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Dear Wangyehong, this is the so-called susceptibility artefact, a common MRI artefact, especially in gradient-echo EPIs. It is absolutely normal that the EPIs look distorted and the anatomical (T1-weighted) volume is affected to a (much) lesser extent. Artefacts are pronounced near the orbitofrontal lobe (at the border to the paranasal sinuses) and in temporal lobe (near the ear channel). In general this is no problem for analyses. If you're specifically interested in regions like the OFC you might want to try to reduce the arefacts by changing slice orientation though, see for example Weiskop et al. (2006) http://dx.doi.org/10.1016/j.neuroimage.2006.07.029 and Weiskopf et al. (2007) http://dx.doi.org/10.1007/s10334-006-0067-6 Best, Helmut