THERMAL CONTROLLING METHOD, MAGNETIC FIELD GENERATOR AND MRI APPARATUS

• US 20080048656A1
• Filed: 07/13/2007
• Published: 02/28/2008
• Est. Priority Date: 07/14/2006
• Status: Active Grant

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Liu, Liang, Shen, Weijun, Hua, Yihe, Tan, Fengshun
• Granted Patent: US 7,639,013 B2
• Time in Patent Office: Days
• US Class Current: 324/307
• CPC Class Codes: G01R 33/3804 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 Class Codes: G01R 33/3806 Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets
• CPC Class Codes: G01R 33/383 using permanent magnets
• CPC Class Codes: H01F 7/0278 for generating uniform fields, focusing, deflecting electrically charged particles for magnetic separation by Lorentz force B03C1/023; specially adapted for NMR applications G01R33/383

Abstract

With a view toward implementing a thermal controlling method for making reversible a temperature characteristic of a magnetic field generator using permanent magnets small in Hcj, a magnetic field generator whose temperature characteristic is reversible, using permanent magnets small in Hcj, and an MRI apparatus provided with such a magnetic field generator, there is provided a method for controlling the temperature of a magnetic field generator having a pair of disc-shaped permanent magnets whose magnetic poles opposite in polarity to each other are opposed to each other with spacing defined therebetween, and a yoke that forms return passes for magnetic fluxes of the permanent magnets, comprising the steps of raising the temperature from room temperature to a temperature higher than the room temperature, maintaining the temperature higher than the room temperature, and lowering the temperature from the temperature higher than the room temperature to the room temperature, whereby the temperature characteristics of the permanent magnets are made reversible.

Claims

1. A method for controlling a temperature of a magnetic field generator having a pair of disc-shaped permanent magnets whose magnetic poles opposite in polarity to each other are opposed to each other with spacing defined therebetween, and a yoke which forms return passes for magnetic fluxes of the permanent magnets, comprising the steps of:

raising the temperature from a room temperature to a temperature higher than the room temperature;

maintaining the temperature higher than the room temperature;

lowering the temperature from the temperature higher than the room temperature to the room temperature; and

making temperature characteristics of the permanent magnets reversible.

2. The temperature controlling method according to claim 1, wherein each of the permanent magnets operates in a non-linear region of a BH curve.

3. The temperature controlling method according to claim 1, wherein the permanent magnet is an Nd—

Fe—

B magnet.

4. The temperature controlling method according to claim 1, wherein the permanent magnet has a pole piece smaller than a magnetic face thereof in area.

5. The temperature controlling method according to claim 1,

wherein said temperature raising step includes a first temperature rise step for raising the temperature from the room temperature to 35°

C., and a second temperature rise step for raising the temperature from 35°

C. to 45°

C.,

wherein said temperature lowering step includes a first temperature fall step for lowering the temperature from 45°

C. to 35°

C., and a second temperature fall step for lowering the temperature from 35°

C. to the room temperature, and

wherein said temperature maintaining step includes a first maintenance step for maintaining a temperature of 35°

C. over two hours after the first temperature rise step, a second maintenance step for maintaining a temperature of 45°

C. over two hours after the second temperature rise step, and a third maintenance step for maintaining the temperature of 35°

C. over one hour after the first temperature fall step.

6. The temperature controlling method according to claim 1, wherein the room temperature ranges from 10°

C. to 25°

C.

7. The temperature controlling method according to claim 1, wherein the temperature controlling is performed before shimming of a magnetic field.

8. A magnetic field generator comprising:

a pair of disc-shaped permanent magnets whose magnetic poles opposite in polarity to each other are opposed to each other with spacing defined therebetween; and

a yoke which forms return passes for magnetic fluxes of the permanent magnets,

wherein each of the permanent magnets includes a first portion relatively large in demagnetization, which is constituted of a magnetic material relatively large in Hcj, and a second portion relatively small in demagnetization, which is constituted of a magnetic material relatively small in Hcj.

9. The magnetic field generator according to claim 8, wherein the first portion is a peripheral edge portion of the permanent magnet, and

wherein the second portion is a portion located inside of the peripheral edge portion of the permanent magnet.

10. The magnetic field generator according to claim 8, wherein the magnetic material is an Nd—

Fe—

B alloy.

11. The magnetic field generator according to claim 8, wherein each of the permanent magnets has a pole piece smaller than a magnetic face thereof in area.

16. The magnetic field generator according to claim 8, wherein each of the permanent magnets operates in a non-linear region of a BH curve.

17. The magnetic field generator according to claim 8, wherein temperature characteristics of the permanent magnets are reversible.

18. The magnetic field generator according to claim 8, wherein the magnetic field generator has a temperature that is controllable by:

raising a temperature of the magnetic field generator from a room temperature to a temperature higher than the room temperature;

maintaining the temperature higher than the room temperature;

lowering the temperature from the temperature higher than the room temperature to the room temperature; and

making temperature characteristics of the permanent magnets reversible.

12. An MRI apparatus comprising:

a magnetic field generator including,

a pair of disc-shaped permanent magnets whose magnetic poles opposite in polarity to each other are opposed to each other with spacing defined therebetween,

a yoke which forms return passes for magnetic fluxes of the permanent magnets,

gradient magnetic field coils, and

RF coils,

wherein each of the permanent magnets includes a first portion relatively large in demagnetization, which is constituted of a magnetic material relatively large in Hcj, and a second portion relatively small in demagnetization, which is constituted of a magnetic material relatively small in Hcj.

13. The MRI apparatus according to claim 12, wherein the first portion is a peripheral edge portion of the permanent magnet, and

wherein the second portion is a portion located inside of the peripheral edge portion of the permanent magnet.

14. The MRI apparatus according to claim 12, wherein the magnetic material is an Nd—

Fe—

B alloy.

15. The MRI apparatus according to claim 12, wherein each of the permanent magnets has a pole piece smaller than a magnetic face thereof in area.

19. The MRI apparatus according to claim 12, wherein each of the permanent magnets operates in a non-linear region of a BH curve.

20. The MRI apparatus according to claim 12, wherein temperature characteristics of the permanent magnets are reversible.