Detection of cervical lesions by multivariate analysis of diffuse reflectance spectra: a clinical study.

Diffuse reflectance (DR) spectroscopy is a non-invasive, real-time, and cost-effective tool for early detection of malignant changes in squamous epithelial tissues. The present study aims to evaluate the diagnostic power of diffuse reflectance spectroscopy for non-invasive discrimination of cervical lesions in vivo. A clinical trial was carried out on 48 sites in 34 patients by recording DR spectra using a point-monitoring device with white light illumination. The acquired data were analyzed and classified using multivariate statistical analysis based on principal component analysis (PCA) and linear discriminant analysis (LDA). Diagnostic accuracies were validated using random number generators. The receiver operating characteristic (ROC) curves were plotted for evaluating the discriminating power of the proposed statistical technique. An algorithm was developed and used to classify non-diseased (normal) from diseased sites (abnormal) with a sensitivity of 72 % and specificity of 87 %. While low-grade squamous intraepithelial lesion (LSIL) could be discriminated from normal with a sensitivity of 56 % and specificity of 80 %, and high-grade squamous intraepithelial lesion (HSIL) from normal with a sensitivity of 89 % and specificity of 97 %, LSIL could be discriminated from HSIL with 100 % sensitivity and specificity. The areas under the ROC curves were 0.993 (95 % confidence interval (CI) 0.0 to 1) and 1 (95 % CI 1) for the discrimination of HSIL from normal and HSIL from LSIL, respectively. The results of the study show that DR spectroscopy could be used along with multivariate analytical techniques as a non-invasive technique to monitor cervical disease status in real time.

Efficacy of antimicrobial photodynamic therapy in the management of chronic periodontitis: a randomized controlled clinical trial.

AIM: To evaluate the potential of antimicrobial photodynamic therapy (aPDT) as an adjunct to scaling and root planing (SRP) in the treatment of chronic periodontitis. MATERIAL AND METHODS: In a single-centred randomized and controlled clinical trial, 90 patients (51 females and 39 males) with untreated chronic periodontitis were randomly assigned to receive SRP with aPDT (test group) or SRP alone (control group). Clinical parameters and halitosis were recorded for 6 months after treatment by a periodontist who was blinded to the procedure. RESULTS: Inter-group and intra-group statistical analyses were performed. Significant difference between the two groups with respect to each variable was assessed using non-parametric Rank Order ancova. Probing pocket depth and clinical attachment levels showed statistically significant reduction in the test group on evaluation at 3 months and 6 months as compared to the control group (p < 0.05). A statistically significant improvement in gingival index and gingival bleeding index was seen for the test group after 2 weeks and 1 month of aPDT (p < 0.01), whereas the improvement in gingival index and gingival bleeding index at 3 months and in plaque index at 2 weeks after aPDT was less (p < 0.05). Also, a significant difference was detected for the test group at 1 month in terms of halitosis (p < 0.05), which did not persist for long. CONCLUSIONS: Antimicrobial photodynamic therapy acts as a beneficial adjunct to SRP in non-surgical treatment and management of chronic periodontitis in short-term. Further studies are required to assess the long-term effectiveness of aPDT.

Diagnostic accuracy of diffuse reflectance imaging for early detection of pre-malignant and malignant changes in the oral cavity: a feasibility study.

BACKGROUND: Diffusely reflected light is influenced by cytologic and morphologic changes that take place during tissue transformation, such as, nuclear changes, extracellular matrix structure and composition as well as blood flow. Albeit with varying degree of sensitivity and specificity, the properties of diffusely reflected light in discriminating a variety of oral lesions have been demonstrated by our group in multiple studies using point monitoring systems. However, the point monitoring system could not identify the region with the most malignant potential in a single sitting. METHODS: In order to scan the entire lesion, we developed a multi-spectral imaging camera system that records diffuse reflectance (DR) images of the oral lesion at 545 and 575 nm with white light illumination. The diagnostic accuracy of the system for 2-dimensional DR imaging of pre-malignant and malignant changes in the oral cavity was evaluated through a clinical study in 55 patients and 23 healthy volunteers. The DR imaging data were compared with gold standard tissue biopsy and histopathology results. RESULTS: In total 106- normal/clinically healthy sites, 20- pre-malignant and 29- malignant (SCC) sites were compared. While the median pixel value of the R545/R575 image ratio for normal/clinically healthy tissue was 0.87 (IQR = 0.82-0.94), they were 1.35 (IQR = 1.13-1.67) and 2.44 (IQR = 1.78-3.80) for pre-malignant and malignant lesions, respectively. Area under the ROC curve to differentiate malignant from normal/clinically healthy [AUC = 0.99 (95% CI: 0.99-1.00)], pre-malignant from normal/clinically healthy [AUC = 0.94 (95% CI: 0.86-1.00)], malignant from pre-malignant [AUC = 0.84 (95% CI: 0.73-0.95)] and pre-malignant and malignant from normal/clinically healthy [AUC = 0.97 (95% CI: 0.94-1.00)] lesions were desirable. CONCLUSION: We find DR imaging to be very effective as a screening tool in locating the potentially malignant areas of oral lesions with relatively good diagnostic accuracy while comparing it to the gold standard histopathology.

