Static magnetic field correction method and MRI system

• US 20020105328A1
• Filed: 12/28/2001
• Published: 08/08/2002
• Est. Priority Date: 02/02/2001
• Status: Active Grant

• Current Assignee: GE Medical Systems Global Technology Company LLC A Delaware Limited Liability Company
• Original Assignee: GE Medical Systems Global Technology Company LLC A Delaware Limited Liability Company
• Inventors: Goto, Takao, Miyamoto, Shoei
• Granted Patent: US 6,700,376 B2
• Time in Patent Office: Days
• US Class Current: 324/307
• 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 33/3875 using correction coil assemblies, e.g. active shimming

Abstract

To correct static magnetic field intensity and homogeneity of an MRI system, B0 correction coil driving power sources respectively supply correction electric currents to B0 correction coils added to a pair of pillar yokes at the position where an imaging region is interposed therebetween, and the pair of B0 correction coils produce correction magnetic fields in which at least one of the direction and intensity is different, which are then applied to static magnetic fields produced by permanent magnets.

Claims

1. A static magnetic field correction method comprising the steps of:

providing a magnetic field correction coil in a yoke constructing a magnetic circuit of an MRI system;

producing a correction magnetic field by flowing a correction electric current to the magnetic field correction coil; and

adding a correction magnetic field to the static magnetic field of an imaging region so as to correct the static magnetic field of the imaging region.

2. The static magnetic field correction method of claim 1, further comprising the steps of:

providing a first magnetic field correction coil in a first yoke;

providing a second magnetic field correction coil in a second yoke across an imaging region from the first yoke;

producing a first correction magnetic field by the first magnetic field correction coil; and

producing a second correction magnetic field having its direction and intensity equal to those of the first correction magnetic field by the second magnetic field correction coil.

3. The static magnetic field correction method of claim 1, further comprising the steps of:

providing a first magnetic field correction coil in a first yoke;

providing a second magnetic field correction coil in a second yoke across an imaging region from the first yoke;

producing a first correction magnetic field by the first magnetic field correction coil; and

producing a second correction magnetic field having at least one of its direction and intensity different from those of the first correction magnetic field by the second magnetic field correction coil.

4. The static magnetic field correction method of claim 1, further comprising the steps of:

collecting FID signals;

determining a resonance frequency from the FID signals;

determining a frequency difference between the resonance frequency and an RF send/receive system; and

deciding a correction electric current from the frequency difference.

5. The static magnetic field correction method of claim 4, further comprising the steps of:

disposing an NMR probe combining a small phantom with a small coil in the vicinity of an imaging region;

sending RF pulses from the small coil to receive FID signals from the small phantom by the small coil; and

determining a resonance frequency from the FID signals.

6. The static magnetic field correction method of claim 1, further comprising the steps of:

measuring a temperature of a member constructing the magnetic circuit;

determining a resonance frequency from a temperature characteristic;

determining a frequency difference between the resonance frequency and a target frequency; and

deciding a correction electric current from the frequency difference.

7. An MRI system comprising:

a yoke constructing a magnetic circuit;

a magnetic field correction coil provided in the yoke for producing a correction magnetic field; and

a power source for the magnetic field correction coil for supplying a correction electric current to the magnetic field correction coil.

8. The MRI system of claim 7, further comprising:

a first yoke and a second yoke at the position where an imaging region is interposed therebetween;

a first magnetic field correction coil provided in the first yoke for producing a first correction magnetic field;

a second magnetic field correction coil provided in the second yoke and connected in series with the first magnetic field correction coil so as to produce a second correction magnetic field having its direction and intensity equal to those of the first correction magnetic field; and

a power source for the magnetic field correction coil for supplying a correction electric current to a series circuit of the first magnetic field correction coil and the second magnetic field correction coil.

9. The MRI system of claim 7, further comprising:

a first yoke and a second yoke at the position where an imaging region is interposed therebetween;

a first magnetic field correction coil provided in the first yoke for producing a first correction magnetic field;

a second magnetic field correction coil provided in the second yoke for producing a second correction magnetic field;

a power source for the first magnetic field correction coil for supplying a first correction electric current to the first magnetic field correction coil; and

a power source for the second magnetic field correction coil for supplying a second correction electric current to the second magnetic field correction coil.

10. The MRI system of claim 7, further comprising:

a correction electric current deciding device which collects FID signals, determines a resonance frequency from tie FID signals, determines a frequency difference between the resonance frequency and an RF send/receive system, and decides a correction electric current from the frequency difference.

11. The MRI system according to claim 9, further comprising:

an NMR probe combining a small phantom with a small coil disposed in the vicinity of an imaging region, wherein

the correction electric current deciding device sends RF pulses from the small coil to receive FID signals from the small phantom by the small coil, and determines a resonance frequency from the FID signals.

12. The MRI system of claim 7, further comprising:

a temperature sensor for measuring a temperature of a member constructing the magnetic circuit; and

a correction electric current deciding device which determines a resonance frequency from the temperature characteristic, determines a frequency difference between the resonance frequency and a target frequency, and decides a correction electric current from the frequency difference.