JP2005279187A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a magnetic resonance imaging apparatus wherein a noise caused by a gradient magnetic field coil can be reduced without requiring an additional member such as a sound absorbing material and without deteriorating the spatial resolution. <P>SOLUTION: When bolts 62 are regularly fixed to an outer periphery of a GC (gradient coil) 2, since vibration sections 80 mutually have same shapes and same resonance frequencies, the adjacent sections of the sections 80 mutually turn round and continue to vibrate if a pulse signal of the GC 2 has an excitation element of the above resonance frequency. When the bolts 62 are disposed on the outer periphery of the GC 2 with a certain randomness in the circumferential direction and the radial direction, a main vibration section 80 of the GC 2 becomes small in its area and the resonance frequency of the same becomes higher. Also, when the bolts 62 are disposed with the randomness, the areas and the shapes of the two or more vibration parts 80 are different and the individual resonance frequencies of the same are different, a vibration transmitting route to the adjacent vibration part 80 becomes random and disturbs the vibration by itself. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a medical magnetic resonance imaging apparatus.

  In an examination using a magnetic resonance imaging apparatus (MRI apparatus), it is not preferable as an apparatus to give mental or physical pain to a subject.

  Here, the gradient magnetic field coil (GC) of the MRI apparatus is an indispensable part for obtaining a diagnostic image, but since it is installed in the static magnetic field and the current flows to the GC, it is converted into a Lorentz force in the static magnetic field. May cause vibration and become a noise source, which may cause discomfort to the subject.

  In particular, the higher the static magnetic field of the MRI magnetic circuit and the higher the value of the current flowing through the GC, the greater the Lorentz force and the greater the vibration, which may cause discomfort to the subject.

  In an apparatus that does not take mute measures in an MRI with a static magnetic field of 1.5 Tesla or more, noise of 90 dB or more is generated, which may be painful not only for the subject but also for the operator of the apparatus.

For this reason, various countermeasures for noise reduction are implemented in the MRI apparatus.
For example, in the technique described in Patent Document 1, a gradient coil assembly is arranged in a vacuum vessel to reduce noise. In the technique described in Patent Document 2, a damping material is attached to the outside of the RF coil, and a restraint plate is attached to the outer surface of the damping material to take measures against noise. Furthermore, the technique described in Patent Document 3 uses a sound absorbing material to suppress noise.

Japanese Patent Laid-Open No. 10-179547 JP 09-271468 A JP 2000-126152 A

  However, in the above-described conventional technology, there is still no complete noise reduction countermeasure. In other words, if the sound is completely silenced, the sound deadening wall becomes large and the placement space of the subject becomes narrow, or if a soft sound deadening damper is attached to the GC, the vibration width of the GC itself increases and the spatial resolution decreases. This is because there is a high possibility that other parts will be adversely affected by noise reduction measures.

  In the MRI apparatus, various noise reduction measures are implemented so that such adverse effects are minimized, but the noise of the GC is a big problem in the high magnetic field MRI apparatus.

  An object of the present invention is to realize a magnetic resonance imaging apparatus that can reduce noise caused by a gradient magnetic field coil without requiring an additional member such as a sound absorbing material and without lowering the spatial resolution.

In order to achieve the above object, the present invention is configured as follows.
(1) A magnetic resonance imaging apparatus of the present invention comprises means for generating a static magnetic field in a measurement space, and a gradient magnetic field generating means fixed on the measurement space side surface of the static magnetic field generating means using a plurality of fixing means. Prepare.
The fixing means are irregularly arranged so that the gradient magnetic field generating means adjacent to each other between the fixing means have different resonance frequencies.

  (2) Preferably, in (1) above, the fixing means is a bolt, and the gradient magnetic field generating means is used as the static magnetic field generating means by passing the bolt through a bolt hole irregularly formed in the gradient magnetic field generating means. Fixed.

  (3) Preferably, in the above (1), the fixing means is a bolt, and the gradient magnetic field generating means is formed with irregularly formed bolt holes having a plurality of types of hole diameters. Fixed to the static magnetic field generating means.

