JP2001068327A - Superconducting magnet device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a superconducting magnet which can prevent deterioration of uniformity of a magnetic field due to change of an environmental temperature with low running cost, and prevent the dimension of air gap between facing vacuum thermal insulation vessels from being reduced. SOLUTION: A pair of vacuum thermal insulation vessels 103 in which superconduding coil groups 101 are accommodated are arranged face to face. These are covered with a decorative cover 15 which can be divided into an inside plate 15a, an outside plate 15b and a side plate 15c. Ferromagnetic segments 21 are detachably arranged on the inside plate of the decorative cover 16. According to temperature change of seasonal long period, the segments 21 exposed by detaching the side plate 15c are attached or detached, and deterioration of uniformity of a magnetic field which is caused by temperature change is compensated. Compensation of deterioration of uniformity of a magnetic field which is caused by temperature change is enabled at a low cost without consuming energy. Since the segments 21 are arranged in a vacant space, the dimension of an air gap is not reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a superconducting magnet device used for, for example, a medical tomographic imaging apparatus.

[0002]

2. Description of the Related Art In recent years, use of a superconducting magnet device as a static magnetic field generation source having high strength, high uniformity and stable in time has become popular. In particular, a medical tomographic imaging apparatus (hereinafter, MR)
I) has been remarkably spread as a static magnetic field generation source. MR
For I magnets, the human body (patient) is precise and has good contrast
In order to take a tomographic image at high speed and to acquire a high-performance image, the diameter of the magnet center, which is the imaging space, is 30 to 45 (cm).
0.5 to 2 (Tesl) in the spherical space S of FIG.
magnetic field strength of a), magnetic field homogeneity of 1 to 10 (ppm),
A time stable static magnetic field characteristic of 0.05 (ppm / hr) is required.

[0003] These characteristics are obtained by using a superconducting coil capable of achieving a high current density without loss and a permanent current mode operation peculiar to the superconducting phenomenon, and employing a coil arrangement based on a strict magnetic field uniformity design. It can only be satisfied with a magnet device.

[0004] In addition to the characteristics required for image acquisition, the MRI magnet has a wide opening and a feeling of openness so that all patients can be consulted with confidence because of the equipment installed in the hospital. Parallel imaging while conducting examinations, minimizing the leakage magnetic field generated by magnets to prevent the effects of magnetic fields on cardiac pacemaker wearers and other devices, minimizing external magnetic field fluctuations There are various demands such as having a disturbance magnetic field shielding function in order to eliminate the influence, a light weight and small size of the device due to easy carrying-in and installation, and the like.

Recently, a superconducting magnet vertical magnetic field type magnet having both the advantages of the conventional superconducting magnet horizontal magnetic field type and permanent magnet vertical magnetic field type has been developed as an MRI magnet and is being commercialized. This type of permanent magnet uses a permanent magnet superconducting magnet, while maintaining the patient's sense of security and openness, accessibility to patients, reduction of leakage magnetic field and shielding of disturbance magnetic field, which the conventional permanent magnet vertical magnetic field method has. Magnetic field strength, magnetic field uniformity, and time stability characteristics equivalent to the superconducting magnet horizontal magnetic field method can be obtained.

[0006] Such an MRI magnet is disclosed in, for example, JP-A-2-136127, JP-A-3-131234, JP-A-10-70027, and the like. And permanent magnet pieces are arranged to compensate for the inhomogeneous magnetic field component at the beginning of production caused by various causes, and to adjust so that the magnetic field of the imaging region becomes uniform,
When the adjustment is completed, a good magnetic field uniformity can be obtained.

However, when the temperature of the magnet installation chamber in which the MRI magnet is installed changes, the magnetic shield plate or the yoke made of a ferromagnetic material slightly expands and contracts, the vacuum insulated container, and the communication pipe connecting the vacuum insulated container. Due to slight expansion and contraction of the magnetic field, the uniformity of the magnetic field is greatly affected.

[0008] Since the MRI magnet is a device operated by a permanent current, it is generally operated continuously for several years once excited. In addition, the air conditioning temperature management of the magnet installation room is usually
Considering the comfort at the time of patient diagnosis, 5-10 in summer and winter
It is common to have a temperature difference of (° C). Further, air conditioning is normally stopped during a long holiday such as a New Year holiday or a summer vacation. Deterioration of magnetic field uniformity due to long-period fluctuations such as seasonal temperature fluctuations has become a major problem in obtaining precise images.

FIG. 9 shows an example of a conventional MRI magnet which takes measures against the deterioration of the magnetic field uniformity due to the long-period temperature fluctuation. FIG. 9 is a cross-sectional view of the MRI magnet. In FIG. 9, the annular superconducting coil group 101 has five solenoid-type superconducting coils 105a coaxially arranged. The two annular superconducting coil groups 101 are:
After individually housed in a vacuum insulation container 103 to be described later via a low-temperature container 102, they are coaxially opposed to a vertical axis and generate a highly uniform and stable high-intensity static magnetic field in a spherical space S that is an imaging region. .

