JP6223707B2 - Damper mechanism, installation method thereof, and magnetic resonance imaging apparatus - Google Patents

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as “MRI”) apparatus, and more particularly to an MRI apparatus including a damper mechanism that effectively reduces vibration of a gradient magnetic field coil in which noise is a problem.

  An MRI examination method for obtaining a tomographic image of a human body using a nuclear magnetic resonance (NMR) phenomenon is widely used in medical institutions. There are many hospitals that perform image diagnosis of a plurality of patients per day, and it is not uncommon to take images of reserved patients one after another. However, although the MRI imaging time varies depending on the examination site, an average of around 30 minutes and an examination time longer than those of other image diagnostic apparatuses are required, and noise caused by a gradient magnetic field coil close to 100 dB during that time has a large burden on the subject. .

  Currently, various technologies have been developed to reduce the vibration of the gradient magnetic field coil. However, it is necessary to keep the space for the subject to be as large as possible, making it necessary to reduce the size of the vibration reduction mechanism, making it difficult to achieve both vibration reduction. doing. Along with this, a technique is known in which a gradient magnetic field coil of a magnetic resonance imaging apparatus is sealed in a vacuum and sealed (see, for example, Patent Document 1).

JP-A-10-118043

  However, in Patent Document 1 described above, a silent effect can be obtained by providing a vacuum vessel in the MRI apparatus. However, the structure in which the entire gradient magnetic field coil is enclosed and sealed reduces the space for the subject to enter. Moreover, the subject that initial cost and running cost, such as a vacuum pump and a vacuum seal, start is mentioned.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a structure that obtains the vibration reduction effect of the gradient magnetic field coil without reducing the space in which the subject enters.

In order to achieve the above object, the main features of the magnetic resonance imaging apparatus according to the present invention are as follows.
(1) A gradient magnetic field including a static magnetic field generating unit including a static magnetic field generating magnet that generates a uniform static magnetic field in a space that accommodates a subject, and a gradient magnetic field coil that generates a gradient magnetic field superimposed on the static magnetic field. A generator, and an image processor for detecting an NMR signal generated from the subject by irradiation of a high-frequency magnetic field and imaging the detected signal, and the gradient coil is a cylindrical cavity of the static magnetic field generating magnet. The gradient magnetic field coil is caused by inserting a stretchable storage bag that is provided along the inner periphery and is filled with a fluid in a gap formed between the inner peripheral side of the static magnetic field generating magnet and the gradient magnetic field coil. It has a damper mechanism for reducing vibration.

The main features of the damper mechanism according to the present invention are as follows.
(2) A damper mechanism for reducing the vibration of the gradient magnetic field coil constituting the magnetic resonance imaging apparatus, having a cavity on the inner peripheral side and a bag-like storage part capable of storing a fluid on the outer peripheral side, The pressure fluctuation applied to the bag-shaped storage unit is adjusted by a pressure chamber that adjusts the storage amount of the fluid injected into the bag-shaped storage unit according to the pressure variation caused by the vibration of the gradient magnetic field coil.

The main features of the damper mechanism manufacturing method according to the present invention are as follows.
(3) A method of manufacturing a damper mechanism for reducing vibration of a gradient magnetic field coil constituting a magnetic resonance imaging apparatus, wherein the gradient magnetic field coil is installed in the magnetic resonance imaging apparatus and a storage container for storing a fluid of a hydraulic damper is statically installed. It is inserted between the magnetic field generating magnet and the gradient magnetic field coil, a pressure chamber is attached to at least one surface of the static magnetic field generating magnet, the fluid is injected from the inlet of the storage container, and the storage container is inserted from the air valve of the pressure chamber. A damper mechanism that sucks excess air mixed in the magnetic field and reduces the vibration of the gradient magnetic field coil is incorporated in the magnetic resonance imaging apparatus.

  According to the present invention, by installing the bag-shaped damper mechanism on the outer peripheral portion of the gradient magnetic field coil, the support area of the gradient magnetic field coil is increased, and vibration due to air-borne sound is absorbed by the viscous damper, and the gradient magnetic field Coil vibration can be reduced.

