%0 Journal Article
%T Characterization of Phase-Based Methods Used for Transmission Field Uniformity Mapping: A Magnetic Resonance Study at 3.0 T and 7.0 T
%A Flavio Carinci
%A Davide Santoro
%A Federico von Samson-Himmelstjerna
%A Tomasz Dawid Lindel
%A Matthias Alexander Dieringer
%A Thoralf Niendorf
%J PLOS ONE
%D 2013
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0057982
%X Knowledge of the transmission field (B1+) of radio-frequency coils is crucial for high field (B0 = 3.0 T) and ultrahigh field (B0¡Ý7.0 T) magnetic resonance applications to overcome constraints dictated by electrodynamics in the short wavelength regime with the ultimate goal to improve the image quality. For this purpose B1+ mapping methods are used, which are commonly magnitude-based. In this study an analysis of five phase-based methods for three-dimensional mapping of the B1+ field is presented. The five methods are implemented in a 3D gradient-echo technique. Each method makes use of different RF-pulses (composite or off-resonance pulses) to encode the effective intensity of the B1+ field into the phase of the magnetization. The different RF-pulses result in different trajectories of the magnetization, different use of the transverse magnetization and different sensitivities to B1+ inhomogeneities and frequency offsets, as demonstrated by numerical simulations. The characterization of the five methods also includes phantom experiments and in vivo studies of the human brain at 3.0 T and at 7.0 T. It is shown how the characteristics of each method affect the quality of the B1+ maps. Implications for in vivo B1+ mapping at 3.0 T and 7.0 T are discussed.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057982