Image analysis – Applications
Reexamination Certificate
1996-12-31
2001-03-13
Bella, Matthew C. (Department: 2721)
Image analysis
Applications
C382S115000, C382S128000, C433S029000, C348S066000
Reexamination Certificate
active
06201880
ABSTRACT:
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyrights whatsoever.
FIELD OF THE INVENTION
This invention relates to method and apparatus for imaging teeth. More particularly, the invention relates to illuminating a tooth with light and creating images of the illuminated tooth.
BACKGROUND OF THE INVENTION
The most commonly used clinical techniques for detecting dental caries are tactile examination and dental radiography, each of which has significant shortcomings. Tactile examination typically uses an explorer, which can accelerate the development of irreversible caries by causing traumatic changes to tooth structure. Radiography requires the use of x-ray radiation, which is an ionizing radiation dangerous to the health of the patient. The use of lower x-ray fluence with digital sensing of the x-ray transmission and computer enhancement of the image contrast, provides poorer resolution than that obtainable with x-ray film.
Another clinical technique is to visually inspect a tooth illuminated by light. Transillumination by light can indicate the presence of caries because decayed tooth material causes greater scattering of light and may provide greater absorption of light, than surrounding healthy tooth tissue. A decayed region will therefore appear darker than surrounding tissue. If the tooth has decayed sufficiently to leave a void, more light would be transmitted through the tooth.
Dental diagnosis by transillumination of teeth using visible light reportedly dates back to 1865. See, for example, G. R. Winter et al., “Transillumination in the Oral Cavity,” Dental Digest 106-109 (March 1949). This technique has evolved into fiberoptic transillumination (“FOTI”), which uses fiber optics to deliver the light to the teeth. FOTI has been used by a relatively small number of dentists for caries examination since 1968. See, for example, J. Friedman and M. I. Marcus, “Transillumination of the Oral Cavity with Use of Fiber Optics,” 80 J Am Dent Assoc 801-809 (Apr. 1970); J. Barenie et al., “The Use of Fiber Optics Transillumination for the Detection of Proximal Caries,” 36 Oral Surg 891-897, No. 6 (Dec. 1973).
A typical FOTI apparatus employs an incandescent light source having two intensity levels for illuminating the tooth via an optical fiber bundle. The light passing through the tooth is conveyed through another fiber bundle to form an image on a ground glass screen on photographic film in a camera, or to be viewed by the eye. See, for example, U.S. Pat. No. 4,446,197 to Provost.
Heretofore, it has been difficult to obtain reliable FOTI images containing clinically significant information. Variations in the intensity, position of the illumination source, and viewing angle of the camera, for example, introduce high degrees of variability to FOTI images, impeding FOTI's practical implementation. It is difficult to obtain identical FOTI images of even the same tooth a second time. It is therefore difficult to compare current FOTI images with prior FOTI images to monitor changes in the tooth over time. It is also difficult to develop standards by which to determine whether or not caries is present based on FOTI images. Unless FOTI can dependably and reproducibly yield images with clinical content of interest, it is likely to remain a rarely used clinical technique. See, for example, K. W. Stephen, et al.; “Comparison of fiber optic transillumination with clinical and radiographic caries diagnosis,” 15 Comm Dent Oral Epidemiol 91-94 (1987); A. D. Sidi, M. N. Naylor, “A comparison of bitewing radiography and interdental transillumination as adjunct to the clinical identification of approximal caries in posterior teeth,” 164 Brit Dent J 15-17 (1988); and S. Eliassen, et al., “Root caries: a consensus conference statement,” 16 Swed Dent J 21-25 (1992).
While several methods of providing reproducible results have been proposed, none appears practical. For example, in one reported variant of FOTI, a collimated light source and a scanning detector are employed. See, for example, A. O. Wist, et al., “Increased spatial resolution for light images of tissues especially for teeth,” 1894 SPIE 52-64 (March 1993). Such a configuration suffers from poor light efficiency and lacks sufficient flexibility for routine clinical use. None of the known versions of FOTI reported to date provides the degree of control over the imaging conditions that is necessary for adequate quality and reproducibility of results.
SUMMARY OF THE INVENTION
The present invention minimizes the sources of variability in imaging conditions which prevent adequate light imaging of a tooth and impede the reproducibility of images of the tooth, improving the capture of clinically significant information. For example, an electronic camera, such as a camera incorporating a charge-coupled-device (“CCD”) or a video camera, is used to image the illuminated tooth. Electronic imaging, particularly with a CCD, enables real time observation of the tooth under a variety of conditions so that the operator can capture a frame of interest for further processing and review in near real time. A CCD is preferred because of its high signal-to-noise ratio. The intensity of the illumination source is preferably automatically controlled to determine the optimum intensity for imaging the tooth, while avoiding saturation of the camera. The range of intensities may then be linearly mapped into a standard range for image representation, providing improved image contrast and resolution. The angle of reception by the camera of the light passing through the tooth may also be controlled in a reproducible manner. The images may be digitized and subjected to digital processing. Wavelet transformations have been found to provide particular improvement in the sensitivity and robustness of the image.
In accordance with the present invention, a method of acquiring images of a tooth comprises illuminating a surface of the tooth with light radiation and electronically imaging the tooth from a non-illuminated surface. The electronic imaging can be conducted by an electronic camera, which preferably includes a CCD, or by a video camera. Preferably, the illuminating step and the imaging step are sequentially conducted a plurality of times and the intensity of the light radiation is automatically adjusted to avoid saturation of the camera. At least some of the imaging steps are conducted at different angles with respect to the tooth. If the electronic camera includes a CCD, the resulting digital images are preferably enhanced by representing the image through wavelet amplitude maps, wavelet phase maps, or both. If the camera is a video camera, the images may be digitized and then enhanced.
A current image of the tooth may be compared to a previously taken image of the same tooth to identify changes in the tooth over time through a numerical correlation, for example.
A plurality of teeth may be illuminated and imaged based on light reflected from the teeth, as well.
Also in accordance with the present invention, a system for acquiring images of a tooth by transillumination is disclosed comprising an illuminator source for illuminating the tooth, an electronic camera, means for transferring light passing through the tooth to the camera, a digital processing unit coupled to the electronic camera, and a monitor for displaying images, coupled to the digital processing unit. The illuminator source may be a high intensity lamp connected to an optical fiber for illuminating a surface of a tooth of interest. A small laser, a laser diode, a light emitting diode, or a miniature light bulb may also be used as the source of illumination, as well. The electronic camera may include a CCD or may be a video camera. Provision is preferably made for automatically changing the intensity of the lig
Elbaum Marek
Greenebaum Michael
Jacobs Adam
Keem Sunguk
Schneiderman Allen H.
Bella Matthew C.
Electro-Optical Sciences
Morgan & Finnegan
LandOfFree
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