A comparison of methods using optical coherence tomography to detect demineralized regions in teeth.

Optical coherence tomography (OCT) is a three- dimensional optical imaging technique that can be used to identify areas of early caries formation in dental enamel. The OCT signal at 850 nm back-reflected from sound enamel is attenuated stronger than the signal back-reflected from demineralized regions. To quantify this observation, the OCT signal as a function of depth into the enamel (also known as the A-scan intensity), the histogram of the A-scan intensities and three summary parameters derived from the A-scan are defined and their diagnostic potential compared. A total of 754 OCT A-scans were analyzed. The three summary parameters derived from the A-scans, the OCT attenuation coefficient as well as the mean and standard deviation of the lognormal fit to the histogram of the A-scan ensemble show statistically significant differences (p < 0.01) when comparing parameters from sound enamel and caries. Furthermore, these parameters only show a modest correlation. Based on the area under the curve (AUC) of the receiver operating characteristics (ROC) plot, the OCT attenuation coefficient shows higher discriminatory capacity (AUC = 0.98) compared to the parameters derived from the lognormal fit to the histogram of the A-scan. However, direct analysis of the A-scans or the histogram of A-scan intensities using linear support vector machine classification shows diagnostic discrimination (AUC = 0.96) comparable to that achieved using the attenuation coefficient. These findings suggest that either direct analysis of the A-scan, its intensity histogram or the attenuation coefficient derived from the descending slope of the OCT A-scan have high capacity to discriminate between regions of caries and sound enamel.

Optical coherence tomography: fundamental principles, instrumental designs and biomedical applications.

The advances made in the last two decades in interference technologies, optical instrumentation, catheter technology, optical detectors, speed of data acquisition and processing as well as light sources have facilitated the transformation of optical coherence tomography from an optical method used mainly in research laboratories into a valuable tool applied in various areas of medicine and health sciences. This review paper highlights the place occupied by optical coherence tomography in relation to other imaging methods that are used in medical and life science areas such as ophthalmology, cardiology, dentistry and gastrointestinal endoscopy. Together with the basic principles that lay behind the imaging method itself, this review provides a summary of the functional differences between time-domain, spectral-domain and full-field optical coherence tomography, a presentation of specific methods for processing the data acquired by these systems, an introduction to the noise sources that plague the detected signal and the progress made in optical coherence tomography catheter technology over the last decade.

Determining the effect of calculus, hypocalcification, and stain on using optical coherence tomography and polarized Raman spectroscopy for detecting white spot lesions.

Optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS) have been shown as useful methods for distinguishing sound enamel from carious lesions ex vivo. However, factors in the oral environment such as calculus, hypocalcification, and stain could lead to false-positive results. OCT and PRS were used to investigate extracted human teeth clinically examined for sound enamel, white spot lesion (WSL), calculus, hypocalcification, and stain to determine whether these factors would confound WSL detection with these optical methods. Results indicate that OCT allowed differentiating caries from sound enamel, hypocalcification, and stain, with calculus deposits recognizable on OCT images. ANOVA and post-hoc unequal N HSD analyses to compare the mean Raman depolarization ratios from the various groups showed that the mean values were statistically significant at P < .05, except for several comparison pairs. With the current PRS analysis method, the mean depolarization ratios of stained enamel and caries are not significantly different due to the sloping background in the stained enamel spectra. Overall, calculus and hypocalcification are not confounding factors affecting WSL detection using OCT and PRS. Stain does not influence WSL detection with OCT. Improved PRS analysis methods are needed to differentiate carious from stained enamel.

Speckle reduction and lesion segmentation of OCT tooth images for early caries detection.

The significance of identifying early non-cavitated carious lesions and monitoring the lesion extent has led to increasing prospects for prevention, early diagnosis, and implementation of conservative treatments. This paper emphasizes the importance of speckle reduction and possible lesion segmentation options of optical coherence tomography (OCT) images prior to caries detection. First, a comparison of popular speckle reduction filters is presented. These filtering algorithms were evaluated to measure the ability of different methods for reducing background noise from raw images. Both qualitative and quantitative results (signal-to-noise ratio, contrast-to-noise ratio) are reported. Image segmentation is then applied to multiple tooth images. With proper thresholding, high intensity response regions are outlined with the possibility of assessing caries and monitoring its regression. Our results show that a rotating kernel transformation (RKT) filter with 9x9 kernel size provides a good compromise between noise reduction yet preserving the pathological features of interest as required for subsequent feature segmentation analyses.

Assessment of early demineralization in teeth using the signal attenuation in optical coherence tomography images.

