The factors, which influence the endoscopist detection are not well studied. Polyp detection rates wary widely, even among experts. Techniques that highlight lesions have advanced in recent years. Chromoendoscopy, the current gold standard technique, relies on spraying dye on the bowel lining, has been shown to help pick up more pre-cancerous polyps in two of three studies; however it is not widely used as it is time consuming and requires extra equipment and training. Narrow band imaging (NBI) is a technique that relies in light filters to improve contrast for the smallest blood vessels in the bowel lining which shows up adenomas as they have a richer vascular network. It is sometimes described as "digital chromoendoscopy" as the images produced are similar to chromoendoscopy, but it is much simpler and quicker to use. Autofluorescence endoscopy uses short wavelength light and light filters to produce a false colour image of the bowel lining where polyps stand out. These techniques have been used with some success in the oesophagus and stomach but little work is available for the colon.