Characterization of airway mucus using quantitative MRI: an in vitro proof-of-concept study

A characteristic of chronic obstructive pulmonary disease is mucus hypersecretion. In this proof-of-concept study, we aimed to characterize airway mucus using a quantitative ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequence in a controlled in vitro synthetic mucus model to establish a technical foundation for future in vivo studies.

UTE double-echo steady-state (UTE-DESS) was performed to acquire the signal from free induction decay-like signal and spin/stimulated echo-like signal echoes; quantitative MRI parameters (T1, T2, and diffusivity) were estimated. Synthetic mucus phantoms were prepared using mucin (0.20%, 0.50%, and 1.0%) mixed with xanthan gum (0.10%, 0.25%, and 0.50%) to replicate the viscoelastic properties of human laryngeal mucus, and samples were embedded in 1% agar for imaging.

The mucus phantoms with varying concentrations of mucin and xanthan exhibited visual differences in color and opacity. Estimated T1 values were 2.23 ± 0.16, 2.37 ± 0.20, and 2.09 ± 0.18 s (mean ± standard deviation) for the three tubes with relative mucus concentrations of 1, 2.5, and 5, respectively. Corresponding T2 values were 806.6 ± 105.6, 687.4 ± 78.0, and 475.0 ± 41.3 ms, while diffusivity values were 2.36 ± 0.14, 2.31 ± 0.18, and 2.33 ± 0.18 µm²/ms for the three tubes. Only the T2 relaxation times showed a significant linear correlation with mucus concentration (r = -0.9998, p = 0.0112).

UTE-DESS MRI could be feasible for characterizing airway mucus. T2 relaxation time showed a strong inverse correlation with increasing mucus concentration, indicating its sensitivity to mucus content.

Question Can a novel quantitative ultrashort echo time MRI sequence noninvasively characterize airway mucus properties and overcome conventional lung imaging limitations in muco-obstructive diseases? Findings In this controlled in vitro model, UTE-DESS MRI mapping demonstrated that T2 relaxation times alone showed a strong inverse correlation with increasing mucus concentrations. Relevance statement This exploratory proof-of-concept establishes a technical foundation for radiation-free, noninvasive T2 mapping to monitor and phenotype chronic obstructive pulmonary disease and other mucoobstructive lung diseases in future in vivo studies.