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On the transient phase of balanced SSFP sequences
Author(s) -
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.10421
Subject(s) - flip angle , steady state free precession imaging , amplitude , transient (computer programming) , steady state (chemistry) , excitation , phase (matter) , physics , nuclear magnetic resonance , relaxation (psychology) , pulse (music) , atomic physics , free induction decay , slew rate , time constant , chemistry , optics , magnetic resonance imaging , spin echo , quantum mechanics , medicine , psychology , social psychology , detector , computer science , radiology , operating system , electrical engineering , voltage , engineering
The signal intensity of balanced steady‐state free precession (SSFP) imaging is a function of the proton density, T 1 , T 2 , flip angle (α), and repetition time (TR). The steady‐state signal intensity that is established after about 5* T 1 /TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady‐state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T 1 and T 2 relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k ‐space line. In addition, transient imaging of hyperpolarized nuclei, such as 3 He, 129 Xe, or 13 C, can be optimized according to their T 1 and T 2 relaxation times. Magn Reson Med 49:781–783, 2003. © 2003 Wiley‐Liss, Inc.