JP5203682B2 - MRI apparatus, NMR analyzer, and static magnetic field generator - Google Patents

Description

  The present invention relates to a gantry that generates a highly uniform static magnetic field, an MRI (Magnetic Resonance Imaging) apparatus and an NMR (Nuclar Magnetic Resonance) analyzer equipped with the gantry.

  The MRI apparatus and the NMR analyzer are equipped with a static magnetic field generating means for the purpose of generating a static magnetic field by quantization of nuclear magnetism that is the source of the MR signal. The static magnetic field generation means includes a static magnetic field generation unit that generates a static magnetic field and a shimming unit that adjusts the uniformity of the static magnetic field.

  FIG. 7 is a schematic cross-sectional view showing the state of the static magnetic field generated by the static magnetic field generator provided in the MRI apparatus or NMR analyzer, and shows the state where the axial length of the static magnetic field generator is relatively long. ing. The static magnetic field generator 10A is composed of a superconducting magnet, and has a superconducting coil 12A housed together with a refrigerant in a substantially cylindrical vacuum vessel. Then, the static magnetic field generator 10A generates a magnetic field (static magnetic field) indicated by a dotted line in the figure in the bore (cylindrical inner space). This static magnetic field is the basis for the MRI imaging operation and the NMR analysis operation, so it needs to be kept highly uniform. In particular, in the imaging region indicated by the alternate long and short dash line in the figure, the uniformity is several ppm or less. It is necessary to correct the static magnetic field inhomogeneity.

  Conventionally, as one technique for correcting static magnetic field inhomogeneity, shimming (passive shim) in which a magnetic field is adjusted by arranging an iron piece (iron shim) at a desired position has been proposed. The shimming structure for realizing this is constituted by, for example, a shim tray (not shown) disposed in the bore of the superconducting magnet device 10A. This shim tray has a plurality of pockets formed continuously, and by storing a predetermined number of iron shims in a predetermined pocket, a desired amount of iron shim is arranged at a desired position, and a static magnetic field is obtained. (See, for example, Patent Document 1).

  FIG. 8 is a schematic cross-sectional view showing a state of a static magnetic field generated by a static magnetic field generator having a relatively short axial length as seen in recent years. In recent years, the MRI apparatus tends to shorten the axial length for the purpose of reducing the feeling of obstruction given to the subject. Here, as shown in FIGS. 7 and 8, the static magnetic field generated by the static magnetic field generating unit composed of the superconducting magnet is influenced by the superconducting coil 12A and the superconducting coil 12B. There is a characteristic of being largely disturbed in the vicinity of the axial end portion of 10B. In the static magnetic field generator 10A having a relatively long axial length as shown in FIG. 7, the imaging region is located away from the position of the disturbance, so that it is not affected so much, and a small amount of iron shim is used. The magnetic field could be corrected. However, in the static magnetic field generation unit 10B having a relatively short axial length as shown in FIG. 8, the distance between the superconducting coil 12B and the imaging region indicated by the alternate long and short dash line in the figure is short, and thus the superconducting coil 12B. A large amount of iron shim was required to make the static magnetic field uniform due to the influence of the magnetic field disturbance due to.

JP-A-8-299304

  However, if a large amount of iron shim is used as described above, the following secondary problems occur, which has been a problem. That is, the magnetic susceptibility of iron changes with temperature, and the magnetic susceptibility decreases with increasing temperature. Since the iron shim is generally placed in the vicinity of the gradient coil, it may be warmed by the gradient coil during operation. When the iron shim is warmed in this way, the iron shim does not correct the initially adjusted amount, and the uniformity of the static magnetic field is reduced, so that the imaging operation and the analysis operation cannot be performed satisfactorily.

  A large amount of iron shim is subjected to a large stress due to the influence of a magnetic field. Therefore, the adhered iron shim may be peeled off, for example, a shim tray that is a support structure of the iron shim may be damaged, or the apparatus may be slightly distorted.

  The present invention has been made to solve the above-described problems caused by the prior art, and can reduce the amount of iron shim disposed in the bore of the static magnetic field generation unit, whereby the static magnetic field during device operation can be reduced. An object of the present invention is to provide an MRI apparatus, an NMR analysis apparatus, and a gantry that can improve the uniformity of the iron shim and suppress the breakage of the iron shim support structure.

