Abstract #2791

Zhao F, Wang P, Jin T, Nagaoka T, Harel N, Hu X, Kim S

The phase change of MRI signal was observed in both BOLD fMRI and CBV-weighted fMRI. For BOLD fMRI, the positive phase change is dominated in the large draining vein area and the negative phase change is also detected in the surrounding area. For CBV-weighted fMRI, the negative phase change is dominated in the middle cortex area where the highest CBV change occurred during the brain activation and the positive change is detected in the surrounding area. All these phase changes are caused by the volume-averaged magnetization change due to Lorentz Sphere effect and the demagnetization effect. The fMRI phase change can be used as the complementary information for the mechanism studies of fMRI and help to interpret the physiology change associated with the brain activation.