Repeatability and robustness of MP-GRASP T₁ mapping

Purpose: To demonstrate the repeatability of fast 3D T₁ mapping using Magnetization-Prepared Golden-angle RAdial Sparse Parallel (MP-GRASP) MRI and its robustness to variation of imaging parameters including flip angle and spatial resolution in phantoms and the brain.

Theory and methods: Multiple imaging experiments were performed to (1) assess the robustness of MP-GRASP T₁ mapping to B₁ inhomogeneity using a single tube phantom filled with uniform MnCl₂ liquid; (2) compare the repeatability of T₁ mapping between MP-GRASP and inversion recovery-based spin-echo (IR-SE; over 12 scans), using a commercial T1MES phantom; (3) evaluate the longitudinal variation of T₁ estimation using MP-GRASP with varying imaging parameters, including spatial resolution, flip angle, TR/TE, and acceleration rate, using the T1MES phantom (106 scans performed over a period of 12 months); and (4) evaluate the variation of T₁ estimation using MP-GRASP with varying imaging parameters in the brain (24 scans in a single visit). In addition, the accuracy of MP-GRASP T₁ mapping was also validated against IR-SE by performing linear correlation and calculating the Lin's concordance correlation coefficient (CCC).

Results: MP-GRASP demonstrates good robustness to B₁ inhomogeneity, with intra-slice variability below 1% in the single tube phantom experiment. The longitudinal variability is good both in the phantom (below 2.5%) and in the brain (below 2%) with varying imaging parameters. The T₁ values estimated from MP-GRASP are accurate compared to that from the IR-SE imaging (R² = 0.997, Lin's CCC = 0.996).

Conclusion: MP-GRASP shows excellent repeatability of T₁ estimation over time, and it is also robust to variation of different imaging parameters evaluated in this study.