JPH10127599A - Rf coil for mri - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an RF coil for MRI to widen the sensitive range in a cylindrical shaped central axis direction and to apply a vibrating magnetic field from outside to inside without attenuating. SOLUTION: This RF coil 100 for MRI(Magnetic Resonance Imaging) has 8-shaped conductive passages 2s and 2b crossed into an 8-shape formed on a part corresponding to cylindrical shape side faces. When a vibration magnetic field By is applied from outside, induced electromotive force Vat generated at the upper half of the 8-shaped conductive passage 2a and induced electromotive force Vab mutually cancel not to flow induced current. Also induced electromotive force Vbt generated at the upper half of the 8-shaped conductive passage 2b and induced electromotive force Vbb mutually cancel not to flow induced current. Accordingly the vibration magnetic field By is not canceled. Thus the sensitive range in the central axis direction of the cylindrical shape can be widened. The vibration magnetic field in the radial direction of the cylindrical shape and the horizontal direction can be applied from outside to inside without attenuating and large RF power for exciting the subject becomes not necessary. It also prevents uniformity lowering of the excitation magnetic field applied to the subject.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an MRI (Magneti)
More specifically, the present invention relates to an RF coil for resonance imaging, and more specifically, an RF coil for MRI having a cylindrical shape as a whole, which has a wide sensitivity range in the central axis direction of the cylindrical shape, and furthermore, has a radial and horizontal direction in the cylindrical shape. The present invention relates to an MRI RF coil that can be applied from outside to inside without attenuating the oscillating magnetic field in the direction. In particular, it is useful as a reception-only RF coil used in a vertical magnetic field type MRI apparatus.

[0002]

2. Description of the Related Art FIG. 9 is a configuration diagram showing a solenoid coil which is an example of a conventional MRI RF coil. This solenoid coil 500 has a structure in which a copper sheet having a relatively narrow width W1 is rolled into a cylindrical shape with a short interval between both ends to form a cylindrical conductor portion 52, and a resonance capacitor 53 is connected between the both ends. It is. The core wire of the coaxial cable L and an external conductor are connected to both ends of the resonance capacitor 53, respectively. Cartesian coordinates in which the central axis direction of the cylindrical conductor portion 52 is the z-axis direction, two axes perpendicular to the z-axis direction are the x-axis and the y-axis, the z-axis and the y-axis are in the horizontal plane, and the x-axis is the vertical direction. Assuming a system, the solenoid coil 50
0 is used in a vertical magnetic field type MRI apparatus having a static magnetic field Bo in the x-axis direction. Then, a cavity surrounded by the cylindrical conductor portion 52 becomes a measurement space. That is, the solenoid coil 500 excites the subject entering the cavity by a rotating magnetic field (the components thereof are oscillating magnetic fields Bz and By) of a transmitting coil (not shown) installed outside, and Oscillating magnetic field Ez in the z-axis direction of the emitted NMR signal
Used to sense

FIG. 10 is an explanatory diagram showing the sensitivity distribution in the z-axis direction of the solenoid coil 500. For convenience of explanation, the center of the coil is set as the z-axis origin. The sensitivity of the solenoid coil 500 suddenly decreases when it comes off the coil end.

FIG. 11 is a configuration diagram showing another example of a conventional solenoid coil. This solenoid coil 600
This is a structure in which a copper sheet having a relatively wide width W is rolled into a tube with a short interval between both ends to form a cylindrical conductor portion 62, and a plurality of resonance capacitors 63 are connected between the both ends. The core wire of the coaxial cable L and an external conductor are connected to both ends of the resonance capacitor 63, respectively. Orthogonal coordinates in which the central axis direction of the cylindrical conductor portion 62 is the z-axis direction, two axes orthogonal to the z-axis direction are the x-axis and the y-axis, the z-axis and the y-axis are in the horizontal plane, and the x-axis is the vertical direction. Assuming a system, the solenoid coil 600 is used in a vertical magnetic field type MRI apparatus having a static magnetic field Bo in the x-axis direction.
Then, a cavity surrounded by the cylindrical conductor portion 62 becomes a measurement space. That is, the solenoid coil 600 excites the subject entering the cavity by the rotating magnetic field (the components thereof are oscillating magnetic fields Bz and By) of the transmitting coil (not shown) provided outside, and It is used to sense the oscillating magnetic field Ez in the z-axis direction of the emitted NMR signal.

