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.Microstructural tissue detail is revealed by differentiating between scattered and transmitted, or reflected, photons.OTC was first proposed for use as a biological imaging system in 1991 by Huang and colleagues.Because of their collaborative work, OCT imaging now is being used in clinical practice in ophthalmology.
DENTAL OPTICAL COHERENCE TOMOGRAPHY
We have developed and tested an OCT system to make images of dental structures. 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 .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.
A single interferometric signal measured at a specific point on the tissue gives the reflective boundary along the axis of the beam .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 in other words, the OCT image is a two-dimensional representation of the optical reflections of tissue in cross-section.
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. 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 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.
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.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.
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.Microstructural tissue detail is revealed by differentiating between scattered and transmitted, or reflected, photons.OTC was first proposed for use as a biological imaging system in 1991 by Huang and colleagues.Because of their collaborative work, OCT imaging now is being used in clinical practice in ophthalmology.
DENTAL OPTICAL COHERENCE TOMOGRAPHY
We have developed and tested an OCT system to make images of dental structures. 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 .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.
A single interferometric signal measured at a specific point on the tissue gives the reflective boundary along the axis of the beam .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 in other words, the OCT image is a two-dimensional representation of the optical reflections of tissue in cross-section.
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. 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 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.
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.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.
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