Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2000-01-18
2001-11-20
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S309000, C324S322000
Reexamination Certificate
active
06320383
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 and RF magnetic field generating apparatus that generates an RF magnetic field in a direction parallel to the coil loop surface, and a magnetic resonance imaging method and apparatus employing such an RF magnetic field generating apparatus.
A magnetic resonance imaging apparatus with a static magnetic field direction 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 hence employs as an RF coil for generating the RF magnetic field an RF coil having a loop surface parallel to the pole piece surface 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 static magnetic field direction. 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 through vector composition of respective RF magnetic fields generated by the two RF coils or can reduce a drive power per coil to generate the RF magnetic field of a desired strength.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a quadrature RF coil and RF magnetic field generating apparatus having a good frequency property and good openness of a magnetic field space, 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: a first electric path forming an annular closed loop; a plurality of second electric paths radially extending from a common connecting portion to the first electric path, the common connecting portion lying inside the closed loop formed by the first electric path; a third electric path facing the first electric path at a distance and forming an annular closed loop parallel to the closed loop of the first electric path; and a plurality of fourth electric paths radially extending from a common connecting portion to the third electric path, the common connecting portion lying inside the closed loop formed by the third electric path.
In accordance with a second aspect of the invention, there is provided an RF magnetic field generating apparatus comprising: a first electric path forming an annular closed loop; a plurality of second electric paths radially extending from a common connecting portion to the first electric path, the common connecting portion lying inside the closed loop formed by the first electric path; a third electric path facing the first electric path at a distance and forming an annular closed loop parallel to the closed loop of the first electric path; a plurality of fourth electric paths radially extending from a common connecting portion to the third electric path, the common connecting portion lying inside the closed loop formed by the third electric path; and an-RF signal supply means for supplying RF signals respectively to first positions each lying at relatively the same location on the first and third electric paths, and supplying RF signals having a phase different from that of the RF signals to the first positions by 90° respectively to second positions each lying at relatively the same location on the first and third electric paths and 90° apart from the first positions with respect to the direction as viewed from the central portion of the closed loop of the first or third electric path.
In accordance with a third aspect of the invention, there is provided a magnetic resonance imaging method comprising the steps of generating a static magnetic field in a z-direction, wherein three mutually orthogonal directions are defined as an x-direction, a y-direction and a z-direction in a space accommodating a subject under study, generating a gradient magnetic field in the space, generating a high frequency magnetic field in the space, measuring a magnetic resonance signal from the space, and producing an image based on the measured magnetic resonance signal, wherein the step of generating the high frequency magnetic field is performed using: a first electric path forming an annular closed loop in a plane perpendicular to the z-direction; a plurality of second electric paths radially extending from a common connecting portion to the first electric path, the common connecting portion lying inside the closed loop formed by the first electric path; a third electric path facing the first electric path at a distance in the z-direction and forming an annular closed loop parallel to the closed loop of the first electric path; a plurality of fourth electric paths radially extending from a common connecting portion to the third electric path, the common connecting portion lying inside the closed loop formed by the third electric path; and an RF signal supply means for supplying RF signals respectively to first positions each lying at relatively the same location on the first and third electric paths, and supplying RF signals having a phase different from that of the RF signals to the first positions by 90° respectively to second positions each lying at relatively the same location on the first and third electric paths and 90° apart from the first positions with respect to the direction as viewed from the central portion of the closed loop of the first or third electric path.
In accordance with a fourth aspect of the invention, there is provided a magnetic resonance imaging apparatus comprising: static magnetic field generating means for generating a static magnetic field in a z-direction, wherein three mutually orthogonal directions are defined as an x-direction, a y-direction and a z-direction in a space accommodating a subject under study; gradient magnetic field generating means for generating a gradient magnetic field in the space; high frequency magnetic field generating means for generating a high frequency magnetic field in the space; measuring means for measuring a magnetic resonance signal from the space; and image producing means for producing an image based on the magnetic resonance signal measured by the measuring means, wherein the high frequency magnetic field generating means comprises: a first electric path forming an annular closed loop in a plane perpendicular to the z-direction; a plurality of second electric paths radially extending from a common connecting portion to the first electric path, the common connecting portion lying inside the closed loop formed by the first electric path; a third electric path facing the first electric path at a distance in the z-direction and forming an annular closed loop parallel to the closed loop of the first electric path; a plurality of fourth electric paths radially extending from a common connecting portion to the third electric path, the common connecting portion lying inside the closed loop formed by the third electric path; and an RF signal supply means for supplying RF signals respectively to first positions each lying at relatively the same location on the first and third electric paths, and supplying RF signals having a phase different from that of the RF signals to the first positions by 90° respectively to second positions each lying at relatively the same location on the first and third electric paths and 90° apart from the first positions with respect to the direction as viewed from the central portion of the closed loop of the first or third electric path.
In any one of the first through fourth aspects of the invention, it is preferred that the first through fourth electric paths be made from a conductive foil, in that the homogeneity of the RF magnetic
Kato Yasushi
Ogino Tetsuo
Shimo Yukitoshi
GE Yokogawa Medical Systems Limited
Kojima Moonray
Shrivastav Brij B.
Williams Hezron
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