@article{HollKupeDale:2010,
  author = {Holland, Dominic and Kuperman, Joshua M. and Dale, Anders
                  M.},
  title = {Efficient correction of inhomogeneous static magnetic
                  field-induced distortion in {Echo} {Planar} {Imaging}},
  journal = {NeuroImage},
  year = 2010,
  volume = 50,
  number = 1,
  pages = {175--183},
  month = {Mar.},
  abstract = {Single-shot Echo Planar Imaging (EPI) is one of the most
                  efficient magnetic resonance imaging (MRI) acquisition
                  schemes, producing relatively high-definition images in 100
                  ms or less. These qualities make it desirable for Diffusion
                  Tensor Imaging (DTI), functional MRI (fMRI), and Dynamic
                  Susceptibility Contrast MRI (DSC-MRI). However, EPI suffers
                  from severe spatial and intensity distortion due to B0 field
                  inhomogeneity induced by magnetic susceptibility
                  variations. Anatomically accurate, undistorted images are
                  essential for relating DTI and fMRI images with anatomical
                  MRI scans, and for spatial registration with other
                  modalities. We present here a fast, robust, and accurate
                  procedure for correcting EPI images from such spatial and
                  intensity distortions. The method involves acquisition of
                  scans with opposite phase encoding polarities, resulting in
                  opposite spatial distortion patterns, and alignment of the
                  resulting images using a fast nonlinear registration
                  procedure. We show that this method, requiring minimal
                  additional scan time, provides superior accuracy relative to
                  the more commonly used, and more time consuming, field
                  mapping approach. This method is also highly computationally
                  efficient, allowing for direct ~real-time~ implementation on
                  the MRI scanner. We further demonstrate that the proposed
                  method can be used to recover dropouts in gradient echo
                  (BOLD and DSC-MRI) EPI images.},
  keywords = {EPI distortion correction; fMRI dropout recovery; Nonlinear
                  registration; Reverse phase encoding},
  doi = {10.1016/j.neuroimage.2009.11.044}
}
 
