JPS61200452A - Method for forming uniform magnetic field in nuclear magnetic resonance image pick-up apparatus - Google Patents

Abstract

PURPOSE:To always obtain a static magnetic field with high uniformity, by correcting a static magnetic field by the auxiliary coil provided inside a static magnetic field generation apparatus and the correction magnetic body provided outside the static magnetic field generation apparatus. CONSTITUTION:If necessary, correction magnetic bodies 25... are inserted in the hollow correction magnetic body insert parts 22, 23, 24 provided to an exterior body 1 so as to open the outer surface thereof. When the effect from the magnetic body 26 present in a floor surface A having an apparatus main body arranged thereto is large, the correction magnetic body 25 is mounted to the side opposite to the magnetic body 26 of the floor surface with respect to a static magnetic field generation apparatus 2, that is, the insert part 22 of a top plate 3 to perform the primary large correction of a magnetic field at first and the secondary minute correction of the magnetic field is subsequently performed by the current adjustment of correction coils 19, 20 to form a uniform magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION B) Industrial Application Field The present invention relates to a method for forming a uniform magnetic field in a nuclear magnetic resonance imaging apparatus (hereinafter referred to as NMR-CT).

(b) Prior Art In NMR-CT, which has recently been in the spotlight in the field of medical equipment, it is important to form a highly uniform static magnetic field in order to improve image quality.

As a method for forming this static magnetic field, there is a method of forming a static magnetic field inside the static magnetic field between a pair of permanent magnets and a yoke that magnetically couples the magnets and forms a nearly sealed space. Although this method has been proposed, it is impossible to achieve the required uniformity of 10 ppm or less. Therefore, a correction coil called a shim coil is used to improve uniformity.

However, when an NMR-CT device is actually installed in a hospital, the uniformity of the static magnetic field may deteriorate significantly due to the influence of reinforcing bars (magnetic materials) such as floors, ceilings, beams, and columns depending on the installation location, and correction coils may be required. This has the disadvantage that it becomes impossible to achieve the required uniformity beyond the correction range.

(c) Problems to be Solved by the Invention The Tachiki invention seeks to provide a method for forming a uniform magnetic field that can always obtain a highly uniform static magnetic field even if the installation location is different.

(D) Means for Solving the Problems The present invention generates a static magnetic field in a static magnetic field generator composed of a pair of permanent magnets and a yoke that magnetically couples the magnets and forms a nearly sealed space. The above problem is solved by correcting the static magnetic field using an auxiliary coil provided within the quiet field generator and a correction magnetic body provided outside the static magnetic field generator. .

(E) Effect By using the above means, the static magnetic field inside the static magnetic field generator is corrected by a correction magnetic body provided outside the static magnetic field generator according to the situation of the surrounding magnetic body existing at the installation location of the device main body, and the surrounding magnetic field is adjusted. The influence of the body on the uniformity of the static magnetic field can be kept within the correction range of the correction coil.

(f) Example An apparatus for carrying out the method of the present invention will be explained according to FIGS. 1 to 3. The device shown in FIG. This is the main body of a nuclear magnetic resonance imaging device for determining the distribution and outputting a cross-sectional image.
).

The exterior body 1) is made of a non-magnetic material, for example F.

Made of R, P and wood, the top plate (3) and this top plate (3)
Front plate (4), rear plate (5), side plate (6), (
7), and the front plate (4) and the rear plate (5) have an elliptical first opening (8) (9) for inserting a subject (for example, a human body).
is completely formed.

The static magnetic field generator 11(2) has the following configuration.

That is, (10) and (11) are a pair of upper and lower disc-shaped permanent magnets made of rare earth magnetic material, and (12) and (13) are disc-shaped disc-shaped permanent magnets made of magnetic material arranged in contact with one surface of each of the permanent magnets. The upper yoke and the lower yoke (14) are cylindrical side yokes made of magnetic material that are electromagnetically connected to the upper yoke and the lower yoke. By arranging the yokes <13), each of these yokes constitutes a magnetic circuit, and a strong static magnetic field can be formed between the pair of opposing permanent magnets (, 10, 11).

Further, the side yoke (14) has a pair of elliptical second openings (15) and (16) provided in opposing arrangement for insertion of a subject into the static magnetic field. This second opening (15) (
16) is located opposite to the first openings (8) and (9). (1
7) (18) are a pair of pole pieces that are provided oppositely on the other surfaces of the permanent magnets (10) and (11) to improve the uniformity of the static magnetic field; (19) and (20) are pole pieces ( 17) A correction coil for magnetic field correction provided inside (18) improves the uniformity of the magnetic field by flowing a constant current. A second opening (15) is provided between the first openings (8) and (9).
) A cylindrical body (21) for inserting a subject that can be inserted through the hole 16)
can be constructed.

(22), (23), and (24) are hollow correction magnetic body insertion parts provided in the exterior body (1) so as to open on the outer surface of the exterior body (1). ... can be inserted.

In the above apparatus, the method of the present invention will be explained with reference to FIG. When the magnetic field formed in the device (2) is expanded in the X7Z orthogonal function system, the non-uniformity of the 2nd term and the 23rd term becomes so large that it cannot be corrected by the above-mentioned correction coils (19) and (20). In order to reduce the non-uniformity of these terms 2 and 23, it is necessary to correct the static magnetic field generator (2) on the opposite side of the magnetic body (26) on the floor, that is, on the insertion part (22) of the top plate (3). Magnetic material (
25) is attached to perform a first-order large magnetic field correction, and then a second-order minute magnetic field correction is performed by adjusting the current of the correction coils (19) and (20), thereby forming a uniform magnetic field.

It is desirable to prepare a plurality of correction magnetic bodies (25) with different shapes in advance so that the shape and quantity can be selected as appropriate.
4) may be divided into a plurality of parts in a direction perpendicular to the insertion direction, and the correction magnetic body (25) may also have a small shape so that the insertion position can be selected.

Note that the present invention is not limited to the above embodiments, and the correction magnetic body (25) may be installed between the inner surface of the exterior body (1) and the outer periphery of the static magnetic field generator (2). Others may be used.

(G) Effect According to the present invention configured as described above, by attaching the correction magnetic body, the influence from the surrounding magnetic body existing at the installation location of the device main body can be suppressed to a range that can be corrected by the correction coil. This makes it possible to always achieve the required uniformity of the static magnetic field even if the installation location is different, and to eliminate restrictions on the installation location of the nuclear magnetic resonance imaging apparatus main body.

[Brief explanation of the drawing]

1 to 3 each show an apparatus equipped with an embodiment of the present invention, FIG. 1 is an overview perspective view, and FIG. 2 is a
3 is a cross-sectional view of the main part for explaining the operation. (2)...Static magnetic field generator, (19)(20)...
Correction coil, (22) (23) (24)...insertion part,
(25)...Magnetic material for correction.

Claims (1)

[Claims] (1) A static magnetic field generating device that generates a static magnetic field in a static magnetic field generator consisting of a pair of permanent magnets and a yoke that magnetically couples the magnets and forms a nearly sealed space,
A method for forming a uniform magnetic field in a nuclear magnetic resonance imaging apparatus, characterized in that the static magnetic field is corrected by a correction coil provided within the static magnetic field generator and a correction magnetic body provided outside the static magnetic field generator.