JP5202491B2 - Magnetic resonance imaging system - Google Patents

Description

  The present invention relates to a horizontal magnetic field type magnetic resonance imaging apparatus, and more particularly to a gradient magnetic field coil used for nuclear magnetic resonance imaging.

  In a horizontal magnetic field type (tunnel type) magnetic resonance imaging (MRI) apparatus, a static magnetic field coil (such as a superconducting coil) that generates a uniform magnetic field in an imaging space is housed in a hollow cylindrical container, and the inside of the inner cylinder of the container In order to add position information to the imaging section, a gradient magnetic field coil that generates a pulsed magnetic field (gradient magnetic field) and an RF coil that excites nuclear spins are arranged.

  A horizontal magnetic field type MRI apparatus inserts a subject (usually a human body) into a static magnetic field generated by a superconducting coil and irradiates an RF pulse, thereby receiving a magnetic resonance signal generated from within the living body of the subject. To obtain a tomographic image for medical diagnosis. At this time, the gradient coil is in the imaging space in which the subject is placed, in the axial direction of the cylinder (z-axis), in the horizontal direction perpendicular to the z-axis and parallel to the floor (x-axis), and perpendicular to the floor. By applying a gradient magnetic field that varies linearly in the vertical direction (y-axis) in a pulsed manner, position information in the living body is given to the magnetic resonance signal. The gradient coil creates an unnecessary magnetic field in addition to the imaging space, and this magnetic field generates eddy currents in surrounding structures, and the magnetic field created by the eddy currents adversely affects the image. In order to suppress the leakage magnetic field to the surroundings, the MRI apparatus is provided with a shield coil through which a current opposite to the main coil flows, in addition to the main coil that creates a gradient magnetic field.

  The gradient magnetic field coil generally has a circular cross-sectional shape perpendicular to the z-axis in accordance with the cylindrical container that houses the superconducting coil, but the cross-sectional shape is reduced in order to reduce the patient's feeling of pressure. It has been proposed to be horizontally long. Patent Document 1 shows an example of a horizontal magnetic field type MRI apparatus in which the cross-sectional shapes of the main coil and the shield coil of the gradient magnetic field are horizontally long ellipses. Further, Patent Document 1 describes a horizontal magnetic field type MRI apparatus including a main coil having an elliptical cross section and a shield coil disposed outside the main coil and having a circular cross section.

  Patent Document 2 describes a horizontal magnetic field type MRI apparatus in which the cross-sectional shape of the gradient magnetic field coil is non-circular. The main coil of this gradient magnetic field has a flat shape in the lower half of the cross-sectional shape and a substantially circular shape in the upper half. Patent Document 2 shows an example of a coil pattern of a z-gradient magnetic field coil that creates a magnetic field having a linear gradient in the z direction, and a current is passed on the upper side where the distance between the main coil and the shield coil is narrow and the lower side where the distance is wide. It shows how conductors have different winding density.

JP 2001-327478 A Japanese Patent Laid-Open No. 2001-170026

  When the cross-sectional shape of the z-gradient magnetic field coil is circular for both the main coil and the shield coil, they form a solenoidal coil. In Patent Document 2, since the cross-sectional shape of the main coil of the z-gradient magnetic field coil is non-circular and the cross-sectional shape of the shield coil is circular, a portion where the interval between the main coil and the shield coil of the z-gradient magnetic field coil is narrow and a wide portion. In the narrow part, the magnetic field created by each coil increases. Therefore, it becomes impossible to form a solenoid coil for both the main coil and the shield coil, and a loop coil that crosses the cross section passing through the center of the apparatus is additionally formed. Thus, when the solenoid coil and the loop coil are mixed, the wiring of the conductor becomes complicated.

  Accordingly, an object of the present invention is to provide a coil pattern that does not include the above-described mixture.

  A feature of the present invention that achieves the above object is that a ring-shaped static magnetic field coil that generates a static magnetic field, a bed apparatus that moves through a ring-shaped opening of the static magnetic field coil, and a gradient magnetic field that has a gradient magnetic field strength. A horizontal magnetic field type magnetic resonance imaging apparatus including a gradient magnetic field coil to be generated, the gradient magnetic field coil including a gradient magnetic field main coil that generates a gradient magnetic field in an imaging space, and the generated gradient magnetic field outside the gradient magnetic field coil A gradient magnetic field shield coil that suppresses leakage; the gradient magnetic field main coil and the gradient magnetic field shield coil are arranged such that the distance between them is different in the circumferential direction; and the gradient magnetic field is in the z-axis direction that is the traveling direction of the bed apparatus The z-gradient magnetic field main coil that generates the current coil has a current flow path in a plane perpendicular to the z-axis, and is a solenoid coil that is stacked in the z-axis direction. A.

