Artifact due to Bo fluctuations in fMRI:: Correction using the k-space central line

Magnetic resonance experiments require the main magnetic field, B-O, to remain very stable, Several external sources, such as moving ferromagnetic objects and/or changing electromagnetic fields, can significantly change the value of B-O over time, This work describes an apparent displacement along the phase-encoding axis caused by a variation in B-O. This artifact was observed in fMRI images acquired with EPI, The effect was characterized and tested using an immobile phantom, The image displacement motion along the phase-encoding axis closely followed the changes in B-O. The phase of the central line in the Fourier space was successfully used to correct this artifact. Fluctuations in B-O may result in artifacts that mimic subject head motion, and must be appropriately corrected. Magn Reson Med 46:198-201, 2001, (C) 2001 Wiley-Liss, Inc.