JP2015039461A - Magnetic resonance imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MRI apparatus that has reduced vibration of a bed top plate transmitted from a floor through a bed body.SOLUTION: A magnetic resonance imaging apparatus includes: a gantry having a static magnetic field generating system for generating a static magnetic field space, a gradient magnetic field generating system for generating a gradient magnetic field in the static magnetic field space, and a high frequency transmission coil for irradiating an object to be examined with a high frequency signal; a bed body arranged in parallel with the gantry; and a bed top plate provided on the bed body so as to be horizontally movable, on which the object to be examined is placed and sent to an imaging space of the gantry. The bed body includes a top plate receiver that supports the bed top plate and slides, and the bed top plate and the top plate receiver are provided with a vibration suppression part for suppressing the vibration of the bed top plate.

Description

  The present invention relates to a magnetic resonance imaging (hereinafter referred to as “MRI”) apparatus, and more particularly to vibration reduction of a couch top.

  The MRI apparatus measures NMR signals generated by nuclear spins constituting a subject, particularly a human tissue, and images the form and function of the head, abdomen, limbs, etc. two-dimensionally or three-dimensionally. Device. In imaging, the NMR signal is given different phase encoding depending on the gradient magnetic field and is frequency-encoded to be measured as time series data. The measured NMR signal is reconstructed into an image by two-dimensional or three-dimensional Fourier transform.

  In order to apply the gradient magnetic field used for obtaining the position information of the subject, the gradient magnetic field coil is caused to flow at a high current in a static magnetic field at high speed. For this reason, Lorentz force acts on the gradient coil, and the gradient coil causes vibration. When this vibration propagates to the couch top on which the subject is placed, the vibration is transmitted to the subject to be imaged, and the position information becomes an inaccurate image. In addition, depending on the imaging conditions, the image in the phase direction is blurred, causing various artifacts such as shading. As a known technique for preventing the vibration of the gradient magnetic field coil from being transmitted to the bed top plate, there is a technique described in Patent Document 1 in which the gradient magnetic field is fixed to the floor. This is the arrangement of the gradient magnetic field coil that is a vibration source. A large facility is required to fix the magnet independently of the superconducting magnet.

JP-A-10-118043

  In order to suppress the vibration of the bed top plate without using the fixing as in the technique of Patent Document 1, the top plate support attached via vibration suppression to vibrationally separate from the superconducting magnet was fixed to the floor. When vibration was suppressed by running the couch top from the couch body, there was a problem that the vibration from the gradient magnetic field coil propagated through the floor and the couch top vibrated through the couch body.

  Accordingly, an object of the present invention is to provide an MRI apparatus in which vibration of a bed top plate transmitted from the floor via the bed body is reduced.

  In order to achieve the above object, a magnetic resonance imaging apparatus according to the present invention includes a static magnetic field generation system that generates a static magnetic field space, a gradient magnetic field generation system that generates a gradient magnetic field in the static magnetic field space, and a high-frequency wave on a subject. A gantry having a high-frequency transmission coil for irradiating a signal, a bed main body arranged in parallel with the gantry, and a bed top plate that is provided on the bed main body so as to be horizontally movable, and places a subject into the imaging space of the gantry The bed main body has a top plate holder that supports and slides the bed top plate, and the bed top plate and the top plate holder are provided with a vibration suppressing unit that suppresses vibration of the bed top plate. And

  ADVANTAGE OF THE INVENTION According to this invention, the vibration transmitted to a bed top plate via a bed main body can be reduced.

1 is a block diagram showing the overall configuration of an MRI apparatus according to the present invention. Sectional drawing which shows the structure of the top-plate receptacle which has a rail structure, and the bed top plate provided with the running wheel. The partial view which shows the upper surface and side surface of a top-plate receptacle shown in FIG. 2A. Sectional drawing which shows another structure of the top-plate receptacle which has a rail structure, and a bed top plate provided with the running wheel. Sectional drawing which shows a structure at the time of attaching a traveling wheel to the top-plate receiving side. The partial view which shows the upper surface and side surface of a top-plate receptacle shown in FIG. 3A. Sectional drawing which shows another structure at the time of attaching a driving wheel to the top-plate receiving side. Sectional drawing which shows a structure at the time of attaching the wheel for pressing a top plate downward to a top plate receptacle. Sectional drawing which shows the structure of a bed main body and a top-plate holder. Sectional drawing which shows the structure of a bed main body at the time of making a rail into diagonal shape, and a top-plate holder.

