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Field-map based distortion correction. (a): Phase field-map generated from the dual-echo gradient echo sequence. The frontal lobe close to the sinuses is typically affected (region R1). (b): Axial acquisition with EPI distortion (b=0s/mm2, phase-encoding direction: anterior to posterior). (c): Corrected image. (d): Coronal acquisition with distortion (sagittal view, phase-encoding direction: head to foot). (e): Corrected image. The red circles highlight regions of high distortion.
