INFORMATICS AND TECHNOLOGY |
JADA Continuing Education
OPTICAL COHERENCE TOMOGRAPHY: A NEW IMAGING
TECHNOLOGY FOR DENTISTRY
LINDA L. OTIS, D.D.S., M.S.,
MATTHEW J. EVERETT, PH.D.,
UJWAL S. SATHYAM, PH.D. and
BILL W. COLSTON JR., PH.D.
 |
ABSTRACT
|
|---|
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, sucular 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.
In plain film radiographic techniques, such as periapical or cephalometric radiography, the radiographic source and film are stationary. All anatomical structures interposed between the X-ray source and the film are present in the image. The disadvantage of plain film radiography is that important diagnostic information often is obscured by the superimposition of regional anatomy; for example, the morphological characteristics of the mandibular condyles are obscured in a cephalometric radiograph by the dense overlying structures of the cranial base.
The term tomography first was used to describe sectional radiographic techniques. When the radiographic tube is moved during exposure synchronous with the film plate, but in the opposite direction, the image of a selected anatomical plane remains stationary on the moving film while the shadows of all other planes are blurred or obliterated. A tomographic image, thus, represents a selected "layer" or "slice" of the structure whose images have been recorded. In tomographic images, for example, the mandibular condyles are clearly visualized without the superimposition of the dense cranial base. Panoramic radiographs are the most common form of tomographic imaging used in dentistry.
Tomography now is used as a general term to describe any imaging method that produces images of selected anatomical planes within a structure. The tomographic images created by panoramic radiography and computed tomography result from the interaction of biological tissues with X-radiation photons. Recent developments in the field of optical engineering have made it possible for researchers to consider optical techniques for biomedical imaging applications. These developments include the increased availability of compact, modular diode light sources and the development of highly sensitive detectors that make it possible to distinguish very small numbers of light photons after they interact with tissue.
|
OPTICAL COHERENCE TOMOGRAPHY
|
|---|
A new imaging technique, called optical coherence tomography, or OCT, creates cross-sectional images of biological structures using differences in the reflection of light. This technique uses broad-band, near-infrared light sources with considerable penetration into tissue, yet it has no known detrimental biological effect.1 Microstructural tissue detail is revealed by differentiating between scattered and transmitted, or reflected, photons.2–7 OTC was first proposed for use as a biological imaging system in 1991 by Huang and colleagues.2 Because of their collaborative work, OCT imaging now is being used in clinical practice in ophthalmology.3,4
|
DENTAL OPTICAL COHERENCE TOMOGRAPHY
|
|---|
We have developed and tested an OCT system to make images of dental structures.8–14 Our prototype dental OCT system consists of a computer, compact diode light source, photodetector with associated electronics and handpiece that scans a fiber-optic cable over the oral tissues (Figure 1
). The system uses a white light fiber-optic Michelson interferometer connected to a handpiece that moves the sample arm linearly to create a tomographic scan. Light from the low-coherence diode is separated by a fiber-optic splitter into sample and reference arms of the interferometer. Reflections from the reference mirror and backscattered light from the tissue are recombined at the splitter and transmitted to the photodetector. An interference signal is detected when the pathlength of light reflected from the tissue and the reference mirror is within the coherence length of the source. Because the position of the reference mirror is known, the location within the tissue of the reflected signal can be precisely determined.
View larger version (17K):
[in this window]
[in a new window]
|
Figure 1. Schematic of the dental optical coherence tomography, or OCT, system. OCT is based on a Michelson white light interferometer.
| |
A single interferometric signal measured at a specific point on the tissue gives the reflective boundary along the axis of the beam (Figure 2A). The locations of reflected signals correspond to their axial position, while the magnitude of the signal is determined by the unique scattering characteristics of a particular tissue. Signals, therefore, are relatively high at tissue interfaces. Signal amplitudes are assigned a gray scale, or false color, value in the computer and are displayed in a linear array. These amplitude differences create a range of contrast that is characteristic of the tissue interactions with the light photons. As the handpiece scans the light across a region of clinical interest, axial signals are serially displayed. The final OCT image is a composite of many axial signal arrays (Figure 2B); in other words, the OCT image is a two-dimensional representation of the optical reflections of tissue in cross-section.
