Single-shot multi-slice T1 mapping at high spatial resolution – Inversion-recovery FLASH with radial undersampling and iterative reconstruction.

Purpose: To develop a method for T1 mapping at high spatial resolution and for multiple slices. Methods: The proposed method emerges as a single-shot inversion-recovery experiment which covers the entire spin- lattice relaxation process by serial acquisitions of highly undersampled radial FLASH images, either in single-slice or multi-slice mode. Serial image reconstructions are performed in time-reversed order and first involve regularized nonline- ar inversion (NLINV) to estimate optimum coil sensitivity profiles. Subsequently, the coil profiles are fixed for the calcu- lation of differently T1-weighted frames and the resulting linear inverse problem is solved by a conjugate gradient (CG) technique. T1 values are obtained by pixelwise fitting with a Deichmann correction modified for multi-slice applications. Results: T1 accuracy was validated for a reference phantom. For human brain, T1 maps were obtained at 0.5 mm resolu- tion for single-slice acquisitions and at 0.75 mm resolution for up to 5 simultaneous slices (5 mm thickness). Correspond- ing T1 maps of the liver were acquired at 1 mm and 1.5 mm resolution, respectively. All T1 values were in agreement with literature data. Conclusion: Inversion-recovery sequences with highly undersampled radial FLASH images and NLINV/CG reconstruc- tion allow for fast, robust and accurate T1 mapping at high spatial resolution and for multiple slices.