JP3516481B2 - RF coil of MRI system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention is applied to MRI (Magnetic).
The present invention relates to a transmission / reception method and an RF (Radio Frequency) coil in a Resonance Imaging) device. More specifically, unnecessary magnetic coupling with the subject and SNR (Signal N
The present invention relates to a transmission / reception method and an RF coil in an MRI apparatus capable of preventing a decrease in oise ratio).

[0002]

2. Description of the Related Art FIG. 9 shows a surface coil type R of an MRI apparatus.
It is a typical perspective view which shows the prior art example of an F coil. This RF
The coil 500 has a configuration including elements E1, E2, E3, E4 and capacitors C1, C2, C3, C4. The elements E1, E2, E3, E4 form a rectangular loop, and a coaxial cable W is connected to the element E4. The capacitors C1, C2, C
3, C4 are provided in the elements E1, E2, E3, E4 to form a resonance circuit. As shown in (a) of FIG. 10, during transmission of an RF (Radio Frequency) magnetic field, a transmission current I flows through the elements E1, E2, E3, E4, and RF magnetic fields H1, H2, H3, H4 are generated. Of these RF magnetic field components, the RF magnetic field components H1 and H3 orthogonal to the main magnetic field B excite the subject. In addition, as shown in FIG.
At the time of receiving the (Magnetic Resonance) signal, M from the subject generated around the elements E1, E2, E3 and E4
A reception current i flows through the elements E1, E2, E3, E4 by the R signal components h1, h2, h3, h4. Among the MR signal components, the MR signal components h1 and h3 orthogonal to the main magnetic field B provide the proton density information of the subject.

FIG. 11 is a schematic perspective view showing a conventional example of a birdcage coil type RF coil of an MRI apparatus.
The RF coil 501H of FIG. 11 (a) is of a high pass type, and has a number of elements E, E, ... Stretched between the ring conductors R1 and R2, and the capacitors C and C are attached to the ring conductors R1 and R2. ,, ... are interposed. The RF coil 501L of FIG. 11 (b) is of a low-pass type and has a large number of elements E, E, ...
1 and R2 are stretched, and capacitors C, C, ... Are interposed between the elements E, E ,. FIG. 12 (a)
As shown in, the element E,
A transmission current I flows through E, ... And ring conductors R1 and R2, and RF magnetic fields EH and RH are generated. These RF
Of the magnetic field components, the RF magnetic field component EH orthogonal to the main magnetic field B
The subject is excited by. In addition, FIG.
As shown in FIG. 5, when the MR signal from the subject is received, the MR signal component E generated around the elements E, E, ... And the ring conductors R1 and R2 by the MR signal from the subject.
A reception current i flows through the elements E, E, ... And the ring conductors R1, R2 by h, Rh. Among the MR signal components, the MR signal component Eh orthogonal to the main magnetic field B provides the proton density information of the subject.

FIG. 13 is a schematic perspective view showing a conventional example of a saddle coil type RF coil of an MRI apparatus. This R
The F coil 502 has the elements E1 and E2 and the arch conductors A1 and A2 arranged in a saddle shape, and the element E3.
This is a configuration in which E4 and arch conductors A3 and A4 are arranged in a saddle shape. W is a coaxial cable. As shown in (a) of FIG. 14, during transmission of the RF magnetic field, the transmission current I is applied to the elements E1 to E4 and the arch conductors A1 to A4.
Flow and RF magnetic fields EH and RH are generated. Of these RF magnetic field components, the RF magnetic field component EH orthogonal to the main magnetic field B excites the subject. Further, as shown in FIG. 12B, when the MR signal from the subject is received, the elements E, E,
, And the MR signal components Eh, Rh generated around the ring conductors R1, R2 cause a reception current i to flow through the elements E, E, ... And the ring conductors R1, R2. MR
Of the signal components, the MR signal component Eh orthogonal to the main magnetic field B
By this, information on the proton density of the subject is obtained.

[0005]

In the above-mentioned conventional RF coils 500, 501H, 501L, 502, in addition to the RF magnetic field components H1, H3, EH orthogonal to the main magnetic field B, the RF magnetic field component parallel to the main magnetic field B is used. There are H2, H4, RH, AH. Also, MR signal components h2 and h orthogonal to the main magnetic field B
In addition to 4, Rh and Ah, MR signal components h2, h4, Rh and Ah parallel to the main magnetic field B are present. However, the main magnetic field B
The RF magnetic field component parallel to is MR (Magnetic Resonance)
In principle, it is not effective for exciting the object, but rather, unnecessary magnetic coupling with the object is increased, so that the excitation power is unnecessarily increased and an extra burden is imposed on the amplifier and the like.
Further, picking up an MR signal from outside the region of interest has a problem of reducing the SNR within the region of interest. Therefore, an object of the present invention is to provide a transmission / reception method and an RF coil in an MRI apparatus capable of preventing unnecessary magnetic coupling with a subject and a decrease in SNR.

