Magnetic resonance imaging apparatus and magnet for magnetic resonance imaging apparatus

Patent metadata

Field	Value
Publication number	US-9784808-B2
Application number	US-201414285138-A
Country	US
Kind code	B2
Filing date	May 22, 2014
Priority date	May 21, 2012
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

According to one embodiment, a magnetic resonance imaging apparatus includes an imaging unit and a shield. The imaging unit is configured to perform magnetic resonance imaging of an object by transmitting a radio frequency signal from a radio frequency coil while magnetic fields are formed by a gradient coil and a superconducting magnet respectively. The shield is configured to form a gradient magnetic field for the magnetic resonance imaging with the gradient coil and to prevent ingress of heat into the superconducting magnet.

First claim

What is claimed is:

1. A magnetic resonance imaging apparatus comprising:
an imaging unit configured to perform a magnetic resonance imaging of an object by transmitting a radio frequency signal from a radio frequency coil when magnetic fields are formed by a gradient coil and a superconducting magnet respectively; and
a shield configured to conduct eddy currents which generate an eddy magnetic field and to prevent ingress of heat into the superconducting magnet, the eddy magnetic field being superposed with a magnetic field generated by the gradient coil having a pattern of windings determined such that a gradient magnetic field for magnetic resonance imaging is formed including the eddy magnetic field.

2. A magnetic resonance imaging apparatus comprising:
a superconducting magnet configured to form a static magnetic field, for magnetic resonance imaging of an object, in an imaging area where the object is set;
a gradient coil;
a radio frequency coil configured to transmit a radio frequency signal to the imaging area; and
a shield configured to conduct eddy currents which generate an eddy magnetic field and to prevent ingress of heat into the superconducting magnet, the eddy magnetic field being superposed with a magnetic field generated by the gradient coil having a pattern of windings determined such that a gradient magnetic field for magnetic resonance imaging is formed including the eddy magnetic field.

3. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is configured to form the gradient magnetic field with the gradient coil by canceling at least a magnetic field generated, from the gradient coil, at a side of the superconducting magnet.

4. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is made of a metal plate whose eddy magnetic field time constant is not less than 500 ms.

5. A magnetic resonance imaging apparatus of claim 4 ,
wherein said shield is made of a tubal aluminum plate having a thickness not less than 10 mm or a tubal copper plate having a thickness not less than 3 mm.

6. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is made of a metal plate whose eddy magnetic field time constant is not less than a time constant required for magnetic resonance imaging.

7. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is set as a passive coil which does not need an input and output current.

8. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is set inside a casing constituting the superconducting magnet.

9. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is configured to form a part of a casing constituting the superconducting magnet.

10. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield has a structure determined with a condition of the windings of the gradient coil so as to form an intended gradient magnetic field appropriate for magnetic resonance imaging.

11. A magnetic resonance imaging apparatus of claim 10 ,
wherein said shield has a diameter or a radius determined with a number of the windings of the gradient coil so as to form the intended gradient magnetic field.

12. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield has a pipe for conducting a cooling media on a side of the gradient coil.

13. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield has a channel for conducting a cooling media inside the shield.

14. A magnetic resonance imaging apparatus of claim 1 ,
wherein said shield is a heat shield to prevent ingress of heat into the superconducting magnet.

15. A magnet for a magnetic resonance imaging apparatus comprising:
a magnet body having liquid helium and a superconducting coil in a casing; and
a shield set inside said magnet body and having an eddy magnetic field time constant that is not less than 500 ms, the eddy magnetic field being superposed with a magnetic field generated by the gradient coil having a pattern of windings determined such that a gradient magnetic field for magnetic resonance imaging is formed including the eddy magnetic field.

Assignees

• Toshiba Medical Sys Corp

Inventors

• Sakakura Yoshitomo
• Nogami Kazuto
• Tanaka Hidekazu

Classifications

• G01R33/4215 Primary

  of the gradient magnetic field, e.g. using passive or active shielding of the gradient magnetic field · CPC title

• G01R33/3804

  Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly · CPC title

• G01R33/3815

  with superconducting coils, e.g. power supply therefor · CPC title

• G01R33/3856 Primary

  Means for cooling the gradient coils or thermal shielding of the gradient coils · CPC title