JP2007159741A - Magnetic resonance imaging apparatus and electromagnet device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconducting magnet apparatus generating a magnetic fields in apparatuses such as a magnetic resonance imaging apparatus (an MRI apparatus) which generates a large static magnetic field having high uniformity and high strength and provides a large effective space for receiving a subject. <P>SOLUTION: Each of main coils (20) located in the vicinity of the effective space receiving a subject has a shape that its minimum inside diameter and maximum inside diameter crosses at right angles and in the middle of themselves (a race track shape or the like). The main coils (20) includes at least inner coils (22) and outer coils (21). Oblateness of the inner coils (22) are larger than that of the outer coils (21). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus) and an electromagnet apparatus, and in particular, a plurality of pairs of annular coils are axially separated in a cylindrical vacuum vessel and imaged at an opening of the vacuum vessel. The present invention relates to a magnetic resonance imaging apparatus and an electromagnet apparatus called a horizontal magnetic field type that forms a magnetic field.

  In recent years, taking a tomographic image of a human body with an MRI (Magnetic Resonance Imaging) apparatus and using it for diagnosis has been widely performed. The principle of capturing a tomographic image with this MRI apparatus is to apply a static magnetic field to a diagnosis part of a subject and further apply a specific high-frequency magnetic field to the part to utilize a resonance phenomenon that occurs.

Therefore, in order to obtain a wide range of tomographic images without distortion and flickering with an MRI apparatus, a static magnetic field that is sufficiently strong and highly uniform to generate a resonance phenomenon is formed over a wide range in the imaging region. It is required to be done.
In order to form such a static magnetic field, the conventional MRI apparatus has a configuration in which a plurality of circular superconducting coils are arranged in a plurality of stages with the central axes aligned. In this way, a horizontal magnetic field type MRI apparatus configured such that a subject is inserted into an air core portion formed by arranging a plurality of superconducting coils in a horizontal direction, or a plurality of superconducting coils in a vertical direction. An open type MRI apparatus configured such that a subject is inserted between coils facing each other is disclosed as a known technique (for example, Patent Document 1).

  In the horizontal magnetic field type MRI apparatus, in order to obtain a wide range of human tomographic images with high image quality as described above, the air core portion formed by arranging the circular superconducting coils has a long distance between both ends and a small radius. It is desirable to be configured. Accordingly, the horizontal magnetic field type MRI apparatus is unavoidably configured such that the size of the bore into which the subject to be imaged enters is smaller than the size of the air core portion of the superconducting coil. Further, considering that the MRI apparatus is separately provided with a superconducting coil cooling container, a gradient magnetic field coil for generating a gradient magnetic field, and a magnetic body for correcting a static magnetic field, a horizontal magnetic field type MRI apparatus It is generally difficult to ensure a sufficiently large bore size.

For this reason, in a conventional horizontal magnetic field type MRI apparatus constituted by a circular superconducting coil, when MRI imaging is performed, the subject feels a blockage entering the bore, and a laboratory technician or doctor accesses the subject. There are specific problems that are difficult to do.
Since the open MRI apparatus has a structure that allows a wide space for the subject to enter, the problems peculiar to the horizontal magnetic field MRI apparatus described above are solved. However, the open MRI apparatus has problems that the structure is complicated and the manufacturing cost is increased, and that it is difficult to generate a high-intensity magnetic field in the imaging region.
On the other hand, in a horizontal magnetic field type MRI apparatus, as a means for solving the above problem, a method of expanding the bore shape from a conventional circle to the side can be considered. In order to realize this, the superconducting coil is also required to have a non-circular shape. As an example of the MRI apparatus using a non-circular coil, in Non-Patent Documents 1 and 2, in order to realize a uniform magnetic field by an elliptical coil. Is being studied.
JP-A-9-153408 Japanese Patent Laid-Open No. 2001-112737 Stuart Crozier et. Al. “A novel, open access, elliptical cross-section magnet for paediatric MRI” Meas. Sci. Technol. 9 (1998) 113. Huawei Zhao and Stuart Crozier “An inverse design method for elliptical MRI magnets” Meas. Sci. Technol. 12 (2001) 566.

In Non-Patent Document 1 and Patent Document 2, since only elliptical coils having the same flatness are used, sufficient performance cannot be achieved in terms of uniformity and size. On the other hand, in Non-Patent Document 2, the coil shape is determined by obtaining a continuous current density that realizes a uniform magnetic field and then discretizing it. Since a slight change in flatness is allowed in the process of discretization, a large number of coils with slightly different flatness are mixed. However, in this method, since the number of coils is determined based on a continuous current density distribution, the resulting structure has a large number of coils and tends to be complicated. As a result, the cost required for the wire rod and the support structure also increases.
In addition, although the elliptical coil is advantageous in the calculation of the magnetic field, it is not necessarily the optimum shape in order to secure a space for the horizontally long bore.

  It is an object of the present invention to make the static magnetic field more uniform in the imaging region with a small number of coils, increase the magnetic field strength, generate a wide static magnetic field, and widen the effective space in which the subject enters. A resonance imaging apparatus and an electromagnet apparatus are provided.