  According to the present invention, the wiring of the conductor can be simplified by making the main coil of the z-gradient magnetic field coil into a solenoid shape in which current flow paths made in a plane perpendicular to the z axis are stacked in the z direction. . In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

It is a developed view of the z gradient magnetic field coil of Example 1 of the present invention, and shows (a) a wiring pattern of a z main coil and (b) a wiring pattern of a z shield coil. It is a figure which shows the bird's-eye view of the magnetic resonance imaging apparatus of the Example of this invention. It is a figure which shows sectional drawing of the magnetic resonance imaging apparatus of the Example of this invention. It is a figure which shows sectional drawing of the gradient magnetic field coil of Example 1 of this invention. It is an expanded view of the x gradient magnetic field coil of Example 1 of this invention, (a) Wiring pattern of x main coil, (b) It is a figure which shows the wiring pattern of x shield coil. It is an expanded view of the y gradient magnetic field coil of Example 1 of this invention, (a) Wiring pattern of y main coil, (b) It is a figure which shows the wiring pattern of y shield coil. It is a figure which shows the bird's-eye view of the z gradient magnetic field coil of the comparative example 1. It is a figure which shows the expanded view of the z gradient magnetic field coil of the comparative example 1. FIG. It is an expanded view of the z gradient magnetic field coil of the comparative example 2, and is a figure which shows the wiring pattern of (a) z main coil and (b) z shield coil. It is a figure which shows the magnetic flux density z component which a z gradient magnetic field coil produces, (a) In the case of the z gradient magnetic field coil of Example 1 of this invention, (b) In the case of the z gradient magnetic field coil of the comparative example 2, (c) It is the figure which plotted z component of the magnetic flux density on the line segment extended in the axial direction from the center part of an imaging region. FIG. 2 shows a part of the wiring pattern of the z main coil of Example 1 of the present invention, (a) a wiring pattern displaying connections of elliptical current flow paths stacked in the z direction, and (b) one of the conductors of the z main coil. FIG. 1 shows a part of the wiring pattern of the z shield coil of Example 1 of the present invention, (a) a wiring pattern displaying connections of elliptical current flow paths stacked in the z direction, and (b) one of conductors of the z main coil. FIG. 2 shows a z-gradient magnetic field coil of Example 2 of the present invention, (a) a sectional view of the z-gradient magnetic field coil, (b) a development view of a wiring pattern of a z-main coil of the z-gradient magnetic field coil, and (c) a z shield coil. It is a figure which shows the expanded view of a wiring pattern. 3 shows a z-gradient magnetic field coil according to a third embodiment of the present invention, (a) a sectional view of the z-gradient magnetic field coil, (b) a development view of a wiring pattern of the z main coil of the z-gradient magnetic field coil, and (c) a z shield coil. It is a figure which shows the expanded view of a wiring pattern. 4 shows a z-gradient magnetic field coil of Example 4 of the present invention, (a) a sectional view of the z-gradient magnetic field coil, (b) a development view of a wiring pattern of a z-main coil of the z-gradient magnetic field coil, and (c) a z shield coil. It is a figure which shows the expanded view of a wiring pattern. 5 shows a z-gradient magnetic field coil of Example 5 of the present invention, (a) a sectional view of the z-gradient magnetic field coil, (b) a development view of a wiring pattern of the z main coil of the z-gradient magnetic field coil, and (c) a z shield coil. It is a figure which shows the expanded view of a wiring pattern.

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

Example 1
A horizontal magnetic field type MRI apparatus (magnetic resonance imaging apparatus) of Example 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. FIG. 2 shows a bird's-eye view of the MRI apparatus, and FIG. 3 shows a cross section of the MRI apparatus when cut perpendicularly to the floor parallel to the z-axis.

  The MRI apparatus 100 includes a static magnetic field coil 1, a gradient magnetic field coil 2, an RF coil 3, a receiving coil (not shown), a helium vessel 4, a radiation shield 5, a vacuum vessel 6, an image processing device (not shown), and a bed device. 41 is provided. The helium container 4, the radiation shield 5 and the vacuum container 6 are hollow cylindrical containers. The radiation shield 5 is disposed inside the vacuum container 6, and the helium container 4 is disposed inside the radiation shield 5. A static magnetic field coil 1 is disposed inside the helium vessel 4. The gradient magnetic field coil 2 and the RF coil 3 are disposed outside the vacuum vessel 6 and in a hollow portion of the cylindrical vacuum vessel 6.

  The static magnetic field coil 1 is composed of, for example, four static magnetic field main coils 1a and two static magnetic field shield coils 1b which are superconducting coils, and an imaging space (imaging region) 7 into which the subject 40 lying on the bed apparatus 41 is inserted. Generates a static magnetic field. The static magnetic field main coil 1a and the static magnetic field shield coil 1b are superconducting coils and have an annular shape (ring shape). The bed apparatus 41 carrying the subject 40 moves through the opening near the center of the ring shape. The radius of the static magnetic field main coil 1a is smaller than the radius of the static magnetic field main coil 1b. The pair of static magnetic field main coils 1a generates a uniform static magnetic field in the imaging space 7, and the pair of static magnetic field shield coils 1b leaks outside the MRI apparatus 100 due to the static magnetic field generated by the static magnetic field main coil 1a. Suppresses the magnetic field.