Characterization of dental caries by LIF spectroscopy with 404-nm excitation.

The potential of laser-induced fluorescence (LIF) spectroscopy for the characterization of different stages of dental caries using 404-nm diode laser excitation was investigated. In vitro spectra from 16 sound, 10 noncavitated carious and 10 cavitated carious molar teeth were recorded on a miniature fibre-optic spectrometer. The areas under the receiver operating characteristics (ROC-AUC) were calculated and one-way analysis of variance (ANOVA) was performed. The LIF spectra of the carious teeth showed two peaks at 635 and 680 nm in addition to a broad band seen at 500 nm in sound teeth. The fluorescence intensity ratios, F500/F635 and F500/F680, in carious teeth were always lower than those in sound teeth. The ROC-AUC for discriminating between carious and sound teeth was 0.94, and for discriminating between noncavitated and cavitated carious teeth was 0.87. Statistically significant differences (p<0.001) were seen between sound, noncavitated carious and cavitated carious teeth. The results showed that LIF spectroscopy has the potential to be useful for characterizing different stages of caries in a clinical setting.

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

BACKGROUND AND OBJECTIVES: Low survival rate of individuals with oral cancer emphasize the significance of early detection and treatment. Optical spectroscopic techniques are under various stages of development for diagnosis of epithelial neoplasm. This study evaluates the potential of a multivariate statistical algorithm to classify oral mucosa from autofluorescence spectral features recorded in vivo. STUDY DESIGN/METHODS: Autofluorescence spectra were recorded in a clinical trial from 15 healthy volunteers and 34 patients with diode laser excitation (404 nm) and pre-processed by normalization, mean-scaling and its combination. Linear discriminant analysis (LDA) based on leave-one-out (LOO) method of cross validation was performed on spectral data for tissue characterization. The sensitivity and specificity were determined for different lesion pairs from the scatter plot of discriminant function scores. RESULTS: Autofluorescence spectra of healthy volunteers consists of a broad emission at 500 nm that is characteristic of endogenous fluorophores, whereas in malignant lesions three additional peaks are observed at 635, 685, and 705 nm due to the accumulation of porphyrins in oral lesions. It was observed that classification design based on discriminant function scores obtained by LDA-LOO method was able to differentiate pre-malignant dysplasia from squamous cell carcinoma (SCC), benign hyperplasia from dysplasia and hyperplasia from normal with overall sensitivities of 86%, 78%, and 92%, and specificities of 90%, 100%, and 100%, respectively. CONCLUSIONS: The application of LDA-LOO method on the autofluorescence spectra recorded during a clinical trial in patients was found suitable to discriminate oral mucosal alterations during tissue transformation towards malignancy with improved diagnostic accuracies.

Oxygenated hemoglobin diffuse reflectance ratio for in vivo detection of oral pre-cancer.

Diffuse reflectance (DR) spectroscopy is a simple, low-cost, and noninvasive modality with potential for distinguishing oral precancer. Recently, in an ex vivo study, the DR spectral ratio (R545/R575) of oxygenated hemoglobin bands at 545 and 575 nm was used for grading malignancy. This work presents the results of clinical trials conducted in 29 patients to detect oral precancer using this ratio. We use site-specific normal spectra from a group of 36 healthy volunteers for comparison with those of patients. Toward this, in vivo DR spectra from 14 anatomical sites of the oral cavity of healthy volunteers are recorded on a miniature fiber optic spectrometer with white light excitation. The R545/R575 ratio is lowest for healthy tissues and appears to increase with the grade of malignancy. As compared to scatter plots that use the mean DR ratio from all anatomical sites, those using site-specific data show improved sensitivity and specificity for early diagnosis and grading of oral cancer. In the case of buccal mucosa, using scatter plots of R545/R575 ratio, we obtain a sensitivity of 100% and specificity of 86% for discriminating precancer (dysplasia) from hyperplasia, and a sensitivity of 97% and specificity of 86% for discriminating hyperplasia from normal.

