Improved T1 mapping with Iterative Actual Flip-angle Imaging (iAFI) Technique

Introduction: Accurate measurement of T1 is essential for many quantitative MRI techniques, such as dynamic contrast enhanced MRI. Variable flip angle (VFA) spoiled gradient echo imaging is one of the most widely used methods for T1 mapping [1]. However, this technique often suffers from flip angle inaccuracies due to inhomogeneous RF fields and slice profile effects [2]. Actual flip-angle imaging (AFI) technique [3] was recently developed to measure the actual flip angle (and equivalently, actual B1) and has been used in conjunction with VFA for improved accuracy [4]. One of the shortcomings of the AFI technique is that the method assumes that T1 is much longer than the repetition time (TR). When this assumption is violated, large errors can result for both the flip angle and T1. We propose an iterative AFI (iAFI) method which yields more accurate T1 values, particularly for relatively short T1s, and which does not require that TR << T1.