Abstract
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 nonlinear inversion (NLINV) to estimate optimum coil sensitivity profiles. Subsequently, the coil profiles are fixed for the calculation 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 resolution for single-slice acquisitions and at 0.75 mm resolution for up to 5 simultaneous slices (5 mm thickness). Corresponding 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 reconstruction allow for fast, robust and accurate T1 mapping at high spatial resolution and for multiple slices.
Highlights
Rapid mapping of the spin-lattice relaxation process with quantitative evaluations of T1 relaxation times is widely used in clinical MRI
Initial studies focused on the human brain and combined a leading inversion pulse with a serial image acquisition scheme termed snapshot FLASH [1]
The actual determination of T1 values has been improved by advanced fitting routines which correct for the disturbance of the native relaxation recovery by repetitive low-flip angle excitations [5, 6], while recent model-based approaches attempt to calculate T1 maps directly from raw data, e.g. see [7]
Summary
The proposed method emerges as a single-shot inversion-recovery experiment which covers the entire spinlattice 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 nonlinear inversion (NLINV) to estimate optimum coil sensitivity profiles. The coil profiles are fixed for the calculation 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
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