Magnetic resonance method and apparatus to determine phase correction parameters
In a magnetic resonance system and operating method to determine phase correction parameters for a phase correction in MR image data, first and second phase correction data sets are thereby acquired and correlations are calculated between data of the second phase correction data set and data of the first phase correction data set. Phase correction parameters are determined, such as coefficients of a power series that approximates a curve of a phase difference between phase curves of the second and first phase correction data sets.
1. A method to determine phase correction parameters for first data and second data acquired with a magnetic resonance data acquisition unit, said first data and said second data respectively representing different segments of a magnetic resonance exposure that exhibit respectively different background phase curves, said method comprising the steps of:
operating said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve; and
supplying said first and second phase correction data sets to a computerized processor and, in said computerized processor, automatically determining phase correction parameters for a phase correction of at least one of said first data and said second data, said phase correction parameters defining a difference curve of a phase difference between said second phase curve and said first phase curve, depending on correlations between data in said second phase correction data set and data in said first phase correction data set.
2. A method as claimed in claim 1 wherein said first phase correction data set comprises at least one first series of pixels extending in a first direction, and wherein said second phase correction data set comprises at least one second series of pixels extending in said first direction, and comprising determining said phase correction parameters as multiple coefficients of a power series in a coordinate of said first direction.
3. A method as claimed in claim 2 , comprising determining the coefficients of the series depending on correlations
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evaluated for a plurality of coordinates along the first direction, wherein S 1 (x n ) is a datum of the first phase correction data set at a position x n and S 2 (x n ) is a datum of the second phase correction data set at the position x n .
4. A method as claimed in claim 3 , comprising determining a coefficient (Δφ) 1 of a term of the 1st order of a power series is determined.
5. A method as claimed in claim 4 , comprising the coefficient (Δφ) 1 of the term of the 1st order by an evaluation of the variable
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wherein f(x n ) is a real-value function.
6. A method as claimed in claim 2 comprising determining the multiple coefficients of the series by determining at least one coefficient of a power of the order ≧2 in the coordinate of the first direction.
7. A method as claimed in claim 2 comprising determining the phase correction parameters respectively for individual segments among multiple segments that are offset relative to each other along said first direction.
8. A method as claimed in claim 1 comprising determining said phase correction parameters by spatially weighting at least one of said data of said first phase correction data set and said data of said second phase correction data set.
9. A method as claimed in claim 8 comprising spatially weighting said at least one of said data of said first phase correction data set and said data of said second phase correction data set using a weighting factor selected from the group consisting of weighting factors that depend on a position of a segment of an examination subject from which said first phase correction data set and said second phase correction data set were acquired, and weighting factors dependent on a position of an isocenter of said magnetic resonance data acquisition unit.
10. A method as claimed in claim 1 comprising acquiring said first and second correction data sets using echo signals selected from the group consisting of spin echo signals and gradient echo signals, by reading out at least one echo signal to a acquire said first phase correction data set and reading out at least one additional echo signal, different from said at least one echo signal, to acquire said second phase correction data set.
11. A method as claimed in claim 1 comprising:
operating said magnetic resonance data acquisition unit to acquire at least one third phase correction data set having a third phase curve; and
in said processor, determining additional phase correction parameters that characterize a difference curve between said third phase curve and said first phase curve, depending on at least one correlation between data of said at least one third phase correction data set and data of said first phase correction data set.
12. A method to determine phase correction parameters for first data and second data acquired with a magnetic resonance data acquisition unit, said first data and said second data respectively representing different segments of a magnetic resonance exposure that exhibit respectively different background phase curves, said method comprising the steps of:
operating said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve; and
supplying said first and second phase correction data sets to a computerized processor and, in said computerized processor, automatically determining phase correction parameters for phase correction of at least one of said first data set and said second data set, dependent on said first phase correction data set and said second phase correction data set by spatially weighting data from at least one of said first phase correction data set and data of said second phase correction data set.
13. A method as claimed in claim 12 comprising spatially weighting said at least one of said data of said first phase correction data set and said data of said second phase correction data set using a weighting factor selected from the group consisting of weighting factors that depend on a position of a segment of an examination subject from which said first phase correction data set and said second phase correction data set were acquired, and weighting factors dependent on a position of an isocenter of said magnetic resonance data acquisition unit.
14. A method as claimed in claim 12 comprising:
operating said magnetic resonance data acquisition unit to acquire said first data and said second data from said different regions of said MR exposure, that respectively exhibit different background phase curves; and
in said processor, phase correcting at least one of said first data and said second data using said phase correction parameters.
15. A method as claimed in claim 14 comprising phase correcting only said first data or only said second data with said phase correction parameters.
16. A magnetic resonance system comprising:
a magnetic resonance data acquisition unit adapted to interact with an examination subject;
a computerized control unit configured to operate said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve; and
a computerized processor supplied with said first and second phase correction data sets, said computerized processor being configured to automatically determine phase correction parameters for a phase correction of at least one of said first data and said second data, said phase correction parameters defining a difference curve of a phase difference between said second phase curve and said first phase curve, depending on correlations between data in said second phase correction data set and data in said first phase correction data set, and to make said correction parameters available in electronic form at an output of said processor.
17. A magnetic resonance system comprising:
a magnetic resonance data acquisition unit adapted to interact with an examination subject;
a computerized control unit configured to operate said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve; and
a computerized processor supplied with said first and second phase correction data sets, said computerized processor being configured to automatically determining phase correction parameters for phase correction of at least one of said first data set and said second data set, dependent on said first phase correction data set and said second phase correction data set by spatially weighting data from at least one of said first phase correction data set and data of said second phase correction data set, and to automatically phase-correct at least one of said first and second data sets using said phase correction parameters.
18. A non-transitory computer-readable storage medium encoded with programming instructions, said storage medium being loadable into a computerized control and processing system of a magnetic resonance system, said magnetic resonance system also comprising a magnetic resonance data acquisition unit that is adapted to interact with an examination subject, said programming instructions causing said computerized control and processing system to:
operate said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve;
automatically determine phase correction parameters for a phase correction of at least one of said first data and said second data, said phase correction parameters defining a difference curve of a phase difference between said second phase curve and said first phase curve, depending on correlations between data in said second phase correction data set and data in said first phase correction data set; and
make said correction parameters available in electronic form at an output of said processor.
19. A non-transitory computer-readable storage medium encoded with programming instructions, said storage medium being loadable into a computerized control and processing system of a magnetic resonance system, said magnetic resonance system also comprising a magnetic resonance data acquisition unit that is adapted to interact with an examination subject, said programming instructions causing said computerized control and processing system to:
operate said magnetic resonance data acquisition unit to acquire first phase correction data and second phase correction data, said first phase correction data having a first phase curve and said second phase correction data having a second phase curve that differs from said first phase curve;
automatically determine phase correction parameters for phase correction of at least one of said first data set and said second data set, dependent on said first phase correction data set and said second phase correction data set by spatially weighting data from at least one of said first phase correction data set and data of said second phase correction data set; and
automatically phase-correct at least one of said first and second data sets using said phase correction parameters.