JP4763124B2 - Magnetic resonance imaging system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus that images a desired portion of a subject using magnetic resonance, and more particularly, to a magnetic resonance imaging apparatus that suppresses gradient coil vibration associated with intermittent generation of a gradient magnetic field. It is about.
[0002]
[Prior art]
Magnetic resonance imaging equipment (hereinafter referred to as MRI equipment) uses the nuclear magnetic resonance (hereinafter referred to as NMR) phenomenon to measure the nuclear spin density distribution and relaxation time distribution at the desired site in the subject. The signal emitted from the sensor is measured and displayed as a tomographic image. Here, in order to simultaneously measure signals emitted from a plurality of points, each signal needs to include information that can specify a signal generation position. For this reason, an MRI apparatus includes a static magnetic field generator for causing an NMR phenomenon, an irradiation coil for irradiating a high-frequency signal to cause nuclear magnetic resonance in an atomic nucleus constituting a living tissue of a subject, and a measurement target. There is a need for a magnetic field generator comprising a gradient coil for providing position information to each signal emitted. Further, the MRI apparatus has a receiving coil for receiving a signal emitted from a subject, an image reconstruction means for obtaining an image representing a physical property of an inspection object using the received signal, and a means for controlling an inspection condition Is provided.
[0003]
A magnetic field generator of a conventional MRI apparatus will be described. As shown in FIG. 9, the magnetic field generator is provided with static magnetic field generators 1a and 1b that are opposed to each other by a distance L through a space H into which the subject is inserted. Gradient magnetic field coils 2a and 2b are arranged on the space side of the static magnetic field generator. The gradient magnetic field coils 2a, 2b are provided with gradient magnetic field attachment means 3a, 3b and magnetic field adjustment means 4a, 4b for fixing the gradient magnetic field coils 2a, 2b on the space side of the static magnetic field generator. Irradiation coils 5a and 5b are arranged on the space side.
[0004]
The magnetic circuit thus formed forms a static magnetic field in a space sandwiched between the static magnetic field generators 1a and 1b, and applies a high frequency pulse to the gradient magnetic field coils 2a and 2b located in the static magnetic field space. To form a gradient magnetic field. The magnetic field adjusting means 4a and 4b are composed of a magnetic group, and the magnetic field uniformity of the space H part in which the subject is inserted is adjusted by changing the amount and arrangement of the magnetic group.
[0005]
[Problems to be solved by the invention]
However, in the magnetic field generator in such a conventional MRI apparatus, the gradient magnetic field coils 2a and 2b are fixed in close contact with the gradient magnetic field attaching means 3a and 3b when no static magnetic field is generated. However, when a static magnetic field is generated, a gap K is generated between the gradient magnetic field coils 2a and 2b and the gradient magnetic field attaching means 3a and 3b as shown in FIG. This is because the magnetic field adjusting means 4a and 4b arranged on the space side of the static magnetic field generating devices 1a and 1b are magnetic bodies, so that the magnetic field adjusting means 4a and 4b indicated by the arrows indicate the direction of the static magnetic field generating source. Power is added to. As a result, the surface of the static magnetic field generator is distorted. Since the gradient magnetic field attaching means 3a and 3b are installed on the surface of the static magnetic field generator, they are affected by this strain.
In addition, when the static magnetic field generator is a superconducting system, the inside of the apparatus is depressurized for the purpose of heat insulation. Regardless of whether or not a static magnetic field is generated, the surface of the static magnetic field generator is Cause distortion.
[0006]
Also, since the gradient magnetic field coils 2a and 2b are used in a state where they are located in the static magnetic field space, when a current is passed through the X-direction and Y-direction gradient magnetic field coils 2a and 2b, it is determined by Fleming's left-hand rule. Force is generated in the direction. Since the current pulse changes with time, the gradient coils 2a and 2b vibrate.
[0007]
When the gradient magnetic field coils 2a and 2b are fixed to the gradient magnetic field attachment means 3a and 3b in the state where the gap K is generated, the mechanical support is incomplete and the gradient magnetic field coils 2a and 2b vibrate as described above. Therefore, the gradient coils 2a and 2b repeat large vibrations as shown in FIG. In such a state, the position information of each signal emitted from the measurement target is incorrect, which adversely affects the obtained image. In addition to this, the gradient magnetic field coils 2a and 2b and the gradient magnetic field attaching means 3a and 3b collide, and the hitting sound gives noise to the subject as discomfort and anxiety.
