Early detection of incipient caries would allow dentists to provide more effective measures to delay or to reverse caries’ progression at earlier stage. Such earlier intervention could lead to improved oral health for the patients and reduced burden to the health system. Previously, we have demonstrated that the combination of morphological and biochemical information furnished by optical coherence tomography (OCT) and polarized Raman spectroscopy (PRS), respectively, provided a unique tool for dental caries management. In this study we will report the first pre-clinical caries detection system that includes a hand-held probe with a size slightly larger than a tooth brush. This probe presents a novel platform combining both OCT and PRS optics in a very tight space ideal for clinical practice. OCT cross-sectional images of near-surface enamel morphology are obtained with miniaturized MEMS scanning device and are processed in real-time to identify culprit regions. These regions are sequentially analyzed with polarized Raman spectroscopy for further confirmation. PRS is performed using 830nm laser line and four detection channels in order to obtain polarized Raman spectroscopic data, i.e. depolarization ratio of the hydroxyapatite Raman band at ~960 cm-1. A detailed description of this hand-held caries detector and ex-vivo/in-vivo test results will be presented.
Treatment of occlusal surfaces with a short-pulsed CO2 9.6 μm wavelength laser has previously been proposed as a
method for caries prevention. A sample of 20 extracted human molars were measured before and after demineralizationremineralization
pH-cycling with ICDAS II visual inspection, DIAGNOdent, quantitative light-induced fluorescence
(QLF), SoproLife in daylight and blue light-induced fluorescence mode, optical coherence tomography (OCT) and
polarized Raman spectroscopy (PRS). Per tooth, one fissure was subjected to laser treatment using a short-pulsed CO2
laser at 9.6 μm wavelength with a fluence of 3.5 J/cm2, 20 Hz pulse repetition rate, 20 μs pulse duration, angulated
handpiece, and focus diameter of 600 μm, while the other fissure was left untreated as control. The teeth were subjected
to a demineralization-remineralization pH-cycling for 9 days.
Cross-sectional micro-hardness testing was done as a gold standard to compare results with findings from the other
detection methods used. Due to the small sample size reported, the trend observed was that laser treated fissures
demonstrated a smaller relative mineral loss ▵Z than the controls. QLF findings followed a similar trend.
Using a rotary catheter probe, OCT measurements were acquired from the various fissures to generate circularly mapped
OCT depth images. PRS measurements of parallel- and cross-polarized spectra were acquired with a Raman microscope
system. Preliminary OCT images showed differences in the initial air-tooth interface, with PRS results indicating a
change in the surface property along with biochemical alterations after pH-cycling. Following pH-cycling, an increase in
the OCT subsurface light backscattering intensity in the control fissures was observed compared to the laser test fissures.
Porphyrin based fluorescence methods like DIAGNOdent and SoproLife, respectively demonstrated only additional light
scattering due to the demineralization process.
Optical coherence tomography (OCT) is emerging as a technology that can potentially be used for the detection and monitoring of early dental enamel caries since it can provide high-resolution depth imaging of early lesions. To date, most caries detection optical technologies are well suited for examining caries at facial, lingual, incisal and occlusal surfaces. The approximal surfaces between adjacent teeth are difficult to examine due to lack of visual access and limited space for these new caries detection tools. Using a catheter-style probe developed at the NRC-Industrial Materials Institute, the probe was inserted into the interproximal space to examine the approximal surfaces with OCT imaging at 1310 nm. The probe was rotated continuously and translated axially to generate depth images in a spiral fashion. The probe was used in a mock tooth arch model consisting of extracted human teeth mounted with dental rope wax in their anatomically correct positions. With this ex vivo model, the probe provided images of the approximal surfaces revealing morphological structural details, regions of calculus, and especially regions of early dental caries (white spot lesions). Results were compared with those obtained from OCT imaging of individual samples where the approximal surfaces of extracted teeth are accessible on a lab-bench. Issues regarding access, regions of interest, and factors to be considered in an in vivo setting will be discussed. Future studies are aimed at using the probe in vivo with patient volunteers.
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.
Nonlinear optical imaging technologies offer some intriguing medical diagnostic applications. Examples include fast
imaging of elastin and collagen distributions in diseased tissues using two-photon fluorescence (TPF) and second
harmonic generation (SHG), respectively. The 3D sectioning capabilities and biochemical specificity that enable fast
imaging in highly scattering biological media lie at the heart of the appeal of these nonlinear approaches for medical
applications. One of these promising nonlinear techniques relies on the resonance enhancement of the third order
nonlinear susceptibility by a vibrational mode of a molecule. Coherent Anti-Stokes Raman Scattering (CARS) can
provide similar vibrational information as a spontaneous Raman spectrum. The technique has been shown to be orders
of magnitude more sensitive than spontaneous Raman, with video rate imaging demonstrated recently. In this work,
we investigate the potential use of broadband CARS spectroscopy and CARS imaging for biochemical analysis of
arterial tissue. Biochemical imaging data from broadband CARS is compared with spontaneous Raman
microspectroscopy. The broadband CARS system comprised of a single femtosecond-laser is presented in detail.
