Patient-to-patient variation of susceptibility-induced B0 field in bilateral breast MRI

Purpose: To evaluate intersubject variability of susceptibility-induced static field inhomogeneity in breast and to assess effectiveness of whole-body high-order shimming applied to bilateral breast. Materials and Methods: A fast, computationally efficient method to calculate susceptibility-induced static field from anatomical images was developed. The method was validated against the conventional multiecho B0 mapping method and was used to generate data for linear and higher-order shim simulation on 13 volunteers. Results: Most volunteers showed a significant anteriorposterior B0 gradient. The majority of the subjects also exhibited a statistically significant leftright gradient. The second- and third-order shimming provided only minor (<5% each) improvement in B0 homogeneity. Conclusion: The shape of the airtissue boundary determines most of the observed B0 distribution in bilateral breast. Despite significant variability among subjects, a common feature traceable to generic anatomy exists in the linear gradient. Nonlinear variation of susceptibility-induced B0 field occurs over a relatively short length scale and is likely best shimmed by slice-dependent or localized shimming. J. Magn. Reson. Imaging 2012;36:873880. (c) 2012 Wiley Periodicals, Inc.