JP2005261806A - Magnetic resonance imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shimming structure permitting facilitating the shimming work, achieving a high uniformity coefficient of magnetic fields, and improving the efficiency in generation of magnetic fields of a gradient magnetic field coil and RF coil. <P>SOLUTION: A high-frequency magnetic field generating means consists of a base plate and a coil mounting plate. A plurality of shim attaching structures are disposed on the base plate, and an electric circuit for generating a high-frequency magnetic field is mounted on the coil mounting plate. The base plate and the coil mounting plate are easily attached to/detached from each other, and a shim material can be attached to/detached from the shim attaching structures with the coil mounting plate being detached. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

 The present invention relates to a magnetic resonance imaging (hereinafter abbreviated as MRI) apparatus, and in particular, a region in which a shim member for increasing the uniformity of a static magnetic field is disposed within a high-frequency coil (hereinafter abbreviated as RF coil) structure. It is related with the technique which makes it easy to make the operation | work which makes a static magnetic field uniform, and can improve the magnetic field generation efficiency of a gradient magnetic field coil and RF coil.

  In general, an MRI apparatus includes a static magnetic field generating means for generating a uniform static magnetic field in a measurement space, a gradient magnetic field coil for generating a linear gradient magnetic field superimposed on the static magnetic field, and an RF coil for transmitting and receiving a high-frequency electromagnetic field. ing. At the time of imaging, a linear gradient magnetic field is superimposed on the subject placed in a uniform static magnetic field in the X, Y, and Z axis directions according to the desired pulse sequence, and the subject's nuclear spin is magnetized with a high frequency magnetic field pulse of Larmor frequency. Excited. With this excitation, a nuclear magnetic resonance (hereinafter abbreviated as NMR) signal is detected, and for example, a two-dimensional tomographic image of the subject is reconstructed.

  In such an MRI apparatus, the spatial uniformity of the static magnetic field is an important characteristic that affects the image quality. For example, a very high homogeneity of about 1 ppm is required in a spherical space with a diameter of 40 cm. To achieve this, so-called shimming is performed in which the spatial homogeneity of the static magnetic field is improved by measuring the magnetic field distribution in a predetermined space and adjusting the position of shim members such as iron pieces and magnet pieces. Are known (for example, [Patent Document 3] and [Patent Document 5]).

 By the way, there are two types of magnet devices that are currently used in MRI apparatuses in terms of form. One is a horizontal magnetic field device, and the other is a counter device (so-called open device). In the case of a horizontal magnetic field device, a region for disposing a shim member is provided between a main coil and a shield coil that constitute a gradient magnetic field coil, and the shim member is generally disposed here (for example, [ Patent Document 1]).

On the other hand, in the case of a counter-type device, techniques as shown in the following patent documents are known.
In [Patent Document 2], a high-frequency shield (hereinafter abbreviated as RF shield), a shim plate, and an RF coil are laminated in this order, and the RF shield and the RF coil are integrally molded, whereby the distance between the RF coil and the RF shield is increased. I try to keep it constant.
[Patent Document 3] has a structure in which a shim member is supported by an RF coil support.
[Patent Document 4] has a structure in which a shim member is disposed between a gradient magnetic field coil and an RF coil.
[Patent Document 5] has a structure in which a shim member is disposed between a gradient coil and a magnet.

JP-A-5-329129 JP 2002-336214 A JP 2000-333932 A Japanese Patent Laid-Open No. 9-238913 JP 2001-68327 A

However, the above-described known technique in the opposed device has the following problems.
In the configuration disclosed in [Patent Document 2], the shim plate is taken in and out from the side surface of the magnet, and access to the shim plate from the side is essential. Therefore, it is difficult to adopt the configuration described in [Patent Document 2] in a structure in which a recess is provided near the center of the magnet on the measurement space side and a shim member is disposed in the recess. Furthermore, some clearance is required to allow the shim plate to be inserted and removed from the side. As a result, the structural strength of the device is reduced, and the entire device is likely to be deformed such as torsion. There are still problems to be solved.

   In the configuration disclosed in [Patent Document 3], since the shim member is arranged on the same surface as the surface on which the RF coil is arranged, the shim is formed only in a portion where there is no electric circuit of the RF coil. The member cannot be placed. Therefore, when adjusting the static magnetic field uniformity, a great restriction is imposed on the arrangement of the shim members, and as a result, it may be necessary to further devise to achieve high static magnetic field uniformity.