A comparative evaluation of diffuse reflectance and Raman spectroscopy in the detection of cervical cancer.

Optical spectroscopic techniques show improved diagnostic accuracy for non-invasive detection of cervical cancers. In this study, sensitivity and specificity of two in vivo modalities, i.e diffuse reflectance spectroscopy (DRS) and Raman spectroscopy (RS), were compared by utilizing spectra recorded from the same sites (67 tumor (T), 22 normal cervix (C), and 57 normal vagina (V)). Data was analysed using principal component - linear discriminant analysis (PC-LDA), and validated using leave-one-out-cross-validation (LOOCV). Sensitivity, specificity, positive predictive value and negative predictive value for classification between normal (N) and tumor (T) sites were 91%, 96%, 95% and 93%, respectively for RS and 85%, 95%, 93% and 88%, respectively for DRS. Even though DRS revealed slightly lower diagnostic accuracies, owing to its lower cost and portability, it was found to be more suited for cervical cancer screening in low resource settings. On the other hand, RS based devices could be ideal for screening patients with centralised facilities in developing countries.

Patients' perceptions of antimicrobial photodynamic therapy in the management of chronic periodontitis.

The aim of this study is to evaluate patients' perception of antimicrobial photodynamic therapy (aPDT) in the management of chronic periodontitis. 90 patients (51 females and 39 males) with untreated localized chronic periodontitis were randomly assigned to receive SRP with aPDT (test group) or SRP alone (control group) in a single-centered double-blinded randomized and controlled clinical trial. Patients' perception in terms of changes in bleeding gums, pain in gums while chewing, bad breath and sensitive gums along with pain during the procedure and patient acceptance were recorded for 6 months after treatment by a periodontist who was blinded to the procedure. Inter-group and intra-group statistical analyses were performed. Significant difference between the frequencies of two groups with respect to each variable was assessed using non-parametric test. Patients' report of bleeding gums and pain in the gums while chewing showed statistically significant reduction in the test group at 2 weeks and 1 month (p<0.05). Also, a significant difference was detected at 1 month between SRP and SRP+aPDT in terms of halitosis (p<0.05). No statistically significant change was observed between two groups in terms of sensitive gums, pain during procedure and patient acceptance. Patients perceived short-term benefits of single session of aPDT therapy due to the reduction in bleeding gums, halitosis and pain while chewing following treatment. Further studies are required to assess the effectiveness of aPDT for a longer-term and following multiple sessions.

Detection and quantification of dental plaque based on laser-induced autofluorescence intensity ratio values.

The aim of this study was to evaluate the applicability of laser-induced autofluorescence (LIAF) spectroscopy to detect and quantify dental plaque. LIAF spectra were recorded in situ from dental plaque (0­3 grades of plaque index) in 300 patients with 404 nm diode laser excitation. The fluorescence intensity ratio of the emission peaks was calculated from the LIAF spectral data following which their scatter plots were drawn and the area under the receiver operating characteristics were calculated. The LIAF spectrum of clinically invisible grade-1 plaque showed a prominent emission peak at 510 nm with a satellite peak around 630 nm in contrast to grade 0 that has a single peak around 500 nm. The fluorescence intensity ratio (F510/F630) has a decreasing trend with increase in plaque grade and the ratio values show statistically significant differences (p<0.01) between different grades. An overall sensitivity and specificity of 100% each was achieved for discrimination between grade-0 and grade-1 plaque. The clinical significance of this study is that the diagnostic algorithm developed based on fluorescence spectral intensity ratio (F510/F630) would be useful to precisely identify minute amounts of plaque without the need for disclosing solutions and to convince patients of the need for proper oral hygiene and homecare practices.

Antimicrobial photodynamic efficiency of novel cationic porphyrins towards periodontal Gram-positive and Gram-negative pathogenic bacteria.

