A new EPI-based dynamic field mapping method: application to retrospective geometrical distortion corrections.
OBJECTIVE
To retrospectively correct for geometrical distortions, a new dynamic field mapping method suitable for dynamic single-shot gradient-echo type echo-planar imaging (GRE-EPI) is proposed.


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-dependent 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.


CONCLUSIONS
Given the minor increase in the acquisition time, this method is well suited for functional magnetic resonance imaging; prospective direction.
Lamberton
Franck
F
Unité Mixte de Recherche (UMR)6194 Centre National de Recherche Scientifique (CNRS), Commissariat à l'Energie Atomique (CEA), Université de Caen et Paris 5, Caen, France.
Delcroix
Nicolas
N
Grenier
Denis
D
Mazoyer
Bernard
B
Joliot
Marc
M
D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000473:pathology; D001931:Brain Mapping; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods; D019047:Phantoms, Imaging; D012044:Regression Analysis; D012189:Retrospective Studies; D012984:Software