[0010] The low-temperature vessel 102 includes the annular superconducting coil group 1.
01, and also serves as a liquid helium container that cools and holds the annular superconducting coil group 101 to a cryogenic temperature at which superconductivity occurs.

A vacuum insulated container 103 houses the cryogenic container 102 and reduces evaporation of liquid helium from the cryogenic container 102. The two vacuum heat insulating containers 103 are coaxially opposed to each other on a vertical axis, and the disk-shaped opposed surfaces 103a are vertically opposed. Cryogenic container 102 and vacuum insulated container 10
In order to further reduce the evaporation of liquid helium, a plurality of heat shield tanks (not shown) are usually provided between them.

Two magnetic shield plates 104 made of ferromagnetic material
Are provided on the opposite side of the opposite surface 103a of the vacuum heat insulating container 103 so as to sandwich the two vacuum heat insulating containers 103 in the vertical direction in the figure to reduce the leakage magnetic field and shield the disturbance magnetic field. Although not shown, a pair of ferromagnetic yokes are provided to sandwich the two vacuum insulation containers 103 from the left and right directions in the figure,
The upper and lower magnetic shield plates 104 are connected to form a magnetic flux flow path. This yoke also serves as a support structure for the magnetic shield plate 104.

The communication tube 106 connects the upper and lower low-temperature containers 102 and the vacuum heat-insulating container 103 in FIG. 9 to form a liquid helium passage and a lead passage for connecting the upper and lower annular superconducting coil groups 101. The iron shim pieces 107 are provided so as to protrude from the opposing surfaces 103a of the vacuum insulated container 103, respectively, and are used to adjust the uniformity of the static magnetic field in the spherical space S. An electric heater 109 is provided on the magnetic shield plate 104 as shown. An electric heater is also provided on a yoke (not shown).

The gradient magnetic field coils 111 have a disc-like shape, and are disposed inside the opposing surface 103a of the opposing vacuum insulated container 103, respectively. Gradient magnetic field coil 1
Reference numeral 11 denotes an upper and lower annular superconducting coil group 1 during MRI imaging.
A pulse-like gradient magnetic field is generated by superimposing on the static magnetic field by the magnetic field 01. The high-frequency coils 112 are respectively arranged at the center and inside the surface facing the gradient coil 111. The high-frequency coil 112 generates a magnetic resonance frequency of water in the body of the subject (patient).

The decorative cover 115 is provided in the vacuum heat insulating container 10.
3, provided so as to cover the magnetic shield plate 104, the yoke (not shown), the electric heater 109, the gradient magnetic field coil 111, and the high-frequency coil 112, and a heat insulating material 114 is filled between these and the decorative cover 115.

Although not shown, the annular superconducting coil group 1
A service port for supplying electricity to 01 and injecting liquid helium, a permanent current switch for operating the annular superconducting coil group 101 in a permanent current mode, and a refrigerator for cooling a plurality of heat shield tanks are provided.

As a countermeasure against the deterioration of the uniformity of the magnetic field due to the temperature fluctuation, the magnetic shield plate 104 and the yoke are covered with a heat insulating material as described above, and the electric heater 109 provided on the surface of the magnetic shield plate 104 and the yoke is provided. By energizing and heating the magnetic shield plate 104, the yoke, and the like to a temperature slightly higher than the maximum value of the room temperature that fluctuates depending on the season, for example, 40 (° C.), the constant temperature including the vacuum insulation container 103 and the communication pipe 106 A method of maintaining the temperature is adopted.

[0018]

In a conventional MRI magnet, an electric heater 10 is used to maintain the magnetic shield plate 104 and the yoke at, for example, 40 (.degree. C.) regardless of summer and winter.
9 has to be energized at all times, and the running cost is high.

On the other hand, there has also been proposed an apparatus which does not perform the above-mentioned heating and holding, for example, provides a shim coil between the vacuum heat insulating container 103 and the gradient magnetic field coil 111 to compensate for the deterioration of the magnetic field uniformity. However, even when compensating for the degradation of the magnetic field uniformity by the shim coil, the power consumption is large and the running cost is expensive because the shim coil is energized, and the attained value of the magnetic field uniformity is low because only the magnetic field component of the shim coil can be corrected. Inferior. Furthermore, since the shim coil is installed, there is a problem that the size of the gap between the vacuum heat insulating containers facing each other is reduced, and the feeling of opening to the patient is reduced.

An object of the present invention is to solve the above-mentioned problems, to prevent the deterioration of the uniformity of the magnetic field due to the fluctuation of the ambient temperature at a low running cost, and to reduce the gap between the opposed vacuum insulated containers. An object of the present invention is to provide a superconducting magnet device capable of preventing a reduction in size.

[0021]

In order to achieve the above object, in a superconducting magnet device according to the present invention, a plurality of annular superconducting coils are accommodated, a space is provided, and a superconducting magnet is disposed coaxially with opposing portions facing each other. A magnet main body having a pair of storage containers that generate a magnetic field between the opposing portions by the coils and a gradient magnetic field coil that is provided on the opposing portion side of each storage container and generates a gradient magnetic field by superimposing on the magnetic field, and It is provided detachably and adjusts the uniformity of the magnetic field, and includes a plurality of magnetic field adjusting members. By attaching and detaching this magnetic field adjusting member according to the temperature fluctuation,
Since the deterioration of the magnetic field uniformity due to the temperature fluctuation can be compensated, no energy is consumed and the running cost is reduced.