Optical coherence tomography imaging is used to improve the detection of incipient carious lesions in dental enamel. Measurements of signal attenuation in images acquired with an 850-nm light source were performed on 21 extracted molars from eight human volunteers. Stronger attenuation was observed for the optical coherence tomography (OCT) signal in healthy enamel than in carious lesions. The measured attenuation coefficients from the two groups form distinct statistical populations. The coefficients obtained from sound enamel fall within the range of 0.70 to 2.14 mm(-1) with a mean value of 1.35 mm(-1), while those in carious regions range from 0.47 to 1.88 mm(-1), with a mean value of 0.77 mm(-1). Three values are selected as the lower threshold for signal attenuation in sound enamel: 0.99, 0.94, and 0.88 mm(-1). These thresholds were selected to provide detection of sound enamel with fixed specificities of 90%, 95%, and 97.5%, respectively. The corresponding sensitivities for the detection of carious lesions are 92.8%, 90.4%, and 87%, respectively, for the sample population used in this study. These findings suggest that attenuation of OCT signal at 850 nm could be an indicator of tooth demineralization and could be used as a marker for early caries detection.

Early dental caries detection using a fibre-optic coupled polarization-resolved Raman spectroscopic system.

A new fibre-optic coupled polarization-resolved Raman spectroscopic system was developed for simultaneous collection of orthogonally polarized Raman spectra in a single measurement. An application of detecting incipient dental caries based on changes observed in Raman polarization anisotropy was also demonstrated using the developed fibre-optic Raman spectroscopic system. The predicted reduction of polarization anisotropy in the Raman spectra of caries lesions was observed and the results were consistent with those reported previously with Raman microspectroscopy. The capability of simultaneous collection of parallel- and cross-polarized Raman spectra of tooth enamel in a single measurement and the improved laser excitation delivery through fibre-optics demonstrated in this new design illustrates its future clinical potential.

Shedding new light on early caries detection.

Dental caries continues to be a common chronic disease among various population groups. Patient care can be improved with detection at the earliest stage. However, current techniques do not have sufficient sensitivity and specificity. We discuss 2 new methods - optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS) - that are potentially useful for early caries detection and monitoring. OCT produces morphologic depth images of near-surface tissue structures with a resolution that is an order of magnitude greater than ultrasound imaging. Based on measurement of back-scattered near infrared light, OCT shows that sound enamel causes high-intensity back-scattering at the tooth surface that decreases rapidly with depth. In contrast, incipient lesions cause higher light back-scattering at the tooth surface and subsurface scattering indicative of porosity caused by demineralization. The scatter region within the enamel correlates well with the classical triangular shape of subsurface lesions observed in histologic sections. OCT imaging not only allows identification of incipient lesions, but also provides information on surface integrity and lesion depth. PRS furnishes biochemical information about the tooth"s composition, mineral content and crystallinity. The depolarization ratio derived from the dominant phosphate peak of hydroxyapatite in sound teeth is consistently lower than that from incipient caries. This difference is attributed to the change in enamel crystallite morphology or orientation that occurs with acid demineralization. Thus, PRS can be used to confirm suspect lesions determined by OCT and rule out false-positive signals from non-carious anomalies. The combination of OCT and PRS provides a new detection method with high sensitivity and specificity that will improve caries management and patient care. Future studies are aimed at developing intraoral probes to validate the findings in vivo.

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel.

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric nu(1) vibration of PO4(3-) at approximately 959 cm(-1) have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.

Semi-parametric estimation in the compositional modeling of multicomponent systems from Raman spectroscopic data.

Identification and quantification of molecular species are central applications of molecular spectroscopy. In complex multicomponent systems like tissue samples, linear parametric models are often used to estimate the relative concentrations of the biochemical components of the sample. In situations where not all of the components of the sample are known or modeled, such parametric models can suffer from omitted variable bias and result in skewed estimates of component concentrations. We propose a semi-parametric approach that tries to avoid this omitted variable bias by effectively including unknown covariates as a non-parametric term in the regression equation. Constituent concentrations estimated with such partial linear models should outperform strict parametric linear models when the user has limited information on the composition of a multi-constituent system.

Detection of early dental caries using polarized Raman spectroscopy.

A new technique based on polarized Raman spectroscopy is demonstrated for detecting early dental caries on extracted human teeth. Sound tooth enamel exhibited strong Raman polarization anisotropy whereas early caries consistently showed a lower degree of Raman polarization anisotropy. In particular, for sound enamel, the Raman peak arising from the symmetric nu1 vibration of PO(4) (3-) at 959 cm(-1) is strongly polarized. This is in contrast to the spectra of carious lesions that displayed weaker polarization dependence at 959 cm(-1). Such difference in the degree of Raman polarization anisotropy allows for discrimination between early dental caries and sound enamel.

Ex vivo detection and characterization of early dental caries by optical coherence tomography and Raman spectroscopy.