  (4) Preferably, in the above (2) and (3), at least one of the bolts has an asymmetric shape, and the longitudinal direction of the washer is arranged perpendicular to the vibration path. ing.

  (5) Preferably, in (1), the fixing means is an adhesive member that adheres the gradient magnetic field generating means to the static magnetic field generating means.

  (6) In the magnetic resonance imaging apparatus of the present invention, the gradient magnetic field generating means has different thickness dimensions such that adjacent forming members between the fixing means have different resonance frequencies.

  It is possible to realize a magnetic resonance imaging apparatus that can reduce noise caused by the gradient magnetic field coil without requiring an additional member such as a sound absorbing material and without lowering the spatial resolution.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
First, an overall schematic configuration of a magnetic resonance imaging apparatus (MRI apparatus) to which the present invention is applied will be described.

FIG. 12 is an overall schematic configuration diagram of the MRI apparatus.
In FIG. 12, the MRI apparatus includes a static magnetic field generation apparatus 1, a gradient magnetic field generation system 30, a transmission system 32, a reception system 33, a signal processing system 34, a sequencer 31, and a central processing unit (CPU) 35. It has.

  The static magnetic field generator 31 generates a uniform static magnetic field around the subject 54 in the direction of the body axis or in a direction perpendicular to the body axis, and in a space having a certain extent around the subject 54. Permanent magnet type, normal conducting type or superconducting type magnetic field generating means is arranged.

  The gradient magnetic field generation system 30 includes a gradient magnetic field coil 2 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 36 for driving each gradient magnetic field coil, and according to a command from a sequencer 31 to be described later. By driving the gradient magnetic field power source 36 of each of the coils X, Y, Z, the gradient magnetic fields Gx, Gy, Gz in the three-axis directions of X, Y, Z are applied to the subject 54. The slice plane for the subject 54 can be set by applying the gradient magnetic field.

  The sequencer 31 repeatedly applies a high-frequency magnetic field pulse that causes nuclear magnetic resonance to the atomic nuclei constituting the living tissue of the subject 54 in a predetermined pulse sequence.

  The sequencer 31 operates under the control of the CPU 35, and sends various commands necessary for collecting tomographic image data of the subject 54 to the transmission system 32, the gradient magnetic field generation system 30, and the reception system 33.

  The transmission system 32 irradiates a high-frequency magnetic field that causes nuclear magnetic resonance to the atomic nuclei constituting the living tissue of the subject 54 by the high-frequency pulse sent out from the sequencer 31. The transmission system 32 includes a high-frequency oscillator 37, a modulator 38, a high-frequency amplifier 39, and the high-frequency coil 3 on the transmission side.

  The high frequency pulse output from the high frequency oscillator 37 is amplitude-modulated by the modulator 38 in accordance with an instruction from the sequencer 31, and the amplitude-modulated high frequency pulse is amplified by the high frequency amplifier 39. Then, by supplying the amplified high-frequency pulse to the high-frequency coil 3 disposed in the vicinity of the subject 54, the subject 54 is irradiated with electromagnetic waves.

  The receiving system 33 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of the nucleus of the living tissue of the subject 54. The reception system 33 includes a reception-side high-frequency coil 3, an amplifier 40, a quadrature phase detector 41, and an A / D converter 42.

  An electromagnetic wave (NMR signal) of the response of the subject 50 due to the electromagnetic wave irradiated from the high-frequency coil 3 on the transmission side is detected by the high-frequency coil 3 disposed in the vicinity of the subject 54, and the amplifier 40 and quadrature detection. The signal is input to the A / D converter 42 via the converter 41 and converted into a digital quantity.

  Further, the signal supplied to the quadrature detector 41 is made into two series of collected data sampled by the quadrature detector 41 at the timing according to the command from the sequencer 31, and the signal is sent to the signal processing system 34.

