Separation and identification of water and fat MR images at mid-field strength with reduced T2/T2* weighting

A method to identify water and fat magnetic resonance images comprising:

• a) obtaining nuclear magnetic resonance image data from a first MR echo signal (S1) and a second MR echo signal (S2), where water and fat signals are orthogonal in the first MR echo signal, and water and fat signals are parallel or anti-parallel in the second MR echo signal;
• b) generating a corrected first MR echo signal (S1′) and a corrected second MR echo signal (S2′) by applying a phase unwrapping algorithm to correct for background magnetic field inhomogeneties
• c) determining an intermediate matrix of complex data for the corrected first MR echo signal based on a group of corrected echo signals consisting of S1′ and S2′;
• d) distinguishing whether a reference used in the phase-unwrapping algorithm is water-dominant or fat-dominant according to the intermediate matrix of complex data;
• and
• e) generating water images and fat images from the corrected first and second MR echo signals knowing whether the reference is water dominant or fat-dominant.

The method to identify water and fat magnetic resonance images comprising:

• a) obtaining nuclear magnetic resonance image data from a first MR echo signal (S1) and a second MR echo signal (S2), where water and fat signals are orthogonal in the first MR echo signal, and water and fat signals are parallel or anti-parallel in the second MR echo signal;
• b) generating a corrected first MR echo signal (S1′) and a corrected second MR echo signal (S2′) by applying a phase unwrapping algorithm to correct for background magnetic field inhomogeneties;
• c) determining an intermediate matrix of complex data for the corrected first MR echo signal;
• d) distinguishing whether a reference used in the phase-unwrapping algorithm is water-dominant or fat-dominant according to the intermediate matrix of complex data;
• e) generating water images and fat images from the corrected first and second MR echo signals knowing whether the reference is water dominant or fat-dominant, and
• wherein the intermediate matrix (S1″) of complex data is determined according to the following algorithm:
• S1″R(S1′)iI(S1′)(−1)n1
• where n1 is an integer number determined by a timing sequence.

A method to identify water and fat magnetic resonance images comprising:

• a) obtaining nuclear magnetic resonance image data from a first MR echo signal (S1) and a second MR echo signal (S2), where water and fat signals are orthogonal in the first MR echo signal, and water and fat signals are parallel or anti-parallel in the second MR echo signal;
• b) generating a corrected first MR echo signal (S1′) and a corrected second MR echo signal (S2′) by applying a phase unwrapping algorithm to correct for background magnetic field inhomogeneties;
• c) determining an intermediate matrix of complex data for the corrected first MR echo signal;
• d) distinguishing whether a reference used in the phase-unwrapping algorithm is water-dominant or fat-dominant according to the intermediate matrix of complex data;
• e) generating water images and fat images from the corrected first and second MR echo signals knowing whether the reference is water dominant or fat-dominant, and
• wherein, if the seed reference is fat dominate, the water image (Iw) is determined according to the following algorithm:
• I W = 1 2 ⁢ [LeftBracketingBar] R ⁡ ( S 1 ′ ) + I ⁡ ( S 1 ′ ) ⁢ ( - 1 ) n 1 ⁢ ( 2 + ( - 1 ) n 2 ) - S 2 ′ [RightBracketingBar]
• where n1 and n2 are integers determined by a timing sequence, and the fat image (IF) is determined according to the following algorithm:
• I F = 1 2 ⁢ [LeftBracketingBar] R ⁡ ( S 1 ′ ) + I ⁡ ( S 1 ′ ) ⁢ ( - 1 ) ( n 2 - n 1 + 1 ) + S 2 ′ [RightBracketingBar] .

A method to identify water and fat magnetic resonance images comprising:

