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.

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.

Threshold and ablation efficiency studies of microsecond ablation of gelatin under water.

BACKGROUND AND OBJECTIVE: Laser thrombolysis is the selective ablation of thrombus occluding vessels by microsecond pulsed laser irradiation. To achieve efficient ablation of thrombus, the optimal wavelength, spot size, and pulse energy need to be determined. STUDY DESIGN/MATERIALS AND METHODS: A gelatin-based thrombus model confined in 3 mm inner diameter tubes was ablated under water using a 1 microsecond pulsed dye laser. Wavelength studies were conducted by varying the absorption of the gelatin between 10-2000 cm-1 corresponding to the waveband between 400-600 nm on the absorption spectrum of thrombus. A unique spectrophotometric method was developed to measure the ablated mass. An acoustic method was used to measure ablation thresholds under water as a function of absorption. RESULTS: The mass removed per pulse per unit energy was nearly equal over an absorption range of 100-1000 cm-1 at pulse energies above threshold. Mass removal increased linearly with pulse energy but did not have a direct relationship with radiant exposure. Ablation thresholds indicate that the gelatin needed to be heated only to 100 degrees C for ablation to commence. Ablation masses measured were an order of magnitude higher than those predicted by thermal ablation models. CONCLUSION: The results suggest that any wavelength between 410-590 nm can be used for effective thrombolysis. The ablation efficiency depends on the total energy delivered rather than the radiant exposure. The high ablation efficiencies suggest a dominance of the mechanical action of vapor bubbles over thermal ablation in the ablation process.