Marta Bianciardi1, 2, Peter van Gelderen1, Jeff H. Duyn1
1Advanced MRI Section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States; 2A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States
Resonance frequency shifts observed from phase signals in gradient echo fMRI may provide information complementary to magnitude signals. However, because of confounding effects of instrumental and physiological noise, these signals are difficult to detect and rarely used. We demonstrate that optimized pre-processing improves detection of task-evoked and spontaneous changes in phase signals over large areas of the cortex. Comparison with magnitude data suggests that the observed phase signal originate from neuronal activity and represent susceptibility changes in pial and intracortical veins. They therefore provide complementary information to magnitude signals.