Optimized 3D UTE and ZTE MRI for high-resolution lung imaging: A comparative study.

Purpose: To optimize and compare the performance of 3D UTE and zero echo time (ZTE) MRI sequences for high-resolution lung imaging at 3 T.

Methods: UTE and ZTE sequences were optimized for lung imaging through phantom studies, and in vivo experiments. Imaging parameters, including bandwidth (BW) and flip angle (FA), were systematically assessed to identify the optimal settings for both sequences. A novel transient UTE sequence was introduced to enhance the SNR by allowing magnetization recovery during the respiratory wait period. Numerical simulations and in vivo experiments were conducted to compare the SNR performance of the proposed transient UTE with conventional steady-state UTE.

Results: UTE imaging with a BW of ±125 kHz and an FA of 2° produced the sharpest lung images without noticeable artifacts. In contrast, ZTE imaging was optimal at a lower BW of ±62.5 kHz and an FA of 2°, but showed greater blurriness and more pronounced inhomogeneous excitation artifacts than UTE. The transient UTE sequence increased lung imaging SNR by approximately 11% to 20% compared to steady-state UTE without introducing obvious artifacts.

Conclusion: UTE outperformed ZTE in terms of image sharpness and artifact reduction for lung imaging. The proposed transient UTE sequence further enhanced SNR, demonstrating the potential for improved lung MRI quality and diagnostic accuracy.