The Gram-negative Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum are major causative agents of aggressive periodontal disease. Due to increase in the number of antibiotic-resistant bacteria, antimicrobial Photodynamic therapy (aPDT) seems to be a plausible alternative. In this work, photosensitization was performed on Gram-positive and Gram-negative bacteria in pure culture using new-age cationic porphyrins, namely mesoimidazolium-substituted porphyrin derivative (ImP) and pyridinium-substituted porphyrin derivative (PyP). The photophysical properties of both the sensitizers including absorption, fluorescence emission, quantum yields of the triplet excited states and singlet oxygen generation efficiencies were evaluated in the context of aPDT application. The studied porphyrins exhibited high ability to accumulate into bacterial cells with complete penetration into early stage biofilms. As compared with ImP, PyP was found to be more effective for photoinactivation of bacterial strains associated with periodontitis, without any signs of dark toxicity, owing to its high photocytotoxicity.

In vivo inflammation mapping of periodontal disease based on diffuse reflectance spectral imaging: a clinical study.

Since conventional techniques using periodontal probes have inherent drawbacks in the diagnosis of different grades of gingival inflammation, development of noninvasive screening devices becomes significant. Diffuse reflectance (DR) spectra recorded with white light illumination is utilized to detect periodontal inflammation from the oxygenated hemoglobin absorption ratio R620/R575. A multispectral imaging system is utilized to record narrow-band DR images at 575 and 620 nm from the anterior sextant of the gingivia of 15 healthy volunteers and 25 patients (N=40). An experienced periodontist assesses the level of gingival inflammation at each site through periodontal probing and assigns diagnosis as healthy, mild, moderate, or severe inflammation. The DR image ratio R620/R575 computed for each pixel (8-µm resolution) from the monochrome images is pseudo-color-mapped to identify gingival inflammation sites. The DR image ratio values at each site are compared with clinical diagnosis to estimate the specificity and sensitivity of the DR imaging technique in inflammation mapping. The high diagnostic accuracy is utilized to detect underlying inflammation in six patients with a previous history of periodontitis.

Discrimination of periodontal diseases using diffuse reflectance spectral intensity ratios.

This clinical study was to demonstrate the applicability of diffuse reflectance (DR) intensity ratio R620/R575 in the quantification and discrimination of periodontitis and gingivitis from healthy gingiva. DR spectral measurements were carried out with white-light illumination from 70 healthy sites in 30 healthy volunteers, and 63 gingivitis- and 58 periodontitis-infected sites in 60 patients. Clinical parameters such as probing pocket depth, clinical attachment level, and gingival index were recorded in patient population. Diagnostic accuracies for discrimination of gingivitis and periodontitis from healthy gingiva were determined by comparison of spectral signatures with clinical parameters. Divergence of average DR spectral intensity ratio between control and test groups was studied using analysis of variance. The mean DR spectrum on normalization at 620 nm showed marked differences between healthy tissue, gingivitis, and periodontitis. Hemoglobin concentration and apparent SO(2) (oxygen saturation) were also calculated for healthy, gingivitis, and periodontitis sites. DR spectral intensities at 545 and 575 nm showed a decreasing trend with progression of disease. Among the various DR intensity ratios studied, the R620/R575 ratio provided a sensitivity of 90% and specificity of 94% for discrimination of healthy tissues from gingivitis and a sensitivity of 91% and specificity of 100% for discrimination of gingivitis from periodontitis.

Comparative evaluation of the diagnostic performance of autofluorescence and diffuse reflectance in oral cancer detection: a clinical study.

Autofluorescence (AF) and diffuse reflectance (DR) spectroscopic techniques have shown good diagnostic accuracies for noninvasive detection of oral cavity cancer. In the present study, AF and DR spectra recorded in vivo from the same set of sites in 65 patients were analyzed using Principal component analysis (PCA) and linear discriminant analysis (LDA). The effectiveness of these two techniques was assessed by comparison with gold standard and their discrimination efficiency was determined from the area under the receiver operator characteristic (AUC-ROC) curve. Analysis using a DR technique shows a higher AUC-ROC of 0.991 as against 0.987 for AF spectral data.

In vivo temporal evolution of ALA-induced normalized fluorescence at different anatomical locations of oral cavity: application to improve cancer diagnostic contrast and potential.

