Micro-optical coherence tomography endoscopic imaging of rat colon ex vivo

Detecting the cellular-level morphological alterations of gastrointestinal (GI) tracts is critical for the early diagnosis of cancers. With the capability to obtain real-time cross-sectional images of the biological tissues at cellular resolution, micro-optical coherence tomography (µOCT) has become a potential tool for such purpose. However, clinical applications of µOCT are still limited by lack of an endoscopic probe. In this study, we designed and fabricated an endoscopic µOCT probe, and tested its capability to obtain the real-time images of GI tracts at the cellular level. The probe diameter is 1.8 mm and the catheter diameter with a glass tube covering the probe is 2.8 mm. A common-path design is achieved by an apodizing prism, which divides the input beam with the central circular beam directed to the reference arm while the annual beam towards the sample for tissue imaging. The probe is rotated by a rotary joint to scan the tissue circumferentially. To evaluate the performances of the fabricated probe, we imaged the phantoms and results showed that the transverse resolution is 6.4 μm and the axial resolution is 2.2 μm in air. The sensitivity was measured to be 90.8 dB with a sample power of 9.65 mW. To test the feasibility for tissue imaging, we visualized the rats' colon ex vivo. The results showed that the layered structures of rat colon could be resolved clearly, meanwhile, the crypt lumens could also be captured.