T1-Corrected Fat Quantification Using Chemical Shift-Based Water/Fat Separation: Application to Skeletal Muscle

Chemical shift-based water/fat separation, like iterative decomposition of water and fat with echo asymmetry and least-squares estimation, has been proposed for quantifying intermuscular adipose tissue. An important confounding factor in iterative decomposition of water and fat with echo asymmetry and least-squares estimation-based intermuscular adipose tissue quantification is the large difference in T-1 between muscle and fat, which can cause significant overestimation in the fat fraction. This T-1 bias effect is usually reduced by using small flip angles. T-1-correction can be performed by using at least two different flip angles and fitting for T-1 of water and fat. In this work, a novel approach for the water/fat separation problem in a dual flip angle experiment is introduced and a new approach for the selection of the two flip angles, labeled as the unequal small flip angle approach, is developed, aiming to improve the noise efficiency of the T-1-correction step relative to existing approaches. It is shown that the use of flip angles, selected such the muscle water signal is assumed to be T-1-independent for the first flip angle and the fat signal is assumed to be T-1-independent for the second flip angle, has superior noise performance to the use of equal small flip angles (no T1 estimation required) and the use of large flip angles (T-1 estimation required). Magn Reson Med 66: 1312-1326, 2011. (C) 2011 Wiley Periodicals, Inc.