T1 Measurements incorporating flip angle calibration and correction in vivo

In this work, we propose a variable FA method that combines in vivo flip angle (FA) calibration and correction with a short TR variable FA approach for a fast and accurate T1 mapping. The precision T1s measured across a uniform milk phantom is estimated to be 2.65% using the conventional (slow) inversion recovery (IR) method and 28.5% for the variable FA method without FA correction, and 2.2% when FA correction is included. These results demonstrate that the sensitivity of the variable FA method to RF nonuniformities can be dramatically reduced when these nonuniformities are directly measured and corrected. The acquisition time for this approach decreases to 10 min from 85 min for the conventional IR method. In addition, we report that the averaged T1s measured from five normal subjects are 900 ± 3 ms, 1337 ± 8 ms and 2180 ± 25 ms in white matter (WM), gray matter (GM) and cerebral spinal fluid (CSF) using the variable flip angle method with FA correction at 3 T, respectively. These results are consistent with previously reported values obtained with much longer acquisition times. The method reduces the total scan time for whole brain T1 mapping, including FA measurement and calibration, to approximately 6 min. The novelty of this method lies in the in vivo calibration and the correction of the FAs, thereby allowing a rapid and accurate T1 mapping at high field for many applications.