  The signal processing system 34 includes a CPU (operation control arithmetic means) 35, a recording device such as a magnetic disk 43 and a magnetic tape 44, and a display 45 such as a CRT. The CPU 35 performs Fourier transform, correction coefficient calculation, and image reconstruction. The signal intensity distribution of an arbitrary cross section or a distribution obtained by performing an appropriate calculation on a plurality of signals is imaged and displayed on the display 45 as a tomographic image.

  The principle of noise reduction measures for the gradient coil 2 in the MRI apparatus configured as described above will be described.

  FIG. 1 shows an example in which the one-dimensional rigid body 60 is regularly attached to each other by the attachment bolts 62 (see FIG. 1A, an example in which the one-dimensional rigid body 60 is irregularly attached (FIG. 1). 1 (b)).

  As shown in FIG. 1, the rigid body 60 between the bolt 62 and the bolt 62 vibrates with one resonance frequency. As shown in FIG. 1A, when the bolts 62 are regularly attached, the nodes (distances between the bolts 62) have almost the same length, so that they have the same resonance frequency, and the rigid body 60 has the same resonance frequency. If the phase of the adjacent node is opposite, a long vibration without interfering with the amplitude motion, that is, the reverberation of the vibration becomes long.

  On the other hand, as shown in FIG. 1B, when the arrangement is made such that the distance between the bolts 62 is random, each node has a different resonance frequency, and the phase of adjacent nodes is opposite at a certain moment. Even if it becomes, since each other's frequency is different, it will suppress each other's vibration. That is, the resonance frequency dispersion means can be configured by making the distance between the bolts 62 random.

  Therefore, a rapid damping action works on the given vibration energy. That is, the silencing effect that suppresses the vibration of the rigid body 60 and shortens the reverberation is exhibited.

This silencing effect will be briefly described using the pendulum 63 shown in FIG.
FIG. 2A shows a case where a plurality of pendulums 63 having the same vibration frequency ω are constrained to each other, as in FIG. In the example shown in FIG. 2A, the pendulum 63 repeats periodic motion as a whole because the vibration frequencies of the plurality of pendulums 63 are the same.

  On the other hand, as shown in FIG. 2B, the plurality of pendulums 63 have mutually different frequencies (ω, ω ′, ω ″, ω ′ ″), and therefore disturb the movement of each other's vibration. And the vibration converges.

  The situation shown in FIG. 1B and FIG. 2B described above can also be applied to a two-dimensional gradient coil (GC).

  Next, a specific example of resonance frequency dispersion means in the gradient magnetic field coil 2 (hereinafter referred to as GC2) will be described.

  FIG. 3 is a schematic explanatory diagram of the gradient magnetic field coil 2 according to the first embodiment of the present invention, and is a schematic diagram when the principle shown in FIG. 1B is applied to the gradient magnetic field coil 2 ( It is (b) of FIG. Further, a case where the fixing bolts 62 of the open-type MRI gradient coil 2 are regularly attached ((a) of FIG. 3) is shown in comparison.

  FIG. 3A shows an example in which a total of 19 bolts 62 are regularly attached in the circumferential direction, 14 on the outer periphery of the circular coil 2, four on the inner periphery, and one on the center. In the case of FIG. 3A, the vibrating surface is mainly four portions 80 shown by knitting. Since the vibration parts 80 have the same shape, the vibration parts 80 have the same resonance vibration frequency.

  For this reason, if there is an element that excites this resonance frequency in the pulse signal of GC2, the four portions 80 will continue to vibrate with the phases of adjacent ones reversed.

  On the other hand, in the example shown in FIG. 3B, twelve bolts 62 are arranged on the outer periphery, six on the inner periphery, and one in the center of the circular coil 2. These bolts 62 have no regularity in the circumferential position and the radial position, and have a certain kind of randomness.

  In the case as shown in FIG. 3B, the main vibration portion 80 of the gradient coil 2 is increased from 4 to 5 as compared with the case shown in FIG. The area of the vibrating surface is also reduced. This generally means that the resonance frequency has increased.

