Narrow band imaging is an electronic, noninvasive technique in which the illuminating light from the endoscope is filtered to enable passage primarily of two narrow bands of light, 415nm and 540nm. These wavelengths correspond to the hemoglobin absorption wavelength in the capillaries and submucosal vessels respectively. This enhances evaluation of the mucosal surface patterns and vascular irregularities. NBI has been shown to be useful in the detection of dysplasia in Barrett's esophagus and characterization of small colonic adenomas.