RF COIL AND MAGNETIC RESONANCE IMAGING APPARATUS

Abstract

For the purpose of making available an RF coil which makes possible a reduction in elements to be controlled in varying the size of the RF coil, there are provided an original loop unit, a conductor so connected to the original loop unit as to split the original loop unit into split loop units, a capacitor connected in series to the conductor, and switching means which makes the conductor either conductive or non-conductive, wherein the electrostatic capacitance of the capacitor is so set as not to allow the split loop units to interfere with each other when the conductor is made conductive by the switching means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus 1 in the first mode for implementing the present invention.

FIGS. 2 a and 2b are partially abridged circuit diagrams showing the configuration of the transmission coil of the magnetic resonance imaging apparatus of FIG. 1.

FIG. 3 is a partially abridged circuit diagram showing the configuration of the RF coil in a second mode for implementing the invention.

FIG. 4 is a time chart showing the methods of transmission and reception by the RF coil of FIG. 3.

FIGS. 5 a and 5b are partially abridged circuit diagrams showing the configuration of the RF coil in a third mode for implementing the invention.

FIG. 6 is a circuit diagram showing a conventional RF coil.

Claims

1. An RF coil of a magnetic resonance imaging apparatus comprising: an original loop unit;a conductor which is so connected to the original loop unit as to split the original loop unit into a plurality of split loop units;an electrostatic capacitance element connected in series to the conductor; anda switching device which makes the conductor either conductive or non-conductive, wherein:the electrostatic capacitance of the electrostatic capacitance element is so set as not to allow the plurality of split loop units to interfere with each other when the conductor is made conductive by the switching device.

2. The RF coil of the magnetic resonance imaging apparatus according to claim 1, wherein: the electrostatic capacitance of the electrostatic capacitance element is so set to hold Cm=1/(ω2M)when Cm is the synthetic static capacitance on the conductor shared by the two mutually adjoining split loop units, M is the mutual inductance between the two split loop units, and ω is the resonance frequency of the original loop unit or the split loop units.

3. The RF coil of the magnetic resonance imaging apparatus according to claim 1, wherein: the electrostatic capacitance of the electrostatic capacitance element is so set as to equalize the resonance frequency of the original loop unit and the resonance frequency or frequencies of at least any of the plurality of split loop units.

4. The RF coil of the magnetic resonance imaging apparatus according to claim 2, wherein: the electrostatic capacitance of the electrostatic capacitance element is so set as to equalize the resonance frequency of the original loop unit and the resonance frequency or frequencies of at least any of the plurality of split loop units.

5. The RF coil of the magnetic resonance imaging apparatus according to claim 1, wherein: the switching device comprised of a parallel oscillation circuit, including: a switch-over electrostatic capacitance element connected in series to the conductor;an inductance element connected in parallel to the switch-over electrostatic capacitance element; anda diode connected in series to the inductance element.

6. The RF coil of the magnetic resonance imaging apparatus according to claim 2, wherein: the switching device comprised of a parallel oscillation circuit, including:a switch-over electrostatic capacitance element connected in series to the conductor;an inductance element connected in parallel to the switch-over electrostatic capacitance element; anda diode connected in series to the inductance element.

7. The RF coil of the magnetic resonance imaging apparatus according to claim 3, wherein: the switching device comprised of a parallel oscillation circuit, including: a switch-over electrostatic capacitance element connected in series to the conductor;an inductance element connected in parallel to the switch-over electrostatic capacitance element; anda diode connected in series to the inductance element.

8. A magnetic resonance imaging apparatus comprising: a magnetostatic field forming unit which forms a magnetostatic field;a gradient magnetic field forming unit which forms a gradient magnetic field;an RF coil which performs at least either the application of a high frequency magnetic field in a subject within the magnetostatic field or the reception of magnetic resonance signals from the subject; andan image forming unit which forms tomographic images of the subject on the basis of the magnetic resonance signals which have been received,the RF coil including an original loop unit;a conductor which is so connected to the original loop unit as to split the original loop unit into a plurality of split loop units;an electrostatic capacitance element connected in series to the conductor; anda switching device which makes the conductor either conductive or nonconductive, wherein:the electrostatic capacitance of the electrostatic capacitance element is so set as not to allow the plurality of split loop units to interfere with each other when the conductor is made conductive by the switching device.

9. The magnetic resonance imaging apparatus according to claim 8, further comprising: a receiver unit which is connected to any one of the plurality of split loop units, the receiver unit amplifying, when the conductor is conductive, the magnetic resonance signals received from the pertinent split loop unit or amplifying, when the conductor is non-conductive, the magnetic resonance signals received from the original loop unit.

10. The magnetic resonance imaging apparatus according to claim 9, wherein: the electrostatic capacitance of the electrostatic capacitance element is so set as to equalize the resonance frequency of the original loop unit and the resonance frequency of the split loop unit to which the receiver unit is connected.

11. The magnetic resonance imaging apparatus according to claim 8, further comprising: a control device for controlling the operation of the switching device.

12. The magnetic resonance imaging apparatus according to claim 9, further comprising: a control device for controlling the operation of the switching device.

13. The magnetic resonance imaging apparatus according to claim 10, further comprising: a control device for controlling the operation of the switching device.

14. A reception coil for a magnetic resonance imaging apparatus, said comprising: an original loop unit;a conductor bisecting said original loop unit to form a second loop unit and a third loop unit; anda switching device coupled to said conductor, said switching device configured to enable said conductor to conduct electricity in a first mode of operation and inhibit said conductor from conducting electricity in a second mode of operation.

15. A reception coil in accordance with claim 14 further comprising an electrostatic capacitance element connected in series to said conductor.

16. A reception coil in accordance with claim 15 wherein said electrostatic capacitance element has a capacitance that is determined in accordance with Cm=1/(ω2M)when Cm is the synthetic static capacitance on the conductor shared by said second and third loop units, M is the mutual inductance between said second and third loop units, and ω is the resonance frequency of the original loop unit or the first and second loop units.

17. A reception coil in accordance with claim 15 wherein said electrostatic capacitance element has a capacitance that is set to equalize the resonance frequency of the original loop unit and the resonance frequency or frequencies of at least one of said second and third loop units.

18. A reception coil in accordance with claim 15 wherein said switching device comprises a parallel oscillation circuit comprising a switch-over electrostatic capacitance element connected in series to said conductor;an inductance element connected in parallel to said switch-over electrostatic capacitance element; anda diode connected in series to said inductance element.

19. A reception coil in accordance with claim 18 wherein said switching device is configured to forward bias said diode to enable said conductor to conduct electricity in a first mode of operation and to reverse bias said diode to inhibit said conductor from conducting electricity in a second mode of operation.

20. A reception coil in accordance with claim 18 wherein said switching device is configured to forward bias said diode such that at least one of said second and third loop units outputs a magnetic resonance signal to a receiver, said switching device further configured to reverse bias said diode such that said original loop unit outputs the magnetic resonance signal to the receiver.