The magnetic field adjusting member includes a ferromagnetic piece,
It is characterized by being at least one of an air-core coil piece having a conductor wound thereon and a ferromagnetic coil composite piece having a conductor wound around a ferromagnetic material. As the magnetic field adjusting member, various members as described above can be used taking advantage of their respective characteristics.

Further, in the superconducting magnet device of the present invention, a plurality of annular superconducting coils are accommodated, a gap is provided, and the opposing portions are coaxially arranged with the opposing portions facing each other. A magnet body having a housing container and a gradient magnetic field coil that is provided on the facing portion side of each of the storage containers and generates a gradient magnetic field by superimposing the magnetic field; and a magnetic field provided on the magnet body having a coil wound with a conductive wire. A plurality of magnetic field adjusting members that are adapted to adjust the uniformity of the coil and that can be attached or detached in accordance with the fluctuation of the ambient temperature or that control the current supplied to the coil in accordance with the fluctuation of the ambient temperature It is a thing. Deterioration of magnetic field uniformity due to temperature fluctuations can be compensated for by attaching / detaching the magnetic field adjusting member according to temperature fluctuations or controlling current supplied to the coil according to temperature fluctuations. Since the current supplied to the coil is small, the energy consumption is small and the running cost is low.

Further, the magnetic field adjusting member is characterized in that it is at least one of an air-core coil piece having a conductive wire wound thereon and a ferromagnetic coil composite piece having a conductive wire wound around a ferromagnetic material. If a current is supplied to the air-core coil piece, the uniformity of the magnetic field can be adjusted. Therefore, the air-core coil piece may be attached or detached according to temperature fluctuations. If the control is performed according to the fluctuation, the deterioration of the uniformity of the magnetic field can be compensated without attaching or detaching them.

The magnetic field adjusting member is characterized in that it also serves as an initial adjusting member for initially adjusting the uniformity of the magnetic field at the beginning of manufacturing. If the magnetic field adjusting member is also used as the initial adjusting member, the configuration is simplified.

Further, the magnetic field adjusting member is provided on at least one of an outer side in a direction orthogonal to the axis of the container, a peripheral portion of the facing portion of the container, and a peripheral portion of the gradient magnetic field coil. It is characterized by. Since these places are vacant, the provision of the magnetic field adjusting member does not reduce the air gap, hindering the sense of openness, or increasing the size of the entire apparatus.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic concept of the present invention will be described. The magnetic field component in the spherical space S (see FIG. 1), which is the imaging region, is represented by the following equation (1) when the spherical space S is represented by polar coordinates as shown in FIG.

[0028]

(Equation 1)

In equation (1), the component of (m, n) = (0, 0) is a necessary uniform magnetic field component, all other components are error magnetic field components, and the magnet reduces all error magnetic field components. Designed and manufactured to

Here, the error in the production of the magnet, the error magnetic field component caused by the magnet installation building, the various devices in the magnet installation room, etc., when adjusting the uniformity of the magnetic field, for example, the mounting position and the installation amount are adjusted in accordance with the amount of the error component. Since the compensation is performed by the strictly specified iron shim pieces (see the iron shim pieces 107 in FIG. 1), all error magnetic field components are minimal at the time of completion of the magnetic field uniformity adjustment in the initial state of manufacture.

On the other hand, if the temperature of the magnet installation room fluctuates after the completion of the adjustment of the magnetic field uniformity, the magnetic shield plate, the yoke, and the vacuum insulation container expand and contract, greatly affecting the magnetic field uniformity. In the formula (1), n = 1, n
= 2. That is, in order to simply and effectively compensate for the deterioration of the magnetic field uniformity due to temperature fluctuation, low-order components of n = 1 and n = 2 are generated, and n =
It is desirable to provide a magnetic field adjusting member such as a detachable ferromagnetic piece, micro coil piece, or ferromagnetic coil composite piece described below at a place where three or more higher order components are not generated. Less than,
This will be specifically described.

Embodiment 1 FIG. 1 shows an MRI magnet according to an embodiment of the present invention, in which FIG. 1 (a) is a sectional view and FIG. 1 (b) is a detailed view of a ferromagnetic piece mounting portion. In FIG. 1, the magnet main body 10 is configured as follows. The annular superconducting coil group 101 has five solenoid type superconducting coils 101a coaxially arranged. The two annular superconducting coil groups 101 are individually accommodated in the vacuum heat insulating container 103 via the low-temperature container 102, and are then disposed coaxially opposite to the vertical axis, and are disposed in a spherical space S, which is an imaging region, in a highly uniform and stable manner. Generates a strong static magnetic field.

The low-temperature vessel 102 includes the annular superconducting coil group 1
01, and also serves as a liquid helium container that cools and holds the annular superconducting coil group 101 to a cryogenic temperature at which superconductivity occurs.