  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.

First, an example of the overall outline of the MRI apparatus according to the present invention will be described with reference to FIG.
FIG. 1 is a block diagram showing the overall configuration of an MRI apparatus according to the present invention. This MRI apparatus obtains a tomographic image of a subject using the NMR phenomenon. As shown in FIG. 1, the MRI apparatus includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, The receiving system 6, the signal processing system 7, the sequencer 4, and a central processing unit (CPU) 8 are provided.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the direction perpendicular to the body axis in the space around the subject 1 if the vertical magnetic field method is used, and in the body axis direction if the horizontal magnetic field method is used. Thus, a permanent magnet type, normal conduction type or superconducting type static magnetic field generation source is arranged around the subject 1.

  The gradient magnetic field generation system 3 includes a gradient magnetic field coil 9 that applies gradient magnetic fields in the three-axis directions of X, Y, and Z, which are coordinate systems (stationary coordinate systems) of the MRI apparatus, and gradient magnetic fields that drive the respective gradient magnetic field coils. A gradient power supply Gx, Gy, Gz is applied in the X, Y, and Z triaxial directions by driving the gradient magnetic field power supply 10 of each coil in accordance with a command from the sequencer 4 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 1, and the remaining two orthogonal to the slice plane and orthogonal to each other. A phase encoding direction gradient magnetic field pulse (Gp) and a frequency encoding direction gradient magnetic field pulse (Gf) are applied in one direction, and position information in each direction is encoded in the echo signal.

  The correction magnetic field generation system 18 includes a correction magnetic field generation coil 20 that applies a magnetic field for compensating the magnetic field, and a correction magnetic field power source 19 that drives each gradient magnetic field coil. In accordance with a command from the sequencer 4 described above. The correction magnetic field is applied by driving the correction magnetic field power supply 19 of the coil.

  The sequencer 4 is a control unit that repeatedly applies a high-frequency magnetic field pulse (hereinafter referred to as “RF pulse”) and a gradient magnetic field pulse in a predetermined pulse sequence. The sequencer 4 operates under the control of the CPU 8 and collects tomographic image data of the subject 1. Various commands necessary for the transmission are sent to the transmission system 5, the gradient magnetic field generation system 3, and the reception system 6. It also has a function of sending a command for generating a correction magnetic field.

  The transmission system 5 irradiates the subject 1 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 1, and includes a high-frequency oscillator 11, a modulator 12, and a high-frequency amplifier. 13 and a high frequency coil (transmission coil) 14a on the transmission side. The RF pulse output from the high-frequency oscillator 11 is amplitude-modulated by the modulator 12 at a timing according to a command from the sequencer 4, and after the amplitude-modulated RF pulse is amplified by the high-frequency amplifier 13, the RF pulse is arranged close to the subject 1. By supplying to the high frequency coil 14a, the subject 1 is irradiated with the RF pulse.

  The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the living tissue of the subject 1. The receiving system 6 receives a high-frequency coil (receiving coil) 14 b on the receiving side and a signal amplifier 15. And a quadrature phase detector 16 and an A / D converter 17. After the NMR signal of the response of the subject 1 induced by the electromagnetic wave irradiated from the high frequency coil 14a on the transmission side is detected by the high frequency coil 14b arranged close to the subject 1 and amplified by the signal amplifier 15, The signals are divided into two orthogonal signals by the quadrature detector 16 at the timing according to the command from the sequencer 4, converted into digital quantities by the A / D converter 17, and sent to the signal processing system 7.