In order to achieve the above-described object, the present invention provides that the plurality of main coils included in the plurality of annular coils surrounding the air core portion are more than the first distance between the coil portions facing each other in the vertical direction across the air core portion. A longitudinal section perpendicular to the axis of the air core part of the plurality of main coils, the second distance between the coil parts facing in the horizontal direction perpendicular to the axis of the air core part across the air core part is increased. The surface has a racetrack shape, and the plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core. , Wherein the first distance is a, the second distance is b, and (ba) / b is defined as the flatness, the flatness of the inner coil is larger than that of the outer coil.
By configuring the invention in this way, the cross section of the air core portion has a racetrack shape, and the effective space for entering the subject placed in a static magnetic field is expanded. Furthermore, since the flatness defined as described above of the inner coil is larger than that of the outer coil, the static magnetic field can be made more uniform. Furthermore, the magnetic field strength can be improved in the imaging space, and the magnetic field strength distribution can be made more uniform.

  Preferably, the symmetry of the intensity distribution of the magnetic field formed around the center is maintained to some extent, and correction of such an intensity distribution is facilitated by appropriately adjusting the shape / arrangement of the coil and the flowing current. In addition, preferably, either one of the inner coil and the outer coil alone cannot make the static magnetic field uniform, but by combining both coils and appropriately adjusting the respective coil shape and flowing current, This static magnetic field can be made uniform. Specifically, the uniformity of the static magnetic field is such that the flatness of the inner coil is larger than that of the outer coil, or a pair of correction coils in which a reverse current flows at the boundary between the outer coil and the inner coil is further arranged. It will be improved by doing.

  Specifically, the racetrack-shaped coil has a plurality of main coils included in the plurality of annular coils, and the air core is more than the first distance between the coil portions facing each other in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the horizontal direction perpendicular to the axis of the air core portion with the portion interposed therebetween is increased, and these main coils are opposed to each other in the vertical direction. A coil portion and a second coil portion, and the first coil portion and the second coil portion are sandwiched between the pair of first curved portions and the pair of first curved portions in the horizontal direction, respectively. It is formed by either a straight line part or a second curve part connected to the first curve part.

  Further, the racetrack-shaped coil, specifically, the plurality of main coils included in the plurality of annular coils is more than the first distance between the coil portions opposed in the vertical direction across the air core portion. The second distance between the coil portions opposed in the horizontal direction perpendicular to the axis of the air core portion with the air core portion interposed therebetween is increased, and these main coils are opposed in the vertical direction in the horizontal direction. A pair of first coil portions in which one of the straight line portion and the first curved portion is formed, and a pair of first coil portions are connected to each other to form a second curved portion in the vertical direction so as to face each other in the horizontal direction. It can be said that it has a pair of 2nd coil parts.

  According to the present invention, by combining coils having racetrack-like shapes with different flatness ratios, the static magnetic field can be made more uniform, the magnetic field strength can be increased, and a wide static magnetic field is generated in the air core part. The effective space where the subject enters can be widened.

<First Embodiment>
A magnetic resonance imaging apparatus (MRI apparatus: not shown) according to a preferred embodiment of the present invention will be described with reference to FIGS. The MRI apparatus according to the present embodiment includes a gantry 1 as shown in FIG. The gantry 1 includes a superconducting magnet device (electromagnet device) 10 as shown in FIG. Such a gantry 1 is formed with a bore (air core portion) B which is an opening into which a bed on which a subject is placed is inserted, and the vacuum container 11 (FIG. 2) of the superconducting magnet device 10. The inside, outside and sides are covered with a cover. The cover of the gantry 1 has an inner cover 2, an outer cover 3, and a pair of side covers 4. This will be described with reference to FIGS. The inner cover 2 covers the inner side of the inner cylinder 13. The outer cover 3 is disposed outside the outer cylinder 14 of the vacuum vessel and surrounds the outer cylinder 14. The side covers 4 that face each other and cover the side plate 15 are attached to the end portions of the inner cover 2 and the outer cover 3, respectively. The bore B is a through hole.

The vacuum vessel 11 provided in the superconducting magnet device 10 has an annular vacuum vessel 11 whose outer appearance surrounds the bore B. As shown in FIG. 2, the vacuum container 11 includes an inner cylinder 13, an outer cylinder 14, and a pair of side plates 15. The outer cylinder 14 surrounds the inner cylinder 13, and an annular space is formed between the inner cylinder 13 and the outer cylinder 14. The pair of side plates 15 are attached to both ends of the inner cylinder 13 and the outer cylinder 14 to seal the annular space. This annular space is a vacuum atmosphere.
The bore B and the vacuum vessel 11 extend in the horizontal direction (first horizontal direction).

In addition to the superconducting magnet device 10, the MRI apparatus according to the present embodiment includes a bed for placing a subject, a detector for detecting a nuclear magnetic resonance signal from the subject, a detected nucleus, not shown. It includes a computer that processes magnetic resonance signals, a display device that displays tomographic images based on the processed nuclear magnetic resonance signals, and the like.
The MRI apparatus configured in this manner uses the nuclear magnetic resonance phenomenon to image the distribution of water and fat of the subject (actually protons of hydrogen nuclei contained therein), and captures a tomographic image of an arbitrary cross section. Is something that can be done.
In the following, as shown in FIG. 2, a coordinate system having the origin at the center of the bore B (air core portion) is defined. As shown in FIGS. 2 and 3, the axial direction penetrating the vacuum vessel 11 is the Z axis, and among the axes orthogonal to the axial direction, the vertical direction is the X axis and the vertical direction is the Y axis.

  A subject enters the bore B, and a tomographic image is taken in the central imaging region R. The shape of the XY cross section of the bore B is a racetrack shape similar to the main coil 20 described later (see FIG. 5).

