JP2641808B2 - MRI antenna coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to nuclear magnetic resonance (N)
The present invention relates to an antenna coil used in an MRI apparatus that performs imaging using MR, and particularly to an orthogonal RF coil (quadrature coil).

[0002]

2. Description of the Related Art Conventionally, quadrature coils have been used in MRI apparatuses in order to obtain a higher S / N ratio. This quadrature coil is composed of two electrically independent RF coils, and these two coils are arranged in a positional relationship such that high-frequency magnetic fields from the two coils are orthogonal to each other. FIG. 1 shows a case where the quadrature coil is applied to a planar coil for imaging a limited portion with high sensitivity, and an Alderman & Grant type or the like is known as an example of application to a cylindrical coil. These quadrature coils have two Rs electrically independent of each other.
Since the orthogonal high-frequency magnetic field is transmitted and received from the F coil, it is equivalent to the addition and averaging of the signals, and the S / N ratio is theoretically improved to twice the route.

FIG. 1 shows a conventional example of a quadrature coil configured as a planar coil. Vertical magnetic field generating coil 1
And a horizontal magnetic field generating coil 2. The former coil 1 is formed in a normal loop shape, and the latter coil 2 is formed in a concave shape, so that the coil 1 overlaps the center of the coil 2. Are located. A coupling capacitor 3 is inserted at an appropriate position in each of the coils 1 and 2, and
Cables 4 are respectively connected for power supply or signal extraction. When high-frequency signals having a phase difference of 90 ° are applied to these coils 1 and 2, the magnetic fields generated from each of the coils 1 and 2 become as shown by solid and dotted arrows in FIG. And electrically orthogonal. Since this planar coil is actually mainly used as a reception-only coil, NMR signals generated in the orthogonal region are applied to the coils 1 and 2 respectively.
It will be received as a signal that is 0 ° out of phase.

[0004]

However, the conventional quadrature coil has a problem that two coils interfere with each other and it is difficult to obtain good characteristics. That is, when a horizontal magnetic field is generated, a current flows through the coil 2 as shown by a solid arrow in FIG.
An induced current flows through the coil 1 as indicated by a dotted arrow. In this case, the induced currents generated in the coil 1 tend to cancel each other during one loop, so that no induced current flows through the entire coil 1 as a result. On the other hand, when a vertical magnetic field is generated, a current flows through the coil 1 as indicated by a solid arrow in FIG. 3, and an induced current is generated in the coil 2 as indicated by a dotted arrow. Since the induced current flowing through the coil 2 does not have a relationship of canceling out during one loop as in the case of the induced current flowing through the coil 1 in FIG. 2, the induced current flows through the entire coil 2. Therefore, in the case of FIG. 3, the interference between the coils 1 and 2 becomes a problem. In order to eliminate the interference in the case of FIG. 3, it is considered to adjust the area ratio of the overlapping portions of the coils 1 and 2, but the adjustment is basically very difficult.

In view of the above, it is an object of the present invention to provide an MRI antenna coil in which interference between two coils forming a quadrature coil is eliminated and characteristics are improved.

[0006]

In order to achieve the above object, in an MRI antenna coil according to the present invention, a first coil formed in a loop shape and an eight-shaped MRI antenna are provided. A second coil whose intersection is located at the center end is symmetrical with respect to a virtual straight line passing through the intersection and bisecting the second coil in the same plane having curvature. And the first coil is disposed at the center of the second coil that does not overlap with the intersection, and the position of the first coil that intersects the virtual straight line and the position of the second coil A coupling capacitor is inserted at a position symmetrical with respect to the virtual straight line and at a position where the coupling capacitor intersects with the virtual straight line parallel to the virtual straight line. Connect It has become a feature that was. According to such a configuration, the first coil or the second coil
In each case, when a current is applied to one coil to generate a vertical or horizontal magnetic field, the current induced in the other coil can be canceled out in the loop of that coil, resulting in the induction A state where no current is generated can be achieved.