[0006]

A transmission / reception method in an MRI apparatus according to the present invention uses at least an RF coil to transmit an RF magnetic field to a subject in a main magnetic field or to receive an MR signal from the subject. In the transmitting / receiving method of the MRI apparatus for performing one, a shield conductor is provided on the RF coil,
The structure is characterized in that an RF magnetic field component parallel to the main magnetic field or an MR signal component parallel to the main magnetic field is shielded.

The RF coil of the MRI apparatus of the present invention performs at least one of transmitting an RF magnetic field to the subject in the main magnetic field and receiving an MR signal from the subject.
In the RF coil of the RI apparatus, R parallel to the main magnetic field
This is characterized in that a shield conductor for shielding the F magnetic field component or the MR signal component outside the region of interest is provided.

[0008]

In the transmitting / receiving method and the RF coil in the MRI apparatus of the present invention, by providing the shield conductor,
The RF magnetic field component parallel to the main magnetic field or the MR signal component outside the region of interest is blocked. Therefore, R parallel to the main magnetic field
It becomes possible to prevent unnecessary magnetic coupling with the subject due to the F magnetic field component. Further, it becomes possible to suppress the pickup of MR signals from outside the region of interest and improve the SNR.

[0009]

The present invention will be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

First Embodiment FIG. 1 is a schematic perspective view showing a surface coil type RF coil according to a first embodiment of the present invention. This RF coil 100
Are elements E1, E2, E3, E4 and capacitor C
1, C2, C3, C4 and shield conductors Q1, Q2. The elements E1, E2, E3, E4
Form a rectangular loop, and the coaxial cable W is connected to the element E4. The capacitor C
1, C2, C3, C4 are the elements E1, E2,
It is interposed between E3 and E4 and forms a resonance circuit. The shield conductors Q1 and Q2 are provided outside the loop along the elements E2 and E4.

As shown in FIG. 2A, at the time of transmitting the RF magnetic field, the transmission current I flows through the elements E1, E2, E3, E4, and the RF magnetic fields H1, H2, H3, H4 are generated. Of these RF magnetic field components, the RF magnetic field components H1 and H3 orthogonal to the main magnetic field B excite the subject. On the other hand, RF magnetic field components H2 and H4 parallel to the main magnetic field B
Are shielded by the shield conductors Q1 and Q2. Therefore, unnecessary magnetic coupling with the subject is eliminated. Further, as shown in FIG. 2B, at the time of receiving the MR signal from the subject, the MR signal components h1 and h3 from the subject generated around the elements E1 and E2 cause the elements E1, E2, E3, and The reception current i flows through E4. By the MR signal components h1 and h3 orthogonal to the main magnetic field B,
Proton density information of the region of interest of the subject is obtained. On the other hand, since it is shielded by the shield conductors Q1 and Q2, MR signal components h2 and h4 do not occur around the elements E2 and E4. Therefore, picking up from outside the region of interest is prevented, and the SNR in the region of interest is improved.

As shown in FIG. 3, shield conductors Q1 'and Q2' made of a plurality of plates may be provided. Further, as shown in FIG. 4, tubular shield conductors Q1 ″ and Q2 ″ may be provided.

Second Embodiment FIG. 5 is a schematic perspective view showing a birdcage coil type RF coil according to a second embodiment of the present invention. FIG. 5 (a)
The RF coil 101H is a high-pass type, and has a large number of elements E, E, ...
2, the capacitors C, C, ... Are interposed between the ring conductors R1 and R2, and the ring-shaped shield conductors Q1 and Q2 are provided along the ring conductors R1 and R2. The RF coil 101L of FIG. 5 (b) is of a low pass type, and a large number of elements E, E, ... Are stretched between the ring conductors R1, R2, and the elements E, E ,.
, And the capacitors C, C, ...
This is a configuration in which ring-shaped shield conductors Q1 and Q2 are provided along 1 and R2.

As shown in FIG. 6A, during transmission of the RF magnetic field, the elements E, E, ... And the ring conductor R are used.
1, a transmission current I flows through R2, and RF magnetic fields EH and RH
Occurs. Of these RF magnetic field components, the RF magnetic field component EH orthogonal to the main magnetic field B excites the subject. On the other hand, the RF magnetic field component RH parallel to the main magnetic field B is shielded by the shield conductors Q1 and Q2. For this reason,
The unnecessary magnetic coupling with the subject is eliminated. Further, as shown in FIG. 6B, when the MR signal from the subject is received, the elements E, E,
.. and ring conductors R1, R2 due to the MR signal component Eh generated around.
Flows. The MR signal component Eh orthogonal to the main magnetic field B provides the proton density information of the subject. On the other hand, the ring conductor R is shielded by the shield conductors Q1 and Q2.
The MR signal component Rh does not occur around 1 and R2. Therefore, picking up from outside the region of interest is prevented, and the SNR in the region of interest is improved.

