Laser‐induced autofluorescence spectral ratio reference standard for early discrimination of oral cancer

Abstract

Laser-induced autofluorescence (LIAF) is an emerging noninvasive technique in the biomedical field, especially for cancer detection. The goal of the study was to develop a spectral ratio reference standard (SRRS) to discriminate different grades of oral cancer. LIAF emission spectra from oral mucosa were recorded in the 420-720 nm spectral range on a miniature fiberoptic spectrometer from 14 anatomical sites of 35 healthy volunteers and 91 sites of 44 patients, with excitation at 404 nm from a diode laser. Histopathologic analysis of biopsy samples showed that oral mucosa of adjoining malignant sites in patients are not usually normal, but showed various degrees of epithelial dysplasia and hyperplasia. Therefore, instead of using LIAF data from apparently normal lesions of patients as control, spectral data values of the oral mucosa of healthy volunteers were used as control. The autofluorescence emission at 500 nm is characteristic of oral mucosa, whereas in malignant lesions a new peak is seen at 685 nm in addition to the previously reported peaks at 635 and 705 nm. Three spectral ratio reference standard (SRRS) scatterplots were created to differentiate the normal mucosa from hyperplasia, hyperplasia from dysplasia, and dysplasia from squamous cell carcinoma (SCC) using the mean fluorescence intensity ratios (F500/F635, F500/705 and F500/F685) measured from 40 sites in 20 patients and 11 sites in 35 healthy volunteers. During blind tests at 21 sites in 17 patients all 3 SRRS plots showed 100% sensitivity and specificity to discriminate hyperplasia from dysplastic and normal tissues, whereas only the F500/F685 SRRS showed the same sensitivity and specificity to differentiate dysplasia from SCC. An SRRS criteria based on scatterplots of autofluorescence spectral intensity ratios is described to discriminate oral mucosal variations and screen early stages of tissue progression toward malignancy.