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Off‐resonance effects in the transient response of SSFP sequences
Author(s) -
Ganter Carl
Publication year - 2004
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.20173
Subject(s) - steady state free precession imaging , nuclear magnetic resonance , quasiperiodic function , physics , perturbation (astronomy) , steady state (chemistry) , perpendicular , larmor precession , computational physics , relaxation (psychology) , statistical physics , chemistry , magnetic field , magnetic resonance imaging , condensed matter physics , quantum mechanics , mathematics , medicine , psychology , social psychology , geometry , radiology
A previously developed eigenvector formalism is adapted to off‐resonance in the transient response of quasiperiodic steady‐state free precession (SSFP) sequences, including TrueFISP as a special case. The effective relaxation rates for essentially parallel and perpendicular deviations from the steady state are determined analytically in leading order perturbation theory. The latter are a known cause of oscillatory artifacts and therefore constitute the main target of a variety of preparation techniques. In addition, the former also play a dominating role in applications such as inversion recovery (IR) TrueFISP, which intentionally measure far away from the equilibrium. For both components, the approach toward equilibrium turns out to depend sensitively on field inhomogeneities, especially for smaller ratios of T 2 / T 1 . For the perpendicular deviations, the calculations show that—except very close to banding artifacts, where the steady‐state signal is almost zero—field inhomogeneities additionally increase their effective relaxation rate almost as much as in the free induction decay (FID). The analytical results are tested against numerical simulation and MR measurements. Magn Reson Med 52:368–375, 2004. © 2004 Wiley‐Liss, Inc.