[0008]
Therefore, the present invention addresses such problems and obtains high-quality images because accurate position information can be given to each signal emitted from the measurement object by suppressing the vibration of the gradient coil. An object of the present invention is to provide an MRI apparatus that can eliminate anxiety and the like in a subject by reducing noise caused by vibration of a gradient coil.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an MRI apparatus according to the present invention includes a pair of static magnetic field generators arranged to face each other across a space in which a subject can be inserted and generate a static magnetic field, and the pair of static magnetic field generators And a plurality of attachment means for attaching the gradient magnetic field generation device to the static magnetic field generation device, and a plurality of attachment means for attaching the gradient magnetic field generation device to the static magnetic field generation device. At least one of the means generates the gradient magnetic field via an adjustment means that fills a gap formed between the surface of the static magnetic field generator and the gradient magnetic field generator due to surface distortion of the static magnetic field generator. Install the device.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to FIGS.
FIG. 2 shows a general view of a magnetic field generator embodying the present invention.
[0011]
The MRI apparatus of the present invention includes a static magnetic field generator, an irradiation coil that irradiates a high frequency signal to cause nuclear magnetic resonance in a nucleus constituting a living tissue of a subject, and positional information on each signal emitted from a measurement target There is a need for a magnetic field generating device composed of gradient magnetic field coils for providing the above. Further, the MRI apparatus has a receiving coil for receiving a signal emitted from the subject, an image reconstruction calculating means for obtaining an image representing a physical property of an inspection object using the received signal, and an inspection condition. It consists of means.
[0012]
That is, in FIG. 2, a pair of static magnetic field generators 1a and 1b form a space H in which a subject can enter between them, and are disposed, for example, facing each other vertically. These static magnetic field generators 1a and 1b are for generating a static magnetic field in the space H. For example, the magnetic field generation method may be a superconducting method or a normal conduction method, and the shape is a disk shape. Is formed.
[0013]
Further, gradient magnetic field attachment means 3a, 3b and magnetic field adjustment means 4a, 4b for fixing the gradient magnetic field coils 2a, 2b are installed on the space H side of the static magnetic field generators 1a, 1b. The gradient magnetic field attaching means 3a, 3b may be fixed to the static magnetic field generators 1a, 1b or may be integrated with the static magnetic field generators 1a, 1b. The magnetic field adjusting means 4a and 4b are composed of a magnetic material group, and the magnetic field uniformity of the space H part in which the subject is inserted is adjusted by changing the amount and arrangement of the magnetic material group. Since the amount of adjustment varies depending on various conditions, it is selected appropriately for each aircraft.
[0014]
Gradient magnetic field coils 2a and 2b are arranged on the space H side of these static magnetic field generators 1a and 1b. For example, the shape is formed in a disk shape, and the internal structure is composed of three sets of coils corresponding to the X, Y, and Z gradient magnetic field directions: three directions. A gradient magnetic field is formed by applying a high frequency pulse to the gradient magnetic field coils 2a and 2b. When a current is passed through the gradient magnetic field coils 2a and 2b located in the static magnetic field space, a force is generated in a certain direction according to Fleming's left-hand rule. Since the current pulse changes with time, the gradient coils 2a and 2b vibrate.
[0015]
Further, a strong force is applied to the magnetic field adjusting means 4a, 4b made of a magnetic material located on the space H side of the static magnetic field generating devices 1a, 1b, and the static magnetic field adjusting means 4a, 4b are attached to the static magnetic field generating means 4a, 4b. Strain is generated on the entire surface of the magnetic field generator 1a, 1b. Further, when the static magnetic field generators 1a and 1b are depressurized, the surfaces of the static magnetic field generators 1a and 1b are further distorted.