Issues related to data analysis, the advantages and current limitations of the CARS technique in biodiagnostics are
discussed.
Incipient dental caries lesions appear as white spots on the tooth surface; however, accurate detection of early
approximal lesions is difficult due to limited sensitivity of dental radiography and other traditional diagnostic tools. A
new fibre-optic coupled spectroscopic method based on polarized Raman spectroscopy (P-RS) with near-IR laser
excitation is introduced which provides contrast for detecting and characterizing incipient caries. Changes in polarized
Raman spectra are observed in PO43- vibrations arising from hydroxyapatite of mineralized tooth tissue.
Demineralization-induced morphological/orientational alteration of enamel crystallites is believed to be responsible for
the reduction of Raman polarization anisotropy observed in the polarized Raman spectra of caries lesions. Supporting
evidence obtained by polarized Raman spectral imaging is presented. A specially designed fibre-optic coupled setup for
simultaneous measurement of parallel- and cross-polarized tooth Raman spectra is demonstrated in this study.
Early dental caries detection facilitates implementation of non-surgical methods for arresting caries progression and
promoting tooth remineralization. We present a method based on Raman spectroscopy with near-IR laser excitation to
provide biochemical contrast for detecting and characterizing incipient carious lesions found in extracted human teeth.
Changes in Raman spectra are observed in PO43- vibrations arising from hydroxyapatite of mineralized tooth tissue. Examination of various intensities of the PO43- ν2, ν3, ν4 vibrations showed consistent increased intensities in spectra of carious lesions compared to sound enamel. The spectral changes are attributed to demineralization-induced alterations of
enamel crystallite morphology and/or orientation. This hypothesis is supported by reduced Raman polarization
anisotropy derived from polarized Raman spectra of carious lesions. Polarized Raman spectral imaging of carious
lesions found on whole (i.e. un-sectioned) tooth samples will also be presented.
Atherosclerosis is traditionally viewed as a disease of uncontrolled plaque growth leading to arterial occlusion. More
recently, however, occlusion of the arterial lumen is being viewed as an acute event triggered by plaque rupture and
thrombosis. An atheromatous plaque becomes vulnerable to sudden activation and/or rupture when a constellation of
processes are activated by various trigger mechanisms. There is growing evidence that the vulnerability (i.e.
susceptibility to rupture) and thrombogenic nature of the plaque need to be taken into account in the planning and
treatment of the disease. X-ray fluoroscopy and intravascular ultrasound, the current clinical diagnostic tools are not
capable of the providing a complete histological picture of the plaque region.
Intravascular diagnostic imaging of coronary atherosclerotic plaques by optical means to assess plaque, patient risk and
assist in planning treatment strategies represents the future in angioplasty treatment by interventional cardiologists. The
techniques which will enable a clinically acceptable and reliable intravascular diagnostic platform are currently being
investigated and compared to the clinical standard of histology.
Currently, we are investigating the use of a number of optical and imaging techniques for biochemical analysis of
arterial tissue including Raman, near infrared and fluorescence spectroscopies. Biochemical imaging will provide
compositional information on collagen, elastin, lipid and thrombogenic by-products as well as gauging inflammation
and tissue remodeling activity levels. To complement the functional biochemical imaging, optical coherence
tomography will be provide structural morphological imaging. The synergistic combination of functional and structural
imagery will provide the interventional cardiologist with a complete clinical picture of the atherosclerotic plaque region.
The clinician can use this diagnostic information to plan a personalized treatment procedure based on the entire clinical
presentation.
The early approximal caries lesion in enamel is observed clinically as a white spot and is difficult to detect and/or
monitor with current methods available to dentists. New methods with high sensitivity and specificity are required to
enable improved early dental caries diagnosis. Using unpolarized Raman spectroscopy to examine unsectioned teeth,
peak intensity changes in the phosphate (PO43-) vibrations (ν2, ν3 and ν4) were observed between spectra of sound and
carious enamel. However, there is little change in the ν1 vibration with this approach. In contrast, when tooth sections
were examined by unpolarized Raman spectroscopy, marked changes in the ν1 peak at 959 cm-1 were noted between
healthy and carious enamel. These differences suggest that sampling orientation play a role in understanding the spectral
changes. Using polarized Raman spectroscopy to examine unsectioned samples, cross polarized measurements from
sound enamel exhibited significant reduction of the ν1 peak compared with parallel polarized measurements. A similar
reduction was observed with carious enamel, however, the reduction was not as prominent. By calculating the
depolarization ratio of the area under the ν1 peak, sound enamel can be clearly distinguished from demineralized
regions. The spectral changes observed are attributed to changes in the structure and/or orientation of the apatite crystals
as a result of the acid demineralization process.
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 µm 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 PO vibrations arising from hydroxyapatite of mineralized tooth tissue. Examination of various ratios of PO 2, 3, 4 vibrations against the 1 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.
