JPH0438931A - Nuclear magnetic resonance apparatus - Google Patents

Abstract

PURPOSE:To achieve a higher efficiency in the generation of an inclined magnetic field and further to realize a smaller size of the apparatus by incorporating an active shielding coil to suppress possible disturbance of an image, while the active shielding coil is arranged being separated at a distance from an inclined magnetic field coil. CONSTITUTION:An active shielding coil 12 is set within a container housing a superconductive coil 1. With such an arrangement, the structure of a nuclear magnetic resistance apparatus can be such that an inclined magnetic field coil 3, an inner circumferential wall 9b of a container 9, an active shielding coil 12 and heat shielding plates 10 and 11 are arranged in the incremental order of radius, which allows the suppression of the generation of an eddy current to be induced in the heat shielding plates 10 and 11, associated with variations in an inclined magnetic field. As a result, adverse effect on an electrostatic magnetic field and the inclined magnetic field otherwise caused by the eddy current can be checked to prevent possible disturbance of an image. In addition, as a distance increase between the active shielding coil 12 and the inclined magnetic field coil 3, generation efficiency of the inclined magnetic field can be improved. Thus, the inner circumferential wall 9b of the container 9 can be positioned in a space make a distance, thereby avoiding a growing size of the superconductive coil 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a nuclear magnetic resonance apparatus, and particularly to a nuclear magnetic resonance apparatus that performs MR imaging using a superconducting coil and a gradient magnetic field coil.

[Conventional technology]

Nuclear magnetic resonance equipment combines nuclear magnetic resonance phenomena and image processing technology to perform so-called MR imaging.
There is an R imaging device. This MR imaging device is used, for example, for image diagnosis of living bodies and the like.

As schematically shown in FIG. 2, the MR imaging apparatus includes a nuclear magnetic resonance apparatus having a main coil 1, a high-frequency coil 2 and a gradient magnetic field coil 3 disposed inside the main coil 1, and an image processing system (not shown). It is equipped with

The main coil 1 generates a uniform static magnetic field (in the Z-axis direction in the figure) at the center of the coil, and changes the magnetic moment of the atomic nucleus of the specimen by 2.
Align in the axial direction. A superconducting coil is used as the main coil 1 in order to generate a uniform static magnetic field in the measurement space. Therefore, although not shown in the figure, the nuclear magnetic resonance apparatus includes a liquid helium tank that houses the superconducting coil, a heat shield plate that surrounds the liquid helium tank, and a cryostat that has a vacuum container that houses them. It also has more.

The high-frequency coil 2 irradiates the subject with a high-frequency electromagnetic field orthogonal to the static magnetic field to cause a nuclear magnetic resonance phenomenon and receives a nuclear magnetic resonance signal.

In the MR imaging apparatus, the gradient magnetic field coil 3 is configured to use Xp'/lZ to identify the spatial position of the nuclear magnetic resonance signal.
3x, 3 so as to create two-component gradients of the magnetic field in the three directions.
Three sets of y and 3z are installed. In addition, in FIG. 2, in order to avoid complicating the notation in the drawing, the X gradient magnetic field coil 3x and the 2 gradient magnetic field coil 3z are shown, and the y
Illustration of the gradient magnetic field coil 3y is omitted.

Since the gradient magnetic field coil 3 is excited in a pulsed manner, its fluctuating magnetic field induces eddy currents on the wall surface of the cryostat container, the heat shield plate housed inside, and the like. This eddy current generates a magnetic field. This magnetic field consists of a uniform magnetic field created by the main coil 1 and a magnetic field created by the gradient magnetic field coil 3.
It disturbs the image spatially and temporally, causing image deterioration. Also,
Joule heat generation due to eddy currents causes the temperature of the heat shield plate to rise.

Active shield coils solve this problem. FIG. 3 shows the X gradient magnetic field coil 4 and the X gradient magnetic field active shield coil 5, and FIG. 4 shows the two gradient magnetic field coils 6 and the two gradient magnetic field active shield coils 7.
are shown conceptually.

Each active shield coil is concentric with the main coil 1 and the gradient coil 3 shown in FIG.
It is constructed by being wound in an appropriate shape onto a cylinder with a larger radius. A current is passed through the active shield coil in the opposite direction to that of the gradient magnetic field coil 3. As a result, the gradient magnetic field coil 3 is placed outside the active shield coil.
This cancels the magnetic field caused by the heat shield and prevents eddy currents from occurring on heat shield plates, etc. On the other hand, the active shield coil is also required to not weaken the necessary gradient magnetic field too much inside the gradient magnetic field coil 3.

Techniques related to this type of active shield coil include those described in, for example, Japanese Patent Application Laid-Open No. 143012/1982 and US Pat. No. 4,733,189.

