Ultrafast and robust T 2 mapping using optimized single-shot multi-echo planar imaging with alternating blips

To develop a rapid, motion-robust $T_2$ mapping technique suitable for clinical use across the body, including traditionally challenging, motion-prone patient populations or body parts.

A novel single-shot multi-echo spin-echo EPI sequence with alternating phase encoding direction on each echo was implemented. This sequence acquires multiple echoes to measure $T_2$ from a single RF excitation. The alternating phase encoding gradient polarity enables the correction of geometric distortions in EPI using post-processing software. Stimulated echoes were removed by optimizing spoiler gradients. Diffusion MRI can also be achieved by incorporating diffusion-encoding gradients.

Phantom experiments showed no significant difference between measured and reference $T_2$ values, indicating high precision and repeatability. In vivo, brain $T_2$ maps exhibited similar anatomical detail and tissue contrast as a reference sequence, with $T_2$ values of 70.0  $\pm$  4.0 ms for gray matter, 56.8  $\pm$  3.4 ms for the white matter at a magnetic field strength of 3 Tesla. High-quality diffusion-weighted images with minimal distortion were generated, even at high b-values. $T_2$ mapping results from the kidney and fetal brain showcased the method's applicability across different anatomical regions and patient populations.

The single-shot multi-echo EPI sequence provided a basis for rapid, accurate $T_2$ relaxation mapping by correcting distortion and mitigating motion artifacts. This sequence enhances the clinical feasibility of quantitative $T_2$ mapping across diverse patient populations and body areas.