  The signal processing system 7 performs various data processing and display and storage of processing results, and includes an external storage device such as an optical disk 22 and a magnetic disk 21 and a display 23 formed of a CRT or the like. When data from the receiving system 6 is input to the CPU 8, the CPU 8 executes processing such as signal processing and image reconstruction, displays the tomographic image of the subject 1 as a result on the display 23, and an external storage device. On the magnetic disk 21 or the like.

  The operation unit 28 inputs various control information of the MRI apparatus and control information of processing performed by the signal processing system 7 and includes a trackball or mouse 26 and a keyboard 27. The operation unit 28 is disposed in the vicinity of the display 23, and the operator controls various processes of the MRI apparatus interactively through the operation unit 28 while looking at the display 23.

  In FIG. 1, the high-frequency coil 14a and the gradient magnetic field coil 9 on the transmission side surround the subject 1 in the static magnetic field space of the static magnetic field generation system 2 in which the subject 1 is inserted if the horizontal magnetic field method is used. It is installed. The high-frequency coil 14b on the receiving side is installed so as to face or surround the subject 1.

  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. Information on the spatial distribution of the proton density and the spatial distribution of the relaxation time of the excited state is imaged, thereby imaging the form or function of the human head, abdomen, limbs, etc. two-dimensionally or three-dimensionally.

  The MRI apparatus described below includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, and a high-frequency oscillator 11 that outputs an RF pulse, and is arranged in parallel with the gantry. A bed top plate is provided on the bed main body so as to be horizontally movable, and places the subject 1 on the bed main body and feeds it into the imaging space of the gantry.

A first embodiment of the present invention will be described with reference to FIGS. 2A to 2C.
FIG. 2A shows a cross-sectional view of a top plate receiver 34 having a rail shape 31 and a bed top plate 33 to which casters 30 are attached, and shows a state when the bed top plate 33 is transferred into the imaging space. Yes.
The caster 30 travels along the rail shape 31. The rail shape 31 and the caster 30 constitute a roller mechanism for moving the bed top plate on the top plate support.

  The caster 30 includes a pulley portion, a support material that supports the pulley portion from both sides, and a pedestal to which the support material is attached. The pedestal is attached to the couch top 33 so that the pulley contacts the upper and lower surfaces of the rail shape 31, and the caster 30 is attached so that the pulley contacts the side surface of the rail shape 31.

  The caster 30 can hold the rail shape 31 by the upper and lower casters 30 attached to the bed top plate 33 and suppress the vibration in the vertical direction. Furthermore, vibration in the left-right direction can be suppressed by the pair of casters 30 attached to the left and right.

  In this embodiment, the example of suppressing the vibration in the vertical direction and the vibration in the horizontal direction is shown. However, the vibration in the vertical direction is suppressed, that is, the bed is set so that the pulley contacts the upper and lower surfaces of the rail shape 31. Only a structure to be attached to the top plate 33 may be used.

2A shows a partial top view in which the corner portion of the top plate receiver 34 is enlarged, and b) shows a side view. As shown to a), the corner part is provided with the taper part 29. FIG.
Further, as shown in b), a tapered portion 29 is also provided in the vertical direction of the side surface. By providing such a shape on the top plate receiver 34, the bed top plate 33 can smoothly move to the top plate receiver 34 side even if the direction of restraint by the casters 30 increases.

  FIG. 2C is a cross-sectional view showing another structure of the top plate receiver having the rail structure and the bed top plate provided with traveling wheels, and the state before the bed top plate 33 is transferred into the imaging space. The case where it is located outside the imaging space is shown.

  The top plate receiver 34 shown in FIG. 2C has a simplified shape in which the lower protrusion of the top plate receiver 34 is cut compared to FIG. 2A, and is placed on the bed main body 32.

  The structure shown in FIG. 2C is similar to FIG. 2A in that the caster 30 holds the rail shape 31 by the upper and lower casters 30 attached to the bed top plate 33, so that vibration in the vertical direction can be suppressed. it can. Furthermore, vibration in the left-right direction can be suppressed by the pair of casters 30 attached to the left and right.

  By using an elastic part (elastic material) on the caster 30 mounting portion (base) or on the pulley running surface of the caster 30, vibration of the bed top plate 33 can be further reduced. Moreover, the said support material can reduce the vibration of the bed top plate 33 more by using a spring mechanism.

  In addition, since the structure of the bed top plate 33 shown in the present embodiment is a structure that can take a wide surface of the top plate, there is an effect that a margin can be given to the area on which the subject 1 is placed.

Next, Example 2 will be described with reference to FIGS. 3A to 3C. The difference from the first embodiment is that casters 30 are arranged on the top plate receiving side.
FIG. 3A shows a cross-sectional view of a couch top 33 provided with a rail shape 31 and a couchtop 34 to which casters 30 are attached, and shows a state when the couch top 33 is transferred into the imaging space. Yes.
The caster 30 travels along the rail shape 31. The pedestal of the caster 30 is attached to the top plate receiver 34 so that the pulley comes into contact with the upper and lower surfaces of the rail shape. Further, the caster 30 is attached so that the pulley contacts the side surface of the rail shape 31.

  The caster 30 can hold the rail shape 31 by the upper and lower casters 30 attached to the top plate receiver 34, and can suppress vibration in the vertical direction. Furthermore, vibration in the left-right direction can be suppressed by the pair of casters 30 attached to the left and right.

  In the case of the present embodiment, instead of FIG. 2B shown in Embodiment 1, a taper portion 29 is provided at the corner portion of the bed top plate 33 as shown in FIG. 3B. With this structure, the couchtop 33 can smoothly travel on the couchtop 34.

  FIG. 3C is a cross-sectional view showing another structure when a traveling wheel is attached to the top plate receiving side, in a state before the bed top plate 33 is transferred into the imaging space, and located outside the imaging space. Is shown.

  The shape of the top plate receiver 34 shown in FIG. 3C can be simplified as compared with the top plate receiver 34 shown in FIG. 3A. Specifically, the top plate receiver 34 shown in FIG. 3C does not have a pair of casters 30 provided to contact the upper and lower surfaces of the rail shape 31 as shown in FIG. 3A. Is provided. This is because when the image is located outside the imaging space, imaging is not executed, and thus vibration of the couch top 33 is allowed. By adopting this structure, there is an effect that the structure of the top plate receiver 34 can be simplified and the parts of the caster 30 can be reduced.

  In addition, the structure of the bed top plate 33 shown in the present embodiment has an effect that the thickness of the top plate can be increased, the occurrence of warping of the top plate is suppressed, and a flat surface can be provided.

  Next, Example 3 will be described with reference to FIG. The difference from the first embodiment and the second embodiment is that the caster 30 for running the top plate receiver 34 on the bed top plate 33 side and the force acting in the direction of pressing the bed top plate 33 on the top plate receiver 34 side are arranged. The caster 30 is provided. When this structure is used, it is not necessary to adopt a configuration that sandwiches the rail structure, and the bed top plate 33 can be constrained to the top plate receiver 34.

  Although the horizontal casters 30 are omitted in FIG. 4, the horizontal vibrations can be suppressed by arranging the casters 30 on the bed top plate side or the top plate receiving side as in the first and second embodiments. .

  FIG. 5 is a diagram for explaining that the restraint structure of the bed top plate 33 provided on the top plate receiver 34 can be omitted on the bed body 32 side. FIG. 5a shows a cross-sectional view similar to FIG. 4 for comparison with b). In b), the rail structure provided in the top plate receiver 34 shown in a) is omitted. That is, the restraining structure of the bed top plate 33 is omitted.

  The shape of the top plate receptacle is such that the bed top plate is constrained in accordance with the shape of the bed top plate, but this structure is not necessary on the side of the bed main body and may be any structure that allows the bed top plate to travel.

  Next, Example 4 will be described with reference to FIG. The difference from the first embodiment, the second embodiment, and the third embodiment is that the rail structure is inclined. With this structure, vibrations in the left and right and up and down directions can be reduced. If this structure is used, the number of casters 30 to be attached can be reduced, which is advantageous in terms of cost.

