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Multiecho sequences with variable refocusing flip angles: Optimization of signal behavior using smooth transitions between pseudo steady states (TRAPS)
Author(s) -
Hennig Juergen,
Weigel Matthias,
Scheffler Klaus
Publication year - 2003
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.10391
Subject(s) - flip angle , echo (communications protocol) , signal (programming language) , nuclear magnetic resonance , physics , spin echo , relaxation (psychology) , fast spin echo , steady state (chemistry) , acoustics , optics , computational physics , chemistry , computer science , magnetic resonance imaging , medicine , psychology , computer network , social psychology , radiology , programming language
A variation of the rapid acquisition with relaxation enhancement (RARE) sequence (also called turbo spin‐echo (TSE) or fast spin‐echo (FSE)) is presented. This technique uses variable flip angles along the echo train such that magnetization is initially prepared into the static pseudo steady state (PSS) for a low refocusing flip angle (α < 180°). It is shown that after such a preparation, magnetization will always stay very close to the static PSS even after significant variation of the subsequent refocusing flip angles. This allows the design of TSE sequences in which high refocusing flip angles yielding 100% of the attainable signal are applied only for the important echoes encoding for the center of k ‐space. It is demonstrated that a reduction of the RF power (RFP) by a factor of 2.5–6 can be achieved without any loss in signal intensity. The contribution of stimulated‐echo pathways leads to a reduction of the effective TE by a factor f t , which for typical implementations is on the order of 0.5–0.8. This allows the use of longer echo readout times, and thus longer echo trains, for acquiring images with a given T 2 contrast. Magn Reson Med 49:527–535, 2003. © 2003 Wiley‐Liss, Inc.