  The gradient magnetic field coil 2 includes a gradient magnetic field main coil 9 and a gradient magnetic field shield coil 10 (FIG. 4), and generates a gradient magnetic field in which the magnetic field strength is spatially inclined in the imaging space 7. The gradient coil 2 is driven in a pulsed manner by a gradient magnetic field power source to generate a pulsed gradient magnetic field. The gradient magnetic field main coil 9 has a function of generating independent gradient magnetic fields in the three directions of the x-axis direction, the y-axis direction, and the z-axis direction and superimposing them on the static magnetic field generated by the static magnetic field coil 1. A current opposite to that of the gradient magnetic field main coil 9 flows through the gradient magnetic field shield coil 10 to generate a magnetic field that suppresses leakage of the gradient magnetic field generated by the gradient magnetic field main coil 9 to the outside of the gradient magnetic field coil 2. The gradient magnetic field coil 2 generates a pulsed gradient magnetic field and superimposes it on the static magnetic field, whereby position information in the imaging space 7 can be obtained. If the gradient magnetic field shield coil 10 is not disposed, the time-varying magnetic field (pulsed magnetic field) generated by the gradient magnetic field main coil 9 leaks to the outside, and eddy currents are generated in the helium vessel, radiation shield, and vacuum vessel, There is a possibility that the gradient magnetic field distribution in the imaging region is distorted by the magnetic field generated by the eddy current. By disposing the gradient magnetic field shield coil 10 as in the present embodiment, it is possible to prevent the pulsed magnetic field generated by the gradient magnetic field main coil 9 from leaking outside the gradient magnetic field coil 2 and cover the static magnetic field coil 1. It is possible to suppress the generation of eddy current in the container (helium container, radiation shield, vacuum container) and obtain a desired gradient magnetic field distribution. Further, by disposing the gradient magnetic field shield coil 10 between the gradient magnetic field main coil 9 and the static magnetic field coil 1, the static magnetic field due to the oscillating electromagnetic force generated by the current flowing through the static magnetic field coil 1 and the magnetic field leaking from the gradient magnetic field main coil 9. The vibration of the coil 1 can be suppressed, and the uniform magnetic field created in the imaging region can be prevented from fluctuating over time.

  The RF coil 3 is driven in a pulse shape by a high frequency power source and irradiates the imaging space 7 with the high frequency pulse. The receiving coil receives a magnetic resonance signal from the subject and transmits it to the image processing apparatus. When the image processing apparatus receives the magnetic resonance signal from the receiving coil, the image processing apparatus processes the magnetic resonance signal to create an MRI image of the subject 40 and displays it on a display device (not shown). The main magnetic field generation sources of the MRI apparatus are a static magnetic field coil 1, a gradient magnetic field coil 2, and an RF coil 3. Here, the direction parallel to the traveling direction of the bed apparatus 41 (the direction of the static magnetic field) is the z axis, the axis perpendicular to the z axis and the vertical direction is the y axis, and the direction perpendicular to the z axis and the y axis is the x axis. And

  As shown in FIG. 3, each of the static magnetic field coil 1a and the static magnetic field shield coil 1b has an annular shape (ring shape) with the z-axis direction as an axis. Such a static magnetic field main coil 1a and a static magnetic field shield coil 1b are housed in a helium container 4 filled with liquid helium as a refrigerant. The helium vessel 4 is enclosed in a radiation shield 5 that blocks heat radiation to the inside. Further, the vacuum vessel 6 is in a vacuum state and encloses the helium vessel 4 and the radiation shield 5. Thus, the static magnetic field main coil 1a and the static magnetic field shield coil 1b are accommodated in a three-layered container (a vacuum container 6, a radiation shield 5, and a helium container 4 in order from the outside). Since the inside of the vacuum vessel 6 is vacuum, it is possible to suppress external heat from being transmitted to the helium vessel 4 by conduction or convection, and by providing the radiation shield 5 between the vacuum vessel 6 and the helium vessel 4, external radiant heat is provided. Can be prevented from entering the helium container 4. For this reason, the temperature of the static magnetic field coil 1 can be stably set to the cryogenic temperature which is the temperature of liquid helium, and the function as a superconducting coil can be given. The static magnetic field coil 1 generates a static magnetic field in the imaging space 7.