[Problem to be solved by the invention]

Conventional M with such an active shield coil
The R imaging device has the following configuration. That is, there is a portion at the center of the coil where a subject such as a human body should exist. Next, in order of increasing radius, there are a high frequency coil, a gradient magnetic field coil, an active shield coil, an inner circumferential wall of a vacuum chamber, a heat shield plate 80, a heat shield plate 20, a liquid helium tank, and a superconducting film.

The high frequency coil and the gradient magnetic field coil are approximately determined by the size of the human body that is the subject. On the other hand, the active shield coil generates a magnetic field in the opposite direction to the gradient magnetic field coil even inside the gradient magnetic field coil, but this magnetic field becomes smaller as the distance between the active shield coil and the gradient magnetic field coil increases. Therefore, in order to increase the efficiency of generating gradient magnetic fields, it is necessary to increase the distance between the active shield coil and the gradient magnetic field coil.

However, in order to increase the distance between the active shield coil and the gradient magnetic field coil, the radius of the cylinder in which the active shield coil is installed must be increased due to the relationship with the size of the subject. It is necessary to increase the radius accordingly. In this case, since the distance between the inner circumferential wall of the vacuum chamber and each heat shield plate cannot be made extremely narrow, the superconducting coil (main coil) inevitably becomes large.

As superconducting coils become larger, the helium tank that houses them has to become larger. Along with this, there is a problem that the amount of liquid helium to be supplied into the helium tank increases, and the amount of helium consumed increases due to the increase in the heat dissipation area. moreover.

Since the volume and outer diameter of the cryostat that accommodates the helium tank are increased, there is a problem in that the entire device becomes larger.

As described above, it is difficult to miniaturize conventional MR imaging devices because if the superconducting coil is made smaller, the distance between the active shield coil and the gradient magnetic field coil becomes shorter, which reduces the efficiency of generating the gradient magnetic field. Met. When downsizing, the device was configured by omitting the active shield coil, knowing that the image would be slightly distorted by eddy currents.

SUMMARY OF THE INVENTION An object of the present invention is to provide a nuclear magnetic resonance apparatus that incorporates an active shield coil to suppress the occurrence of image disturbances, and that can be miniaturized without reducing the efficiency of generating gradient magnetic fields.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a container having a normal temperature space forming a measurement space, and a storage section provided in a space surrounded by an inner circumferential wall surrounding the normal temperature space and an outer circumferential wall outside the normal temperature space, The housing section accommodates a superconducting coil, at least one heat shield plate that surrounds and thermally shields the superconducting coil, and an active shield coil, and the normal temperature space accommodates a high frequency coil and a gradient magnetic field coil that surround a measurement space. It is characterized by being configured as follows.

The superconducting coil is configured to be maintained at a temperature at which its superconducting phenomenon occurs. For example, in order to be cooled by a refrigerant such as liquid helium or liquid nitrogen, it is stored in a refrigerant tank filled with such refrigerant. The heat shield plate surrounds the superconducting coil together with the refrigerant tank to perform heat shielding.

One embodiment of the heat shield plate preferably includes a first heat shield plate surrounding the superconducting coil and a second heat shield plate surrounding the first heat shield plate. In this case, the active shield coil is preferably provided between the inner peripheral wall of the container and the second heat shield plate. For example, as the first heat shield plate, 20
A heat shield plate 20 cooled to K is preferably used, and a heat shield plate 80 cooled to 80 K is preferably used as the second heat shield plate.

The active shield coil is preferably.

It is located just outside the inner circumferential wall of the container.

The storage portion of the container is preferably maintained in a vacuum state and configured to have a heat insulating function.

Further, according to one aspect of the present invention, for example, a superconducting coil that generates a uniform static magnetic field in a measurement space, at least one heat shield plate that surrounds the superconducting coil and shields it from heat, and a superconducting coil that is inclined in the measurement space. A gradient magnetic field coil that generates a magnetic field, a high frequency coil that causes a subject to undergo nuclear magnetic resonance and receives a nuclear magnetic resonance signal, and an active shield coil that is disposed between the heat shield plate and the gradient magnetic field coil. The arrangement position of the active shield coil is such that when the distance between the central axis of the measurement space and the heat shield plate on the outside of the active shield coil is 1, the coil winding portion of the active shield coil is A nuclear magnetic resonance apparatus is provided that is set to be located within a range of 0.88 to 1 from the central axis.

Further, according to the present invention, as a more specific aspect, a superconducting coil that generates a uniform static magnetic field in a measurement space, a refrigerant tank that houses and cools the superconducting coil, and at least one refrigerant tank that surrounds the refrigerant tank. a container having a room temperature space in the center and a storage section surrounding the room temperature space for accommodating the refrigerant tank and the heat shield board;
A gradient magnetic field coil that generates a gradient magnetic field and a high frequency coil that causes a subject to undergo nuclear magnetic resonance and receives a nuclear magnetic resonance signal are arranged in the normal temperature space, and a superconducting coil in the storage section is arranged. There is provided a nuclear magnetic resonance apparatus characterized in that an active shield coil is disposed at a position closer to the center axis than a heat shield plate located closest to the superconducting coil in the inner space.

