Robust Susceptibility Weighted Imaging Using Single-Slab 3D GRASE with Removal of Background Phase Variation

Hahnsung Kim¹, Dong-Hyun Kim¹, Jaeseok Park²

In susceptibility weighted imaging, it is important to remove background phase variations while retaining only local field information. The projection onto dipole field method was recently introduced, employing image-based convolution with ROI masks to decompose a background field within the ROI into one originating from dipoles outside the ROI. However, the image-based convolution is sensitive to rapid field variations at the boundaries of the ROI, leading to loss of important phase information particularly at the air-tissue interfaces. To regionally correct rapid phase aliasing at the boundaries while locally removing smoothly varying background phases, we develop a robust SWI method employing: 1) Single-slab 3D GRASE to simultaneously acquire both artifact-free magnitude images from spin echo and phase images from free induction decay signals, 2) Removal of rapid background field at the boundaries using forward field calculation, and 3) Removal of local background field with the ROI extended to the boundaries to preserve susceptibility induced phase information over the entire image.