JPS63281411A - Magnetostatic field magnet for magnetic resonance imaging system - Google Patents

Abstract

PURPOSE:To make it possible to generate a high magnetic field and render the operation cost substantially zero by arranging a plurality of superconducting blocks oppositely so that a space is formed, and so that a substantially uniform magnetostatic field appears in the space, said superconducting blocks having been made so that their magnetic field directions are in agreement with each other. CONSTITUTION:A magnetostatic field magnet 6 is constructed using a plurality of superconducting blocks 34. That is, six superconducting blocks 34a-34f are arranged oppositely, three for each, so that a space for forming a cold bore 7 is provided, and so that the sides of the space form recessed, curved planes relative to the space. The superconducting blocks 34c, 34d and 34e, 34f generating magnetic lines of force suppressing the widening of the magnetic lines of force are attached to the end parts of the superconducting blocks 34a, 34b having an appropriate slope. The fixed magnetic fields 27 generated by cylindrical superconductors 23 are collected within a superconducting block 34, become a uniformly distributed magnetic field emanating from the superconducting block. By making the cross-section area of the cylindrical superconductors sufficiently small relative to the area of the surface of a superconducting block 34 from which a magnetic field emanates, the uniformity of the magnetic field emanating from the superconducting block can have a value sufficiently corresponding to the level required by a magnetic resonance imaging system.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to magnetic resonance (MR) technology.
So-called computed tomography (CT) is based on the density distribution of specific atomic nuclear spins in a specific cross section of a living subject using the sonance phenomenon.
Computed tomography (CT image)
edTomogram) as an image (Imagin
g) A static magnetic field magnet used in a magnetic resonance imaging apparatus.

(Prior Art) For example, in a medical magnetic resonance imaging apparatus used for living body diagnosis, in order to obtain a tomographic image of a specific part of a living subject, the 31 subject P is scanned in the illustrated Z direction as shown in FIG. Very uniform static magnetic field along the direction H
8 is generated and acted upon by a static magnetic field magnet (not shown), and a pair of gradient coils 100A, 1
00B applies a linear magnetic field gradient Gx to the static magnetic field H8. Here, the specific atomic nucleus for the static magnetic field H8 has an angular frequency ω expressed by the following equation. It resonates with me.

ω. =γH11 (1) In this ω equation, γ is the gyromagnetic ratio, which is unique to the type of atomic nucleus. Therefore, the angular frequency ω makes only specific atomic nuclei resonate. A rotating magnetic field H□ is applied to the subject P via, for example, a pair of transmitting coils 200A and 200B provided within an RF coil (probe head).

In this way, the linear magnetic field gradient Gx selectively acts only on the illustrated x-y plane portion that is selectively set in the Z-axis direction, and a specific slice portion S (a portion on a plane) from which a tomographic image is obtained. In reality, it has a certain thickness)
Magnetic resonance phenomena occur only in This magnetic resonance phenomenon is caused by, for example, a pair of receiving coils 30 provided within the RF coil.
Free induction damping signal (free
It is abbreviated as "1 ducton decay signal 2 or less rFID signal". ) and is used as an MR multiplied signal. By Fourier transforming this FID signal, a single spectrum can be obtained for the rotating tube wavenumber of a specific nuclear spin.

To obtain a tomographic image as a CT image, x-
Projections in multiple directions within the y-plane are required. Therefore, after exciting the slice portion S to cause a magnetic resonance phenomenon, the magnetic field H8 is applied in the X'-axis direction (X'-axis direction) as shown in FIG.
When a linear magnetic field gradient GXY having a linear slope (coordinate system rotated by an angle O from the axis) is applied by a gradient coil (not shown), the isomagnetic field line E in the sliced portion S of the subject P becomes a straight line, and this isomagnetic field The rotational frequency of a specific nuclear spin on the line E is given by the above equation (2).

For convenience of explanation, it is assumed that the equal magnetic field lines E are assumed to be E1 to En, and the magnetic fields on these equal magnetic field lines E to En generate signals D□ to Dn, which are a type of FID signal, respectively. The amplitudes of the signals D~Dn are proportional to the spin densities of specific atomic nuclei on the isomagnetic field lines E□~Eo passing through the slice portion S, respectively. However, the FID signal that is actually observed is a composite FID signal that is the sum of all the signals D to Dn. Therefore, projection information (one-dimensional image) PD of the slice portion S onto the X' axis is obtained by Fourier transforming the composite FID signal. Next, this X' axis is rotated within the x-y plane, which is caused by, for example, a magnetic field gradient Gx in the X ry direction caused by two pairs of gradient coils.