Furthermore, according to the present invention, there is provided a nuclear magnetic resonance apparatus that uses a superconducting coil to form a static magnetic field, comprising at least one heat shield plate that surrounds and thermally shields the superconducting coil, the heat shield plate being Provided is a nuclear magnetic resonance apparatus characterized in that it is comprised of a laminate of an electrical insulator and a metal foil.

According to the present invention, as an example of its application, a superconducting coil that is housed in a container having a cooling function and generates a uniform static magnetic field in a measurement space, a gradient magnetic field coil that generates a gradient magnetic field in a measurement space, Regarding a nuclear magnetic resonance apparatus having a high frequency coil that causes nuclear magnetic resonance in a specimen and receives a nuclear magnetic resonance signal, and a nuclear magnetic resonance signal that is detected,
An MR imaging apparatus is provided, comprising an image processing system that performs image processing to improve the image, and the nuclear magnetic resonance apparatus is configured by providing an active shield coil in the container. Also, as another example, this MR
A diagnostic device is provided that includes an imaging device and a conveyance means for conveying a subject in the axial direction of a measurement space.

In addition, there is a superconducting coil that generates a uniform static magnetic field in the measurement space, a gradient magnetic field coil that generates a gradient magnetic field in the measurement space, and a nuclear magnetic resonance signal that causes nuclear magnetic resonance in the subject inside the coil. A nuclear magnetic resonance apparatus is provided, comprising: a high-frequency coil that receives a radio frequency coil; and an active shield coil disposed between the superconducting coil and the gradient magnetic field coil, and a cooling means for cooling the active shield coil. .

[Effect]

By installing the active shield coil in the container containing the superconducting coil, the configuration of the nuclear magnetic resonance apparatus can be changed to
For example, in order of increasing radius.

It can be a gradient magnetic field coil, an inner circumferential wall of the container, an active shield coil, and a heat shield plate (heat shield plate 80, heat shield plate 20). Therefore, compared to the conventional configuration of a gradient magnetic field coil, an active shield coil, an inner circumferential wall of the container, and a heat shield plate (heat shield plate 80, heat shield plate 20), the distance between the active shield coil and the gradient magnetic field coil is greater. The efficiency of generating gradient magnetic fields increases.

Furthermore, by locating the inner peripheral wall of the container in the space for increasing the distance between the active shield coil and the gradient magnetic field coil, it is possible to eliminate wasted space and avoid increasing the size of the superconducting coil.

In the present invention, since the active shield coil is incorporated, the generation of eddy currents induced in the heat shield plate due to variations in the gradient magnetic field is suppressed. Therefore, the adverse effect of eddy currents on the static magnetic field and the gradient magnetic field is suppressed, and image disturbance can be prevented from occurring.

Note that if the active shield coil is cooled to a low temperature, the resistance of the coil conductor will be lowered, so the excitation current may be small, and the burden on the excitation power source can be reduced.

(The following is a margin) [Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows the configuration of an embodiment of a nuclear magnetic resonance apparatus according to the present invention.

As shown in FIG. 1, the nuclear magnetic resonance apparatus of this embodiment includes a main coil 1, a liquid helium tank 8 housing the main coil 1, a first heat shield plate 20, a heat shield plate 11, and a second heat shield plate 20. Heat shield plate IQ and heat shield plate 80,
An active shield coil 12, a container 9 having a storage section 9c and a room temperature space 9a in the center thereof, and a gradient magnetic field coil 3 and a high frequency coil 2 arranged inside the room temperature space 9a of the container 9. configured.

The main coil 1 is made of a superconducting coil, and generates a uniform static magnetic field near the center of the coil in the Z-axis direction, as shown in FIG. The liquid helium tank 8 houses the main coil 1,
4. The main coil 1 is heated using liquid helium as a refrigerant.
Cool and maintain at 2K.

In this state, a current is flowing through the main coil 1, realizing a superconducting magnet using persistent current. Further, this liquid helium tank 8 can be replenished with liquid helium from a liquid helium storage tank (not shown).

The container 9 constitutes a cryostat, and the inside of the storage section 9c is kept in a vacuum state. This insulates the main coil 1 etc. housed inside. This container 9 is 1, for example,
Manufactured from stainless steel. External connection portions 9d of the heat shield plates 11 and 80 to the liquid helium tank 8.20 are provided in a part of the storage portion 9c.

In addition, the connection part for energization of the active shield coil 12 (
(not shown) is provided.