FIG. 12 is an explanatory diagram showing the sensitivity distribution in the z-axis direction of the solenoid coil 600. Since the width W of the solenoid coil 600 in the z-axis direction is wider than the width W1 of the solenoid coil 500, the width in the z-axis direction at which the sensitivity required for receiving the NMR signal can be increased.

[0006]

In the above-described conventional solenoid coil 500, as shown in FIG.
However, there is a problem that the width that can detect is narrow. Further, in the above-mentioned conventional solenoid coil 600, as shown in FIG.
2 shields the oscillating magnetic field By, so that there is a problem that a large RF power is required to excite the subject in the cavity, and the uniformity of the oscillating magnetic field By is deteriorated.

On the other hand, like a solenoid coil 700 shown in FIG.
It is conceivable that the oscillating magnetic field By is easily transmitted by opening the oscillating magnetic field By. However, as shown in FIG. 14, the induced current i flows through the conductive path formed by the conductor around the opening K, and the oscillating magnetic field By is generated, so that the oscillating magnetic field By is also attenuated. There is a problem.

Accordingly, an object of the present invention is to provide a wide sensitivity range in the direction of the central axis (z axis) of the cylindrical shape, and to reduce the radial and horizontal oscillating magnetic field (By) of the cylindrical shape. An object of the present invention is to provide an MRI RF coil that can be applied from outside to inside.

[0009]

According to a first aspect of the present invention, there is provided an MRI RF coil having a cylindrical shape as a whole, wherein a portion corresponding to a side surface of the cylindrical shape intersects with a figure eight. An MRI characterized by forming a figure-eight conductive path.
An RF coil is provided. R for MRI of the first aspect
In the F coil, the sensitivity range in the central axis direction of the cylindrical shape can be widened by relatively widening the width of the cylindrical shape in the central axis direction. In addition, induced electromotive forces are generated in the upper and lower halves of the 8-shaped conductive path in opposite directions to the radial and horizontal oscillating magnetic field of the cylindrical shape. Absent. As a result, no oscillating magnetic field that cancels the radial and horizontal oscillating magnetic field of the cylindrical shape is generated. Therefore, the cylindrical oscillating magnetic field in the radial and horizontal directions can be applied from outside to inside without attenuating. Further, it is possible to prevent a decrease in the uniformity of the oscillating magnetic field.

According to a second aspect, the present invention relates to an MRI RF coil having a cylindrical shape as a whole, wherein a radially and horizontally oscillating magnetic field of the cylindrical shape is provided on a portion corresponding to a side surface of the cylindrical shape. The present invention provides an MRI RF coil characterized in that a conductive path is formed so as to generate induced electromotive forces in opposite directions that cancel each other out when added. In the MRI RF coil of the second aspect, the sensitivity range in the central axis direction of the cylindrical shape can be widened by relatively widening the width of the cylindrical shape in the central axis direction. In addition, an induced electromotive force is generated that cancels each other against the oscillating magnetic field in the radial and horizontal directions of the cylindrical shape, so that no induced current flows. As a result, no oscillating magnetic field that cancels the radial and horizontal oscillating magnetic field of the cylindrical shape is generated. Therefore, the cylindrical oscillating magnetic field in the radial and horizontal directions can be applied from outside to inside without attenuating. Further, it is possible to prevent a decrease in the uniformity of the oscillating magnetic field.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the embodiments of the invention shown in the drawings. Note that the present invention is not limited by this.

First Embodiment FIG. 1 is an MRI RF according to a first embodiment of the present invention.
It is a block diagram showing a coil. This MRI RF coil 1
00 is a figure-eight conductive path 2a, 2b that intersects the figure eight
Is formed in a portion corresponding to the side surface of the cylindrical shape, and is provided between the cylindrical conductor portion 2 having a short interval between the conductor portions corresponding to the upper sides of the figure-shaped conductive paths 2a and 2b; , And a plurality of resonance capacitors 3 connected to each other. The tubular conductor 2 is made of, for example, copper or aluminum, and has a relatively large width W. The upper half and the lower half of the figure 8 are symmetric with respect to the intersection. The core wire and the outer conductor of the coaxial cable L are respectively connected to both ends of one of the resonance capacitors 3 (the coaxial cable may not be directly connected but may be led out via a balun). The central axis direction of the cylindrical conductor portion 2 is defined as a z-axis direction, and two directions orthogonal to the z-axis direction are defined as x-axis and y-axis.
When assuming an orthogonal coordinate system in which the z axis and the y axis are in a horizontal plane and the x axis is a vertical direction, the MRI RF coil 100 has a vertical magnetic field type M having a static magnetic field Bo in the x axis direction.
Used in RI equipment. Then, a cavity surrounded by the cylindrical conductor portion 2 becomes a measurement space. That is, this M
The RF coil for RI 100 excites the subject in the cavity by a rotating magnetic field (the components thereof are oscillating magnetic fields Bz and By) of a transmitting coil (not shown) provided outside, and radiates from the subject. It is used to sense the oscillating magnetic field Ez in the z-axis direction of the obtained NMR signal.

FIG. 2 is an explanatory diagram showing an induced electromotive force generated when the oscillating magnetic field By is applied to the MRI RF coil 100. When the oscillating magnetic field By is applied, the induced electromotive force V in the direction of flowing an induced current for generating an oscillating magnetic field in a direction to cancel the oscillating magnetic field By is provided in the upper half of the figure-shaped conductive path 2a.
at occurs. On the other hand, an induced electromotive force Vab is generated in the lower half of the figure-shaped conductive path 2a in the direction in which an induced current is generated to generate an oscillating magnetic field in a direction to cancel the oscillating magnetic field By. However, since these are in opposite directions on the figure-eight conductive path 2a, no induced current flows to cancel each other out and generate an oscillating magnetic field in a direction to cancel the oscillating magnetic field By. Also,
An induced electromotive force Vbt in the direction of flowing an induced current for generating an oscillating magnetic field in a direction to cancel the oscillating magnetic field By is generated in the upper half of the figure-eight conductive path 2b. On the other hand, the figure-shaped conductive path 2b
In the lower half, an induced electromotive force Vbb in the direction of flowing an induced current for generating an oscillating magnetic field in a direction to cancel the oscillating magnetic field By is generated. However, since these are in the opposite directions on the figure-eight conductive path 2b, no induced current flows to cancel each other out and generate an oscillating magnetic field in a direction to cancel the oscillating magnetic field By. As a result, no oscillating magnetic field for canceling the oscillating magnetic field By is generated, and the oscillating magnetic field By can be applied from outside to inside without attenuating the oscillating magnetic field By.

FIG. 3 is an explanatory diagram showing a distribution state of induced current generated when the oscillating magnetic field Ez is sensed by the MRI RF coil 100. When a magnetic field Ez in the direction of the arrow is applied, an upward induced current ia is applied to the 8-shaped conductive path 2a.
t, iab flows. Further, downward induced currents ibt and ibb flow through the figure-eight conductive path 2b. That is, MRI
11 and FIG.
As in the case of the solenoid coils 600 and 700 shown in FIG. 3, an induced current flows, and the oscillating magnetic field Ez in the z-axis direction of the NMR signal can be sensed.

FIG. 4 is an explanatory diagram showing the sensitivity distribution in the z-axis direction of the MRI RF coil 100. R for MRI
If the width W of the F coil 100 in the z-axis direction is increased, NMR
The width in the z-axis direction at which the sensitivity required for receiving a signal can be obtained can be made sufficiently large.