To solve the above problems and achieve an object, MRI apparatus according to the present invention, a static magnetic field generator for generating a static magnetic field, gradient magnetic field for applying a gradient magnetic field to the subject disposed within the static magnetic field A coil, a high-frequency coil that receives a magnetic resonance signal from the subject to which the gradient magnetic field is applied, and an inner side of a cylinder of the static magnetic field generation unit, and a central part in the central axis direction of the static magnetic field generation unit a first iron shims, are disposed outside the cylinder, and a second iron shims arranged on the end in the central axis direction of the static magnetic field generating section, the inside of the cylinder, said static An iron shim is not disposed at an end portion in the central axis direction of the magnetic field generation unit .

Further, NMR analysis apparatus according to the present invention, a static magnetic field generator for generating a static magnetic field, a gradient magnetic field coil for applying a gradient magnetic field in the analysis sample placed in the static magnetic field, the gradient magnetic field is applied a radio frequency coil for receiving magnetic resonance signals from the analysis sample, wherein is arranged inside the cylinder of the static magnetic field generating portion, a first iron shims disposed in the central portion in the central axis direction of the static magnetic field generating section, the A second iron shim disposed outside the cylinder and disposed at an end portion in the central axis direction of the static magnetic field generation unit, and inside the cylinder, an end portion in the central axis direction of the static magnetic field generation unit An iron shim is not disposed on the surface.

Further, the static magnetic field generating unit according to the present invention is immersed in a cooling liquid in a cylindrical container and stored, and a superconducting coil that generates a static magnetic field is disposed inside the cylinder, and the superconducting coil comprising of a first iron shims disposed in the central portion in the central axis direction, are disposed outside the cylinder, and a second iron shims arranged on the end in the central axis direction of the superconducting coil, An iron shim is not disposed at the end of the superconducting coil in the central axis direction inside the cylinder .

According to the present invention, it is possible to reduce the amount of iron shim disposed in the bore of the static magnetic field generation unit, thereby improving the uniformity of the static magnetic field during operation of the apparatus and suppressing damage to the iron shim support structure. be able to.

  Exemplary embodiments of an MRI apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

  This embodiment avoids placing iron shims at the axial ends in bores that previously required the placement of large amounts of iron shims and replaces other irons as an alternative to compensate for the static magnetic fields in those parts. The shim is arranged at the end of the static magnetic field generation unit outside the bore.

  FIG. 1 is a system configuration diagram of an MRI apparatus according to the present invention. For example, the MRI apparatus 100 includes a gantry 90, a top plate 40 provided on a bed (not shown), a gradient magnetic field power supply 45, a transmission unit 48, a reception unit 49, and an operator console unit 80. The gantry 90 includes a static magnetic field generation unit 10, a gradient magnetic field coil structure 20, and a high frequency coil 30.

  In the static magnetic field generator 10, a superconducting coil 12 is stored in a cooling liquid in a substantially thick cylindrical vacuum vessel 11. The superconducting coil 12 accommodates a coil that generates a large magnetic field at both axial ends of the vacuum vessel 11. The static magnetic field generator 10 generates a static magnetic field in the bore (the space inside the cylinder of the static magnetic field generator 10). An iron shim 51 and an iron shim 52 constituting a second iron shim, which is a feature of the present embodiment, are attached to both ends in the axial direction of the vacuum vessel 11. The iron shim 51 is fixed to both end surfaces 11 a of the vacuum vessel 11 in the axial direction. On the other hand, the iron shim 52 is fixed to the outer peripheral surface 11 b at both axial ends of the vacuum vessel 11. These iron shim 51 and iron shim 52 correct the static magnetic field mainly at both ends in the axial direction of the cylindrical imaging region in the bore.

  The gradient magnetic field coil structure 20 is fixed inside the static magnetic field generator 10. The gradient magnetic field coil structure 20 has a substantially cylindrical shape, and includes a main coil (gradient magnetic field coil) 21 that applies a gradient magnetic field to the X, Y, and Z axes, and a shield coil 22 that cancels the leakage magnetic field of the main coil 21. doing. A shim tray 60 that is an iron shim support structure is disposed between the main coil 21 and the shield coil 22. The shim tray 60 accommodates an iron shim 71 constituting the first iron shim. The iron shim 71 corrects the static magnetic field mainly in the middle of the cylindrical imaging region in the bore. And the iron shims 51 and 52 which comprise the 2nd iron shim, and the iron shim 71 which comprises the 1st iron shim comprise the shimming structure part which adjusts a static magnetic field uniformity.