Further, in the center of this container 9, a normal temperature space 9a is provided. The gradient magnetic field coil 3 and the high frequency coil 2 are arranged inside the normal temperature space 9a. Furthermore, a space is secured inside the high-frequency coil 2 in which the subject is placed. Therefore, the container 9 has a normal-temperature space 9a that accommodates the space in which the subject is placed, the high-frequency coil 2 surrounding this space, and the gradient magnetic field coil 3 disposed outside the high-frequency coil 2. It is stipulated to ensure the necessary space for

The heat shield plates 1o and 11 are usually made of a metal with high thermal conductivity, such as copper. And these are
Each is thermally connected to a refrigerator (not shown), and each has 80
It is then cooled to 20K.

The former shields radiant heat from the container 9 (approximately 300K),
The latter shields 80 from radiant heat from the heat shield plate 10.

The gradient magnetic field coil 3 generates a gradient magnetic field necessary for taking a tomographic image near the center of the main coil 1. Although not shown in FIG. 1, the gradient magnetic field coils 3 are provided in three sets: an X gradient magnetic field coil, an X gradient magnetic field coil, and a 2-gradient magnetic field coil, assuming that the main coil 1 has two axes. Of these, the X gradient magnetic field coil 3x and the two gradient magnetic field coil 3z are shown in FIG. The gradient magnetic field coils 3 are each connected to an excitation circuit (not shown) and excited by a pulse current.

The high-frequency coil 2 serves both as a transmitting coil that irradiates a high-frequency electromagnetic field to the subject and as a receiving coil that receives nuclear magnetic resonance signals from the subject. This high frequency coil 2 has a first
Although not shown in the figure, it is connected to an oscillator and an image processing system, for example, as shown in FIG. 12, which will be described later. This high frequency coil 2 is excited by an oscillator when functioning as a transmitting coil. In addition, when this high frequency coil 2 functions as a receiving coil, the detected nuclear magnetic resonance signal is subjected to amplification, detection, arithmetic processing, etc. by an image processing system, and the results are recorded and converted into image data. , is displayed on a display (not shown). Further, the image is printed out as necessary.

The active shield coil 12 is located at a position 20 which is closest to the main coil 1 in the inner space of the main coil in the housing portion 9C, and is located at a position inner than the heat shield plate 11, that is, 80 in this embodiment. Shield plate 10 and room temperature space 9a wall surface of container 9 (hereinafter simply referred to as inner peripheral wall of container) 9b
installed between.

Further, the active shield coil 12 is connected to an excitation circuit (not shown), or connected in series or parallel with the gradient magnetic field coil to the same excitation circuit as the gradient magnetic field coil, and is excited by a pulse current. This excitation is applied to the gradient magnetic field coil 3
This is done by supplying a current that generates a magnetic field in the opposite direction to cancel out the eddy currents caused by the magnetic field. In principle, for example, a pulse current of the same magnitude and opposite polarity is supplied to a coil similar to the gradient magnetic field coil to excite it.

The position where this active shield coil 12 is installed is
There are various possibilities. For example, 80 has heat shield plates 1o and 2.
0 and the heat shield plate 11. in this case,
20, there are solutions for the range and current of the active shield coil that makes the magnetic field O on the heat shield plate 11. In that case, the heat shield plate 80 may be made of a material that does not easily generate eddy currents.

Although not intended to limit the invention, in this example and in the following examples, the active shield coil 12 has an 80
It is installed between the heat shield plate 10 and the container 9.

Furthermore, if the distance between the heat shield plate 10 and the central axes 0 and 80 of the nuclear magnetic resonance apparatus is 1.0, the active shield coil 12 is located within a range of 0°88 to 1.0° from the central axis ○. It is preferable that the coil winding portion is located at the same position. Specifically, in this embodiment, it is arranged at a position 0.9 from the central axis O.

The active shield coil 12 may have any shape as long as it has a winding pattern that has little influence on the gradient magnetic field in the measurement space and can effectively suppress the generation of eddy currents in the heat shield plate 10 . Therefore, its shape is not particularly limited, and any conventionally used winding pattern can be used. for example,
As shown in FIGS. 3 and 4, the shape can be similar to that of the gradient magnetic field coil.

Next, the operation of this embodiment will be explained.

In the nuclear magnetic resonance apparatus configured in this manner, a static magnetic field is formed in the measurement space within the normal temperature space 9a of the container 9 by a persistent current caused by the superconductivity of the main coil 1. Further, the heat shield plate 1o at 80 and the heat shield plate 11 at 20 are each cooled by a refrigerator, and the radiant heat received by each is removed. This reduces heat radiation to the liquid helium tank 8 and reduces loss of liquid helium.

In this state, first, the subject is placed in the measurement space. Then, a pulse current is supplied to the gradient magnetic field coil 3 to generate two-component gradients of the magnetic field in three directions: x, y, and z. Further, a high frequency excitation current is supplied to the high frequency coil 2 to apply a high frequency electromagnetic field to the subject within the measurement space.

This causes the nuclear magnetic resonance phenomenon to occur in the atomic nuclei constituting the subject. This is detected as a unique nuclear magnetic resonance signal by the high frequency coil 2, and sent to an image processing system (not shown) for processing.