It is sectional drawing which shows the structure of a MRI static magnetic field generating magnet and a gradient magnetic field coil. It is sectional drawing which shows the structure of the vibration reduction mechanism of this invention, a MRI static magnetic field generation | occurrence | production magnet, and a gradient magnetic field coil. It is a figure which shows the bag-shaped oil damper container in the vibration reduction mechanism of this invention. It is a front view which shows the structure of a gradient magnetic field coil support structure and an oil damper pressure chamber. It is a processing flow which shows the procedure of the vibration reduction of a gradient magnetic field coil.

Hereinafter, preferred embodiments of the MRI apparatus of the present invention will be described in detail with reference to the accompanying drawings.
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments of the invention, and the repetitive description thereof is omitted.

  FIG. 1 is a sectional view of an MRI apparatus having a closed structure to which the present invention is applied, and shows the configuration of an MRI static magnetic field generating magnet and a gradient magnetic field coil. This MRI apparatus includes a static magnetic field generating magnet 11 that generates a uniform magnetic field in an imaging space area 17 where the subject 10 is installed, and a patient table in which the subject 10 is disposed in the central space of the static magnetic field generating magnet 11. 12, a gradient magnetic field coil 13, a high-frequency coil disposed on the inside thereof, and a detection coil (not shown) for detecting an NMR signal generated from the subject 10.

  The gradient coil 13 of the MRI apparatus is attached to the inside of the cylindrical cavity of the static magnetic field generating magnet 11 as shown in FIG. The support structure of the gradient magnetic field coil 13 has a structure in which an aluminum metal block 14 is provided on both sides of the static magnetic field generating magnet 11 and is supported on the block by a rubber damper 15 for vibration damping. The attachment position of the gradient magnetic field coil 13 is arranged inside the static magnetic field generating magnet 11 so as to be concentric with the cylindrical cavity. At that time, the gradient magnetic field coil 13 is interposed between the cylindrical cavity of the static magnetic field generation magnet 11 and the gradient magnetic field coil 13. A minute gap 16 is born. That is, the gradient magnetic field coil 13 is a doubly supported beam supported by both end faces of the static magnetic field generating magnet 11, and is about 1 of the length of the cylindrical cavity of the static magnetic field generating magnet 11 (distance between the support structures). .5m is the range without support.

  Since a pulse current flows through the gradient coil 13 disposed in the measurement space during operation, Lorentz force is generated, causing the gradient coil 13 itself to vibrate. The vibration of the gradient magnetic field coil 13 becomes air propagation sound, reflects through the gap 16 and appears as noise. Further, since both end faces of the static magnetic field generating magnet 11 are doubly supported beams as described above, the presence of the gap 16 means a situation in which vibration is easily excited toward the center of the gradient magnetic field coil 13. Furthermore, the magnetic field is transmitted to the static magnetic field generation source via the support system of the gradient magnetic field coil 13 to vibrate the static magnetic field generation source.

  In view of the above-described factors for generating vibration of the gradient magnetic field coil, the present invention is a mechanism in which a hydraulic damper structure is used in the gap space between the cylindrical cavity of the static magnetic field generating magnet 11 and the gradient magnetic field coil 13. Is provided, and the middle of the both-end support beam of the gradient magnetic field coil 13 is elastically supported by a hydraulic damper to thereby reduce the vibration of the noise source.

A structure for specifically damping vibration will be described below with reference to FIGS.
After the gradient magnetic field coil 13 is installed in the cylindrical cavity of the static magnetic field generating magnet 11, the oil container 20 in which the oil of the hydraulic damper is stored is inserted into the gap 16 around the entire circumference of the static magnetic field generating magnet 11. The oil container 20 can be deformed so as to be stretchable so that it can be inserted even in a narrow space, and in consideration of the environment of the space, a fluororesin (fluorocarbon resin) having excellent heat resistance, cold resistance, and chemical resistance is used. The shape of the bag is a bag.

FIG. 2 is a cross-sectional view showing the configuration of the vibration reducing mechanism, MRI static magnetic field generating magnet, and gradient magnetic field coil of the present invention.
FIG. 2 is a cross-sectional view of the cylinder of the static magnetic field generating magnet 11 and the gradient magnetic field coil 13, so that only the upper side and the lower side of the static magnetic field generating magnet 11 and the gradient magnetic field coil 13 are shown in the figure. Actually, the upper side and the lower side are continuously connected.

