Echo time-range effects on gradient-echo based myelin water fraction mapping at 3T

Purpose: To investigate the effect of the range of TE on multi-echo gradient echo–based myelin water fraction (MWF) mapping at 3 T. Methods: Myelin water fraction estimation was performed using 3 widely used models: magnitude multipool, magnitude 3-pool, and complex 3-pool model. Simulations were conducted using a hollow cylinder model with susceptibility anisotropy. The TE range was varied, and its effect on MWF estimation was observed. The same analysis was also performed with in vivo data from 4 healthy volunteers. Results: Different MWFs were obtained depending on the range of TE data acquired. In the simulations, the results of both magnitude models had a bias with respect to the true values: a maximum bias of up to 20% for the multipool model, and a maximum bias of up to 8% for the 3-pool model. This bias was reduced using the complex 3-pool model (maximum bias was under 2%). These effects were also found in the in vivo data. The MWF values using the complex model was most stable with respect to the TE range. Conclusion: The results of the simulation and in vivo data suggest that MWF values fitted using magnitude models are more influenced by the TE range collected for fitting than using the complex model. The complex model is helpful in mitigating bias due to dependencies over the TE range selection.