Autofluorescence spectroscopy of epithelial tissues

Abstract

Autofluorescence of rabbit and human epithelial tissues were studied by using a depth-resolved fluorescence spectroscopy system with multiple excitations. Keratinization was found to be common in the squamous epithelium. Strong keratin fluorescence with excitation and emission characteristics similar to collagen were observed in the topmost layer of the keratinized squamous epithelium. The keratin signal created interference in the assessment of the endogenous fluorescence signals (NADH/FAD fluorescence in epithelium and collagen fluorescence in stroma) associated with the development of epithelial precancer. Furthermore, the keratinized epithelial layer attenuated the excitation light and reduced the fluorescence signals from underlying tissue layers. The autofluorescence of columnar epithelium was found to be dominated by NADH and FAD signals, identical to the autofluorescence measured from nonkeratinized squamous epithelium. The study also demonstrated that a fluorescence signal excited at 355 nm produced sufficient contrast to resolve the layered structure of epithelial tissue, while the signal excited at 405 nm provided the information for a good estimation of epithelial redox ratios that are directly related to tissue metabolism. Overall, the depth-resolved measurements are crucial to isolate the fluorescence signals from different sublayers of the epithelial tissue and provide more accurate information for the tissue diagnosis.

Dual-wavelength excitation of mucosal autofluorescence for precise detection of diminutive colonic adenomas

“…The fluorophores excited at 405 nm may include flavoproteins. 20,29 It is reported that flavoprotein fluorescence exhibits behavior inverse to NADH fluorescence in response to the reduction oxidation of the mitochondrial nicotinamide adenine dinucleotide system. 20,26 There are several types of commercially available autofluorescence endoscopy systems, [30][31][32] and their potential usefulness for detecting gastrointestinal neoplasms has been shown by previous studies including ours.…”

“…The wavelengths of 365 and 405 nm were selected to detect NADH fluorescence and reference fluorescence, respectively, based on results of previous studies, which showed that mucosal autofluorescence excited at 365 nm corresponds to NADH fluorescence. 14,[20][21][22] To minimize the effect of scattering or absorption in tissues, a 470-nm band-pass filter (HQ470/40m; Chroma) was used as a barrier filter corresponding to both 365-and 405-nm excitations so that each emission light was affected by scattering or absorption to a similar degree. Autofluorescence images were obtained with the CCD camera.…”

Discriminant analysis of autofluorescence spectra for classification of oral lesions in vivo

“…The technique involves illumination of suspicious lesions with monochromatic light and recording the fluorescence spectra emitted by endogenous tissue fluorophores such as nicotinamide adenine dinucleotide (NADH), collagen, elastin, keratin, flavin adenine dinucleotide (FAD), and porphyrins. The presence of disease results in alteration in concentration of these fluorophores as well as the light scattering and absorption properties of tissue, nuclear size distribution, collagen content, and epithelial thickness, which leads to the spectral variations [4].…”

Development of thin skin mimicking bilayer solid tissue phantoms for optical spectroscopic studies

“…Clinical studies have shown that the changes in FAD fluorescence can be strongly correlated to tissue pathology [20,21] in primary as well as metastatic tumors, wherein different types of cancer can have dermatological manifestations [22][23][24]. As FAD is a cofactor related with cellular metabolic activity, increase in FAD fluorescence can be attributed to the increase in metabolic activity in abnormal tissues [25].…”