Optimized gradient spoiling of UTE VFA-AFI sequences for robust T1 estimation with B1-field correction

Abstract

Quantifying T1 relaxation times is a challenge because inhomogeneities of the B1 field have to be corrected to obtain proper values. It is a particular challenge in tissues with short T2⁎ values, for which conventional MRI techniques do not provide sufficient signal. Recently, a B1-field correction technique called AFI (Actual Flip angle Imaging) has been introduced that can be combined with UTE (ultra-short echo-time) sequences, which have much shorter echo times compared to conventional MRI techniques, allowing quantification of signal in short T2⁎ tissues. A disadvantage of AFI is that it requires very long relaxation delays between repetitions to minimize the influence of imperfect spoiling of transverse magnetization on signal behavior. In this work, we propose a novel spoiling scheme for the AFI sequence that efficiently provides accurate B1 correction maps with strongly reduced acquisition time. We validated the method with both phantom and preliminary in vivo results.