Method of B0 Mapping With Magnitude-Based Correction for Bipolar Two-Point Dixon Cardiac MRI

Purpose: The conventional two-point (2pt) Dixon technique explicitly estimates B0 map by performing phase unwrapping. When signal loss, phase singularity, artifacts, or spatially isolated regions corrupt the measured phase images, this unwrapping-based technique will face difficulty. This work aims to improve the reliability of B0 mapping by performing unwrapping error correction. Method: To detect the unwrapping-caused phase errors, we determined a magnitude-based fat/ water mask and used it as reference to identify pixels being mismatched by the phasebased mask, which was derived from the B0-corrected phase term of the Hermitian product between echoes. Then, we corrected the afore-determined phase error on a region-by-region basis. We tested the developed method with nine patients' data, and the results were compared with a well-established region-growing technique. Results: By adding the step to correct unwrapping-caused error, we improved the robustness of B0 mapping, resulting in better fat-water separation when compared with the conventional 2pt and the phasor-based region-growing techniques. Conclusion: We showed the feasibility of B0 mapping with bipolar 2pt human cardiac data. The software is freely available to the scientific community. (C) 2016 International Society for Magnetic Resonance in Medicine.