Optimized gradient spoiling of UTE VFA-AFI sequences for robust T estimation with B-field correction.

Quantifying T relaxation times is a challenge because inhomogeneities of the B field have to be corrected to obtain proper values. It is a particular challenge in tissues with short T values, for which conventional MRI techniques do not provide sufficient signal. Recently, a B-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 T 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 B correction maps with strongly reduced acquisition time. We validated the method with both phantom and preliminary in vivo results.