Estimation of field inhomogeneity map following magnitude-based ambiguity-resolved water-fat separation

• Published in: Magnetic resonance imaging Vol. 97; pp. 102 - 111
• Main Authors: Triay Bagur, Alexandre, McClymont, Darryl, Hutton, Chloe, Borghetto, Andrea, Gyngell, Michael L., Aljabar, Paul, Robson, Matthew D., Brady, Michael, Bulte, Daniel P.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.04.2023
• Subjects: B0 field; Fat-water swap; Humans; Liver; Magnetic Resonance Imaging - methods; MRI-PDFF; Proton density fat fraction; Protons; Reproducibility of Results; Water; B0 field; Proton density fat fraction; Fat-water swap; MRI-PDFF
• ISSN: 0730-725X; 1873-5894; 1873-5894
• DOI: 10.1016/j.mri.2023.01.002

Magnitude-based PDFF (Proton Density Fat Fraction) and R2∗ mapping with resolved water-fat ambiguity is extended to calculate field inhomogeneity (field map) using the phase images. The estimation is formulated in matrix form, resolving the field map in a least-squares sense. PDFF and R2∗ from magnitude fitting may be updated using the estimated field maps. The limits of quantification of our voxel-independent implementation were assessed. Bland-Altman was used to compare PDFF and field maps from our method against a reference complex-based method on 152 UK Biobank subjects (1.5 T Siemens). A separate acquisition (3 T Siemens) presenting field inhomogeneities was also used. The proposed field mapping was accurate beyond double the complex-based limit range. High agreement was obtained between the proposed method and the reference in UK. Robust field mapping was observed at 3 T, for inhomogeneities over 400 Hz including rapid variation across edges. Field mapping following unambiguous magnitude-based water-fat separation was demonstrated in-vivo and showed potential at 3 T.