Ex-vivo ultra-high-resolution optical coherence tomography imaging of fine lung structure by use of a high-power Gaussian-like supercontinuum at 0.8-μm wavelength

Optical coherence tomography (OCT) is an emerging technology for non-invasive cross-sectional imaging of biological tissue and material with um resolution. Recently, non-invasive high resolution cross-sectional imaging is desired for investigation of diseases in lung in the field of pulmonary medicine. So far, a few works have been reported about OCT imaging of lung. Since the lung consists of alveoli separated by thin wall, ultrahigh resolution (UHR) OCT is supposed to be effective for the imaging of fine structure in lung tissue. In this work, ex vivo cross-sectional imaging of isolated rat lungs was demonstrated using UHR-OCT. A 120 nm-wide, high-power, Gaussian-like supercontinuum (SC) was generated at wavelength of 0.8 um region and it was used as the light source in time domain UHR-OCT. An ultrahigh resolution of 2.1 um in tissue was obtained and the achieved sensitivity was 105 dB. For the UHR-OCT imaging of trachea, the detailed structures of the tracheal cartilage and tracheal mucosa overlying the cartilage were observed clearly. The epithelium and lamina propria were also distinguishable. For the imaging of visceral pleura and alveoli, when saline was instilled into the lung, the penetration depth was improved, and clear images of the fine structure of the lung, including alveoli, were observed owing to the index matching effect. The clear images of up to about 4 alveoli were observed below the visceral pleura. The shape of the alveolar septum was clearly observed, and the alveolar sac was clearly visible.