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Image‐based EPI ghost correction using an algorithm based on projection onto convex sets (POCS)
Author(s) -
Lee K.J.,
Barber D.C.,
Paley M.N.,
Wilkinson I.D.,
Papadakis N.G.,
Griffiths P.D.
Publication year - 2002
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10101
Subject(s) - projection (relational algebra) , reduction (mathematics) , algorithm , line (geometry) , image (mathematics) , regular polygon , fourier transform , k space , phase (matter) , mathematics , space (punctuation) , physics , computer science , artificial intelligence , mathematical analysis , geometry , quantum mechanics , operating system
This work describes the use of a method, based on the projection onto convex sets (POCS) algorithm, for reduction of the N/2 ghost in echo‐planar imaging (EPI). In this method, ghosts outside the parent image are set to zero and a model k ‐space is obtained from the Fourier transform (FT) of the resulting image. The zeroth‐ and first‐order phase corrections for each line of the original k ‐space are estimated by comparison with the corresponding line in the model k ‐space. To overcome problems of phase wrapping, the first‐order phase corrections for the lines of the original k ‐space are estimated by registration with the corresponding lines in the model k ‐space. It is shown that applying these corrections will result in a reduction of the ghost, and that iterating the process will result in a convergence towards an image in which the ghost is minimized. The method is tested on spin‐echo EPI data. The results show that the method is robust and remarkably effective, reducing the N/2 ghost to a level nearly comparable to that achieved with reference scans. Magn Reson Med 47:812–817, 2002. © 2002 Wiley‐Liss, Inc.