Simultaneous variable flip angle - Actual flip angle imaging method for improved accuracy and precision of three-dimensional T 1 and B 1 measurements

摘要

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 1maps. 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.