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Abstract #0928

Inter-frame phase alignment for Echo Planar Imaging calibration data acquired with opposite read-out polarities

Yulin V Chang1, Kun Zhou2, W. Scott Hoge3, Uvo Hoelscher4, Wei Liu2, and Jonathan R Polimeni5

1Siemens Medical Solutions USA, Boston, MA, United States, 2Siemens Shenzhen Magnetic Resonance, Shenzhen, China, 3Brigham and Women's Hospital, Boston, MA, United States, 4Siemens Healthcare GmbH, Erlangen, Germany, 5Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, United States

Echo-planar imaging is subject to Nyquist ghosting due to its use of fast gradient switching. To correct for this artifact, several methods have been proposed that involve a pair of calibration imaging frames acquired with opposite readout polarities. We show that a small, relative shift in the phase-encoding direction often exists between these calibration frames that may lead to compromised image quality. A simple method is proposed to account for the shift and it is shown to be effective at correcting residual Nyquist ghost in the dual-polarity GRAPPA approach. This is demonstrated in in vivo and phantom data from 3T and 7T.

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