Noninvasive Monitoring of the Response of Human Lungs to Low-Dose Lipopolysaccharide Inhalation Challenge Using MRI: A Feasibility Study

BACKGROUND

Development of antiinflammatory drugs for lung diseases demands novel methods for noninvasive assessment of inflammatory processes in the lung.

PURPOSE

To investigate the feasibility of hyperpolarized ¹²⁹ Xe MRI, ¹ H T₁ time mapping, and dynamic contrast-enhanced (DCE) perfusion MRI for monitoring the response of human lungs to low-dose inhaled lipopolysaccharide (LPS) challenge compared to inflammatory cell counts from induced-sputum analysis.

STUDY TYPE

Prospective feasibility study.

POPULATION

Ten healthy volunteers underwent MRI before and 6 hours after inhaled LPS challenge with subsequent induced-sputum collection.

FIELD STRENGTH/SEQUENCES

1.5T/hyperpolarized ¹²⁹ Xe MRI: Interleaved multiecho imaging of dissolved and gas phase, ventilation imaging, dissolved-phase spectroscopy, and chemical shift saturation recovery spectroscopy. ¹ H MRI: Inversion recovery fast low-angle shot imaging for T₁ mapping, time-resolved angiography with stochastic trajectories for DCE MRI.

ASSESSMENT

Dissolved-phase ratios of ¹²⁹ Xe in red blood cells (RBC), tissue/plasma (TP) and gas phase (GP), ventilation defect percentage, septal wall thickness, surface-to-volume ratio, capillary transit time, lineshape parameters in dissolved-phase spectroscopy, ¹ H T₁ time, blood volume, flow, and mean transit time were determined and compared to cell counts.

STATISTICAL TESTS

Wilcoxon signed-rank test, Pearson correlation.

RESULTS

The percentage of neutrophils in sputum was markedly increased after LPS inhalation compared to baseline, P = 0.002. The group median RBC-TP ratio was significantly reduced from 0.40 to 0.31, P = 0.004, and ¹ H T₁ was significantly elevated from 1157.6 msec to 1187.8 msec after LPS challenge, P = 0.027. DCE MRI exhibited no significant changes in blood volume, P = 0.64, flow, P = 0.17, and mean transit time, P = 0.11.

DATA CONCLUSION

Hyperpolarized ¹²⁹ Xe dissolved-phase MRI and ¹ H T₁ mapping may provide biomarkers for noninvasive assessment of the response of human lungs to LPS inhalation. By its specificity to the alveolar region, hyperpolarized ¹²⁹ Xe MRI together with ¹ H T₁ mapping adds value to sputum analysis.

LEVEL OF EVIDENCE

1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:1669-1676.

[Distribution and Environmental Risk of Pharmaceutically Active Compounds in the Traditionally Aqueous Phase of Effluent-receiving Rivers]

Colloid media are not only an important "sink" for pollutants in the aquatic environment, but also a crucial regulating unit for the biogeochemical cycle of pollutants. In this study, the distribution and environmental risk levels of ten typical pharmaceutically active compounds (PhACs) in the water phase of effluent-receiving rivers were investigated using cross-flow ultrafiltration, solid-phase extraction, and liquid chromatography-tandem mass spectrometry as the pretreatment and analysis methods. The results showed that the total concentrations of the ten PhACs in the dissolved phase and colloidal phase ranged from 27.2 to 168.1 ng·L^-1 and 164.5 to 751.1 ng·g^-1, respectively. Ibuprofen (IPF), roxithromycin (ROX), and erythromycin (ETM) are the dominating pollutants in the dissolved phase and colloidal phase, accounting for more than 80% of the total concentration. Strong adsorption properties for ROX, ketoconazole, ETM, and sertraline were found in the colloid phase, their colloid/water distribution coefficients (lgK_col) ranged from 3.2 to 4.0, and the percentage of PhACs absorbed to the colloidal phase reached 21.1%-34.5%. The risk assessment of acute and chronic toxicity to algae, daphnia, and fish showed that only IPF presented a high chronic risk to fish, while the risk levels of the other PhACs were at or below medium risk. It is worth noting that, in comparison with their acute risk, most PhACs have chronic negative effects on higher aquatic organisms.

Probing the regional distribution of pulmonary gas exchange through single-breath gas- and dissolved-phase 129Xe MR imaging

Although some central aspects of pulmonary function (ventilation and perfusion) are known to be heterogeneous, the distribution of diffusive gas exchange remains poorly characterized. A solution is offered by hyperpolarized 129Xe magnetic resonance (MR) imaging, because this gas can be separately detected in the lung's air spaces and dissolved in its tissues. Early dissolved-phase 129Xe images exhibited intensity gradients that favored the dependent lung. To quantitatively corroborate this finding, we developed an interleaved, three-dimensional radial sequence to image the gaseous and dissolved 129Xe distributions in the same breath. These images were normalized and divided to calculate "129Xe gas-transfer" maps. We hypothesized that, for healthy volunteers, 129Xe gas-transfer maps would retain the previously observed posture-dependent gradients. This was tested in nine subjects: when the subjects were supine, 129Xe gas transfer exhibited a posterior-anterior gradient of -2.00 ± 0.74%/cm; when the subjects were prone, the gradient reversed to 1.94 ± 1.14%/cm (P < 0.001). The 129Xe gas-transfer maps also exhibited significant heterogeneity, as measured by the coefficient of variation, that correlated with subject total lung capacity (r = 0.77, P = 0.015). Gas-transfer intensity varied nonmonotonically with slice position and increased in slices proximal to the main pulmonary arteries. Despite substantial heterogeneity, the mean gas transfer for all subjects was 1.00 ± 0.01 while supine and 1.01 ± 0.01 while prone (P = 0.25), indicating good "matching" between gas- and dissolved-phase distributions. This study demonstrates that single-breath gas- and dissolved-phase 129Xe MR imaging yields 129Xe gas-transfer maps that are sensitive to altered gas exchange caused by differences in lung inflation and posture.