The vacuum insulated container 103 as a storage container is
The cryogenic container 102 is accommodated, and the evaporation of liquid helium from the cryogenic container 102 is reduced. Two vacuum insulated containers 10
3 is coaxially opposed to the vertical axis and has a disk-shaped opposed surface 10.
3a are mutually opposed in the up-down direction. Although not shown, between the low-temperature container 102 and the vacuum insulated container 103,
In order to further reduce the evaporation of liquid helium, a plurality of heat shield tanks are usually installed.

The magnetic shield plate 104 made of a ferromagnetic material is provided on the opposite side of the opposite surface 103a of the vacuum heat insulating container 103 so as to sandwich the two vacuum heat insulating containers 103 in the vertical direction in the figure to reduce the leakage magnetic field. Shield disturbance magnetic field. Although not shown, a pair of ferromagnetic yokes is provided so as to sandwich the two vacuum insulating containers 103 from the left and right directions in the figure, and connects the upper and lower magnetic shield plates 104 to form a magnetic flux flow path. are doing. This yoke also serves as a support structure for the magnetic shield plate 104.

The communication tube 106 connects the upper and lower low-temperature containers 102 and the vacuum heat insulating container 103 in FIG. 1 to form a liquid helium passage and a lead passage for connecting the upper and lower annular superconducting coil groups 101.

The iron shim pieces 107 are provided so as to protrude from the facing surface 103a of the vacuum heat insulating container 103, respectively. The iron shim piece 107 compensates for an inhomogeneous magnetic field component caused by magnetization generated in the magnetic shield plate 104 and the yoke, a manufacturing error of the superconducting coil group 101, and an inhomogeneous magnetic field component caused by a magnet installation building and various equipment in a magnet installation room, and performs imaging. In order to adjust the magnetic field in the spherical space S, which is the region, to be highly uniform, the mounting position and the mounting amount are strictly specified in accordance with the generation amount of the non-uniform component.

The gradient magnetic field coil 111 has a disk shape and is disposed inside the opposing surface 103 a of the vacuum heat insulating container 103. The gradient coil 111 is
At the time of MRI imaging, a pulse-like gradient magnetic field is generated by being superimposed on the static magnetic field generated by the upper and lower annular superconducting coil groups 101. The high-frequency coil 112 is disposed inside the central portion jp4 and on the inner side of the surface facing the gradient magnetic field coil 111. The high-frequency coil 112 generates a magnetic resonance frequency of water in the body of the subject.

The decorative cover 15 is a disc-shaped inner plate 15.
a, the outer plate 15b, and the side plate 15c are assembled in a box shape by connecting them with bolts so that they can be easily separated and detached. The makeup cover 15 is used for the vacuum insulation container 10.
3. The magnetic shield plate 104, the yoke (not shown), the gradient magnetic field coil 111, and the high frequency coil 112 are covered. By removing the outer plate 15b or the side plate 15c, the inner surface of the inner plate 15a can be easily exposed. The magnet main body 10 is configured as described above.

The minute cylindrical ferromagnetic piece 21 projects from the outer edge inside the inner plate 15a of the decorative cover 15 as shown in FIG.
As shown in (b), the number is changed according to the position of the outer edge portion, and is fixed detachably by bolts (not shown).

Next, a description will be given of an actual operation for compensating for the deterioration of the magnetic field uniformity due to the temperature fluctuation by attaching and detaching the ferromagnetic piece 21 according to the fluctuation of the ambient temperature. After the magnetic field uniformity of the MRI magnet is sufficiently achieved by the type test, the relationship between the generation component and the generation amount of the error magnetic field with respect to the change in the room temperature or the temperature of the magnetic shield plate or the yoke is measured. Similar measurements are made for long-period magnetic field fluctuations other than those caused by temperature fluctuations.

On the other hand, when the ferromagnetic piece 21 is arranged at the position as shown in FIG. 1B, the generation component and the generation amount of the error magnetic field with respect to the construction position and the construction amount (the number of ferromagnetic pieces) Is analytically obtained in advance, and finally, the relationship between the temperature and the application of the ferromagnetic piece is summarized.

As described above, since the seasonal temperature fluctuation has the greatest effect on the temperature fluctuation of the magnet installation room, the decorative cover 15 is applied approximately every two to three months in accordance with the relationship between the temperature and the application of the ferromagnetic piece. By removing the side plate 15c or the outer plate 15b, the inner surface side of the flat plate portion 15a is exposed, and the installation and removal of the ferromagnetic piece 21 and the change of the installation position are performed.

The MRI magnet shown in FIG. 1 has the following advantages. Only by attaching / detaching the ferromagnetic piece 21 or changing the position according to the temperature fluctuation, it is possible to take measures against the deterioration of the magnetic field uniformity due to the temperature fluctuation.
Energy is not consumed and running costs are reduced.
The same applies to the MRI magnet devices described in the following second to fifth embodiments.

In this embodiment, since the ferromagnetic piece 21 is detachably fixed to the inner plate 15a of the decorative cover 15, when the ferromagnetic piece 21 is detached,
If the side plate 15c or the outer plate 15b is removed, the work can be easily performed. In addition, since the ferromagnetic piece 21 is provided in a place where the decorative cover 15 is vacant, the provision of the ferromagnetic piece 21 does not reduce the air gap and hinder the feeling of opening, and there is no possibility that the entire device becomes large.

