Sub-millimeter T₁ mapping of rapidly relaxing compartments with gradient delay corrected spiral TAPIR and compressed...

The TAPIR sequence is an accurate and efficient method for T₁ 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 T₁ fitting performance. This is especially problematic for substances exhibiting rapid T₂^* relaxation (e.g., myelin water).

The T₁ 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.

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 T₁ 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.

Using a spiral read-out trajectory, the established TAPIR sequence enables measurement of rapidly relaxing T₁ compartments, while improving T₁ mapping performance and imaging speed.