MAGNETIC RESONANCE IMAGING APPARATUS AND ANTENNA DEVICE

• US 20140253126A1
• Filed: 10/17/2012
• Published: 09/11/2014
• Est. Priority Date: 11/01/2011
• Status: Active Grant

• Current Assignee: FUJIFILM Healthcare Corp. (Fujifilm Holdings Corporation)
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Habara, Hideta, Soutome, Yoshihisa, Takeuchi, Hiroyuki, Ochi, Hisaaki
• Granted Patent: US 9,684,044 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/34092 RF coils specially adapted for NMR spectrometers
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/3453 Transverse electromagnetic [TEM] coils
• CPC Class Codes: G01R 33/36 Electrical details, e.g. matching or coupling of the coil to the receiver
• CPC Class Codes: G01R 33/365 Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array

Abstract

In order to provide a technique which can suppress coupling to homogenize the spatial distribution of an RF magnetic field and can improve penetration of the RF magnetic field into the subject, pad-like electric field conductors having a predetermined area are provided outside both ends of a rung conductor as a part of a configuration which forms a loop-like circuit and is driven as an antenna. An antenna device includes a sheet-like conductor, a rung conductor which is arranged at a predetermined distance from the sheet-like conductor, two electric field conductors which are arranged in both end portions of the rung conductor at a predetermined distance from the sheet-like conductor, and connection terminals which are transmission and reception terminals provided in the rung conductor and the sheet-like conductor. The rung conductor and the sheet-like conductor configure a loop circuit which resonates at a preset frequency.

Claims

1. A magnetic resonance imaging apparatus comprising:

a magnet which generates a magnetostatic field and forms a magnetostatic field; and

an RF coil which performs at least one of transmission of a high-frequency signal to the magnetostatic field and reception of a nuclear magnetic resonance signal generated from a subject placed inside the magnetostatic field,

wherein the RF coil includes

a sheet-like conductor, and

an antenna unit,

the antenna unit includes

a rung conductor which is arranged at a predetermined distance from the sheet-like conductor, and

two electric field conductors which are arranged in both end portions of the rung conductor at a predetermined distance from the sheet-like conductor, and

the rung conductor and the sheet-like conductor configure a loop circuit which resonates at the frequency of the high-frequency signal transmitted from the RF coil or the nuclear magnetic resonance signal received by the RF coil.

2. The magnetic resonance imaging apparatus according to claim 1,

wherein the electric field conductors generate an electric field for suppressing a shielding current flowing on the surface of the subject by a magnetic field produced by a current flowing in the rung conductor.

3. The magnetic resonance imaging apparatus according to claim 1,

wherein the RF coil is a multichannel antenna including a plurality of antenna units, and

the electric field conductors of each antenna unit cause the electric field conductors of the adjacent antenna unit to generate a voltage for suppressing magnetic field coupling between the rung conductors of the adjacent antenna units.

4. The magnetic resonance imaging apparatus according to claim 1,

wherein the width of each of the electric field conductors in a minor axis direction of the rung conductor is wider than the width of the rung conductor.

5. The magnetic resonance imaging apparatus according to claim 3,

wherein the space between the electric field conductors of the adjacent antenna units is narrower than the space between the rung conductors of the adjacent antenna units.

6. The magnetic resonance imaging apparatus according to claim 1, further comprising:

two frequency adjustment capacitors which connect both end portions of the rung conductor and the sheet-like conductor substantially directly beneath the rung conductor,

wherein the value of each of the frequency adjustment capacitors is adjusted such that the loop circuit resonates at the frequency of the high-frequency signal or the nuclear magnetic resonance signal.

7. The magnetic resonance imaging apparatus according to claim 1,

wherein the rung conductor has a shape in which the length of the rung conductor is adjustable, and

the length of the rung conductor is adjusted such that the loop circuit resonates at the frequency of the high-frequency signal or the nuclear magnetic resonance signal.

8. The magnetic resonance imaging apparatus according to claim 1,

wherein the antenna unit includes a plurality of rung conductors.

9. The magnetic resonance imaging apparatus according to claim 1,

wherein a plurality of antenna units are provided,

each of the antenna units includes a connection terminal which connects the RF coil to the magnetic resonance imaging apparatus,

the connection terminal is connected to the rung conductor and the sheet-like conductor,

the sheet-like conductor has a tubular shape, and

the phase and amplitude of a voltage supplied to each antenna unit through each connection terminal are controlled separately such that the high-frequency signal transmitted from the RF coil is optimized.

10. The magnetic resonance imaging apparatus according to claim 9,

wherein the sheet-like conductor has an elliptic cylindrical shape.

11. The magnetic resonance imaging apparatus according to claim 10,

wherein the antenna unit is arranged on a virtual curve with a decreasing distance from the sheet-like conductor along a major axis radial direction of a section of the elliptic cylinder.

12. The magnetic resonance imaging apparatus according to claim 1,

wherein the rung conductor and the electric field conductors are electrically connected together.

13. The magnetic resonance imaging apparatus according to claim 2,

wherein the electric field conductors have an area which is determined so as to generate the electric field.

14. The magnetic resonance imaging apparatus according to claim 2,

wherein the rung conductor and the electric field conductors are not electrically connected,

a voltage is provided to the electric field conductors separately from the rung conductor, and

the voltage has magnitude to generate the electric field.

15. The magnetic resonance imaging apparatus according to claim 1, further comprising:

gradient magnetic field application means for applying a gradient magnetic field which provides positional information to the nuclear magnetic resonance signal,

wherein each of the electric field conductors includes

a slit, and

a slit connection capacitor which connects both sides of the slit, and

the slit connection capacitor is adjusted such that both sides of the slit are electrically disconnected from each other at the frequency of an AC magnetic field to be used in the gradient magnetic field.

16. The magnetic resonance imaging apparatus according to claim 3, further comprising:

a coupling reduction capacitor which connects the electrical conductors of adjacent channels and suppresses the magnetic field coupling.

17. The magnetic resonance imaging apparatus according to claim 7,

wherein the rung conductor has a spiral shape.

18. The magnetic resonance imaging apparatus according to claim 7,

wherein the rung conductor has a flat plate shape and includes notches which are alternately recessed left and right.

19. A magnetic resonance imaging apparatus comprising:

a magnet which generates a magnetostatic field and forms a magnetostatic field; and

an RF coil which performs either transmission of a high-frequency signal to the magnetostatic field or reception of a nuclear magnetic resonance signal generated from a subject placed inside the magnetostatic field,

wherein the RF coil includes

a sheet-like conductor, and

an antenna unit,

the antenna unit includes

a rung conductor which is arranged at a predetermined distance from the sheet-like conductor,

two electric field conductors which are arranged in both end portions of the rung conductor at a predetermined distance from the sheet-like conductor, and

a diode which connects the rung conductor and one of the electric field conductors, and

the rung conductor and the sheet-like conductor configure a loop circuit which resonates at the frequency of the high-frequency signal transmitted from the RF coil or the nuclear magnetic resonance signal received by the RF coil.

20. An antenna device comprising:

a sheet-like conductor; and

an antenna unit,

wherein the antenna unit includes

a rung conductor which is arranged at a predetermined distance from the sheet-like conductor, and

two electric field conductors which are arranged in both end portions of the rung conductor at a predetermined distance from the sheet-like conductor, and

the rung conductor and the sheet-like conductor configure a loop circuit which resonates at a preset frequency.