Narrow band imaging (NBI)
Principle- All tumor growth is angiogenesis-dependent. An in vivo means for visualizing angiogenesis or microvessel morphological changes in superficial neoplasms would constitute a promising method for the diagnosis of early gastrointestinal tumors. NBI is based on this principle.
Conventional white light imaging uses the entire spectrum of visible light (400-700nm). NBI technology is based on the use of optic filters to isolate two specific bands of light: 415 nm (blue) and 540 nm (green). The penetration depth of the light depends on the wavelength. The depth of penetration into the GI mucosa is superficial for the blue band, intermediate for the green band and deep for the red band. So using NBI, an image is produced that enhances the visualization of superficial structures (blue: superficial capillary; green: subepithelial vessels)
The NBI mode on an endoscope can be activated or deactivated with a control button on the endoscope.
NBI is also called 'digital chromoendoscopy' because it enhances the mucosa and vasculature similar to that seen in chromoendoscopy, a technique in which mucosa is sprayed with a dye during the endoscopy procedure.
Current uses of NBI
Upper GI endoscopy Barrett's surveillance
Colonoscopy-detect and assess colon polyps (esp. flat ones) and for surveillance colonoscopy in patients with ulcerative colitis (UC) and hereditary nonpolyposis colon cancer (HNPCC)
Current evidence
Are yields of small and flat adenomas higher with NBI? Unclear, due to differences in the Japanese and Western literature.
NBI can better distinguish the hyperplastic from neoplastic (adenoma's) polyps by the pit pattern. It is hypothesized that this will lead to less sampling thus resulting in less risk to the patient, saving time during the procedure and decreasing overall health care costs.
Detection of dysplastic lesions in UC or Crohn's colitis- study so far shows that the sensitivity of NBI in detecting neoplasia in patients was similar to conventional colonoscopy. However NBI allows targeted biopsy and hence picks more suspicious lesions.
NBI in HNPCC surveillance- Few studies on the issue however early results appear promising in greater detection of flat adenomas
Barrett's surveillance- Limited number of studies, however early results are promising. Presently NBI is used as an adjunct to white light endoscopy for targeted investigation of suspicious areas
Although NBI is already commercially available, the classification of mucosal and vascular patterns with NBI is not yet standardized and validated. Thus, additional studies are needed before it can be incorporated into routine clinical practice. The combination of the mucosal and vascular pattern may ultimately prove to be an accurate endoscopic tool that can help in increased detection of abnormal areas and targeted biopsies of areas with suspicious superficial morphology.