Early dental caries detection will facilitate implementation of nonsurgical methods for arresting caries progression and promoting tooth remineralization. We present a method that combines optical coherence tomography (OCT) and Raman spectroscopy to provide morphological information and biochemical specificity for detecting and characterizing incipient carious lesions found in extracted human teeth. OCT imaging of tooth samples demonstrated increased light backscattering intensity at sites of carious lesions as compared to the sound enamel. The observed lesion depth on an OCT image was approximately 290 microm matching those previously documented for incipient caries. Using Raman microspectroscopy and fiber-optic-based Raman spectroscopy to characterize the caries further, spectral changes were observed in PO4 (3-) vibrations arising from hydroxyapatite of mineralized tooth tissue. Examination of various ratios of PO4 (3-) nu2, nu3, nu4 vibrations against the nu1 vibration showed consistent increases in carious lesions compared to sound enamel. The changes were attributed to demineralization-induced alterations of enamel crystallite morphology and/or orientation. OCT imaging is useful for screening carious sites and determining lesion depth, with Raman spectroscopy providing biochemical confirmation of caries. The combination has potential for development into a new fiber-optic diagnostic tool enabling dentists to identify early caries lesions with greater sensitivity and specificity.

Distinguishing and grading human gliomas by IR spectroscopy.

As a molecular probe of tissue composition, IR spectroscopy can potentially serve as an adjunct to histopathology in detecting and diagnosing disease. This study demonstrates that cancerous brain tissue (astrocytoma, glioblastoma) is distinguishable from control tissue on the basis of the IR spectra of thin tissue sections. It is further shown that the IR spectra of astrocytoma and glioblastoma affected tissue can be discriminated from one another, thus providing insight into the malignancy grade of the tissue. Both the spectra and the methods employed for their classification reveal characteristic differences in tissue composition. In particular, the nature and relative amounts of brain lipids, including both the gangliosides and phospholipids, appear to be altered in cancerous compared to control tissue. Using a genetic classification approach, classification success rates of up to 89% accuracy were obtained, depending on the number of regions included in the model. The diagnostic potential and practical applications of IR spectroscopy in brain tumor diagnosis are discussed.

Prevention of peptide fibril formation in an aqueous environment by mutation of a single residue to Aib.

The behavior of a number of 16 residue polypeptides with a sequence Acetyl-EACARXZAACEAAARQ-amide, where X = V or A and Z = A or Aib, is studied under aqueous conditions. It is shown that the substitution of a single alanine residue by alpha-aminoisobutyric acid (Aib) completely alters both the conformation and the aggregation properties of the peptides. The Ala-Ala (X,Z = A,A) peptide is shown by circular dichroism and FTIR methods to adopt a predominately beta-sheet conformation. Furthermore, the peptide has limited solubility and is shown to form fibrils by electron microscopy and thioflavin T binding assays. In contrast, a single substitution at the center of peptide of alanine to Aib (X,Z = A,Aib) completely abolishes fibril formation and alters the conformation to a mixture of random coil and alpha-helix. The results show that Aib is a strong beta-sheet disrupter that is also able to adopt a helical conformation. This is linked to its role in peptaibol antibiotics. Aib provides an attractive alternative to proline and other substitutions in producing peptide variants with a lower tendency to produce fibril aggregates.

Discriminating vital tumor from necrotic tissue in human glioblastoma tissue samples by Raman spectroscopy.

Vital and necrotic glioblastoma tissues were studied by Raman microspectroscopy to identify possibilities for the development of an in vivo Raman method for real-time intraoperative brain biopsy guidance. The histologic malignancy grade of gliomas depends on the presence of parameters such as endothelial proliferation and necrosis, which are often not evenly distributed within the tumor. Because tissue samples obtained by stereotactic surgery are relatively small, sampling errors may easily occur by missing these crucial features. Although necrosis is important for grading, specimens containing only necrosis are diagnostically useless. Raman microspectroscopic mapping experiments were performed on unfixed cryosections of glioblastoma, obtained from 20 patients. After spectral acquisition, a clustering analysis was performed, resulting in groups of similar spectra. Each cluster was assigned a color, and pseudo-color Raman maps of the tissue sections were constructed. After the Raman experiments, the tissue sections were stained for histopathologic analysis, enabling identification of the histologic origin of the Raman spectra and assignment of the Raman spectral clusters to either vital or necrotic tissue. A classification model for discrimination between vital and necrotic tumor tissue based on linear discriminant analysis was developed. The classification model was evaluated using independent Raman data obtained from nine other tissue sections and yielded 100% accuracy. Information about the biochemical differences between necrosis and vital tumor was obtained by the analysis of difference spectra. Necrotic tissue was found to consistently contain higher levels of cholesterol (-esters). This in vitro result indicates that Raman spectra contain the information to distinguish vital glioblastoma from necrosis and makes Raman spectroscopy a powerful candidate for guidance of stereotactic brain biopsy.