A pressure chamber 30 is provided on at least one surface of the static magnetic field generating magnet 11, and the pressure chamber 30 is mounted on the surface of the aluminum metal block 14. An example of the attached state of the pressure chamber 30 will be described with reference to FIG. The pressure chamber 30 includes an area 31 filled with oil and several orifices 32. The tip of the pressure chamber 30 has a structure in which the oil passage of the oil container 20 is fixed to the pressure chamber by a hydraulic packing 33.
An oil container 20 filled with silicon oil is disposed in the gap between the static magnetic field generating magnet 11 and the gradient magnetic field coil 13.

FIG. 3 is a view showing a bag-like oil damper container in the vibration reducing mechanism of the present invention.
The oil container 20 has a ring-like shape and is constituted by a bag-like storage portion that can store oil in an outer peripheral portion thereof. Oil passages 21 leading to the pressure chamber 30 are provided at both ends of the container. In this figure, three are provided at each end, but the number is not limited to three, and it is only necessary that the oil passage 21 is provided.

  As shown in FIG. 3, since the bag-like oil container 20 has a ring shape, the outer peripheral portion of the gradient magnetic field coil 13 can be covered.

  The oil container 20 is first installed by inserting the bag-like oil storage portion of the oil container 20 into the gap 16 in an empty state. Since the oil container 20 can be expanded and contracted and is not filled with oil, the oil container 20 is easily inserted into the gap 16. After the oil container 20 is inserted, the bag-like oil storage portion is filled with oil and the gap 16 is filled. The bag-like oil storage part can be expanded and contracted depending on the presence or absence of oil, and has the convenience of changing the container volume following the tolerance of the gap.

FIG. 4 is a front view showing the configuration of the gradient coil support structure and the oil damper pressure chamber.
The front view of FIG. 4 is the figure seen from the direction A shown in FIG.
A gradient magnetic field coil 13 is arranged on the inner periphery of the static magnetic field generating magnet 11, and the subject 10 is shown on the MRI patient table 12 inside. The end of the static magnetic field generating magnet 11 supports the gradient magnetic field coil 13 with a metal block 14 via a rubber damper 15. In this figure, it supports at three places. An oil container 20 filled with silicon oil is disposed in the gap between the static magnetic field generating magnet 11 and the gradient magnetic field coil 13. In this figure, there is a portion where the oil container 20 is hidden by the rubber damper 15 but cannot be seen, but actually, it is continuously connected in a bag shape as shown in FIG.

  In this figure, the pressure chamber 30 is provided in three places. Further, an oil supply port 40 for injecting oil, an air valve 41 for releasing air, and a hydraulic packing 33 are shown on the side surface of the pressure chamber 30.

  The oil is silicon oil having heat resistance, cold resistance, and viscosity stability, and is injected from the oil supply port 40. The bag-like oil container 20 in the gap 16 between the cylindrical cavity of the static magnetic field generating magnet 11 and the gradient magnetic field coil 13 is filled with silicon oil. In the oil container 20 filled with silicon oil, since air is additionally mixed, air is vented from the air valve 41.

The damper mechanism according to the present invention has the effect of damping vibrations according to the following principle.
The oil that receives the vibration of the gradient coil 13 flows out through the orifice 32, and pressure is generated in the pressure chamber. The pressure generated at that time attenuates the vibration of the gradient coil 13.

  Further, the degree of vibration attenuation can be adjusted by adjusting the amount of oil injected from the oil supply port 40 or the amount of extraction. The adjustment can also be made by the amount of air released from the air valve 41.

  According to the present invention, by installing the bag-shaped damper mechanism on the outer peripheral portion of the gradient magnetic field coil, the support area of the gradient magnetic field coil is increased, and vibration due to air-borne sound is absorbed by the viscous oil damper, Reduction is possible.

  In addition, solid propagation sound propagating to the bed is reduced due to the effect of vibration reduction, and improvement of the comfort of the subject during imaging is expected.

