NBI (Narrow Band Imaging) was first introduced in the market in 2005 as a technique enabling to enhance image
contrast of capillaries on a mucosal surface(1). It is classified as an Optical-Digital Method for Image-Enhanced
Endoscopy(2). To date, the application has widely spread not only to gastrointestinal fields such as esophagus, stomach
and colon but also the organs such as bronchus and bladder. The main target tissue of NBI enhancement is capillaries.
However, findings of many clinical studies conducted by endoscopy physicians have revealed that NBI observation
enables to enhance more other structures in addition to capillaries. There is a close relationship between those enhanced
structures and histological microstructure of a tissue. This report introduces the tissue microstructures enhanced by NBI
and discusses the possibility of optimized illumination wavelength in observing living tissues.