JPH073802B2 - Magnetic resonance device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a permanent magnet type magnetic resonance apparatus.

(Prior Art) A magnetic resonance apparatus applies a uniform static magnetic field to a desired site of a subject and forms an RF magnetic field in a direction perpendicular to the static magnetic field for transmission.
A magnetic resonance is generated only in a specific slice part where a tomographic image is obtained by the coil, and a magnetic field resonance signal (hereinafter referred to as MR signal) generated from the core of the original paper after the RF magnetic field is released is detected by the receiving RF coil. It is a thing. Further, a linear magnetic field gradient having a linear gradient is applied to the static magnetic field to obtain a composite MR signal, and the MR image of the slice portion is formed by Fourier transforming this signal.

As a method of forming the above-mentioned static magnetic field, a normal conduction method and a superconduction method are known. In both of these methods, a static magnetic field is formed by passing a current through the coil. on the other hand,
A so-called permanent magnet system that uses a permanent magnet to form a static magnetic field has recently been in the limelight due to its economical efficiency.

It is also known that there are a body axis (horizontal) magnetic field method and a vertical magnetic field method as a direction in which a magnetic field is applied.

By the way, in the permanent magnet system, as shown in FIG. 6, a yoke 1 made of pure iron and having a substantially rectangular shape, and a permanent magnet 2 attached to a substantially central portion of the yoke 1 in the vertical direction in the drawing.
The magnetic pole 3 is attached to the other surface of the permanent magnet 2.

In the conventional device having such a configuration, the leakage magnetic flux Q is generated from the side surface of the permanent magnet 2 fixed to the yoke 1 in the drawing or the side surface of the magnetic pole 3 to the yoke member arranged around the permanent magnet.

(Problems to be Solved by the Invention) As described above, in the conventional device, the side surface of the permanent magnet 2 shown in the drawing or the side surface of the magnetic pole 3 shown in the figure is fixed to the yoke member arranged around the permanent magnet. Leakage magnetic flux was generated. That is, the magnetic field generated is determined by the strength of the permanent magnet. In the figure, the magnetic flux from the upper permanent magnet enters the lower permanent magnet through the air gap 4, passes through the yoke 1, and returns to the upper permanent magnet. However, due to leakage flux, all flux does not go through such a path.

Since the magnetic field has the property of easily passing through the magnetic body and hardly passing through the non-magnetic body, a large amount of magnetic field is generated in the portion closer to the air gap 4, and this becomes the leakage magnetic flux. As a result, only about 30 (%) to 40 (%) of the magnetic field strength of the permanent magnet works effectively. Furthermore, in order to obtain the required magnetic field strength in the air gap part, it is necessary to increase the amount of permanent magnets, and in order to obtain the above required magnetic field strength, the amount of permanent magnets must be approximately 1.6 to 1.7 times that of the permanent magnets. There is a problem.

[Structure of the Invention] (Means for Solving the Problems) According to the structure of the present invention for solving the above problems, the structure is attached to a yoke forming a closed magnetic circuit and is arranged to face each other with an air gap. A magnetic resonance apparatus including a static magnetic field generating means including at least a pair of permanent magnets, and placing the test object in a static magnetic field formed in the air gap to obtain information on the cross section of the test object by utilizing a magnetic resonance phenomenon. In the above, at least a side surface of the permanent magnet is provided with a magnetic shielding member made of a non-magnetic material.

(Operation) The operation of the present invention having the above-described configuration is to form recesses on both sides of the yoke member of the static magnetic field generating means fixed to the yoke, which consists of, for example, permanent magnets and magnetic poles, and at least the static magnetic field generating means. A magnetic shielding member made of a non-magnetic material is provided on the side surface of the permanent magnet to increase the magnetic flux path of the leakage magnetic flux from the side surface to reduce the leakage magnetic flux, and the air between the static magnetic field arranging means arranged opposite to each other. The magnetic field strength in the gap is increased.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view of an embodiment of the device of the present invention.

The apparatus of the embodiment shown in FIG. 1 includes a yoke 5 formed of, for example, pure iron and having a substantially quadrangular shape, and a static magnetic field generation that is fixed by being opposed to central portions of upper and lower yoke members of the yoke 5 in the figure. And a concave member 5a, 5a is formed on the mounting support surface of the magnetic field generating means 9 in which the magnetic field generating means 9 is mounted. In this embodiment, the yoke member and at least the permanent magnet (described later) forming the static magnetic field generating means 9 are fixed by being held by the magnetic shielding member 15 made of a non-magnetic material.

That is, as shown in FIG. 2, after arranging a plurality of permanent magnets 7 constituting the static magnetic field generating means 9 as shown in FIG. 2, a non-magnetic material such as nickel steel, manganese steel, 1
The band-shaped member made of 8-8 stainless steel or the like is clamped and fixed as a whole from the side surface direction of the permanent magnets 7 arranged in a line as described above by the ring-shaped magnetic shielding member 15. At this time, the tip portion of the yoke member (the portion sandwiched between the recesses 5a, 5a) for fixing the permanent magnet 7 shown in FIG. 1 is simultaneously held and fixed by the side portion 15a of the magnetic shield member 15.
Then, the magnetic pole is fixed to the side of the permanent magnet 7 fixed as described above facing the air gap 8 by an appropriate method such as a conductive adhesive.