Therefore, the interference between the two coils is eliminated, the mutual independence becomes extremely high, and the characteristics can be improved. Also, in the case of the second coil, which is formed in an eight-shape, the intersection is located at the end rather than at the center, and the first and second coils pass through the intersection of the second coil, and the second coil is divided into 2 and so on. Bilaterally symmetric with respect to the imaginary straight line, and
It is located at the center of the second coil that does not overlap with the intersection. Further, power supply to the first coil or signal extraction therefrom is performed by connecting a cable to one end of each of coupling capacitors inserted at positions intersecting with the virtual straight line, and supplying power to the second coil or the like. The signal extraction is performed by connecting cables to both ends of one of the coupling capacitors inserted at a position which is symmetrical with respect to the virtual straight line and intersects with the virtual straight line parallel to the virtual straight line. For this reason, the symmetry does not collapse either mechanically or electrically, so that even if a curved surface is provided, the magnetic field will not be disturbed. Further, since the first and second coils are arranged in the same plane, it is easy to actually manufacture them. Further, the plane on which the first and second coils are arranged is not flat but has a curvature, and can be adapted to the shape of the human body, so that the sensitivity can be increased.

[0008]

An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 4 shows an embodiment of the present invention. As shown in FIG.
Is formed in a simple rectangular or circular loop shape as in the prior art, but the horizontal magnetic field generating coil 6 is formed in an eight-character shape that intersects at the center, and the intersection P is
Is located at the end deviated from the center of. 8-shaped coil 6
And the coil 5 pass through the intersection P, and connect the figure-eight coil 6 to 2
As shown in the drawing, the imaginary straight line l is equally symmetrical, and the coil 5 is superimposed on the central portion of the figure-shaped coil 6 which does not overlap with the intersection P of the figure-shaped coil 6 so as to match the shape of the human body. And are arranged in the same curved plane.
In FIG. 4, both coils 5 and 6 are shown in plan view for simplification of the drawing. As shown in the drawing, the coupling capacitors are respectively provided at positions where the coil 5 intersects the virtual straight line 1 and at appropriate positions where the coil 6 intersects a straight line which is symmetrical with respect to the virtual straight line 1 and parallel to the virtual straight line l. 3 is inserted. Further, one of the coupling capacitors 3 inserted into each of the coils 5 and 6
A cable 4 for power supply or signal extraction is connected to each of the two ends.

When a current is applied to the coil 6, a horizontal magnetic field is generated as shown by a solid arrow in FIG. At this time, a current flows through the coil 6 as shown by a solid arrow in FIG. The induced current of this coil 5 is shown in FIG.
, And the directions of the entire loop of the coil 5 cancel each other. When a current is applied to the coil 5, a vertical magnetic field can be generated as shown by a dotted arrow in FIG. At this time, a current flows through the coil 5 as shown by a solid arrow in FIG. Then, a current as shown by a dotted arrow in FIG. The induced currents tend to cancel each other when viewed as a whole of the figure-eight coil 6.

Therefore, even when a vertical or horizontal magnetic field is generated, the current induced in one of the coils does not cancel each other and make one turn. Therefore, interference between the two coils 5 and 6 can be eliminated, and the independence between the two coils can be improved to improve the characteristics. Further, the two coils 5 and 6 are disposed in a symmetrical positional relationship with respect to a virtual straight line l passing through the intersection P and bisecting the second coil.
Coupling capacitor 3 inserted at a position intersecting virtual line l
The cable 4 is connected to both ends of the first coil, and power is supplied to the second coil or signal is extracted from the second coil at a position which is symmetrical with respect to the virtual straight line and intersects with the virtual straight line parallel to the virtual straight line. One of the inserted coupling capacitors
Since the cable is connected to both ends, the magnetic field balance of both coils is ensured. Even if the coils are arranged with a curvature, the magnetic field is not disturbed and the characteristics are improved. In addition, 8
In general, it becomes difficult to resonate at a higher frequency due to an increase in inductance of the figure-shaped coil 6, but it is possible to resonate at a higher frequency by inserting the coupling capacitor 3 at several places.