  Further, the areas and shapes of the plurality of vibration locations 80 are different from each other, and the resonance frequencies are different. When the bolts 62 are regularly arranged as shown in FIG. 3A, the vibration transmission path to the vibration location 80 adjacent to the vibration location 80 is two circumferences C1 and C2. They have symmetry. In addition, as a whole, it becomes a single vibration source, and vibration propagation occurs without being disturbed.

  In comparison, as shown in FIG. 3B, when the bolts 62 are arranged and tightened with randomness, not only the resonance frequencies of the plurality of vibration points 80 are different from each other, The path for transmitting vibrations to the adjacent vibration point 80 is also a random path, which itself hinders vibration.

Here, a function that gives the randomness of the arrangement position of the bolt 62 is defined as the following equation (1).
Rand (a1, a2) --- (1)
The function shown in the above equation (1) is a function that gives one random number between the ranges (a1, a2). The positions of the 14 bolts 62 on the outer periphery of the coil 2 shown in FIG. 3A are given by the following equation (2).
[R ・ cos {2π (i-1) / n}, R ・ sin {2π (i-1) / n}] −−− (2)
However, i is 1-14, R is the distance from the center of the circular coil 2 to the arrangement position of the bolt 62, and n is an arbitrary natural number.

Next, in order to give randomness to the 14 bolts 62 on the outer periphery shown in FIG. 3A, the following equation (3) is obtained using equations (1) and (2).
[[R-Rand (-r1, r2)] ・ cos {2π (i-1) / n} + Rand (-θ, θ), [R-Rand (-r1, r2)] ・ sin {2π (i -1) / n} + Rand (-θ, θ)] ---- (3)
In the above formula (3), r1 and r2 are bolt arrangement range limit values in the radial direction centered on R, and ± θ is the arrangement range limit angle in the circumferential direction.

  The above formula (3) is randomly arranged in the range of (R−r2, R + r1) in the radial direction compared to the regular bolt 62 arrangement position shown in FIG. This means that they are randomly arranged in an angle range of (−θ, θ) with respect to the original position.

  In this case, if the angle θ is too large, the arrangement positions of the bolts 62 may overlap each other. Further, the positions of the bolts 62 can be obtained from the positions of the four bolts 62 on the inner periphery according to the above formula (3).

  As described above, according to the first embodiment of the present invention, the arrangement positions of the plurality of fixing bolts 62 of the gradient magnetic field coil 2 are not arranged at regular intervals, but at random arrangement intervals, and the bolts 62 and 62 are arranged. The vibrations of the coil 2 constituent members between the two are restrained from each other, so that no additional members such as a sound absorbing material are required, and further, the noise caused by the gradient magnetic field coils without reducing the spatial resolution. Can be realized.

Next, a second embodiment of the present invention will be described.
The above-described first embodiment is an example in which randomness is given based on the regular arrangement of the bolts 62 shown in FIG. On the other hand, 2nd Embodiment of this invention is an example which gives randomness to arrangement | positioning irrespective of the regular basic arrangement | positioning of the volt | bolt 62. FIG.

In the second embodiment of the present invention, when the position i of the bolt 62 is ri, the position ri is defined as the following equation (4).
ri = (xi, yi)
= [Rand (0, R) · cos {Rand (0,2π)}, Rand (0, R) · sin {Rand (0,2π)}] ---- (4)
Here, the distance Dij between every i and j is given to be larger than a certain size. That is, the distance Dij is defined as the following equation (5).
Dij = | ri-rj | = √ {(xi-xj) ² + (yi-yj) ² } −−− (5)
However, Dij> d for all i and j. d is a specific number.

As an example, the case of R = 10 and d = 3.8 is shown in FIG. 4A, and the case of R = 10 and d = 2.5 is shown in FIG. 4B.
In the example shown in FIG. 3B, there are five main vibration surfaces (shaded portions). This is because the reference array is the regular array shown in FIG.

