Abstract
Diffusion MRI using hyperpolarized gases is sensitive to lung microstructure. Computer simulations used to investigate the relationship between diffusivity (ADC) and airway dimensions are generally limited by non-realistic geometric assumptions (e.g. infinite cylindrical airways). In this work, we use histology sections to generate realistic models of acinar airways that are used in finite element computer simulations of 3He and 129Xe gas diffusion and 129Xe exchange between gas and tissue.
Results:
For 3He, the distribution over the largest airway is nearly uniform due to motional averaging. For 129Xe, its reduced diffusivity limits the mixing between intra and extra-alveolar gas resulting in a non-uniform distribution, which can be described with a two-compartment analytical model.
These results suggest that 129Xe MRI may be more sensitive to alveolar structure than 3He, while being less sensitive to branching and localized diffusion effects.
Conclusion: Computer simulation and visualization of maps of microscopic diffusivity distributions in realistic acinar geometries have helped provide a better understanding of the length scales and diffusion regimes relevant to hyperpolarized gas lung MRI and may help simplify the development of 129Xe-based MR lung morphometry techniques.
- © 2011 ERS