Journal
NEUROIMAGE
Volume 50, Issue 1, Pages 175-183Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.neuroimage.2009.11.044
Keywords
EPI distortion correction; fMRI dropout recovery; Nonlinear registration; Reverse phase encoding
Funding
- NIH [AG031224, NS056883, AG22381, AG18386]
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [U54NS056883] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE ON AGING [R01AG018386, R01AG022381, R01AG031224] Funding Source: NIH RePORTER
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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 B(0) 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. (C) 2009 Elsevier Inc. All rights reserved.
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