This is done by creating a magnetic field gradient axy as a composite magnetic field of GY, and changing the composite ratio of the magnetic field gradients GX and GY.

By rotating this magnetic field gradient axy, x-
Projection information in the angular direction within the y-plane is obtained, and a CT image is synthesized based on this information.

The above is the principle of magnetic resonance imaging. Next, as a specific example, a conventional magnetic resonance imaging apparatus is shown in FIG. A subject, ie, a patient 1, is placed on a bed 2. An RF coil (probe head: high frequency transmitting/receiving coil) 3 is disposed surrounding the patient 1, and furthermore, a shim coil 4 for magnetic field correction and a gradient coil 5 for generating a gradient magnetic field are disposed around the RF coil. All of these coil systems are housed inside a normal temperature bore 7 (usually a bore inner diameter of about 1 m) of a large static magnetic field magnet 6. As the static field magnet, any one of a superconducting magnet, a normal conducting magnet, and a permanent magnet is used.

This static field magnet 6 is excited and demagnetized by an excitation power source 8 via a current lead 9 (this is not necessary in the case of a permanent magnet system). In the case of superconducting magnets, the current lead 9 is usually removed after excitation because it is operated in persistent current mode and to reduce consumption of liquid helium, which is a coolant, so that a magnetic field is always generated. ing. Normally, the direction of this static magnetic field is the 10 directions shown in the figure for many magnets,
That is, the direction is the body axis direction of the patient 1. The gradient coil 5 is composed of a GX coil that provides a magnetic field gradient in the X-axis direction, a GY coil in the Y-axis direction, and a GZ coil in the Y-axis direction.
Each excitation power supply! 1.12.13.

These excitation power supplies 11 , 12 , 13 are connected to a central control unit 14 . The RF coil 3 is composed of a transmitter coil and a receiver coil, which are connected to an RF oscillator 15 and an RF receiver 16, respectively, and these are further connected to a central controller 14.
It is connected to the. The central control device 14 is a display/operation panel 1
7 and is operated by this.

The above description of static field magnets has mainly been about superconducting magnets. Here, the structure and operation of a conventional permanent magnet for a magnetic resonance imaging apparatus will be explained using FIGS. 12 and 13. Regarding this permanent magnet, for example, "DIAG
NOS T I CI MAG I NG” Magazine 1984
Details are given in the April issue.

FIG. 12 shows the appearance of the permanent magnet. The permanent magnet 20 is made of a permanent magnet material and includes eight trapezoidal blocks 19 arranged in an annular shape. A normal temperature bore 7 is placed in the center of the magnet. In this case, the magnetic field applied to the patient is perpendicular to the patient's body axis. As permanent magnet materials, ferrite ceramics, rare earth samarium/cobalt, neodymium, boron, iron, etc. are used.

FIG. 13 shows the magnetization direction 21 of each trapezoidal block 19 and the lines of magnetic force 22 when assembled as a permanent magnet.

In order to obtain a uniform magnetic field, that is, a uniform distribution of lines of magnetic force within the room-temperature bore 7, the magnetization direction of each trapezoidal block is individually determined as shown in the figure. Due to this magnetization direction, the lines of magnetic force penetrate through the trapezoidal blocks arranged in an annular manner without leaking to the outside of the permanent magnet, and a uniform line of magnetic force distribution is obtained in the normal temperature bore.

Next, the operation of the conventional magnetic resonance imaging apparatus configured as described above will be described.

In order to obtain a whole body tomographic image of the patient 1, the magnetic field uniform space 18
Usually has a wide range of 40 to 50 al+ bulbs, and 50 ppm
The following high uniformity is required. For this reason, the static magnetic field magnet 6
For example, in the case of the superconducting method, the length is 2.4 m, the width is 2 m,
It would need to be huge, with a height of 2.4 meters and a weight of 5 to 6 tons.

Even with such a large magnet, the uniformity within a 40-50an sphere due to the magnet alone is only a few hundred points at most.
It only becomes pm. In order to reduce this to 50 ppm or less, a shim coil 4 for magnetic field correction is used.

The patient's diagnostic site is brought into this magnetic field uniform space 18. RF oscillator 15 in the direction perpendicular to the static magnetic field 10,
A high frequency magnetic field is applied by the RF coil 3 to excite a desired atomic nucleus, such as a hydrogen atomic nucleus, within a human cell. At the same time, gradient magnetic fields are applied in the x, y, and z directions by the GX excitation power supply 11, the GY excitation power supply 12, the GZ excitation power supply 13, and the gradient coil 5.

