Gisela E. Hagberg1,2, David Balla3, Hannes M. Wiesner4, Nikos K. Logothetis
1Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tbingen, Germany, Germany; 2Fondazione Santa Lucia, Rome, Italy; 3High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tubingen, Germany; 4High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Germany
We investigated localized fluctuations during resting state dynamics of 7T phase and magnitude fMRI signals (voxels of 98 and 64nl) at two echo times (13 and 36ms) in rats. We could confirm the presence of TE-dependent signal fluctuations mediated by BOLD susceptibility that was greatest in voxels with strong vascular components and decreased with the distance from such areas. Interestingly, both high phase and magnitude instabilities were observed in the callosal fibers, containing oriented white matter structures. In view of differences in susceptibility between these structures and the surrounding grey matter these fluctuations may result from minute displacements caused for instance by heart pulsations.