View larger version (31K):
[in this window]
[in a new window]
|
Figure 2. A. An optical coherence tomographic image is a computer compilation of a series of axial interferometric signals. B. The resulting image is a two-dimensional representation of optical reflections of the tissue in cross-section. DEJ: Dentino-enamel junction.
| |
|
DENTAL OPTICAL COHERENCE TOMOGRAPHIC IMAGES
|
|---|
In previous studies, we verified the accuracy of OCT for taking in vitro images of dental structures using an animal model.8,9,14 We found that these images corresponded to histologic images, and we correlated probing depths to sulcular depth measurements made in OCT images.
To test the capacity of our system to take in vivo images of dental structures, we used our prototype system to take dental OCT images of healthy adults with normal dentitions and no clinical evidence of gingivitis or periodontal disease; this test was approved by the Institutional Review Board at The University of Connecticut Health Center School of Dental Medicine. Our system uses a 140-microwatt, 1310-nanometer superluminescent diode light source and detects up to 70 femtowatts of reflected light. It has an imaging depth of approximately 3 millimeters; imaging depth is limited by the amount of light that is propagated through the tissue, as well as the image acquisition time. Image acquisition time in our current system is 45 seconds.
The images we made represent the first in vivo OCT images of human dental tissue. Figure 3 is an OCT image of the midbuccal surface of a mandibular premolar. The OCT scans were made along the long axis of the tooth near the cervical region. The images represent a labial-lingual cross-section of the tooth at a resolution determined by the diameter of the OCT beam (20 micrometers). The axial resolution of 12 µm in periodontal tissue is given by the coherence length of the light source (16 µm) separated by the refractive index of the tissue.1,3
View larger version (51K):
[in this window]
[in a new window]
|
Figure 3. Optical coherence tomographic, or OCT, image of the facial surface of a mandibular premolar. OCT signals are high at tissue interfaces like the gingival sulcus. OCT images provide a visual recording of periodontal structure. DEJ: Dentino-enamel junction.
| |
Our in vivo dental OCT images clearly depict anatomical structures that are important in the diagnostic evaluation of both hard and soft oral tissue. Periodontal tissue contour, sulcular depth and connective tissue attachment are visualized at high resolution using this technology. We are evaluating its clinical usefulness for periodontal assessments in ongoing clinical studies. Because OCT reveals microstructural detail of the periodontal soft tissues, it offers the potential for identifying active periodontal disease before significant alveolar bone loss occurs.14 OCT images of the periodontium can be stored in the patient record, providing visual documentation of disease progression, response to therapy or both. More extensive clinical studies that will correlate OCT parameters to current diagnostic assessments such as probing depths are ongoing.
|
OPTICAL COHERENCE TOMOGRAPHIC IMAGES OF RESTORED TEETH
|
|---|
While intraoral radiographs are highly sensitive and specific for diagnosing primary caries, they are less reliable in the detection of recurrent caries around existing restorations. OCT offers a potentially more sensitive method for detecting recurrent caries. Moreover, images of the fit and marginal adaptation restoration margins can be made and quantified.
An OCT image of the margin of a cemented, functional porcelain-fused-to-metal crown is seen in Figure 4A. The marginal adaptation of the metal coping to the cavosurface margin is easily identified, and the internal contours of the restoration and various enamel layers can be seen.
View larger version (42K):
[in this window]
[in a new window]
|
Figure 4. A. Optical coherence tomographic, or OCT, image of the facial surface of a mandibular first molar. The margins and contours of a porcelain-fused-to-metal restoration are seen. B. OCT image of the occlusal surface of a maxillary second molar. The internal contours of an occlusal composite restoration are visualized. C. OCT image of the labial surface of a maxillary incisor reveals the margins and internal contours of a Class V composite restoration.
| |
Figures 4B and 4C
show OCT images of composite restorations. Figure 4B is an OCT scan across the occlusal surface of a Class I composite restoration in a maxillary second molar. The intact enamel marginal ridge and the cavosurface marginal adaptation are easily identified. The dentin-composite interface and the contour of the occlusal floor of the preparation also are seen. Figure 4C shows the labial aspect of the beveled margin of a Class V composite restoration in a maxillary central incisor.
