We have been investigating ultrahigh resolution optical coherence tomography (UHR-OCT) imaging of lung tissues
using fiber based super continuum (SC) sources. The high power, low-noise, Gaussian shaped SC generated with
ultrashort pulses and optical fibers at several wavelength regions were used as the broadband light sources for UHROCT. Since the lung consists of tiny alveoli which are separeted by thin wall, the UHR-OCT is supposed to be effective for lung imaging. The normal and diseased lung tissues were observed without invasive procedures to the lung itself. The clear images of alveoli were observed with index matching effect by saline. In this work, we investigated the three-dimensional UHR-OCT imaging of lung structure. The lungs of rats inflated with 10% formalin at 5 cmH2O, 15 cmH2O, and 20 cmH2O pressure were prepared as the sample for investigation of size and shape of the lung structure. These samples were fixed with 10% formalin. The interalveolar septa, thin walls separating the alveoli, were clearly observed. The difference of size and shape of alveoli and thier three-dimensional network was clearly observed from the UHR-OCT images. The clear images of alveoli were observed with index matching effect of 10% formalin. We investigated the wavelength dependence of 3D UHR-OCT image of lung structure at 800 nm, 1060 nm, and 1700 nm wavelength regions. The 3D UHR-OCT images of structure of rat lung were clearly observed in all wavelength regions and wavelength dependence of imaging was discussed.