Magnetic Susceptibility and Field Map Estimation in fMRI Time Series Using a High Resolution Static Field Map

Hiroyuki Takeda¹, Boklye Kim²

In practice, the field map dynamically changes with head motion during the scan, and such a changing field leads to variations in geometric distortions in EPI. A previous retrospective approach of approximating a dynamic field map by applying rigid body transformations to an observed static field map may be insufficient in the presence of significant out-of-plane rotations. Our approach is to retrospectively estimate the objects susceptibility map from an observed high-resolution static field map using an estimator derived from a probability density function of non-uniform noise. This approach is capable of finding the susceptibility map regardless of the wrapping effect.