The appearance of the present apparatus configured as described above is as shown in FIG. In addition, what is shown by P in FIG. 3 is a subject to be inserted and placed in the air gap 8 portion.

The static magnetic field generating means 9 is, for example, as shown in FIG.
It is composed of a permanent magnet 7 such as ferrite, and a magnetic pole 6 made of a magnetic material that makes the magnetic field generated by the permanent magnet 7 uniform. The magnetic pole 6 is to make the magnetic field generated by the permanent magnet 7 uniform in the air gap 8. For this reason, the shape of the portion of the magnetic pole 6 facing the air gap 8 is a shape provided with a gentle concave portion in the drawing. The shape of the magnetic pole is not limited to that having a gentle recess as shown in the figure, and a curved surface having an appropriate curvature may be formed on the magnetic pole (see FIG. 4).

Next, the yoke 5 has the static magnetic field generating means 9 as described above.
On the mounting support surface of the yoke member to which the
a is formed.

That is, the recesses 5a, 5a have a semicircular shape, and if the distance between the both side surfaces of the permanent magnet 7 in the figure and the yoke member facing the both side surfaces is R, then in the present embodiment, The radius of the semicircle is R / 2. In this way, the distance between the permanent magnet 7 and the adjacent yoke member is increased.

FIG. 4 is a front view showing a modification of the device of the present invention.

The concave portion shown in FIG. 1 has a semicircular shape, but
For example, as shown in the figure, a substantially U-shaped recess may be provided on the mounting support surface of the yoke member to which the static magnetic field generating means 9 is mounted. The same members as those in FIG. 1 are designated by the same reference numerals in FIG.

The operation and effect of the device of the present invention configured as described above will be described with reference to FIGS. 1 and 5.

In FIG. 1, the magnetic field emitted from the permanent magnet 7 on the upper side of the drawing passes through the magnetic pole 6 and the air gap 8, passes through the magnetic pole 6 and the permanent magnet 7 which are arranged to face each other, and enters the yoke 5, and again the permanent magnet. Return to 5a. At this time, in the apparatus of this embodiment, since the magnetic shield member 15 made of a non-magnetic material is present on the side surface of the permanent magnet 7 so as to surround the permanent magnet 7, leakage from the side surface to the adjacent yoke member is prevented. It has the function of diverting the magnetic flux. Therefore, the leakage flux from the side surface of the permanent magnet 7 can be reduced. still,
Although the figure shows an example in which the magnetic shield member is provided only on the side surface of the permanent magnet, it may be provided by extending it to the side surface of the magnetic pole.
In such a case, the leakage flux can be further reduced, and the yoke member, the permanent magnet, and the magnetic pole can be simultaneously clamped and fixed by the same magnetic shield member, so that the manufacturing process can be simplified. it can.

Further, since the concave portion is formed on the mounting support surface of the static magnetic field generating means of the yoke member, the distance between the permanent magnets constituting the static magnetic field generating means and the surrounding yoke member is increased, and this is conventionally generated in this portion. We are trying to reduce the leakage flux. That is, as shown in FIG. 5, the leakage magnetic flux from, for example, the right side surface of the permanent magnet 7 intersects at the points A and B when the yoke member is located at the position indicated by the dotted line in the related art. On the other hand, in the present invention, since the concave portion is formed in this portion,
The magnetic flux intersecting at points A and B will move to points C and D, respectively. That is, since the magnetic flux path becomes large, the magnetic resistance increases, and the magnetic flux that has conventionally passed through this portion now passes through the air gap 8. Therefore, the leakage magnetic flux, that is, the magnetic field loss decreases, and the effective magnetic field passing through the air gap 8 increases. From this, it is possible to reduce the amount of permanent magnets when obtaining the required effective magnetic field.

Air gap 8 between magnetic poles for better results
It is good to shorten the distance of.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist of the present invention.

[Advantages of the Invention] As described in detail above, according to the device of the present invention, it is possible to provide a magnetic resonance device capable of reducing leakage flux.

[Brief description of drawings]

FIG. 1 is a front view of an apparatus according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing a state in which a permanent magnet is fixed by a magnetic shield member,
FIG. 3 is an external perspective view of the device shown in FIG. 1, FIG. 4 is a front view of a modified example of a recess formed in a yoke member, and FIG. 5 is a side view of a permanent magnet leaking to a nearby yoke member. FIG. 6 is an explanatory view of magnetic flux, and is a front view of a conventional magnetic resonance apparatus. 5 ... Yoke, 6 ... Magnetic pole, 7 ... Permanent magnet, 8 ... Air gap, 9 (6, 7) ... Static magnetic field generating means, 15 ... Magnetic shielding member.

Claims (2)

[Claims] 1. A static magnetic field generating means, which is attached to a yoke forming a closed magnetic path and has a pair of at least permanent magnets facing each other with an air gap, and including a static magnetic field formed in the air gap. In a magnetic resonance apparatus for placing a subject in a magnetic field and obtaining information of a cross section of the subject by using a magnetic resonance phenomenon, at least a side surface of the permanent magnet is provided with a magnetic shield member made of a non-magnetic material. Magnetic resonance device. 2. The magnetic resonance apparatus according to claim 1, wherein the yoke is a mounting surface side of the permanent magnet and a recess is formed in a mounting support surface of the permanent magnet.