  The vacuum vessel 11 includes therein a superconducting coil 12 shown in FIG. 3, a coil cooling vessel (not shown), a high-frequency magnetic field applying means, a gradient magnetic field coil, and a magnetic body. Here, the superconducting coil 12 forms a static magnetic field in the bore (air core portion) B. The coil cooling container cools the superconducting coil 12 so that the superconducting state of the superconducting coil 12 is maintained. The high frequency magnetic field applying means generates a nuclear magnetic resonance signal by irradiating a subject with a radio wave (high frequency magnetic field). The gradient magnetic field coil gives a magnetic field gradient to the static magnetic field and gives positional information necessary for imaging to the generated nuclear magnetic resonance signal. The magnetic body is appropriately disposed to correct the magnetic field so that a uniform static magnetic field is formed in the imaging region R.

  The superconducting coil 12 is arranged inside the vacuum vessel 11 so that a plurality of racetrack-shaped coils surround the outer periphery of the bore B with the Z axis as a common central axis. The superconducting coil 12 is roughly classified into a main coil 20 and a shield coil 30. With such a configuration, the superconducting coil 12 is configured such that the position, size, and flowing current of the plurality of coils are appropriately set, thereby forming a uniform and high-intensity static magnetic field in the imaging region R. This prevents the magnetic field from leaking outside the conductive magnet device 10.

  The main coil 20 is disposed close to the outer periphery (inside the vacuum vessel 11) of the bore B (see FIG. 2) at a predetermined interval so as to be orthogonal to the Z axis that is a common central axis. With this configuration, the shape of the main coil 20 determines the shape of the XY cross section of the bore B. Note that the magnetic field formed by the main coil 20 penetrates the bore B and leaks to the outside of the superconducting magnet device 10.

  The shield coil 30 has a central axis (Z axis) common to the main coil 20, and is formed so that the inner diameter intersecting with the Z axis is larger than the inner diameter of the main coil 20. That is, the main coil 20 is configured to be included in the air core formed by the shield coil 30. The shield coil 30 functions to suppress the leakage magnetic field as much as possible when a current flows in a direction to cancel the magnetic field leaked to the outside. Note that the shape of the shield coil 30 may be a racetrack shape or a conventional circular shape.

The main coil 20 further includes an outer coil 21 and an inner coil 22.
The outer coil 21 is arranged at both ends of the group of the inner coils 22 and is composed of a pair of coils in which a forward current that determines the magnetic field direction (Z-axis direction) of the static magnetic field flows and has the same shape. In FIG. 4, a coil pair including the first outer coil 21 a and the second outer coil 21 b is illustrated, but there may be a case where the number of stages is further increased outward.
The inner coil 22 is arranged at the center of the bore (air core part) B, and a forward current that determines the magnetic field direction (Z-axis direction) of the static magnetic field flows through the plurality of or single coils having the same shape. It will be. In FIG. 3, a coil composed of two coils, a first inner coil 22a and a second inner coil 22b, is illustrated. However, the number of coils constituting the inner coil 22 is not limited to two, and includes one case and three or more cases.

  Next, the shape of the main coil 20 will be described using the outer coil 21 as an example with reference to FIG. The outer coil 21 has a horizontal direction (hereinafter simply referred to simply as the bore B axis (Z-axis)) with the inner cylinder 13 interposed therebetween, rather than a first distance between the coil portions opposed vertically in the inner cylinder 13. The second distance between the coil portions facing each other in the second horizontal direction) is increased. The outer coil 21 includes a pair of first coil portions (a straight portion ef and a straight portion hi) that face each other in the vertical direction, and a pair of second coil portions (the arc portions ed) that face each other in the second horizontal direction. -I and circular arc part fgh). The first coil portion is formed in the second horizontal direction, and the second coil portion is formed in the vertical direction. Each first coil portion is connected to each second coil portion. The arc part ed-i and the arc part fgh are semicircles having centers O1 and O2 at positions shifted in the second horizontal direction from the axis O of the bore B.

  Further, the outer coil 21 includes a first coil portion, an arc portion g-h, and a linear portion hi that are formed by the arc portion de, the linear portion ef, and the arc portion vg in the second horizontal direction. It can also be said that it has the 2nd coil part formed of circular arc part id. The first coil portion and the second coil portion are arranged to face each other in the vertical direction, and are connected by an arc portion de and arc portion id, and are connected by an arc portion f-g and an arc portion gh. Yes. The straight line portion ef is disposed between the circular arc portion de and the circular arc portion f-g, and is connected to these circular arc portions. The straight line part h-i is disposed between the arc part g-h and the arc part id, and is connected to these arc parts.

The inner coil 22 has the same configuration as the outer coil 21. The outer coil 21 and the inner coil 22 have a racetrack shape as described above.
Each of the main coils 20 has a racetrack shape as described above, but there may be some modifications to make it an advantageous shape for actual production. Comparing an elliptical coil inscribed in a rectangle of the same size with a racetrack-shaped coil, the cross-sectional area, that is, the portion corresponding to the bore into which the subject enters, has a wider racetrack-like shape, and the degree of openness From the viewpoint of

  In a racetrack-shaped coil, the distance between the coil parts facing each other in the second horizontal direction is b (see FIG. 5), and the distance between the coil parts facing each other in the vertical direction is a (see FIG. 5). (Ba) / b defines the flatness of the coil as (ba) / b, which is used as an index representing the deviation of the shape of the racetrack from the circular shape. In the present embodiment, the flatness defined above of the inner coil 22 is larger than that of the outer coil 21.

  As described above, since all the main coils 20 (20 ′) have a flat racetrack shape, the XY cross section of the bore B can be formed in such a flat shape. As a result, the space in the second horizontal direction of the bore B is expanded, so that the effective space is expanded, and the feeling of opening received by the subject entering there is also improved.