  The gradient coil 2 of the present embodiment will be described with reference to FIG. FIG. 4 shows a cross section when the gradient coil 2 is cut perpendicularly to the z-axis. The gradient coil 2 is disposed outside the vacuum vessel 6 and at a position closer to the imaging space 7 than the vacuum vessel 6. The gradient magnetic field coil 2 includes a gradient magnetic field main coil 9 and a gradient magnetic field shield coil 10 in order from the side closer to the imaging space 7. The cross-sectional shape of the gradient magnetic field coil 2 shown in this embodiment is a case where the gradient magnetic field main coil 9 is elliptical and the gradient magnetic field shield coil 10 is circular. The gradient magnetic field main coil 9 has an elliptical shape having a major axis in the x-axis direction and a minor axis in the y-axis direction. The gradient coil 2 generates a gradient magnetic field that changes linearly in the x-axis direction, the y-axis direction, and the z-axis direction with respect to a magnetic field component parallel to the static magnetic field 8. Specifically, the gradient magnetic field main coil 9 includes an x gradient magnetic field main coil (x main coil) 9x that generates a gradient magnetic field in the x axis direction, and a y gradient magnetic field main coil (y main coil) that generates the gradient magnetic field in the y axis direction. 9y is composed of a z-gradient magnetic field main coil (z main coil) 9z generated in the z-axis direction, and is laminated with an insulating layer sandwiched in each cross-sectional direction. The gradient magnetic field shield coil 10 is an x gradient magnetic field shield coil (x shield coil) 10x, y gradient magnetic field shield coil (y shield coil) that suppresses the magnetic field generated by the gradient magnetic field main coil 9 from leaking outside the gradient magnetic field coil 2. ) 10y, z gradient magnetic field shield coil (z shield coil) 10z, each of which is laminated with an insulating layer sandwiched in the cross-sectional direction.

  Each of the x main coil 9x and the x shield coil 10x of the x gradient magnetic field coil is arranged with four spiral saddle coils at symmetrical positions with respect to the z = 0 symmetry plane and the x = 0 symmetry plane. The y main coil 9y and the y shield coil 10y of the y gradient magnetic field coil have different shapes from the x gradient magnetic field coil, and the x gradient magnetic field coil is rotated by 90 degrees with respect to the z axis.

  Next, the wiring pattern of the gradient coil 2 according to the present embodiment will be described with reference to FIGS. 1 shows a 1/4 wiring pattern of the z-gradient magnetic field coil of this embodiment, FIG. 5 shows a 1/4 wiring pattern of the x-gradient magnetic field coil, and FIG. 6 shows a 1/4 wiring pattern of the y-gradient magnetic field coil. . Each of the x main coil 9x (FIG. 5A) and the x main coil 10x (FIG. 5B) of the x gradient magnetic field coil is a spiral saddle type coil. The y main coil 9y (FIG. 6A) and the y main coil 10y (FIG. 6B) of the y gradient magnetic field coil are also spiral saddle coils. The wiring pattern of the above-described x gradient magnetic field coil and y gradient magnetic field coil is a spiral saddle type coil that has substantially the same number of turns, but has the same number of turns as the circular magnetic field main coil and the gradient magnetic field shield coil. Here, the connection part which connects each current loop is not displayed.

  On the other hand, the wiring pattern (FIG. 1) of the z gradient magnetic field coil 10 is greatly different from the wiring patterns of the conventional z main coil and z shield coil in which the sectional shape of the gradient magnetic field coil is circular. When describing the difference, first, as a comparative example, the wiring pattern of the z-gradient magnetic field coil in the case where the cross-sectional shapes of the gradient magnetic field main coil and the gradient magnetic field shield coil are circular will be described with reference to FIGS. I will explain. FIG. 7 shows a bird's eye view of the wiring pattern 11 of the z main coil and the wiring pattern 12 of the z shield coil of the first comparative example. FIG. 8 is a development view of the wiring pattern of the z-gradient magnetic field coil when the angle θ rotating counterclockwise with respect to the z-axis is taken on the horizontal axis and z is taken on the vertical axis in Comparative Example 1. FIG. 8A shows the wiring pattern 11 of the z main coil, and FIG. 8B shows the wiring pattern 12 of the z shield coil. In Comparative Example 1, since the cross-sectional shapes of both the z main coil and the z shield coil are circular, the magnetic field distribution created by the wiring pattern 11 and the wiring pattern 12 is uniform in the circumferential direction. Therefore, these two wiring patterns of Comparative Example 1 have a circular current flow path in a plane perpendicular to the z-axis, and form a solenoidal coil in which they are stacked in the z direction. In FIG. 7 and FIG. 8, the connection part which connects the adjacent circular current flow paths is not shown. Next, as Comparative Example 2, a wiring pattern of a z-gradient magnetic field coil having a cross-sectional shape that is an xy plane will be described with reference to FIG. FIG. 9A shows a developed view of the wiring patterns 13 and 14 of the z main coil, and FIG. 9B shows a development of the wiring patterns 15 and 16 of the z shield coil. This is a case where there are a narrow portion and a wide portion between the main coil and the shield coil as described in Patent Document 2, and the magnetic field produced by each coil becomes strong in the x direction where the space is narrow. . Therefore, to reproduce the magnetic field, a loop that crosses the z = 0 plane is formed, such as the wiring pattern 14 for the z main coil and the wiring pattern 16 for the z shield coil. The other z main coil wiring pattern 13 and z shield coil wiring pattern 15 form a generally solenoidal coil meandering around the z axis on a cylindrical surface or an elliptical cylindrical surface. In FIG. 9, as in FIG. 7 and FIG. 8, connection portions that connect adjacent current flow paths are not shown.