As described above, since the MRI magnet is usually operated in the permanent current mode for several years once it is excited, the attaching and detaching work of the ferromagnetic piece is generally performed in a magnetic field. The place where the ferromagnetic piece 21 is installed is a place where the work can be easily performed without moving the gradient coil 111 or the high frequency coil 112 in the magnetic field.

The vicinity of the high-frequency coil 112 is a place where the high-frequency characteristics, that is, the imaged image characteristics are greatly affected. Is provided, the influence on the image characteristics can be reduced.

As described above, a. By providing the magnetic field adjusting member (the ferromagnetic piece 21 in this embodiment), there is no danger that the air gap becomes small and the feeling of opening is not hindered or the whole device becomes large. A magnetic field adjusting member (a ferromagnetic piece 21 in this embodiment) is moved in a magnetic field by a gradient coil 11.
(1) that the attachment / detachment operation can be performed easily without moving the high-frequency coil 112 or The fact that the influence of the magnetic field adjusting member (the ferromagnetic piece 21 in this embodiment) on the image characteristics can be reduced is an advantage common to all the embodiments including Embodiments 2 to 7 described later.

Embodiment 2 FIG. 3 is a sectional view of an MRI magnet showing still another embodiment of the present invention. In FIG. 3, the cylindrical ferromagnetic piece 22 is located on the side of the magnetic shield plate 121 on the side of the vacuum heat-insulating container, and
4 protrudingly provided at the outer edge. Ferromagnetic piece 2
2 is detachably fixed by bolts (not shown), the number of which varies according to the position of the outer edge. Other configurations are the same as those of the first embodiment shown in FIG. 1, and the corresponding components are denoted by the same reference numerals and description thereof is omitted.

Since the ferromagnetic piece 22 is provided on the outer edge of the magnetic shield plate 104, which is located farthest from the high frequency coil 112, the influence on the image characteristics can be further reduced.

Embodiment 3 FIG. FIG. 4 is a sectional view of an MRI magnet showing still another embodiment of the present invention. In FIG. 4, the cylindrical ferromagnetic piece 23 protrudes from the opposing surface 103a on the opposing surface 103a of the vacuum heat insulating container 103 and closer to the outer edge than the iron shim piece 107.
7, that is, so as to overlap with the iron shim piece 107 when viewed from the left and right directions in FIG. 4. The number of the ferromagnetic material pieces 23 is changed according to the position of the outer edge,
It is detachably fixed by bolts (not shown). Other configurations are the same as those of the first embodiment shown in FIG. 1, and the corresponding components are denoted by the same reference numerals and description thereof is omitted.

Since the ferromagnetic pieces 23 are provided, the gaps between the vacuum heat-insulating containers 103 are opposite to each other because they are provided side by side with the iron shim pieces 107 protruding from the facing surface 103a of the vacuum heat-insulating container 103. Can be prevented from becoming smaller. Also, the ferromagnetic piece 23 is connected to the high-frequency coil 11
2 opposite surface 1 of vacuum insulation container 103
Since it is provided on the outer edge side of 03a, the influence on image characteristics can be reduced.

Embodiment 4 FIG. 5 is a sectional view of an MRI magnet showing still another embodiment of the present invention. In FIG. 5, the cylindrical ferromagnetic piece 24 is provided at the outer edge of the surface (inner surface) where the gradient magnetic field coils 111 face each other.
The high-frequency coil 11 protruding from the gradient coil 111
2, that is, so as to overlap with the high-frequency coil 112 when viewed from the left and right directions in FIG. The number of the ferromagnetic material pieces 24 is changed depending on the position of the outer edge portion, and is detachably fixed by bolts (not shown). Other configurations are the same as those of the first embodiment shown in FIG. 1, and the corresponding components are denoted by the same reference numerals and description thereof is omitted.

Embodiment 5 FIG. FIGS. 6A and 6B show a ferromagnetic piece according to another embodiment of the present invention. FIG. 6A is a perspective view of a cylindrical ferromagnetic piece, and FIG. FIG. 3C is a perspective view of a magnetic piece, and FIG. In FIG. 6, reference numeral 61 denotes a cylindrical ferromagnetic piece that is mounted while changing the amount and size of mounting according to the mounting position; 62, a rectangular parallelepiped ferromagnetic piece;
Numeral 63 denotes a fan-shaped ferromagnetic piece, which is appropriately used similarly to the ferromagnetic pieces 21 to 24 shown in the first to fourth embodiments.

Embodiment 6 FIG. FIG. 7 shows a micro coil piece as a magnetic field adjusting member according to another embodiment of the present invention. FIG. 7 (a) is a perspective view of a cylindrical micro coil piece, and FIG. FIG. 4C is a perspective view of a rectangular parallelepiped micro coil piece, and FIG. In FIG. 7, reference numeral 71 denotes a cylindrical micro coil piece, 72 denotes a rectangular parallelepiped micro coil piece, and 73 denotes a fan-shaped micro coil piece. These minute coil pieces 71 to 73 are air-core coil pieces in which a copper wire is wound once or plural times in various shapes as shown in the figure.

These are appropriately used in the same manner as the ferromagnetic pieces 21 to 24 shown in the first to fourth embodiments. At this time, one having a different number of turns according to the mounting position is mounted. Although not shown, an excitation power supply is provided to supply current to the small coil pieces.

Next, the actual construction will be described. The places where the micro coil pieces 71 to 73 are installed are the same as those of the ferromagnetic multi pieces 21 to 24 shown in the first to fourth embodiments. M
After the RI magnet achieves sufficient magnetic field uniformity in its type test, the relationship between the generation component and the generation amount of the error magnetic field with respect to the change in the room temperature or the temperature of the magnetic shield plate or the yoke is measured. Similar measurements are made for long-period magnetic field fluctuations other than those caused by temperature changes.

On the other hand, for example, when the minute coil piece 71 is arranged in place of the magnetic piece 21 shown in FIG. 1A, the relationship between the construction position and the ampere turn and the generation component and the generation amount of the error magnetic field is determined in advance. Analytically, and finally summarize the relationship between the temperature and the ampere-turn of each micro coil piece,
A set of a plurality of micro coil pieces wound around the number of turns corresponding to the ampere turn ratio is prepared.

As described above, since the influence of the seasonal temperature fluctuation is the largest in the temperature fluctuation of the magnet installation room, the temperature and the construction of the set of small coil pieces are set approximately every two to three months.
The side plate 15c of the decorative cover 15 is removed to install or replace a set of minute coil pieces, or change the position, and further adjust current supplied to the minute coil pieces.

The reason for preparing a set of a plurality of micro coil pieces wound with the number of turns corresponding to the ampere turn ratio is to reduce the number of excitation power supplies of the micro coil pieces and the connection of lead wires. . The reason why the set of micro coil pieces is exchanged about every two to three months is to more flexibly cope with temperature fluctuations.

It is possible to take measures against the deterioration of the uniformity of the magnetic field due to the temperature fluctuation only by installing or exchanging the set of the small coil pieces according to the temperature fluctuation and controlling the supplied minute current. Consumption can be reduced.

Although the small coil pieces of the embodiment shown in FIG. 7 are detachably installed, these small coil pieces are removed because of the method of adjusting the current value to compensate for the uniformity of the magnetic field. It is also possible to compensate for the deterioration of the uniformity of the magnetic field by keeping the current fixed and adjusting the supplied current. Further, the micro coil piece can be used together with the ferromagnetic piece shown in the first to fifth embodiments. Further, the micro coil piece may be used together with the iron shim piece 107 or may be used alone as an initial adjustment adjusting member for adjusting the uniformity of the magnetic field at the beginning of manufacture.

Compensation by the set of small coil pieces shown in this embodiment makes it possible to finely correct the uniformity of the magnetic field by finely adjusting the current value supplied to the small coil pieces as compared with the embodiment of FIG. In addition, there are advantages that the compensation range can be widened because the reverse polarity can be compensated according to the polarity of the current value, and the work of attaching the small coil piece is easy because the small coil piece does not receive the electromagnetic force even in the static magnetic field. Have.

Embodiment 7 FIG. FIG. 8 shows a ferromagnetic coil composite piece as a magnetic field adjusting member according to another embodiment of the present invention. FIG. 8A is a perspective view of a cylindrical ferromagnetic coil composite piece. (B) is a perspective view of a rectangular parallelepiped ferromagnetic coil composite piece, and (c) is a perspective view of a fan-shaped ferromagnetic coil composite piece.

In FIG. 8, 81 is a cylindrical ferromagnetic coil composite piece, 82 is a rectangular parallelepiped ferromagnetic coil composite piece,
Reference numeral 83 denotes a fan-shaped ferromagnetic coil composite piece, which is appropriately used in place of the ferromagnetic piece and the micro coil piece shown in the first to sixth embodiments. These ferromagnetic coil composite pieces 81 to 83 are formed by winding coils 81b, 82b, 83b in each of which a copper wire is wound a predetermined number of times on cylindrical, rectangular, or fan-shaped ferromagnetic pieces 81a, 82a, 83a as shown in FIG. A coil having different numbers of turns of the coils 81b, 82b, 83b according to the mounting position is mounted.

The location and method of application of these coiled ferromagnetic coil composite pieces are the same as those of the ferromagnetic pieces and micro coil pieces shown in the first to sixth embodiments.

This embodiment is, for example, a combination of the embodiment of FIG. 1 and the embodiment of FIG. 7, and has a large temperature fluctuation value and a large influence on the magnetic field uniformity. It is suitable when both relatively large compensation for deterioration and fine adjustment are required.

According to this embodiment, the magnetic field uniformity caused by the temperature fluctuation can be reduced by merely installing or replacing the set of ferromagnetic coil composite pieces in accordance with the temperature fluctuation, or controlling the minute current to be supplied. As we can take measures against deterioration,
Energy consumption can be reduced, and running costs can be reduced.

