Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2000-01-11
2001-10-02
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000
Reexamination Certificate
active
06297636
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an RF (radio frequency) coil, RF magnetic field generating apparatus and magnetic resonance imaging method and apparatus, and more particularly to an RF coil having a plurality of electric paths carrying electric current for generating an RF magnetic field and an annular electric path linking respective ends of the plurality of electric paths, an RF magnetic field generating apparatus employing such an RF coil, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
A magnetic resonance imaging apparatus having the direction of a static magnetic field perpendicular to the body axis of a subject, commonly referred to as a vertical magnetic field-type magnetic resonance imaging apparatus, generates an open static magnetic field space, and employs as an RF coil for generating an RF magnetic field an RF coil having a loop surface parallel to pole piece surfaces of a static magnetic field generating unit. The RF coil of this type generates the RF magnetic field in the direction parallel to the coil loop surface to form the RF magnetic field perpendicular to the direction of the static magnetic field. Such an RF coil is disclosed in U.S. Pat. No. 5,760,583 of the present applicant.
On the other hand, there is another type of an RF coil referred to as a quadrature RF coil, which consists of a combination of two RF coils, and can provide an RF magnetic field having an increased strength by vector composition of respective RF magnetic fields generated by the two RF coils or can reduce a drive power per coil to obtain the RF magnetic field of a desired strength.
However, in the conventional RF coils, an unwanted RF magnetic field is generated from electric current flowing through tie paths for linking main paths. Since the unwanted RF magnetic field cancels the RF excitation magnetic field generated from the main paths, efficiency in generating the RF magnetic field is reduced and a larger electric power for excitation is required to obtain a desired magnetic field strength.
Moreover, the electric current flowing through the main paths and the tie paths becomes larger correspondingly, raising additional problem that the high frequency electric power absorption, i.e., the whole SAR (specific absorption rate), of the subject is increased.
Furthermore, the unwanted RF magnetic field generated by the tie paths not only cancels the RF excitation but also increases the local high frequency electric power absorption, i.e., the local SAL, of the subject.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an RF coil and RF magnetic field generating apparatus that generates an RF magnetic field efficiently, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
It is another object of the present invention to provide an RF coil and RF magnetic field generating apparatus that provides a small SAL of a subject, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
In accordance with a first aspect of the invention, there is provided an RF coil comprising: radially extending electric paths carrying electric current for generating an RF magnetic field within a space containing a subject; and an annular electric path located farther from the space than the radially extending electric paths from the space, for linking respective ends of the radially extending electric paths.
In accordance with a second aspect of the invention, there is provided an RF coil comprising: a plurality of mutually parallel electric paths carrying electric current for generating an RF magnetic field within a space containing a subject; and annular electric paths disposed on both ends of the plurality of electric paths, located farther from the space than the plurality of electric paths from the space, for linking respective ends of the plurality of electric paths.
In accordance with a third aspect of the invention, there is provided an RF magnetic field generating apparatus comprising: radially extending electric paths carrying electric current for generating an RF magnetic field within a space containing a subject; an annular electric path located farther from the space than the radially extending electric paths from the space, for linking respective ends of the radially extending electric paths; and RF signal supply means for supplying RF signals having respective phases different by 90° from each other, respectively to two positions on the annular electric path having respective directions from the center of the annular electric path different by 90° from each other.
In accordance with a fourth aspect of the invention, there is provided an RF magnetic field generating apparatus comprising: a plurality of mutually parallel electric paths carrying electric current. for generating an RF magnetic field within a space containing a subject; annular electric paths disposed on both ends of the plurality of electric paths, located farther from the space than the plurality of electric paths from the space, for linking respective ends of the plurality of electric paths; and RF signal supply means for supplying RF signals having respective phases different by 90° from each other, respectively to two positions on either one of the annular electric paths having respective directions from the center of the annular electric path different by 90° from each other.
According to the present invention, the distance between the annular electric path and the subject is increased to reduce cancellation effect of the annular electric path on the RF excitation magnetic field, and also reduce the SAR of the subject.
Therefore, the present invention can provide an RF coil and RF magnetic field generating apparatus that generates an RF magnetic field efficiently, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
Moreover, the present invention can provide an RF coil and RF magnetic field generating apparatus that provides a small SAL of a subject, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 4506224 (1985-03-01), Krause
patent: 4592363 (1986-06-01), Krause
patent: 5696449 (1997-12-01), Boskamp
patent: 5699802 (1997-12-01), Duerr
patent: 5777474 (1998-07-01), Srinivasan
I. Viohl “Circular polarized RF cois for open magnetic system” Proceedings of Society of Magnetic Resonance; 3rd meeting, Aug. 19-25, 1995, vol. 1, p. 183.
S. Junge “Optimization of a quadrature whole body resonator for 2I”, Proceeding of Internation Society for Mag. Res. May 22-28, 1999; vol. 3, p 2053.
E.B. Boskamp “Vertifical Field Open RF body cois” Proceedings of Int. Soc. for Magnetic Resoance in Medicine May 22-28, 1999, vol. 1 p. 736.
Hoshino Kazuya
Shimo Yukitoshi
GE Yokogawa Medical Systems Limited
Kojima Moonray
Patidar Jay
Shrivastav Brij B.
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