BACKGROUND: The focal goal of this study is to identify optimal accumulation periods for ALA-induced PpIX in different healthy anatomical sites of human oral cavity and different types of abnormal mucosa to improve the accuracy of the clinical applications such as photodiagnosis and tissue grading. MATERIALS AND METHODS: Laser-induced fluorescence (LIF) emission spectra, with excitation at 404 nm from a diode laser, were recorded with a miniature fiber-optics spectrometer from 13 anatomical sites of oral mucosa in 15 healthy volunteers and 30 suspicious sites in 15 patients after topical application of 0.4% 5-ALA solution for 15 min. The optimal accumulation time in different anatomical sites of healthy subjects and abnormal tissues were determined by studying the temporal variation in normalized fluorescence intensities (NFI) at 635, 685 and 705 nm. RESULTS AND DISCUSSIONS: In masticatory anatomical locations such as (gingival and hard palate) and in lining mucosa (inner lip, soft palate, floor of mouth, transition to floor of mouth, alveolus and ventral tongue) except vermillion border of lip (VBL) of healthy subjects (designated as group I), it was observed that optimum time for maximum accumulation of PpIX is 90 min. In comparison, for lateral side of tongue (LST) and dorsal side of tongue (DST) tissues (designated as group II), maximum accumulation of PpIX was observed in 150 min of ALA application. For diverse grade lesions of group I mucosa in patients, maximum accumulation of PpIX was observed in 90 min, whereas, in group II mucosa the optimum accumulation time was 150 min as in the case of healthy mucosa. Further, between different grades oral mucosa, maximum variation in NFI take place at these optimal time periods. CONCLUSIONS: The determination of the optimum accumulation time of ALA in oral mucosa based on NFI helps to improve the diagnostic contrast and accuracy of oral cancer diagnosis, and to plan appropriate timing for ensuing PDT.

Clinical grading of oral mucosa by curve-fitting of corrected autofluorescence using diffuse reflectance spectra.

BACKGROUND: Laser-induced autofluorescence (LIAF) and diffuse reflectance (DR) were collectively used in this clinical study to improve early oral cancer diagnosis and tissue grading. METHODS: LIAF and DR emission from oral mucosa were recorded on a fiber-optic spectrometer by illumination with a 404-nm diode laser and tungsten halogen lamp in 36 healthy volunteers and 40 lesions of 20 patients. RESULTS: Absorption dips in LIAF spectra at 545 and 575 nm resulting from changes in oxygenated hemoglobin were corrected using DR spectra of the same site. These corrected spectra were curve-fitted using Gaussian spectral functions to determine constituent emission peaks and their relative contribution. The Gaussian peak intensity and area ratios F500/F635 and F500/F685 were found to be useful indicators of tissue transformation. The diagnostic capability of various ratios in differentiating healthy, hyperplastic, dysplastic, and squamous cell carcinomas (SCCs) were examined using discrimination scatterplots. CONCLUSIONS: The LIAF/DR technique, in conjunction with curve-fitting, differentiates different grades of dysplasia and SCC in this clinical trial and proves its potential for early detection of oral cavity cancer and tissue grading.

Clinical trial for detection of dental caries using laser-induced fluorescence ratio reference standard.

We present the clinical applicability of fluorescence ratio reference standard (FRRS) to discriminate different stages of dental caries. Toward this, laser-induced autofluorescence emission spectra are recorded in vivo in the 400- to 800-nm spectral range on a miniature fiber optic spectrometer from 65 patients, with a 404-nm diode laser as the excitation source. Autofluorescence spectra of sound teeth consist of a broad emission at 500 nm that is typical of natural enamel, whereas in caries teeth additional peaks are seen at 635 and 680 nm due to emission from porphyrin compounds in oral bacteria. Scatter plots are developed to differentiate sound teeth from enamel caries, sound teeth from dentinal caries, and enamel caries from dentinal caries using the mean fluorescence intensity (FI) and ratios F500F635 and F500F680 measured from 25 sites of sound teeth and 65 sites of carious teeth. The sensitivity and specificity of both the FI and FRRS are determined. It is observed that a diagnostic algorithm based on FRRS scatter plots is able to discriminate enamel caries from sound teeth, dentinal caries from sound teeth, and enamel from dentinal caries with overall sensitivities of 85, 100, and 88% and specificities of 90, 100, and 77%, respectively.

Investigation of in vitro dental erosion by optical techniques.