The optimum RF and gradient pulse sequence is selected depending on the lesion site and image processing method.

This pulse sequence operation is controlled by central controller 14. Gradient 1~, after RF application, a magnetic resonance signal is emitted from inside the patient 1's body. This signal is received and amplified by the RF receiver 16 and input to the central controller 14. Here, the image is processed and the required human body tomographic image is displayed on the CRT of the display/operation panel 17.

(Problems to be Solved by the Invention) The conventional static field magnet for magnetic resonance imaging apparatus described above has the following advantages and disadvantages.

That is, in the case of superconducting magnets, a high magnetic field can be easily generated as an advantage, so that it can be applied to spectroscopy diagnosis which requires a magnetic field of 15,000 Gauss or more.

The drawback is that current superconducting coils exhibit superconductivity only at extremely low temperatures. For this reason, it is necessary to regularly inject liquid helium, which cools the superconducting coils, in order to maintain the superconducting coils at extremely low temperatures. In addition, liquid helium is expensive, which increases operating costs and makes it an expensive medical device.
Even if hospitals introduce RI, they will not be able to recover the investment funds. Furthermore, handling of liquid helium, which is a cryogenic refrigerant, is difficult, and regular injection work is complicated.

Permanent magnets have the advantage of not requiring any electricity or refrigerant, so operating costs are zero and regular maintenance is not required.

The disadvantages include:

■Unable to generate high magnetic field. The limit is 3000 Gauss. For this reason, it is essentially impossible to perform spectroscopy diagnosis, and even in proton imaging, the image quality deteriorates compared to the superconducting method because the magnetic field is weak, and the diagnosis time is reduced because high-speed imaging that requires a high magnetic field is not possible. As the length of time increases, diagnostic efficiency declines, resulting in poor hospital profits.

■The magnetic properties of permanent magnet materials are easily affected by changes in external temperature. Therefore, when the temperature in the magnet film storage room changes, the magnetic field strength changes. The essence of an MRI magnet is the uniformity and stability of the magnetic field, and if these vary, image quality will deteriorate.

Ordinary permanent magnets perform complicated temperature control to avoid this.

■The permanent magnet material has the same specific gravity as iron, so the magnet has a
It becomes a heavy object of 0 ton to 100 ton. The strength of the floor in which permanent magnets are installed is less than 10 tons, which limits the number of hospitals that can install permanent magnets.

As mentioned above, the superconducting magnets and permanent magnets currently in use have advantages and disadvantages, and there was no magnet that could fully meet market needs, which hindered the spread of MRI.

Therefore, an object of the present invention is to eliminate the drawbacks of conventional superconducting magnets and permanent magnets, and to provide a static field magnet that has the advantages of both magnets. In other words, it can generate a high magnetic field.

Reduce operating costs to almost zero.

Eliminate maintenance work.

The purpose of the present invention is to provide a static field magnet that is lightweight, compact, and inexpensive, and to promote the spread of MRI.

[Structure of the invention]

(Means for Solving the Problems) The static field magnet for a magnetic resonance imaging apparatus according to the present invention is constructed as follows in order to solve the above problems and achieve the object. That is, a ceramic-based superconducting material that exhibits a superconducting phenomenon above the temperature of liquid nitrogen is used as the superconducting material, and this is sintered to form a cylindrical or ring-shaped superconductor. A plurality of superconducting blocks made by exciting these cylindrical or ring-shaped superconductors and aligning the magnetic field directions and assembling them are placed facing each other so that an air gap is formed, and a substantially uniform static current is created within the air gap. Arrange the superconducting blocks so that a magnetic field is generated.

(Function) Cylindrical or ring-shaped superconductors retain persistent current even after the external magnetic field is removed due to their basic properties.
This persistent current generates a magnetic field of a required strength in the axial direction of the cylindrical superconductor. Therefore, a superconducting block in which a plurality of superconductors are assembled with the same magnetic field direction functions in the same manner as a permanent magnet.

(Example) An example of the present invention will be described with reference to FIGS. 1 to 5.

(Configuration of Example) A cylindrical superconductor 23 shown in FIG. 3 or A ring-shaped superconductor 24 shown in FIG. 4 is made.

During sintering, large voids occur between grain boundaries when using only ceramics, but Pb, Id, etc.
By mixing metal powder with high electrical conductivity such as , Cu, Aρ, etc., the metal powder can fill these voids, and a cylindrical or ring-shaped superconductor with better electrical properties can be obtained.

