Magnetic resonance imaging system

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a magnetic resonance imaging apparatus in which a subject is placed in a uniform static magnetic field, a gradient magnetic field, a high-frequency pulse, or the like is applied to the subject to generate a magnetic resonance diagnostic image based on a magnetic resonance phenomenon. The present invention relates to suppression of noise generated by driving a gradient magnetic field coil.

【0002】

[Conventional technology]

Generally, this type of magnetic resonance imaging device includes a static magnetic field magnet that generates a static magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and an RF coil that generates a high frequency (RF) pulse. The subject is placed in a uniform static magnetic field generated by a static magnetic field magnet, a pulse sequence according to the imaging method is executed, and a gradient magnetic field by the gradient magnetic field coil and an RF pulse by the RF coil are applied under predetermined conditions. Collect the echo signal from the subject. The collected echo signal is reconstructed to obtain a magnetic resonance image showing a cross section of the subject.

【0003】

In recent years, in the technical field of magnetic resonance imaging equipment, high-speed imaging technology has been advanced, and active research and development is being promoted. In MRI high-speed imaging, high-speed switching of the gradient magnetic field and its high intensity are indispensable. In this case, a force due to the interaction between the current flowing through the gradient magnetic field coil and the static magnetic field is generated in the gradient magnetic field coil, which causes the gradient magnetic field coil to vibrate, and the vibration noise causes noise. This noise is usually 100db (A) or more, and soundproofing measures are taken for the subject such as wearing earplugs and headphones.

【0004】

In addition, there are some known techniques for noise reduction in conventional magnetic resonance imaging devices. For example, as described in JP-A-63-246146, United States Patent No. 5,793,210, and Japanese Patent Application Laid-Open No. 8-274609, the gradient magnetic field coil is housed in a vacuum vessel and generated from the gradient magnetic field coil. There is a technology to suppress the air propagation of the vibrating sound.

【0005】

Further, there is also known a technique for suppressing solid vibration propagation of the gradient magnetic field coil itself by supporting the gradient magnetic field coil via a vibration absorber (damper).

【0006】

[Problems to be Solved by the Invention]

The noise reduction effect of the conventional magnetic resonance imaging apparatus is not sufficient. That is, in the above-mentioned conventional example, regarding noise reduction related to the gradient magnetic field coil, only the gradient magnetic field coil is considered as a noise generation source, and components such as cables connected to the gradient magnetic field coil can be a cause of noise generation. Not considered.

【0007】

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a magnetic resonance imaging apparatus having an excellent noise reduction effect. In particular, it is an object of the present invention to provide a magnetic resonance imaging apparatus capable of effectively exerting an effect of suppressing air propagation of vibration sound from a gradient magnetic field coil due to vacuum accommodation and solid vibration propagation by a vibration absorber.

【0008】

[Means for solving problems]

In order to solve the above problems and achieve the object, the magnetic resonance imaging apparatus of the present invention is configured as follows. (1) The magnetic resonance imaging apparatus of the present invention includes a static magnetic field magnet that generates a static magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and a high-frequency coil that generates a high-frequency pulse, and the static magnetic field magnet is uniformly generated. A pulse sequence according to the imaging method is executed on a subject placed in a static magnetic field, and a gradient magnetic field generated by the gradient magnetic field coil and a high-frequency pulse generated by the high-frequency coil are applied under predetermined conditions to the subject. In a magnetic resonance imaging device that collects an echo signal and reconstructs the echo signal to obtain a magnetic resonance image of the subject, at least a cable connected to the gradient magnetic field coil and supplying a current to the gradient magnetic field coil. It is characterized in that a part of the arrangement direction is a direction along the magnetic flux direction created by the static magnetic field magnet.

【0009】

(2) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (1) above, and can accommodate the gradient magnetic field coil and suppress air propagation of vibration sound generated by the gradient magnetic field coil. It is characterized by providing a housing means having a degree of vacuum of.