  In contrast, FIG. 1 shows a first embodiment of the present invention. The present embodiment is a wiring pattern of a z-gradient magnetic field coil having the cross-sectional shape shown in FIG. 4 (cross-sectional shape in the xy plane). The wiring pattern 17 of the z main coil has a horizontally long elliptical current flow path in the x direction in a plane perpendicular to the z axis, and forms a solenoid coil stacked in the z direction. On the other hand, the wiring pattern 18 of the z shield coil forms a substantially solenoidal coil meandering around the z axis on the cylindrical surface, and the wiring pattern 19 forms a loop that crosses the z = 0 plane. Thus, the z shield coil is formed in a saddle shape (a loop is formed) near the center of the magnetic resonance imaging apparatus in the z axis direction, and meanders around the z axis on the cylindrical surface outside the region formed in the saddle shape. The wiring pattern is formed in a generally solenoid shape. In other words, as shown in FIG. 12 (a), the z shield coil is a wiring portion formed in a generally solenoid shape that meanders around the z axis on the cylindrical surface in order along the traveling direction of the bed apparatus 41. A wiring portion formed in a saddle shape and a wiring portion formed in a generally solenoid shape meandering around the z-axis on a cylindrical surface. Also in FIG. 1 of the present embodiment, the connecting portion that connects adjacent current flow paths is not shown. According to the present embodiment, the z main coil has a horizontally long elliptical current flow path in the x direction in a plane perpendicular to the z axis, and is formed into a solenoid shape stacked in the z direction. Can be simplified. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Further, since the distortion of the magnetic field distribution created in the imaging region by the z main coil is reduced, cross-sectional information can be obtained with high accuracy during imaging.

  In the following, this effect will be confirmed by comparing the magnetic flux density created by the z-gradient coil. FIG. 10A shows the contour lines of the z component of the magnetic flux density formed by the z gradient magnetic field coil of Comparative Example 2 on the xz plane. The width of the contour line is 1 (mT) or more and -1 (mT) or less, and is 1 (mT) interval, and otherwise, 0.1 (mT) interval. FIG. 10B is a contour line of the magnetic flux density z component in this embodiment. These two have almost the same distribution, and in order to compare in more detail, a plot of the magnetic flux density z component on the line segment extending in the axial direction from the center of the imaging region as shown in FIG. Show. In FIG. 10C, the one plotted with diamonds shows the distribution of Comparative Example 2, the one plotted with squares shows the distribution of this example, and the one plotted with triangles shows the ideal distribution. The deviation from the ideal distribution at a certain position zm in the axial direction is such that the value of this example is smaller than the value of Comparative Example 2, and the z-gradient magnetic field coil of this example provides a highly accurate magnetic field distribution. Can be seen to form.

  The structure of the z-gradient magnetic field coil of the present embodiment described above will be described below. FIG. 11A shows the z main coil wiring pattern of the z gradient magnetic field coil of the present embodiment with a connection portion of an elliptical current flow path stacked in the z direction. The current flows through the connection wiring 20 installed in the y direction parallel to the z axis, flows from the elliptical flow path wiring in the region of z <0 to the elliptical flow path wiring 21 of z> 0, and the connection wiring 22. To. Here, the connecting portion may be installed in either the x-direction or the y-direction, but the installation space has a margin in the y-direction where the interval between the z main coil and the z shield coil is wider than the x-direction where the interval is narrow. It is optimal to install in the y direction. FIG. 11B shows a part of the conductor of the z main coil of the first embodiment. The conductor 23 is optimally structured to allow the coolant 24 to flow inside. The reason is described below. The amplitude of the current flowing through the conductor of the gradient coil during imaging is several hundred (A) and the voltage for driving it is about 1000 (V). With such high power, the amount of heat generated inside the conductor cannot be ignored, A mechanism for cooling the conductor must be provided. On the other hand, the installation space of the gradient magnetic field coil disposed between the hollow cylindrical container in which the superconducting coil is accommodated and the imaging region is limited. Therefore, it is desirable to adopt the structure of the present embodiment that does not require a separate cooling pipe. In the following, it is assumed that the z gradient magnetic field coil is composed of this conductor.

  As shown in FIG. 11A, the z main coil can be implemented without crossing the wirings once except for the connection wiring 20. In addition, since the connection wiring 20 is installed in the y direction where there is a sufficient installation space, there is no problem in installation space. On the other hand, since the z shield coil has a mixture of almost solenoidal wiring and loop wiring, the wiring intersects. Therefore, a portion that cannot be stored in the installation space is generated. The solution is described below.

