Optimizing EPI for Functional MRI using Multi-Directional Shimming in a Single Shot Acquisition

Jaemin Shin¹, Sinyeob Ahn¹, Xiaoping P. Hu¹

Susceptibility-induced field inhomogeneity is a major cause of signal loss in functional MRI. Z-shimming has been widely used in the slice selection (SS) direction. Shimming technique has been extended to the phase encoding (PE) direction. However, the gradient of a fixed amplitude in PE direction may not achieve the optimal signal recovery of whole brain. In this work, we describe a single shot EPI sequence that can optimally compensate for the inhomogeneity in both SS and PE directions. Signal recovery with only Z- shimming was only 38% of the optimal shimming in the two directions. In conclusion, multi directional shimming is better than Z-shimming alone for signal recovery in fMRI.