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Pseudo Steady‐State Free Precession for MR‐Fingerprinting
Author(s) -
Assländer Jakob,
Glaser Steffen J.,
Hennig Jürgen
Publication year - 2017
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.26202
Subject(s) - steady state (chemistry) , flip angle , dephasing , precession , imaging phantom , physics , nuclear magnetic resonance , steady state free precession imaging , signal (programming language) , spin echo , magnetic resonance imaging , computer science , condensed matter physics , chemistry , optics , programming language , medicine , radiology
Purpose This article discusses the signal behavior in the case the flip angle in steady‐state free precession sequences is continuously varied as suggested for MR‐fingerprinting sequences. Flip angle variations prevent the establishment of a steady state and introduce instabilities regarding to magnetic field inhomogeneities and intravoxel dephasing. We show how a pseudo steady state can be achieved, which restores the spin echo nature of steady‐state free precession. Methods Based on geometrical considerations, relationships between the flip angle, repetition and echo time are derived that suffice to the establishment of a pseudo steady state. The theory is tested with Bloch simulations as well as phantom and in vivo experiments. Results A typical steady‐state free precession passband can be restored with the proposed conditions. The stability of the pseudo steady state is demonstrated by comparing the evolution of the signal of a single isochromat to one resulting from a spin ensemble. As confirmed by experiments, magnetization in a pseudo steady state can be described with fewer degrees of freedom compared to the original fingerprinting and the pseudo steady state results in more reliable parameter maps. Conclusion The proposed conditions restore the spin‐echo‐like signal behavior typical for steady‐state free precession in fingerprinting sequences, making this approach more robust to B 0 variations. Magn Reson Med 77:1151–1161, 2017. © 2016 International Society for Magnetic Resonance in Medicine