US5157330A
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Method and apparatus for compensating magnetic field inhomogeneity artifact in MRI
Assignee: CALIFORNIA 300 LAKESIDE DRIVE 22ND FLOOR OAKLAND CA 94612-3550 A CORP OF CALIFORNIA, University of, Regents of
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Filing: 1991-02-22
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Granted: 1992-10-20
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Expires: 2011-02-22
Abstract
Abstract A measure of magnetic field inhomogeneity along a phase-encoded (e.g. y-axis) dimension is derived in k-space from previously acquired MRI phase-encoded projection data. From this, a measure of MRI data skewing caused by such inhomogeneity is obtained and used to compensate therefor. Since the MRI data is to be multi-dimensionally Fourier Transformed in most instances anyway, a transform in the relevant phase encoded dimension (e.g., y-axis) is taken followed with phase shifting each digitized data point by an amount proportional to the measured magnitude of inhomogeneity and to the datum coordinate in the read-out dimension (e.g., x-axis) and to the datum coordinate in each phase-encode dimension (e.g., y-axis) before the data is further Fourier Transformed with respect to the read-out dimension (e.g., x-axis). If two-dimensional phase encoding is employed (e.g., as in 3DFT), then a second level of similar inhomogeneity compensation can be had in the third dimension (e.g., z-axis) as well.
Inventors
- 👤 Leon Kaufman
- 👤 Joseph W. Carlson
- 👤 David M. Kramer
- 👤 James D. Hale
- 👤 Kingman Yee
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 11:19
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/565; G01R33/56563
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
46 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method comprising (a) measuring relative data skewing in k-space MRI data caused by a magnetic field gradient in a phase-encoded dimension; and (b) phase-shifting Fourier Transformed MRI data to compensate for said measured data skewing.
Claim 2
Independent Claim
46 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method comprising (a) measuring relative data skewing in k-space MRI data caused by a magnetic field gradient in a phase-encoded dimension; and (b) phase-shifting Fourier Transformed MRI data to compensate for said measured data skewing.
Claim 3
Independent Claim
95 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method comprising: (a) measuring the relative magnitude of said inhomogeneity from MRI data in k-space; (b) transforming acquired multi-dimensional MRI data in k-space with respect to a first dimension representing a phase-encoded dimension; (c) phase-ramping the resulting transformed MRI data by an amount proportional to the magnitude of measured inhomogeneity in said phase-encoded dimension and to a MRI datum coordinate in a second dimension, transverse to said phase-encoded dimension; and (d) further transforming the resulting phase-shifted MRI data with respect to said second dimension.
Claim 4
Independent Claim
95 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method comprising: (a) measuring the relative magnitude of said inhomogeneity from MRI data in k-space; (b) transforming acquired multi-dimensional MRI data in k-space with respect to a first dimension representing a phase-encoded dimension; (c) phase-ramping the resulting transformed MRI data by an amount proportional to the magnitude of measured inhomogeneity in said phase-encoded dimension and to a MRI datum coordinate in a second dimension, transverse to said phase-encoded dimension; and (d) further transforming the resulting phase-shifted MRI data with respect to said second dimension.
Claim 5
Dependent Claim
67 words
A method as in claim 2 further comprising, after step (c): (c1) first transforming the phase-ramping MRI data with respect to a third dimension representing a further phase-encoded dimension; and (c2) further phase-ramping the resulting transformed MRI data from step (c1) by an amount proportional to the magnitude of measured inhomogeneity in a second phase-encoded dimension and to a MRI datum coordinate in said second phase-encoded dimension.
Claim 6
Dependent Claim
20 words
A method as in claim 1, 2 or 3 wherein said measuring step includes use of gradient echo MRI data.
Claim 7
Dependent Claim
26 words
A method as in claim 4 wherein less than a full set of gradient echo MRI data is acquired and used to determine magnetic field inhomogeneity.
Claim 8
Dependent Claim
17 words
A method as in claim 4 wherein said transforming and phase-ramping steps use spin echo MRI data.
Claim 9
Dependent Claim
17 words
A method as in claim 4 wherein said transforming and phase-ramping steps use gradient echo MRI data.
Claim 10
Dependent Claim
15 words
A method as in claim 2 or 3 wherein said transforming steps comprise Fourier Transformation.
