PT  - JOURNAL ARTICLE
AU  - Carolin Unglert
AU  - William Warger
AU  - Jeroen Hostens
AU  - Eman Namati
AU  - Reginald Birngruber
AU  - Brett Bouma
AU  - Guillermo Tearney
TI  - Optical coherence tomography measurements of subpleural alveolar size compared to micro-CT and ray-trace modeling
DP  - 2012 Sep 01
TA  - European Respiratory Journal
PG  - P641
VI  - 40
IP  - Suppl 56
4099  - http://erj.ersjournals.com/content/40/Suppl_56/P641.short
4100  - http://erj.ersjournals.com/content/40/Suppl_56/P641.full
SO  - Eur Respir J2012 Sep 01; 40
AB  - Optical frequency domain imaging (OFDI) is a promising second-generation optical coherence tomorgraphy (OCT) modality for visualization of alveolar structure and function in vivo due to its microscopic resolution (∼10µm) and fast imaging speed (>100fps). In order to enable quantitative conclusions about alveolar behavior under various ventilation strategies or pathologies, it was crucial to investigate the validity of alveolar size measurements obtained from OFDI images.Therefore, we compared the cross-sectional area, perimeter, volume, and surface area of matched subpleural alveoli from micro-CT (2.9µm resolution) and OFDI images of fixed air-filled swine samples. Furthermore, we developed a ray-tracing model that approximates the reconstructed alveolar size within OFDI images based on potential refraction effects that are not visible in micro-CT images.We discovered that the relative change in size between alveoli was extremely well correlated between the two imaging techniques (r>0.9, p<0.0001), but OFDI images underestimated absolute sizes compared to micro-CT images by 27% (area), 7% (perimeter), 46% (volume), and 25% (surface area) on average. Using our model and OFDI measurements of the refractive index for fixed and fresh lung tissue, the experimentally obtained OFDI measurements could be re-scaled to approximate the micro-CT measurements with dramatically reduced error (<10% for all size parameters).In this study, we have successfully validated relative alveolar sizes as measured within OFDI images and show the potential to obtain absolute size measurements with the use of predictive correction factors.