By the way, unlike the circular coil conventionally used, either the outer coil 21 or the inner coil 22 is independent, and the Z axis on the XY cross section of the static magnetic field formed in the imaging region R (see FIG. 3). The surrounding rotational symmetry is naturally lost. This is because a non-circular coil has a strong magnetic field and a weak magnetic field even if the distance from the Z axis is the same because the distance and curvature of the Z axis differ from coil to coil. is there.
Thus, when the magnetic field intensity distribution in the imaging region R is non-uniform, the obtained tomographic image has a low image quality. Therefore, it is necessary to correct this non-uniformity and make the magnetic field strength distribution in the imaging region R uniform.
By the way, the superconducting magnet device 10 using the racetrack-shaped coil has an inherent problem that the magnetic field strength with respect to the XY section is non-uniform as described above. It also has directional inhomogeneities and must be corrected so that the uniformity of these two magnetic field strengths is achieved simultaneously.

  Therefore, in the following explanation, the inner coil 22 is configured to have a higher flatness than the outer coil 21, so that the asymmetry of the mutual magnetic field strength is canceled and corrected and formed in the imaging region R. It will be shown that the non-uniformity of the applied magnetic field is eliminated. Although explanation is omitted, magnetic field inhomogeneity can be similarly eliminated by appropriately adjusting the current values flowing through the outer coil 21 and the inner coil or adjusting the arrangement of the two. is there.

  First, it will be verified that the magnetic field distribution of the XY cross section in the imaging region R is corrected. Here, the main coil 20 having the racetrack shape shown in FIG. 5 will be described as an example.

  First, as shown in FIG. 6A, the magnetic field strength distribution in the XY section in the imaging region R is considered for the magnetic field formed solely by the outer coil 21. Here, point a and point c on the outer circumferential arc on the XY cross section of the imaging region R indicate points on the curve side of the outer coil 21, and point b indicates a point on the straight line side. At this time, the magnetic field intensity distribution on the arc connecting the points a, b, and c is schematically a concave curve shown in FIG. 6B, and the magnetic fields at the points a and c are more relative to the point b than the point b. Thus, the distribution of the magnetic field strength is large.

  Next, as shown in FIG. 7A, the magnetic field strength distribution of the XY cross section in the imaging region R is considered for the magnetic field formed solely by the inner coil 22. Here, points a and c on the outer peripheral arc on the XY cross section of the imaging region R indicate points close to the curve side of the inner coil 22, and point b indicates a point on the straight line side. At this time, the magnetic field strength distribution on the arc connecting point a, point b, and point c is schematically a convex curve shown in FIG. 7B, and the magnetic fields at points a and c are relatively relative to point b. The distribution of magnetic field strength is small.

  Thus, in the XY cross section of the imaging region R, the magnetic field strengths of the magnetic fields separately formed by the outer coil 21 and the inner coil 22 are reversed. Therefore, as a result, by combining the two coils of the outer coil 21 and the inner coil 22, the magnetic field around the Z-axis of the imaging region R is obtained by adding the two magnetic field distributions to cancel each other's non-uniform components. As a result, the non-uniformity of the magnetic field in the XY cross section is eliminated.

Next, the reason why the preferable results as described above can be obtained when the flatness of the outer coil 21 and the inner coil 22 are different will be examined.
Here, it is assumed that the flatness of the outer coil 21 and the inner coil 22 is approximately the same. In this case, in the magnetic field strength distribution of the inner coil 22 shown in FIG. 7B, the difference in magnetic field strength between the points a (or c) and b is the magnetic field of the outer coil 21 shown in FIG. It becomes smaller compared with the intensity difference in the intensity distribution.
However, by increasing the length b of the maximum inner diameter of the inner coil 22 in comparison with the maximum inner diameter of the outer coil 21, the magnetic field intensity distribution is canceled by weakening the magnetic field from the curved side of the inner coil 22. It becomes like this. That is, the inner coil 22 is formed to have a higher flatness than the outer coil 21 (large deviation from the circle) is a preferable configuration for forming a uniform magnetic field.

  Next, it will be verified that the magnetic field distribution in the Z-axis direction is corrected with reference to FIGS. In general, in the case of a circular coil, the magnetic field formed on the Z axis by a pair of coils 21a and 21b arranged along the Z axis as shown in FIG. 8A is when the distance between both coils is longer than the coil radius. It is known that there are two local maximum points of magnetic field strength. On the other hand, when the distance between the two coils is shorter than the coil radius, it is known that the magnetic field becomes maximum at the center of the two coils 22a and 22b as shown in the magnetic field strength curve shown in FIG.

  Such a property is considered to be the same for a general non-circular coil. For example, according to the arrangement of the main coil 20 as shown in FIG. 9, the magnetic field distribution formed by the outer coil 21 arranged at the interval L1 is obtained. When the simulation is performed by calculation, the same result as in the case of the circular coil shown in FIG. Further, when the magnetic field distribution formed by the inner coil 22 arranged at the interval L2 is simulated by calculation, the same result as in the case of the circular coil shown in FIG. 7B is obtained.

  Therefore, when the main coil 20 is arranged as shown in FIG. 9, the magnetic field distribution formed by the outer coil 21 is strongest on both sides so that the center is a valley as shown in FIG. 8A. The magnetic field generated by the inner coil 22 has a distribution that is strongest at the center as shown in FIG. 8B, and by adding these, a uniform magnetic field is formed over the entire Z-axis direction of the imaging region R. In this way, non-uniformity of the magnetic field distribution in the Z-axis direction can be eliminated by combining two or more sets of coils.