[0016]
The gradient magnetic field coils 2a, 2b and the gradient magnetic field attachment means 3a, 3b are not in close contact with each other due to the distortion of the surface of the static magnetic field generator 1a, 1b described above, and the vibration of the gradient magnetic field coils 2a, 2b cannot be suppressed. Since the height adjusting mechanism described in detail below is employed between the gradient magnetic field attaching means 3a, 3b and the gradient magnetic field coils 2a, 2b, vibrations of the gradient magnetic field coils 2a, 2b can be suppressed.
[0017]
First, as a first embodiment, spacers 6a and 6b made of at least one spacer are provided between gradient magnetic field attachment means 3a and 3b and gradient magnetic field coils 2a and 2b as shown in FIG. The thickness of each installation location is a thickness suitable for the gap K caused by strain. In this way, by installing the spacers 6a and 6b, the gradient magnetic field coils 2a and 2b are fixed to the gradient magnetic field attaching means 3a and 3b in a state of being in close contact with the spacers 6a and 6b and being completely mechanically supported. Therefore, vibrations of the gradient magnetic field coils 2a and 2b can be suppressed.
[0018]
Further, the spacers 6a and 6b may also be used as the gradient magnetic field attaching means 3a and 3b. In this way, since any material and shape can be used, an inexpensive height adjustment means can be configured, and accurate position information can be given to each NMR signal, so that image quality is improved, and gradient coils 2a and 2b are provided. By suppressing the noise caused by the vibration of the subject, discomfort and anxiety to the subject can be eliminated.
[0019]
As a second embodiment, a height adjusting mechanism is provided that allows the gradient magnetic field coils 2a and 2b to move up and down. For example, the structure includes jacks 7a and 7b as shown in FIG. 3, bolt nuts 8, 9, and 10 as shown in FIG. 4, and blocks 11, 12, and 13 as shown in FIG.
The jacks 7a and 7b are arranged at multiple locations so as to abut against the static magnetic field generators 1a and 1b and the gradient magnetic field coils 2a and 2b, respectively, and can be adjusted by simply moving the jacks 7a and 7b up and down regardless of the height. it can.
[0020]
Next, the bolts and nuts 8, 9, and 10 pass the fixing pin 10 through the gradient magnetic field coils 2a and 2b, and are threaded to reach the gradient magnetic field attaching means 3a and 3b. It is arranged between the gradient magnetic field coils 2a and 2b and the gradient magnetic field attaching means 3a and 3b, and is arranged on the space H side of the fixing nut 8 and the gradient magnetic field coils 2a and 2b. The nut 9 may have any shape as long as it has a screw hole. By doing so, the nut 9 can freely move up and down via the fixing pin 10, and the gradient magnetic field coils 2a and 2b can be fixed.
[0021]
Next, the blocks 11, 12, and 13 are composed of the block 11, the side block 12, and the stopper 13, and the block 11 moves up and down when the side block 12 moves in the horizontal direction. With this structure, the gap between the gradient magnetic field coils 2a and 2b is adjusted, and mechanically supported in a state of being in close contact with the gradient magnetic field coils 2a and 2b and fixed to the gradient magnetic field attachment means 3a and 3b. The vibration of the gradient magnetic field coils 2a and 2b can be suppressed. In this case, fine adjustment can be easily performed, so that workability is high, and firmer fixing can be performed as compared with the jack type or the bolt nut type.
[0022]
Moreover, it is good also as a structure as shown in FIG. 6 as a modification of a bolt nut type.
That is, the side surface of the pin 14 is threaded, the pin 14 is fitted into the screw hole provided in the gradient magnetic field coils 2a and 2b, and the size of the gap K between the gradient magnetic field coils 2a and 2b and the gradient magnetic field attaching means 3a and 3b. The gradient magnetic field attachment means 3a and 3b are fixed in accordance with. Further, a nut 15 is disposed on the space H side of the pin 14 for preventing loosening. Therefore, since fine adjustment can be easily performed, the workability is high and the fixation can be performed more firmly, and the image quality can be improved and the discomfort and anxiety about the subject can be eliminated.
Further, when the pin 14 is fixed to the gradient magnetic field attachment means 3a, 3b, the attachment means 3a, 3b may be provided with screw holes.
[0023]
By using a vibration damping material as the material of the height adjustment mechanism as described above, further vibration suppression can be achieved, and image quality can be improved and discomfort and anxiety can be eliminated from the subject due to noise.
