Simultaneous variable flip angle-actual flip angle imaging method for improved accuracy and precision of three-dimensional T1 and B1 measurements

A new time-efficient and accurate technique for simultaneous mapping of T1 and B1 ishttp://runonce.msn.com/runonce3.aspx proposed based on a combination of the actual flip angle (FA) imaging and variable FA methods. Variable FAactual 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 T1/B1 maps. The advantage of variable FAactual FA imaging is high accuracy at either short T1 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 T1 for ratios of repetition time to T1 time over the range of 0.010.45. 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 T1 maps and T1 measurements within 10% of previously published values and within a clinically acceptable scan time. The variable FAactual FA imaging method will increase the accuracy and clinical feasibility of many quantitative MRI methods requiring T1/B1 mapping such as dynamic contrast enhanced perfusion and quantitative magnetization transfer imaging. Magn Reson Med, 2012. (c) 2011 Wiley Periodicals, Inc.