JP3422559B2 - RF coil and MRI apparatus for MRI - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface coil used in a magnetic resonance imaging (MRI) apparatus, and in particular, an MRI including a surface coil using a loop coil.
RF coil and MR using the MRI RF coil
I device.

[0002]

2. Description of the Related Art An MRI apparatus measures the density distribution, relaxation time distribution, etc. of nuclear spins at a desired examination site in a subject by utilizing the nuclear magnetic resonance phenomenon, and the cross section of the subject is determined from the measured data. The image is displayed.

Nuclear spins of a subject placed in a uniform and strong static magnetic field generator perform precession around the direction of the static magnetic field at a frequency (Larmor frequency) determined by the strength of the static magnetic field. Therefore, when a high frequency pulse having a frequency equal to this Larmor frequency is irradiated from the outside, spins are excited and transition to a high energy state. This is called a nuclear magnetic resonance phenomenon. When the irradiation of this high-frequency pulse is stopped, the spin returns to the original low energy state with a time constant corresponding to each state, and at this time, the electromagnetic wave is emitted to the outside. A high-frequency receiver coil (R
F coil) to detect. At this time, a triaxial gradient magnetic field is applied to the static magnetic field space for the purpose of adding position information to the space. As a result, position information in the space can be captured as frequency information.

Further, such an MRI apparatus is provided with a surface coil having a high sensitivity particularly in imaging a specific portion of a subject, and this surface coil is used as the RF coil for MRI. There is. As a result, the desired imaged region can be imaged.

FIG. 5 is a configuration diagram showing a conventional configuration of this type of surface coil, and FIG. 6 is an explanatory diagram showing a state in which the surface coil is arranged on a subject. In this FIG.
The surface coil 1 is formed of a one-turn loop coil, and is arranged so as to be in close contact with the subject by taking advantage of its thinness and small size.

Further, as shown in FIG. 5, a current flows along the loop coil of the surface coil 1 as shown. Thereby, the magnetic field in the direction perpendicular to the coil surface is detected.

[0007]

However, since the signal generated by the precession motion of the nuclear spins is a rotating magnetic field, when only the vertical magnetic field component is received by the surface coil 1 as shown in FIG. 5, the horizontal magnetic field included in the NMR signal is received. There is a problem that reception efficiency deteriorates because no component is used.

In order to be able to receive an NMR signal using a one-turn coil, it is necessary to arrange two sets of coils so that they are orthogonal to each other, and the advantage of the surface coil is lost.

The present invention has been made in view of the above points, and an object thereof is an MR using a surface coil capable of receiving quadrature, which is thin and small by using a one-turn coil.
It is to realize the RF coil for I and the MRI apparatus.

[0010]

A first means for solving the above-mentioned problems is a loop coil having a loading coil, which is formed so as to be tuned to the frequency of the NMR signal and is parallel to the coil surface of the loop coil. A loop coil formed by a first loop coil having a sensitivity in various directions and a one-turn coil arranged in parallel with the first loop coil, and having a sensitivity in a direction perpendicular to a coil surface of the loop coil. And a second loop coil having the RF coil for MRI.

A second means for solving the above-mentioned problems is a loop coil having a loading coil, which is an NMR
A first loop coil formed to be tuned to the frequency of the signal and having a sensitivity in a direction parallel to the coil surface of the loop coil; and a first loop coil arranged in parallel with the first loop coil.
A loop coil formed of a turn coil, the second loop coil having a sensitivity in a direction perpendicular to a coil surface of the loop coil, a reception signal of the first loop coil, and a reception of the second loop coil. Phase adjustment means for adjusting both or one of the phases of the signals to match the phases of the two signals, and addition means for adding the received signals whose phases have been adjusted are provided, and the first loop coil and the first loop coil are provided. Two
The MRI apparatus is arranged so that the receiving sensitivity direction formed by the loop coil and the rotating coil is parallel to the rotation direction of the nuclear spins.

A third means for solving the above problems is a loop coil having a loading coil, which is an NMR
A first loop coil formed to be tuned to the frequency of the signal and having a sensitivity in a direction parallel to the coil surface of the loop coil; and a first loop coil arranged in parallel with the first loop coil.
A loop coil formed of a turn coil, the second loop coil having a sensitivity in a direction perpendicular to a coil surface of the loop coil, a reception signal of the first loop coil, and a reception of the second loop coil. A level adjusting means for adjusting both or one of the signal levels so that the signal-to-noise ratio after addition is maximized with reference to the signal level and the noise level of the signal, and reception of the first loop coil. Phase adjusting means for adjusting the phase of both or one of the signal and the received signal of the second loop coil to match the phases of both signals, and adding means for adding the received signals of which level and phase have been adjusted And arranged so that the receiving sensitivity direction formed by the first loop coil and the second loop coil is parallel to the rotation direction of the nuclear spins. A MRI apparatus, characterized in that the.