  However, unlike the circular coil conventionally used, the non-circular coil as shown in FIG. 5 is restricted in its arrangement in order to eliminate such non-uniformity of the magnetic field distribution in the Z-axis direction. There is a case. This is because, in the case of only a circular coil, the magnetic field around the Z axis is always a symmetric magnetic field, so the coil interval can be freely adjusted so that the magnetic field is uniform in the direction along the Z axis. it can. However, in the case of a non-circular coil, changing the coil interval to eliminate non-uniformity in the Z-axis direction affects the magnetic field distribution in the XY cross section. As described above, in the non-circular coil, the degree of freedom of the coil position arranged on the Z-axis is restricted as compared with the case where the circular coil is used, so it is necessary to compensate by increasing the number of coils as necessary. .

Second Embodiment
Next, the MRI apparatus of 2nd Embodiment which is other embodiment of this invention is demonstrated. In the MRI apparatus of this embodiment, a main coil 20 ′ shown in FIGS. 10 and 11 is arranged in a vacuum vessel 11. The main coil 20 ′ is obtained by adding a correction coil 23 to the main coil 20 described above. Specific differences in configuration between the main coil 20 ′ shown in the second embodiment and the main coil 20 (see FIGS. 4 and 9) shown in the first embodiment are as follows. That is, the racetrack-shaped correction coil 23 is disposed between the outer coil 21 and the inner coil 22. The correction coil 23 also has a racetrack shape shown in FIG. The correction coil 23 also surrounds the bore B. Also in this embodiment, the flatness defined in the first embodiment of the inner coil 22 is larger than that of the outer coil 21.

  That is, the correction coil 23 is arranged such that a pair of coils (first correction coil 23a and second correction coil 23b) having the same shape are orthogonal to each other with the Z axis as a common central axis. The first correction coil 23 a and the second correction coil 23 b are arranged so as to sandwich the inner coil 22, and the outer coil 21 is further arranged outside thereof. Further, a current flows through the correction coil 23 in the direction opposite to the outer coil 21 and the inner coil 22.

  Next, referring to FIG. 12, the effect of the correction coil 23 on the magnetic field formed in the imaging region R will be verified. Here, FIG. 12A is the same graph as FIG. 6B and shows the magnetic field strength distribution of the XY cross section formed by the outer coil 21 alone. FIG. 12B is the same graph as FIG. 7B and shows the magnetic field strength distribution in the XY section formed by the inner coil 22 alone. FIG. 12D is the same graph as FIG. 8A and shows the magnetic field strength distribution on the Z-axis formed by the outer coil 21 alone. FIG. 12E is the same graph as FIG. 8B and shows the magnetic field strength distribution on the Z-axis formed by the inner coil 22 alone.

FIG. 12C shows the magnetic field strength distribution on the XY cross section formed by the correction coil 23 alone. The magnetic field strength distribution on the XY cross section formed by the correction coil 23 is characterized in that the magnetic field strength distribution having a sharp single peak having a convex shape shown in FIG. It shows that the shape is reduced.
Here, when verifying the effect of homogenizing the magnetic field on the XY cross section in the first embodiment, the magnetic field intensity distribution shown in FIG. 12A, which is a single peak having a sharp concave shape, and a broad convex shape. When the magnetic field intensity distribution shown in FIG. 12B, which is a single peak of the above, is added, the magnetic field inhomogeneity is certainly improved, but still fluctuations cannot be completely eliminated. .
In the second embodiment, as shown in FIG. 12C, the magnetic field strength distributions obtained by reversing such fluctuations are added, so that the complete uniformity of the magnetic field strength distribution on the XY cross section is obtained. Will be achieved.

FIG. 12F shows the magnetic field strength distribution on the Z-axis that the correction coil 23 independently creates. The characteristic of the magnetic field strength distribution on the Z-axis formed by the correction coil 23 is that the double peak is narrower than that shown in FIG. That is, it shows a simple shape.
Here, when verifying the effect of homogenizing the magnetic field on the Z-axis in the first embodiment, the magnetic field strength distribution shown in FIG. 12 (d), which is a sharp double peak of the convex shape, and the sharp shape of the convex shape. When the magnetic field strength distribution shown in FIG. 12 (e), which is a single peak, is added, the magnetic field strength non-uniformity is certainly improved, but still fluctuations cannot be completely eliminated. .
In the second embodiment, as shown in FIG. 12 (f), the magnetic field strength distributions obtained by reversing such fluctuations are added, so that the complete uniformity of the magnetic field strength distribution on the Z axis is obtained. Will be achieved.

In this way, the correction coil 23 through which a reverse current flows effectively acts to further improve the uniformity of the magnetic field generated jointly by the outer coil 21 and the inner coil 22 in the imaging region R.
In addition, although the correction coil 23 is arrange | positioned 1 each in the boundary of the outer side coil 21 and the inner side coil 22 in FIG. 10, multiple may be arrange | positioned suitably.

  As described above, in the present invention, in order to expand the effective space of the bore (air core portion) B, the shape of the main coil 20 adjacent to the bore B is made noncircular. Then, the problem of non-uniformity of the magnetic field strength of the static magnetic field in the imaging region R, which is derived by adopting such a non-circular coil, has been solved by adjusting the shape, arrangement, and current of the non-circular coil.

And the superconducting magnet apparatus 10 which concerns on this invention can also aim at the improvement of intensity | strength, maintaining the uniformity of a static magnetic field by making the amount of electric currents sent through these main coils 20 increase suitably. Furthermore, the superconducting magnet device 10 according to the present invention can appropriately set the range of such a high uniform and high strength static magnetic field by appropriately adjusting the quantity and arrangement of the main coils 20. The imaging region R can be expanded.
This embodiment can also obtain the effects produced in the first embodiment.