Claim 11
Independent Claim
59 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method including: acquiring multi-dimensional gradient echo MRI data in k-space; locating the maximum magnitude datum of said MRI data; detecting the dimensional shift, if any, in the location of said maximum from its expected location without magnetic field inhomogeneity as a measure of the magnitude of said inhomogeneity.
Claim 12
Independent Claim
59 words
A method for compensating magnetic field inhomogeneity artifact in MRI, said method including: acquiring multi-dimensional gradient echo MRI data in k-space; locating the maximum magnitude datum of said MRI data; detecting the dimensional shift, if any, in the location of said maximum from its expected location without magnetic field inhomogeneity as a measure of the magnitude of said inhomogeneity.
Claim 13
Dependent Claim
52 words
A method as in claim 9 wherein said acquiring, locating and detecting steps are performed both before and after acquisition of MRI data which is subsequently processed to produce a visual MR image, the before-acquisition and after-acquisition measures of inhomogeneity both being used to compensate for inhomogeneity artifact in said visual image.
Claim 14
Dependent Claim
26 words
A method as in claim 9 wherein said acquiring step includes acquisition of less than a full set of phase-encoded projections of MRI data in k-space.
Claim 15
Dependent Claim
36 words
A method as in claim 9 wherein said acquiring, locating and detecting steps use gradient echo MRI data and where the resulting measure of inhomogeneity magnitude is used to compensate artifact in spin echo MRI data.
Claim 16
Dependent Claim
62 words
A method as in claim 9 comprising: Fourier Transforming acquired multi-dimensional MRI data with respect to a phase-encoded dimension y, phase-ramping the thus transformed MRI data by an amount proportional to the inhomogeneity magnitude and to a read-out dimension x, transverse to said phase-encoded dimension y, and Fourier Transforming the thus phase shifted MRI data with respect to said read-out dimension x.
Claim 17
Dependent Claim
73 words
A method as in claim 13 wherein: the acquiring, locating and detecting steps are further performed to obtain a further measure of magnetic field inhomogeneity magnitude along a second phase-encoded dimension z; and the phase-shifted MRI data are further Fourier Transformed with respect to the second phase-encoded dimension and further phase-ramped by an amount proportional to the z-dimension inhomogeneity magnitude and to elapsed time prior to said Fourier Transformation with respect to x.
Claim 18
Independent Claim
68 words
A method for compensating magnetic field inhomogeneity along a phase encoded dimension y transverse to a read-out dimension x in a magnetic resonance imaging system which acquires MRI data generated subsequent to an RF nutation pulse occurrence, said method comprising the step of: shifting acquired MRI data in the phase-encoded dimension y by an amount proportional to the magnitude of said magnetic field inhomogeneity and to elapsed time.
Claim 19
Independent Claim
68 words
A method for compensating magnetic field inhomogeneity along a phase encoded dimension y transverse to a read-out dimension x in a magnetic resonance imaging system which acquires MRI data generated subsequent to an RF nutation pulse occurrence, said method comprising the step of: shifting acquired MRI data in the phase-encoded dimension y by an amount proportional to the magnitude of said magnetic field inhomogeneity and to elapsed time.
Claim 20
Dependent Claim
42 words
A method as in claim 15 further comprising the steps of: measuring the magnitude of said magnetic field inhomogeneity by acquiring phase-encoded NMR RF data and determining what, if any, non-zero phase-encoding value is required to produce maximum NMR RF response magnitude.
Claim 21
Dependent Claim
32 words
A method as in claim 16 wherein said measuring step is performed using NMR gradient echo MRI data that is also subsequently used in said shifting step and to generate an image.
Claim 22
Dependent Claim
20 words
A method as in claim 15 or 16 wherein said MRI data is initially acquired as gradient echo MRI data.
Claim 23
Dependent Claim
40 words
A method as in claim 16 wherein said measuring step includes acquisition of phase-encoded MRI projection data using read-out gradient reversal while said shifting step is performed on spin echo MRI data produced by a succession of RF nutation pulses.
Claim 24
Dependent Claim
39 words
A method as in claim 16 wherein said measuring step includes acquisition of phase-encoded spin echo MRI projection data using mis-adjusted spin echo MRI data produced by a succession of RF nutation pulses and a delaying read-out gradient pulse.
