Chronic obstructive pulmonary disease, or COPD, is defined in part by mucus hypersecretion, and the plugs that form when excess mucus accumulates in the airways are increasingly recognized as markers of declining lung function and heightened exacerbation risk. Yet measuring that mucus directly has long been difficult. Bronchoscopy, the gold standard for visualizing mucus, is invasive, costly, and limited to regions beyond the medium-sized bronchi, while conventional magnetic resonance imaging struggles in the lung because of low proton density and rapid signal decay at air-tissue interfaces. A new proof-of-concept study now reports that a quantitative ultrashort echo time MRI sequence, applied to carefully controlled synthetic mucus samples in the laboratory, can track mucus concentration through a single measurable parameter: the T2 relaxation time.
The study, published in European Radiology Experimental, tested a sequence known as ultrashort echo time double-echo steady-state, or UTE-DESS. The concentrations were raised in tandem to simulate the pathophysiological progression of mucus thickening in airway disease, so the team measured what they call the total relative mucus concentration rather than pure mucus concentration alone.
Preparation of the phantoms was deliberately meticulous. Each mucin solution was placed on an adjustable-speed rocker and mixed at 4 degrees Celsius for 24 hours to ensure complete dissolution and homogeneity. The corresponding xanthan gum concentrations were then added, and the samples were mixed for another 24 hours under the same refrigerated conditions to achieve stable viscoelastic properties. After thorough mixing, the samples were stored at 4 degrees Celsius until imaging. Before scanning, the mucus solutions were transferred into syringes and embedded in 1 percent agar to provide mechanical support, prevent leakage, and ensure consistent positioning. Visual examination confirmed the phantoms were distinct: increasing mucus concentration produced a progressively darker appearance and reduced transparency, qualitatively confirming successful preparation before any MRI work began.
Imaging took place on a 3-Tesla clinical scanner, a MAGNETOM Prisma from Siemens Healthineers, using a receive-only 32-channel head coil. The UTE-DESS protocol used flip angles of 10 or 30 degrees, a repetition time of 15 milliseconds, an echo time for the free induction decay-like signal of just 0.03 milliseconds, gradient amplitudes of 6 or 24 mT/m, a gradient pulse width of 5 milliseconds, a field of view of 200 by 200 by 192 cubic millimeters, a matrix size of 400 by 400 by 400, a readout bandwidth of 113.6 kilohertz, and a scan time of 225 seconds per scan across four scans. A vendor-provided B1 mapping sequence, taking roughly 20 seconds, estimated the actual flip angle. The phantom was allowed to equilibrate at room temperature for two hours before acquisition to ensure thermal stability at approximately 20 degrees Celsius.
The physics behind UTE-DESS is what makes it attractive for lung work. The sequence builds on steady-state free precession signal formation, in which repeated radiofrequency pulses with a constant net gradient moment establish steady-state magnetization. Because that gradient moment is non-zero, the signal splits into two components: a free induction decay-like signal observed immediately after each pulse, and a spin or stimulated echo-like signal measured before the subsequent pulse, which is weighted by the combined T1 relaxation time, T2 relaxation time, and diffusivity of water molecules. By varying the flip angle to adjust T1 weighting and the gradient moment to adjust diffusion weighting, and by fitting the acquired signals to the steady-state signal model, the researchers could simultaneously estimate proton density, T1, T2, and diffusivity from a single acquisition scheme.
The resulting numbers tell a clear story. The estimated T1 values were 2.23 plus or minus 0.16 seconds, 2.37 plus or minus 0.20 seconds, and 2.09 plus or minus 0.18 seconds for the three tubes with relative mucus concentrations of 1, 2.5, and 5, respectively. The corresponding T2 values were 806.6 plus or minus 105.6 milliseconds, 687.4 plus or minus 78.0 milliseconds, and 475.0 plus or minus 41.3 milliseconds, falling steadily as concentration rose. Diffusivity values, by contrast, barely moved: 2.36 plus or minus 0.14, 2.31 plus or minus 0.18, and 2.33 plus or minus 0.18 square micrometers per millisecond across the same three tubes. Only the T2 relaxation times showed a significant linear correlation with total relative mucus concentration, with a Pearson correlation coefficient of -0.9998 and a p-value of 0.0112.
