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SSFP signal with finite RF pulses
Author(s) -
Bieri Oliver,
Scheffler Klaus
Publication year - 2009
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.22116
Subject(s) - steady state free precession imaging , signal (programming language) , flip angle , pulse (music) , radio frequency , physics , nuclear magnetic resonance , computer science , optics , telecommunications , magnetic resonance imaging , medicine , detector , radiology , programming language
Abstract The theoretical description of steady state free precession (SSFP) sequences is generally well accepted and unquestioned, although it is based on instantaneously acting radiofrequency (RF) pulses. In practice, however, all excitation processes are finite, thereby questioning the overall validity of the common SSFP signal description for use with finite RF pulses. In this paper, finite RF pulse effects on balanced SSFP signal formation are analyzed as a function of the RF time, the pulse repetition time, the flip angle (α) and relaxation times ( T 1,2 ). The observed signal modulations from finite RF pulses (compared to infinitesimal ones) can range from only a few percent (for RF time/pulse repetition time ≪ 1, α ≪ 90°, T 2 / T 1 ∼ 1) to over 10% (for RF time/pulse repetition time ≪ 1, α ∼ 90°, T 2 / T 1 ≪ 1) and may even exceed 100% in the limit of RF time/pulse repetition time → 1 (for α ∼ 90°, T 2 / T 1 ≪ 1). As a result, a revision of SSFP signal theory is indicated not only for reasons of completeness but also seems advisable, e.g., for all quantitative SSFP methods. A simple modification for the common balanced SSFP equation is derived that provides an accurate framework for SSFP signal description over a wide variety of practical and physiologic parameters. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.