<Third Embodiment>
In each of the above-described embodiments, the outer surface of the bore B, that is, the inner surface of the inner cover 2 is connected to the pair of first surfaces and the pair of first surfaces that form a straight portion in the second horizontal direction. Thus, the present invention relates to an MRI apparatus using a gantry that includes a pair of second surfaces that face the second horizontal direction and form an arc portion in the axial direction. The configuration of another MRI apparatus in which the shape of the inner surface of the inner cover is changed will be described below with reference to FIG.

  The MRI apparatus 25 shown in FIG. 13A includes a gantry 1A. The gantry 1A has a superconducting magnet device, and covers the surface of the vacuum container 11 of the superconducting magnet device with a cover. The cover includes a cylindrical outer cover 3, a cylindrical inner cover 2 </ b> A, and a pair of side covers 4. The inner cover 2A is located inside the vacuum vessel and covers the inner surface of the vacuum vessel, and the bore B is formed by the inner surface 5A.

  The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surface 5A of the inner cover 2A will be described. The distance between the inner surfaces 5A facing in the second horizontal direction (the width of the bore B) of the inner cover 2A is longer than the distance between the inner surfaces 5A facing each other in the vertical direction. The inner surface 5A includes a pair of first surfaces (curved part ef and curved part hi) facing in the vertical direction, and a pair of second surfaces (circular arc part edi and Arc portion f-g-h). The first surface is formed in the second horizontal direction, and the second surface is formed in the vertical direction. The pair of first surfaces are connected to the pair of second surfaces, respectively. The arc part ed-i and the arc part fgh are semicircles having centers O1 and O2 at positions shifted from the axis O of the bore B in the second horizontal direction. The curved part ef and the curved part hi are arc parts having a larger curvature (radius) than the arc part ed-i and the circular arc part fgh, for example.

  In addition, the inner surface 5A has a first surface and an arc portion g-h, a curve portion hi, and an arc formed by the arc portion de, the curve portion ef, and the arc portion vg in the second horizontal direction. It can also be said that it has the 2nd surface formed by the part id. The first surface and the second surface are disposed so as to face each other in the vertical direction, and are connected by the arc part de and the arc part id, and are connected by the arc part f-g and the arc part gh. The curved line part ef is arranged between the circular arc part f-g and the circular arc part de, and is connected to these circular arc parts. The curved line part h-i is disposed between the arc part g-h and the arc part id, and is connected to these arc parts.

The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surface of the inner cylinder of the vacuum vessel used in the MRI apparatus 25 is similar to that of the inner surface 5A.
An MRI apparatus 25A shown in FIG. 13B includes a gantry 1B. The gantry 1B uses a cover having an inner cover 2B as a cover that covers the surface of the vacuum vessel.

  The vertical cross-sectional shape orthogonal to the axis of the bore B of the inner surface 5B of the inner cover 2B will be described. The distance between the inner surfaces 5B facing each other in the second horizontal direction is longer than the distance between the inner surfaces 5B facing each other in the vertical direction. The inner surface 5B is formed of a pair of first surfaces (surfaces formed by a curved portion de, a straight portion ef, and a curved portion vg, a curved portion hi, and a straight portion i-) that face each other in the vertical direction. j and the surface formed by the curved portion jk) and a pair of second surfaces (a straight portion dk and a straight portion gh) facing in the second horizontal direction. The pair of first surfaces formed in the second horizontal direction is connected to the pair of second surfaces formed in the vertical direction. The curved portion in the present embodiment is, for example, an arc portion.

The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surface of the inner cylinder of the vacuum vessel used in the MRI apparatus 25B is similar to that of the inner surface 5B.
An MRI apparatus 25B shown in FIG. 13C includes a gantry 1C. The gantry 1CB uses a cover having an inner cover 2C as a cover that covers the surface of the vacuum vessel.

  The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surface 5C of the inner cover 2C will be described. The distance between the inner surfaces 5C facing each other in the second horizontal direction is longer than the distance between the inner surfaces 5C facing each other in the vertical direction. The inner surface 5C includes a pair of first surfaces (curved portion ef and curved portion hi) facing in the up-down direction and a pair of second surfaces (curved portion ed-i and Curve portion f-g-h). The pair of first surfaces formed in the second horizontal direction is connected to the pair of second surfaces formed in the vertical direction. The curved portion in the present embodiment is, for example, an arc portion.

  Further, the inner surface 5C has a first surface, a curved portion g-h, a curved portion hi, and a curved line formed by the curved portion de, the curved portion ef, and the curved portion gg in the second horizontal direction. It can also be said that it has the 2nd surface formed by the part id. The first surface and the second surface are disposed so as to face each other in the vertical direction, and are connected by a curved portion de and a curved portion id, and are connected by a curved portion f-g and a curved portion gh. The curved line part ef is arranged between the curved line part f-g and the curved line part de, and is connected to these curved parts. The curve part hi is arranged between the curve part gh and the curve part id, and is connected to these curve parts. The curved portions ef and hi have a larger curvature than the curved portions ed and gh. For example, the curved portions ef and hi and the curved portions ed and fi and gh are arc portions, and the radii of the curved lines ef and hi are curved portions ed. It is larger than the radius of −i, f−g−h.

