Improved body quantitative susceptibility mapping by using a variable‐layer single‐min‐cut graph‐cut for field‐mapping

Purpose To develop a robust algorithm for field‐mapping in the presence of water–fat components, large B0 field inhomogeneities and MR signal voids and to apply the developed method in body applications of quantitative susceptibility mapping (QSM). Methods A framework solving the cost‐function of the water–fat separation problem in a single‐min‐cut graph‐cut based on the variable‐layer graph construction concept was developed. The developed framework was applied to a numerical phantom enclosing an MR signal void, an air bubble experimental phantom, 14 large field of view (FOV) head/neck region in vivo scans and to 6 lumbar spine in vivo scans. Field‐mapping and subsequent QSM results using the proposed algorithm were compared to results using an iterative graph‐cut algorithm and a formerly proposed single‐min‐cut graph‐cut. Results The proposed method was shown to yield accurate field‐map and susceptibility values in all simulation and in vivo datasets when compared to reference values (simulation) or literature values (in vivo). The proposed method showed improved field‐map and susceptibility results compared to iterative graph‐cut field‐mapping especially in regions with low SNR, strong field‐map variations and high R2∗ values. Conclusions A single‐min‐cut graph‐cut field‐mapping method with a variable‐layer construction was developed for field‐mapping in body water–fat regions, improving quantitative susceptibility mapping particularly in areas close to MR signal voids.