Low spatial-frequency ripple artifacts in layer-fMRI EPI: Identification, cause, and mitigation strategies with Dual-polarity readout

High-resolution layer-fMRI has great potential to inform network-neuroscience. However, it is limited by EPI artifacts. Here, we discuss a class of fuzzy EPI ghosts arising from asymmetric trapezoidal gradients with ramp sampling. A meta analysis across layer-fMRI datasets finds this artifact everywhere, without exceptions. We believe that this artifact is constraining spatiotemporal resolutions more than SNR. In this abstract we aim to raise awareness for this artifact and evaluate mitigation strategies: dual-polarity EPI. We show that dual-polarity EPI allows layer-fMRI to break the barriers of current resolution limits: It allows 0.53mm imaging at 3T, and whole-brain 0.6mm fMRI at 7T.