  The high frequency coil 30 is fixed to the uniform magnetic field region side of the gradient magnetic field coil structure 20. Then, the subject P is laid on a top plate 40 that is disposed in the uniform magnetic field region and is movable in the horizontal direction. As an example, the size of the bore in this embodiment is a patient bore axial length of 1.495 m and an opening diameter of 65.5 cm. At this time, the magnet axis length of the static magnetic field generation unit 10 is 1.400 m. The high frequency coil 30 receives a high frequency pulse from the transmitter 48 and generates a high frequency magnetic field. The high frequency coil 30 receives a magnetic resonance signal radiated from the subject P due to the influence of the high frequency magnetic field.

  The transmission unit 48 includes an oscillation unit, a phase selection unit, a frequency conversion unit, an amplitude modulation unit, and a high frequency power amplification unit. The oscillation unit generates a high-frequency signal having a resonance frequency unique to the target nucleus in the static magnetic field. The phase selection unit selects the phase of the high frequency signal. The frequency modulation unit modulates the frequency of the high-frequency signal output from the phase selection unit. The amplitude modulation unit modulates the amplitude of the high-frequency signal output from the frequency modulation unit, for example, according to a sync function. The high frequency power amplification unit amplifies the high frequency signal output from the amplitude modulation unit. As a result of the operation of each of these units, the transmission unit 48 transmits a high-frequency pulse corresponding to the Larmor frequency to the high-frequency coil 30.

  The receiving unit 49 includes a selector, a pre-stage amplifier, a phase detector, and an analog / digital converter. The selector selectively inputs a magnetic resonance signal output from the high frequency coil 30. The receiving unit 49 amplifies the magnetic resonance signal output from the selector. The phase detector detects the phase of the magnetic resonance signal output from the preamplifier. The analog-digital converter converts the signal output from the phase detector into a digital signal.

  The operator console unit 80 includes an interface unit 81, a data collection unit 82, a reconstruction unit 83, a storage unit 84, a display unit 85, an input unit 86, and a control unit 87. The interface unit 81 is connected to the gradient magnetic field power supply 45, the transmission unit 48, and the reception unit 49. The interface unit 81 inputs and outputs signals exchanged between these connected units and the operator console unit 80.

  The data collection unit 82 collects digital signals output from the reception unit 49 via the interface unit 81. The data collection unit 82 stores the collected digital signal, that is, magnetic resonance signal data, in the storage unit 84. The reconstruction unit 83 performs post-processing, that is, reconstruction such as Fourier transform, on the magnetic resonance signal data stored in the storage unit 84, and obtains spectrum data or image data of a desired nuclear spin in the subject P. Ask.

  The storage unit 84 stores magnetic resonance signal data and spectrum data or image data for each subject P. The display unit 85 displays various information such as spectrum data or image data under the control of the control unit 87. A display device such as a liquid crystal display can be used as the display unit 85. The input unit 86 accepts various commands and information inputs from engineers. The control unit 87 controls these parts collectively to control the imaging operation of the MRI apparatus.

  FIG. 2 is a perspective view showing a state in which the iron shims 51 and 52 are fixed to one end of the static magnetic field generating unit 10. FIG. 3 is an enlarged perspective view showing the iron shims 51 and 52 fixed by overlapping two sheets. FIG. 4 is a top view of the iron shims 51 and 52. In the figure, the thickness of the iron shim is highlighted. The iron shim 51 and the iron shim 52 of the present embodiment have the same shape and a rectangular flat plate shape, and a through hole 51a through which the fastening bolt 53 passes is formed at the center. As for the size of the iron shim 51 and the iron shim 52, for example, the long side is 50 mm, the short side is 40 mm, and the thickness is 20 mm. The through hole 51a is a long hole extending in the longitudinal direction so that the attachment position can be finely adjusted. Furthermore, as shown in FIG. 4, a scale 51b for facilitating fine adjustment is engraved on the surfaces of the iron shims 51 and 52.

  The iron shims 51 and 52 are fixed by fastening bolts 53 in female screw holes (not shown) formed in the end surface 11 a and the outer peripheral surface 11 b of the vacuum vessel 11. Twenty-four female screw holes for fixing the iron shim 51 are formed at equal intervals along concentric circles at positions close to the inner diameter hole of the end surface 11a of the vacuum vessel 11. Further, 24 female screw holes for fixing the iron shim 52 are formed at equal intervals over the entire circumference at a position close to the end surface 11 a of the outer peripheral surface 11 b of the vacuum vessel 11. The iron shim 51 and the iron shim 52 are attached as many as necessary at necessary locations for the purpose of correcting the static magnetic field at both ends of the imaging region. The iron shims 51 and 52 and the female screw hole to which the iron shims 51 and 52 are attached are produced by strictly controlling the dimensions. Regarding the iron shims 51 and 52, the iron content of the material is also strictly controlled. And the static magnetic field of the axial direction both ends of an imaging region is correctly correct | amended by the attachment position and the number of attachments. The fastening bolt 53 is made of a non-magnetic material such as stainless steel so as not to affect the magnetic field because dimensional control is difficult. In this embodiment, adjustment is performed by changing the number of iron shims 51 and 52 having a thickness of 20 mm, but an iron shim having a different thickness is prepared in advance and an appropriate one is selected and attached. You may make adjustments. In addition, although the 2nd iron shims 51 and 52 of a present Example are intermittently provided in the circumferential direction, it is good also as a ring-shaped arrangement | positioning by bringing an adjacent iron shim closer. Finer adjustments can be made by using a ring-like arrangement. The second iron shims 51 and 52 themselves may be ring-shaped.

  FIG. 5 is a perspective view of the gradient coil structure 20. The gradient magnetic field coil structure 20 includes a substantially cylindrical main coil 21 and a shield coil 22, and 24 shim tray insertion guides 23 are formed between the two coils 21 and 22. The shim tray insertion guide 23 is a through-hole that is formed over the entire length in the longitudinal direction of the gradient magnetic field coil structure 20 by forming openings in both end faces of the gradient magnetic field coil structure 20. The shim tray insertion guide 23 is formed at equal intervals in the circumferential direction in parallel to each other in a region sandwiched between the two coils 21 and 22. The 24 shim trays 60 are each inserted into the shim tray insertion guide 23 and fixed to the central portion of the gradient coil structure 20. The shim tray 60 is made of a resin that is a non-magnetic and non-conductive material, has a substantially rod shape, and has a length excluding both ends of the gradient coil structure 20. That is, both ends of the shim tray 60 of this embodiment are shorter than the conventional shim tray by a predetermined length.

  FIG. 6 is a perspective view showing details of the shim tray 60. The shim tray 60 includes an elongated box-shaped tray body 61 and a lid 62. A plurality of pockets 61 a are formed in the tray body 61 continuously in the longitudinal direction. As many iron shims 71 as necessary are stored in the pockets 61a where necessary for the purpose of correcting the static magnetic field in the middle of the imaging region. As an example, the size of the iron shim 71 is such that the long side is 40 mm, the short side is 30 mm, the thickness is 3 mm, and a maximum of 10 sheets are stacked and stored. The iron shim 71 and the shim tray 60 are manufactured by strictly controlling the iron content and size, and the static magnetic field in the axial intermediate portion of the imaging region is accurately corrected by the position and number of iron shims 71 stored. The

  As described above, the shimming structure portion of this embodiment does not place iron shims at both ends in the axial direction of the imaging region in the bore, which conventionally required a large amount of iron shims. Iron shims to be corrected are arranged at both ends of the static magnetic field generation unit 10 outside the bore. An iron shim moved out of the bore will require a larger amount of iron shim because it is away from the magnetic field to be corrected. However, since the iron shim moved out of the bore is separated from the gradient coil structure 20, it is not affected by temperature. Further, since there is no iron shim in the place where the gradient of the static magnetic field at the end of the tray is large, the electromagnetic force acting on the gradient coil and the shim tray is reduced.

  As a result of simulation and experiment, when the patient bore axial length of this example is 1.495 m, the opening diameter is 65.5 cm, and the magnetic axial length of the static magnetic field generating unit 10 is 1.400 m, it is fixed to the end face 11a. The second iron shim 51 is arranged in a ring shape with a thickness of several centimeters to 10 centimeters within a range of 0.7 m to 0.75 m in the radial direction from the central axis of the static magnetic field generator 10, and is formed on the outer peripheral surface 11 b. The second iron shim 52 to be fixed is 0.99 m in the radial direction from the central axis of the static magnetic field generating unit 10, 0.5 m to 0.7 m and −0.7 m to −0. When the first iron shim 71 is arranged in the range of +/− 20 cm from the axial center of the static magnetic field generator 10 in the front-rear direction by arranging in a ring shape with a thickness of several cm to 10 cm within a range of 5 m. The influence of the superconducting coil 12 It is most efficiently found that can be corrected for the static magnetic field homogeneity without.

  As described above, the MRI apparatus 100 according to the present embodiment has a substantially cylindrical shape, and includes the static magnetic field generation unit 10 that generates a static magnetic field in the internal space, and the shimming structure unit that adjusts the uniformity of the static magnetic field. The shimming structure portion is disposed at the axially intermediate portion inside the bore of the static magnetic field generation unit 10 and the second iron shims 51 and 52 disposed at the axial end portion outside the bore of the static magnetic field generation unit 10. The first iron shim 71 is provided. Therefore, the amount of iron shim disposed in the bore of the static magnetic field generation unit 10 can be reduced, thereby further improving the uniformity of the static magnetic field during device operation. Moreover, damage to the iron shim support structure such as the shim tray 60 can be suppressed.

  The second iron shims 51 and 52 are fixed to the end surface 11 a and the outer peripheral surface 11 b of the vacuum vessel 11 of the static magnetic field generation unit 10. Therefore, it can be fixed relatively easily and firmly with a fastener such as the fastening bolt 53.

  Furthermore, since the shim tray 60 is arranged in the center of the bore of the static magnetic field generating unit 10 as in the conventional case to correct the static magnetic field in the middle part of the imaging region, fine adjustment of the static magnetic field is good as before. Can be done.

  The iron shims 51 and 52 (second iron shims) of the present embodiment are fixed by fastening bolts 53, but are not limited to such fasteners, and are fixed by, for example, an adhesive. Also good. Further, when the adjustment of the static magnetic field is finally completed, welding may be performed.

  In addition, the iron shims 51 and 52 constituting the second iron shim are intermittently arranged in the circumferential direction. However, when uniform magnetic field correction is desired in the circumferential direction, the iron shims 51 and 52 are continuously arranged in the circumferential direction. An iron shim to be used, that is, an annular iron shim may be arranged.

  Moreover, although the iron shim 71 (first iron shim) of the present embodiment is housed and arranged in the shim tray 60, the gradient magnetic field coil structure 20 is not limited by such a method but by a fastener or an adhesive. It may be directly fixed to. The magnetic field coil structure 20 may be fixed to the gradient coil structure 20 with a fastener or an adhesive while being housed in the shim tray 60.

  Furthermore, although the iron shim 71 of the present embodiment is stored in the shim tray 60 that is shorter than the conventional one, the same shim tray may be used so that the iron shim 71 is not stored at both ends of the shim tray. .

  In the present embodiment, the case where the gradient magnetic field coil structure 20 is not surrounded by a vacuum vessel has been described. However, as a silencer mechanism for suppressing noise generated in the gradient magnetic field coil structure 20, the gradient magnetic field coil structure 20 is provided. May be surrounded by a vacuum vessel. FIG. 9 is a cross-sectional view showing structures in the vicinity of the side ends of the static magnetic field generator 10 and the gradient coil structure 20 when the gradient coil structure 20 is surrounded by a vacuum vessel. FIG. 9 shows a cross section on a vertical plane passing through the center of the static magnetic field. 10 is a cross-sectional view taken along the line AA in FIG. Further, the static magnetic field generation unit 10 and the gradient magnetic field coil structure 20 show only the outer frame.

  A bore tube 31 is disposed inside the gradient coil structure 20. The bore tube 31 has a hollow cylindrical shape and prevents the subject P from directly contacting the gradient magnetic field coil structure 20.

  Further, in the vicinity of the side ends of the static magnetic field generating unit 10 and the gradient magnetic field coil structure 20, a vacuum vessel 32, fixtures 33 and 34, an O-ring 35, an O-ring retainer 36, a vibration isolator 37, a support member 38a, and a vibration isolator A material 39a and a support member 38b are disposed.

  The vacuum vessel 32 has a disk shape with a circular hole in the center. The diameter of the central hole is slightly larger than the outer diameter of the bore tube 31, and the bore tube 31 is passed through this hole. The vacuum vessel 32 is fixed to the fixed shaft 10 a provided in the static magnetic field generation unit 10 by fixtures 33 and 34 in the vicinity of the outer peripheral edge. The vacuum vessel 32 has an arcuate convex portion 32a. The convex portion 32 a is in contact with the static magnetic field generation unit 10.

  A taper 32b that extends outward is formed on the edge of the vacuum vessel 32 facing the hole. An O-ring 35 is disposed between the taper 32 b and the outer surface of the bore tube 31. The O-ring 35 is pressed by the O-ring press 36 so as to be in contact with the taper 32 b and the bore tube 31. Further, a vibration isolating material 37 is disposed on a part of the upper side of the bore tube 31 in the gap between the vacuum vessel 32 and the outer surface of the bore tube 31.

The bore tube 31 is supported by a support member 38a attached below contacting a convex portion 32c provided in the vacuum vessel 32 via a vibration isolator 39a.
The gradient magnetic field coil structure 20 is brought into contact with a support portion 10b provided in the static magnetic field generation unit 10 via a support member 38b and a vibration isolator 39b attached to the side ends thereof. The convex portion 32a is formed so as not to interfere with the fixed shaft 10a.

  Thus, with the structure as described above, a space S surrounded by the static magnetic field generating unit 10, the bore tube 31, and the vacuum vessel 32 is formed around the gradient magnetic field coil structure 20. By making this space S into a vacuum, it is possible to prevent noise generated in the gradient coil structure 20 from being transmitted to the surroundings.

  When the space S is evacuated, the vacuum container 32 is pressed against the space S by the atmospheric pressure, that is, in the axial direction. However, since the vacuum vessel 32 is in contact with the static magnetic field generation unit 10 by the convex portion 32a in addition to the fixed portion to the static magnetic field generation unit 10, the axial load from the vacuum vessel 32 is the vacuum vessel 32 itself. And the static magnetic field generation unit 10. For this reason, the bore tube 31 does not need to receive an axial load from the vacuum vessel 32, and the bore tube 31 and the vacuum vessel 32 do not need to be rigidly coupled. As a result, vibration transmission from the vacuum vessel 32 to the bore tube 31 can be reduced, and the thickness of the bore tube 31 can be reduced.

  Further, by adopting a flexible structure in which the gradient coil structure 20 and the static magnetic field generator 10 are in contact with each other via the vibration isolator 39b, the vibration of the gradient coil structure 20 is transmitted to the static magnetic field generator 10. It is possible to prevent the generation of noise due to the vibration of the gradient coil structure 20. Therefore, it is important to connect the gradient coil structure 20 and the static magnetic field generator 10 with a flexible structure from the point of the noise reduction mechanism, and a part of the iron shim 71 in the shim tray is brought out of the static magnetic field. Thus, the force received by the shim tray 60 from the iron shim 71 can be reduced, the positional change of the gradient coil structure 20 can be reduced, and the gradient magnetic field support structure can be made more flexible.

  The gantry 90 of the MRI apparatus 100 of this embodiment is for the MRI apparatus, but the technical idea of the present invention is also effective when applied to the static magnetic field generating means equipped in the NMR analyzer. . Furthermore, the present invention is not limited to both devices, and any device including a static magnetic field generation unit that generates a static magnetic field and a shimming structure that adjusts the uniformity of the static magnetic field with an iron shim is effective.

  The present invention is suitably applied to an MRI apparatus and an NMR analyzer that require generation of a highly uniform static magnetic field.

1 is a system configuration diagram of an MRI apparatus according to the present invention. It is a perspective view which shows a mode that the iron shim was fixed to the edge part of the one side of a static magnetic field generation | occurrence | production part. It is a perspective view which expands and shows the iron shim fixed by overlapping two sheets. It is an iron shim top view. It is a perspective view of a gradient magnetic field coil structure. It is a perspective view which shows the detail of a shim tray. It is a schematic sectional drawing which shows the mode of the static magnetic field which the static magnetic field generation | occurrence | production part with a long axial direction length generate | occur | produces. It is a schematic sectional drawing which shows the mode of the static magnetic field which the static magnetic field generation | occurrence | production part with a short axial direction length produces. It is a figure which shows the structure of the side end vicinity of a static magnetic field generation | occurrence | production part and gradient magnetic field coil structure in the case of providing a noise reduction mechanism. It is sectional drawing in the position of the AA line in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Static magnetic field generation | occurrence | production part 10a Fixed shaft 10b Support part 11 Vacuum vessel 11a End surface 11b Outer peripheral surface 12 Superconducting coil 20 Gradient magnetic field coil structure 21 Main coil (gradient magnetic field coil)
22 Shield Coil 23 Shim Tray Insertion Guide 30 High Frequency Coil 31 Bore Tube 32 Vacuum Container 32a, 32c Projection 32b Taper 33, 34 Fixing Tool 35 O Ring 36 O Ring Press 37, 39a, 39b Vibration Isolator 38a, 38b Support Member 40 Top Plate 45 Gradient magnetic field power supply 48 Transmitter 49 Receiver 51, 52 Iron shim (second iron shim)
51a Through hole 51b Scale 53 Fastening bolt 60 Shim tray 61 Tray body 61a Pocket 62 Lid 71 Iron shim (first iron shim)
80 operator console section 81 interface section 82 data collection section 83 reconstruction section 84 storage section 85 display section 86 input section 87 control section 90 platform 100 MRI apparatus P subject

