• Magn Reson Med · Dec 2013

    B1+-mapping with the transient phase of unbalanced steady-state free precession.

    • Carl Ganter, Marcus Settles, Isabel Dregely, Francesco Santini, Klaus Scheffler, and Oliver Bieri.
    • Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
    • Magn Reson Med. 2013 Dec 1; 70 (6): 1515-23.

    PurposeA novel B1+-mapping technique (B1-TRAP) is presented, which derives the actual flip angle from the frequency of signal oscillations, observed in the transient phase of unbalanced steady-state free precession sequences.TheoryFor short repetition times (TR), the angular frequency of distinct oscillations in the transient phase of steady-state free precession sequences is proven to be approximately proportional to the actual flip angle: ω⋅TR≈α. The result is not influenced by off-resonance and it can be shown that deviations are only of second order in the small parameter TR/T2.MethodsB1-TRAP makes use of this effect through a frequency analysis of the transient phase of a train of steady-state free precession signals.ResultsIn terms of reliability and time efficiency, a two-dimensional multislice implementation was found to be optimal. Unlike many steady-state B1+-mapping methods, the accuracy of B1-TRAP was not impaired by imperfect slice profiles.ConclusionSimulations, phantom, and in vivo measurements showed that B1-TRAP offers a good compromise with respect to speed, robustness, and accuracy.Copyright © 2013 Wiley Periodicals, Inc.

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