  Furthermore, the vibration reduction of the imaging object is related to the image quality of the magnetic resonance imaging apparatus, and an improvement in image quality is expected.

  In the embodiment of the present invention, as shown in FIGS. 1 to 4, the purpose is to install a bag-like oil container 20 on the outer periphery of the gradient magnetic field coil 13, to reduce vibration of the gradient magnetic field coil 13, and to reduce air propagation sound. As long as the patient space area permits, an oil container 20 that can be installed on the inner periphery of the gradient coil 13 is attached, and the vibration reduction effect may be increased by covering the gradient coil 13 from both sides.

  The present embodiment has a feature that it is easy to attach a damper mechanism for reducing vibration even to a magnetic resonance imaging apparatus already installed in a facility.

  In the embodiment of the present invention, as shown in FIG. 3, the oil container 20 is filled with silicon oil to reduce vibration as an oil damper. However, as an alternative to oil, nitrogen gas is injected to reduce vibration as a gas spring. May be.

Below, the installation method of the hydraulic damper mechanism described in Example 1-3 will be described.
FIG. 5 is a processing flow showing a procedure for reducing vibration of the gradient coil.
First, the gradient coil 13 is installed on the static magnetic field generating magnet 11 (step 50).
Next, a mechanism for damping vibration is attached (step 60).
Finally, the vibration of the gradient coil is reduced by taking an image with a mechanism for damping vibration attached (step 70).

Further, step 60 will be described in detail.
First, the oil container 20 for storing the oil of the hydraulic damper is inserted between the static magnetic field generating magnet 11 and the gradient magnetic field coil 13 (step 61).
Next, the pressure chamber 30 is installed on at least one surface of the static magnetic field generating magnet 11 (step 62).
Subsequently, silicon oil is injected into the oil supply port 40 (step 63).
Finally, excess air mixed in the oil container 20 is sucked from the air valve 41 (step 64).

Through the above steps, a damper mechanism for reducing vibration of the gradient magnetic field coil is installed on the static magnetic field generating magnet, and preparation for imaging by the MRI apparatus is completed.
In step 61, the oil container 20 for storing the oil of the hydraulic damper is inserted between the static magnetic field generating magnet 11 and the gradient coil 13. However, the oil container 20 is attached to the inner peripheral side of the gradient coil 13. May be.

  In the fourth embodiment, the installation method for attaching the oil container 20 between the already installed static magnetic field generating magnet 11 and the gradient magnetic field coil 13 or on the inner peripheral side of the gradient magnetic field coil 13 has been described. Then, the installation method of the hydraulic damper mechanism with respect to the gradient magnetic field coil 13 before installation will be described.

The procedure for attaching the oil container 20 is shown below.
(1) First, the bag-like oil container 20 is wound around the outer periphery of the gradient magnetic field coil 13 while contacting the inner periphery of the oil container 20.
(2) Next, the gradient magnetic field coil 13 around which the oil container 20 is wound is inserted into the cavity of the installed static magnetic field generation magnet 11, and the oil is inserted between the static magnetic field generation magnet 11 and the gradient magnetic field coil 13. The container 20 is installed.
(3) The pressure chamber 30 is installed on at least one surface of the static magnetic field generating magnet 11.
(4) Subsequently, silicon oil is injected into the oil supply port 40 provided in the pressure chamber 30.
(5) Finally, excess air mixed in the oil container 20 is sucked from the air valve 41.

  In the above description, the oil container 20 that stores the oil of the hydraulic damper is wound around the outer periphery of the gradient magnetic field coil 13, but the oil container 20 may be attached to the inner peripheral side of the gradient magnetic field coil 13. The attachment procedure is the same as the case of winding around the outer periphery after the above (2).

  Further, imaging is performed in the same manner as Step 70 of the fourth embodiment.

  The present embodiment can be applied to work during assembly of the MRI apparatus, and is characterized in workability improvement that it is easy to work.

10: Subject,
11: Static magnetic field generating magnet,
12: MRI patient table,
13: Gradient field coil,
14: Metal block,
15: Rubber damper,
16: A gap between the side surface of the static magnetic field generating magnet and the side surface of the gradient magnetic field coil,
17: Imaging space area,
20: Oil container,
21: Oil passage,
30: pressure chamber,
31: Oil filling area,
32: Orifice 33: Hydraulic packing
40: Refueling port,
41: Air valve.

