Visualization of the airway smooth muscle (ASM) layer is crucial in understanding its role in normal and abnormal airway function. Increased thickness of the ASM layer is one of the pathological hallmarks of airway remodeling in asthma and chronic obstructive pulmonary disease (COPD). The thickness of the ASM layer cannot be measured using current imaging techniques such as CT. Recently, Adams et al. introduced a birefringence microscopy platform, based on polarization sensitive optical coherence tomography (OCT), that enabled identification of ASM by its optic axis orientation in humans and allowed investigation of ASM contractile force ex vivo. In this work, we implemented passive depth-encoded polarization multiplexing and polarization-diversity detection in a 1300-nm swept-source OCT system. Compared with the previous inter-A-line modulation, such a strategy offers a simpler, more noise-resistant measure of the full polarization response of the tissue captured from a single A-line. We also refined the reconstruction of the depth-resolved birefringence properties to obtain the local optic axis orientation, corrected for the effect of preceding tissue layers and system distortions. Human bronchial samples were measured ex vivo in benchtop configuration. ASM layers, featuring muscle bundles oriented roughly at 90 degrees to the long axis of the airway, were extracted from 3D volumes by careful mapping of depth-resolved optic-axis orientation. Comparison of OCT measurements with H&E stained histological sections was performed to assess the accuracy of ASM delineation.
Karol Karnowski, Qingyun Li, Peter B. Noble, Martin Villiger, Alan James, and David D. Sampson, "Assessment of airway smooth muscle layers in human airways with single-measurement, polarization-sensitive OCT (Conference Presentation)," Proc. SPIE 10470, Endoscopic Microscopy XIII, 1047009 (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291222.5751476021001.
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