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Bloch‐Siegert B 1 + ‐mapping for human cardiac 31 P‐MRS at 7 Tesla
Author(s) -
Clarke William T.,
Robson Matthew D.,
Rodgers Christopher T.
Publication year - 2016
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.26005
Subject(s) - phosphocreatine , nuclear magnetic resonance , physics , flip angle , skeletal muscle , magnetic resonance imaging , medicine , anatomy , energy metabolism , radiology
Purpose Phosphorus MR spectroscopy ( 31 P‐MRS) is a powerful tool for investigating tissue energetics in vivo. Cardiac 31 P‐MRS is typically performed using surface coils that create an inhomogeneous excitation field across the myocardium. Accurate measurements ofB 1 +(and hence flip angle) are necessary for quantitative analysis of 31 P‐MR spectra. We demonstrate a Bloch‐SiegertB 1 + ‐mapping method for this purpose. Theory and Methods We compare acquisition strategies for Bloch‐SiegertB 1 + ‐mapping when there are several spectral peaks. We optimize a Bloch‐Siegert sensitizing (Fermi) pulse for cardiac 31 P‐MRS at 7 Tesla (T) and apply it in a three‐dimensional (3D) chemical shift imaging sequence. We validate this in phantoms and skeletal muscle (against a dual‐TR method) and present the first cardiac 31 PB 1 + ‐maps at 7T. Results The Bloch‐Siegert method correlates strongly (Pearson's r = 0.90 and 0.84) and has bias <25 Hz compared with a multi‐TR method in phantoms and dual‐TR method in muscle. Cardiac 3DB 1 + ‐maps were measured in five normal volunteers.B 1 +maps based on phosphocreatine and alpha‐adenosine‐triphosphate correlated strongly (r = 0.62), confirming that the method is T 1 insensitive. Conclusion The 3D 31 P Bloch‐SiegertB 1 + ‐mapping is consistent with reference methods in phantoms and skeletal muscle. It is the first method appropriate for 31 PB 1 + ‐mapping in the human heart at 7T. Magn Reson Med 76:1047–1058, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.