  In the case of the example shown in FIG. 4B in which the random arrangement of the bolts 62 is performed from the beginning, the main vibration surfaces are approximately eight places (shaded portions) as shown in FIG. This is because the resonance frequency of the vibration surface is increased, and the shape of the vibration surface is changed from a circle to an ellipse.

  In the case of the example shown in FIG. 4A, it is difficult to specify the vibration surface. This means that GC2 does not have a resonance frequency, so even if excited by a specific frequency, it is assumed that the frequency becomes broader and decays with time.

  Also in the second embodiment of the present invention, the same effect as in the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIGS.
The random arrangement of the bolts 62 in the GC 2 can be set in the same manner as in the first or second embodiment.

  Here, the resonance frequency of the vibration surface 64 and the vibration surface 65 in the main vibration surface shown in FIG. 5 can be measured by vibration analysis or experiment. In this case, when the primary resonance frequency in the horizontal direction of the vibration surface 64 and the resonance frequency in the vertical direction of the vibration surface 65 are close to each other, they interact through the portion of the arrow shown in FIG. Resonates and promotes vibration. In this case, it is conceivable that vibration increases and noise increases.

  In order to prevent such an operation, a washer 66 is used for the bolt 62 as shown in FIG. Thus, by using the washer 66, it becomes possible to cut off the interaction of the vibration surfaces.

  In addition, such a washer 66 not only prevents an interaction in which vibration is large, but can also induce an interaction that attenuates each other's vibration. For this reason, it is possible to act so as to inhibit the mutual vibration between the surfaces of the vibration surfaces having mutually different resonance frequencies.

  Further, the silencing effect can be enhanced by attaching the washer 66 in a direction that obstructs the vibration propagation path. For example, when the washer 66 has a rectangular shape, the vibration propagation suppressing effect, that is, the silencing effect can be improved by attaching the washer 66 so that the longitudinal direction of the washer 66 is perpendicular to the vibration path. .

  As described above, according to the third embodiment of the present invention, by adding the washer 66, the vibration of the gradient magnetic field coil 2 can be further suppressed and the silencing effect can be improved.

Next, a fourth embodiment of the present invention will be described.
The examples shown in FIGS. 4 (a) and 4 (b) are both bolt arrangement positions incorporating randomness. However, both examples do not always achieve the same effect.

  That is, the silencing effect by suppressing the vibration of the GC2 is the structure of the GC2, for example, the FRP shape, the thickness of the copper wire pattern, the physical properties such as the adhesive and FRP's Young's modulus and Poisson's ratio, and the pulse current flowing through the copper wire pattern. This involves elements such as patterns. Therefore, the vibration suppression effect differs depending on the difference in the random arrangement position of the bolts 62.

This means that there is a random arrangement position of the bolts 62 that provides the maximum silencing effect due to the structure of GC2.
For this reason, the random arrangement position of the bolts 62 for obtaining the vibration suppression effect equal to or higher than the target value can be achieved by using the above equation (4) for creating the random arrangement and the vibration analysis of the rigid body of the gradient magnetic field coil.

  That is, in the fourth embodiment of the present invention, the vibration calculation is performed based on the determined random arrangement and the physical property value of GC2 at the arrangement position according to the above formula (4), and the vibration suppressing effect is obtained. The calculation of the arrangement position of the bolt 62 is repeated until it becomes appropriate.

  As described above, according to the fourth embodiment of the present invention, the random arrangement of the bolts 62 with the most appropriate vibration suppression effect is determined in consideration of the physical characteristic value of GC2. Further, it is possible to further suppress the vibration of the gradient magnetic field coil 2 and improve the silencing effect.

Here, as an example of the irregular fixing means according to the present invention, a typical cross-sectional structure when the bolt 62 is used as described above is shown in FIG.
In FIG. 7, the gradient magnetic field coil 2 is provided with a through hole. By passing the fixing bolt 62 through the through hole and fastening with a magnet container 67 as a static magnetic field generating means, the gradient magnetic field coil 2 and the magnet are arranged. The container 67 is mechanically fixed. The effect of the present invention can be exhibited when the in-plane arrangement of the fixing holes is irregular.

  Further, as shown in FIG. 7, the effect can be effectively exhibited by arranging a rectangular washer 66 between the gradient coil 2 and the head of the bolt 63.

Next, a fifth embodiment of the present invention will be described with reference to FIG.
FIG. 8 is a view showing a fifth embodiment of the present invention, and is a cross-sectional view of the main part of an open permanent magnet MRI apparatus.

  In FIG. 8, the GC 2 including the copper wire pattern 69 and the pole piece 68 are connected to each other via a bolt 62. Since GC <b> 2 is a vibration source, the vibration is transmitted to the pole piece 68, the magnet 67, and the yoke 70 via the bolt 62.

  The vibrations of the pole piece 68, the magnet 67, and the yoke 70 not only cause disturbance of the static magnetic field, but also become a new noise source. In this case, when the entire MRI apparatus is regarded as one structure, the vibration source is GC2.

  In such a structure, since the GC 2 and the pole piece 68 are connected via the bolt 62, the position of the bolt 62 is the most important factor in vibration transmission. From the viewpoint of the pole piece 68, the vibration source is the bolt. 62. The vibration of the bolt 62 causes the ball piece 68, the magnet 67, and the yoke 70 to vibrate.

  Even in this case, the vibration attenuation is related to the position of the bolt 62 as in the case of GC2. That is, the vibration is determined by the structure of the MRI apparatus and its physical property values, the structure of the GC2 and its physical property values, the pulse current, and the position of the bolt 62.

  Therefore, as in the example shown in FIG. 3, FIG. 4, or FIG. 6, vibration analysis or experiment is performed in consideration of the randomly arranged bolts 62 and elements such as the structure of the MRI apparatus to suppress vibration. It is possible to determine the random arrangement position of the bolt 62 that is most effective.

  As described above, according to the fifth embodiment of the present invention, the random arrangement of the bolts 62 with the most appropriate vibration suppression effect is determined in consideration of the physical characteristic values of elements such as the structure of the MRI apparatus. Thus, since it comprised, the vibration of the gradient magnetic field coil 2 can further be suppressed and the silencing effect can be improved.

Next, a sixth embodiment of the present invention will be described with reference to FIG.
In the 1st-5th embodiment of this invention mentioned above, the arrangement position of the volt | bolt 62 was a random position. On the other hand, in the sixth embodiment, the arrangement positions of the bolts 62 are regularly arranged as in the example shown in FIG.

  The arrangement positions of the bolts 62 are regular, but the diameters of the bolt holes are small ones 71a, medium ones 71b, and large ones 71c, and these positions are random.

  As shown in FIG. 9, even if the position of the bolt 62 is regular, if the bolt hole diameter is random, the vibration of the coil 2 constituting member between the bolts 62 and 62 is suppressed mutually. be able to. Therefore, it is possible to realize a magnetic resonance imaging apparatus capable of reducing noise due to the gradient magnetic field coil 2 without requiring an additional member such as a sound absorbing material and without lowering the spatial resolution.

Next, a seventh embodiment of the present invention will be described with reference to FIG.
In the above-described sixth embodiment of the present invention, the positions of the bolts 62 are regular, and the bolt hole diameter is random.

  On the other hand, in the seventh embodiment of the present invention, the arrangement positions of the bolts 62 are random as shown in FIG. 3B and FIG.

  The diameters of the bolt holes are small, and the hole diameters of the small one 71a, the middle one 71b, and the large one 71c are also random.

  As shown in FIG. 10, if the arrangement position of the bolts 62 is random and the bolt hole diameter is also random, the vibration suppressing effect of the gradient magnetic field coil 2 can be further improved.

