Junmin Liu1, Dana C Peters2, Maria Drangova1,3. 1. Imaging Research Laboratories, Robarts Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada. 2. Department of Radiology and Biomedical Imaging, Yale Medical School, New Haven, Connecticut, USA. 3. Department of Medical Biophysics, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
Abstract
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 phase-based 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. Magn Reson Med 78:1862-1869, 2017.
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 phase-based 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. Magn Reson Med 78:1862-1869, 2017.