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Increased flexibility in GRASE imaging by k space‐banded phase encoding
Author(s) -
Feinberg David A.,
Johnson Glyn,
Kiefer Berthold
Publication year - 1995
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.1910340204
Subject(s) - echo (communications protocol) , sampling (signal processing) , fourier transform , phase (matter) , spin echo , signal (programming language) , k space , computer science , modulation (music) , nuclear magnetic resonance , residual , physics , optics , fourier analysis , spatial frequency , algorithm , acoustics , magnetic resonance imaging , detector , medicine , computer network , quantum mechanics , radiology , programming language
GRASE (GRadient and Spin Echo) is an echo train imaging technique that combines gradient and RF refocusing. Although overall signal decay is with T 2 and field inhomogeneity phase errors do not accumulate, the small residual phase errors are periodic with echo number. The echo order described previously eliminates the phase error periodicity in k space but instead creates periodicity in the T 2 modulation function that can also cause artifacts. In addition, with this order, the effective TE must be half the echo train time, and asymmetric Fourier sampling is difficult to implement. A new method is described that greatly reduces artifacts due to T 2 decay, permits greater control of T 2 contrast, and lends itself to asymmetric Fourier sampling. Different time segments of the echo train are encoded with different bands of spatial frequency in k space (hence “ k banding”). Both computer simulations and experimental results demonstrate improvements in GRASE images acquired by this method.