Compensation by the set of ferromagnetic coil composite pieces shown in this embodiment is different from that of the embodiment shown in FIG. 1 in that the current supplied to the ferromagnetic coil composite pieces is finely adjusted to reduce the magnetic field. This has the advantage that the uniformity can be finely corrected, and that the opposite polarity can be compensated according to the polarity of the current value, so that the compensation range is wide.

Although the ferromagnetic coil composite pieces of the embodiment of FIG. 8 are detachably installed, these ferromagnetic coil composite pieces adjust the current value to compensate for the uniformity of the magnetic field. Because of this method, it is possible to compensate for the deterioration of the uniformity of the magnetic field by keeping the fixed without removing and adjusting the supplied current. Further, the ferromagnetic coil composite piece can be used in combination with the ferromagnetic material piece and the micro coil piece shown in the first to sixth embodiments. Further, the ferromagnetic coil composite piece can be used in combination with the iron shim piece 107 or independently as an adjusting member for initial adjustment for adjusting the magnetic field uniformity at the beginning of manufacture.

In addition to the mounting locations shown in the above embodiments, for example, the vacuum insulated container 1 shown in FIG.
A vacant place such as the outer peripheral cylindrical surface 03, the inner surface of the side plate 15c of the decorative cover 15, and the like can also be used as a mounting place. Also, in the actual construction and work, it is not necessary to install a ferromagnetic piece, a micro coil piece, a ferromagnetic coil composite piece, etc. in all of these mounting locations. I just need.

If the method of fixing the ferromagnetic material piece, the micro coil piece, the ferromagnetic coil composite piece, and the like can also be attached and detached, they can be fixed by bolts, fixed by screws, held by detachable holders, and fixed with an adhesive or adhesive tape. Any fixing method can be selected. Furthermore, the shape of the ferromagnetic piece, the micro coil piece, and the like shown in each of the above embodiments is not limited to the shape, and any shape and size may be used without impairing the object of the present invention. However, it is desirable to be able to have various shapes and sizes.

In each of the above embodiments, the example of the MRI magnet of the superconducting vertical magnetic field type has been described. However, the split horizontal magnetic field in which two vacuum insulated containers are coaxially opposed to each other in a horizontal axis. Any type of magnet for MRI or a magnet other than for MRI can be used as long as it requires compensation for temperature fluctuation.

[0074]

Since the present invention is constructed as described above, it has the following effects.

In the superconducting magnet device of the present invention, a pair of storage containers for accommodating a plurality of annular superconducting coils, providing a gap, and coaxially opposing opposing portions, and generating a magnetic field between the opposing portions by the superconducting coils. And a magnetic field coil which is provided on the facing portion side of each container and has a gradient magnetic field coil which generates a gradient magnetic field by being superimposed on the magnetic field, and a plurality of magnets which are detachably mounted on the magnetic body and adjust the uniformity of the magnetic field. Since the magnetic field adjusting member is provided, by attaching and detaching the magnetic field adjusting member according to the temperature fluctuation,
It is possible to obtain a device which can compensate for the deterioration of the magnetic field uniformity due to the temperature fluctuation, consumes no energy, and can compensate for the deterioration of the magnetic field uniformity due to the temperature fluctuation at a low running cost without consuming energy.

The magnetic field adjusting member is a ferromagnetic piece,
Since it is characterized in that it is at least one of an air-core coil piece having a conductive wire wound thereon and a ferromagnetic coil composite piece having a conductive wire wound around a ferromagnetic material, as a magnetic field adjusting member, Various things can be used taking advantage of each characteristic.

Further, in the superconducting magnet device of the present invention, a pair of annular superconducting coils are accommodated, a gap is provided, and the opposing portions are coaxially arranged so that the opposing portions face each other. A magnet body having a housing container and a gradient magnetic field coil that is provided on the facing portion side of each of the storage containers and generates a gradient magnetic field by superimposing the magnetic field; and a magnetic field provided on the magnet body having a coil wound with a conductive wire. With a plurality of magnetic field adjusting members adapted to be attached or detached in accordance with changes in ambient temperature or controlled in current supplied to a coil in accordance with temperature changes Therefore, by attaching and detaching the magnetic field adjusting member according to the temperature fluctuation, or controlling the current supplied to the coil according to the temperature fluctuation, the magnetic field uniformity due to the temperature fluctuation Since the deterioration can be compensated for and the current supplied to the coil is small, it is possible to obtain an apparatus which consumes little energy and can compensate for the deterioration of the magnetic field uniformity due to temperature fluctuation at a low running cost. it can.

Further, the magnetic field adjusting member is characterized in that it is at least one of an air-core coil piece having a conductor wound thereon and a ferromagnetic coil composite piece having a conductor wound around a ferromagnetic material. If a current is supplied to the air-core coil piece, the uniformity of the magnetic field can be adjusted, so the air-core coil piece may be attached or detached according to temperature fluctuations. By controlling according to the fluctuation, it is possible to compensate for the deterioration of the uniformity of the magnetic field without attaching and detaching these,
Adjustment is easy.

Since the magnetic field adjusting member also serves as an initial adjusting member for initially adjusting the uniformity of the magnetic field at the beginning of the production, the structure of the apparatus is simplified.

Further, the magnetic field adjusting member is provided on at least one of the outer side in the direction perpendicular to the axis of the container, the peripheral portion of the facing portion of the container, and the peripheral portion of the gradient magnetic field coil. Since these places are vacant, by providing a member for adjusting the magnetic field,
There is no fear that the air gap becomes small and the feeling of opening is hindered, and the entire device does not become large.

[Brief description of the drawings]

FIG. 1 is an MRI according to an embodiment of the present invention.
FIG. 3A is a sectional view, and FIG. 3B is a detailed view of a mounting portion of a ferromagnetic piece.

FIG. 2 is an explanatory diagram of a magnetic field component.

FIG. 3 is a block diagram showing another embodiment of the present invention;
It is sectional drawing of a magnet for RI.

FIG. 4 is a diagram showing another embodiment of the present invention;
It is sectional drawing of a magnet for RI.

FIG. 5 is a block diagram showing another embodiment of the present invention;
It is sectional drawing of a magnet for RI.

6 (a) and 6 (b) show another embodiment of the present invention, wherein FIG. 6 (a) is a perspective view of a cylindrical ferromagnetic piece, and FIG. 6 (b) is a perspective view of a rectangular parallelepiped ferromagnetic piece. FIG. 3C is a perspective view of a fan-shaped ferromagnetic piece.

FIG. 7 shows a micro coil piece as a magnetic field adjusting member according to another embodiment of the present invention;
FIG. 1A is a perspective view of a cylindrical micro coil piece, FIG. 2B is a perspective view of a rectangular parallelepiped micro coil piece, and FIG. 1C is a perspective view of a fan-shaped micro coil piece.

FIG. 8 shows a ferromagnetic coil composite piece as a magnetic field adjusting member according to another embodiment of the present invention. FIG. 8A is a perspective view of a cylindrical ferromagnetic coil composite piece. FIG. 1B is a perspective view of a rectangular parallelepiped ferromagnetic coil composite piece, and FIG. 2C is a perspective view of a fan-shaped ferromagnetic coil composite piece.

FIG. 9 is a sectional view of a conventional MRI magnet.

[Explanation of symbols]

10 magnet body, 15 decorative cover, 15a inner plate,
21, 22, 23, 24, 61, 62, 63 Ferromagnetic pieces, 71, 72, 73 Micro coil pieces, 81, 82, 8
3 Ferromagnetic coil composite piece, 101 superconducting coil group,
103 vacuum insulation container, 103a facing surface, 104 electromagnetic shield plate, 111 gradient magnetic field coil.

Continuing on the front page (72) Inventor Hajime Tanabe 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Hirotaka Takeshima 1-11-1 Uchikanda, Chiyoda-ku, Tokyo Stock Company Hitachi Medical Corporation (72) Inventor Takao Real Name 1-1-1 Uchikanda, Chiyoda-ku, Tokyo F-term in Hitachi Medical Corporation 4C027 AA10 CC00 EE00 4C096 AA01 AB31 CA02 CA22 CA25

Claims (6)

[Claims] 1. A pair of storage containers for accommodating a plurality of annular superconducting coils, providing an air gap, and coaxially opposing opposing portions and generating a magnetic field between the opposing portions by the superconducting coils. A magnet main body having a gradient magnetic field coil provided on the side of the opposing portion and superimposed on the magnetic field to generate a gradient magnetic field, and a plurality of magnetic field adjustments detachably provided on the magnet main body for adjusting the uniformity of the magnetic field A superconducting magnet device provided with members. 2. The magnetic field adjusting member is at least one of a ferromagnetic piece, an air-core coil piece with a conductive wire wound thereon, and a ferromagnetic coil composite piece with a conductive wire wound on a ferromagnetic material. The superconducting magnet device according to claim 1, wherein: 3. A pair of storage containers for accommodating a plurality of annular superconducting coils, providing a gap and coaxially opposing opposing portions, and generating a magnetic field between the opposing portions by the superconducting coils, and A magnet main body having a gradient coil superposed on the magnetic field and generating a gradient magnetic field provided on the facing portion side, and a coil wound with a conductive wire, provided on the magnet main body and having a uniformity of the magnetic field. A superconducting magnet having a plurality of magnetic field adjusting members, which are to be adjusted and made detachable in accordance with a change in the ambient temperature or in which the current supplied to the coil is controlled in accordance with the change in the ambient temperature apparatus. 4. The magnetic field adjusting member is at least one of an air-core coil piece around which a conductor is wound and a ferromagnetic coil composite piece around which a conductor is wound around a ferromagnetic material. 4. The superconducting magnet device according to 3. 5. The superconducting magnet device according to claim 4, wherein the magnetic field adjusting member doubles as an initial adjusting member for initially adjusting the uniformity of the magnetic field at the beginning of manufacturing. 6. The magnetic field adjusting member is provided on at least one of an outer side in a direction orthogonal to an axis of the storage container, a peripheral portion of the facing portion of the storage container, and a peripheral portion of the gradient magnetic field coil. The superconducting magnet device according to claim 1 or 3, wherein: