Methods and apparatus for adjusting center magnetic field of a magnetic field generator for MRI

1. A product line of MRI systems, said product line comprising:

a first MRI system comprising:

a first yoke; and

a plurality of magnet blocks forming a first central assembly disposed on said first yoke; and

a second MRI system comprising:

a second yoke;

a plurality of magnet blocks forming a second central assembly disposed on said second yoke and shaped the same as said first central assembly; and

a first set of magnet blocks mounted to said second yoke at a periphery of said second central assembly.

2. A product line in accordance with claim 1 wherein said first MRI system further comprises:

a second set of magnet blocks mounted to said first yoke at a periphery of said first central assembly, said second set in a different configuration than said first set.

3. A product line in accordance with claim 1 wherein said first set of magnet blocks comprises a set of half blocks.

4. A product line in accordance with claim 3 wherein said second MRI system further comprises a second set of half blocks disposed on said second yoke adjacent said first set.

5. A method of manufacturing MRI systems, said method comprising:

providing a plurality of magnet blocks forming a central assembly disposed on a yoke;

measuring a center magnetic field; and

adding additional magnet blocks to the yoke when the center magnetic field is not within a predetermined range.

6. A method in accordance with claim 5 wherein said adding additional magnet blocks comprises adding additional magnet blocks to the yoke at a periphery of the central assembly when the center magnetic field is not within a predetermined range.

7. A method in accordance with claim 5 wherein at least some additional magnet blocks comprises a first set of half blocks.

8. A method in accordance with claim 7 wherein at least some additional magnet blocks comprise a second set of half blocks disposed adjacent the first set at periphery of the central assembly.

9. A method for altering a magnetic field, said method comprising:

measuring a center magnetic field of an MRI system to obtain a center magnetic field value; and

regulating a temperature of at least one component of the MRI system to change the center magnetic field to a value different the measured value.

10. A method in accordance with claim 9 further comprising comparing the measured value to a pre-determined value, said regulating a temperature further comprises regulating a temperature of at least one component of the MRI system to change the center magnetic field to a value substantially equal to the pre-determined value.

11. A method in accordance with 9 wherein said regulating a temperature comprises regulating a temperature of at least one component of the MRI system and using a B0 controlled shimming to change the center magnetic field to a value different the measured value.

12. A method in accordance with claim 9 further comprising comparing the measured value to a pre-determined value, said regulating a temperature further comprises regulating a temperature of at least one component of the MRI system and using a B0 controlled shimming to change the center magnetic field to a value to a value substantially equal to the pre-determined value.

13. A method for altering a magnetic field, said method comprising:

measuring a center magnetic field of an MRI system to obtain a center magnetic field value; and

using a B0 controlled shimming to change the center magnetic field to a value different the measured value.

14. A method in accordance with claim 13 further comprising comparing the measured value to a pre-determined value, said using a B0 controlled shimming further comprises using a B0 controlled shimming to change the center magnetic field to a value substantially equal to the pre-determined value.

15. A method in accordance with claim 13 wherein said measuring further comprises measuring a center magnetic field of an MRI system to obtain a center magnetic field value, wherein the MRI system comprises:

a first yoke;

a plurality of magnet blocks forming a first central assembly disposed on said first yoke;

a second yoke positioned opposite said first yoke and separated from said first yoke by an imaging gap;

a plurality of magnet blocks forming a second central assembly disposed on said second yoke and shaped the same as said first central assembly; and

a first set of magnet blocks mounted to said second yoke at a periphery of said second central assembly.

16. A method in accordance with claim 15 further comprising comparing the measured value to a pre-determined value, said using a B0 controlled shimming further comprises using a B0 controlled shimming to change the center magnetic field to a value substantially equal to the pre-determined value.

17. A method in accordance with claim 15 wherein said using a B0 controlled shimming comprises using a B0 controlled shimming and regulating a temperature of at least one magnet block to change the center magnetic field to a value different the measured value.

18. A method in accordance with claim 17 further comprising comparing the measured value to a predetermined value, said using a B0 controlled shimming comprises using a B0 controlled shimming and regulating a temperature of at least one component of the MRI system to change the center magnetic field to a value substantially equal to the pre-determined value.

19. A method in accordance with claim 18 wherein said measuring further comprises measuring a center magnetic field of an MRI system to obtain a center magnetic field value, wherein the first set of magnet blocks of the MRI system comprises a first set of half blocks.

20. A method in accordance with claim 19 wherein said measuring further comprises measuring a center magnetic field of an MRI system to obtain a center magnetic field value, wherein the MRI system comprises a second set of half blocks disposed on said second yoke adjacent said first set.