According to the MRI RF coil 100 of the first embodiment, the width W of the cylindrical conductor 2 can be widened to widen the sensitivity range in the z-axis direction, and the oscillating magnetic field By is not attenuated. Can be applied from outside to inside, and a large RF power is not required to excite the subject. Further, since the uniformity of the oscillating magnetic field By is not impaired, the subject can be preferably excited.

Second Embodiment FIG. 5 shows an RF for MRI according to a second embodiment of the present invention.
It is a block diagram showing a coil. This MRI RF coil 2
In FIG. 00, the figure-eight conductive path 22 of the cylindrical conductor portion 22
A plurality of resonance capacitors 23a and 23b are connected to two gaps between the conductor portions corresponding to the upper side and the lower side, respectively. According to the RF coil 200 for MRI according to the second embodiment, the width of the cylindrical conductor portion 22 can be widened, and the sensitivity range in the central axis direction of the cylindrical shape can be widened. Further, the oscillating magnetic field in the radial and horizontal directions of the cylindrical shape can be applied from outside to inside without attenuating, so that a large RF power is not required to excite the subject. Further, since the resonance capacitors 23a and 23b are connected to the two gaps of the cylindrical conductor 22, respectively, it is easy to adjust the resonance frequency to the frequency of the NMR signal.

Third Embodiment FIG. 6 shows an RF for MRI according to a third embodiment of the present invention.
It is a block diagram showing a coil. This MRI RF coil 3
The 00-shaped cylindrical conductor portion 32 includes a conductor portion in which an eight-shaped conductive path 32a is formed, a conductor portion in which an eight-shaped conductive path 32b is formed, and a conductor portion in which the eight-shaped conductive paths 32a and 32b are formed. And a peripheral conductor formed along the cylindrical peripheral surface with a short interval between the conductor and the conductor corresponding to the lower side. Then, the figure-shaped conductive paths 32a, 3
2b, between the conductor corresponding to the upper side of the figure-eight conductive path 32a, between the part corresponding to the lower side of the figure-shaped conductive path 32a and the peripheral conductor part, and to the lower side of the figure-shaped conductive path 32b. A plurality of resonance capacitors 33a, 33b, 33c are connected to three gaps between the portion and the peripheral conductor portion, respectively. According to the MRI RF coil 300 according to the third embodiment, the width of the cylindrical conductor portion 32 can be widened, and the sensitivity range in the center axis direction of the cylindrical shape can be widened. Further, the oscillating magnetic field in the radial and horizontal directions of the cylindrical shape can be applied from outside to inside without attenuating, so that a large RF power is not required to excite the subject. Further, the resonance capacitors 33 are respectively provided in three gaps of the cylindrical conductor portion 32.
a, 33b, and 33b are connected, so that the resonance frequency is set to NM.
Adjustment to match the frequency of the R signal is facilitated.

Fourth Embodiment FIG. 7 shows an MRI RF according to a fourth embodiment of the present invention.
It is a block diagram showing a coil. This MRI RF coil 4
00 is a figure-shaped conductive path 42a, 42b connected in series.
(In this case, the upper half and the lower half of the meandering conductive path are each regarded as a figure-eight shape) and the figure-shaped conductive paths 42c and 42d connected in series are formed and the figure-shaped conductive path 42a is formed. , 42c are provided with a cylindrical conductor portion 42 having a short interval between conductor portions corresponding to the upper sides thereof, and a plurality of resonance capacitors 43 connected between the conductor portions. FIG. 8 is an explanatory diagram showing the direction of the induced electromotive force generated when the oscillating magnetic field By is applied to the MRI RF coil 400. When the oscillating magnetic field By is applied, induced electromotive forces Vat and Vab in opposite directions are generated in the upper half and the lower half of the figure-shaped conductive path 42a, and cancel each other. In addition, induced electromotive forces Vbt and Vbb in opposite directions are generated in the upper half and the lower half of the figure-eight conductive path 42b, and cancel each other. In addition, induced electromotive forces Vct and Vcb in opposite directions are generated in the upper half and the lower half of the figure-shaped conductive path 42c, and cancel each other. Furthermore, induced electromotive forces Vdt and Vdb in opposite directions are generated in the upper half and the lower half of the figure-shaped conductive path 42d,
Cancel each other out. Therefore, no induced current flows and no oscillating magnetic field that cancels the oscillating magnetic field By is generated. According to the RF coil 400 for MRI according to the fourth embodiment, the width of the cylindrical conductor portion 42 can be widened, and the sensitivity range in the central axis direction of the cylindrical shape can be widened. In addition, the oscillating magnetic field By can be applied from outside to inside without attenuating, so that a large RF power is not required to excite the subject. Further, the number of conductive paths running in the z-axis direction of the tubular conductor 42 can be increased.