Claims (11)

A static magnetic field generating unit including a static magnetic field generating magnet for generating a uniform static magnetic field in a space for accommodating a subject;
A gradient magnetic field generator comprising a gradient magnetic field coil provided along an inner periphery of a cylindrical cavity of the static magnetic field generating magnet and generating a gradient magnetic field superimposed on the static magnetic field;
Have a, a damper mechanism gaps fluid can comprise a bag-shaped housing part having been stretch filled generated between the inner peripheral side to the gradient coil of the static magnetic field generating magnet,
The damper mechanism includes a pressure chamber that adjusts a storage amount of the fluid injected into the bag-shaped storage unit according to a pressure variation caused by vibration of the gradient magnetic field coil, and a pressure applied to the bag-shaped storage unit A magnetic resonance imaging apparatus characterized by adjusting fluctuations . The pressure chamber includes a first storage portion that stores the fluid and a second storage portion that stores air,
An orifice is provided on a side wall that partitions the first storage portion and the second storage portion,
The magnetic resonance imaging apparatus according to claim 1 , wherein the pressure fluctuation is adjusted by the fluid entering and exiting from the orifice. The magnetic resonance imaging apparatus according to claim 1, wherein the bag-shaped storage portion is formed in a ring shape so as to cover an outer peripheral portion of the gradient magnetic field coil . A damper mechanism for reducing vibration of a gradient magnetic field coil constituting a magnetic resonance imaging apparatus,
It has a bag-like storage part that has a hollow part on the inner peripheral side and can store a fluid on the outer peripheral side,
Adjusting the pressure fluctuation applied to the bag-like storage portion by a pressure chamber for adjusting the storage amount of the fluid injected into the bag-like storage portion according to the pressure fluctuation caused by the vibration of the gradient magnetic field coil. A characteristic damper mechanism. The pressure chamber includes a first storage portion that stores the fluid and a second storage portion that stores air,
An orifice is provided on a side wall that partitions the first storage portion and the second storage portion,
The damper mechanism according to claim 4 , wherein a pressure fluctuation is adjusted by the fluid entering and exiting from the orifice. Wherein the pressure chamber, according to claim 5, characterized in that it comprises a supply port for supplying fluid to said first housing portion, and an air valve for adjusting the air pressure to be housed in the second housing part Damper mechanism. The damper mechanism according to claim 4 , further comprising an inlet for injecting the fluid into one end of the bag-like storage portion. The damper mechanism according to claim 4 , wherein the fluid is silicon oil. The damper mechanism according to claim 4 , wherein the fluid is nitrogen gas. A method of installing a damper mechanism for reducing the vibration of the gradient coil to the magnetic resonance imaging apparatus provided with a gradient coil static magnetic field generating magnet,
A bag-like storage container for storing a fluid of a hydraulic damper is inserted between the static magnetic field generating magnet and the gradient coil;
A pressure chamber is attached to at least one surface of the static magnetic field generating magnet,
Injecting the fluid from the inlet of the storage container,
The excess air mixed in the storage container is sucked from the air valve of the pressure chamber,
A damper mechanism installation method, wherein a damper mechanism for reducing vibration of the gradient magnetic field coil is incorporated in the magnetic resonance imaging apparatus. A method of installing a damper mechanism for reducing the vibration of the gradient coil to the magnetic resonance imaging apparatus provided with a gradient coil static magnetic field generating magnet,
Wrap a bag-shaped storage container for storing a fluid of a hydraulic damper so that the inner periphery of the bag-shaped storage container is in contact with the outer periphery of the gradient coil.
Inserting a gradient magnetic field coil around which the bag-like storage container is wound in the imaging space area of the static magnetic field generating magnet,
A pressure chamber is attached to at least one surface of the static magnetic field generating magnet,
Injecting the fluid from the inlet of the storage container,
The excess air mixed in the storage container is sucked from the air valve of the pressure chamber,
A damper mechanism installation method, wherein a damper mechanism for reducing vibration of the gradient magnetic field coil is incorporated in the magnetic resonance imaging apparatus.

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