JP4789254B2 - Magnetic resonance imaging apparatus having a horizontal static magnetic field type elliptic cylindrical gantry and an active shield type gradient magnetic field coil apparatus adapted thereto - Google Patents

Description

  The present invention relates to an improvement in a magnetic resonance imaging (hereinafter referred to as MRI) apparatus having an elliptic cylindrical gantry including a horizontal static magnetic field type egg-shaped, racetrack-shaped, and rectangular shape and an active shield type gradient magnetic field coil apparatus adapted thereto.

  An MRI apparatus having a horizontal static magnetic field type elliptic cylindrical gantry is disclosed in, for example, Patent Documents 1, 2, 3, 4 and the like.

  In these MRI apparatuses, a conventional cylindrical gantry is crushed in the vertical direction, that is, in the Y-axis direction so as to have an elliptical cylinder shape, whereby the opposing gradient coil pairs in the Y-axis direction in the gradient coil apparatus are moved in the gantry. The Y-axis gradient magnetic field strength is increased by the Y-axis gradient magnetic field coil and placed in close proximity to the subject to be inserted and placed in the measurement space to improve the resolution of the MRI image, or the Y-axis gradient magnetic field coil Thus, the switching speed of the pulse current applied to the Y-axis gradient magnetic field coil is increased to facilitate the application of the high-speed pass sequence to the imaging method.

  In an active shield type gradient magnetic field coil in a horizontal static magnetic field type MRI apparatus, each X, Y, Z direction gradient magnetic field coil is inserted into a uniform static magnetic field measurement space in the Z direction and arranged on the side close to the subject to be placed. And a main gradient magnetic field coil that applies a gradient magnetic field in each direction of the measurement space, and a shield gradient magnetic field coil that shields the magnetic field generated by each main gradient magnetic field coil and leaking to the opposite side of the measurement space It is.

  Patent Documents 3 and 4 refer to active shield type gradient magnetic field coils, but the former only discloses individual design methods for X, Y, and Z direction gradient magnetic field coils. No mention is made of the overall arrangement of the directional gradient coil as a whole. In the latter, the first and second gradient coils that carry the transverse gradient magnetic field are respectively composed of the first and second main gradient coils and the first and second shield gradient coils. The two main gradient magnetic field coils are arranged on the elliptic cylindrical surface close to the subject, and the first and second shield gradient magnetic field coils are arranged on the cylindrical surface outside the elliptic cylindrical surface without overlapping each other. Disclosure.

  Patent Document 5 discloses an active shield type gradient coil device of an MRI apparatus having a horizontal static magnetic field type cylindrical gantry, and here, the main gradient coil and shield of each of the X, Y and Z direction gradient coils. The gradient coil is an X-direction main gradient coil, a Z-direction main gradient coil, a Y-direction gradient gradient coil, an X-direction shield gradient coil, and a Z-direction shield gradient coil from the inner side to the outer side closest to the measurement space. The Y direction shield gradient coil, the main gradient coil and the shield gradient coil are arranged in the same order with respect to the direction.

  In such a gradient magnetic field coil having a circular cross section, the X- and Y-direction main and shield gradient magnetic field coils having the same shape can be used. Therefore, at least the distance between the X-direction main and shield gradient magnetic field coils and the Y-direction main and shield It was necessary to have the same spacing between the gradient coils. If this is different, the magnetic field balance by the gradient coil in both directions will be lost, and the leakage magnetic field to the outside of the gradient coil will increase, and as a result, it will be induced by an electric conductor such as a superconducting magnet cryostat around the gradient coil. Eddy current increases, which acts as a cause of degrading the image quality of the MRI image.

On the other hand, in many of these conventional devices, the inner diameter of the gantry cover surrounding the measurement space, that is, the inner diameter in the X direction is about 60 cm. With this inner diameter, there is almost no space to move left and right in an adult subject. It is narrow. For this reason, the subject has a feeling of blockage, and it is virtually impossible for the examiner to access the internal subject from outside the gantry.
Japanese Patent Laid-Open No. 2-1238 JP-A-5-269100 JP 2001-327478 A JP 2001-112737 A Japanese Patent Laid-Open No. 11-239569

  An object of the present invention is to widen the width of the inner diameter of the gantry cover that surrounds the measurement space, that is, the inner diameter in the X direction to improve the openness and accessibility, and to increase the width of the inner diameter of the gantry cover, that is, the X direction. Horizontal static magnetic field type elliptic cylindrical gantry in which reduction of the magnetic field generation efficiency of the X direction gradient magnetic field coil composed of the X direction main and shield gradient magnetic field coils arranged so as to straddle the X direction is suppressed, and the same It is an object to provide an MRI apparatus having an active shield type gradient magnetic field coil apparatus adapted to the above.

