Imaging of the oral cavity using optical coherence tomography.

Optical coherence tomography is a new method for noninvasively imaging internal tooth and soft tissue microstructure. The intensity of backscattered light is measured as a function of depth in the tissue. Low coherence interferometry is used to selectively remove the component of backscattered signal that has undergone multiple scattering events, resulting in very high resolution images (< 15 microns). Lateral scanning of the probe beam across the biological tissue is then used to generate a 2-D intensity plot, similar to ultrasound images. This imaging method provides information that is currently unobtainable by any other means, making possible such diverse applications as diagnosis of periodontal disease, caries detection, and evaluation of restoration integrity. This chapter presents an overview of this exciting new imaging technique and its current application to dental diagnosis.

Dental optical coherence tomography: a comparison of two in vitro systems.

OBJECTIVE: To compare the imaging results obtained with two different in vitro prototype dental optical coherence tomography (OCT) systems. METHODS: Two prototypes were evaluated: an 850 nm wavelength, 700 microW OCT system with a relatively low numerical aperture (0.03) and a 1310 nm wavelength, 140 microW system with a higher numerical aperture (0.20). RESULTS: Using the 850 nm system a characteristic scattering signal was observed that correlated with the depth of a periodontal probe. There was, however, insufficient light penetration to create images with adequate resolution. Improved image quality was achieved with the 1310 nm OCT system; these images had sufficient resolution to allow identification of anatomical structures important for the diagnostic assessment of oral structures. CONCLUSIONS: These results illustrate the improvement in imaging dental structures that can be obtained with a prototype 1310 nm OCT system. The feasibility of OCT as a dental imaging technique is verified.

Optical coherence tomography: a new imaging technology for dentistry.

BACKGROUND: Optical coherence tomography, or OCT, is a new diagnostic imaging technique that has many potential dental applications. The authors present the first intraoral dental images made using this technology. METHODS: The authors constructed a prototype dental OCT system. This system creates cross-sectional images by quantifying the reflections of infrared light from dental structures interferometrically. RESULTS: We used our prototype system to make dental OTC images of healthy adults in a clinical setting. These OCT images depicted both hard and soft oral tissues at high resolution. CONCLUSIONS: OCT images exhibit microstructural detail that cannot be obtained with current imaging modalities. Using this new technology, visual recordings of periodontal tissue contour, secular depth and connective tissue attachment now are possible. The internal aspects and marginal adaptation of porcelain and composite restorations can be visualized. CLINICAL IMPLICATIONS: There are several advantages of OCT compared with conventional dental imaging. This new imaging technology is safe, versatile, inexpensive and readily adapted to a clinical dental environment.

Evaluation of optical coherence quantitation of analytes in turbid media by use of two wavelengths.

We introduce a novel method for determining analyte concentration as a function of depth in a highly scattering media by use of a dual-wavelength optical coherence tomography system. We account for the effect of scattering on the measured attenuation by using a second wavelength that is not absorbed by the sample. We assess the applicability of this technique by measuring the concentration of water in an Intralipid phantom, using a probe wavelength of 1.53 microm and a reference wavelength of 1.31 microm. The results of our study show a strong correlation between the measured absorption and the water content of the sample. The accuracy of the technique, however, was limited by the dominance of scattering over absorption in the turbid media. Thus, although the effects of scattering were minimized, significant errors remained in the calculated absorption values. More-accurate results could be obtained with the use of more powerful superluminescent diodes and a choice of wavelengths at which absorption effects are more significant relative to scattering.

Birefringence characterization of biological tissue by use of optical coherence tomography.

An improved polarization-sensitive optical coherence tomography (OCT) system is developed and used to measure birefringence in porcine myocardium tissue and produce two-dimensional birefringence mapping of the tissue. Signal-to-noise issues that cause systematic measurement errors are analyzed to determine the regime in which such measurements are accurate. The advantage of polarization-sensitive OCT systems over standard OCT systems in avoiding image artifacts caused by birefringence is also demonstrated.

Imaging of hard- and soft-tissue structure in the oral cavity by optical coherence tomography.

We have developed a prototype optical coherence tomography (OCT) system for the imaging of hard and soft tissue in the oral cavity. High-resolution images of in vitro porcine periodontal tissues have been obtained with this system. The images clearly show the enamel-cementum and the gingiva-tooth interfaces, indicating OCT is a potentially useful technique for diagnosis of periodontal diseases. To our knowledge, this is the first application of OCT for imaging biologic hard tissue.

Mapping of Birefringence and Thermal Damage in Tissue by use of Polarization-Sensitive Optical Coherence Tomography.

We demonstrate cross-sectional birefringence- and polarization-independent backscatter imaging of laser-induced thermal damage in porcine myocardium in vitro, using a polarization-sensitive optical coherence tomography system. We compare the generated images with histological sections of the tissue and demonstrate that birefringence is a more sensitive indicator of thermal damage than is backscattered light. Loss of birefringence in thermally damaged regions is quantified and shown to have significant contrast with undamaged sections of the tissue. A detailed theoretical analysis of the birefringence measurements is provided, including a calculation of the systematic errors associated with background noise, system imperfections, and tissue dichroism.

A fiber-optic sensor system for monitoring chlorinated hydrocarbon pollutants.

We have developed and field-tested a fiber-optic chemical sensor system for use in environmental monitoring and remediation. The system detects chlorinated hydrocarbon pollutants with colorimetry, and is based on an irreversible chemical reaction between the target compound and a specific reagent. The reaction products are detected by their absorption at 560 nm and can be monitored remotely with optical fibers. Continuous measurements are made possible by renewing the reagent from a reservoir with a miniature pumping system. The sensor has been evaluated against gas chromatography standards and has demonstrated accuracy and sensitivity (5 ppbw) sufficient for the environmental monitoring of trichloroethylene and chloroform. Successful preliminary field tests have been conducted in a variety of contamination monitoring scenarios.

Dermal absorption of dilute aqueous chloroform, trichloroethylene, and tetrachloroethylene in hairless guinea pigs.

Percutaneous absorption was measured in female hairless guinea pigs dermally exposed for 70 min to very dilute (approximately 10 to 100 ppb) aqueous solutions of 14C-labeled chloroform (CF), trichloroethylene (TCE), or tetrachloroethylene (PCE) in an airtight glass chamber containing no headspace. Similar experiments were conducted using aqueous solutions of TCE at 100,000 ppb. Dermal uptake was estimated by comparing the rate of radiolabel loss from chamber water in systems with and without experimental animals. After each low-concentration dermal-uptake experiment, radiolabel in total urine and feces excreted postexposure was measured and expressed as a fraction of corresponding estimated dermal uptake. For each of the compounds studied, the mean value of these fractions did not differ significantly from that obtained using animals injected with a known dose of that compound, indicating that our experimental system yielded accurate dermal-uptake estimates. The mean permeability coefficients obtained range from 0.13 cm/hr (CF) to 0.37 cm/hr (PCE); those obtained using low- vs high-concentration TCE are not significantly different. The value for CF is very close to one we calculate here from recently published data on CF uptake in human volunteers dermally exposed to aqueous CF while showering with normal tap water. Our results suggest that dermal absorption may be an important route of human exposure to chlorinated volatile organic compounds in domestic water supplies.