BALUN AND MAGNETIC RESONANCE IMAGING APPARATUS

• US 20110267062A1
• Filed: 01/28/2010
• Published: 11/03/2011
• Est. Priority Date: 02/04/2009
• Status: Active Grant

• Current Assignee: FUJIFILM Healthcare Corp. (Fujifilm Holdings Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Hirata, Koji, Otake, Yosuke, Bito, Yoshitaka, Ochi, Hisaaki, Soutome, Yoshihisa, Kaneko, Yukio
• Granted Patent: US 8,803,526 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/3685 Means for reducing sheath currents, e.g. RF traps, baluns

Abstract

The present invention provides a technique for maintaining a function for effectively blocking common mode noise with a simple configuration, even in the case where unbalance occurs in characteristic impedance of a coaxial cable in an MRI apparatus, and improving the performance of an RF coil. In a circuit where a balun is established by parallel connection with the coaxial cable, multiple serial resonance circuits having different resonance frequencies are connected in parallel. A value of each constitutional element of each of the serial resonance circuits is adjusted in such a manner that the frequency for blocking the common mode noise of the entire balun falls into a range between the resonance frequencies of these serial resonance circuits.

Claims

1. A balun for blocking common mode noise flowing in a coaxial cable, comprising,

a part of the coaxial cable, and

a parallel circuit connected in parallel with a shield of the part of the coaxial cable, wherein,

the parallel circuit comprises multiple serial resonance circuits each connected in parallel,

each of the multiple serial resonance circuits comprises a capacitor and an inductor being connected in series, and resonance frequencies of the respective serial resonance circuits are adjustable by capacitance of the capacitor and by inductance of the inductor, and

at least one of the resonance frequencies of the multiple serial resonance circuits is adjusted to be lower than a frequency at which the balun s the common mode noise, and at least one of the resonance frequencies is adjusted to be higher than the frequency at which the balun s the common mode noise.

2. The balun according to claim 1, wherein,

the multiple serial resonance circuits are two circuits;

a first serial resonance circuit and a second serial resonance circuit, and

any one of a first resonance frequency being the resonance frequency of the first serial resonance circuit and a second resonance frequency being the resonance frequency of the second serial resonance circuit is adjusted to be lower than the frequency at which the balun s the common mode noise, and the other frequency is adjusted to be higher than the frequency at which the balun s the common mode noise.

3. The balun according to claim 2, wherein,

a resonance frequency that is adjusted to be lower than the frequency at which the balun s the common mode noise, either of the first resonance frequency and the second resonance frequency, is adjusted to be a range from 70% to 95% of the frequency at which the balun s the common mode noise.

4. The balun according to claim 2, wherein,

a resonance frequency that is adjusted to be higher than the frequency at which the balun s the common mode noise, either of the first resonance frequency and the second resonance frequency, is adjusted to be a range from 105% to 130% of the frequency at which the balun s the common mode noise.

5. The balun according to claim 1, wherein,

the multiple serial resonance circuits are three circuits;

a first serial resonance circuit, a second serial resonance circuit, and a third serial resonance circuit, and

a resonance frequency f_A of the first serial resonance circuit, a resonance frequency f_B of the second serial resonance circuit, a resonance frequency f_C of the third serial resonance circuit, a first resonance frequency f₁ at which the balun s the common mode noise, and a second resonance frequency f₂ (>

f₁) at which the balun s the common mode noise are adjusted so that those frequencies satisfy a relationship of f_A<

f₁<

f_B<

f₂<

f_C.

6. The balun according to claim 1, wherein,

the part of the coaxial cable has a loop shape.

7. The balun according to claim 1, wherein,

the part of the coaxial cable has a linear shape.

8. The balun according to claim 1, wherein,

the part of the coaxial cable has a figure-eight shape.

9. The balun according to claim 1, wherein,

the parallel circuit comprises a magnetic coupling means, and the parallel circuit is magnetically connected with the shield of the part of the coaxial cable.

10. The balun according to claim 1, wherein,

a radio shielding is applied on the part of the coaxial cable and the parallel circuit.

12. A magnetic resonance imaging apparatus, comprising,

a static magnetic field forming means for forming a static magnetic field,

a gradient magnetic field forming means for forming a gradient magnetic field,

an RF magnetic field forming means for forming an RF magnetic field,

a transmit-receive coil for applying the RF magnetic field to a test subject and receiving a magnetic resonance signal from the test subject,

a signal processing means for processing the magnetic resonance signal received from the transmit-receive coil,

a transmit-receive switching means for connecting the RF magnetic forming means with the transmit-receive coil when the RF magnetic field is applied to the test subject and for connecting the transmit-receive coil with the signal processing means when the magnetic resonance signal received by the transmit-receive coil is processed, and

a control means for controlling the gradient magnetic field forming means, the RF magnetic field forming means, and the signal processing means, wherein,

the transmit-receive coil is connected with the transmit-receive switching means via a coaxial cable,

the coaxial cable comprises a balun, and

the balun is defined in claim 1 and connected to the coaxial cable.

13. A magnetic resonance imaging apparatus, comprising,

a static magnetic field forming means for forming a static magnetic field,

a gradient magnetic field forming means for forming a gradient magnetic field,

an RF magnetic field forming means for forming an RF magnetic field,

a transmit coil for applying the RF magnetic field to a test subject,

a receive coil for receiving a magnetic resonance signal from the test subject,

a signal processing means for processing the magnetic resonance signal received from the receive coil, and

a control means for controlling the gradient magnetic field forming means, the RF magnetic field forming means, and the signal processing means, wherein,

the magnetic resonance imaging apparatus further comprising,

a first coaxial cable for transmitting the RF magnetic field formed by the RF magnetic field forming means to the transmit coil, and

a second coaxial cable for transmitting the magnetic resonance signal received by the receive coil to the signal processing means, wherein,

each of the first coaxial cable and the second coaxial cable comprises a balun, and

the balun is defined in claim 1 and connected to each of the first coaxial cable and the second coaxial cable.

14. The magnetic resonance imaging apparatus, according to claim 12, wherein,

the coaxial cable comprises the balun more than one.

15. The magnetic resonance imaging apparatus, according to claim 13, wherein,

at least one of the first coaxial cable and the second coaxial cable comprises the balun more than one.

11. (canceled)