The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surface of the inner cylinder of the vacuum vessel used in the MRI apparatus 25C is similar to that of the inner surface 5C.
The longitudinal cross-sectional shape orthogonal to the axis of the bore B of the inner surfaces 5A, 5B, 5C described above is a racetrack shape. The shapes of the pair of outer coils 21 and the pair of inner coils 22 installed in the vacuum vessels of the MRI apparatuses 25, 25A, and 25B as viewed from the axial direction of the bore B are also different in size. It has a race track shape similar to the race track shape of the inner surfaces 5A, 5B, 5C. Also in the MRI apparatuses 25, 25 A, and 25 B, the flatness defined in the first embodiment of the inner coil 22 is larger than that of the outer coil 21.
The MRI apparatus 27, 27A, 27B having the inner surface shape of each inner cylinder described above can obtain the effects produced in the first embodiment.

<Fourth embodiment>
In the second embodiment, the correction coil 23 is arranged so that the central axis (the axis O of the bore B) coincides with the central axis (the axis O of the bore B) of the main coil 20 ′. It can also be arranged around the main coil 20 '. In the racetrack-shaped main coil 20 ', since the distance from the central axis to the coil differs in the second horizontal direction and the vertical direction, the partial magnetic field strength is supplemented by such a correction coil to ensure uniformity.
An example is given in FIG. The correction coil 27 is arranged in the circumferential direction outside the main coil 20. The axis of the correction coil 27 and the axis of the main coil 20 intersect each other. For example, by arranging the correction coil 27 on the upper side and the lower side of the main coil 20, the magnetic field distribution in the vertical direction (Y-axis direction) can be locally improved.

  The correction coil 27 can be manufactured by winding a superconducting wire around a winding frame of an arbitrary shape such as a circle or an ellipse. Alternatively, when the current density may be relatively low, a current pattern can be generated on the base substrate. Since the correction means of this embodiment is intended to generate a local magnetic field, it may have a relatively small size of up to about 40 cm and can be easily manufactured. In any case, the number of turns and the shape of the current pattern are determined by the required magnetic field distribution and intensity, and the amount of current that can be passed through the current pattern. In addition, since it is placed in a strong magnetic field generated by the main coil or the like, consideration must be given to the deformation of the superconducting wire due to the critical magnetic field or electromagnetic force.

  In addition, it is desirable that the correction coil is connected in series with the current path of the main coil and allows the same amount of current to flow. This is because the purpose of the correction coil is not so-called shimming but a means for correcting the irregular magnetic field component calculated at the time of magnet design. That is, the magnetic field is designed at the same time as the main coil and the like, and a constant magnetic field can always be generated by supplying the same current value as that of the main coil, so that a stable magnetic field distribution can be obtained.

It is the block diagram seen from the axial direction of the bore | bore B of the MRI apparatus of 1st Embodiment which is one preferable embodiment of this invention. It is a whole perspective view of the superconducting magnet apparatus used for the MRI apparatus of FIG. It is a longitudinal cross-sectional view containing the Z-axis of the superconducting magnet apparatus shown in FIG. It is a whole perspective view which shows the main coil used by 1st Embodiment. It is a top view which illustrates the shape of the main coil which is a racetrack shape. (A) shows the magnetic field which an outer coil forms in the XY cross section of an imaging region, (b) is a graph which shows the magnetic field strength distribution. (A) shows the magnetic field which an inner coil forms in the XY cross section of an imaging region, (b) is a graph which shows the magnetic field strength distribution. (A) is a graph which shows the magnetic field strength distribution which an outer side coil forms on the Z-axis of an imaging region, (b) is a graph which shows the magnetic field strength distribution which an inner side coil forms on the Z-axis of an imaging region. It is a top view of the main coil used in 1st Embodiment. It is a whole perspective view which shows the main coil of the MRI apparatus of 2nd Embodiment which is other embodiment of this invention. It is a top view of the main coil used in 2nd Embodiment. (A) is a graph which shows the magnetic field strength distribution which an outer coil forms in the XY cross section of an imaging region, (b) is a graph which shows the magnetic field strength distribution which an inner coil forms in the XY cross section of an imaging region, (c ) Is a graph showing the magnetic field strength distribution formed on the XY cross section of the imaging region by the correction coil, (d) is a graph showing the magnetic field strength distribution formed by the outer coil on the Z axis of the imaging region, and (e). Is a graph showing the magnetic field strength distribution formed by the inner coil on the Z axis of the imaging region, and (f) is a graph showing the magnetic field strength distribution formed by the correction coil on the Z axis of the imaging region. It is a block diagram of the MRI apparatus of 3rd Embodiment which is other embodiment of this invention. It is a block diagram of the MRI apparatus of 3rd Embodiment which is other embodiment of this invention.

Explanation of symbols

10 Superconducting magnet device (electromagnet device)
12 Superconducting coil 20, 20 'Main coil 21 Outer coil 22 Inner coil 23 Correction coil 30 Shield coil B Bore (air core)
R Imaging area

Claims (17)