When the gradient magnetic field coil 3 is excited in a pulsed manner for imaging,
80 is a heat shield plate 10, and 20 is a heat shield plate 11.
In particular, an eddy current is generated in the heat shield plate 1o at 80.

In contrast, in this embodiment, when the gradient magnetic field coil 3 is excited in a pulsed manner, the active shield coil 12 is also excited at the same time. Therefore, the influence of the magnetic field generated by exciting the gradient magnetic field coil 3 in a pulsed manner is suppressed by the magnetic field generated by the active shield coil 12.
Also, the generation of eddy current in the heat shield plate 11 is suppressed.

According to this example, as is clear from the cross-sectional structure,
The main coil 1.20, the heat shield plate 11.80, the heat shield plate 1o, the active shield coil 12, the inner peripheral wall 9b of the container 9, the gradient magnetic field coil 3, and the high frequency coil 2,
They are arranged in this order from the outside to the inside in a coaxial cylindrical shape. The active shield coil 12 and the gradient magnetic field coil 3 are located apart from each other because the inner circumferential wall 9b of the container 9 exists between them. Therefore, the influence of the magnetic field generated by the active shield coil 12 on the imaging region (measurement space) is small, so that the efficiency of generating the necessary gradient magnetic field in the imaging region is improved.

In addition, the active shield coil is connected to the inner circumferential wall 9 of the container 9.
b, in other words, in the normal temperature space 9a, in order to obtain the necessary gradient magnetic field generation efficiency in the imaging area similar to the above, the active shield coil 12 and the gradient magnetic field are placed inside the normal temperature space 9a. It is necessary to space it apart from the coil 3. Therefore, the inner diameter of the normal temperature space 9a becomes larger,
Along with this, not only the main coil 1 on the outside but also the shape of the container 9 have to become larger. In contrast, in this embodiment, it is necessary to provide one interval between the active shield coil 12 and the gradient magnetic field coil 3.

Since the inner circumferential wall 9b of the container is located, that is.

The container 9 can be made smaller.

Therefore, according to this embodiment, the superconducting coil constituting the main coil 1 is miniaturized. Accordingly, the heat receiving area becomes smaller, and the amount of liquid helium consumed can be reduced. Also,
The size of the device itself can be reduced, and the weight can also be reduced. Furthermore, since the superconducting coil can be miniaturized, the amount of expensive superconducting material used can be reduced, and the main coil 1 can be manufactured at low cost.

In addition, in this example, for reasons described later, 0.8
The coil winding portion of the active shield coil 12 is arranged in a range of 8 to 1.0. This position is set based on new knowledge obtained through research by the present inventor, that is, when the distance from the central axis O of the nuclear magnetic resonance apparatus to the heat shield plate 10 at 80 degrees is 1.0. This is based on the new knowledge that the active shield coil works most effectively in the range of 0.88 to 1.0 from the central axis O. This will be explained with reference to FIG.

FIG. 5 shows the results of a study on the active shield coil for two gradient magnetic fields. The figure shows the excitation current value of the active shield coil at which the magnetic field at the position of the heat shield plate becomes 0 when the radius of the active shield coil is set variously when a constant current is passed through the two gradient magnetic field coils. and the value of the magnetic field gradient at the center of the imaging region at that time. Here, the value of the radius of the active shield coil is expressed by normalizing the distance of the heat shield plate from the central axis of the nuclear magnetic resonance apparatus to 1.

From this figure, the radius of the active shield coil is 0.8
It can be seen that when the value is 8 to 1.0, the current value of the active shield coil is small, and the gradient magnetic field required for imaging does not decrease much. Therefore, it is preferable to locate the coil winding portion of the active shield coil in this range.

Note that this positional relationship is similar to that of the active shield coil 12.
It is not affected by whether or not the inner circumferential wall 9b of the container is located between the gradient magnetic field coil 3 and the gradient magnetic field coil 3. Therefore, even if the active shield coil is not housed in the container 9, setting the radius of the active shield coil to 0.88 to 1.0 means that
This is effective in improving the efficiency of generating the necessary gradient magnetic field in the imaging region.

Next, regarding other embodiments of the nuclear magnetic resonance apparatus of the present invention,
This will be explained with reference to FIG.

As shown in FIG. 6, this embodiment includes a main coil 1, a superconducting shim coil 20, a liquid helium tank 8 housing them, a first heat shield plate 20, a heat shield plate 11, and a second heat shield plate 20. A heat shield plate 80, a heat shield plate 10, an active shield coil 12, a storage part 9c for housing these, a container 9 having a room temperature space 9a in the center, and a container 9 arranged inside the room temperature space 9a of the container 9. It is configured to include a gradient magnetic field coil 3 and a high frequency coil 2.

This embodiment has the same structure and functions as the embodiment shown in FIG. 1 above, except for the superconducting shim coil 20. Therefore, here, the explanation will focus on the differences.

