Radu Mutihac1,
2, Allen Braun3, Thomas J. Balkin2
1Department
of Physics, University of Bucharest, Bucharest, Bucharest-Magurele, Romania; 2Psychiatry
& Neuroscience, Department of Behavioral Biology, Walter Reed Army
Institute of Research, Silver Spring, MD, United States; 3Language
Section, NIDCD / National Institutes of Health, Bethesda, MD, United States
Sleep data acquisition was carried out using uncommon low bandwidth in the phase encoding direction and low gradient amplitude for functional EPI readout resulting in low scanner noise, but substantially increasing the static magnetic field inhomogeneity. EPI images are prone to substantial signal dropout and spatial distortion in regions where the field is inhomogeneous. Two major sources of artifacts affect EPI reconstructions: Nyquist ghosts and geometric distortion. Post-processing optimization of geometric distortion correction in EPI FSE images based on paired field maps (magnitude and phase at different echo times)acquired at 3T in terms of spin-echo time difference is presented hereafter.