|
CONCLUSION
|
|---|
We have constructed a prototype clinical dental OCT system and have demonstrated the feasibility of using it in a clinical setting. Our research to date has shown that OCT is a powerful method for generating high-resolution, cross-sectional images of oral structures. We have used OCT to take images of the teeth, locate soft- and hard-tissue boundaries of the periodontium and evaluate restoration margins. Our goals in our ongoing research are to characterize normal dental structures using OCT and verify that this new technology can be used to take images of and quantify common dental problems including caries, defective restorations and periodontal disease.
|
FOOTNOTES
|
|---|
Dr. Otis is an assistant professor, Department of Oral Diagnosis, The University of Connecticut School of Dental Medicine, 263 Farmington Ave., MC-1605, Farmington Conn. 06030-1605. Address reprint requests to Dr. Otis.
Dr. Everett is a research scientist, Medical Technology Program, Lawrence Livermore National Laboratory, Livermore, Calif.
Dr. Sathyam is a research scientist, Medical Technology Program, Lawrence Livermore National Laboratory, Livermore, Calif.
Dr. Colston is a research scientist, Medical Technology Program, Lawrence Livermore National Laboratory, Livermore, Calif.
Dr. Otis was granted U.S. patent 5,570,182 on Oct. 29, 1996, for a method for detection of dental caries and periodontal disease using optical imaging.
Dr. Otis received grant 1RO1 DE11154-03 from the National Institute of Dental and Craniofacial Research.
|
REFERENCES
|
|---|
- Delpy DT, Cope M, van der Zee P, Arridge S, Wray S, Wyatt J. Estimation of optical pathlength through tissue from direct time of flight measurement. Phys Med Biol 1988;33:1433–42.[Medline]
- Huang D, Swanson EA, Lin P, et al. Optical coherence tomography. Science 1991; 254:1178–81.[Abstract/Free Full Text]
- Fujimoto JG, Brezinski ME, Tearney GJ, et al. Optical biopsy and imaging using optical coherence tomography. Nat Med 1995; 1:970–2.[Medline]
- Puliafito CA, Hee MR, Lin CP, et al. Imaging of macular diseases with optical coherence tomography. Ophthalmology 1995; 102:217–29.[Medline]
- Tearney GJ, Brezinski ME, Bouma BE, et al. In vivo endoscopic optical biopsy with optical coherence tomography. Science 1997; 276(5321):2037–9.[Abstract/Free Full Text]
- Schmitt JM, Yadlowsky MJ, Bonner RF. Subsurface imaging of living skin with optical coherence microscopy. Dermatology 1995; 191:93–8.[Medline]
- Schuman JS, Pedut-Kloizman T, Hertzmark E, et al. Reproducibility of nerve fiber layer thickness measurements using optical coherence tomography. Ophthalmology 1996; 103:1889–98.[Medline]
- Otis LL, Colston B, Armitage G, Nathel H. Specular reflectivity of teeth (abstract 2578). J Dent Res 1996;75(special issue):340.
- Otis LL, Colston BW, Armitage G, Everett MJ. Optical imaging of periodontal tissues (abstract 2956). J Dent Res 1997;76 (special issue):383.
- Colston BW, Everett MJ, DaSilva LB, Otis LL, Stroeve P, Nathel H. Imaging of hard and soft tissue in the oral cavity by optical coherence tomography. Appl Optics 1998;37:3582–5.
- Otis LL, Colston BW, Everett MJ. Dental optical coherence tomography: a novel assessment of oral tissues (abstract 977). J Dent Res 1998;77(A):228.
- Ziemiecki TL, Colston BW, Everett MJ, Otis LL. Optical coherence tomography: a novel assessment of composite wear (abstract 1367). J Dent Res 1998;77(A);276.
- Otis LL, Everett M, Colston BW. Optical coherence tomography: a novel assessment of coronal restorations (abstract 1541). J Dent Res 1998;77(B):824.
- Otis LL, Colston BW, Everett MJ. Dental OCT: a comparison of two in vitro systems. Dentomaxillofac Radiol 2000;29:86–90.
TOP
ABSTRACT
OPTICAL COHERENCE TOMOGRAPHY
