AbstractPurposeSusceptibility maps reconstructed from thin slabs may suffer underestimation due to background‐field removal imperfections near slab boundaries and the increased difficulty of solving a 3D‐inversion problem with reduced support, particularly in the direction of the main magnetic field. Reliable QSM reconstruction from thin slabs would enable focal acquisitions in a much‐reduced scan time.MethodsThis work proposes using additional rapid low‐resolution data of extended spatial coverage to improve background‐field estimation and regularize the inversion‐to‐susceptibility process for high resolution, thin slab data. The new method was tested using simulated and in‐vivo brain data of high resolution (0.33 × 0.33 × 0.33 mm3 and 0.54 × 0.54 × 0.65 mm3, respectively) at 3T, and compared to the standard large volume approach.ResultsUsing the proposed method, in‐vivo high‐resolution QSM at 3T was obtained from slabs of width as small as 10.4 mm, aided by a lower‐resolution dataset of 24 times coarser voxels. Simulations showed that the proposed method produced more consistent measurements from slabs of at least eight slices. Reducing the mean ROI error to 5% required the low‐resolution data to cover ˜60 mm in the direction of the main field, have at least 2‐mm isotropic resolution that is not coarser than the high‐resolution data by more than four‐fold in any direction.ConclusionApplying the proposed method enabled focal QSM acquisitions at sub‐millimeter resolution within reasonable acquisition time.