Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2003-11-13
2004-11-30
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C335S298000
Reexamination Certificate
active
06825668
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese Application No. 2002-330665 filed Nov. 14, 2002.
The present invention relates to a static magnetic field generating apparatus and a magnetic resonance imaging apparatus employing permanent magnets supported by columnar yokes and base yokes forming a magnetic circuit.
In recent years, magnetic resonance imaging apparatuses in which a static magnetic field is generated by permanent magnets have become widespread. Because high accuracy is required in such apparatuses, a technique of adjusting the static magnetic field has been applied mainly by using iron pieces or the like on the permanent magnets themselves or on base yokes attached with the permanent magnets.
Another technique involves winding coils around columnar yokes for supporting the permanent magnets to electrically generate magnetic flux, thereby correcting the static magnetic field (see Patent Document 1, for example).
Patent Document 1
Japanese Patent Application Laid Open No. 2002-238872 (page 1, FIG. 10).
The conventional techniques, however, did not allow easy adjustment of the static magnetic field. Specifically, the technique of adjusting the static magnetic field on the permanent magnets themselves or on the base yokes attached with the permanent magnets must be completed in the assembling process of the magnetic resonance imaging apparatus on account of the weight of the permanent magnets, for example. On the other hand, the technique of electrically correcting the static magnetic field requires extra instruments because coils and a control device therefor are used.
Especially, the permanent magnet is more vulnerable to environmental conditions such as temperature change than a superconductive magnet, and the fact that the adjustment for maintaining accuracy of the static magnetic field cannot be easily achieved at an installation site such as a hospital, is not preferable from the viewpoint of performance and servicing efficiency.
It is therefore important to find a way to realize a static magnetic field generating apparatus and a magnetic resonance imaging apparatus employing permanent magnets that allow easy adjustment of a static magnetic field.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a static magnetic field generating apparatus and a magnetic resonance imaging apparatus employing permanent magnets that allow easy adjustment of a static magnetic field.
For solving the aforementioned problems and attaining this object, a static magnetic field generating apparatus, in accordance with a first aspect of the invention, is characterized in comprising: a pair of permanent magnets opposingly disposed across a space in which a subject is placed; a pair of base yokes for supporting said permanent magnets; and columnar yokes for magnetically connecting said base yokes and structurally supporting them, said columnar yokes having magnetic resistance modifying means.
In the invention of the first aspect, permanent magnets are opposingly disposed across a space in which a subject is placed, the permanent magnets are supported by a pair of base yokes, and the base yokes are magnetically connected and structurally supported by columnar yokes having magnetic resistance modifying means; and therefore, magnetic flux generated in the space by the permanent magnets, hence, a static magnetic field that is equal to magnetic flux per unit area, can be easily changed and adjusted by modifying magnetic resistance of the columnar yokes.
The static magnetic field generating apparatus, in accordance with a second aspect of the invention, is characterized in that: said modifying means comprises a groove on a side surface of at least one of said columnar yokes, said side surface lying in a longitudinal direction of said columnar yoke.
In the invention of the second aspect, since a groove is provided on a side surface of the columnar yoke lying in a longitudinal direction of the columnar yoke as the modifying means, the cross-sectional area of the columnar yoke perpendicular to the longitudinal direction is reduced at the groove, thereby increasing magnetic resistance.
The static magnetic field generating apparatus, in accordance with a third aspect of the invention, is characterized in that: said groove has a rectangular cross section.
In the invention of the third aspect, since the groove has a rectangular cross section, it can be easily machined.
The static magnetic field generating apparatus, in accordance with a fourth aspect of the invention, is characterized in that: said modifying means comprises an insert member of a shape generally conforming to said groove.
In the invention of the fourth aspect, since an insert member of the modifying means has a shape generally conforming to the groove, magnetic resistance at the groove can be modified by inserting/removing the insert member into/from the groove.
The static magnetic field generating apparatus, in accordance with a fifth aspect of the invention, is characterized in that: said modifying means comprises a through hole passing through a side surface of at least one of said columnar yokes, said side surface lying in parallel with a longitudinal axis of said columnar yoke.
In the invention of the fifth aspect, since a through hole is provided to pass through a side surface of the columnar yoke lying in parallel with a longitudinal axis of the columnar yoke as the modifying means, the cross-sectional area of the columnar yoke perpendicular to the longitudinal axis is reduced at the through hole, thereby increasing magnetic resistance.
The static magnetic field generating apparatus, in accordance with a sixth aspect of the invention, is characterized in that: said through hole has a circular cross section.
In the invention of the sixth aspect, since the through hole has a circular cross section, reduction in strength of the columnar yokes for supporting the permanent magnets can be mitigated.
The static magnetic field generating apparatus, in accordance with a seventh aspect of the invention, is characterized in that: said modifying means comprises a filling member of a shape generally conforming to said through hole, said filling member being insertable/removable into/from said columnar yoke.
In the invention of the seventh aspect, since the modifying means comprises a filling member of a shape generally conforming to the through hole to be insertable/removable into/from the columnar yoke, magnetic resistance at the through hole can be modified by inserting/removing the filling member into/from the through hole.
The static magnetic field generating apparatus, in accordance with an eighth aspect of the invention, is characterized in that: said modifying means comprises a threaded hole provided on a side surface of at least one of said columnar yokes, said side surface lying in parallel with a longitudinal axis of said columnar yoke.
In the invention of the eighth aspect, since the modifying means comprises a threaded hole provided on a side surface of the columnar yoke lying in parallel with a longitudinal axis of the columnar yoke, the cross-sectional area of the columnar yoke perpendicular to the longitudinal axis is reduced at the threaded hole, thereby increasing magnetic resistance.
The static magnetic field generating apparatus, in accordance with a ninth aspect of the invention, is characterized in that: said modifying means comprises a screw of a shape generally conforming to said threaded hole, said screw being insertable/removable into/from said columnar yoke.
In the invention of the ninth aspect, since a screw of a shape generally conforming to the threaded hole serving as the modifying means is inserted/removed into/from the columnar yoke, magnetic resistance at the threaded hole can be modified by inserting/removing the screw into/from the threaded hole.
The static magnetic field generating apparatus, in accordance with a tenth aspect of the invention, is characterized in that: said groove, said through hole or said threaded hole is disposed on the s
Arana Louis
Armstrong Teasdale LLP
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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