Quantitative T₂ mapping using accelerated 3D stack-of-spiral gradient echo readout

To develop a rapid T₂ mapping protocol using optimized spiral acquisition, accelerated reconstruction, and model fitting.

A T₂-prepared stack-of-spiral gradient echo (GRE) pulse sequence was applied. A model-based approach joined with compressed sensing was compared with the two methods applied separately for accelerated reconstruction and T₂ mapping. A 2-parameter-weighted fitting method was compared with 2- or 3-parameter models for accurate T₂ estimation under the influences of noise and B₁ inhomogeneity. The performance was evaluated using both digital phantoms and healthy volunteers. Mitigating partial voluming with cerebrospinal fluid (CSF) was also tested.

Simulations demonstrates that the 2-parameter-weighted fitting approach was robust to a large range of B₁ scales and SNR levels. With an in-plane acceleration factor of 5, the model-based compressed sensing-incorporated method yielded around 8% normalized errors compared to references. The T₂ estimation with and without CSF nulling was consistent with literature values.

This work demonstrated the feasibility of a T₂ quantification technique with 3D high-resolution and whole-brain coverage in 2-3 min. The proposed iterative reconstruction method, which utilized the model consistency, data consistency and spatial sparsity jointly, provided reasonable T₂ estimation. The technique also allowed mitigation of CSF partial volume effect.