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Simultaneous variable flip angle–actual flip angle imaging method for improved accuracy and precision of three‐dimensional T 1 and B 1 measurements
Author(s) -
Hurley Samuel A.,
Yarnykh Vasily L.,
Johnson Kevin M.,
Field Aaron S.,
Alexander Andrew L.,
Samsonov Alexey A.
Publication year - 2012
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.23199
Subject(s) - flip angle , variable (mathematics) , magnetic resonance imaging , echo time , computer science , nuclear magnetic resonance , nuclear medicine , algorithm , mathematics , physics , medicine , mathematical analysis , radiology
A new time‐efficient and accurate technique for simultaneous mapping of T 1 and B 1 is proposed based on a combination of the actual flip angle (FA) imaging and variable FA methods. Variable FA–actual FA imaging utilizes a single actual FA imaging and one or more spoiled gradient‐echo acquisitions with a simultaneous nonlinear fitting procedure to yield accurate T 1 / B 1 maps. The advantage of variable FA–actual FA imaging is high accuracy at either short T 1 times or long repetition times in the actual FA imaging sequence. Simulations show this method is accurate to 0.03% in FA and 0.07% in T 1 for ratios of repetition time to T1 time over the range of 0.01–0.45. We show for the case of brain imaging that it is sufficient to use only one small FA spoiled gradient‐echo acquisition, which results in reduced spoiling requirements and a significant scan time reduction compared to the original variable FA method. In vivo validation yielded high‐quality 3D T 1 maps and T 1 measurements within 10% of previously published values and within a clinically acceptable scan time. The variable FA–actual FA imaging method will increase the accuracy and clinical feasibility of many quantitative MRI methods requiring T 1 / B 1 mapping such as dynamic contrast enhanced perfusion and quantitative magnetization transfer imaging. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.