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What is Narrow Band Imaging (NBI) bronchoscopy?
Normal bronchoscopy uses white light as illumination source. In narrow band imaging only limited wavelength of white light in the blue and the green spectrum (415 nm and 540 nm) are allowed and the rest of the light is filtered. The advantage of using narrow band imaging is that dysplasia, atypical cells and malignant lesion in the airway can be delineated from normal mucosa using NBI mode.  The dysplastic and malignant cells and tissue look green in narrow band imaging mode. Hence targeted biopsies can be taken from airway wall and mucosa (from the green areas) resulting in higher diagnostic yield.

What is the principle behind the narrow band imaging bronchoscopy?
Since the blue and the green spectrum correspond to the absorption spectrum of oxyhemoglobin, the blood vessels are more pronounced when a tissue is viewed through narrow band imaging bronchoscopy. Malignant tissue has abnormal microvasculature. In NBI mode on the surface of malignant tissue, in addition to the green light certain specific patterns can be recognized. The vasculature over a malignant tissue appears as dotted, tortuous or as large caliber vessels with abrupt ending.

Can it be used for screening people with high risk of lung cancer such as smokers?
This is a potentially exciting possibility with the narrow band imaging bronchoscopy. Any tool that detects the cancer earlier can be of immense benefit as lung cancer is curable in the early stages. Narrow band imaging bronchoscopy can indeed detect early pre-cancerous lesions in the airways. But the NBI is in its infancy and largely used only in academic centres as research tool. It has started slowly to come into clinical use. But certain questions remain unanswered including what do to if we indeed detect a pre-cancerous lesion in a patient’s airway. Clear cut recommendations are not available to deal with the precancerous lesions when identified.  But it is perfectly reasonable to imagine that NBI or similar technology may be used in the near future to screen smokers on a yearly basis. For the time being until guidelines are developed, NBI mode may be used in all smokers undergoing bronchoscopy for unrelated reason. After all we are going inside the lungs; why not turn on the NBI mode for a few minutes to check if any suspicious lesions are present.

How does narrow band imaging bronchoscopy compare to that of normal white light bronchoscopy and auto fluorescence (AF) bronchoscopy?
Research studies show that using NBI bronchoscopy resulted in greater than 20% detection of dysplasia or malignancy over the normal white light bronchoscopy. When AF bronchoscopy is compared to white light bronchoscopy, AF bronchoscopy increased the detection of dysplasia and carcinoma by a factor of 1.5 to 6.3 times. Head on comparison between NBI bronchoscopy and AF bronchoscopy is not available.

What are the characteristic features of dysplasia or malignancy while using the NBI mode?
The surface of dysplatic or malignant lesions appear
1) Dotted
2) Tortuous
3) Large calibre
4) Abrupt ending vessels

How is narrow banding imaging bronchoscopy different from the auto fluorescence bronchoscopy?
In narrow band imaging bronchoscopy the white light is filtered except for the blue and the green spectrum. Since this spectrum corresponds to the absorption spectrum of oxyhemoglobin, the NBI bronchoscopy is good in displaying the surface microvasculature of the tissue. Since malignancy has abnormal surface vasculature, it can be detected easily using the NBI bronchoscope.

In Auto Fluorescence bronchoscopy,  the alteration in the fluorescent properties of the tissue when malignant transformation occurs is detected. In short the fluorescent property of malignant tissue is different from that of normal non-malignant tissue. This difference is attributed to variety of factors including loss of extracellular matrix protein, thickening of superficial mucosa and increased vessel concentration.