  FIG. 12A shows the wiring pattern of the z shield coil of the z gradient magnetic field coil of the present embodiment with a connection portion. The current flows through the connection wiring 25 arranged in the y direction parallel to the z axis, and passes from the almost solenoidal wiring 26 in the region of z> 0 via the loop wiring 27a, and the almost solenoidal wiring and the loop wiring of z <0. 27 b and reaches the connection wiring 28. Here, similarly to the z main coil, the connecting portion may be installed in either the x direction or the y direction, but the installation space is larger in the y direction where the distance between the z main coil and the z shield coil is wider than the x direction. Therefore, it is optimal to install in the y direction. In this embodiment, the loop wiring 27a is connected to the approximately solenoidal wiring in the region of z> 0, and the loop wiring 27b is connected to the approximately solenoidal wiring in the region of z <0. However, the loop wiring 27a is connected to z <0. The approximately solenoidal wiring in the region and the loop wiring 27b may be connected to the approximately solenoidal wiring in the region of z> 0, respectively. FIG. 12B shows a part of the conductor shape of the z shield coil of the present embodiment. As shown in FIG. 12A, the z shield coil is formed by a combination of a generally solenoid coil and a loop coil. The generally solenoid-like part can be structured such that the coolant 24 flows inside the conductor like the conductor 29. However, if the structure of the conductor 29 is used for the loop conductor 30 part, the conductor is spirally formed from the outside. Since the wiring intersects when it goes to the outside after winding and reaching the center, it cannot fit in the installation space of the gradient coil. Therefore, the loop coil is formed of a thin plate-like conductor from which a groove, which is a region where no current flows, is cut off. This is electrically joined with the solenoid coil to form a z shield coil. At that time, an insulating layer 31 is provided in the vicinity of the conductor 30 so that a current flows from the conductor 29 to the conductor 30. In this way, the portion of the z shield coil that has a generally solenoid shape is allowed to flow with a coolant therein to have a cooling function, and the portion that becomes the loop uses a thin conductor, so that the installation space for the gradient magnetic field coil is reduced. Can be afforded.

  According to the present embodiment, the wiring of the conductor can be simplified by forming the main coil of the z gradient magnetic field coil into a solenoid shape in which the current flow paths formed in the plane perpendicular to the z axis are stacked in the z direction. it can. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

(Example 2)
A horizontal magnetic field type MRI apparatus according to another embodiment of the present invention will be described below with reference to FIG.

  The MRI apparatus 100A of the present embodiment has a configuration in which the gradient magnetic field coil 2 in the MRI apparatus 100 of the first embodiment is replaced with a gradient magnetic field coil 2A. That is, in the first embodiment, a case has been described in which the cross-sectional shape of the gradient magnetic field main coil 9 in the gradient magnetic field coil 2 is elliptical and the cross-sectional shape of the gradient magnetic field shield coil 10 is circular. As shown in FIG. 13A, the magnetic field coil 2A has a configuration in which the gradient magnetic field main coil 9 has a racetrack shape and the gradient magnetic field shield coil 10 has a circular shape. Since the gradient magnetic field main coil 9 has a racetrack shape in which the major axis is in the x-axis direction and the minor axis is in the y-axis direction, the degree of openness of the MRI apparatus is further improved. In the gradient magnetic field coil 2A of this embodiment, the interval between the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10 varies depending on the circumferential direction, and the interval between the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10 on the x axis is y. The configuration is narrower than the interval on the shaft. Similarly, the interval between the z main coil and the z shield coil is different in the circumferential direction.

  FIG. 13 (a) shows the cross-sectional shape of the gradient magnetic field coil 2A of the present embodiment. The z gradient magnetic field coil obtained by this cross-sectional shape is the z main coil in FIG. 13 (b), and the z shield coil in FIG. 13 (c). The wiring pattern shown in FIG. In the present embodiment, like the first embodiment, the wiring pattern 17 of the z main coil can be formed in a solenoid shape in which current flow paths in a plane perpendicular to the z axis are stacked in the z direction. Similarly to the first embodiment, the z shield coil includes a wiring pattern 18 having a generally solenoid shape and a wiring pattern 19 forming a loop.

  According to the present embodiment, the wiring of the conductor can be simplified by forming the main coil of the z gradient magnetic field coil into a solenoid shape in which the current flow paths formed in the plane perpendicular to the z axis are stacked in the z direction. it can. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

(Example 3)
A horizontal magnetic field type MRI apparatus according to another embodiment of the present invention will be described below with reference to FIG.

  The MRI apparatus 100B of the present embodiment has a configuration in which the gradient magnetic field coil 2 in the MRI apparatus 100 of the first embodiment is replaced with a gradient magnetic field coil 2B. As shown in FIG. 14A, the gradient coil 2B of the present embodiment has a configuration in which the gradient magnetic field main coil 9 has a combined arc shape, and the gradient magnetic field shield coil 10 has a circular shape. The cross-sectional shape of the gradient magnetic field main coil 9 has an elliptical shape and a shape obtained by further combining an arc with the elliptical long axis portion (a shape obtained by combining a plurality of arcs having different curvatures). Thus, the gradient magnetic field coil 2B of the present embodiment also has a gap between the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10 that differs depending on the circumferential direction, and the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10 on the x-axis. Is smaller than the distance on the y-axis. Similarly, the interval between the z main coil and the z shield coil has a different shape in the circumferential direction.

