Quantitative susceptibility mapping in water–fat regions using in-phase echoes introduces significant quantification bias

Gradient echo imaging using in-phase echoes has been proposed to reduce the field-map estimation in water–fat regions to a convex nonlinear least squares problem. However, it is known that the fat spectrum is complex and the definition of in-phase echo times remains problematic. In this work, the in-phase assumption is compared to standard water–fat imaging with respect to field- and quantitative susceptibility-mapping. The in-phase assumption is shown to be associated with quantification bias when subsequently estimating the field map and magnetic susceptibility in the spine, the liver and the breast.