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Missing pulse steady‐state free precession
Author(s) -
Patz S.,
Wong S. T. S.,
Roos M. S.
Publication year - 1989
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.1910100205
Subject(s) - steady state free precession imaging , precession , flip angle , pulse (music) , physics , spins , nuclear magnetic resonance , signal (programming language) , steady state (chemistry) , contrast (vision) , free induction decay , computational physics , spin echo , optics , chemistry , magnetic resonance imaging , computer science , condensed matter physics , detector , medicine , radiology , programming language
A fast imaging technique, missing pulse steady‐state free precession (MP‐SSFP), is described. MP‐SSFP is one of a class of steady‐state free precession techniques in which every n th RF pulse is missing. MP‐SSFP has been implemented for the case where every third RF pulse is omitted: {‐θ 1 ,‐τ‐θ 2 ‐echo‐τ‐}. A RF‐refocused echo forms at the time of the missing pulse. This echo is less sensitive to field inhomogeneities than the gradient‐recalled echoes used in most fast imaging methods. An analytical expression is obtained for the signal strength as a function of the flip angles θ 1 and θ 2 , the interpulse interval τ, and the amount of interpulse dephase. The expression shows that θ 1 and θ 2 provide two degrees of freedom to optimize the signal‐to‐noise ratio and improve tissue contrast. Two different cases, θ 1 =θ 2 and θ 1 = ‐θ 2 , are described to demonstrate the difference in contrast. The first case gives a strong signal from spins with short T 1 and short T 2 while the second case has contrast very similar to a conventional SSFP technique. The theoretical expression predicts that the signal consists of multiple components which may be observed experimentally by adjusting the gradient pulses.