  FIG. 14A shows the cross-sectional shape of the gradient magnetic field coil 2B of the present embodiment, and the z gradient magnetic field coil obtained by this cross-sectional shape is shown in FIG. 14B for the z main coil and in FIG. 14B for the z shield coil. A wiring pattern as shown in FIG. In the present embodiment, like the first embodiment, the wiring pattern 17 of the z main coil can be formed in a solenoid shape in which current flow paths in a plane perpendicular to the z axis are stacked in the z direction. Similarly to the first embodiment, the z shield coil includes a wiring pattern 18 having a generally solenoid shape and a wiring pattern 19 forming a loop.

  According to the present embodiment, the wiring of the conductor can be simplified by forming the main coil of the z gradient magnetic field coil into a solenoid shape in which the current flow paths formed in the plane perpendicular to the z axis are stacked in the z direction. it can. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

Example 4
A horizontal magnetic field type MRI apparatus according to another embodiment of the present embodiment will be described below with reference to FIG.

  The MRI apparatus 100C of the present embodiment has a configuration in which the gradient magnetic field coil 2 in the MRI apparatus 100 of the first embodiment is replaced with a gradient magnetic field coil 2C. As shown in FIG. 15, the gradient magnetic field coil 2C of the present embodiment has a circular shape in cross section of both the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10, but these circles are not concentric circles, but are circular. Has a shape that is shifted in the y-axis direction (the center position of the circle is different). The gradient coil 2C of the present embodiment also has a configuration in which the interval between the gradient magnetic field main coil 9 and the gradient magnetic field shield coil 10 differs depending on the circumferential direction. Similarly, since the cross-sectional shapes of the z main coil and the z shield coil of this embodiment are both circular but not concentric, the intervals between the z main coil and the z shield coil have different shapes in the circumferential direction. .

  FIG. 15A shows a cross-sectional shape of the gradient magnetic field coil 2C of the present embodiment. As for the z gradient magnetic field coil obtained by this cross-sectional shape, the z main coil is shown in FIG. 15B, and the z shield coil is shown in FIG. The wiring pattern shown in FIG. In the present embodiment, like the first embodiment, the wiring pattern 17 of the z main coil can be formed in a solenoid shape in which current flow paths in a plane perpendicular to the z axis are stacked in the z direction. The z shield coil includes a wiring pattern 18 having a generally solenoid shape and a wiring pattern 19 forming a loop.

  In Examples 1, 2, and 3, since the z main coil cross-sectional shape was symmetric with respect to the yz plane and the xz plane, there are two regions closest to the z shield coil, the + x direction and the −x direction. Although one or a plurality of wiring patterns 19 are formed in the region, in the present embodiment, the closest region between the z main coil and the z shield coil is one in the + y direction, and therefore the wiring pattern 19 is provided only in this region. Is formed.

  According to the present embodiment, the wiring of the conductor can be simplified by forming the main coil of the z gradient magnetic field coil into a solenoid shape in which the current flow paths formed in the plane perpendicular to the z axis are stacked in the z direction. it can. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

(Example 5)
A horizontal magnetic field type MRI apparatus according to another embodiment of the present invention will be described below with reference to FIG.

  The MRI apparatus 100B of the present embodiment has a configuration in which the gradient magnetic field coil 2 in the MRI apparatus 100 of the first embodiment is replaced with a gradient magnetic field coil 2D. As shown in FIG. 16A, the gradient magnetic field coil 2D of the present embodiment has a configuration in which the cross-sectional shape of the gradient magnetic field main coil 9 is a combination of elliptical arcs, and the gradient magnetic field shield coil 10 is circular. Have. The gradient magnetic field main coil 9 has a cross-sectional shape in which an upper ellipse and a lower ellipse are different. As in this embodiment, the upper elliptical shape is made larger than the lower elliptical shape (in the cross-sectional shape shown in FIG. 16A, the opening area in the positive region is made larger than the negative region of the y-axis). By this, the area through which the subject 40 can pass can be widened.

  FIG. 16A shows a cross-sectional shape of the gradient magnetic field coil 2D of the present embodiment. The z gradient magnetic field coil obtained by this cross-sectional shape is the z main coil in FIG. 16B, and the z shield coil in FIG. 16B. A wiring pattern as shown in FIG. In the present embodiment, like the first embodiment, the wiring pattern 17 of the z main coil can be formed in a solenoid shape in which current flow paths in a plane perpendicular to the z axis are stacked in the z direction. Similarly to the fourth embodiment, the z shield coil includes a wiring pattern 18 having a generally solenoid shape and a wiring pattern 19 forming a loop. The wiring pattern 19 is formed only at one place in the + y direction.

  According to the present embodiment, the wiring of the conductor can be simplified by forming the main coil of the z gradient magnetic field coil into a solenoid shape in which the current flow paths formed in the plane perpendicular to the z axis are stacked in the z direction. it can. In addition, the solenoid coil is easy to manufacture because the z position of the conductor is constant in the circumferential direction except for the connection portion between adjacent wiring patterns. Furthermore, since the distortion of the magnetic field distribution created by the main coil in the imaging region is reduced, cross-sectional information can be obtained with high accuracy during imaging.

