A new EPI-based dynamic field mapping method: Application to retrospective geometrical distortion corrections

Purpose: To restrospectively correct for geometrical distortions, a new dynamic field mapping method suitable for dynamic single-short gradient-echo type echo-planar imaging (GRE-EPI) is proposed. Materials and Methods: The method requires a single volume additional acquisition and allows the extraction of a field map from each phase volume, assuming invariance across time of the echo time-independent phase component. Performances of the method are assessed using three sets of experiments: the first tests the prerequisite and the modeling; the second tests the method with time-depedent geometrical distortions; and the third presents a comparison with two other methods. Results: Our results legitimize the modeling procedure and demonstrate that the dynamic method is less sensitive to noise than the other methods. A theoretical explanation for this is proposed in the discussion section. Conclusion: Given the minor increase in the acquisition time, this method is well suited for functional magnetic resonance imaging; prospective direction.