The superconducting shim coil 20 is placed outside the main coil 1,
The static magnetic field generated by the superconducting coils constituting the main coil 1 is uniformly corrected. Since there is no interaction between the superconducting shim coil 20 and the active shield coil 12, the active shield coil 12 functions effectively even if the superconducting coil 20 is installed as in this embodiment.

Although the superconducting shim coil 20 is used in this embodiment, a configuration may also be adopted in which a normal conducting shim coil is used to correct the static magnetic field. Alternatively, a configuration may be adopted in which the static magnetic field is corrected using a magnetic piece.

Even in these cases, active shield coils work effectively regardless of where they are installed.

Although the description will not be repeated here, the effects described in the embodiment shown in FIG. 1 can also be obtained with this embodiment.

By cooling the active shield coil 12 used in each of the above embodiments, the resistance of its conductor can be reduced, and accordingly, the wire size of the coil can be reduced. This can be achieved by providing suitable cooling means. For example, heat may be removed from the active shield coil 12 using the heat shield plate 1o at 80, the heat shield plate 11 at 20, or a separate refrigerant system.

7 to 10 show an embodiment in which an active shield coil according to the present invention is provided with cooling means.

The embodiment shown in FIG. 7 uses a heat shield plate 10 and an active shield coil 12 at 80, and a heat contact body 13.
In order to prevent current from flowing into the heat shield plate, the heat shield plate is connected at a negative point for cooling. According to this, the active shield coil 12 is cooled by a refrigerator (not shown) connected to the heat shield plate 10 at 80 via the heat shield plate.

In the embodiment shown in FIG. 8, the cooling channel 15 from the refrigerator 14 is divided into two, and the heat shield plate 10 and the active shield coil 12 are independently cooled at 80. According to this embodiment, the active shield coil 12 can be cooled without interposing the heat shield plate 10 to the active shield coil 80 .

In the embodiment shown in FIG. 9, the active shield coil 12
is constructed of a copper tube, attached to the winding frame 16, and cooled by flowing a refrigerant such as liquid nitrogen or gas helium into the copper tube.

In the embodiment shown in FIG. 10, a copper tube 17 through which a refrigerant such as liquid nitrogen or gas helium flows is attached to a winding frame 16 installed between a container 9 and an active shield coil 12.
The active shield coil 12 and the copper tube 17 are connected at one point using a thermal contact member 23 so that no current flows into the copper tube 17, and are cooled.

According to the above four embodiments, the inside of the container can be maintained at a low temperature by removing the Joule heat generated when the active shield coil is excited. Furthermore, if the active shield coil is cooled to a low temperature, the resistance of the five coil conductors will be reduced, so that the burden on the excitation power source can be reduced.

Next, another embodiment of the heat shield plate used in the present invention will be described with reference to FIG. 11.

FIG. 11 partially shows the structure of this embodiment.

In this embodiment, a heat shield plate 80 is constructed as a laminated plate of an insulator 18 and a metal foil 19. Further, an active shield coil 12 is wound around this laminated plate.

The thickness of the metal foil 19 is made thinner than the skin effect thickness determined by the electrical conductivity of the metal foil 19 and the ramp-up time of the gradient magnetic field, and is connected to a refrigerator (not shown) to be cooled to 80K. It has become.

According to this embodiment, the active shield coil can be indirectly cooled by heat conduction even though the heat shield plate and the active shield coil are MiU.

In addition, by reducing the thickness of the metal foil as described above, the fluctuating magnetic fields generated by the gradient magnetic field coil and the active shield coil can penetrate through the metal foil with almost no attenuation.
Eddy currents generated in the metal foil can be ignored. For this reason, 20
eddy currents will be induced in the heat shield plate. Therefore, in this embodiment, the active shield coil has 20
The heat shield plate is set to provide magnetic shielding from the gradient coils.

Further, according to this embodiment, the active shield coil and the heat shield plate 80 can be integrated, thereby making it possible to downsize the entire device.

Although each of the above embodiments uses a superconducting coil cooled by liquid helium, the present invention is not limited to this. For example, a superconducting coil cooled using liquid nitrogen as a refrigerant may be used.

In addition, in each of the above embodiments, the heat shield plate 20 and the heat shield plate 8
A heat shield plate is used at 0, but these temperatures are 2
It is not limited to 0K and 80K. Furthermore, the number of heat shield plates is not limited to two, that is, the first or second shield plates, but may be one or three or more.

The nuclear magnetic resonance apparatus of each of the above embodiments can be downsized as described above. Therefore, in the case of a device used for diagnosing the human body, the cross section of the device can be configured to fit within a plane of, for example, 1.8 m x 1.8 m. As a result,
It becomes easier to carry the device into examination rooms such as hospitals, and the volume occupied by the device is reduced even indoors. By downsizing, of course.

The total weight of the device is also reduced, and there are fewer restrictions on the installation location due to weight restrictions and the like.

