Light scattering by pulmonary alveoli and airway surface liquid using a concentric sphere model

Abstract

We employ a concentric sphere Mie scattering model to describe light scattering by pulmonary alveoli and airway surface liquid (ASL). Using this layered sphere model, we compare alveolar scattering at different points along the respiratory cycle and observe the effect of ASL thickness on light scattering in the lung. We have also extrapolated the model to investigate alveolar scattering in various animal models of pulmonary disease. This model of pulmonary light scattering can estimate in vivo optical properties for normal and pathological states, potentially aiding the design of optical systems for diagnosis and investigation of pulmonary pathologies.

Fig. 1.

Spherical particles modeled in traditional Mie scattering (a) and in the concentric sphere model (b).

Fig. 2.

Lung parenchyma consists of microscale air sacs connected by airway branches (a). Alveoli expand and contract over the respiratory cycle for passive and forced inspiration and expiration (b-c). RV is the minimal airspace a living organism can achieve without alveolar collapse. ERV is the difference between RV and passive exhale. FRC is the air volume in the lung at the end of passive exhale. TV is the volume fluctuation during passive breathing. IRV is the difference between passive breathing and TLC.

Fig. 3.

Phantom validation of the concentric sphere model shows a fairly constant n for each volume fraction over the visible spectrum (a). μ_s is linearly correlated with volume fraction in phantoms and model (b).

Fig. 4.

At a constant lung volume, μ_s is similar for all ASL thicknesses modeled (a). The change in baseline and phase of g (b) causes a shift in μ_s’ and leads to unique spectral features (c).