  The present invention is an MRI apparatus having an elliptic cylindrical gantry of a horizontal static magnetic field system and an active shield type gradient magnetic field coil apparatus adapted thereto, and is arranged across the wide left-right direction, that is, the X direction of the elliptic cylindrical gantry. The main gradient coil of the X-direction gradient magnetic field coil is disposed closest to the inner wall of the elliptic cylindrical gantry, and the shield gradient magnetic field coil is disposed farthest from the inner wall of the elliptic cylindrical gantry. The main and shield gradient magnetic field coils of the Y-direction gradient magnetic field coil arranged across the narrow vertical direction, that is, the Y direction, are arranged adjacent to the X-direction main and shield gradient magnetic field coils, respectively.

  According to the present invention, the lateral width of the inner diameter of the gantry cover, that is, the distance between the left and right gantry covers is wider than about 60 cm of the conventional apparatus, for example, 70 to 90 cm. It is possible to move to the open area, and openness and accessibility are improved. Also, the reduction of the magnetic field generation efficiency of the gradient magnetic field coil device, particularly the X direction gradient magnetic field coil, due to the widening of the lateral width of the gantry is suppressed by improving the arrangement structure of the X, Y, Z direction gradient magnetic field coils. Is done.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an MRI apparatus having a horizontal gantry including a horizontal magnetic field type ellipse, racetrack shape and rectangle of the present invention (hereinafter collectively referred to as an elliptical cylinder shape) and an active shield type gradient magnetic field coil apparatus adapted to the gantry. It is sectional drawing of the gantry part for demonstrating one Example.

  In FIG. 1, only the inner wall of the superconducting magnet is shown. By this cylindrical superconducting magnet, an axial direction, that is, a Z-axis direction static magnetic field is generated in the center of the gantry. This superconducting magnet is composed of a superconducting coil for generating a static magnetic field, a cooling container, a refrigerator, and the like. An active shield type gradient coil device (GC), an RF coil, and a gantry cover are disposed inside the inner wall of the superconducting magnet, but the illustration of the RF coil is omitted. Also, illustration of RF shields, cables, piping, etc. is omitted. In this embodiment, the lateral direction of the gantry cover, that is, the width in the X direction is expanded to about 70 to 90 cm.

  FIG. 2 is a view for explaining the arrangement structure of each coil in the active shield type gradient magnetic field coil apparatus (GC) in FIG.

  The active shield type gradient coil device (GC) of the present invention is a pair of X-direction gradient magnetic field coils (XGC) arranged to face each other so as to straddle the X axis, and are arranged to face each other so as to straddle the Y axis. A pair of Y-direction gradient magnetic field coils (YGC) and a Z-direction gradient magnetic field coil (ZGC) wound in a solenoid shape along the Z axis, and gradient magnetic field coils in the X, Y, and Z directions Each of (XGC, YGC, ZGC) is an X, Y, Z direction main gradient magnetic field coil (XGCm, YGCm, ZGCm) and a main inclination in each direction of X, Y, Z arranged on the side close to the measurement space. X, Y, Z direction shield gradient magnetic field coils XGCs, YGCs that shield magnetic fields generated by the magnetic field coils (XGCm, YGCm, ZGCm) and leaking to the outside on the opposite side of the measurement space, respectively. And a ZGCs).

  Furthermore, the X direction main gradient magnetic field coil (XGCm) disposed on the long axis side where the width of the elliptical cylindrical gantry is expanded, that is, the X axis side, is disposed on the short axis side, that is, the Y axis side. Compared with the Y-direction main gradient magnetic field (YGCm), the magnetic field generation efficiency is low because the distance to the center of the elliptic cylindrical gantry, that is, the Z-axis is long. Therefore, in the present invention, the X-direction main gradient coil (XGCm) is disposed at a position closest to the gantry cover and is generated by the X-direction main gradient coil (XGCm) and leaks to the outside on the opposite side of the measurement space. X-direction shield gradient magnetic field coils (XGCs) are arranged at the farthest position from the gantry cover in order to shield the magnetic field generated most efficiently, and the overall decrease in magnetic field generation efficiency by the X-direction gradient magnetic field coil (XGC) is suppressed. Yes.