As shown in FIG. 5, a cylindrical superconductor 23 or a ring-shaped superconductor 24 is placed coaxially with the direction of a magnetic field B26 generated by an external superconducting magnet 25. At this time, each superconductor is in a superconducting state by immersion in liquid nitrogen or the like. In the case of room-temperature superconductors, place them as they are. If this external magnetic field 26 is removed, the basic property of superconductivity is to preserve the original magnetic field, so this removed external magnetic field 26
A persistent current 28 flows in the circumferential direction within the cylindrical wall of the cylindrical or ring-shaped superconductor so as to generate a magnetic field equivalent to the magnetic field B.
is saved. That is, a constant magnetic field z7 is always generated in the axial direction of the cylindrical superelectric body 23 or the ring-shaped superconductor 24 due to the persistent current 28 flowing within the superconductor.

In order to further improve the uniformity, intensity accuracy, and magnetic field direction accuracy of the constant magnetic field 27, thin ring-shaped superconductors 24 may be laminated in the axial direction to form a cylindrical superconductor as shown in FIG. The reason for this is that in the case of a thin ring, the component of the persistent current flowing in the axial direction can be almost ignored, resulting in a complete circumferential current, and a highly accurate constant magnetic field 27 can be obtained.

A liquid nitrogen container filled with liquid nitrogen 29 as shown in FIG. Store it in 30. At this time, the magnetic field directions of the cylindrical superelectric elements 23 are made to coincide with each other, and the cylindrical superelectric elements 23 are assembled together. Liquid nitrogen container 30
The outer periphery of is surrounded by a vacuum layer 31, and the vacuum layer 31 is filled with a multilayer heat insulating material 32 to improve heat insulation. All of these are housed in a vacuum container 33. The cold container (cryostat) configured in this manner is called a superconducting block 34. Note that the liquid nitrogen container 30 may be directly cooled with a small refrigerator such as a GM (Gifford McMahon) system.

A plurality of these superconducting blocks 34 are used to constitute the static magnetic field magnet 6 shown in FIG. That is, six superconducting blocks 34a, 34b, 34c, 34d, 34e,
34f are arranged in groups of three facing each other so as to form a gap forming the normal temperature bore 7, and so that the side surfaces of the gap form a concave curved surface with respect to the gap. Superconducting block 34 in the middle
a (34b) with both ends superconducting block 34c.

The angle of inclination of 34e (34d, 34f) is chosen such that the required magnetic field homogeneity within the diagnostic space in the cold bore 7 is achieved. Superconducting blocks 34a and 34b have six yokes 35 along the surface opposite to the void side of the superconducting blocks.

It surrounds 34c, 34d, 34e, and 34f.

Note that the ring-shaped or cylindrical superconductor may be magnetized after being assembled into a superconducting block.

(Operation of the embodiment) A constant magnetic field 27 generated by the cylindrical superconductor 23 is collected within the superconducting block 34, and becomes a uniformly distributed magnetic field that is emitted from the superconducting block. This situation corresponds to the superconducting block 34 acting as a magnetic field generation source like a single permanent magnet.

By making the cross-sectional area of the cylindrical superconductor sufficiently smaller than the area of the magnetic field generation surface of the superconducting block 34, the uniformity of the magnetic field generated by the superconducting block can be made to a value that sufficiently corresponds to the level required by magnetic resonance imaging equipment. can do.

A main magnetic field 10 used for diagnosis is formed by superconducting blocks 34a and 34b placed in parallel and facing each other so that the generated magnetic fields are in the same direction. At the end of the main magnetic field 10, the lines of magnetic force tend to spread outward due to the end effect of the magnetic pole surface. In such a situation, the disturbance in the lines of magnetic force affects the center, and the uniformity of the magnetic field in the diagnostic space deteriorates.

In order to avoid this, superconducting blocks 34c, 34d and 3 generate magnetic lines of force that suppress the spread of magnetic lines of force.
4e and 34f with appropriate inclinations to the superconducting block 3.
It is attached to the ends of 4a and 34b. 34c, 34
The end magnetic field lines of the main magnetic field 10 are suppressed by the magnetic lines of force curved toward the center, generated by the magnetic field lines d, 34e, and 34f, thereby ensuring uniformity of the magnetic field in the diagnostic space.

Superconducting blocks 34a, 34b, 34c, 34d
, 34e, 34f, a magnetic return path 36 is formed by the yoke 35 attached to the outer periphery of the magnets 34e, 34f, and the magnetic flux does not leak to the outside of the static field magnet 6.