【0010】

(3) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (2) above, and the cable is provided so as to extend from the accommodation space of the accommodation means to the outside through the accommodation means. It is characterized by that.

【0011】

(4) The magnetic resonance imaging apparatus of the present invention is the apparatus according to any one of (1) to (3) above, and supports the gradient magnetic field coil and absorbs the vibration of the gradient magnetic field coil. Equipped with an absorber.

【0012】

(5) The magnetic resonance imaging apparatus of the present invention includes a static magnetic field magnet that generates a static magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and a high-frequency coil that generates a high-frequency pulse, and the static magnetic field magnet is uniformly generated. A pulse sequence according to the imaging method is executed on a subject placed in a static magnetic field, and a gradient magnetic field generated by the gradient magnetic field coil and a high-frequency pulse generated by the high-frequency coil are applied under predetermined conditions to the subject. In a magnetic resonance imaging device that collects an echo signal and reconstructs the echo signal to obtain a magnetic resonance image of the subject, at least a part of the cable connected to the gradient magnetic field coil vibrates the cable itself. Alternatively, it is characterized by having flexibility to the extent that vibration propagation from one end to the other end can be blocked.

【0013】

(6) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (5) above, and can accommodate the gradient magnetic field coil and suppress air propagation of vibration sound generated by the gradient magnetic field coil. It is characterized by providing a housing means having a degree of vacuum of.

【0014】

(7) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (6) above, and the cable is provided so as to extend from the accommodation space of the accommodation means to the outside through the accommodation means. It is characterized by that.

【0015】

(8) The magnetic resonance imaging apparatus of the present invention is the apparatus according to any one of (5) to (7) above, and supports the gradient magnetic field coil and absorbs the vibration of the gradient magnetic field coil. Equipped with an absorber.

【0016】

(9) The magnetic resonance imaging apparatus of the present invention includes a static magnetic field magnet that generates a static magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and a high-frequency coil that generates a high-frequency pulse, and the static magnetic field magnet is uniformly generated. A pulse sequence according to the imaging method is executed on a subject placed in a static magnetic field, and a gradient magnetic field generated by the gradient magnetic field coil and a high-frequency pulse generated by the high-frequency coil are applied under predetermined conditions to the subject. In a magnetic resonance imaging device that collects an echo signal and reconstructs the echo signal to obtain a magnetic resonance image of the subject, at least a part of the cable connected to the gradient magnetic field coil vibrates the cable itself. Alternatively, it is fixed to the static magnetic field magnet via an elastic member that absorbs vibration propagation from one end to multiple ends.

【0017】

(10) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (9) above, and includes a fixing member in which a plurality of the cables are concentrated and fixed, and the fixing member is via the elastic member. It is characterized in that it is fixed to the static magnetic field magnet.

【0018】

(11) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (10) above, and the fixing member is fixed to the housing accommodating the static magnetic field magnet via the elastic member. It is characterized by that.

【0019】

(12) The magnetic resonance imaging apparatus of the present invention includes a static magnetic field magnet that generates a static magnetic field, a gradient magnetic field coil that generates a gradient magnetic field, and a high-frequency coil that generates a high-frequency pulse, and the static magnetic field magnet is uniformly generated. A pulse sequence according to the imaging method is executed on a subject placed in a static magnetic field, and a gradient magnetic field generated by the gradient magnetic field coil and a high-frequency pulse generated by the high-frequency coil are applied under predetermined conditions to the subject. In a magnetic resonance imaging device that collects an echo signal and reconstructs the echo signal to obtain a magnetic resonance image of the subject, at least a part of the cable connected to the gradient magnetic field coil vibrates the cable itself. Alternatively, it is characterized in that it is fixed to a base member having a rigidity sufficient to block vibration propagation from one end to multiple ends.