A gantry having an air core part into which a subject is inserted and having an electromagnet device including a plurality of annular coils for generating a magnetic field;
The plurality of annular coils are arranged in an axial direction of the air core portion so as to surround the air core portion,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
These main coils have a first coil part and a second coil part that are opposed to each other in the vertical direction and connected to each other,
Straight lines in which the first coil portion and the second coil portion are respectively sandwiched between the pair of first curved portions and the pair of first curved portions in the horizontal direction and connected to the first curved portions. Part and the second curve part,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flatness, the flatness of the inner coil is larger than that of the outer coil. Resonance imaging device.   The main coil is opposed to the first coil portion and the second coil portion in the horizontal direction, and a pair of other linear portions and a third curve that respectively connect the first coil portion and the second coil portion. The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic resonance imaging apparatus is formed by any one of the units.   The magnetic resonance imaging apparatus according to claim 1, wherein a curvature of the second curved portion is smaller than a curvature of the first curved portion. A gantry having an air core part into which a subject is inserted and having an electromagnet device including a plurality of annular coils for generating a magnetic field;
The plurality of annular coils are arranged in an axial direction of the air core portion so as to surround the air core portion,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
The main coils are connected to the pair of first coil portions, which are opposed to each other in the vertical direction and in which either the linear portion or the first curved portion is formed in the horizontal direction, and the pair of first coil portions, respectively. Having a pair of second coil portions facing each other in the horizontal direction and forming a second curved portion in the vertical direction;
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flatness, the flatness of the inner coil is larger than that of the outer coil. Resonance imaging device.   5. The magnetic resonance imaging apparatus according to claim 4, wherein each second curved line part forming the second coil part is an arc part. A gantry having an electromagnet apparatus including a plurality of annular coils that have a horizontal core extending in a horizontal direction in which a subject is inserted and generate a magnetic field;
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
These main coils have a racetrack shape,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flatness, the flatness of the inner coil is larger than that of the outer coil. Resonance imaging device.   The plurality of main coils each include a correction coil disposed between the outer coil and the inner coil, according to any one of claims 1, 4, and 6. The magnetic resonance imaging apparatus described. A vacuum vessel having an outer cylinder and an inner cylinder disposed inside the outer cylinder, in which an annular space is formed between the outer cylinder and the inner cylinder; and disposed in the annular space surrounding the inner cylinder A plurality of annular coils arranged apart in the axial direction of the vacuum vessel,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
These main coils have a first coil part and a second coil part that are opposed to each other in the vertical direction and connected to each other,
Straight lines in which the first coil portion and the second coil portion are respectively sandwiched between the pair of first curved portions and the pair of first curved portions in the horizontal direction and connected to the first curved portions. Part and the second curve part,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flat rate, the flat rate of the inner coil is larger than that of the outer coil. apparatus.   The main coil is opposed to the first coil portion and the second coil portion in the horizontal direction, and a pair of other linear portions and a third curve that respectively connect the first coil portion and the second coil portion. The electromagnet device according to claim 8, formed by any one of the parts.   The electromagnet device according to claim 8 or 9, wherein a curvature of the second curved portion is smaller than a curvature of the first curved portion. A vacuum vessel having an outer cylinder and an inner cylinder disposed inside the outer cylinder, in which an annular space is formed between the outer cylinder and the inner cylinder; and disposed in the annular space surrounding the inner cylinder A plurality of annular coils arranged apart in the axial direction of the vacuum vessel,
The plurality of annular coils are arranged in an axial direction of the air core portion so as to surround the air core portion,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
The main coils are connected to the pair of first coil portions, which are opposed to each other in the vertical direction and in which either the linear portion or the first curved portion is formed in the horizontal direction, and the pair of first coil portions, respectively. Having a pair of second coil portions facing each other in the horizontal direction and forming a second curved portion in the vertical direction;
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flat rate, the flat rate of the inner coil is larger than that of the outer coil. apparatus.   The electromagnet apparatus according to claim 11, wherein each second curved line portion forming the second coil portion is an arc portion. A vacuum vessel having an outer cylinder and an inner cylinder disposed inside the outer cylinder, in which an annular space is formed between the outer cylinder and the inner cylinder; and disposed in the annular space surrounding the inner cylinder A plurality of annular coils arranged apart in the axial direction of the vacuum vessel,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
These main coils have a racetrack shape,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flat rate, the flat rate of the inner coil is larger than that of the outer coil. apparatus.   The plurality of main coils include correction coils arranged between the outer coil and the inner coil, respectively. The electromagnet device described.   A correction superconducting coil for correcting a magnetic field inhomogeneity component is provided in addition to the main coil, and the central axis direction of the correction superconducting coil does not coincide with the direction of the static magnetic field. The electromagnet device according to any one of claims 8 to 14. A gantry having an electromagnet device including a plurality of annular coils that have a hollow core portion that extends in a horizontal direction and into which a subject is inserted, and that generates a magnetic field;
The plurality of annular coils are arranged in an axial direction of the air core portion so as to surround the air core portion,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
A longitudinal section of the plurality of main coils perpendicular to the axis of the air core portion has a racetrack shape,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flatness, the flatness of the inner coil is larger than that of the outer coil. Resonance imaging device. A vacuum vessel having an outer cylinder and an inner cylinder disposed inside the outer cylinder, extending in a horizontal direction and having an annular space formed between the outer cylinder and the inner cylinder; and surrounding the inner cylinder A plurality of annular coils disposed in the annular space and spaced apart in the axial direction of the vacuum vessel;
The plurality of annular coils are arranged in an axial direction of the air core portion so as to surround the air core portion,
The plurality of main coils included in the plurality of annular coils are configured such that the air core portion has an axis that is sandwiched between the air core portion and a first distance between the coil portions that are opposed in the vertical direction across the air core portion. The second distance between the coil portions facing each other in the orthogonal horizontal direction is configured to be long,
A longitudinal section of the plurality of main coils perpendicular to the axis of the air core portion has a racetrack shape,
The plurality of main coils include a pair of outer coils, and a plurality or a single inner coil disposed between the pair of outer coils in the axial direction of the air core portion,
When the first distance is defined as a, the second distance is defined as b, and (ba) / b is defined as a flat rate, the flat rate of the inner coil is larger than that of the outer coil. apparatus.

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