[0013]

The RF for MRI which is the first means for solving the problems
In the coil, a first loop coil having a loading coil formed so as to be tuned to the frequency of the NMR signal has sensitivity in a direction horizontal to the loop coil surface, and
Since the second loop coil formed by the turn coil has sensitivity in the direction perpendicular to the coil surface, it has magnetic field sensitivity in the rotation direction. Since both loop coils are arranged so that the sensitivity direction is parallel to the rotation direction of the nuclear spins, the reception sensitivity direction is parallel to the rotation direction of the nuclear spins, and it is possible to effectively detect the NMR signal. Become. Further, the S / N ratio is improved by making the received signals of the loop coils in-phase and adding them.

In the MRI apparatus which is the second means for solving the problems, the first loop coil having the loading coil formed so as to be tuned to the frequency of the NMR signal and the second loop coil formed of one turn coil are provided. Since the reception signals of both coils arranged in such a position that the reception sensitivity direction formed by the loop coil and the rotation direction of the nuclear spin are parallel to each other, the phases are adjusted and in-phase addition is performed. Be improved.

In the MRI apparatus which is the third means for solving the problem, the first loop coil having the loading coil formed so as to be tuned to the frequency of the NMR signal and the second loop coil formed of one turn coil are provided. For the reception signals of both coils arranged in such a position that the reception sensitivity direction formed by the loop coil and the direction parallel to the rotation direction of the nuclear spin, the phase and the signal level are adjusted and in-phase addition is performed. The improvement in the SN ratio is the largest.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an overall configuration of an MRI RF coil (hereinafter, simply referred to as a coil) and an MRI apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing in detail the shape of the coil, and FIG. It is explanatory drawing which shows the relationship between a coil and a rotating magnetic field.

In these figures, the first loop coil 11 has output terminals provided at both ends of a capacitor 11a, and also has loading coils 11b and 11c for shortening loading as shown in FIG. ing.
The first loop coil 11 is configured to be tuned to the frequency of the NMR signal by the loading coils 11b and 11c. The second loop coil 12 is a conventional one-turn coil, has output terminals provided from both ends of the capacitor 12a, and has sensitivity in a direction perpendicular to the coil surface. And the first loop coil 1
The first and second loop coils 12 are arranged in parallel at a predetermined interval. The amplifier 13 and the amplifier 14 are amplifiers for amplifying the received signals of the first loop coil 11 and the second loop coil 12, respectively, and have variable gains. The delay unit 15 delays the reception signal of the second loop coil 12 by 90 °. The adding unit 16 is the delay unit 1
5 and the output of the amplifier 14 are added and output, and the added output is processed by the signal processing unit 17.

The operation of the coil thus constructed and the MRI apparatus using this coil is as follows. First,
Reception of the NMR signal of each loop coil 11 and 12 will be described.

The reception of the NMR signal of the first loop coil 11 is performed in the y direction as shown by the arrow in the center of the coil in FIG. That is, the loading coil 11b,
By having 11c, the first loop coil has NMR
Because it resonates with the signal, the direction of the current (current distribution) is the same near the output terminal and at the position facing the output terminal, and this current has sensitivity in the y direction parallel to the coil surface. There is.

The reception of the NMR signal from the second loop coil 12 is performed in the x direction perpendicular to the coil surface, as shown in FIG. Then, the signal of the x-direction component in the NMR signal generated on the plane parallel to the xy plane perpendicular to the main magnetic field in the z-direction is received by the second loop coil 12, and a high-frequency current flows as a reception signal. Similarly, the signal of the y-direction component in the NMR signal is received by the first loop coil 11, and a high frequency current flows as a received signal.

The reception signal of the x-direction component thus obtained is amplified by the amplifier 13, and the reception signal of the y-direction component is amplified by the amplifier 14. Then, the delay unit 15 makes 90 °.
Is corrected and the received signals are made into signals of the same phase and added by the adder 16. The added reception signal is subjected to predetermined processing in the signal processing unit.

