title: Validation of two-dimensional and three-dimensional measurements of subpleural alveolar size parameters by optical coherence tomography.
abstract: Optical coherence tomography (OCT) has been increasingly used for imaging pulmonary alveoli. Only a few studies, however, have quantified individual alveolar areas, and the validity of alveolar volumes represented within OCT images has not been shown. To validate quantitative measurements of alveoli from OCT images, we compared the cross-sectional area, perimeter, volume, and surface area of matched subpleural alveoli from microcomputed tomography (micro-CT) and OCT images of fixed air-filled swine samples. The relative change in size between different alveoli was extremely well correlated (r>0.9, P<0.0001), but OCT images underestimated absolute sizes compared to micro-CT by 27% (area), 7% (perimeter), 46% (volume), and 25% (surface area) on average. We hypothesized that the differences resulted from refraction at the tissue-air interfaces and developed a ray-tracing model that approximates the reconstructed alveolar size within OCT images. Using this model and OCT measurements of the refractive index for lung tissue (1.41 for fresh, 1.53 for fixed), we derived equations to obtain absolute size measurements of superellipse and circular alveoli with the use of predictive correction factors. These methods and results should enable the quantification of alveolar sizes from OCT images in vivo.
authors.affiliation: Harvard Medical School and Massachusetts General Hospital, Wellman Center for Photomedicine, 40 Parkman Street, RSL 160, Boston, Massachusetts 02114, USA. cunglert@mgh.harvard.edu
authors.forename: Carolin I
authors.initials: CI
authors.lastname: Unglert
authors.forename: William C
authors.initials: WC
authors.lastname: Warger
authors.forename: Jeroen
authors.initials: J
authors.lastname: Hostens
authors.forename: Eman
authors.initials: E
authors.lastname: Namati
authors.forename: Reginald
authors.initials: R
authors.lastname: Birngruber
authors.forename: Brett E
authors.initials: BE
authors.lastname: Bouma
authors.forename: Guillermo J
authors.initials: GJ
authors.lastname: Tearney
mesh_terms: D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008954:Models, Biological; D009929:Organ Size / Q000502:physiology; D010363:Pattern Recognition, Automated / Q000379:methods*; D010994:Pleura; D011650:Pulmonary Alveoli / Q000033:anatomy & histology* / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D041623:Tomography, Optical Coherence / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods