Magnetically shielded room with internal active magnetic field cancellation, and its use

• US 6,731,968 B2
• Filed: 07/03/2002
• Issued: 05/04/2004
• Est. Priority Date: 07/29/2003
• Status: Expired due to Fees

• Current Assignee: YNI Limited
• Original Assignee: 4-D Neuroimaging
• Inventors: Buchanan, D. Scott
• Primary Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US10/189,092
• Publication Number:
  US 20040006267A1
• Time in Patent Office: 671 Days
• Field of Search: 600/407, 600/409, 324/260, 324/207.21, 522/67, 522/71
• US Class Current: 600/409
• CPC Class Codes: A61B 5/0046 Arrangements of imaging apparatus in a room, e.g. room provided with shielding or for improved access to apparatus
• CPC Class Codes: A61B 5/242 Detecting biomagnetic fields, e.g. magnetic fields produced by bioelectric currents
• CPC Class Codes: G01R 33/025 Compensating stray fields G01R33/0017 takes precedence
• CPC Class Codes: H05K 9/0003 Shielded walls, floors, ceilings, e.g. wallpaper, wall panel, electro-conductive plaster, concrete, cement, mortar
• CPC Class Codes: H05K 9/0075 Magnetic shielding materials

Abstract

An apparatus includes an enclosure having a wall defining an interior of the enclosure and having a layer of a magnetically permeable material disposed such that there is no layer of an electrically conductive material located closer to the interior of the enclosure than the layer of the magnetically permeable material. A background-field magnetometer and an electrical coil structure are positioned within the enclosure. The electrical coil structure is driven by a controllable electrical current source. A background-field-reducing feedback controller has a controller input responsive to a background-field magnetometer output signal, and a controller output in communication with the current source command signal input. A signal magnetometer, such as a biomagnetometer, within the enclosure detects a magnetic field produced by a source within the enclosure. The electrical coil structure operating responsive to the feedback controller reduces the background magnetic field within the enclosure, so that the signal magnetometer may operate in an environment having less interference.

Claims

1. An apparatus comprising:

an enclosure having a wall defining an interior of the enclosure, the wall comprising a layer of a magnetically permeable material disposed such that there is no layer of an electrically conductive material located closer to the interior of the enclosure than the layer of the magnetically permeable material;

a background-field magnetometer within the enclosure and having a background-field magnetometer output signal;

an electrical coil structure within the interior of the enclosure and producing a magnetic output field responsive to an electrical coil input;

a controllable electrical current source having

a current source output in communication with the electrical coil input, and

a current source command signal input; and

a background-field-reducing feedback controller having

a controller input responsive to the background-field magnetometer output signal, and

a controller output in communication with the current source command signal input.

2. The apparatus of claim 1, wherein the electrical coil structure includes at least three electrical coils each producing a magnetic field output responsive to a respective electrical coil input and arranged such that output magnetic field vectors of the respective electrical coils are noncollinear, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

3. The apparatus of claim 1, wherein the electrical coil structure includes at least eight electrical coils arranged such that each electrical coil produces a magnetic output field gradient responsive to a respective electrical coil input and arranged such that no two magnetic output field gradients produced are redundant with each other, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

4. The apparatus of claim 1, where in the electrical coil structure includes at least one electrical coil which produces a magnetic output field responsive to a respective electrical coil input and at least one electrical coil which produces a magnetic output field gradient responsive to a respective electrical coil input, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

5. The apparatus of claim 1, wherein the background-field magnetometer is a vector magnetometer.

6. The apparatus of claim 1, wherein the background-field magnetometer includes a magnetic gradiometer.

7. The apparatus of claim 6, wherein the signal magnetometer comprises a superconducting quantum interference device.

8. The apparatus of claim 6, wherein the signal magnetometer is a biomagnetometer.

9. The apparatus of claim 1, wherein the wall comprises

the layer of magnetically permeable material, and

a layer of an electrically conductive material disposed exteriorly of the layer of magnetically permeable material.

10. The apparatus of claim 1, wherein the layer of magnetically permeable material comprises mu metal.

11. The apparatus of claim 1, wherein the layer of magnetically permeable material comprises material with an initial magnetic permeability greater than 4000.

12. The apparatus of claim 1, wherein the apparatus further comprises:

a signal magnetometer positioned to detect a magnetic field produced by a source within the enclosure.

13. The apparatus of claim 1, wherein the interior of the enclosure has a volume of at least about 500 cubic feet.

14. The apparatus of claim 1, wherein the layer of magnetically permeable material comprises material with an initial magnetic permeability greater than 4000.

15. An apparatus comprising:

an enclosure having a wall defining an interior of the enclosure, the wall comprising

a layer of a magnetically permeable material, and

an innermost layer of an electrically conductive material disposed exteriorly of the layer of the magnetically permeable material;

a background-field magnetometer within the enclosure and having a background-field magnetometer output signal;

an electrical coil structure within the interior of the enclosure and having an electrical coil input;

a controllable electrical current source having

a current source output in communication with the electrical coil input, and

a current source command signal input;

a background-field-reducing feedback controller having

a controller input responsive to the background-field magnetometer output signal, and

a controller output in communication with the current source command signal input; and

a signal magnetometer positioned to detect a magnetic field produced by a source within the enclosure.

16. The apparatus of claim 15, wherein the electrical coil structure includes at least three electrical coils each producing a magnetic field output responsive to a respective electrical coil input and arranged such that output magnetic field vectors of the respective electrical coils are noncollinear, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

17. The apparatus of claim 15, wherein the electrical coil structure includes at least eight electrical coils arranged such that each electrical coil produces a magnetic output field gradient responsive to a respective electrical coil input and arranged such that no two magnetic output field gradients produced are redundant with each other, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

18. The apparatus of claim 15, where in the electrical coil structure includes at least one electrical coil which produces a magnetic output field responsive to a respective electrical coil input and at least one electrical coil which produces a magnetic output field gradient responsive to a respective electrical coil input, and wherein the current source output includes a separate current source output connected with the electrical coil input of each of the respective electrical coils.

19. The apparatus of claim 15, wherein the layer of magnetically permeable material comprises mu metal.

20. The apparatus of claim 15, wherein the signal magnetometer is a biomagnetometer.