Early dental caries result from destruction of the tooth's outer mineral matrix by acid-forming bacteria found in dental plaques. Early caries begin as surface disruptions where minerals are leached from the teeth resulting in regions of decreased mineral matrix integrity. Visually, these early carious regions appear as white spots due to the higher backscattering of incident light. With age these areas may become stained by organic compounds. Optical coherence tomography (OCT) examination of human teeth demonstrates a difference in penetration depth of the OCT signal into the carious region in comparison with sound enamel. However, while OCT demonstrates a structural difference in the enamel in the region of the caries, this technique provides little insight into the source of this difference. Raman spectroscopy provides biochemical measures derived from hydroxyapatite within the enamel as well as information on the crystallinity of the enamel matrix. The differences in the biochemical and morphological features of early caries and intact sound enamel are compared. Histological thin sections confirm the observations by OCT morphological imaging while Raman spectroscopy allows for biochemical identification of carious regions by a non-destructive method. Visual examination and conventional radiographic imaging of the intact tooth are used in clinical assessment prior to optical measurements. The combination of OCT, Raman spectroscopy and thin section histology aid in determining the changes that give rise to the visual white spot lesions.
A new approach is presented to distinguish cancerous from normal brain tissue via linear discriminant analysis of Fourier transform infrared (FTIR) spectra. FTIR microspectroscopy was used to map various thin-section tumor samples with different malignancy grades (grades II-VI) and non-tumor samples obtained from various patients by surgical removal. Spectral analysis revealed features characteristic of tumors with increasing malignancy. A genetic region selection algorithm combined with linear discriminant analysis was used to derive classifiers distinguishing among spectra of control tissue, astrocytoma grade II, astrocytoma grade III and glioblastoma grade IV. Employing the World Health Organization histopathological diagnostic scheme as the gold standard, the spectra were classified with a success rate of approximately 85 percent. These results demonstrate the potential of the combination of FTIR spectroscopy and pattern recognition routines in providing a more objective method for brain tumour grading and diagnosis.
Routine clinical microbiological identification of pathogenic micro-organisms is largely based on nutritional and biochemical tests. Laboratory results can be presented to a clinician after 2 - 3 days for most clinically relevant micro- organisms. Most of this time is required to obtain pure cultures and enough biomass for the tests to be performed. In the case of severely ill patients, this unavoidable time delay associated with such identification procedures can be fatal. A novel identification method based on confocal Raman microspectroscopy will be presented. With this method it is possible to obtain Raman spectra directly from microbial microcolonies on the solid culture medium, which have developed after only 6 hours of culturing for most commonly encountered organisms. Not only does this technique enable rapid (same day) identifications, but also preserves the sample allowing it to be double-checked with traditional tests. This, combined with the speed and minimal sample handling indicate that confocal Raman microspectroscopy has much potential as a powerful new tool in clinical diagnostic microbiology.
The abnormal abundance of (beta) -amyloid plaques and neurofibrillary tangles are the hallmark of Alzheimer's disease (AD). Human central nervous system (CNS) grey matter was probed for characteristics arising from these pathological features. In AD but not normal grey matter, an IR band at 1615 cm-1 is seen, characteristic of a protein in an aggregated state. We speculate that this band arises from (beta) A4-amyloid protein. AD, and 18q- grey matter spectra show increased intensity of phosphate bands in accordance with known hyperphosphorylation of proteins found in neurofibrillary tangles. These spectral features may be useful in the diagnosis of AD.
FT-IR spectroscopy has been used to characterize white matter, grey matter, and multiple sclerosis (MS) plaques from human central nervous system (CNS) tissue. Discrimination among these three tissue types is possible due to variations in composition. Spectra of white matter exhibit strong lipid absorptions. In contrast, spectra of grey matter reveal a reduced lipid contribution and a significant absorption from water. MS plaques exhibit spectra indicative of lipid loss and, depending upon whether the plaques are chronic or acute, changes in the protein and/or water content.
The secondary structure of the naturally occurring isoforms of myelin basic protein (MBP1-8) from human myelin was studied by Fourier transform infrared spectroscopy under a variety of experimental conditions. In aqueous solution each isoform was found to be unstructured. In the presence of negatively charged liquid bilayers MBP1-4 were shown to exhibit an amide I band maximum indicative of the adoption of (alpha) -helical secondary structures. A detailed analysis revealed that significant proportions of (beta) -sheet secondary structure were also present. MBP5 and MBP8, which have significantly less cationic charge than MBP1-4, exhibited an amide I maximum identical to that seen in solution, suggesting that no interaction with the bilayer occurred. Analysis of the lipid CH2 and C equals O stretching vibrations also pointed towards significant interaction of MBP1-4 with the bilayer. The changes in intensity and frequency of these bands which typically accompany the phase transition in the pure bilayer were abolished by addition of the proteins. No such effect was seen for MBP5 and 8, the normal lipid phase transition being apparent. The implications of these results in the aetiology of multiple sclerosis is discussed.
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