   The configuration of [Patent Document 4] is devised based on a cylindrical magnet, a gradient coil, and an RF coil in a horizontal magnetic field device. This facilitates access to the shim member from the axial direction of the cylinder. However, in a counter-type device in which a recess is provided near the center of the measurement space side of the magnet and a shim member is disposed in the recess, it is difficult to access the shim member from the lateral direction. Similarly to [Patent Document 2], the configuration of [Patent Document 4] cannot be applied to the mold apparatus.

   In the configuration of [Patent Document 5], when the gradient magnetic field coil is attached, the uniformity may change due to the weight of the gradient magnetic field coil or the influence of the magnetic substance slightly contained in the gradient magnetic field coil or fixture. Yes, no response to this issue is disclosed.

  [Patent Document 4] and [Patent Document 5] require a space for disposing a shim member, so that a space for disposing an RF coil unit and a gradient coil unit becomes narrow. For this reason, it is difficult to increase the thickness of the RF coil unit or gradient magnetic field coil unit. Generally, an RF coil is placed on the measurement space side of the RF coil unit, and an RF shield that shields the high-frequency magnetic field is placed on the back side. The higher the distance between the RF coil and the RF shield, the higher the high-frequency magnetic field generation efficiency. . In addition, a main coil that generates a gradient magnetic field is arranged on the measurement space side of the gradient magnetic field coil unit, and a shield coil that shields the gradient magnetic field is arranged on the back side, and the gradient increases as the distance between the main coil and the shield coil increases. Magnetic field generation efficiency increases. Accordingly, the configurations of [Patent Document 4] and [Patent Document 5] leave room for improvement in terms of high-frequency magnetic field and gradient magnetic field generation efficiency.

Accordingly, the present invention has been made to solve the above-mentioned problems, and a first object of the present invention is to facilitate a shimming operation and to achieve high static magnetic field uniformity.
The second object of the present invention is to further improve the high-frequency magnetic field generation efficiency of the RF coil.
The third object of the present invention is to further improve the magnetic field generation efficiency of the gradient coil.

In order to solve the above problems, the present invention is configured as follows. That is, (1) having a static magnetic field generating means having at least one static magnetic field generator provided with a recess on the measurement space side, and a high-frequency magnetic field generating means and a gradient magnetic field generating means having at least a part thereof accommodated in the recess. In MRI equipment
Each of the high-frequency magnetic field generating means has a first flat plate on which a high-frequency electric circuit for generating a high-frequency magnetic field is arranged, and a second flat plate on which a static magnetic field correcting means is arranged, and the first flat plate is The first flat plate is detachably attached to the second flat plate. The first flat plate is disposed closer to the measurement space than the second flat plate. (Claim 1).

Particularly, the static magnetic field correcting means is a shim member, and the second flat plate has a structure in which at least one shim member can be detachably attached (Claim 2).
This makes it possible to easily repeat the operation of removing the first flat plate and adjusting the static magnetic field correction means on the second flat plate. In particular, when the static magnetic field correction means is a shim member, a so-called shimming operation that improves the static magnetic field uniformity by adjusting the arrangement position and the arrangement amount of the shim member by adopting a structure that can be easily attached and detached. It becomes easy to achieve high static magnetic field uniformity by repeating the shimming operation. As a result, the first object can be achieved.

(2) In a preferred embodiment of the present invention, an electric conductor is further disposed between the first flat plate and the second flat plate so as to cover the shim member (claim 3). In particular, an electric conductor is disposed so as to cover only the shim member.
This reduces electromagnetic interference between the shim member and the RF coil high-frequency electric circuit, so that it is possible to prevent the adjustment of the high-frequency electric circuit due to the arrangement of the shim member, and to adjust the high-frequency electric circuit. It is possible to carry out the measurement with or without the shim member. In particular, by arranging the electric conductor so as to cover only the shim member as much as possible, the RF shield can be prevented from substantially approaching the RF coil. As a result, the second object can be further achieved.

(3) In a preferred embodiment of the present invention, the second flat plate is further detachably divided into two, and a shim member is arranged on the upper portion.
As a result, the upper part (that is, the measurement space side part) is created as a shim plate and removed, so that the shim member can be attached and detached outside the static magnetic field, so that the shimming operation is further facilitated.

  In addition, because of the above (1) to (3), it is not necessary to provide a separate layer for disposing the shim member in the recess, so that the distance between the RF coil and the RF shield in the RF coil unit and the main component in the gradient magnetic field coil unit are eliminated. The distance between the coil and the shield coil can be increased, and the second and third objects can be achieved indirectly.

  As described above, according to the present invention, a magnet for an open type MRI apparatus that has a recess on the magnet surface facing the measurement space and accommodates at least a part of the RF coil in the recess can be easily and statically. Magnetic field uniformity can be adjusted. In addition, the magnetic field generation efficiency of the RF coil and the gradient magnetic field coil can be increased.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings for explaining the embodiments of the invention, those having the same function are given the same reference numerals, and their repeated explanation is omitted.
First, an outline of an MRI apparatus to which the present invention is applied will be described with reference to FIG. FIG. 8 is an overall perspective view of an embodiment of an MRI apparatus of a vertical magnetic field type (also called an opposed type or an open type) to which the present invention is applied.

  This MRI apparatus uses a NMR phenomenon to obtain a tomographic image of a subject. As shown in FIG. 8, a gantry 51 that houses various apparatuses for inducing a NMR phenomenon in a subject and receiving NMR signals. A table 52 on which the subject is placed, a power source for driving various devices in the gantry 51, a housing 53 that houses various control devices to be controlled, and a received NMR signal to process a tomographic image of the subject. The processing unit 54 is connected to each other by a power source / signal line 55. The gantry 51 and the table 52 are arranged in a shield room that shields high-frequency electromagnetic waves and static magnetic fields (not shown), and the casing 53 and the processing device 54 are arranged outside the shield room.

  FIG. 9 shows a block configuration diagram in which the configuration of the MRI apparatus of FIG. 8 is disassembled for each more detailed function. As shown in FIG. 9, the MRI apparatus includes a static magnetic field generation system 2, a gradient magnetic field generation system 3, a transmission system 5, a reception system 6, a signal processing system 7, a sequencer 4, and a central processing unit (CPU). 8 and configured.

  The static magnetic field generation system 2 generates a uniform static magnetic field in the space around the subject 1 in the direction of the body axis (horizontal magnetic field method) or in the direction orthogonal to the body axis (vertical magnetic field method). A static magnetic field generator (for example, a container containing a static magnetic field generation source therein) having a normal magnetic field generation source or a superconductivity type static magnetic field generation source is disposed around the space. Further, in order to correct the non-uniformity of the static magnetic field and improve the uniformity, a shim coil and a shim member (not shown) are arranged. The static magnetic field generation system 2 is accommodated in the gantry 51.

  The gradient magnetic field generating system 3 includes a gradient magnetic field coil 9 wound in three axial directions of X, Y, and Z, and a gradient magnetic field power source 10 for driving each gradient magnetic field coil 9. By driving the gradient magnetic field power supply 10 of each coil in accordance with the above command, gradient magnetic fields GZ, GY, and GX in the three-axis directions of X, Y, and Z are applied to the subject 1. More specifically, a slice direction gradient magnetic field pulse (GS) is applied in one of X, Y, and Z to set the slice plane for the subject 1, and the phase encode direction gradient magnetic field is applied to the remaining two directions. A pulse (GP) and a frequency encoding direction gradient magnetic field pulse (GF) are applied, and position information in each direction is encoded in the echo signal. The gradient magnetic field coil 9 is accommodated in the gantry 51, and the gradient magnetic field power source 10 is accommodated in the casing 53.

  The sequencer 4 is a control means that repeatedly applies a high-frequency magnetic field pulse and a gradient magnetic field pulse in a predetermined pulse sequence. The sequencer 4 operates under the control of the CPU 8, and sends various commands necessary for collecting tomographic image data of the subject 1. 5. Send to gradient magnetic field generation system 3 and reception system 6. The sequencer 4 is accommodated in the housing 53.

  The transmission system 5 irradiates a high frequency magnetic field pulse 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, a high frequency amplifier 13, and a transmission side RF coil 14a. The high-frequency 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 the amplitude-modulated high-frequency pulse is amplified by the high-frequency amplifier 13 and then placed close to the subject 1. By supplying to the RF coil 14a, the subject 1 is irradiated with the high frequency magnetic field pulse. Generally, the RF coil 14a is accommodated in the gantry 51, and the others are accommodated in the casing 53.

In the MRI apparatus to which the present invention is applied, the RF coil 14a is configured as a part of an RF coil unit described below.
The receiving system 6 detects an echo signal (NMR signal) emitted by nuclear magnetic resonance of nuclear spins constituting the biological tissue of the subject 1, and receives the RF coil 14b on the receiving side, the signal amplifier 15, and quadrature detection. And an A / D converter 17. The NMR signal of the response of the subject 1 induced by the electromagnetic wave irradiated from the RF coil 14a on the transmission side is detected by the RF coil 14b arranged close to the subject 1 and amplified by the signal amplifier 15, The signal is divided into two orthogonal signals by the quadrature phase detector 16 at the timing according to the command from the sequencer 4, and each signal is converted into a digital quantity by the A / D converter 17 and sent to the signal processing system 7. Generally, the device group constituting the receiving system 6 is accommodated in a gantry 51.

  The signal processing system 7 includes an external storage device such as an optical disk 19 and a magnetic disk 18 and a display 20 made up of a CRT or the like. When data from the receiving system 6 is input to the CPU 8, the CPU 8 performs signal processing, image processing, and image processing. Processing such as reconstruction is executed, and the resulting tomographic image of the subject 1 is displayed on the display 20 and recorded on the magnetic disk 18 or the like of the external storage device. The signal processing system 7 is accommodated in the processing device 54.

  In FIG. 7, the transmission-side RF coil 14a and the gradient magnetic field coil 9 are placed opposite to the subject 1 in the static magnetic field space of the static magnetic field generation system 2 into which the subject 1 is inserted. The RF coil 14b on the receiving side is installed so as to face or surround the subject 1.

  Currently, 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 in clinical practice. By imaging information on the spatial distribution of proton density and the spatial distribution of relaxation time in the excited state, the form or function of the human head, abdomen, limbs, etc. is imaged two-dimensionally or three-dimensionally.

The present invention will be described below. The present invention is mainly characterized in that an RF coil unit is provided with a static magnetic field correction means in an MRI apparatus having opposed magnets in which a pair of magnets each having a recess is disposed in the vicinity of the central portion on the measurement space side. That is,
The RF coil unit is composed of a coil mounting plate (first flat plate) and a base plate (second flat plate), which is placed in the concave portion of the magnet so that the coil mounting plate can be easily detached from the base plate. And Then, a shim member disposition area is provided in the base plate, and the shim member is detachably disposed (first embodiment). As a result, the operation of removing the coil mounting plate and adjusting the arrangement of the shim members can be easily repeated. As a result, the shimming operation is facilitated, so that high static magnetic field uniformity can be achieved. become.

  When the present invention is applied to one embodiment of the MRI apparatus shown in FIG. 9, the RF coil 14a is configured by arranging a high-frequency electric circuit for generating a high-frequency magnetic field on the surface of the coil mounting plate. Further, a shim member for improving the static magnetic field uniformity is disposed in a base plate to which the coil mounting plate is detachably attached. Then, a coil mounting plate is attached to the base plate to constitute an RF coil unit.

  In the present invention, an electric conductor is disposed between the coil mounting plate and the base plate so as to cover the shim member. Preferably, the electric conductor is disposed so as to cover only the shim member (second embodiment). As a result, electromagnetic interference between the shim member and the high-frequency electric circuit is reduced, so that the high-frequency electric circuit can be adjusted constantly regardless of the presence or absence of the shim member. As a result, the high frequency magnetic field generation efficiency of the RF coil can be improved.

 Furthermore, the base plate is divided into two so that the measurement space side portion can be attached to and detached from the other portion, and the measurement space side portion is a shim plate provided with mounting holes for shim members (third embodiment) ). Accordingly, by removing the shim plate, the shim member can be attached and detached outside the static magnetic field, so that the shimming operation is further facilitated.

  In addition, according to the present invention described above, there is no need to newly provide a layer for disposing a shim member in the recess, in addition to the RF coil unit and the gradient magnetic field coil unit. The layer of the gradient coil unit can be thickened. As a result, since the distance between the RF coil and the RF shield in the RF coil unit and the distance between the main coil and the shield coil in the gradient magnetic field coil unit can be separated, the generation efficiency of the high-frequency magnetic field and the gradient magnetic field can be increased. .

  Hereinafter, a static magnetic field generator having the configuration described with reference to FIGS. 8 and 9 and using a superconducting magnet as a static magnetic field generation source is disposed so as to face each other, and a recess is formed on the measurement space side of each static magnetic field generator. An embodiment of the present invention will be described based on a counter-type MRI apparatus having a static magnetic field generation system including However, the present invention is not limited to the vertically opposed type, and can be widely applied to an MRI apparatus having a static magnetic field generator in which a recess is provided on the measurement space side.

  FIG. 1 shows an example of a vertically opposed MRI apparatus using a superconducting magnet as a static magnetic field generation source. The MRI apparatus shown in FIG. 1 generates a uniform static magnetic field in the central portion (measurement space) 107 of the gantry 51 by means of a static magnetic field generation source (superconducting coil) 102 arranged opposite to the top and bottom. In order to exhibit the superconducting characteristics, the superconducting coil 102 is disposed in a cryogenic container (not shown) that maintains an extremely low temperature. This cryogenic container is enclosed in a vacuum chamber (accommodating means; constituting a static magnetic field generator including this vacuum chamber and its internal configuration) 101 for insulating heat from the outside by heat insulation. In order to make it easy to see, illustrations of commonly used components such as a refrigerator and a helium tank are omitted in this figure. In the case of a superconducting magnet using conduction cooling, a helium bath is not necessary.

  In addition, a concave portion 106 is provided in the central portion of the upper and lower vacuum chambers 101, and an RF coil unit 104, a gradient magnetic field coil unit 105, and the like are disposed in a vertically opposed manner.

  FIG. 2 shows the arrangement of each component in the lower recess 106 in the MRI apparatus of FIG. In the upper recess, the same components are arranged symmetrically with the measurement space 107 in between. In each component, an RF coil unit 104, a gradient magnetic field coil (corresponding to the gradient magnetic field coil 9 in FIG. 7), and a shim region 204 are arranged in this order from the measurement space 107 side. Here, shim coils and shim members are fixed to the vacuum chamber 101 in the shim region 204 and correct most of the static magnetic field inhomogeneity. On the other hand, the shim member disposed in the RF coil unit 104 of the present invention performs fine adjustment of static magnetic field nonuniformity correction. The uniformity of the static magnetic field is improved by the shim region 204 and the shim member in the RF coil unit 104.

  First, the first embodiment of the present invention will be described in detail. In this embodiment, the RF coil unit is composed of a coil mounting plate and a base plate, and the coil mounting plate is arranged closer to the measurement space than the base plate. At this time, the coil mounting plate is attached to the base plate so as to be easily removable. A high-frequency electric circuit for generating a high-frequency magnetic field is arranged on the surface of the coil mounting board on the measurement space side, and a shim member arrangement area for improving the static magnetic field uniformity is provided in the base board. The shim member is detachably disposed there.

  Examples of this embodiment are shown in FIGS. 3 and 4 are sectional views of the RF coil unit, and FIG. 5 is an overall perspective view of the RF coil unit in an exploded state.

  As shown in FIG. 3, the RF coil unit of the present embodiment is roughly composed of a coil mounting plate 104-1 (corresponding to the RF coil 14a in FIG. 9) and a base plate 104-2. Further, a high-frequency electric circuit for generating a high-frequency magnetic field is disposed on the measurement space 107 side of the coil mounting plate 104-1. This high-frequency electric circuit is the substance of the transmission coil, and is mainly configured by adding an electric element (capacitor, inductor, diode, etc.) 301 to a conductor 302 that becomes a high-frequency current path. As the conductor 302, for example, a thin copper plate of about 1 mm is used. The electric element is adjusted so that the transmission coil has a high irradiation sensitivity (Q value) at a proton resonance frequency (for example, about 21 MHz at 0.5 T) determined by the static magnetic field strength.

On the other hand, at least one mounting hole 306 is formed in the base plate 104-2 for mounting the shim member 305. With the base plate 104-2 fixed at a predetermined position of the recess 106, the shim member 305 is attached to and removed from the mounting hole 306, and the arrangement positions in the directions parallel and perpendicular to the static magnetic field direction and the respective arrangements are arranged. The uniformity of the static magnetic field is adjusted by adjusting the amount. When the adjustment of the static magnetic field uniformity is completed, the RF coil unit can be completed by generating the high-frequency magnetic field by mounting the coil mounting plate 104-1 on the base plate 104-2.
In order to facilitate attachment / detachment work of the coil mounting plate 104-1, for example, a screw hole is provided in the base plate 104-2, and the coil mounting plate 104-1 can be attached to the base plate 104-2 with a bolt. .

As an example of how to attach the shim member 305 to the base plate 104-2, the shim member 305 has a screw shape, and the mounting hole 306 is also screwed so that the shim member 305 can be attached to and detached from the mounting hole 306. It becomes easy. Further, by preventing the mounting hole 306 for mounting the shim member 305 from penetrating the base plate 104-2, the bending rigidity of the base plate 104-2 can be kept high. As a result, the deflection of the RF coil unit is reduced, and a stable high-frequency magnetic field can be generated.
Alternatively, as shown in FIG. 4, it is possible to provide the mounting holes 306 of the shim member 305 so as to penetrate the base plate 104-2. In this case, the process of manufacturing the mounting hole 306 is facilitated.

  In order not to reduce the generation efficiency of the high-frequency magnetic field, it is preferable to use a member having a small dielectric loss for the coil mounting plate 104-1 and the base plate 104-2, for example, a member such as glass epoxy or polytetrafluoroethylene. Is preferably used. Further, the thickness of the coil mounting plate 104-1 is preferably 3 to 20 mm, for example, and the thickness of the base plate is preferably in the range of 10 to 40 mm, for example. The thickness of the entire RF coil unit is preferably about 20 to 50 mm, for example.

 Furthermore, in order to uniformly irradiate the measurement space with the high-frequency magnetic field, the distance between the high-frequency electric circuit and the RF shield needs to be made constant with high accuracy. Since it is easy to process the thicknesses of the coil mounting plate 104-1 and the base plate 104-2 with high accuracy, the RF shield plate 203 is fixed to the bottom surface of the base plate 104-2 as shown in FIG. Accordingly, the distance between the high-frequency electric circuit (301 and 302) and the RF shield plate 203 can be made constant with high accuracy. As a result, the measurement space can be uniformly irradiated with a high-frequency magnetic field. Since the RF shield plate 203 shields the high-frequency magnetic field, interference with the gradient magnetic field coil disposed thereunder can be prevented, so that the high-frequency magnetic field can be stably generated.

  Next, the second embodiment of the present invention will be described in detail. In this embodiment, in addition to the first embodiment, an electric conductor is arranged so as to cover the shim member between the coil mounting plate and the base plate, that is, on the high frequency electric circuit side of the coil mounting plate. The electric conductor is arranged so that the shim member is hidden behind the electric conductor when viewed from above, and the influence of the shim member on the high-frequency electric circuit is suppressed. This is to prevent electromagnetic interference between the shim member and the high-frequency electric circuit and the adjustment of the high-frequency electric circuit due to the arrangement of the shim member. That is, by arranging an electrical conductor between the coil mounting board and the base board in advance, regardless of the presence or absence of shim members in the base board, a high-frequency electrical circuit has a certain environment in terms of high frequency. Therefore, the high-frequency electric circuit can be adjusted constantly.

  Further, it is preferable that the electric conductors are arranged so as to cover the shim member and to reduce the area of the electric conductor as much as possible, that is, to cover only the shim member as much as possible. From the viewpoint of the generation efficiency of the high-frequency magnetic field, it is preferable to keep the distance between the RF coil and the RF shield as much as possible. However, when an electric conductor is arranged on the entire surface of the base plate, the RF shield is substantially This is to avoid this because the generation result of the high-frequency magnetic field is reduced.

  FIG. 6 shows an arrangement example of the electric conductor 303 which is an example of this embodiment. FIG. 6 shows an example of the arrangement of the electric conductor 303 when the shim member 305 is arranged in the mounting holes 306 arranged as shown in FIG. The arrangement of the electric conductors shown in FIG. 6 is an arrangement view of the electric conductors when the back surface of the coil mounting board is viewed from the direction A shown in FIG. An electric conductor 303 is disposed so as to cover the mounting portion of the shim member 305. In the example of FIG. 5 (a), the electric conductor 303 is arranged on the line of the mounting hole 306, but the influence on the high-frequency magnetic field is minimized by arranging the electric conductor 303 finely for each mounting hole 306. It can also be limited. An example of this is shown in FIG.