【0020】

(13) The magnetic resonance imaging apparatus of the present invention is the apparatus according to (12) above, and includes a fixing member in which a plurality of the cables are concentrated and fixed, and the fixing member is fixed to the base member. It is characterized by being done.

【0021】

BEST MODE FOR CARRYING OUT THE INVENTION

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

【0022】

FIG. 1 is a front view showing the internal configuration of the magnetic resonance imaging device according to the embodiment of the present invention, and FIG. 2 is a cross-sectional view of the device when viewed from the side.

【0023】

A superconducting coil (not shown) is housed in the static magnetic field magnet 1 in a vacuum vessel, and the superconducting coil is in a superconducting state at an extremely low temperature state to generate a uniform static magnetic field. The static magnetic field strength required for normal MR imaging is about 0.1 to 1 tesla. The spatial uniformity of the static magnetic field is required to be several tens of ppm or less, and the imaging region is spherical with a diameter of about 50 cm.

【0024】

The gradient magnetic field coil 2 is for giving a linear gradient to the main magnetic field for the purpose of determining an arbitrary imaging cross section or adding position information to the RF signal from the subject. In general, the gradient magnetic field coil 2 is composed of three independent sets of coils Gx, Gy, and Gz that create magnetic fields inclined in each of the orthogonal x, y, and z axes. In particular, the gradient magnetic field coil 2 of the present embodiment is an Actively Shield Gradient Coil (ASGC), and the active shielded gradient magnetic field coil is formed on a main coil that generates a gradient magnetic field and on the outside of the main coil. It consists of an active shield coil that is provided and generates a magnetic field in the opposite direction to prevent the gradient magnetic field generated by the main coil from leaking to the outside of the gradient magnetic field coil.

【0025】

The RF coil 10 is arranged further inside the cylindrical magnetic field coil 2. The RF coil 10 is an RF coil for the whole body (Hole Body) for transmitting a radio frequency (RF) magnetic field to a subject and receiving a magnetic resonance (MR) signal from the subject. ..

【0026】

The inclined magnetic field coil 2 is supported by the support arm 13 via the anti-vibration rubber 12 and the position adjusting bolt 11. Its support points are four points on the side surface and two points on the bottom surface of the gradient magnetic field coil 2. The anti-vibration rubber 12 made of an elastic material constitutes a vibration absorber (damper) in a broad sense, attenuates the solid vibration of the inclined magnetic field coil 2, and propagates this to the support arm 13 via the position adjusting bolt 11. Can be effectively prevented. The position adjusting bolt 11 is for finely adjusting the arrangement of the gradient magnetic field coil 2. The support arm 13 is attached to the base 15 via the shaft 14.

【0027】

The gradient magnetic field coil 2 is housed in the vacuum vessel 3 like the static magnetic field magnet 1. FIG. 1 shows a state in which the front portion of the vacuum vessel 3 is removed. As is clear from FIG. 2, a part of the vacuum vessel 3 is a part of the vacuum vessel of the static magnetic field magnet 1.

【0028】

A vacuum tube 6 and a vacuum pump 7 are connected to the vacuum vessel 3 via an O-shaped ring 17. The inside of the vacuum vessel 3 is kept in a vacuum by the intake operation of the vacuum pump 7. The degree of vacuum is sufficient to block the air propagation of the vibration sound by the gradient magnetic field coil 2, and specifically, about several hundred pascals is sufficient. The sound insulation effect is expressed as follows. In addition, P1 in the following equation is the degree of vacuum (Pascal) in the vacuum vessel 3.

【0029】

S = 20log₁₀(P1 / 1.01325 × 10⁵) (Decibel: dB) For example, if the degree of vacuum in the vacuum vessel 3 is 1000 pascals, a sound insulation effect of about 40 dB can be obtained.

【0030】

Further, as shown in FIG. 2, the vacuum vessel 3 is connected to a coupler and a tube 18 that discharge heat generated from the gradient magnetic field coil 2 by water cooling.

