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Traditional electronic endoscopes use xenon lamps as illumination light, and this NBI endoscope imaging blue light spectrum, known as 'white light,' is actually composed of three types of light: R/G/B (red/green/blue), with wavelengths of 605nm, 540nm, and 415nm, respectively. The NBI system uses narrowband filters instead of traditional broadband filters to confine light of different wavelengths, leaving only red, green, and blue narrowband light waves at 605nm, 540nm, and 415nm wavelengths. The depth at which narrowband light waves penetrate the gastrointestinal mucosa varies in narrowband cold light source imaging. The blue band (415nm) penetrates shallowly, the red band (605nm) can penetrate deep into the submucosal layer and display the submucosal vascular network, while the green band (540nm) can better display the blood vessels in the middle layer. Due to the strong absorption of blue and green light by the optical properties of blood within the mucosa, using light waves that are difficult to diffuse and can be absorbed by blood can increase the contrast and clarity of mucosal epithelium and submucosal blood vessels. Therefore, NBI has the equivalent effect of mucosal staining, and only requires button switching without spraying staining agents when applied, hence it is called electronic staining endoscope. Autofluorescence imaging can detect subtle changes in tissues by emitting longer wavelength fluorescence through special short wavelength light. The most commonly used target is collagen. The discovery of gastrointestinal abnormalities by the autofluorescence system mostly relies on the loss of collagen in dysplasia tissues, leading to a decrease in green fluorescence and an increase in red fluorescence. However, AFI has limitations such as insufficient image resolution and high false positive rate. The so-called triple imaging mode, which combines NBI endoscopic imaging with blue light white light endoscopy and virtual staining endoscopy, can enhance its specificity. Under the triple imaging mode, observers can utilize the advantage of AFI to detect red fluorescent lesions in the gastrointestinal tract, and then further observe their surface features through narrowband cold light source imaging with high-definition endoscopy and virtual staining endoscopy.

NBI endoscopic imaging optical coherence tomography (OCT) OCT is a new technology that uses a short coherence length light source interferometer to measure backscattered or reflected light, thereby enabling high-resolution tomographic imaging of shallow microstructures in biological tissues. One end of the interferometer is equipped with a scanning system, and the other end is equipped with a scanning reference path delay system. Only when the optical delay matches the coherent light length will optical interference occur in the light from the sample and reference. High resolution can display the microstructure of tissues, but at the cost of reducing the imaging depth (1-2 mm). Therefore, OCT narrowband cold light imaging can easily and accurately distinguish normal epithelial tissue from abnormal tissue, but the detection and grading of dysplasia and early cancer still pose challenges.