US4698591A
Expired / Lapsed
US
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Method for magnetic field gradient eddy current compensation
Assignee: General Electric Co
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Filing: 1986-01-03
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Granted: 1987-10-06
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Expires: 2006-01-03
Abstract
Abstract A method is provided for characterizing the spurious, time-dependent magnetic field gradient response and for compensating therefor. In accordance with the method a small sample object is placed away from the system isocenter where the gradient to be compensated is non-zero. A magnetic field gradient pulse is applied to the sample, followed by the application after a variable time of a 90° radio frequency pulse. The phase of the resulting free induction decay (FID) signal is monitored as a function of total time since the end of the gradient pulse. These data are related to the gradient impulse response and are fit to a set of (e.g., two or three) exponentials by regression techniques wherein an initial estimate is improved in one embodiment by chi-squared minimization of a Taylor's series expansion about the initial estimate point.
Inventors
- 👤 Gary H. Glover
- 👤 Norbert J. Pelc
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 10:14
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/565; G01R33/56518; G01R33/28; G01R33/38; G01R33/385
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
148 words
A method for magnetic field gradient coil compensation comprising the steps of: (a) positioning an NMR-active sample within a polarizing magnetic field and away from the isocenter of an MR scanner apparatus; (b) applying along at least one axis of said MR scanner apparatus a gradient pulse; (c) irradiating said sample with an RF excitation pulse within a predetermined time following application of said gradient pulse so as to generate an NMR signal; (d) measuring and storing as data the phase of said NMR signal with respect to a reference phase and as a function of the total time since the application of said gradient pulse; (e) calculating the impulse response to said gradient pulse using the stored phase data and storing the same as data; and (f) calculating the values of a compensation circuit which is employed with the gradient coil using the stored impulse response data.
Claim 2
Independent Claim
148 words
A method for magnetic field gradient coil compensation comprising the steps of: (a) positioning an NMR-active sample within a polarizing magnetic field and away from the isocenter of an MR scanner apparatus; (b) applying along at least one axis of said MR scanner apparatus a gradient pulse; (c) irradiating said sample with an RF excitation pulse within a predetermined time following application of said gradient pulse so as to generate an NMR signal; (d) measuring and storing as data the phase of said NMR signal with respect to a reference phase and as a function of the total time since the application of said gradient pulse; (e) calculating the impulse response to said gradient pulse using the stored phase data and storing the same as data; and (f) calculating the values of a compensation circuit which is employed with the gradient coil using the stored impulse response data.
Claim 3
Dependent Claim
76 words
The method as recited in claim 1 in which steps (b) through (d) are repeated a plurality of times to produce a plurality of sets of phase data, each of which sets represent the phase of said NMR signal over a different time interval after the application of said gradient pulse; and the stored phase data over the total time since the application of the gradient pulse is produced by concatenating said sets of phase data.
Claim 4
Dependent Claim
34 words
The method as recited in claim 1 in which steps (a) through (f) are repeated for each axis of the MR scanner along which a magnetic field gradient coil produces a magnetic field gradient.
Claim 5
Dependent Claim
38 words
The method as recited in claim 1 in which the calculation of the values of the compensation circuit recited in step (f) includes a regression technique to fit a plurality of exponentials to the stored impulse response data.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1990-10-05 | 1991-04-06 | 1991-10-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-10-05 | 1995-04-06 | 1995-10-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-10-05 | 1999-04-06 | 1999-10-06 | $7700.00 | Window Closed / Lapsed |