Phase unwrapping methods are discussed for water fat separation in magnetic resonance imaging(MRI). Weighted multi-grid algorithm is applied to solve the discrete partial differential equation of phase array. A new weight method is propased
which is composed from maximum gradient array and phase differential coefficient array.The residues and discontinuous points are labeled by this composed weight array
where the error propagation the process of can be restrained by residues and noises during solving the discrete partial differential equation. By means of the weighted least squares solutions for partial differential equations
the phase unwrapping starts from the high-quality regions and avoids the low-quality regions effectively to improve the reliability. The simulation data and experiments for brain scan on 0.3 T low field MRI system show the validity.
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