Microstructural Analysis of Peripheral Lung Tissue through CPMG Inter-Echo Time R2 Dispersion.

Area of Science:

• Medical Imaging and Physics
• Pulmonary Medicine
• Biophysics

Background:

• Lung microstructure changes are key indicators of early lung pathology, particularly emphysematous changes.
• Quantifiable data from challenging clinical cases, like peripheral lung tissue, is needed for accurate diagnosis.
• Alveoli can be modeled as spherical air spaces surrounded by lung tissue.

Purpose of the Study:

• To derive a model for quantifying lung microstructure, specifically alveolar diameter and air-tissue volume fraction.
• To validate the model against experimental data from rat lungs and hydrogel foam.
• To establish a method for early detection of lung pathologies through microstructure analysis.

Main Methods:

• Developed a biophysical model for Carr-Purcell-Meiboom-Gill transverse relaxation rates (R2).
• Incorporated dependencies on inter-echo time, air-tissue volume fraction, diffusion coefficient, and alveolar diameter.
• Tested the model using experimental data from passively deflated rat lungs and ageing hydrogel foam.

Main Results:

• The model accurately predicts alveolar radius (RA = 31.46 ± 13.15 μm) in rat lungs, closely matching literature values.
• Modeled radii from hydrogel foam relaxometry agreed well with μCT imaging (mean relative error: 0.06 ± 0.01).
• The derived relaxation rate shows a hyperbolic tangent dependency, consistent with existing models.

Conclusions:

• The developed model provides a quantitative method to assess peripheral lung microstructure.
• This approach is valuable for evaluating early emphysematous changes and other lung pathologies.
• The model's ability to determine alveolar radius and air volume fraction enhances clinical diagnostic capabilities.