[0020]

According to the RF coil for MRI of the present invention,
By increasing the width of the cylindrical conductor, the sensitivity range in the central axis direction of the cylindrical shape can be widened. Further, the oscillating magnetic field in the radial and horizontal directions of the cylindrical shape can be applied from outside to inside without attenuating, so that a large RF power is not required to excite the subject. Further, it is possible to prevent a decrease in the uniformity of the excitation magnetic field applied to the subject.

[Brief description of the drawings]

FIG. 1 is an RF for MRI according to a first embodiment of the present invention.
It is a block diagram showing a coil.

FIG. 2 is an explanatory diagram showing a distribution state of an induced current generated when an oscillating magnetic field By is applied to the MRI RF coil of FIG. 1;

FIG. 3 shows an oscillating magnetic field Bz by the MRI RF coil of FIG.
FIG. 4 is an explanatory diagram showing a distribution state of an induced current generated when sensing is detected.

FIG. 4 is an explanatory diagram of a sensitivity distribution in the z-axis direction in the MRI RF coil of FIG. 1;

FIG. 5 is an RF for MRI according to a second embodiment of the present invention.
It is a block diagram showing a coil.

FIG. 6 is an RF for MRI according to a third embodiment of the present invention.
It is a block diagram showing a coil.

FIG. 7 is an RF for MRI according to a fourth embodiment of the present invention.
It is a block diagram showing a coil.

8 is an explanatory diagram showing a distribution state of an induced current generated when an oscillating magnetic field By is applied to the MRI RF coil of FIG. 7;

FIG. 9 is a configuration diagram illustrating an example of a conventional solenoid coil.

FIG. 10 is an explanatory diagram of a sensitivity distribution in the z-axis direction in the solenoid coil of FIG.

FIG. 11 is a configuration diagram showing another example of a conventional solenoid coil.

FIG. 12 is an explanatory diagram of a sensitivity distribution in the z-axis direction in the solenoid coil of FIG.

FIG. 13 is an explanatory diagram of a solenoid coil assuming a case where an opening is opened in a side surface of a cylindrical conductor.

FIG. 14 shows an oscillating magnetic field By applied to the MRI RF coil of FIG.
FIG. 9 is an explanatory diagram showing a distribution state of an induced current generated when a signal is added.

[Explanation of symbols]

100, 200, 300, 400 MRI
RF coil 2, 22, 32, 42 Cylindrical conductor portions 2a, 2b, 22a, 22b, 32a, 32b 8-shaped conductive paths 42a, 42b, 42c, 42d 8-shaped conductive paths 3, 23a, 23b, 33a, 33b, 33c, 43
Resonant capacitor L Coaxial cable S Saddle coil

Claims (2)

[Claims] 1. An MRI RF coil having a cylindrical shape as a whole, characterized in that a figure-eight conductive path crossing an figure eight is formed in a portion corresponding to a side surface of the cylindrical shape. RF coil for MRI. 2. An MRI RF coil having a cylindrical shape as a whole, wherein the RF coils cancel each other when a radial and horizontal oscillating magnetic field is applied to a portion corresponding to a side surface of the cylindrical shape. An RF coil for MRI, wherein a conductive path that generates a reverse induced electromotive force is formed.