Image-based EPI ghost correction using an algorithm based on projection onto convex sets (POCS).
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.
Lee
K J
KJ
Department of Academic Radiology, Royal Hallamshire Hospital, University of Sheffield, Sheffield, UK. k.j.lee@sheffield.ac.uk
Barber
D C
DC
Paley
M N
MN
Wilkinson
I D
ID
Papadakis
N G
NG
Griffiths
P D
PD
D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology; D017352:Echo-Planar Imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods