Spectroscopic analysis of the autofluorescence from human bronchus using an ultraviolet laser diode

A GaN based ultraviolet (UV) laser diode (LD) was used to study the autofluorescence (AF) spectrum of the normal and tumor human bronchial tissues under ex vivo conditions. The UV LD generates a coherent short wavelength (around 400 nm) light beam with an intensity of about a few watts. AF spectrum data can be obtained without interference by excitation light. A clear blue peak located at around 483 nm was observed along with a green peak at around 560 nm in the normal tissue. The peak intensities observed were very weak for the tumor tissues. The AF imaging and spectrum analysis were performed along with a histopathological study. The spatial distribution of the elastin in the bronchial tissue affected the intensity of the AF whereas the spectrum shape was not affected. Strong AF was observed from regions that include a high density of the elastin. Biopsy measurements were performed for ex vivo samples, and depth profiling of the elastin was studied along with variations of the AF spectrum. AF spectra excited by the UV LD for fluorescence materials including FAD, NADH, and elastin were measured. The spectrum shape of the elastin as well as of NADH was similar to that of normal bronchial tissues.