Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2000-01-03
2001-12-04
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S309000, C324S307000
Reexamination Certificate
active
06326789
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a receive coil and a magnetic resonance imaging method and apparatus, and more particularly to a receive coil comprising a plurality of conductive loops having series capacitors, and a magnetic resonance imaging method and apparatus employing such a receive coil.
In a magnetic resonance imaging apparatus, a receive coil is disposed closed to and around the subject so that a magnetic resonance signal is measured at a position as close to an imaging site as possible to improve the SNR (signal-to-noise ratio) of the signal.
Typical examples of such a receive coil include a solenoid-type receive coil for use in spine imaging. Since the spine is generally recognized as three parts, i.e., the C(cervical)-spine, the T(thoracic)-spine and the L(lumbar)-spine, three types of the receive coils are provided to be properly used according to which part of the spine is to be imaged.
If a plurality of the receive coils are simultaneously used, electromagnetic coupling occurs and it changes the resonance frequency of the coil. Therefore, when two or more parts of the spine in the same subject are to be imaged, respective dedicated receive coils are used and exchanged appropriately according to use so that the coupling can be avoided.
When the plurality of parts of the spine are imaged as described above, the need to exchange the receive coils makes operation cumbersome, and requires the subject to change his/her position, for example, which may cause a burden to the subject.
On the other hand, the plurality of parts of the spine can be simultaneously imaged if the axial length of the solenoid coil is extended to widen the receive sensitivity range in the body axis direction. However, the coil having such an extended length reduces the SNR of the received signal.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a receive coil comprising a plurality of coils that make no coupling, and a magnetic resonance imaging method and apparatus employing such a receive coil.
In accordance with a first aspect of the invention, there is provided a receive coil comprising a plurality of conductive loops having series capacitors, each of the loops comprising a low input-impedance amplifier with an input circuit of the low input-impedance amplifier connected in parallel to both ends of the capacitor via an inductor.
In accordance with a second aspect of the invention, there is provided a magnetic resonance imaging method comprising the steps of generating a static magnetic field in a space holding a subject, 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 measuring a magnetic resonance signal is performed using a receive coil comprising a plurality of conductive loops having series capacitors, each of the loops having a low input-impedance amplifier with an input circuit of the low input-impedance amplifier connected in parallel to both ends of the capacitor via an inductor.
In accordance with a third aspect of the invention, there is provided a magnetic resonance imaging apparatus having static magnetic field generating means for generating a static magnetic field in a space holding a subject, 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 measuring means comprises a receive coil comprising a plurality of conductive loops having series capacitors, each of the loops having a low input-impedance amplifier with an input circuit of the low input-impedance amplifier connected in parallel to both ends of the capacitor via an inductor.
In accordance with a fourth aspect of the invention, there is provided the magnetic resonance imaging apparatus as described regarding the third aspect, wherein the measuring means comprises: a second receive coil consisting of a conductive loop having series capacitors, the second receive coil having sensitivity in the direction perpendicular to the sensitivity direction of the receive coil, the loop having a low input-impedance amplifier with an input circuit of the low input-impedance amplifier connected in parallel to both ends of the capacitor via an inductor; and a frequency selective signal block circuit for connecting a ground side of an output signal line of at least one of the low input-impedance amplifiers to a common ground.
In any one of the first through fourth aspects of the invention, it is preferred that the loop have disable means that is controlled by an external signal, in that decoupling performance is further improved.
Moreover, in the second or third aspect of the invention, it is preferred that a frequency selective signal block circuit be provided for each low input-impedance amplifier, for connecting a ground side of an output signal line of each low input-impedance amplifier to a common ground, in that a received signal is obtained with a good SNR.
Furthermore, in the third or fourth aspect of the invention, it is preferred that the frequency selective signal block circuit be a trap circuit, in that the signal blocking is effectively achieved.
Still furthermore, in the fourth aspect of the invention, it is preferred that the second receive coil be a saddle-type coil, in that quadrature reception is effectively achieved.
EFFECT
According to the present invention, the inductor is connected in parallel to the capacitor in the loop via a low input impedance of the amplifier, and hence an LC parallel circuit is established. A high impedance caused by the parallel resonance blocks coupling between the loops.
Thus, the present invention can provide a receive coil comprising a plurality of coils that make no coupling, and a magnetic resonance imaging method and apparatus employing such a receive coil.
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: 5208534 (1993-05-01), Okamoto et al.
patent: 5383903 (1995-01-01), Young
patent: 5757189 (1998-05-01), Molyneaux et al.
Encyclopeaudia of NMR ed. Grant et al (1996) pp 1841-1846.
Morita Kensaku
Sato Kenji
Yoshida Masaru
GE Yokogawa Medical Systems Limited
Kojima Moonray
Shrivastav Brij B.
Williams Hezron
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