Accelerated Simultaneous T₂ and T₂* Mapping of Multiple Sclerosis Lesions Using Compressed Sensing Reconstruction of Radial RARE-EPI MRI

(1) Background: Radial RARE-EPI MRI facilitates simultaneous T₂ and T₂* mapping (2in1-RARE-EPI). With modest undersampling (R = 2), the speed gain of 2in1-RARE-EPI relative to Multi-Spin-Echo and Multi-Gradient-Recalled-Echo references is limited. Further reduction in scan time is crucial for clinical studies investigating T₂ and T₂* as imaging biomarkers. We demonstrate the feasibility of further acceleration, utilizing compressed sensing (CS) reconstruction of highly undersampled 2in1-RARE-EPI. (2) Methods: Two-fold radially-undersampled 2in1-RARE-EPI data from phantoms, healthy volunteers (n = 3), and multiple sclerosis patients (n = 4) were used as references, and undersampled (R_extra = 1-12, effective undersampling R_eff = 2-24). For each echo time, images were reconstructed using CS-reconstruction. For T₂ (RARE module) and T₂* mapping (EPI module), a linear least-square fit was applied to the images. T₂ and T₂* from CS-reconstruction of undersampled data were benchmarked against values from CS-reconstruction of the reference data. (3) Results: We demonstrate accelerated simultaneous T₂ and T₂* mapping using undersampled 2in1-RARE-EPI with CS-reconstruction is feasible. For R_extra = 6 (TA = 01:39 min), the overall MAPE was ≤8% (T₂*) and ≤4% (T₂); for R_extra = 12 (TA = 01:06 min), the overall MAPE was <13% (T₂*) and <5% (T₂). (4) Conclusion: Substantial reductions in scan time are achievable for simultaneous T₂ and T₂* mapping of the brain using highly undersampled 2in1-RARE-EPI with CS-reconstruction.