In the second embodiment, the cylindrical or ring-shaped superconductors 23 and 24 are made of a material that exhibits superconductivity above the temperature of liquid nitrogen. However, refrigerant and cryostat are not required.

(Effects of Example) The above embodiment has the following effects.

Because it uses superconductivity, it can generate the high magnetic fields necessary for spectroscopy diagnosis and high-speed imaging.

Since the superconducting state can be maintained using liquid nitrogen, operating costs can be drastically reduced compared to the conventional case of using liquid helium.

Since the superconducting material can be used as a sintered body without being made into a wire, manufacturing is easy and manufacturing costs are drastically reduced.

Since liquid nitrogen is used, the maintenance work required with conventional liquid helium is reduced.

The uniformity of the magnetic field can be improved by reducing the cross section of the cylindrical or ring-shaped superconductor that is the magnetic field generating unit and increasing the number of aggregates.

Since ceramic materials are used, the weight can be reduced compared to conventional permanent magnets.

The leakage magnetic field can be reduced by the yoke.

(Other Example 1) Other Example 1 is shown in FIG. A pair of superconducting blocks 34 are arranged in parallel and facing each other so that the lines of magnetic force generated are in the same direction. A yoke 35 is attached to surround the outer periphery of this superconducting block.

In the case of this embodiment, unlike the previous embodiment, a superconducting block that suppresses the spread of the main magnetic field is not attached, so the magnetic field uniformity deteriorates accordingly, but the manufacturing cost is greatly reduced. There is.

(Other Example 2) Another Example 2 is shown in FIG. Eight trapezoidal superconducting blocks 37 are arranged in a ring shape to form a ring-shaped magnet. The center of the ring is a room temperature bore 7.

The magnetization direction 21 of each trapezoidal superconducting block 37 is set as shown in FIG. 7 so as to obtain the same magnetic field line distribution 22 as the conventional permanent magnet 20 shown in FIG. 13. In order for the magnetization direction of each trapezoidal superconducting block 37 to be as shown in the figure, a plurality of cylindrical superconductors 23 are gathered together so that the axes of the plurality of cylindrical superconductors 23 are coaxial with this required magnetization direction, and the trapezoidal superconductor 23 is assembled into a trapezoidal shape. A superconducting block 37 is configured. At this time, since a trapezoid is formed by the accumulation of cylindrical superconductors, the lengths of the cylindrical superconductors do not match and there are lengths and shortenings as shown in FIG.

With the above configuration, the trapezoidal superconducting block 37 in FIG. 7 becomes the conventional permanent magnet trapezoidal block 19 in FIG.
It has the same magnetic function as . Therefore, the generated lines of magnetic force are uniform within the normal temperature bore 7, and since the trapezoidal superconducting block 37 itself serves as a magnetic path return path, there is almost no leakage of the lines of magnetic force to the outside of the magnet. That is,
The operation is exactly the same as that of the conventional example shown in FIG.

The effect is the same as that of the first embodiment shown in FIG.

(Other Example 3) Other Example 3 is shown in FIG. Each cylindrical superconductor 23 is structured to be able to be finely moved in its axial direction. Any mechanism may be used for this fine adjustment movement.

When the cylindrical superconductor 23 moves in its axial direction toward the normal temperature bore 7, the magnetic field intensity in the diagnostic space to which this cylindrical superconductor contributes increases slightly. On the contrary, when it is moved to the side opposite to the normal temperature bore 7, the magnetic field strength decreases slightly.

Due to this effect, by moving each cylindrical superconductor, it is possible to finely adjust the magnetic field uniformity in the diagnostic space.

As described above, it is possible to achieve the high degree of magnetic field uniformity required for a magnetic resonance imaging apparatus.