FIG. 7 shows the present invention applied to a cylindrical coil. That is, as shown in FIG.
And a figure-eight coil 6 formed on a semi-cylindrical insulating substrate 7 (a planar shape in FIG. 4, but it is equivalent to a whole which is curved into a semi-cylindrical shape). Two such semi-cylindrical insulating substrates 7 are joined to form a cylindrical shape. This means that quadrature coils are formed on each of the two semi-cylindrical insulating substrates 7. Cables (not shown in FIG. 7 but refer to FIG. 4 and the like) are connected in parallel to the two loop coils 5, and cables are connected in parallel to the two figure-eight coils 6. Thereby, magnetic fields perpendicular to each other can be generated inside the cylinder in a plane perpendicular to the axis of the cylinder. That is, the two magnetic coils 5 form a vertical magnetic field in FIG. 7 and the two 8-shaped coils 6 generate a magnetic field in the horizontal direction.

In the case of FIG. 7, the loop coils 5 and 8
The point that the interference with the U-shaped coil 6 can be reduced and the magnetic field is not disturbed even when curved into a semi-cylindrical shape is shown in FIG.
Is the same as In the case of the cylindrical coil of FIG.
A quadrature coil is formed on each of the two semi-cylindrical insulated substrates 7 and there is no conductor connection between them.
It can be easily divided into two or combined into one.

Therefore, as shown in FIGS. 8 and 9, two semi-cylindrical insulating substrates 7 can be opened and closed by connecting them by a hinge structure, or two semi-cylindrical insulating substrates 7 are detachable (not shown). Can also be separated. As a result, when it is mounted on the imaging site of the subject, it can be mounted very easily by being opened or removed. In the case of a cylindrical coil that cannot be divided, for example, when a cylindrical coil for a knee joint is attached to the knee joint of a subject, an unreasonable posture is imposed. It can be mounted in the posture of. The conventional cylindrical quadrature coil has a geometric four-fold symmetry, and it is necessary to provide a conductor so as to go around the cylindrical side surface.
In order to divide in this way, electrical contacts must be provided at any point, which may cause anxiety in reliability, but this is solved.

[0014]

As described above, according to the embodiment,
ADVANTAGE OF THE INVENTION According to the antenna coil for MRI of this invention, the interference between two coils which comprise a quadrature coil is eliminated,
The characteristics can be improved, the magnetic field can be prevented from being disturbed, and the sensitivity can be increased because it is easy to manufacture and can be adapted to the shape of the human body.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conventional planar quadrature coil.

FIG. 2 is a diagram showing an induced current in a conventional planar quadrature coil.

FIG. 3 is a diagram showing an induced current in a conventional planar quadrature coil.

FIG. 4 is a schematic view of one embodiment of the present invention.

FIG. 5 is a view showing an induced current in the embodiment.

FIG. 6 is a view showing an induced current in the embodiment.

FIG. 7 is a schematic view of another embodiment.

FIG. 8 is a schematic view of another state of FIG. 7;

FIG. 9 is a schematic view of another state of FIG. 7;

[Description of Signs] 1, 5 Vertical magnetic field generating coil 2, 6 Horizontal magnetic field generating coil 3 Coupling capacitor 4 Cable 7 Semi-cylindrical insulating substrate

Claims (1)

(57) [Claims] A first coil formed in a loop shape;
The second coil, which is formed in an eight-shape and whose intersection is located at the center end, is connected to the second coil through the intersection in the same plane having curvature. The first coil is disposed at a central portion of a second coil that does not overlap with the intersection and has a symmetrical positional relationship with respect to the virtual straight line that is equally divided, and intersects the virtual straight line of the first coil. A coupling capacitor is inserted between the position and the position of the second coil, which is symmetrical with respect to the virtual straight line and intersects with the virtual straight line parallel to the virtual straight line, and one of the coupling capacitors connected to both coils is inserted. MR characterized in that power supply or signal extraction cables are connected to both ends.
I antenna coil.