Premium
Rapid radiofrequency field mapping in vivo using single‐shot STEAM MRI
Author(s) -
Helms Gunther,
Finsterbusch Jürgen,
Weiskopf Nikolaus,
Dechent Peter
Publication year - 2008
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.21676
Subject(s) - flip angle , distortion (music) , signal (programming language) , calibration , nuclear magnetic resonance , field (mathematics) , radiofrequency coil , physics , excitation , scanner , materials science , optics , electromagnetic coil , mathematics , computer science , magnetic resonance imaging , medicine , radiology , amplifier , optoelectronics , cmos , quantum mechanics , pure mathematics , programming language
Abstract Higher field strengths entail less homogeneous RF fields. This may influence quantitative MRI and MRS. A method for rapidly mapping the RF field in the human head with minimal distortion was developed on the basis of a single‐shot stimulated echo acquisition mode (STEAM) sequence. The flip angle of the second RF pulse in the STEAM preparation was set to 60° and 100° instead of 90°, inducing a flip angle‐dependent signal change. A quadratic approximation of this trigonometric signal dependence together with a calibration accounting for slice excitation‐related bias allowed for directly determining the RF field from the two measurements only. RF maps down to the level of the medulla could be obtained in less than 1 min and registered to anatomical volumes by means of the T 2 ‐weighted STEAM images. Flip angles between 75% and 125% of the nominal value were measured in line with other methods. Magn Reson Med 60:739–743, 2008. © 2008 Wiley‐Liss, Inc.