US4980641A
Expired / Lapsed
US
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Method and apparatus of reducing magnetic hysteresis in MRI systems
Assignee: General Atomics Corp
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Filing: 1989-08-11
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Granted: 1990-12-25
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Expires: 2009-08-11
Abstract
Abstract An apparatus for minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged parallel pole faces forming a magnetic field therebetween, and gradient coils spaced apart from each pole face for producing time varying magnetic fields, comprises a layer of nonferromagnetic conducting material interposed between the pole face and the gradient coil. The interposed layer carries eddy currents induced by time varying magnetic fields produced by the gradient coils, thereby minimizing AC induced eddy current hysteresis from the pole faces. The layer preferably has a thickness of at least one skin depth at the frequency associated with the time varying magnetic field. The layer is preferably contiguous with the pole face, and comprises copper or aluminum. In another embodiment, each pole face has a plurality of slits therethrough radiating inward from the circumference for eliminating the eddy currents in the pole face. The slits in one pole face are preferably symmetrical to those in the other. There are preferably twenty-four (24) slits spaced fifteen degrees (15°) apart. There is also disclosed the method for accomplishing the same.
Inventors
- 👤 Bruce C. Breneman
- 👤 Raymond E. Sarwinski
- 👤 Yen-Hwa L. Hsu
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:43
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/28; G01R33/42; G01R33/421; G01R33/38; G01R33/3806; G01R33/383; G01R33/385
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
83 words
An apparatus for minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising: a layer of nonferromagnetic conducting material interposed between said pole face and said gradient coil to carry eddy currents induced by said time varying magnetic fields produced by said gradient coils.
Claim 2
Independent Claim
83 words
An apparatus for minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising: a layer of nonferromagnetic conducting material interposed between said pole face and said gradient coil to carry eddy currents induced by said time varying magnetic fields produced by said gradient coils.
Claim 3
Dependent Claim
29 words
An apparatus as recited in claim 1, wherein said layer has a thickness of at least one skin depth at the frequency associated with said time varying magnetic field.
Claim 4
Dependent Claim
16 words
An apparatus as recited in claim 2, wherein said layer is contiguous with said pole face.
Claim 5
Dependent Claim
12 words
An apparatus as recited in claim 3, wherein said layer is copper.
Claim 6
Dependent Claim
12 words
An apparatus as recited in claim 3, wherein said layer is aluminum.
Claim 7
Independent Claim
79 words
An apparatus for minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising: each said pole face having a plurality of slits therethrough radiating inward from the circumference thereof to a point within the smallest diameter of said gradient coil.
Claim 8
Independent Claim
79 words
An apparatus for minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising: each said pole face having a plurality of slits therethrough radiating inward from the circumference thereof to a point within the smallest diameter of said gradient coil.
Claim 9
Dependent Claim
16 words
An apparatus as recited in claim 6, wherein each said slit is filled with insulation material.
Claim 10
Dependent Claim
16 words
An apparatus as recited in claim 7, wherein said slits are positioned equidistant from one another.
Claim 11
Dependent Claim
22 words
An apparatus as recited in claim 8, wherein there are twenty-four (24) slits spaced apart at angles of fifteen degrees (15° ).
Claim 12
Dependent Claim
17 words
An apparatus as recited in claim 9, wherein each said slit is approximately one-sixteenth (1/16) inch wide.
Claim 13
Independent Claim
93 words
A method of minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising the steps of: providing a layer of nonferromagnetic conducting material having a thickness of at least one skin depth at the frequency associated with said time varying magnetic field; and positioning said layer between said pole face and said gradient coil.
Claim 14
Independent Claim
93 words
A method of minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising the steps of: providing a layer of nonferromagnetic conducting material having a thickness of at least one skin depth at the frequency associated with said time varying magnetic field; and positioning said layer between said pole face and said gradient coil.
Claim 15
Dependent Claim
20 words
A method as recited in claim 11, wherein said positioning step includes placing said layer contiguous with said pole face.
Claim 16
Independent Claim
87 words
A method of minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel, generally circular pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising the step of: cutting a plurality of slits radially through each said pole face, said slits being located in one of said pole faces symmetrical to said slits in said opposite pole face.
Claim 17
Independent Claim
87 words
A method of minimizing hysteresis in a magnetic resonance imaging device of the type utilizing a pair of oppositely charged, flat, parallel, generally circular pole faces forming a magnetic field therebetween, and a gradient coil spaced apart from and parallel to each pole face for producing time varying magnetic fields at a frequency, comprising the step of: cutting a plurality of slits radially through each said pole face, said slits being located in one of said pole faces symmetrical to said slits in said opposite pole face.
Claim 18
Dependent Claim
21 words
A method as recited in claim 13, wherein said cutting step includes cutting said slits spaced apart equally from one another.
Claim 19
Dependent Claim
26 words
A method as recited in claim 14, wherein said cutting step includes cutting twenty-four (24) slits at angles of fifteen degrees (15° ) from one another.
Claim 20
Dependent Claim
13 words
A method as recited in claim 15, wherein said slits alternate in length.
References Cited (Backward Citations)
US2777099A
Cited
US4445102A
Cited
US4498048A
Cited
US4642569A
Cited
US4672346A
Cited
US4737716A
Cited
US4737716B1
Cited
US4829252A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-12-24 | 1994-06-25 | 1994-12-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-12-24 | 1998-06-25 | 1998-12-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-12-24 | 2002-06-25 | 2002-12-25 | $7700.00 | Window Closed / Lapsed |