Dynamic oxygen-enhanced MRI of the lung at 3 T: feasibility, repeatability and reproducibility

Purpose: Dynamic T1-weighted lung oxygen enhanced MRI (OE-MRI) is challenging at 3 T due to decreased longitudinal relaxivity of oxygen and increased magnetic susceptibility difference between air and tissue interfaces relative to 1.5 T, leading to poor signal quality. In this work, we evaluate the robustness of an alternative T2*-sensitised lung dynamic OE-MRI protocol in humans at 3 T. Methods: Simulations were performed to predict OE contrast behaviour and optimise the MRI protocol. Sixteen healthy subjects underwent dynamic free-breathing OE-MRI acquisitions using a dual echo RF-spoiled gradient echo acquisition at 3 T on two MRI scanners at different institutions. Non-linear registration and tissue density variation correction were applied. Percent signal enhancement (PSE) maps and ΔR2* were derived. Intra-class correlation coefficient (ICC) and Bland-Altman analyses were used to evaluate reproducibility of the OE indices across two sites and vendors as well as scan-rescan repeatability. Results: Simulations and experimental data show negative contrast on oxygen inhalation due to substantial dominance of ΔR2* at TE longer than 0.2 ms when using our chosen flip angle and TR. Mean PSE values were TE dependent and mean ΔR2* was 0.14 ms-1 ± 0.03 ms-1, ICC values for intra-scanner (ICCintra) and inter-scanner (ICCinter) variability for OE indices were high (ICCintra > 0.74; ICCinter = 0.70) and 95% limits of agreement showed strong agreement of repeated measures. Conclusion: Our results demonstrate excellent scan-rescan repeatability for the PSE indices and good reproducibility for ΔR2* across two sites and vendors, suggesting potential utility in multi-centre clinical studies.