Multi-echo spin-echo (MSE) transverse relaxometry mapping using multicomponent models is used to study disease activity in neuromuscular disease by assessing the T2 of the myocytic component (T2water). Current extended phase graph algorithms are not optimized for fat fractions above 50% and the effects of inaccuracies in the T2fat calibration remain unexplored. Hence, we aimed to improve the performance of extended phase graph fitting methods over a large range of fat fractions, by including the slice-selection flip angle profile, a through-plane chemicalshift displacement correction, and optimized calibration of T.