Sources of distortion in functional MRI data

Functional magnetic resonance image (fMRI) experiments rely on the ability to detect subtle signal changes in magnetic resonance image time series. An y areas of signal change that correlate with the neurological stimulus can then be identified and compared with a corresponding high-resolution anatom ical scan. This report reviews some of the several artefacts that are frequ ently present in fMRI data, degrading their quality and hence their interpr etation. Zn particular, the effects of magnetic field inhomogeneities are d escribed, both on echo planar imaging (EPI) data and on spiral imaging data . The modulation of these distortions as the subject moves in the magnet is described. The effects of gradient coil nonlinearities and EPI ghost corre ction schemes are also discussed. (C) 1999 Wiley-Liss, Inc.