Fig. 1. The number of publications on OCT studies in ophthalmology, endoscopy, and dermatology in 1991‒2022 (data from PubMed)

Fig. 2. OCT system schematics. (a) Schematic of a time-domain OCT system; (b) schematic of a spectral domain OCT system; (c) schematic of a swept-source OCT system

Fig. 3. Different types of OCT endoscopic scanning probes. (a) Lateral view endoscopic OCT imaging probe^[29]; (b) proximal scanning endoscopic OCT probe^[30]; (c) distal scanning endoscopic OCT probe^[31]; (d) anterior view endoscopic OCT imaging probe^[33]

Fig. 4. Other types of OCT probes. (a) Lens-free endoscopic probe^[37]; (b) endoscopic probe based on polarization-sensitive GTIN lens^[39]; (c) dual-modality endoscopic probe combining white light microscopy and OCT^[40]; (d) multimodality endoscopic probe combining OCT and fluorescence imaging^[43]

Fig. 5. UHR-OCT imaging of in vitro porcine coronary arteries^[47], where the left panel shows the image of the intact artery, and the right panel shows the image of the artery after stripping the endothelial layer

Fig. 6. Imaging of isolated human lung tissue using an endoscope with integrated superlens^[52], the characteristic structures of the alveoli are clearly visible

Fig. 7. Dual-modality imaging with OCT combined with fluorescence. (a) OCT- LIF dual-modality endoscopic structure^[55]; (b) OCT-NIRAF for coronary arteriosclerosis assessment^[56]; (c) OCT-AFI for in vivo imaging of the fallopian tube^[57]

Fig. 8. OCT and US-OCT dual-modality imaging^{of normal rabbit aorta[58]. (a) OCT image; (b) US-OCT image}

Fig. 9. Imaging of rabbit abdominal aorta^[61]. (a) OCT cross-sectional images of atherosclerotic microstructures in rabbits; (b) OCT images of calcified plaques; (c) OCT image of lipid plaques

Fig. 10. Representative images of porcine coronary arterie^[65]. (a) Angiogram after stent implantation; (b) OCT image (because of the polymeric nature, the stent does not reflect light and therefore appears as a transparent (black) diamond shape)

Fig. 11. Images of radial strain due to pressure changes^[66]. (a)‒(d) Phase shift between two frames; (e)‒(h) the gradient of phase shifts

Fig. 12. OCT cross-sectional views of benign and malignant bronchial lesions^[72]. (a) Benign bronchial lesion; (b) malignant bronchial lesion

Fig. 13. OCT endoscopic image^[77] (the mucosal morphology is irregular in the white line region with a nonproliferative Barrett’s esophagus below it and normal squamous epithelium to its right. Star dots indicate motion artifacts, asterisks indicate areas where the duct does not touch the mucosa, and arrows indicate atypical proliferative lesions)

Fig. 14. OCT images of ischemic ileum with white arrows pointing to the interstitial fluid accumulation^[81]

Fig. 15. OCT imaging of the small intestine allograft on the day of transplantation versus one day later when it produced a rejection reaction^[82]

Fig. 16. OCT and OCTA images of intestinal hyperplastic polyps^[84]. (a) OCT image at 150 μm depth; (b) OCTA image at 150 μm depth; (c) OCT image at 200 μm depth; (d) OCTA image at 150 μm depth

Fig. 17. OCT images of different tumor tissues. (a) Magnified view of biliopancreatic duct tumor tissue^[86]; (b) OCT image of ureteral carcinoma^[87]; (c) images of normal, early cancerous, and cancerous cervical tissues^[88]

Fig. 18. OCT images of the human vagina with 1.3 μm and 1.7 μm OCT system^[89]