  Also, as shown in FIG. 4, it is preferable to electrically insulate the shim member 305 and the electric conductor 303 by covering at least the surface on the shim member side of the electric conductor 303 with an insulating material 304. If the shim member 305 is in electrical contact with the electric conductor 303, electrical contact is intermittently generated between the shim member 305 and the electric conductor 303 due to vibration of the gradient coil 105, etc. This is because there is a possibility that electrical noise is generated.

  Next, the third embodiment of the present invention will be described in detail. In this embodiment, in the first or second embodiment, the base plate is further divided into two parts, and the upper part (that is, the measurement space side part) is a shim plate provided with a mounting hole for the shim member. . The upper part is detachably attached to the lower part.

  An example of this embodiment is shown in FIG. In FIG. 7, the base plate 104-2 is divided into an upper part 104-2-1 and a lower part 104-2-2, and shim plate mounting holes 306 are provided in the upper part 104-2-1 to form a shim plate. The shim member 305 is disposed in the mounting hole 306. The upper and lower parts are fixed with screws, for example. The rest is the same as FIG.

The above describes the embodiment in which the present invention is applied to an opposed MRI apparatus in which a pair of static magnetic field generators using a superconducting magnet as a static magnetic field generation source are arranged facing each other up and down. Are not limited to the above-described embodiments, and various modifications can be made. For example, the same structure can be applied to an MRI apparatus using a permanent magnet or a normal conducting magnet. Further, the present invention can be similarly applied to an MRI apparatus having a flat magnet structure having no recess on the measurement space side.
Further, the present invention is also applied to an MRI apparatus in which a static magnetic field generator is arranged only on either the left or right side or the left and right side and generates a static magnetic field in a direction perpendicular to the body axis of the subject arranged in the measurement space. can do.

  Alternatively, the present invention can be applied not only to a pair of static magnetic field generators but also to an MRI apparatus having a single static magnetic field generator in which a recess is provided on the measurement space side.

A cross-sectional view of a vertically opposed MRI apparatus using a superconducting magnet as a static magnetic field generation source. FIG. 2 is a cross-sectional view of a lower concave portion 106 in the MRI apparatus of FIG. Sectional drawing of the RF coil unit in which the attachment hole of a shim member does not penetrate a base board. Sectional drawing of RF coil unit in which the mounting hole of a shim member penetrates a base board. The figure which shows the example of arrangement | positioning of a shim member. The figure which shows the example which has arrange | positioned the electrical conductor in the line shape by which a shim member is arrange | positioned. The figure which shows the example which has arrange | positioned the electrical conductor so that a shim member may be covered. 1 is an overall perspective view of an embodiment of a vertical magnetic field type (open type) MRI apparatus according to the present invention. FIG. FIG. 9 is a diagram showing a block configuration obtained by disassembling the configuration of the MRI apparatus of FIG. 8 for each more detailed function.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 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 source, 11 High frequency transmitter, 12 Modulator, 13 High frequency amplifier, 14 a High frequency coil (transmitting coil), 14 b High frequency coil (receiving coil), 15 Signal amplifier, 16 ... Quadrature detector, 17 ... A / D converter, 18 ... Magnetic disk, 19 ... Optical disk, 20 ... Display, 51 ... Gantry, 52 ... Table, 53 ... Housing, 54 ... Processing device

Claims (3)

A magnetic resonance imaging apparatus having a static magnetic field generating means having at least one static magnetic field generator provided with a recess on the measurement space side, a high-frequency magnetic field generating means and a gradient magnetic field generating means having at least a part thereof accommodated in the recess. In
Each of the high-frequency magnetic field generating means has a first flat plate on which a high-frequency electric circuit for generating a high-frequency magnetic field is arranged, and a second flat plate on which a static magnetic field correcting means is arranged,
The first flat plate is disposed closer to the measurement space than the second flat plate;
The magnetic resonance imaging apparatus according to claim 1, wherein the first flat plate is detachably attached to the second flat plate. 2. The magnetic resonance imaging apparatus according to claim 1, wherein the static magnetic field correction means is a shim member, and the second flat plate has a structure in which at least one shim member can be detachably attached. Magnetic resonance imaging device. 3. The magnetic resonance imaging apparatus according to claim 2, wherein an electric conductor is disposed between the first flat plate and the second flat plate so as to cover the shim member.

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