• a) obtaining nuclear magnetic resonance image data from a first MR echo signal (S1) and a second MR echo signal (S2), where water and fat signals are orthogonal in the first MR echo signal, and water and fat signals are parallel or anti-parallel in the second MR echo signal;
• b) generating a corrected first MR echo signal (S1′) and a corrected second MR echo signal (S2′) by applying a phase unwrapping algorithm to correct for background magnetic field inhomogeneties;
• c) determining an intermediate matrix of complex data for the corrected first MR echo signal;
• d) distinguishing whether a reference used in the phase-unwrapping algorithm is water-dominant or fat-dominant according to the intermediate matrix of complex data;
• e) generating water images and fat images from the corrected first and second MR echo signals knowing whether the reference is water dominant or fat-dominant, and
• wherein, if the reference is water dominate, the water image (Iw) is determined according to the following algorithm:
• I W = 1 2 ⁢ [LeftBracketingBar] R ⁡ ( S 1 ′ ) + I ⁡ ( S 1 ′ ) ⁢ ( - 1 ) ( n 2 - n 1 ) + S 2 ′ [RightBracketingBar]
• where n1 and n2 are integer numbers determined by a timing sequence, and the fat image (IF) is determined according to the following algorithm:
• I F = 1 2 ⁢ [LeftBracketingBar] R ⁡ ( S 1 ′ ) + I ⁡ ( S 1 ′ ) ⁢ ( - 1 ) n 1 + 1 ⁢ ( 2 + ( - 1 ) n 2 ) - S 2 ′ [RightBracketingBar] .

A method of separating and identifying water and fat magnetic resonance (MR) images using an MRI apparatus, comprising:

• a) obtaining nuclear magnetic resonance (NMR) image data from at least a first MR echo signal and a second MR echo signal, where water and fat signals are orthogonal in the first MR echo signal and water and fat signals are either parallel or anti-parallel in the second MR echo signal;
• b) obtaining a field map of background main magnetic field from the second MR echo signal by applying a seed-guided phase unwrapping algorithm to the image data obtained from the second MR echo signal;
• c) removing an effect of the background field inhomogeneties according to the field map to yield a corrected first MR echo signal and a corrected second MR echo signal;
• d) calculating an intermediate data for the corrected first MR echo image according to sequence parameters of data acquisition;
• e) summing an imaginary portion of the intermediate data;
• f) distinguishing whether a seed reference used in applying the phase unwrapping is water-dominant or fat-dominant based on a polarity of the sum of the imaginary portion of the intermediate data, and
• g) determining water and fat images based on a group of corrected MR echo images consisting of the corrected first and second MR echo images, and based on whether the seed reference is water-dominant or fat-dominant.

A method of separating and identifying water and fat magnetic resonance (MR) images using an MRI apparatus, comprising:

• a) obtaining nuclear magnetic resonance (NMR) image data from at least a first MR echo signal (S1) and a second MR echo signal (S2), where water and fat signals are orthogonal in the first MR echo signal and water and fat signals are either parallel or anti-parallel in the second MR echo signal, and the echo signals are defined as follows:
• S 1 = ( W + F ⁢ ⁢ ⅇ - ⅈ ⁡ ( 1 2 + n 1 ) ⁢ π ) ⁢ ⅇ - ⅈ ⁢ ⁢ ϕ , ⁢ and S 2 = ( W + F ⁢ ⁢ ⅇ - ⅈ ⁢ ⁢ n 2 ⁢ π ) ⁢ ⅇ - ⅈλ ⁢ ⁢ ϕ
• where W represents an echo signal from precessing water nuclei, F represents an echo signal from precessing fat nuclei, n1 and n2 are integer numbers determined by a timing sequence;
• φ is a static magnetic field (BO) inhomogeneity-induced phase;
• and λ is equal to n2/(½+n1);
• b) obtaining a field map of background main magnetic field (P) from the second MR echo signal by applying a seed-guided phase unwrapping algorithm to the image data obtained from the second MR echo signal according to P = 1 2 ⁢ λ ⁢ unwrap ⁢ { arg ⁡ ( S 2 × S 2 ) } ,
• where arg() is an operation which yields a principal phase angle of a complex input, and unwrap represents algorithms for phase unwrapping to yield true phase angles from the principal values;
• c) removing the effect of background field inhomogeneties according to the unwrapped field map to yield a corrected first MR echo signal (S1′) and a corrected second MR echo signal (S2′);
• d) calculating an intermediate data for the corrected first MR echo signal according to sequence parameters of data acquisition;
• e) summing an imaginary portion of the intermediate data;
• f) distinguishing whether a seed reference used in applying the phase unwrapping is water-dominant or fat-dominant based on the polarity of the sum of the imaginary portion of the intermediate data, and
• g) determining water and fat images from the corrected first and second MR echo images based on whether the seed reference is water-dominant or fat-dominant.