In each of the above embodiments, means for heating or cooling the subject may be provided in the normal temperature space.

Next, MR configured using the nuclear magnetic resonance apparatus of the present invention
One embodiment of the imaging device will be described with reference to FIG. 12.

The MR imaging apparatus of this embodiment includes a nuclear magnetic resonance apparatus 100 similar to the embodiment described above, an oscillator 300 that excites a high-frequency coil 2 of the nuclear magnetic resonance apparatus, and a nuclear magnetic resonance signal detected by the high-frequency coil 2. The image processing system 200 performs image processing based on the above. Note that a diagnostic apparatus can be constructed by adding a conveyance means (not shown) for conveying a subject such as a patient in the axial direction of the main coil.

The image processing system 200 includes an amplifier 201 that amplifies a nuclear magnetic resonance signal, a detector 202 that detects the signal, and a signal processing unit 20 that performs processing such as waveform shaping, sample hold, and analog/digital conversion on the detected signal.
3, and an arithmetic processing unit 204 that performs arithmetic processing based on the processed digital signal) and generates an image signal.
, a storage device 205 that stores and holds digital data, image data, etc., a display such as a CRT (preferably a color display) 206 that displays image data, and a printer 207 that prints out image data and the like. We are prepared.

With the MR imaging apparatus configured in this manner, it is possible to detect nuclear magnetic resonance signals from a subject and obtain a collected image thereof. In this case, since the above-described nuclear magnetic resonance apparatus of the present invention is used, disturbances in the static magnetic field and gradient magnetic field are suppressed by the action of the active shield coil.
A high-precision image with no disturbances can be obtained.

Moreover, as already mentioned, since the nuclear magnetic resonance apparatus can be made smaller, the MR imaging apparatus using this can also be made smaller.

[Effects of the Invention] According to the present invention, by incorporating the active shield coil, the occurrence of image disturbance can be suppressed, and the active shield coil can be arranged at a distance from the gradient magnetic field coil, which improves the efficiency of gradient magnetic field generation. This has the effect of making it possible to reduce the size of the device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the configuration of an embodiment of the nuclear magnetic resonance apparatus of the present invention, FIG. 2 is a perspective view conceptually showing the configuration of the nuclear magnetic resonance apparatus, and FIGS. 3 and 4 is a perspective view conceptually showing the configuration of an active shield coil, and FIG.
A graph showing the optimum range of the radius of the active shield coil for gradient magnetic fields, FIG. 6 is a sectional view schematically showing the configuration of another embodiment of the nuclear magnetic resonance apparatus of the present invention, and FIGS.
Fig. 0 shows an embodiment of the cooling method of the active shield coil according to the present invention, Fig. 7 is a sectional view partially showing an embodiment of cooling by bringing it into thermal contact with a heat shield plate, and Fig. 8
The figure is a partial cross-sectional view showing an example in which the cooling channels 80 from the refrigerator are divided into two systems and the heat shield plate and active shield coil are independently cooled. FIG. 1o is a sectional view partially showing an example of cooling by making thermal contact with a steel pipe through which a refrigerant flows, and FIG. 11 is a perspective view of another embodiment of the heat shield plate. FIG. 12, which is a perspective view partially showing an example, is a block diagram showing an embodiment of an MR imaging apparatus constructed using the nuclear magnetic resonance apparatus of the present invention. 17... Copper tube, 18... Insulator, 19... Metal foil, 20... Superconducting shim coil, 100... Nuclear magnetic resonance apparatus, 200... Image processing system, 300...
oscillator. Applicant Hitachi Ltd. Representative Patent Attorney Tomi 1) Kazuko 1... Main coil (superconducting coil), 2... High frequency coil, 3 (3x, 3z)... Gradient magnetic field coil, 4・
...X gradient magnetic field coil, 5...X active shield coil for gradient magnetic field, 6...2 gradient magnetic field coil, 7...
・2 active shield coil for gradient magnetic field, 8...liquid helium tank, 9...container, 10...80 heat shield plate, 11...20 heat shield plate, 12...active shield coil , 13... thermal contact body, 14...
・Refrigerating machine, 15...80, cooling channel, 16...
・Reeling frame, Figure 1, Figure 3, Figure 2, Figure 4, Figure 7

Claims (1)

[Claims] 1. A container having a normal temperature space forming a measurement space and a storage section provided in a space surrounded by an inner circumferential wall surrounding the normal temperature space and an outer circumferential wall outside the normal temperature space; In the storage section,
A superconducting coil, at least one heat shield plate that surrounds and thermally shields the superconducting coil, and an active shield coil are accommodated, and a high frequency coil and a gradient magnetic field coil surrounding a measurement space are accommodated in the room temperature space. A nuclear magnetic resonance apparatus characterized by: 2. The nuclear magnetic resonance apparatus according to claim 1, wherein the active shield coil is disposed immediately outside the inner circumferential wall of the container. 3. The heat shield plate includes a first heat shield plate surrounding the superconducting coil and a second heat shield plate surrounding the first heat shield plate, and the active shield coil is arranged inside the container. The nuclear magnetic resonance apparatus according to claim 1, wherein the nuclear magnetic resonance apparatus is provided between the peripheral wall and the second heat shield plate. 4. A superconducting coil that generates a uniform static magnetic field in the measurement space, at least one heat shield plate that surrounds and thermally shields the superconducting coil, a gradient magnetic field coil that generates a gradient magnetic field in the measurement space, and a nuclear magnetic field that is applied to the subject. It includes a high frequency coil that causes resonance and receives nuclear magnetic resonance signals, and an active shield coil that is disposed between the heat shield plate and the gradient magnetic field coil, and the position of the active shield coil is determined according to the measurement above. When the distance between the central axis of the space and the heat shield plate on the outside of the active shield coil is 1, the coil winding portion of the active shield coil is 0.8 from the central axis.
A nuclear magnetic resonance apparatus, characterized in that the nuclear magnetic resonance apparatus is set to be located in a range of 8 to 1. 5. A superconducting coil that generates a uniform static magnetic field in a measurement space, a refrigerant tank that houses and cools the superconducting coil, at least one heat shield plate that surrounds the refrigerant tank, a normal temperature space in the center, and , a container having a storage section for accommodating the refrigerant tank and a heat shield plate in a portion surrounding the room temperature space, and a gradient magnetic field coil that generates a gradient magnetic field and a gradient magnetic field coil that causes nuclear magnetic resonance in the subject in the room temperature space. and a high-frequency coil for receiving nuclear magnetic resonance signals, and in a position closer to the center axis than the heat shield plate that is closest to the superconducting coil in the inner space of the superconducting coil in the storage part, A nuclear magnetic resonance apparatus characterized by arranging an active shield coil. 6. The arrangement position of the active shield coil is such that when the distance between the center axis of the container and the heat shield plate on the outside of the active shield coil is 1, the position of the coil winding portion of the active shield coil is Claim 1: The distance is set within a range of 0.88 to 1 from the central axis.
, 2, 3 or 5. 7. The nuclear magnetic resonance apparatus according to claim 1, 2, 3, 4, 5, or 6, further comprising a cooling means for cooling the active shield coil. 8. The nuclear magnetic resonance apparatus according to claim 7, wherein the cooling means cools the active shield coil by bringing it into thermal contact with a heat shield plate. 9. The nuclear magnetic resonance apparatus according to claim 7, wherein the cooling means cools the active shield coil using a refrigerator. 10. The nuclear magnetic resonance apparatus according to claim 7, wherein the cooling means is configured to cool the active shield coil by forming the active shield coil with a conductive pipe and flowing a coolant through the pipe. 11. The cooling means arranges a pipe through which a refrigerant flows,
8. The nuclear magnetic resonance apparatus according to claim 7, wherein the active shield coil is cooled by bringing it into thermal contact with the pipe. 12. A nuclear magnetic resonance apparatus that forms a static magnetic field using a superconducting coil, comprising at least one heat shield plate that surrounds and thermally shields the superconducting coil, the heat shield plate comprising an electrical insulator and a metal A nuclear magnetic resonance apparatus characterized by being composed of a laminated plate with foil. 13. The nuclear magnetic resonance apparatus according to claim 12, further comprising an active shield coil, the active shield coil being wound directly onto the heat shield plate. 14. Claims 1, 2, 3, 4, 5, 6, and 7, comprising a superconducting shim coil that corrects the static magnetic field generated by the superconducting coil.
, 8, 9, 10, 11, 12 or 13. 15. A superconducting coil that is housed in a container with a cooling function and generates a uniform static magnetic field in the measurement space, a gradient magnetic field coil that generates a gradient magnetic field in the measurement space, and a superconducting coil that causes nuclear magnetic resonance in the subject. , a nuclear magnetic resonance apparatus having a high-frequency coil that receives a nuclear magnetic resonance signal, and an image processing system that performs image processing on the detected nuclear magnetic resonance signal and outputs an image, the nuclear magnetic resonance apparatus comprising: An MR imaging apparatus characterized in that an active shield coil is provided in the container. 16. A diagnostic apparatus comprising the MR imaging apparatus according to claim 15 and a conveying means for conveying the subject in the axial direction of the measurement space. 17. A superconducting coil that generates a uniform static magnetic field in the measurement space, a gradient magnetic field coil that generates a gradient magnetic field in the measurement space, and inside them, a nuclear magnetic resonance is caused in the subject and a nuclear magnetic resonance signal is received. What is claimed is: 1. A nuclear magnetic resonance apparatus comprising: a high-frequency coil; an active shield coil disposed between the superconducting coil and the gradient magnetic field coil; and a cooling means for cooling the active shield coil.