Fast T2 Mapping with Improved Accuracy Using Undersampled Spin-echo MRI   and Model-based Reconstructions with a Generating Function
  A model-based reconstruction technique for accelerated T2 mapping with improved accuracy is proposed using undersampled Cartesian spin-echo MRI data. The technique employs an advanced signal model for T2 relaxation that accounts for contributions from indirect echoes in a train of multiple spin echoes. An iterative solution of the nonlinear inverse reconstruction problem directly estimates spin-density and T2 maps from undersampled raw data. The algorithm is validated for simulated data as well as phantom and human brain MRI at 3 T. The performance of the advanced model is compared to conventional pixel-based fitting of echo-time images from fully sampled data. The proposed method yields more accurate T2 values than the mono-exponential model and allows for undersampling factors of at least 6. Although limitations are observed for very long T2 relaxation times, respective reconstruction problems may be overcome by a gradient dampening approach. The analytical gradient of the utilized cost function is included as Appendix. 
Tilman J. Sumpf (1), Andreas Petrovic (2), Martin Uecker (3), Florian   Knoll (4), Jens Frahm (1) ((1) Biomedizinische NMR F...
physics.med-ph cs.CE q-bio.QM