Photodiagnosis of oral malignancy using laser-induced fluorescence and diffuse reflectance spectroscopy

Abstract

Oral cancer represents a significant and growing concern worldwide due to its high prevalence. Current clinical procedure for detection of oral cancer involves visual inspection and ensuing biopsy guided histopathological analysis, which is considered as “gold standard”. This intact procedure is subjective, time consuming, agonizing and costly. Consequently, exploration and development of new techniques for early oral cancer diagnosis assume great significance. Researchers have been trying to develop various instruments based on optical spectroscopic techniques for detection of different types of cancer during the last two decades. These optical spectroscopic techniques could facilitate noninvasive and real-time tissue characterization and help to eliminate or reduce the need for multiple biopsies and increase the cure and survival rates. However, development of an optimal cost-effective optical system with adequate sensitivity and specificity for clinical use is still a challenge. Two non-thermal regimens of light interaction with biological tissues are mainly discussed in the present work, namely laser-induced autofluorescence (LIAF) and diffuse reflectance (DR) for detection of oral malignancy or pre-malignancy. The work described in this thesis is mainly of applied nature, focusing on the analysis of data from ex-vivo tissue samples and extending these results to diagnose oral cancer in a clinical environment. The present work mainly aims to improve and contribute to the contemporary research on fluorescence and diffuse reflectance for tissue characterization. Towards this, a portable and compact laser-induced fluorescence and reflectance spectroscopic system (LIFRS) has been developed for point monitoring of fluorescence and diffuse reflectance spectra of oral tissues/lesions. The LIFRS system uses a 405 nm diode laser in the violet region for excitation of tissue fluorescence and a white light source (tungsten halogen lamp) for tissue DR studies. Both LIAF and DR studies were performed for oral cancer diagnosis, but special emphasis was given to discern between different tissue types and for early detection of the disease. The normal LIAF and DR fingerprint spectra form healthy population exhibit different characteristics with the tissue abnormality. In DR studies, a novel approach that uses oxygenated hemoglobin absorption band ratio (R545/R575) was introduced for tissue grading and early detection of cancer. This work also introduces a new criteria based on spectral ratio reference standard (SRRS) scatter plots of fluorescence intensity ratios (F500/F635, F500/F685 and F500/F705) for oral pre-cancer detection and tissue grading with excellent diagnostic accuracies, validated with the blind-tests. In addition, optimum accumu- Abstract