  As mentioned above, although the Example of this invention was described, this invention is not limited to these.

1: subject, 2: static magnetic field generation system, 3: gradient magnetic field generation system, 4: sequencer, 5: transmission system, 6: reception system, 7: signal processing system, 8: central processing unit (CPU), 9: Gradient magnetic field coil, 10: Gradient magnetic field power supply, 11: High frequency oscillator, 12: Modulator, 13: High frequency amplifier, 14a: High frequency coil (transmitting coil), 14b: High frequency coil (receiving coil), 15: Signal amplifier, 16: Quadrature phase detector, 17: A / D converter, 18: correction magnetic field generation system, 19: correction magnetic field power supply, 20: correction magnetic field generation coil, 21: magnetic disk, 22: optical disk, 23: display, 24: ROM, 25: RAM, 26: trackball or mouse, 27: keyboard, 28: operation unit, 29: taper unit, 30: caster, 31: rail shape, 32: bed, 33: bed top, 34: top It received.

Claims (10)

A gantry having a static magnetic field generating system for generating a static magnetic field space, a gradient magnetic field generating system for generating a gradient magnetic field in the static magnetic field space, a high-frequency transmission coil for irradiating a subject with a high-frequency signal, and a parallel to the gantry A bed main body provided, and a bed top plate provided on the bed main body so as to be horizontally movable, and placing the subject and feeding it into the imaging space of the gantry,
The bed body has a top plate holder that supports and slides the bed top plate,
A magnetic resonance imaging apparatus, wherein a vibration suppressing unit that suppresses vibration of the bed top plate is provided on the bed top plate and the top plate support. The vibration suppression unit includes a protruding portion provided so as to extend along the surface of the top plate receiver, and a roller mechanism provided on the bed top plate,
The roller mechanism has a pair of casters provided on both sleeves of the projecting portion so as to sandwich one main surface of the projecting portion and another main surface facing the one main surface. The magnetic resonance imaging apparatus described in 1. The magnetic resonance imaging apparatus according to claim 2, wherein the roller mechanism further includes a caster pair installed on the couch top so as to be in sliding contact with both side surfaces of the protrusion. The vibration suppression unit includes a protruding portion provided so as to extend along the surface of the bed top plate, and a roller mechanism provided on the top plate support,
The roller mechanism has a first caster pair provided on both sleeves of the protruding portion so as to sandwich one main surface of the protruding portion and another main surface facing the one main surface, and the protruding portion The magnetic resonance imaging apparatus according to claim 1, further comprising: a second caster pair installed on the top plate support so as to be in sliding contact with both side surfaces of the top plate. The vibration suppressing portion extends along the L-shaped portion provided at the lower end of the bed top plate and the top plate receiving surface, and is surrounded by the L-shaped portion and the lower end of the bed top plate. A roller mechanism provided on each of the protrusions loosely inserted into the space,
The roller mechanism includes a caster provided at a lower end of the protruding portion so as to press the surface of the L-shaped portion,
The magnetic resonance imaging apparatus according to claim 1, further comprising: a caster provided at a lower end of the bed top plate and provided to press the top plate support. The vibration suppressing portion includes a forward tapered shape portion provided at a lower end of the bed top plate, and a reverse tapered shape portion provided at the top plate support,
The roller mechanism includes a caster provided on a reverse tapered shape portion of the top plate receiver so as to press the surface of the forward tapered shape portion,
The magnetic resonance imaging apparatus according to claim 1, further comprising: a caster provided at a lower end of the bed top plate and provided to press the top plate support. The magnetic resonance imaging apparatus according to claim 1, wherein each corner portion of the bed top plate has a tapered shape in a planar direction and a cross-sectional direction. The magnetic resonance imaging apparatus according to claim 2, wherein the caster includes a pulley, a support portion that supports an axle of the pulley, and a pedestal portion that fixes the support portion. The magnetic resonance imaging apparatus according to claim 8, wherein the pulley or the pedestal portion is made of an elastic material. The magnetic resonance imaging apparatus according to claim 8, wherein the support portion has a spring mechanism.

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