  The Y-direction main gradient coil (YGCm), which is close to the center of the elliptic cylindrical gantry, that is, the distance to the Z-axis, is adjacent to the X-direction main gradient coil (XGCm) on the outer peripheral side, and the Y-direction shield gradient magnetic field. The coils (YGCs) are disposed adjacent to the X-direction shield gradient magnetic field coils (XGCs) on the inner peripheral side thereof.

  Since the gradient magnetic field coil (ZGC) has an efficient relationship between the gradient magnetic field direction and the coil arrangement, the main gradient coil and the shield gradient magnetic field coil are different from those in the X and Y direction gradient coils (XGC, YGC). The Z-direction main gradient coil (ZGCm) is adjacent to the Y-direction main gradient coil (YGCm) on the outer peripheral side and the Z-direction shield gradient coil (ZGCs). Is disposed adjacent to the Y-direction shield gradient coil (YGCs) on the inner peripheral side, and as a result, both are arranged between the Y-direction main gradient coil (YGCm) and the Y-direction shield gradient coil (YGCs). Is disposed adjacent to.

  Accordingly, each of the gradient magnetic field coils is arranged in the gradient coil apparatus from the gantry cover toward the outer circumferential direction, the X-direction main gradient magnetic field coil (XGCm), the Y-direction main gradient magnetic field coil (YGCm), and the Z-direction main gradient. The magnetic field coil (ZGCm), the Z direction shield gradient magnetic field coil (ZGCs), the Y direction shield gradient magnetic field coil (YGCs), and the X direction shield gradient magnetic field coil (XGCs) are arranged in this order.

  In this manner, by arranging the respective gradient magnetic field coils (XGCm, XGCs, YGCm, YGCs, ZGCm, ZGCs), it is possible to generate the same gradient magnetic field strength in each direction, which is required of the MRI apparatus. It is possible to capture a uniform image with respect to a cross section in an arbitrary direction.

  Since the Z-direction gradient magnetic field coil (ZGC) can be designed with high magnetic field generation efficiency, it is reasonable for the gradient magnetic field coil (GC) drive to be arranged as described above.

  However, in order to suppress heat generation as a whole of the gradient magnetic field coil (GC), the Z-direction gradient magnetic field coil (ZGC) is constituted by a hollow conductor and cooling water is supplied to the Z-direction gradient magnetic field coil (ZGC). Is disposed between the X-direction gradient coil (XGC) and the Y-direction gradient coil (YGC), that is, the Z-direction main gradient coil (ZGCm) is replaced with the X-direction main gradient coil (XGCm). By arranging the Z-direction shield gradient coil (ZGCs) between the main gradient coil (YGCm) and the Y-direction shield gradient coil (YGCs) and the X-direction shield gradient coil (XGCs). The cooling efficiency of the entire gradient coil (GC) can be improved.

  Further, since the shield gradient coils (XGCs, YGCs, ZGCs) have a lower current density than the main gradient coils (XGCm, YGCm, ZGCm), the power generation amount is relatively low. Since the cooling requirement for XGCs, YGCs, ZGCs) is relaxed compared to the main gradient coils (XGCm, YGCm, ZGCm), the Y-direction shield gradient coils (YGCs) and the water-cooled hollow conductor in the above-described modification Even if the arrangement of the Z-direction shield gradient magnetic field coils (ZGCs) is changed, the cooling effect can be sufficiently maintained depending on the size and shape of the gantry.

  In this embodiment, the external shape of the gradient magnetic field coil device (GC) is substantially similar to the shape of the inner wall of the magnet, and the internal shape is similar to the shape of the gantry cover, so that each main gradient magnetic field coil (XGCm, YGCm, ZGCm) and the shield gradient magnetic field coils (XGCs, YGCs, ZGCs) can be increased, so that the magnetic field generation efficiency of the entire gradient magnetic field coil device (GC) can be further increased.