Third Embodiment FIG. 7 shows a saddle coil type RF according to a second embodiment of the present invention.
It is a typical perspective view showing a coil. This RF coil 10
2, the elements E1 and E2 and the arch conductors A1 and A2 are arranged in a saddle shape, and the elements E3 and E4 and the arch conductors A3 and A4 are arranged in a saddle shape.
1, a ring-shaped shield conductor Q1 is provided along A3, and a ring-shaped shield conductor Q2 is provided along the arch conductors A2 and A4. W is a coaxial cable. As shown in FIG. 8A, during transmission of the RF magnetic field, the elements E1 to E4 and the arch conductors A1 to A4 are used.
A transmission current I flows in the RF magnetic field, and RF magnetic fields EH and AH are generated. Of these RF magnetic field components, the RF magnetic field component EH orthogonal to the main magnetic field B excites the subject. On the other hand, the RF magnetic field component AH parallel to the main magnetic field B is shielded by the shield conductors Q1 and Q2. Therefore, unnecessary magnetic coupling with the subject is eliminated. Also, FIG. 8B
As shown in FIG. 5, when the MR signal from the subject is received, the MR signal component Eh generated around the elements E1 to E4 by the MR signal from the subject causes the element E,
The reception current i flows through E, ... And the arch conductors A1 to A4. The MR signal component Eh orthogonal to the main magnetic field B provides the proton density information of the subject. On the other hand, since the shield conductors Q1 and Q2 shield the arch conductors A to A4.
The MR signal component Ah does not occur around. Therefore, picking up from outside the region of interest is prevented, and the SN in the region of interest is
R is improved.

-Other Embodiments-In place of the elements E2 and E4 and the shield conductors Q1 and Q2 in the first embodiment, a coaxial cable can be used. In addition, the ring conductors R1 and R in the second embodiment
Instead of 2 and the shield conductors Q1 and Q2, a coaxial cable may be used. Moreover, a coaxial cable may be used instead of the arch conductors A1 to A4 and the shield conductors Q1 and Q2 in the third embodiment.

[0017]

According to the transmitting / receiving method and the RF coil in the MRI apparatus of the present invention, it becomes possible to prevent unnecessary magnetic coupling with the object due to the RF magnetic field component parallel to the main magnetic field. Therefore, the pump power is not wasted, and an unnecessary load is not imposed on the amplifier or the like. In addition, the subject is not burdened. Furthermore, it becomes possible to suppress the pickup of MR signal components outside the region of interest. Therefore, the SNR in the region of interest can be improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an RF coil according to a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the RF coil according to the first embodiment of the present invention.

FIG. 3 is a schematic perspective view of a modified embodiment of the RF coil according to the first embodiment of the present invention.

FIG. 4 is a schematic perspective view showing another modification of the RF coil according to the first embodiment of the present invention.

FIG. 5 is a schematic perspective view showing an RF coil according to a second embodiment of the present invention.

FIG. 6 is an operation explanatory view of the RF coil according to the second embodiment of the present invention.

FIG. 7 is a schematic perspective view showing an RF coil according to a third embodiment of the present invention.

FIG. 8 is an operation explanatory view of the RF coil according to the third embodiment of the present invention.

FIG. 9 is a schematic perspective view showing an example of a conventional RF coil.

FIG. 10 is an operation explanatory diagram of the RF coil in FIG.

FIG. 11 is a schematic perspective view showing another example of a conventional RF coil.

12 is an explanatory diagram of the operation of the RF coil shown in FIG.

FIG. 13 is a schematic perspective view showing still another example of a conventional RF coil.

14 is an explanatory diagram of the operation of the RF coil in FIG.

[Explanation of symbols]

100, 101H, 101L, 102 RF coil E1, E2, E3, E4, E Element R1, R2 Ring conductor A1, A2, A3, A4 Arch conductor Q1, Q2, Q1'Q2 ', Q1 ", Q2" Shielding conductor B Main magnetic field H1, H2, H3, H4, EH, RH, AH RF magnetic field component h1, h2, h3, h4, Eh, Rh, Ah MR signal component

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-43706 (JP, A) JP-A-2-19138 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 5/055

Claims (2)

(57) [Claims] 1. An RF coil of an MRI apparatus that performs at least one of transmitting an RF magnetic field to a subject in a main magnetic field and receiving an MR signal from the subject, wherein the RF coil comprises four elements. In the surface type coil forming a square loop, the RF coil is arranged such that a surface formed by the loop is parallel to the direction of the main magnetic field, and an RF magnetic field component parallel to the main magnetic field. Or M outside the region of interest
In order to block the R signal component, a shield conductor is provided outside the loop along a plane including the loop along the two elements located at opposite positions in the square loop, and the RF of the MRI apparatus. coil. 2. An RF coil of an MRI apparatus that performs at least one of transmitting an RF magnetic field to a subject in a main magnetic field and receiving an MR signal from the subject, wherein the RF coil comprises four elements. In the surface type coil forming a square loop, the RF coil is arranged such that a surface formed by the loop is parallel to the direction of the main magnetic field, and an RF magnetic field component parallel to the main magnetic field. Or M outside the region of interest
In order to shield the R signal component, a tubular shield conductor is provided toward the outside of the loop so as to cover the two elements located at opposite positions in the square loop, and the RF coil of the MRI apparatus. .