Next, an eighth embodiment of the present invention will be described with reference to FIG.
FIG. 11: is a principal part schematic sectional drawing of the 8th Embodiment of this invention. In the eighth embodiment, the cross-sectional thickness of the GC coil 2 and the depths of the fixing holes 72a to 72g of the bolt 62 are random to each other.

  As shown in FIG. 11, if the cross-sectional thickness of the GC coil 2 and the depths of the fixing holes 72 a to 72 g of the bolt 62 are made random, the vibration suppressing effect of the gradient magnetic field coil 2 can be improved.

  As another embodiment of the present invention, the material density of GC2 can be random to provide a resonance frequency dispersion means.

  Moreover, although the example mentioned above is an example which attaches the GC coil 2 to the pole piece 68 with the volt | bolt 62, it is applicable also to the example at the time of attaching GC2 to the pole piece 68 with an adhesive instead of a volt | bolt. That is, a plurality of adhesion portions between the GC coil 2 and the pole piece 68 can be provided, and the plurality of adhesion portions can be calculated based on the above formula (4) or the like, and can be adhered to each other at random positions. It is also possible to make the adhesion area random.

It is a figure explaining the principle of this invention. It is a figure explaining the principle of this invention. It is explanatory drawing of the 1st Embodiment of this invention. It is explanatory drawing of the 2nd Embodiment of this invention. It is explanatory drawing of the 3rd Embodiment of this invention. It is explanatory drawing of the 3rd Embodiment of this invention. It is principal part structure sectional drawing at the time of using a volt | bolt as an irregular fixing means. It is explanatory drawing of the 5th Embodiment of this invention. It is explanatory drawing of the 6th Embodiment of this invention. It is explanatory drawing of the 7th Embodiment of this invention. It is explanatory drawing of the 8th Embodiment of this invention. 1 is a schematic configuration diagram of an MRI apparatus to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Static magnetic field generator 2 Gradient magnetic field coil 3 High frequency magnetic field coil 30 Gradient magnetic field generation system 31 Sequencer 32 Transmission system 33 Reception system 34 Signal processing system 35 CPU
36 Gradient magnetic field power supply 37 High frequency oscillator 38 Modulator 39, 40 Amplifier 41 Quadrature detector 42 A / D converter 62 Volt 66 Washer 67 Magnet 68 Pole piece 69 Copper wire pattern 70 Yoke 71a-71c Bolt hole 72a-72g Bolt hole

Claims (6)

In a magnetic resonance imaging apparatus, comprising: a means for generating a static magnetic field in a measurement space; and a gradient magnetic field generation means fixed using a plurality of fixing means on the measurement space side surface of the static magnetic field generation means.
The magnetic resonance imaging apparatus according to claim 1, wherein the fixing means are irregularly arranged such that adjacent gradient magnetic field generating means between the fixing means have different resonance frequencies.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the fixing means is a bolt, and the gradient magnetic field generating means is fixed to the static magnetic field generating means through the bolt through a bolt hole irregularly formed in the gradient magnetic field generating means. A magnetic resonance imaging apparatus.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the fixing means is a bolt, and the gradient magnetic field generating means has irregularly formed bolt holes having a plurality of types of hole diameters, and the static magnetic field using the bolt. A magnetic resonance imaging apparatus fixed to a generating means.   4. The magnetic resonance imaging apparatus according to claim 2, wherein at least one of the bolts has an asymmetric shape and is arranged so that a longitudinal direction of the washer is perpendicular to a vibration path. Magnetic resonance imaging apparatus.   2. The magnetic resonance imaging apparatus according to claim 1, wherein the fixing means is an adhesive member that adheres the gradient magnetic field generating means to the static magnetic field generating means. In a magnetic resonance imaging apparatus, comprising: a means for generating a static magnetic field in a measurement space; and a gradient magnetic field generation means fixed using a plurality of fixing means on the measurement space side surface of the static magnetic field generation means.
The magnetic resonance imaging apparatus, wherein the gradient magnetic field generating means has different thickness dimensions so that adjacent forming members between the fixing means have different resonance frequencies.

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