Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
2001-07-03
2003-01-21
Nguyen, Matthew (Department: 2838)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
Reexamination Certificate
active
06510035
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coil driving method, a coil driving apparatus and an MRI (Magnetic Resonance Imaging) apparatus, and more specifically to a coil driving method, a coil driving apparatus and an MRI apparatus capable of preventing variations in sensitivity even if samples inserted between a coil on one side and a coil on the other side, both of which are opposed to each other, are different in body frame.
FIG. 5
is an explanatory view showing examples of a transmitting coil driving circuit and a transmitting coil employed in an MRI apparatus which is related to the present invention.
The transmitting coil driving circuit
9
-J is provided with an amplifier
21
for power-amplifying a drive pulse Dp, and a splitter
22
for splitting the output of the amplifier
21
In four for four coils that constitute a transmitting coil
5
.
The transmitting coil
5
comprises an upper coil
5
A and a lower coil
5
B opposite to each other in a vertical direction.
The upper coil
5
A comprises an upper first coil
51
A ant an upper second coil
52
A.
The lower coil
5
B comprises lower first coil
51
B and a lower second coil
52
B.
When power is supplied to the upper first coil
51
A, current flows in the form of a figure of 8, so that a magnetic field H
1
which extends in the direction orthogonal to a current I
1
A that travels across the center of the coil and which is parallel with the surface of the coil, is formed in a space away slightly downward from the center of the coil surface.
When power is supplied to the upper second coil
52
A, a current flows in the form of a figure of 8, so that a magnetic field H
2
which extends in the direction orthogonal to a current I
2
A that travels across the center of the coil and which is parallel with the surface of the coil, is formed in a space away slightly downward from the center of the coil surface.
The upper first coil
51
A and the upper second coil
52
A are identical to each other in structure but different 90° from each other in the directions of the currents I
1
A and I
2
A. Thus, the magnetic fields H
1
and H
2
intersect at right angles.
While the lower first coil
51
B is identical in structure to the upper first coil
51
A, the direction of a current I
1
B, which travels across the center of the coil, is opposite to and parallel with that of the current I
1
A. Thus, when power is supplied to the lower fist coil
51
B, a magnetic field for intensifying the magnetic field H
1
is formed.
While the lower second coil
523
is identical En structure to the upper second coil
52
A, the direction of a current I
2
B, which travels across the center of the coil, is opposite to and parallel with that of the current I
2
A. Thus, when power is supplied to the lower second coil
52
B, a magnetic field for intensifying the magnetic field H
2
is formed.
In the transmitting coil driving circuit
9
-J, power has uniformly been supplied to all the coils
51
A,
52
A,
51
B and
52
B from the splitter
22
Such a power supplying method shows no problem because electromagnetic coupling between the upper coil
5
A and a sample and electromagnetic coupling between the lower coil
5
B and the sample become equivalent to each other in a state in which the sample is inserted into a space defined between the upper coil
5
A and the lower coil
5
B as shown in FIG.
6
.
However, when a sample small in body frame is used as shown in FIG.
7
, the sample is brought into a state of being located near the lower coil
5
B rather than the upper coil
5
A and hence electromagnetic coupling between the upper coil
5
A and t he sample and electromagnetic coupling between the lower coil
5
B and the sample are brought into unbalance. Therefore, the uniform supply of the power from the splitter
22
to all the coils
51
A,
52
A,
51
B and
52
B yields the unbalance between a magnetic field formed by the upper coil
5
A and a magnetic field formed by the lower coil
5
B, thus causing a problem that variations in sensitivity occur.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a coil driving method, a coil driving apparatus and an MRI apparatus capable of preventing variations in sensitivity even if samples inserted between a coil on one side and a coil on the other side both of which are opposed to each other, are different in body frame.
In a first aspect, the present invention provides a coil driving method comprising steps of inserting a sample between a coil on one side and a coil or the other side both of which are disposed so as to be opposite to each other, adjusting a balance in the supply of power to the both coils and thereafter supplying power to the both coils.
In the coil driving method according to the first aspect, the balance in the supply of the power to both coils is adjusted after the sample is actually inserted into a space defined between the coil on one side and the coil on the other side. Therefore, a magnetic filed formed by the coil on one side and a magnetic field formed by the coil on the other side always become equal to each other regardless of a body frame and a position of the sample, thus causing no variations in sensitivity.
In a second aspect, the present invention provides a coil driving method having the above configuration, which includes steps of measuring reflected waves sent from the both coils and controlling a power-supply balance so that the voltages of the reflected waves coincide with each other.
The coil driving method according o the second aspect has an advantage in that since the power-supply balance is adjusted with the voltages of the reflected waves from the coil on one side and the coil on the other side as indexes, the coil on one side and the coil on the other side need no work.
In a third aspect, the present invention provides a coil driving method having the above configuration, wherein magnetic field detecting means are provided in the vicinity of the coils and further including a step of controlling a power-supply balance so that the magnitudes of signals detected by the magnetic field detecting means coincide with each other.
The coil driving method according to the third aspect has an advantage in that since magnetic fields generated by the coil on one side and the coil on the other side are actually measured to adjust the power-supply balance, the power-supply balance can directly be adjusted as compared with the case where the voltages of the reflected waves are set as the indexes.
In a fourth aspect, the present invention provides a coil driving method comprising steps of controlling a balance in the supply of power to a coil on one side and a coil on the other side, both of which are disposed so as to be opposite to each other, the balance being determined in advance in association with a body frame of a sample inserted between the two coils, and thereafter supplying power to the both coils.
A shift in the balance of the supply of power to each of the coil on one side and the coil on the other side depends on the body frame of the sample. In other words, the amount of compensation for the shift in the power-supply balance can be recognized from the body frame of the sample.
In the coil driving method according to the fourth aspect, the power-supply balance is adjusted according to the amount of compensation determined in advance in association with the body frame of the sample. Therefore, a magnetic filed formed by the coil on one side and a magnetic field formed by the coil on the other side can evenly be adjusted, thus causing no variations in sensitivity. Since it is also unnecessary to actually insert the sample into a space defined between the coil on one side and the coil on the other coil and measure the power-supply balance, an advantage is brought about in that a work load is lightened.
In a fifth aspect, the present invention provides a coil driving method having the above configuration, including a step of using the weight of the sample as the body frame of the sample.
While the weight of the sample and i
GE Medical Global Technology Company, LLC
Kojima Moonray
Nguyen Matthew
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