  FIG. 3 is a sectional view of a gantry for explaining another embodiment of the MRI apparatus having the horizontal magnetic field type elliptic cylindrical gantry of the present invention and the active shield type gradient magnetic field coil apparatus adapted thereto.

  In this embodiment, in order to further improve the magnetic field generation efficiency of the gradient coil device (GC), the curved inner wall of the elliptical cylindrical gantry that does not contribute much as a space for receiving the subject is cut and substantially flat. It is what. Thereby, since the distance from the X direction main gradient coil (XGCm) to the center of the elliptical cylindrical gantry can be substantially shortened, the magnetic field generation efficiency of the X direction main gradient coil (XGCm) is improved. As for the Y-direction and Z-direction main gradient magnetic field coils (YGCm, ZGCm), the distance to the center of the elliptical cylindrical gantry is locally shortened.

  FIG. 4 is a sectional view of a gantry portion for explaining still another embodiment of the MRI apparatus having the horizontal magnetic field type elliptic cylindrical gantry of the present invention and the active shield type gradient magnetic field coil apparatus adapted thereto.

  As shown in FIG. 4, according to this embodiment, the table can be moved left and right by increasing the lateral width of the inner periphery of the gantry cover. As a result, since it is possible to place the part of the sample to be photographed at the center of the magnetic field, a good image can be acquired. In addition, since a space can be taken in one direction, it becomes possible to access the subject from outside the gantry. As a result, it is possible to give a sense of security to the subject and to perform a procedure such as biopsy.

  Usually, an irradiation coil is arranged between the gradient magnetic field coil device (GC) and the gantry cover. For this reason, in order to ensure the widest possible space as the subject space, the shape of the gantry cover is basically similar to the inner shape of the irradiation coil. Alternatively, when the irradiation coil is used as a transmission / reception coil and is arranged on the inner side of the gantry cover, the shape of the gantry cover can be basically similar to the inner shape of the gradient coil device (GC). In addition, it is possible to further widen the lateral open space.

  In the second and third embodiments, the side wall of the gantry is vertical, but the side wall is not necessarily vertical, and may have a large curvature.

1 is a cross-sectional view of a gantry portion for explaining an embodiment of an MRI apparatus having an elliptical cylindrical gantry of the horizontal magnetic field system of the present invention and an active shield type gradient magnetic field coil apparatus adapted thereto. FIG. The figure for demonstrating the arrangement | positioning structure of each coil in the active shield type gradient magnetic field coil apparatus in FIG. It is sectional drawing of the gantry part for demonstrating another Example of the MRI apparatus which has an elliptical cylindrical gantry of the horizontal magnetic field system of this invention, and an active shield type gradient magnetic field coil apparatus corresponding to it. It is sectional drawing of the gantry part for demonstrating another Example of the MRI apparatus which has an elliptical cylindrical gantry of the horizontal magnetic field system of this invention and an active shield type gradient magnetic field coil apparatus corresponding to it.

Claims (11)

