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US5886524A
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Method of distortion correction for gradient non-linearities in nuclear magnetic resonance tomography apparatus
Assignee: Siemens Healthcare GmbH
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Filing: 1996-10-29
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Granted: 1999-03-23
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Expires: 2016-10-29
Abstract
Abstract In a method of distortion correction for gradient non-linearities in a nuclear magnetic resonance tomography apparatus, two auxiliary datasets h(x,), f(x,y) are measured that describe the shift of a measured location (x',y') relative to an actual location (x,y) of a signal origin. A corrected auxiliary dataset h(x+f(x,y), y) is produced from the auxiliary dataset h(x,y). A location correction in y-direction ensues in an image dataset upon employment of the corrected auxiliary dataset h(x+f(x,y), y). A first intensity correction also ensues. A location correction in x-direction subsequently ensues with a second intensity correction. Alternatively, the location correction can also ensue by Fresnel transformation of the raw dataset upon involvement of the corrected auxiliary data h(x+f(x,y), y).
Inventors
- 👤 Robert Krieg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 05:23
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/565; G01R33/56572; G01R33/56518
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
123 words
A method for distortion correction for gradient non-linearities in a nuclear magnetic resonance tomography apparatus, comprising the steps: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset h(x+f(x,y), y); measuring a raw dataset from an examination subject; acquiring an image dataset from the raw dataset by two-dimensional Fourier transformation; location correcting of the image dataset in the y-direction using the corrected auxiliary dataset h(x+f(x,y), y); conducting a first intensity correction of the image dataset; location correcting the image dataset in x-direction using the auxiliary dataset f(x,y); and conducting a second intensity correction of the image dataset.
Claim 2
Independent Claim
123 words
A method for distortion correction for gradient non-linearities in a nuclear magnetic resonance tomography apparatus, comprising the steps: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset h(x+f(x,y), y); measuring a raw dataset from an examination subject; acquiring an image dataset from the raw dataset by two-dimensional Fourier transformation; location correcting of the image dataset in the y-direction using the corrected auxiliary dataset h(x+f(x,y), y); conducting a first intensity correction of the image dataset; location correcting the image dataset in x-direction using the auxiliary dataset f(x,y); and conducting a second intensity correction of the image dataset.
Claim 3
Dependent Claim
61 words
A method according to claim 1, wherein the intensity correction is conducted with the following steps: determining the intensity at the actual location (x,y) by interpolation from the grid points of the image data matrix that surround the point (x',y'); multiplying the intensity value by a Jacobi determinant ##EQU7## in the x-direction and by a Jacobi determinant ##EQU8## in the y-direction.
Claim 4
Dependent Claim
50 words
A method according to claim 1, wherein the intensity of the image pixel at the actual location (x,y) is determined by weighted summation of the intensities of the pixels in a region around the measured location (x',y'), said the region covering an enlargement of a pixel due to the distortion.
Claim 5
Dependent Claim
55 words
A method according to claim 3, further comprising determining an upper limit (x' o ) of the region around the measured location (x',y') in a unit grid by x'.sub.o =x+0.5+f(x+0.5, y); and determining a lower limit (x' u ) of the region around the measured location (x',y') in a unit grid by x'.sub.u =x-0.5+f(x-0.5, y).
Claim 6
Dependent Claim
55 words
A method according to claim 4 further comprising determining an upper limit (y' o ) of the region around the measured location (x',y') in a unit grid by y'.sub.o =y+0.5+h(x+f(x,y), y+0.5); and determining a lower limit (y' u ) of the region around the measured location (x',y') in a unit grid by y'.sub.u =y-0.5+h(x+f(x,y), y-0.5).
Claim 7
Independent Claim
121 words
A method for distortion correction for gradient non-linearities in a nuclear magnetic resonance tomography apparatus, comprising the steps of: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset f(x+h(x,y), y); measuring a raw dataset from an examination subject; acquiring an image dataset from the raw dataset by two-dimensional Fourier transformation; location correcting of the image dataset in the y-direction using the corrected auxiliary dataset f(x,y+h(x,y)); conducting an intensity correction of the image dataset; location correcting the image dataset in x-direction using the auxiliary dataset h(x,y); and conducting an intensity correction of the image dataset.