Nitrogen laser-induced fluorescence (LIF) and tungsten halogen lamp excited diffuse reflectance spectra were recorded in 350- to 700-nm range on a miniature fiber-optic spectrometer from in vitro premolar tooth during various stages of artificial erosion with 36% phosphoric acid. Both the LIF spectral intensity and the diffuse reflectance intensity gradually increased during tooth erosion. The LIF spectra were analyzed by curve fitting using Gaussian spectral functions to determine the true contribution of different bands in the spectra during erosion. Thus, the broad bands at 440 and 490 nm in the LIF spectra of sound enamel were resolved into four peaks centered at 409.1, 438.1, 492.4 and 523.1 nm and of sound dentin into peaks at 412.0, 440.1, 487.8 and 523.4 nm. The F410/F525 ratios derived from curve-fitted Gaussian peak amplitudes and curve areas were found to be more sensitive to erosion as compared to the diffuse reflectance ratio R500/R700 or the raw LIF spectral ratio F440/F490.

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

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Tooth caries detection by curve fitting of laser-induced fluorescence emission: a comparative evaluation with reflectance spectroscopy.

BACKGROUND AND OBJECTIVES: Nitrogen laser-induced fluorescence (LIF) spectra of sound tooth consists of two broad bands centered at 440 and 490 nm, with two apparent side bands on either side. In order to locate the exact peak position of these bands and to effectively utilize the LIF spectral signatures for detection of tooth caries, the LIF spectra were curve-fitted using Gaussian spectral functions and the results were compared with those from diffuse reflectance spectral measurements. STUDY DESIGN/MATERIALS AND METHODS: The excitation light at 337.1 nm was guided to the sound and caries-affected tooth samples through the central fiber of the fiber-optic probe of a laser-induced fluorescence reflectance spectroscopy (LIFRS) system. Six surrounding fibers of the probe collect tooth fluorescence or diffuse reflectance from the lesion and direct it to a miniature spectrometer. The in vitro spectra were obtained from healthy enamel, dentin, and pulp level tooth caries. RESULTS: As compared to sound tooth, the caries tooth showed lower fluorescence and reflectance intensities in the 350-700 nm region. The deconvoluted peaks in the LIF spectra of sound tooth were found centered at 403.80, 434.20, 486.88, and 522.45 nm, whereas in the case of pulp level caries, a new peak was observed at 636.78 nm. Curve-fitted parameters, such as peak center, Gaussian curve area, full width at half intensity maximum (FWHM), and their ratios, were also found to vary with the stage of tooth caries. The ratios involving the 435 nm band, such as F405/F435, F435/F490, and F435/F525 ratios derived from curve-fitted areas and amplitudes, were found to be sensitive to discriminate between sound, dentin, and pulp level caries. Among the various diffuse reflectance spectral intensity ratios, the R500/R700 was found to be most sensitive to distinguish between pulp and dentin level caries. CONCLUSIONS: Nitrogen laser-excited fluorescence spectral studies were found to be more suited for detection of caries lesions. The LIF measurement with spectral analysis, done by curve fitting, outscores the diffuse reflectance methodology and shows the potential to screen different levels of tooth decay in a clinical setting.

Quantification of stress adaptation by laser-induced fluorescence spectroscopy of plants exposed to engine exhaust emission and drought.

The effects of drought and petrol engine exhaust pollutants, such as SO2 and NO2 and suspended particulate matter (SPM), on the photosynthetic activity of colocasia [Colocasia esculenta (L.) Schott], kacholam (Kaempferia galanga L.) and tapioca (Manihot esculenta Crantz) plants were studied from in vivo laser-induced chlorophyll fluorescence (LICF) spectra. An open-top chamber (OTC) of 2.5 m diameter and 3 m height incorporating an air-filtering unit was developed for this study. Plants grown inside the OTC were exposed to exhaust emissions from a two-stroke Birla Yamaha genset for 10 d, while a control group was maintained outside. Gaseous pollutants and SPM present inside the OTC during the exposure period were measured with a high-volume air sampler. The steady-state LICF spectra of the control and treated plants were recorded in the 650-750-nm region. Fluorescence induction kinetics (Kautsky effect) was also recorded during the stress period from dark-adapted intact plant leaves at the chlorophyll bands of 685 and 730 nm. The vitality indexes (Rfd-685 and Rfd-730) and stress adaptation index (Ap) derived from the induction kinetics were utilised along with the chlorophyll fluorescence intensity ratio (F685 / F730) for evaluation of stress-induced changes in plants.