Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Patent
1994-01-18
1997-04-15
Arana, Louis M.
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
324320, G01V 300
Patent
active
056213247
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to improvement of a magnetic generating apparatus used in a magnetic resonance imaging (hereinafter referred to as an MRI) and the like, particularly, it relates to a magnetic field generating apparatus having a good magnetic effect, which is constituted by disposing a plurality of permanent magnet constituents along the inner surface of a polygonal tubular yoke, and is easy to assemble by directing a magnetizing direction of a plurality of permanent magnet blocks constituting the permanent magnet constituents in a specific direction.
TECHNICAL BACKGROUND
An MRI is a system, wherein a portion or an entire subject is inserted into a hollow space of a magnetic field generating apparatus forming a strong magnetic field to obtain a tomographic image of the subject, thereby to draw out even characteristics of the tissue.
The hollow space of the magnetic generating apparatus must be so large that the porting or entire subject can be inserted, and for the purpose of obtaining the clear tomographic image, usually, it is necessary to form a strong stable uniform magnetic field having an accuracy of 0.22 to 2.0T or less at 1.times.10.sup.-4 .OMEGA..multidot.m, in an image pickup visual field (in a spherical space of about 150 to 250 mm radius at the center porting of the hollow space).
As a magnetic field generating source of the magnetic field generating apparatus, though those using a superconductive magnet and as paraconductive magnet are known, in recent years, those using a permanent magnet are frequently used by the reason that, the apparatus has a relatively simple configuration and the running cost is low.
As the magnetic field generating apparatus for MRI using the permanent magnets as the magnetic field generating source, a configuration, in which a pair of permanent magnet constituents opposing one another as forming a hollow space are connected by a yoke as shown in the U.S. Pat. No. 4,672,346(EP 0161782 B1) is widely adopted.
In the above-mentioned magnetic field generating apparatus, the permanent magnet constituents are usually constituted by a plural number of permanent magnet blocks by the reason of manufacturing problems and assembling workability.
In this configuration, since a magnetizing direction of the permanent magnet constituents is in the same direction as a direction of magnetic field in the hollow space, and also a transverse cross section is substantially a square, a direction of thickness of the permanent magnet constituents is the magnetizing direction, thus it is easy to assemble by laminating and integrating the plural number of cubical or rectangular parallel-piped permanent magnet blocks having the magnetizing direction in the direction of thickness.
While, a configuration, in which a plural number of permanent magnet constituents are disposed angularly, and an uniform magnetic field is formed at a center portion in the permanent magnet constituents, is known (U.S. Pat. No. 4,498,048, EP 0120927 B1 and Japanese Patent pablication No. Hei 4-10334).
In the magnetic field generating apparatus having such configuration, since respective permanent magnet constituents have, for example, a sectionally trapezoid shape, and the direction of magnetic field in the hollow space differs form the magnetizing direction of the permanent magnet constituents depending on locations where the permanent magnet constituents are arranged, in order to obtain a desired magnetizing direction, the permanent magnet blocks must be formed into a specific shape, or at the time of their magnetization, a magnetizer capable of positioning the permanent magnet constituents very precisely is required, results in a very complicated assembling work.
As the configuration for solving such problem, a configuration, in which a plurality of bar-shaped permanent magnet constituents having a triangular or substantially square and triangular transverse section are disposed angularly along the inner surface of a polygonal tubular yoke, is proposed (U.S. Pat. No. 4,695,802, EP 01
REFERENCES:
patent: 4695802 (1987-09-01), Zijlstra
patent: 4703276 (1987-10-01), Beer
patent: 5467769 (1995-11-01), Yoshino et al.
Aoki Masaaki
Marukawa Yasuhiro
Nakamura Chikako
Ota Kimiharu
Takeshima Hirotaka
Arana Louis M.
Sumitomo Special Metals Company Limited
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