Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2003-03-03
2004-06-15
Arana, Louis (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000
Reexamination Certificate
active
06750654
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese Application No. 2002-058861 filed Mar. 5, 2002.
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic resonance imaging apparatus in which an examination region is established by a first magnetic field generating section and a second magnetic field generating section disposed facing each other, and a magnetic resonance image of a subject placed within the examination region is captured, and more particularly to a magnetic resonance imaging apparatus in which stable operation is achieved, control devices are efficiently cooled, and the examination region can be maximized, with a simple configuration.
A magnetic resonance imaging apparatus (“MRI apparatus” hereinbelow) that uses a nuclear magnetic resonance phenomenon to image the internal structure of a subject to be imaged is known. Since the nuclear magnetic resonance phenomenon is harmless to a living body, the MRI apparatus is useful especially for medical applications, and is used for diagnosis of brain tumor, etc.
The nuclear magnetic resonance phenomenon is a phenomenon wherein, in a substance subjected to a uniform static magnetic field, spins of nuclei of atoms constituting the substance align in the same direction and absorb and emit electromagnetic waves at a frequency proportional to the static magnetic field strength (which frequency will be referred to as a “resonance frequency” hereinbelow). The MRI apparatus can utilize the nuclear magnetic resonance phenomenon for a specific nuclear species (mainly hydrogen atoms) to image an arbitrary cross-sectional plane through the subject to be imaged in an arbitrary thickness.
In imaging the internal structure of the subject to be imaged using the nuclear magnetic resonance phenomenon, a gradient magnetic field, aside from the static magnetic field, that varies with space and time is applied to the subject to be imaged to measure spatial information. By applying the gradient magnetic field, the magnetic field applied to the subject to be imaged is differentiated with position, and the resonance frequency of atoms constituting the subject to be imaged varies with position. Thus, which atoms exist at which position in the subject to be imaged can be known by applying the gradient magnetic field and measuring the resonance frequency. Up to this point, the mechanism of imaging the internal structure of an object by the MRI apparatus has been described.
FIG. 4
is an explanatory diagram for explaining an overall configuration of an MRI apparatus in the prior art, and
FIG. 5
is an explanatory diagram for explaining RF coils disposed in the MRI apparatus shown in FIG.
4
.
FIG. 6
is a vertical cross-sectional view of the MRI apparatus shown in FIG.
4
. In
FIGS. 4
,
5
and
6
, the MRI apparatus
101
establishes an examination region
10
using a lower magnetic field generating section
103
, which is a first magnetic field generating section, and an upper magnetic field generating section
102
, which is a second magnetic field generating section, disposed facing each other; and the MRI apparatus
101
generates a static magnetic field and a gradient magnetic field in the examination region
10
by an upper magnetic field coil
11
inside the upper magnetic field generating section
102
and a lower magnetic field coil
12
inside the lower magnetic field generating section
103
.
Moreover, a lower first-direction RF coil
121
that generates electromagnetic waves in a predefined direction (B1 direction hereinbelow) and a lower second-direction RF coil
131
that generates electromagnetic waves in a second direction orthogonal to the B1 direction (B2 direction hereinbelow) are disposed on the upper surface of the lower magnetic field generating section
103
. Similarly, an upper first-direction RF coil
141
that generates electromagnetic waves in the B1 direction, and an upper second-direction RE coil
151
that generates electromagnetic waves in the B2 direction are disposed an the lower surface of the upper magnetic field generating section
102
. The MRI apparatus
101
emits electromagnetic waves of frequencies in a certain range toward the examination region
10
using the lower first-direction RF coil
121
, lower second-direction RF coil
131
, upper first-direction RF coil
141
and upper second-direction RF coil
151
, and receives electromagnetic waves radiated from atoms constituting the subject to be imaged by the nuclear magnetic resonance phenomenon. In such a configuration, the lower first-direction RF coil
121
, lower second-direction RF coil
131
, upper first-direction RE coil
141
and upper second-direction RF coil
151
are each made by connecting a plurality of control devices
109
with a coil element. The control devices
109
are for stabilizing the phase of electromagnetic waves transmitted by the coil element and for switching between transmission and reception of electromagnetic waves. The control devices
109
are disposed on the surfaces of the upper magnetic field generating section
102
and the lower magnetic field generating section
103
.
The lower first-direction RF coil
121
is connected to RE wiring
122
. The lower first-direction RF coil is supplied with electric power from the RF wiring
122
when transmitting electromagnetic waves and sends received electromagnetic waves via the RF wiring
122
when receiving electromagnetic waves. The lower second-direction RF coil
131
is connected to RF wiring
132
. The lower second-direction RF coil
131
is supplied with electric power from the RF wiring
132
when transmitting electromagnetic waves and sends received electromagnetic waves via the RF wiring
132
when receiving electromagnetic waves. Similarly, the upper first-direction RF coil
141
transmits/receives electromagnetic waves via RF wiring
142
, and the upper second-direction RF coil
151
transmits/receives electromagnetic waves via RF wiring
152
.
Moreover, the RF wiring
122
and RF wiring
142
are disposed along a post
104
, one of two posts
104
and
105
that support the upper magnetic field generating section
102
, and the wiring
122
and wiring
142
are connected to a phase control section
106
. Similarly, the RF wiring
132
and wiring
152
are disposed along the post
105
, and are connected to the phase control section
106
. The phase control section
106
controls the phase of the RF wiring
122
,
132
,
142
and
152
to thereby control the phase of electromagnetic waves transmitted/received by the lower first-direction RF coil
121
, lower second-direction RF coil
131
, upper first-direction RF coil
141
, and upper second-direction RF coil
151
.
In the MRI apparatus
101
, the lower first-direction RF coil
121
and upper first-direction RF coil
141
generate an electromagnetic field in the B1 direction in the examination region
10
, and the lower second-direction RF coil
131
and upper second-direction RF coil
151
generate an electromagnetic field in the B2 direction. By thus generating electromagnetic fields in two orthogonal directions in the examination region
10
, uniform electromagnetic waves can be generated inside the examination region
10
with high excitation efficiency, and also accuracy of reception of electromagnetic waves from the examination region
10
can be made uniform.
Additionally, the phase control section
106
controls the phase of electromagnetic waves to avoid coupling between electromagnetic waves in the B1 direction and those in the B2 direction. The phase control section
106
is implemented using a 4-channel phase control section, for example, a QHD (quadrature hybrid drive), because the phase of the four RF coils of the lower first-direction RF coil
121
, lower second-direction RF coil
131
, upper first-direction RF coil
141
and upper second-direction RF coil
151
must be controlled.
Thus, the conventional MRI
101
is implemented as an MRI apparatus in which accuracy of transmission and reception of electromagnetic waves inside the examination r
Arana Louis
Armstrong Teasdale LLP
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
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