【0031】

A metal bellows 8 is provided at the bottom of the vacuum vessel 3 at a position corresponding to the shaft 14 to ensure the required degree of vacuum and disassembly / assembly.

【0032】

In the magnetic resonance imaging device of the present embodiment, as described above, the gradient magnetic field coil 2 is housed in the vacuum vessel 3, and the gradient magnetic field coil 2 is connected to the base 15 via a vibration absorber (damper). The air propagation and solid vibration propagation of the vibration sound generated from the gradient magnetic field coil 2 are suppressed, and four types of noise suppression measures are taken in more detail.

【0033】

The first noise suppression measure suppresses the vibration of the cable that supplies the current to the gradient magnetic field coil 2. That is, a Lorentz force is generated in the cable due to the influence of the magnetic field generated by the static magnetic field magnet 1, and the Lorentz force suppresses the cable itself from vibrating.

【0034】

Therefore, as shown in FIG. 1, the arrangement direction of the cable connected to the end of the inclined magnetic field coil 2 and extending in and out of the vacuum vessel 3 is along the direction of the magnetic flux created by the static magnetic field magnet 1, here from the front of the gantry. As seen, the directions are approximately along the radial directions I1, I2, and I3 centered on the central axis O of the cylinder.

【0035】

That is, the cable including the portion 41a inside the vacuum vessel 3 and the portion 42a extending to the outside of the vacuum vessel 3 via the flange 43a is arranged in a direction substantially along the radial direction I1, and the portion 41b and the flange inside the vacuum vessel 3 are arranged. The cable consisting of the portion 42b extending to the outside of the vacuum vessel 3 via 43b is arranged in a direction substantially along the radial direction I2 and extends to the outside of the vacuum vessel 3 via the portion 41c inside the vacuum vessel 3 and the flange 43c. The cable consisting of the portion 42c is arranged approximately along the radial direction I2.

【0036】

In any of the cable portions, the direction of the current flowing through the cable portion is along the magnetic flux generated by the static magnetic field magnet 1, so that almost no Lorentz force is generated, that is, no mechanical vibration is generated and no noise is generated. If the cable placement space is limited, only the cable portions (41a, 41b, and 41c) in the vacuum vessel 3 may be radiated as described above.

【0037】

The second noise suppression measure suppresses the propagation of vibration via the above cable. That is, although the vibration of the gradient magnetic field coil 2 is absorbed by the vibration absorber (damper) described above and the solid vibration propagation to the position adjusting bolt 11 and thereafter is suppressed, the cable acts as a medium for the vacuum vessel. Prevents vibration from propagating to 3 and the static magnetic field magnet 1.

【0038】

For this reason, a cable having flexibility to the extent that vibration propagation from one end to the other end disappears is used as all or part of the cable portion (41a, 42a, 41b, 42b, ...). In order to impart flexibility, it is preferable that the constituent material of the cable is a suitable material and that the wire is as thin as possible.

【0039】

Therefore, it is possible to prevent the vibration from propagating to the vacuum vessel 3 and the static magnetic field magnet 1 via the cable. Further, even if the Lorentz force is generated in the cable due to the influence of the magnetic field generated by the static magnetic field magnet 1 as described above and the cable itself vibrates due to this Lorentz force, the vibration propagates to the vacuum vessel 3 and the static magnetic field magnet 1. Can be deterred.

【0040】

The third noise suppression measure is to prevent the vibration from the cable from propagating at its fixed position. FIG. 3 is an enlarged cross-sectional view showing the vicinity of the cable fixing position to the static magnetic field magnet.

【0041】

An elastic member 18 is interposed between the fixing plate 16 for fixing the cable portions 42a, 42b, and 42c extending to the outside of the vacuum vessel 3 to the static magnetic field magnet 1 and the static magnetic field magnet 1. In addition, in FIG. 3 and FIG. 2, only the cable portion 42a is shown for simplification. The elastic member 18 is made of, for example, rubber.

