Feasibility of dynamic T₂ *-based oxygen-enhanced lung MRI at 3T

Purpose: To demonstrate proof-of-concept of a T₂ *-sensitized oxygen-enhanced MRI (OE-MRI) method at 3T by assessing signal characteristics, repeatability, and reproducibility of dynamic lung OE-MRI metrics in healthy volunteers.

Methods: We performed sequence-specific simulations for protocol optimisation and acquired free-breathing OE-MRI data from 16 healthy subjects using a dual-echo RF-spoiled gradient echo approach at 3T across two institutions. Non-linear registration and tissue density correction were applied. Derived metrics included percent signal enhancement (PSE), ∆R₂ * and wash-in time normalized for breathing rate (τ-nBR). Inter-scanner reproducibility and intra-scanner repeatability were evaluated using intra-class correlation coefficient (ICC), repeatability coefficient, reproducibility coefficient, and Bland-Altman analysis.

Results: Simulations and experimental data show negative contrast upon oxygen inhalation, due to substantial dominance of ∆R₂ * at TE > 0.2 ms. Density correction improved signal fluctuations. Density-corrected mean PSE values, aligned with simulations, display TE-dependence, and an anterior-to-posterior PSE reduction trend at TE₁ . ∆R₂ * maps exhibit spatial heterogeneity in oxygen delivery, featuring anterior-to-posterior R₂ * increase. Mean T₂ * values across 32 scans were 0.68 and 0.62 ms for pre- and post-O₂ inhalation, respectively. Excellent or good agreement emerged from all intra-, inter-scanner and inter-rater variability tests for PSE and ∆R₂ *. However, ICC values for τ-nBR demonstrated limited agreement between repeated measures.

Conclusion: Our results demonstrate the feasibility of a T₂ *-weighted method utilizing a dual-echo RF-spoiled gradient echo approach, simultaneously capturing PSE, ∆R₂ * changes, and oxygen wash-in during free-breathing. The excellent or good repeatability and reproducibility on intra- and inter-scanner PSE and ∆R₂ * suggest potential utility in multi-center clinical applications.