[0024]
【The invention's effect】
Since the present invention is configured as described above, the height adjusting means is disposed between the gradient magnetic field coils 2a, 2b and the static magnetic field generators 1a, 1b or the gradient magnetic field attaching means 3a, 3b, and the gradient magnetic field coil 2a By supporting 2b mechanically, vibration of the gradient magnetic field coils 2a and 2b can be suppressed, and accurate position information can be given to the NMR signal, thereby improving the image quality. Further, by reducing noise due to vibration, it is possible to eliminate discomfort and anxiety about the subject.
[Brief description of the drawings]
FIG. 1 is a view showing an embodiment of a height adjusting means which is a characteristic part of a magnetic resonance imaging apparatus according to the present invention.
FIG. 2 is an overall configuration diagram of a magnetic field generator according to the present invention.
FIG. 3 is a view showing another embodiment of the height adjusting means according to the present invention.
FIG. 4 is a view showing another embodiment of the height adjusting means according to the present invention.
FIG. 5 is a view showing another embodiment of the height adjusting means according to the present invention.
FIG. 6 is a view showing another embodiment of the height adjusting means according to the present invention.
FIG. 7 is a view showing generation of strain by a magnetic field adjusting unit of a conventional magnetic field generator.
FIG. 8 is a diagram showing vibration of a gradient magnetic field coil of a conventional magnetic field generator.
FIG. 9 is an overall configuration diagram of a conventional magnetic field generator.
[Explanation of symbols]
1a, 1b ... static magnetic field generator, 2a, 2b ... gradient magnetic field coil, 3a, 3b ... gradient magnetic field coil mounting means, 4a, 4b ... magnetic field adjustment means, 5a, 5b ... irradiation coil, 6a, 6b ... spacer, 7a, 7b ... jack, 8 ... fixing nut, 9 ... nut, 10 ... fixing pin, 11 ... block, 12 ... side block, 13 ... stopper, 14 ... pin, 15 ... nut

Claims (6)

A pair of static magnetic field generators arranged opposite to each other across a space in which a subject can be inserted, and generating a static magnetic field in a state where the inside is decompressed ,
A pair of gradient magnetic field generators arranged on the space side of each of the pair of static magnetic field generators to generate a gradient magnetic field; and
A plurality of attachment means for attaching the gradient magnetic field generator to the space-side surface of the static magnetic field generator;
In a magnetic resonance imaging apparatus having
At least one of the plurality of attachment means, the surface strain of the static magnetic field generating apparatus wherein based on the internal reduced pressure of the static magnetic field generating apparatus, between the surface and the attachment means the static magnetic field generator via an adjusting means to fill the resulting gap, a magnetic resonance imaging apparatus characterized by attaching the gradient magnetic field generating device to a surface of the space side of the static magnetic field generating apparatus.   The magnetic resonance imaging apparatus according to claim 1, wherein the adjustment unit is made of a vibration damping material or includes a vibration damping mechanism.   The magnetic resonance imaging apparatus according to claim 1, wherein the adjusting unit includes any one of a spacer and a bolt and a nut. A pair of static magnetic field generators arranged opposite to each other across a space in which a subject can be inserted, and generating a static magnetic field in a state where the inside is decompressed ,
A pair of gradient magnetic field generators arranged on the space side of each of the pair of static magnetic field generators to generate a gradient magnetic field; and
A plurality of attachment means for attaching the gradient magnetic field generator to the space-side surface of the static magnetic field generator;
In a magnetic resonance imaging apparatus having
Before according to the surface strain of the interior of the static magnetic field generating devices based on vacuum of Kisei magnetic field generator, an adjustment means for adjusting the distance between the surface of the static magnetic field generating device and the gradient magnetic field generating device magnetic resonance imaging apparatus characterized by being. The magnetic resonance imaging apparatus according to claim 4, wherein the adjustment unit includes a mechanism that widens a distance between the static magnetic field generation apparatus and the gradient magnetic field generation apparatus and a mechanism that reduces the mechanism.   6. The magnetic resonance imaging apparatus according to claim 5, wherein the attachment means includes any one of a jack and a block.

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