As described above, the mutually orthogonal NMR signals are received, the phases are corrected and added, so that the received signals are doubled because they have the same phase, and the noise component is √2 times because there is no correlation. become. As a result, the SN ratio is √2 times (+3 dB)
To be improved.

A combination of a 1-turn coil capable of receiving a magnetic field in a direction perpendicular to the coil surface and a 1-turn coil having a loading coil capable of receiving a horizontal magnetic field and arranged in parallel at a predetermined interval. As a result, a coil for quadrature reception can be realized with a size equivalent to that of a conventional one-turn coil. Therefore, in the surface coil, it becomes possible to realize quadrature reception, which was impossible in terms of size in the past.

As the loading coils 11b and 11c of the first loop coil 11 described above, general cylindrical solenoid coils can be used. In addition, when a solenoid coil is used, magnetic field leakage may occur at the end of the coil, which may affect MRI reception. In such a case, instead of the solenoid coil, as shown in FIG.
It is also possible to use the annular coil shown in (a).
The loading coil 11 having such an annular coil
d and 11e, as shown in FIG. 4B, the first loop coil 1
By configuring No. 1, the magnetic field of the loading coil can be confined inside and the influence on the outside can be reduced.

Further, in the above description, the received signal in the x direction is delayed by 90 °, but a configuration in which the received signal in the y direction is delayed or advanced is also possible. That is, 90 ° relative to the x and y directions.
It suffices that a phase difference of 1 occurs.

In the above description of the SN ratio, assuming that the SN ratio of both coils and the received signal strength are equal, S after the addition is performed.
The N ratio is √2 times. When the reception level or the noise component of each loop coil is different, the gain (or signal level) of either or both of the amplifiers 13 and 14 is controlled so that the SN ratio in the signal processing unit 17 becomes the maximum value. It may be adjusted from the department. By such adjustment, the best signal-to-noise ratio can be obtained.

As described above, the loop coil having the loading coil is formed so as to be tuned to the frequency of the NMR signal, and has the sensitivity in the direction parallel to the coil surface of the loop coil. A loop coil formed of a one-turn coil arranged in parallel with the first loop coil, the loop coil having a sensitivity in a direction perpendicular to a coil surface of the loop coil; According to the MRI RF coil of the embodiment,
Since the first loop coil has sensitivity in the direction horizontal to the coil surface and the second loop coil has sensitivity in the direction perpendicular to the coil surface, it has magnetic field sensitivity in the rotating direction. Since both loop coils are arranged so that the sensitivity direction is parallel to the rotation direction of the nuclear spins, the reception sensitivity direction is parallel to the rotation direction of the nuclear spins.
It becomes possible to effectively detect the MR signal. And
It is possible to realize an MRI RF coil using a surface coil that is thin and small and can receive quadrature by using a one-turn coil.

A loop coil having a loading coil, which is formed so as to be tuned to the frequency of the NMR signal and has a sensitivity in a direction parallel to the coil surface of the loop coil, and the first loop coil. A loop coil formed by a one-turn coil arranged in parallel with the loop coil, and a second loop coil having sensitivity in a direction perpendicular to a coil surface of the loop coil, and reception of the first loop coil. A phase adjusting means for adjusting the phases of both or one of the signal and the received signal of the second loop coil to match the phases of both signals; and an adding means for adding the received signals whose phases have been adjusted. , So that the receiving sensitivity direction formed by the first loop coil and the second loop coil is parallel to the rotation direction of the nuclear spins. According to the MRI apparatus of the second embodiment, since the phases of the received signals of both coils are adjusted and added in phase, the MRI apparatus has sensitivity to the rotating magnetic field and improves the SN ratio. . Further, it is possible to realize a thin and compact MRI apparatus using a surface coil capable of receiving quadrature by using a one-turn coil.

A loop coil having a loading coil, which is formed so as to be tuned to the frequency of the NMR signal, has a sensitivity in a direction parallel to the coil surface of the loop coil, and the first loop coil. A loop coil formed by a one-turn coil arranged in parallel with the loop coil, and a second loop coil having sensitivity in a direction perpendicular to a coil surface of the loop coil, and reception of the first loop coil. A level adjusting means for adjusting both or one of the signal levels so that the signal-to-noise ratio after addition is maximized with reference to the signal and the signal level and the noise level of the received signal of the second loop coil. And both signals by adjusting the phase of both or one of the reception signal of the first loop coil and the reception signal of the second loop coil. A phase adjusting means for making the phases of the two loop coils coincide with each other and an adding means for adding the received signals whose levels and phases have been adjusted, and the receiving sensitivity direction formed by the first loop coil and the second loop coil is Third position arranged parallel to the rotation direction of the nuclear spin
According to the MRI apparatus of the above embodiment, the receiving sensitivity is provided in the rotating magnetic field direction, and the phase and signal levels are adjusted and in-phase addition is performed, so that the SN ratio is most improved. Therefore, it is possible to realize a thin and compact MRI apparatus using a surface coil capable of receiving quadrature by using a one-turn coil.

[0030]

As described in detail above, according to the present invention,
A loop coil having a loading coil, wherein N
A first loop coil formed so as to be tuned to the frequency of the MR signal and having a sensitivity in a direction parallel to the coil surface of the loop coil, and a one-turn coil arranged in parallel with the first loop coil. Loop coil,
A second loop coil having a sensitivity in a direction perpendicular to a coil surface of the loop coil, and a reception sensitivity direction formed by the first loop coil and the second loop coil is a rotation direction of a nuclear spin. By arranging them in parallel, it is possible to realize an MRI RF coil that uses a one-turn coil and is thin and small and that uses a surface coil capable of quadrature reception.

Further, by adding in-phase the received signals of the respective loop coils, a one-turn coil is used, and a thin and compact surface coil capable of quadrature reception is used.
RI equipment can be realized.

[Brief description of drawings]

FIG. 1 is an RF coil for MRI and M according to an embodiment of the present invention.
It is a block diagram which shows the structural example of RI apparatus.

FIG. 2 is a configuration diagram showing details of a configuration example of an MRI RF coil according to an embodiment of the present invention.

FIG. 3 is a configuration diagram showing details of a configuration example of an MRI RF coil according to an embodiment of the present invention.

FIG. 4 is a configuration diagram showing details of a configuration example of an MRI RF coil according to an embodiment of the present invention.

FIG. 5 is a configuration diagram showing details of a configuration example of a conventional surface coil.

FIG. 6 is an explanatory diagram showing a state of a conventional surface coil.

[Explanation of symbols]

11 First loop coil 11b, 11c loading coil 12 Second loop coil 13 amp 14 amplifier 15 Delay section 16 adder 17 Signal processing unit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) A61B 5/055

Claims (3)

(57) [Claims] 1. A first loop coil having a loading coil, the first loop coil being formed so as to be tuned to a frequency of an NMR signal, and having a sensitivity in a direction parallel to a coil surface of the loop coil. An MRI comprising a one-turn coil arranged in parallel with the first loop coil, and a second loop coil having sensitivity in a direction perpendicular to the coil surface of the loop coil. RF coil. 2. A loop coil having a loading coil, the first loop coil being formed so as to be tuned to a frequency of an NMR signal, and having a sensitivity in a direction parallel to a coil surface of the loop coil, and the first loop coil. A loop coil formed by a one-turn coil arranged in parallel with the loop coil, and a second loop coil having sensitivity in a direction perpendicular to a coil surface of the loop coil, and reception of the first loop coil A phase adjustment unit that adjusts the phases of both or one of the signal and the reception signal of the second loop coil to match the phases of the two signals; and an addition unit that adds the reception signals whose phases have been adjusted. Is arranged such that the receiving sensitivity direction formed by the first loop coil and the second loop coil is parallel to the rotation direction of the nuclear spins. MR, characterized in that
I device. 3. A loop coil having a loading coil, the first loop coil being formed so as to be tuned to the frequency of an NMR signal, and having a sensitivity in a direction parallel to a coil surface of the loop coil. A loop coil formed by a one-turn coil arranged in parallel with the loop coil, and a second loop coil having sensitivity in a direction perpendicular to a coil surface of the loop coil, and reception of the first loop coil A level adjusting means for adjusting both or one of the signal levels so that the signal-to-noise ratio after addition is maximized with reference to the signal and the signal level and the noise level of the received signal of the second loop coil. And adjusting the phase of both or one of the reception signal of the first loop coil and the reception signal of the second loop coil to adjust the position of both signals. A phase adjusting means for making the phases coincide with each other, and an adding means for adding the received signals whose levels and phases are adjusted, and the receiving sensitivity direction formed by the first loop coil and the second loop coil is a nucleus. MR characterized by being arranged so as to be parallel to the rotation direction of the spin
I device.