Model-based estimation of T2 maps with dual-echo steady-state MR imaging

Fast and accurate quantification of spin-spin relaxation parameter T₂ is of importance for clinical MRI applications. Classical spin echo (SE) sequences yield straightforward T₂ estimates, but require undesirably long scans. By contrast, steady-state sequences such as the Dual-Echo Steady-State (DESS) sequence are considerably faster, but produce signals that depend on more complex functions of both desired and nuisance parameters. Conventional method-of-moments estimators exhibit systematic error because of the approximations used to bypass nuisance parameter estimation. To improve T₂ mapping accuracy, we propose a novel, model-based approach to this nonlinear estimation problem. We use a fast scan to estimate nuisance parameters M₀^* and T₁, and then use the exact DESS signal model for regularized T₂ estimation from DESS data, with minimal approximations. MR brain simulation results show that the proposed approach substantially improves T₂ estimation accuracy and precision, compared to conventional method-of-moments estimators.