Claims (14)

A static magnetic field generator for generating a static magnetic field;
A gradient coil for applying a gradient magnetic field to a subject arranged in the static magnetic field;
A high frequency coil for receiving a magnetic resonance signal from a subject to which the gradient magnetic field is applied ;
A first iron shim disposed inside a cylinder of the static magnetic field generation unit, and disposed at a central part in a central axis direction of the static magnetic field generation unit;
A second iron shim disposed outside the cylinder and disposed at an end portion in a central axis direction of the static magnetic field generation unit ;
The MRI apparatus is characterized in that an iron shim is not disposed at an end portion in the central axis direction of the static magnetic field generating portion inside the cylinder . The MRI apparatus according to claim 1, wherein the second iron shim is fixed to an outer peripheral surface of the static magnetic field generation unit. The MRI apparatus according to claim 1, wherein the second iron shim is fixed to an end face of the static magnetic field generation unit. The static magnetic field generator is composed of a superconducting magnet,
The second iron shims, MRI apparatus according to any one of claims 1 to 3, characterized in that it is fixed to the vacuum vessel of the superconducting magnet. The MRI apparatus according to claim 4, wherein the second iron shim is an iron piece arranged in a circumferential direction of the vacuum vessel. The MRI apparatus according to claim 4, wherein the second iron shim is an annular member along a cylindrical shape of the vacuum vessel. The MRI apparatus according to claim 4, wherein the second iron shim is fixed to the vacuum vessel with a fastening bolt made of a nonmagnetic material. The MRI apparatus according to claim 1, wherein the first iron shim is housed in a shim tray and disposed in a bore of the static magnetic field generation unit. The MRI apparatus according to any one of claims 1 to 3, wherein the first iron shim is attached to the gradient magnetic field coil disposed in a bore of the static magnetic field generation unit. The MRI apparatus according to claim 1, wherein the second iron shim is fixed in a range of 0.7 m to 0.75 m in a radial direction from a central axis of the static magnetic field generation unit. The MRI apparatus according to claim 1, wherein the first iron shim is fixed in a range of 20 cm in the front-rear direction from the axial center of the static magnetic field generation unit. The MRI apparatus according to claim 1, further comprising a structure that flexibly supports the gradient magnetic field coil as a silencer mechanism that suppresses noise generated by the gradient magnetic field coil. A static magnetic field generator for generating a static magnetic field;
A gradient magnetic field coil for applying a gradient magnetic field to the analysis sample disposed in the static magnetic field;
A high-frequency coil for receiving a magnetic resonance signal from the analysis sample to which the gradient magnetic field is applied ;
A first iron shim disposed inside a cylinder of the static magnetic field generation unit, and disposed at a central part in a central axis direction of the static magnetic field generation unit;
A second iron shim disposed outside the cylinder and disposed at an end portion in a central axis direction of the static magnetic field generation unit ;
An NMR analyzer characterized in that an iron shim is not disposed at an end portion in the central axis direction of the static magnetic field generating portion inside the cylinder . A superconducting coil that is immersed in a cooling liquid and stored in a cylindrical container and generates a static magnetic field;
A first iron shim disposed inside the cylinder and disposed in a central portion in a central axis direction of the superconducting coil ;
A second iron shim disposed outside the cylinder and disposed at an end in the central axis direction of the superconducting coil ;
A static magnetic field generating unit , wherein an iron shim is not disposed at an end of the superconducting coil in a central axis direction inside the cylinder .

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