Method for geometric distortion correction in fMRI based on three echo planar phase images

Functional magnetic resonance imaging (fMRI) is a quickly developing method for non-invasive dynamic brain studies. It uses swift acquisition sequences like echo planar imaging (EPI) that are very sensitive to susceptibility artifacts. These artifacts relate to magnetic field inhomogeneities and may cause geometric distortions. Many methods for correcting these distortions are currently used. Most common are the field mapping methods that use the map of field strength. To create a field map, different approaches can be used and different data must be acquired for each method. This paper compares a commonly used conventional gradient echo (GE) field mapping method with a 3EPI phase images based method. Although the EPI method is more sophisticated and was expected to perform better, the GE field maps showed better results in distortion correction. The cause of this is not in the method's principle itself, but in its high requirements.