INADEQUACY OF MOTION CORRECTION ALGORITHMS IN FUNCTIONAL MRI - ROLE OF SUSCEPTIBILITY-INDUCED ARTIFACTS

Functional MR (fMR) has been useful in providing insight into the loca lization and detection of neural cortical activity. However, patient h ead motion is inevitable over the course of most fMR experiments. Alth ough methods to align the control and activation fMR images may correc t for some of this motional error, they will be incomplete in correcti ng for those that depend on spatial orientation. MR signal amplitude o f structures that lie along air-tissue interfaces, for example, are se nsitive to susceptibility errors introduced by their reorientation wit h respect to the main magnetic field. This analysis, using phantoms, c adaver brain, and volunteers, has shown that this reorientation betwee n control and activation images can create regions of ''false activati on'' that increase in area with rotation. Anatomic regions that are ex pected to be most affected by these susceptibility-induced magnetic he ld homogeneity variations are those adjacent to bone or air, such as t he mesial and inferior temporal lobes and the inferior and anterior fr ontal lobes. Interpretation of ''activation'' in these areas on fMR st udies must be performed with careful consideration of this important s ource of error.