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Flip‐angle mapping of 31 P coils by steady‐state MR spectroscopic imaging
Author(s) -
Chmelík Marek,
Považan Michal,
Jírů Filip,
Kukurová Ivica Just,
Dezortová Monika,
Krššák Martin,
Bogner Wolfgang,
Hájek Milan,
Trattnig Siegfried,
Valkovič Ladislav
Publication year - 2014
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.24401
Subject(s) - flip angle , nuclear magnetic resonance , excitation , homogeneity (statistics) , physics , image quality , materials science , magnetic resonance imaging , nuclear medicine , computational physics , optics , mathematics , computer science , medicine , radiology , quantum mechanics , statistics , artificial intelligence , image (mathematics)
Purpose Phosphorus ( 31 P) MR spectroscopic imaging (MRSI) is primarily applied with sensitive, surface radiofrequency (RF) coils that provide inhomogeneous excitation RF field (B 1 + ) and rough localization due to their B 1 + and sensitivity (B 1 − ) profiles. A careful and time‐consuming pulse adjustment and an accurate knowledge of flip angle (FA) are mandatory for quantification corrections. Materials and Methods In this study, a simple, fast, and universal 31 P B 1 + mapping method is proposed, which requires fast steady‐state MRSI (typically one sixth of normal measurement time) in addition to the typical MRSI acquired within the examination protocol. The FA maps are calculated from the ratio of the signal intensities acquired by these two measurements and were used to correct for the influence of B 1 + on the metabolite maps. Results In vitro tests were performed on two scanners (3 and 7 Tesla) using a surface and a volume coil. The calculated FA maps were in good agreement with adjusted nominal FAs and the theoretical calculation using the Biot‐Savart law. The method was successfully tested in vivo in the calf muscle and the brain of healthy volunteers (n = 4). The corrected metabolite maps show higher homogeneity compared with their noncorrected versions. Conclusion The calculated FA maps helped with B 1 + inhomogeneity corrections of acquired in vivo data, and should also be useful with optimization and testing of pulse performances, or with the construction quality tests of new dual‐channel 1 H/ 31 P coils. J. Magn. Reson. Imaging 2014;40:391–397 . © 2013 Wiley Periodicals, Inc .