Claim 8
Independent Claim
121 words
A method for distortion correction for gradient non-linearities in a nuclear magnetic resonance tomography apparatus, comprising the steps of: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset f(x+h(x,y), y); measuring a raw dataset from an examination subject; acquiring an image dataset from the raw dataset by two-dimensional Fourier transformation; location correcting of the image dataset in the y-direction using the corrected auxiliary dataset f(x,y+h(x,y)); conducting an intensity correction of the image dataset; location correcting the image dataset in x-direction using the auxiliary dataset h(x,y); and conducting an intensity correction of the image dataset.
Claim 9
Dependent Claim
61 words
A method according to claim 6, wherein the intensity correction is conducted with the following steps: determining the intensity at the actual location (x,y) by interpolation from the grid points of the image data matrix that surround the point (x',y'); multiplying the intensity value by a Jacobi determinant ##EQU9## in the x-direction and by a Jacobi determinant ##EQU10## in the y-direction.
Claim 10
Dependent Claim
50 words
A method according to claim 7, wherein the intensity of the image pixel at the actual location (x,y) is determined by weighted summation of the intensities of the pixels in a region around the measured location (x',y'), said the region covering an enlargement of a pixel due to the distortion.
Claim 11
Dependent Claim
55 words
A method according to claim 6, further comprising determining an upper limit (x' o ) of the region around the measured location (x',y') in a unit grid by x'.sub.o =x+0.5+f(x+0.5, y); and determining a lower limit (x' u ) of the region around the measured location (x',y') in a unit grid by x'.sub.u =x-0.5+f(x-0.5, y).
Claim 12
Dependent Claim
55 words
A method according to claim 6 further comprising determining an upper limit (y' o ) of the region around the measured location (x',y') in a unit grid by y'.sub.o =y+0.5+h(x+f(x,y), y+0.5); and determining a lower limit (y' u ) of the region around the measured location (x',y') in a unit grid by y'.sub.u =y-0.5+h(x+f(x,y), y-0.5).
Claim 13
Independent Claim
86 words
A method for distortion correction for gradient non-linearities in nuclear magnetic resonance tomography apparatus, comprising the steps of: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset h(x+f(x,y), y); measuring a raw dataset from an examination subject; and acquiring an image dataset from the raw dataset with a Fresnel transformation, taking the corrected auxiliary dataset h(x+f(x,y), y) into consideration.
Claim 14
Independent Claim
86 words
A method for distortion correction for gradient non-linearities in nuclear magnetic resonance tomography apparatus, comprising the steps of: determining two auxiliary datasets h(x,y), f(x,y) that describe a shift of a measured location (x',y') compared to an actual location (x,y) of a signal origin according to the relationships y'=y+h(x,y) x'=x+f(x,y); producing a corrected auxiliary dataset h(x+f(x,y), y); measuring a raw dataset from an examination subject; and acquiring an image dataset from the raw dataset with a Fresnel transformation, taking the corrected auxiliary dataset h(x+f(x,y), y) into consideration.
Claim 15
Dependent Claim
109 words
A method for distortion correction according to claim 11, wherein the image data s(x m ,y n ) are acquired from the raw data S( m x n y) on the basis of the following relationship: ##EQU11## wherein m is a row number of the raw data matrix and of the image data matrix, n is a column number of the raw data matrix and of the image data matrix, k x =∫γ·g x dt with g x =gradient field strength in the x-direction, whereby k y =∫γ·g y dt with g y =gradient field strength in the y-direction, and I(x m ,y n ) is an intensity factor.
Claim 16
Dependent Claim
24 words
A method according to claim 12, wherein the intensity correction factor I(x m ,y n ) is calculated according to the following relationship: ##EQU12##
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 2002-03-22 | 2002-09-21 | 2003-03-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-03-22 | 2006-09-21 | 2007-03-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-03-22 | 2010-09-21 | 2011-03-23 | $7700.00 | Window Closed / Lapsed |