Golabchi Ali, Faust J, Golabchi F N, Brooks D H, Gouldstone A, Dimarzio C A
Biomed Opt Express. 2012 May 1;3(5):1101-9. doi: 10.1364/BOE.3.001101. Epub 2012 Apr 25.
Visualization and correct assessment of alveolar volume via intact lung imaging is important to study and assess respiratory mechanics. Optical Coherence Tomography (OCT), a real-time imaging technique based on near-infrared interferometry, can image several layers of distal alveoli in intact, ex vivo lung tissue. However optical effects associated with heterogeneity of lung tissue, including the refraction caused by air-tissue interfaces along alveoli and duct walls, and changes in speed of light as it travels through the tissue, result in inaccurate measurement of alveolar volume. Experimentally such errors have been difficult to analyze because of lack of 'ground truth,' as the lung has a unique microstructure of liquid-coated thin walls surrounding relatively large airspaces, which is difficult to model with cellular foams. In addition, both lung and foams contain airspaces of highly irregular shape, further complicating quantitative measurement of optical artifacts and correction. To address this we have adapted the Bragg-Nye bubble raft, a crystalline two-dimensional arrangement of elements similar in geometry to alveoli (up to several hundred μm in diameter with thin walls) as an inflated lung phantom in order to understand, analyze and correct these errors. By applying exact optical ray tracing on OCT images of the bubble raft, the errors are predicted and corrected. The results are validated by imaging the bubble raft with OCT from one edge and with a charged coupled device (CCD) camera in transillumination from top, providing ground truth for the OCT.
通过完整肺部成像对肺泡体积进行可视化和正确评估，对于研究和评估呼吸力学非常重要。光学相干断层扫描（OCT）是一种基于近红外干涉测量的实时成像技术，能够对完整的离体肺组织中的多层远端肺泡进行成像。然而，与肺组织异质性相关的光学效应，包括沿肺泡和导管壁的气 - 组织界面引起的折射，以及光在组织中传播时的速度变化，会导致肺泡体积测量不准确。由于缺乏“地面真值”，在实验中这些误差很难分析，因为肺具有独特的微观结构，即相对较大的气腔被液体包裹的薄壁所环绕，这很难用细胞泡沫进行建模。此外，肺和泡沫都包含形状高度不规则的气腔，这使得光学伪像的定量测量和校正更加复杂。为了解决这个问题，我们采用了布拉格 - 奈伊气泡筏，它是一种元素的晶体二维排列，其几何形状与肺泡相似（直径可达数百微米，壁薄），作为充气肺模型，以便理解、分析和校正这些误差。通过对气泡筏的OCT图像应用精确的光线追踪，预测并校正了误差。通过从一侧用OCT对气泡筏成像，并从顶部用电荷耦合器件（CCD）相机进行透照成像，验证了结果，为OCT提供了地面真值。