  In a magnetic resonance imaging apparatus including a horizontal static magnetic field type horizontally long cylindrical gantry and an active shield type gradient magnetic field coil apparatus adapted thereto, the active shield type gradient magnetic field coil apparatus (GC) includes the direction of the horizontal magnetic field, that is, the Z axis. A pair of X-direction gradient magnetic field coils (XGC) disposed opposite to each other so as to straddle the X axis, and the vertical direction of the plane orthogonal to the Z axis direction, that is, the Y axis. It is composed of a pair of Y-direction gradient magnetic field coils (YGC) disposed so as to face each other and a Z-direction gradient magnetic field coil (ZGC) wound along the Z-axis, and the X, Y, Z Each of the gradient magnetic field coils (XGC, YGC, ZGC) in each direction is arranged in the X, Y, Z direction main gradient magnetic field coil disposed on the side close to the measurement space at the center of the horizontally long cylindrical gantry. X (XGCm, YGCm, ZGCm) and the main gradient magnetic field coils (XGCm, YGCm, ZGCm) in the X, Y and Z directions, respectively, which shield the magnetic field leaking outside the measurement space on the opposite side , Y, Z direction shield gradient magnetic field coils (XGCs, YGCs, ZGCs), and the X direction main gradient magnetic field coil (XGCm) is closest to the inner wall of the horizontally long cylindrical gantry and is in the X direction. The shield gradient magnetic field coils (XGCs) are arranged farthest from the inner wall of the horizontally long cylindrical gantry, and the Y direction gradient magnetic field coil (YGC) and the Z direction gradient magnetic field coil (ZGC) are respectively the X direction main gradient magnetic field coils. (XGCm) and an X-direction shield gradient magnetic field coil (XGCs) Magnetic resonance imaging apparatus.   The Y-direction main gradient coil (YGCm) and the Y-direction shield gradient coil (YGCs) are disposed adjacent to the X-direction main gradient coil (XGCm) and the X-direction shield gradient coil (XGCs), respectively. The Z-direction main gradient coil (ZGCm) and the Z-direction shield gradient coil (ZGCs) are disposed between the Y-direction gradient coil (YGCm) and the Y-direction gradient gradient coil (YGCs). The magnetic resonance imaging apparatus according to claim 1.   The Z direction main gradient coil (ZGCm) and the Z direction shield gradient coil (ZGCs) are disposed adjacent to the X direction main gradient coil (XGCm) and the X direction shield gradient coil (XGCs), respectively. The Y direction main gradient coil (YGCm) and the Y direction shield gradient coil (YGCs) are disposed between the Z direction gradient coil (ZGCm) and the Z direction shield gradient coil (ZGCs). The magnetic resonance imaging apparatus according to claim 1.   The Z direction main gradient coil (ZGCm) and the Y direction shield gradient coil (YGCs) are disposed adjacent to the X direction main gradient coil (XGCm) and the X direction shield gradient coil (XGCs), respectively. The Y direction main gradient coil (YGCm) and the Z direction shield gradient coil (ZGCs) are disposed between the Z direction main gradient coil (ZGCm) and the Y direction shield gradient coil (YGCs). The magnetic resonance imaging apparatus according to claim 1. Magnetic resonance imaging apparatus according to any one of claims 1 to 4, wherein the X direction inner wall of the oblong cylindrical gantry, which is formed in a substantially vertical plane. The magnetic resonance imaging apparatus according to any one of claims 1 to 5, wherein a width dimension in the X direction of the horizontally long cylindrical gantry is wider than 70 cm. According to any one of claims 1 to 6 table for carrying and placing the subject in the measurement space of the horizontal tubular gantry, characterized in that it is movable in the in the X direction Magnetic resonance imaging device. A main gradient magnetic field coil that generates a main gradient magnetic field in a measurement space whose first direction is a static magnetic field direction, and a shield gradient magnetic field for canceling a magnetic field leaking to the opposite side of the measurement space by the main gradient magnetic field coil A gradient magnetic field coil device formed in a cylindrical shape,
The main gradient magnetic field coil includes a first main gradient magnetic field coil that generates a gradient magnetic field in the first direction, and a second main gradient that generates a main gradient magnetic field in a second direction perpendicular to the first direction. A magnetic field coil, and a third main gradient coil that generates a main gradient magnetic field in a third direction perpendicular to the first direction and the second direction,
The shield gradient coil includes a first shield gradient coil for canceling a magnetic field leaking to the opposite side of the measurement space by the first main gradient coil, and the second main gradient coil. A second shield gradient magnetic field coil for canceling the magnetic field leaking to the opposite side of the measurement space, and a third shield for canceling the magnetic field leaking to the opposite side of the measurement space by the third main gradient magnetic field coil A shield gradient magnetic field coil,
The gradient magnetic field coil apparatus, wherein the second main gradient magnetic field coil is arranged on the inner side closest to the measurement space, and the second shield gradient magnetic field coil is arranged on the outer side farthest from the measurement space. . The gradient magnetic field coil apparatus according to claim 8,
The gradient magnetic field coil apparatus according to claim 1, wherein the main gradient coil has a length in the second direction longer than a length in the third direction.   A magnetic resonance imaging apparatus comprising the gradient magnetic field coil apparatus according to claim 8. The magnetic resonance imaging apparatus according to claim 10.
A magnetic resonance imaging apparatus comprising: a table on which a subject is placed and carried in the measurement space; and the table is configured to be movable also in the second direction.