【0042】

As described above, even when the cable mediates the vibration from the gradient magnetic field coil 2 or the cable itself vibrates due to the Lorentz force, these vibrations are absorbed by the elastic member 18 and the static magnetic field magnet 1 It can be suppressed from propagating to.

【0043】

The fourth noise suppression measure blocks the vibration from the vibration source by guiding it to a highly rigid non-vibration part. FIG. 4 is a perspective view showing another magnetic resonance imaging apparatus different from that shown in FIGS. 1 to 3.

【0044】

In FIG. 4, the cables 22 extending from the gradient magnetic field coil 30 are bundled in a small number and fixed to the cable fixing plate 20. Two places of the cable fixing plate 20 are attached to the mounting plate 24 and the mounting plate 25 of the static magnetic field magnet 1 via an elastic member, and one place is attached to the base 15. The base 15 is a non-vibrating part firmly fixed to a rigid body such as an installation floor.

【0045】

By fixing the cable fixing plate 20 to the base 15 which is a non-vibrating member in this way, the cable 22 due to the vibration from the vibration source, that is, the vibration of the gradient magnetic field coil 2 propagating through the cable 22 and the Lorentz force. The vibration of itself can be blocked by the presence of the base 15.

【0046】

As described above, in the magnetic resonance imaging apparatus of the present embodiment, the vibration of the cable itself that supplies the current to the gradient magnetic field coil is suppressed, the propagation of the vibration mediated by the cable is suppressed, and the vibration from the cable is suppressed. Is prevented from propagating at its fixed position, and the vibration from the vibration source is guided to a highly rigid non-vibration part to block it.

【0047】

According to such an embodiment, it is possible to effectively exert the effect of suppressing the air propagation of the vibration sound from the gradient magnetic field coil by the vacuum accommodation and the solid vibration propagation by the vibration absorber, and the noise reduction effect is excellent. A magnetic resonance imaging apparatus can be provided.

【0048】

The present invention is not limited to the above-described embodiment, and can be modified in various ways.

【0049】

For example, the above-mentioned four types of noise suppression measures are independent, and even if each of them is implemented independently, the effect can be obtained. Further, the present invention may be implemented in a magnetic resonance imaging device having a device configuration in which the gradient magnetic field coil is not housed in a vacuum vessel or a device configuration in which the gradient magnetic field coil is not provided with a vibration absorber. Needless to say, the static magnetic field generation method is not limited to the superconducting coil, and the gradient magnetic field coil is not limited to the active shielding type gradient magnetic field coil.

【0050】

[Effect of the invention]

As described above, according to the present invention, the magnetic resonance imaging device having an excellent noise reduction effect, particularly the air propagation of vibration sound from the gradient magnetic field coil due to vacuum accommodation, and the effect of suppressing the solid vibration propagation by the vibration absorber. It is possible to provide a magnetic resonance imaging apparatus that can be effectively exerted.

[Simple explanation of drawings]

[Figure 1]

Front view showing the internal configuration of the magnetic resonance imaging apparatus according to the embodiment of the present invention. [Figure 2]

Cross-sectional view of the magnetic resonance imaging apparatus according to the same embodiment when viewed from the side. [Fig. 3]

A cross-sectional view showing an enlarged view of the vicinity of the cable fixing position to the static magnetic field magnet according to the same embodiment. [Fig. 4]

Perspective view showing another magnetic resonance imaging apparatus according to the same embodiment. [Explanation of symbols]

1 ... Static magnetic field magnet 2 ... Inclined magnetic field coil 3 ... Vacuum container 6 ... Vacuum tube 7 ... vacuum pump 10 ... RF coil 11 ... Position adjustment bolt 12 ... Anti-vibration rubber 13 ... Support arm 14 ... shaft 15 ... base 16 ... Fixed plate 41a, 42a, 41b, 42b, 41c, 42c ... Cable part 43a, 43b, 43c ... Flange