〔Effect of the invention〕

According to the present invention, the disadvantages of conventional superconducting magnets and permanent magnets are eliminated, and the advantages of both magnets, namely, high magnetic field generation, reduced operating costs, reduced maintenance,
It is possible to provide a high-performance static field magnet for a magnetic resonance imaging device that is lightweight, compact, and inexpensive. This has the effect of promoting the spread of magnetic resonance imaging devices.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a static field magnet according to an embodiment of the present invention;
Figure 3 is a structural diagram of a superconducting block used in an embodiment of the present invention, Figure 3 is a structural diagram of a cylindrical superconductor used in an embodiment of the present invention, and Figure 4 is a ring-shaped superconductor used in an embodiment of the present invention. Structural diagram of superconductor, No. 5 = 23- Figures (a) and (b) are diagrams showing a method of applying a constant magnetic field in one embodiment of the present invention, and Figure 6 is another first embodiment of the present invention. FIG. 7 is a configuration diagram of a static magnetic field magnet according to another second embodiment of the present invention, and FIG. 8 is a configuration diagram of a static magnetic field magnet according to another third embodiment of the present invention. Fig. 9 is a configuration diagram of a conventional magnetic resonance imaging device, Fig. 10 is a principle diagram of magnetic resonance imaging, Fig. 11 is a system diagram of a conventional magnetic resonance imaging device, and Fig. 12 is a conventional magnetic resonance imaging device. FIG. 13, which is a structural diagram of a permanent magnet for an apparatus, is a magnetic force line distribution diagram of a conventional permanent magnet for a magnetic resonance imaging apparatus. 6... Static field magnet 7... Room temperature bore 10...
・Static magnetic field direction 19... Trapezoidal block 20... Permanent magnet 21... Magnetization direction 22... Lines of magnetic force
23...Cylindrical superconductor 24...Ring-shaped superconductor 8
Body 34, 34a, 34b, 34c, 34d, 34
e, 34f-super rM, grave block 35... Yoke 37... Trapezoidal superconducting block Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 9 Fig. 10

Claims (12)

[Claims] (1) A plurality of cylindrical superconductors made of superconducting material, in which a persistent current circulates in the circumferential direction inside the cylinder wall and a magnetic field of the required strength is generated in the direction of the cylinder axis, with the magnetic field directions aligned. 1. A static field magnet for a magnetic resonance imaging apparatus, characterized in that two superconducting blocks are arranged to face each other so as to form a gap and to generate a substantially uniform static magnetic field within the gap. (2) In a superconducting block, a cylindrical superconductor is housed in a liquid nitrogen container filled with liquid nitrogen, and the liquid nitrogen container is surrounded by a heat insulating material and a vacuum layer, and the entire structure is placed in a vacuum container. A static magnetic field magnet for a magnetic resonance imaging apparatus according to claim 1, characterized in that it has a housed cryostat structure. (3) A static field magnet for a magnetic resonance imaging apparatus according to claim 2, characterized in that the liquid nitrogen container is directly cooled by a small refrigerator such as a GM system. (4) A static field magnet for a magnetic resonance imaging apparatus according to claim 1, wherein the cylindrical superconductor is formed by laminating a plurality of ring-shaped superconductors coaxially in the axial direction. (5) A static field magnet for a magnetic resonance imaging apparatus according to claim 1, wherein the side surfaces of the air gaps of the plurality of superconducting blocks form concave curved surfaces with respect to the air gaps. (6) A static field magnet for a magnetic resonance imaging apparatus according to claim 1, characterized in that a plurality of superconducting blocks are surrounded by a yoke along a surface opposite to the air gap of the superconducting blocks. (7) A static magnetic field magnet for a magnetic resonance imaging apparatus according to claim 1, characterized in that a plurality of superconducting blocks each having a different magnetization direction are arranged in a ring shape, and the magnet is configured in a ring shape. . (8) The magnetic resonance imaging apparatus according to claim 1, wherein the magnetic field uniformity within the gap is adjusted by finely moving the cylindrical superconductor within the superconducting block in the axial direction. static field magnet. (9) A patent claim characterized in that the superconducting material is a ceramic-based superconducting material that exhibits a superconducting phenomenon above the temperature of liquid nitrogen, and that a cylindrical superconductor or a ring-shaped superconductor is formed by sintering the ceramic material. A static magnetic field magnet for the magnetic resonance imaging apparatus according to item 1. (10) When sintering ceramic superconducting materials,
The magnetism according to claim 9, characterized in that a ceramic powder is mixed with a metal powder having high electrical conductivity such as Pb, Id, Cu, Al, etc., and the voids in the ceramic grain boundaries are filled with a metal base material. Static field magnet for resonance imaging equipment. (11) A cylindrical or ring-shaped superconductor is one in which a persistent current based on electromagnetic induction is circulated in the circumferential direction by a process of applying and not applying a magnetic field using an external superconducting magnet that applies a strong magnetic field in the axial direction. A static field magnet for a magnetic resonance imaging apparatus according to claim 1, characterized in that: (12) A static field magnet for a magnetic resonance imaging apparatus according to claim 11, characterized in that a superconductor block is used instead of a cylindrical or ring-shaped superconductor.