That near-perfect inverse relationship is the study’s central finding. The technical images themselves also behaved as the signal model predicts: lower gradient moments and higher flip angles produced contrast dominated by T2 relaxation, higher flip angles strengthened T1 weighting, and the free induction decay-like signal was minimally affected by diffusion weighting while the echo-like signal showed varying diffusion weighting depending on the gradient moment applied.
The clinical context gives the work its urgency. COPD is the fourth leading cause of death worldwide, responsible for approximately 3.5 million deaths in 2021 and accounting for 5 percent of all global deaths, with cases projected to reach 600 million by 2050. Oxidative stress and protease-antiprotease imbalance in the disease promote goblet cell hyperplasia and reduce ciliated cells, driving both increased mucus production and impaired mucociliary clearance. Previous studies have demonstrated significant associations between mucus plug scores and reduced functional outcomes, including lower forced expiratory volume and decreased peripheral oxygen saturation. Mucus plugs can impair ventilation, limit oxygen diffusion, create local hypoxia that favors microbial growth, disrupt airway clearance, and contribute to ventilation-perfusion mismatch that may progress toward hypoxemia and respiratory failure.
Most previous imaging studies of airway mucus in COPD have relied on chest computed tomography rather than MRI, because CT offers high spatial resolution and wide availability for visualizing mucus plugs, airway wall thickness, and emphysema in medium-sized airways. MRI has historically been less suitable for this task, but ultrashort echo time sequences have recently emerged as promising tools for direct lung visualization, and recent studies suggest UTE-MRI can provide diagnostic performance comparable to high-resolution CT while avoiding ionizing radiation. The authors expect that in future work with COPD patients, the free induction decay-like signal of UTE-DESS will provide morphological information about lung tissues, while the echo-like signal and fitted T2 parameters will provide information about mucus itself.
The researchers are careful about what the study does and does not establish. Because mucin and xanthan gum concentrations were varied simultaneously, the individual effects of each component on T2 relaxation cannot be distinguished, though they note that the total solid-to-liquid ratio is the primary driver of mucus plugging and disease severity from a clinical perspective. The linear correlation analysis rested on only three concentration levels, making the statistical interpretation highly exploratory despite the encouraging near-perfect linearity. The phantom does not fully replicate the biochemical and biophysical properties of native airway mucus, the absence of respiratory motion limits applicability to clinical lung imaging, no reference standard comparison with other sequences was performed, and no intra- or inter-session repeatability data were collected. The relatively long acquisition time compared to CT may also restrict clinical feasibility in patients with severe COPD. Future work will pursue accelerated imaging with compressed sensing and parallel imaging, motion compensation through respiratory gating, application in COPD patients and healthy controls, ex vivo studies with human sputum, and extension to cystic fibrosis and other bronchiectatic diseases. For now, the study stands as a technical foundation: a demonstration that a radiation-free MRI sequence can, in a controlled laboratory model, detect mucus concentration through T2 alone.
Subject of Research: Quantitative ultrashort echo time MRI for characterizing airway mucus in synthetic phantoms
Article Title: Characterization of airway mucus using quantitative MRI: an in vitro proof-of-concept study
Article References: Sedaghat, S., Park, J. I., Fu, E., Piran, M., Ghasemiesfe, A., Jung, Y., & Jang, H. (2026). Characterization of airway mucus using quantitative MRI: an in vitro proof-of-concept study. European Radiology Experimental, 10(1), Article 163. https://doi.org/10.1186/s41747-026-00842-8
Image Credits: AI Generated
DOI: 10.1186/s41747-026-00842-8
Keywords: MRI, airway mucus, COPD, ultrashort echo time, T2 relaxation, phantom study, mucus plugging, lung imaging, UTE-DESS, diffusivity, muco-obstructive disease, radiation-free imaging
News Source: Ophelia Keating. (October 27, 2026). Research report: Characterization of airway mucus using quantitative MRI: an in vitro proof-of-concept study. Scienmag.
