Sub‐millimeter T1 mapping of rapidly relaxing compartments with gradient delay corrected spiral TAPIR and compressed sensing at 3T

Purpose The TAPIR sequence is an accurate and efficient method for T 1 mapping. It combines a slice‐interleaving Look‐Locker read‐out with an acquisition of multiple k‐space lines in 1 shot. Whereas the acquisition of multiple lines per excitation increases imaging speed, the corresponding increase in TR and TE is detrimental to the T 1 fitting performance. This is especially problematic for substances exhibiting rapid T 2 * relaxation (e.g., myelin water). Methods The T 1 fitting performance of TAPIR is enhanced by using an interleaved spiral read‐out with shorter TE and TR. Furthermore, an improvement to a method for fast gradient delay estimation is presented. Whereas previous methods assume the gradient delay to be stationary, the presented approach corrects the spiral k‐space trajectory by using a polynomial fit of the measured gradient delays. Results Gradient delay artifacts are largely eliminated, requiring very little additional scanning time. The sampling efficiency of the spiral read‐out allows for a significant reduction of the acquisition time in comparison to Cartesian TAPIR. Spiral TAPIR enables the sampling of more slices and an accurate measurement of rapidly relaxing compartments. Over a wide T 1 range (448–3115 ms), spiral TAPIR reduces the mean fitting error from −2.5% to −0.1%. Combining 50% undersampling with the shorter TR of spiral TAPIR, an increase in imaging speed by a factor of up to 3.3 was achieved. Conclusion Using a spiral read‐out trajectory, the established TAPIR sequence enables measurement of rapidly relaxing T 1 compartments, while improving T 1 mapping performance and imaging speed.