DESCRIPTION OF SYMBOLS 1 Static magnetic field coil 2 Gradient magnetic field coil 3 RF coil 4 Helium container 5 Radiation shield 6 Vacuum container 7 Imaging space 8 Static magnetic field 9 Gradient magnetic field main coil 10 Gradient magnetic field shield coil 11 of z main coil of the comparative example whose cross-sectional shape is circular Wiring pattern 12 Wiring pattern 13 of the comparative example z-shield coil having a circular cross-sectional shape The main coil cross-sectional shape is elliptical and the shielding coil cross-sectional shape is a circular shape. Wiring pattern 14 that forms a coil Wiring pattern 15 that forms a loop coil out of the conductor centerline of the z main coil of the comparative example in which the cross-sectional shape of the main coil is elliptical and the cross-sectional shape of the shield coil is circular. The cross-sectional shape of the main coil is elliptical. The z-shield coil of the comparative example having a circular shield coil cross-sectional shape Wiring pattern 16 for forming an approximately solenoidal coil among the center lines. Wiring pattern 17 for forming a loop coil among the conductor center lines of the z shield coil of the comparative example in which the main coil cross-sectional shape is elliptical and the shield coil cross-sectional shape is circular. The wiring pattern 18 indicated by the conductor center line of the z main coil The wiring pattern 19 that forms the loop coil of the conductor center line of the z shield coil The wiring pattern 20 z that forms the generally solenoidal coil of the conductor center line of the z shield coil Main coil connection wiring 21 z Main coil solenoid-like coil wiring 22 z Main coil connection wiring 23 z Main coil solenoid-like coil conductor 24 z Gradient magnetic field coil inside the conductor 25 z shield Coil connection wiring 26 z Soleno of the main coil Wiring 27 for forming an id-shaped coil 28 Wiring for forming a loop coil of the z main coil 28 Connecting wiring for the z shield coil 29 Conductor 30 for forming the solenoidal coil of the z shield coil Conductor (loop for forming the loop coil of the z shield coil conductor)
31 z shield coil insulation layer

Claims (6)

A ring-shaped static magnetic field coil for generating a static magnetic field;
A bed apparatus for moving the ring-shaped opening of the static magnetic field coil;
A horizontal magnetic field type magnetic resonance imaging apparatus including a gradient magnetic field coil that generates a gradient magnetic field with a gradient magnetic field strength,
The gradient coil is
A gradient magnetic field main coil for generating the gradient magnetic field in the imaging space;
A gradient magnetic field shield coil that suppresses leakage of the generated gradient magnetic field outside the gradient coil;
An interval between the gradient magnetic field main coil and the gradient magnetic field shield coil is arranged to be different in the circumferential direction,
A solenoid in which a z-gradient magnetic field main coil for generating the gradient magnetic field has a current flow path in a plane perpendicular to the z-axis and is stacked in the z-axis direction in the z-axis direction that is the traveling direction of the bed apparatus. A horizontal magnetic field type magnetic resonance imaging apparatus characterized by being a coil-like coil.   2. The horizontal magnetic field type according to claim 1, wherein the gradient magnetic field shield coil has a z gradient magnetic field shield coil that suppresses a gradient magnetic field generated by the z gradient magnetic field coil from leaking outside the gradient magnetic field coil. Magnetic resonance imaging equipment.   The z-gradient magnetic field shield coil is formed in a saddle shape near the center of the magnetic resonance imaging apparatus in the z-axis direction, and is generally a solenoid that meanders around the z-axis on a cylindrical surface outside the region formed in the saddle shape. The horizontal magnetic field type magnetic resonance imaging apparatus according to claim 2, further comprising a wiring pattern formed in a shape.   The z gradient magnetic field shield coil is, in order along the traveling direction of the bed apparatus, a wiring portion formed in a generally solenoid shape meandering around the z axis on a cylindrical surface, a wiring portion formed in a saddle shape, The horizontal magnetic field type magnetic resonance imaging apparatus according to claim 2, further comprising a wiring portion formed in a substantially solenoid shape that meanders around the z-axis on the cylindrical surface.   The horizontal magnetic field type magnetic resonance imaging according to any one of claims 1 to 4, wherein the z-gradient magnetic field main coil is formed of a hollow cylindrical conductor having a flow path for flowing a refrigerant therein. apparatus. The substantially solenoidal wiring portion of the z gradient magnetic field shield coil is constituted by a hollow cylindrical conductor having a flow path for flowing a refrigerant therein, and the saddle-shaped wiring portion of the z gradient magnetic field shield coil is a plate-like conductor. Consists of
6. The horizontal magnetic field type magnetic resonance imaging apparatus according to claim 4, wherein the generally solenoid-like wiring portion and the saddle-like wiring portion are electrically joined.

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