Artifact due to B₀ fluctuations in fMRI: Correction using the k-space central line

Magnetic resonance experiments require the main magnetic field, B₀, to remain very stable. Several external sources, such as moving ferromagnetic objects and/or changing electromagnetic fields, can significantly change the value of B₀ over time. This work describes an apparent displacement along the phase-encoding axis caused by a variation in B₀. 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 B₀. The phase of the central line in the Fourier space was successfully used to correct this artifact. Fluctuations in B₀ may result in artifacts that mimic subject head motion, and must be appropriately corrected.