13 and the perforation 14, it is possible to obtain a resonance frequency to be absorbed.

  Furthermore, since the damping material exhibits its damping performance by being distorted, the damping material is preferably arranged at a position where the distortion is large. Therefore, the perforations 14 are preferably provided at a position where the strain energy of the vibration natural mode of the vibration damping unit 13 is small. For example, in the low-order mode, the strain energy at the position of the outer layer support member 10 is increased, and therefore the perforations 14 are preferably provided at positions away from the outer layer support member 10. In the higher-order mode, the distortion energy at the node position of the eigenmode is reduced, so that the perforations 14 are preferably provided in the node of the eigenmode. By doing so, it is possible to achieve both the vibration attenuation performance of the vibration attenuation section 13 and the sound attenuation performance of the perforations 14.

  Since the vibration damping portion 13 is floated from the circuit portion 9 by the outer layer support member 10, the heat dissipation of the circuit portion 9 is not hindered. Further, the perforation 14 provided in the vibration attenuating unit 13 can prevent the vibration attenuating unit 13 from radiating heat from the circuit unit 9. Therefore, the vibration of the RF coil 8 can be reduced without deteriorating the cooling performance of the circuit unit 9.

  With the configuration of the embodiment described above, the vibration of the RF coil can be reduced and the noise can be reduced without reducing the bore diameter and without reducing the cooling performance of the circuit portion of the RF coil. It is. Further, since the structure can be installed between the RF coil and the gradient magnetic field coil, it can be additionally installed in an existing apparatus.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for better understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment. For example, although the static magnetic field magnet has been described as a superconducting magnet, the present invention can be applied to a normal conducting magnet and a permanent magnet. Moreover, although the superconducting magnet which generates a static magnetic field in the horizontal direction is illustrated in the embodiments described above, the present invention can be similarly applied to a superconducting magnet which generates a static magnetic field in the vertical direction.

1, 21 Subject 2 Superconducting magnet 3, 34a, 34b RF coil 4, 29 Gradient magnetic field coil 5 Gantry cover 6 Vacuum vessel 7 Vacuum vessel support leg 8 RF bobbin 9 RF coil circuit unit 10 Outer layer support member 11 Outer layer member 12 Vibration material 13 Vibration damping unit 14 Perforation 22 Static magnetic field generation system 23 Gradient magnetic field generation system 24 Sequencer 25 Transmission system 26 Reception system 27 Signal processing system 28 CPU
29 Vertical coil 30 Gradient magnetic field power supply

Claims (12)

A static magnetic field generation system for generating a static magnetic field in the imaging space;
A gradient magnetic field generating system for generating a gradient magnetic field in the imaging space;
An RF coil having a circuit unit that radiates radio frequency (RF) electromagnetic waves and an RF bobbin that supports the circuit unit;
A vibration damping unit disposed between the tilt field generation system and the RF coil,
The vibration damping portion is composed of an outer layer member and a damping material, and the outer layer member is supported by the RF bobbin with a gap from the circuit portion by a plurality of outer layer support members.
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
Providing a plurality of perforations in the vibration damping portion;
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 2,
A plurality of said perforations having a plurality of dimensions;
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 2,
The perforations are circular or slit-shaped,
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 2,
The perforation is provided at a position where the distortion energy of the natural mode of the vibration damping portion is small.
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 5,
Providing the perforation at a position away from the outer layer support member;
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 5,
Providing the perforation at the node of the eigenmode;
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
The gradient magnetic field generation system comprises a gradient magnetic field coil,
The vibration attenuating unit is arranged with a gap from the gradient coil.
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
The outer layer member has a cylindrical shape,
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 9,
The outer layer member is divided into a plurality of axial directions or circumferential directions of the cylindrical shape.
A magnetic resonance imaging apparatus. The magnetic resonance imaging apparatus according to claim 10,
The vibration damping material is divided into a plurality of axial directions or circumferential directions of the cylindrical shape.
A magnetic imaging apparatus. The magnetic resonance imaging apparatus according to claim 1,
The outer layer support member has a columnar shape or a rib shape, and is disposed on the RF bobbin without the circuit portion.
A magnetic resonance imaging apparatus.

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