Claim 25
Dependent Claim
48 words
A method as in claim 16 wherein said measuring step is performed both before and after-acquisition of the MRI data to be shifted and where said shifting step uses as field gradient magnitude a value interpolated from the values obtained by said before-acquisition and said after-acquisition measuring steps.
Claim 26
Dependent Claim
49 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus comprising: (a) means for measuring relative data skewing in k-space MRI data caused by a magnetic field gradient in a phase-encoded dimension; and (b) means for phase-shifting Fourier Transformed MRI data to compensate for said measured data skewing.
Claim 27
Dependent Claim
49 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus comprising: (a) means for measuring relative data skewing in k-space MRI data caused by a magnetic field gradient in a phase-encoded dimension; and (b) means for phase-shifting Fourier Transformed MRI data to compensate for said measured data skewing.
Claim 28
Dependent Claim
102 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus comprising: (a) means for measuring the relative magnitude of said inhomogeneity from MRI data in k-space; (b) means for transforming acquired multi-dimensional MRI data in k-space with respect to a first dimension representing a phase-encoded dimension; (c) means for phase-ramping the resulting transformed MRI data by an amount proportional to the magnitude of measured inhomogeneity in said phase-encoded dimension and to a MRI datum coordinate in a second dimension, transverse to said phase-encoded dimension; and (d) means for further transforming the resulting phase-shifted MRI data with respect to said second dimension.
Claim 29
Dependent Claim
102 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus comprising: (a) means for measuring the relative magnitude of said inhomogeneity from MRI data in k-space; (b) means for transforming acquired multi-dimensional MRI data in k-space with respect to a first dimension representing a phase-encoded dimension; (c) means for phase-ramping the resulting transformed MRI data by an amount proportional to the magnitude of measured inhomogeneity in said phase-encoded dimension and to a MRI datum coordinate in a second dimension, transverse to said phase-encoded dimension; and (d) means for further transforming the resulting phase-shifted MRI data with respect to said second dimension.
Claim 30
Dependent Claim
64 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus including: means for acquiring multi-dimensional gradient echo MRI data in k-space; means for locating the maximum magnitude datum of said MRI data; means for detecting the dimensional shift, if any, in the location of said maximum from its expected location without magnetic field inhomogeneity as a measure of the magnitude of said inhomogeneity.
Claim 31
Dependent Claim
64 words
Apparatus for compensating magnetic field inhomogeneity artifact in MRI, said apparatus including: means for acquiring multi-dimensional gradient echo MRI data in k-space; means for locating the maximum magnitude datum of said MRI data; means for detecting the dimensional shift, if any, in the location of said maximum from its expected location without magnetic field inhomogeneity as a measure of the magnitude of said inhomogeneity.
Claim 32
Dependent Claim
72 words
Apparatus for compensating magnetic field inhomogeneity along a phase-encoded dimension y transverse to a read-out dimension x in a magnetic resonance imaging system which acquires MRI data generated subsequent to an RF nutation pulse occurrence, said apparatus comprising: means for acquiring MRI data, and means for shifting said acquired MRI data in the phase-encoded dimension y by an amount proportional to the magnitude of said magnetic field inhomogeneity and to elapsed time.
Claim 33
Dependent Claim
72 words
Apparatus for compensating magnetic field inhomogeneity along a phase-encoded dimension y transverse to a read-out dimension x in a magnetic resonance imaging system which acquires MRI data generated subsequent to an RF nutation pulse occurrence, said apparatus comprising: means for acquiring MRI data, and means for shifting said acquired MRI data in the phase-encoded dimension y by an amount proportional to the magnitude of said magnetic field inhomogeneity and to elapsed time.
Claim 34
Dependent Claim
40 words
Apparatus as in claim 25 further comprising: means for measuring the magnitude of said magnetic field inhomogeneity by acquiring phase-encoded NMR RF data and determining what, if any, non-zero phase-encoding value is required to produce maximum NMR RF response magnitude.
Claim 35
Dependent Claim
32 words
Apparatus as in claim 26 wherein said means for measuring includes means using NMR gradient echo MRI data that is also subsequently used in said means for shifting to generate an image.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1995-10-20 | 1996-04-20 | 1996-10-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1999-10-20 | 2000-04-20 | 2000-10-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2003-10-20 | 2004-04-20 | 2004-10-20 | $7700.00 | Window Closed / Lapsed |