Fat Fraction Bias Correction Using T-1 Estimates and Flip Angle Mapping

PurposeTo develop a new method of reducing T-1 bias in proton density fat fraction (PDFF) measured with iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). Materials and MethodsPDFF maps reconstructed from high flip angle IDEAL measurements were simulated and acquired from phantoms and volunteer L4 vertebrae. T-1 bias was corrected using a priori T-1 values for water and fat, both with and without flip angle correction. Signal-to-noise ratio (SNR) maps were used to measure precision of the reconstructed PDFF maps. PDFF measurements acquired using small flip angles were then compared to both sets of corrected large flip angle measurements for accuracy and precision. ResultsSimulations show similar results in PDFF error between small flip angle measurements and corrected large flip angle measurements as long as T-1 estimates were within one standard deviation from the true value. Compared to low flip angle measurements, phantom and in vivo measurements demonstrate better precision and accuracy in PDFF measurements if images were acquired at a high flip angle, with T-1 bias corrected using T-1 estimates and flip angle mapping. ConclusionT(1) bias correction of large flip angle acquisitions using estimated T-1 values with flip angle mapping yields fat fraction measurements of similar accuracy and superior precision compared to low flip angle acquisitions. J. Magn. Reson. Imaging 2014;39:217-223. (c) 2013 Wiley Periodicals, Inc.