Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
  • A61B5/0082—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence adapted for particular medical purposes
  • A61B5/0088—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence adapted for particular medical purposes for oral or dental tissue
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
  • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
  • A61B2562/0233—Special features of optical sensors or probes classified in A61B5/00
  • A61B2562/0238—Optical sensor arrangements for performing transmission measurements on body tissue
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C19/00—Dental auxiliary appliances
  • A61C19/04—Measuring instruments specially adapted for dentistry

Definitions

• This invention relates to a non-invasive diagnostic method and apparatus and in particular to a method of and apparatus for two-dimensional imaging by differential absorption detection.
• This invention relates to an infra- red imaging system which provides visualisation of hidden tooth structures for, for example, the detection and identification of dental hard tissue disease in dentistry and oral medicine.
• caries may be detected at a somewhat earlier stage by visual or more often mechanical means.
• the latter basically probing with a pointed instrument, can find regions where overlying enamel has softened but not yet fully decomposed. It is less likely that detection will be possible when the site is at a point of contact or near contact between adjacent teeth. Unfortunately, since this region is the hardest to maintain free from lodged food particles, this is the most likely site for decay.
• a method of two-dimensional imaging of tissue by differential absorption detection comprising the steps of transmitting radiation of two wavelengths through tissue, detecting transmitted radiation, measuring the absorption of said transmitted radiation, and comparing absorption of said two wavelengths .
• the radiation has wavelengths of size sufficient to preclude scattering in tissue.
• the radiation is preferably infra-red light. More preferably the light comprises two wavelengths within the range 1.1 to 1.6 micrometres.
• the first wavelength is preferably greater than 1.4 micrometres, most preferably within the range 1.4 to 1.5 micrometres, and may show a dominant change in transmission characteristics.
• the second wavelength is preferably less than 1.4 micrometres, most preferably within the range 1.2 to 1.3 micrometres, and may act as a reference.
• the two wavelengths are modulated at the same frequency. More preferably the two wavelengths are in antiphase.
• a The method may include detection of the transmitted radiation by optical means. Preferably the method includes the step of filtering out all transmitted radiation not at the modulated frequency.
• the method may include the step of restricting detection to radiation transmitted in a substantially direct path through the tissue.
• Said restriction may be by optical spatial filtering.
• the method is applied to the detection of dental caries.
• the method is applied to distinguish between different dental structures such as enamel, dentine, root canals and pulp chambers.
• an apparatus for differential absorption detection comprising two modulated light sources, each source producing light of a different wavelength, optic transmission means to train the light from said light sources to illuminate a first side of a tissue sample in vivo, and optic detection means to detect light transmitted through said tissue sample to a second side of said tissue sample.
• the apparatus further includes means to combine the output of said sources to provide a single beam of incident light.
• the optic detection means includes an electronic filter.
• the apparatus may comprise means to spatially filter transmitted light.
• the apparatus comprises means to display detected transmitted light as an image.
• an apparatus for detection of dental caries and/or visualisation of dental structures by differential absorption detection comprising two modulated light sources, optic means to combine light from said sources to train a single beam on a first side of a tooth, receiving means on a second side of the tooth for receiving light transmitted through the tooth, an optic filter to spatially filter the transmitted light, and optic detection means to detect the spatially filtered light.
• the apparatus may comprise means to display detected transmitted light as an image of the tooth. More preferably the apparatus comprises means to display the image in real time. The apparatus may comprise means to electronically enhance the image. The apparatus may comprise means to produce hard copies of said image.
• Figure 1 is a comparative graphic representation of transmission characteristics of light through healthy and decayed dental tissue
• Figure 2a is a schematic drawing of a laboratory arrangement of a differential absorption detection device in accordance with an aspect of the present invention
• Figure 2b is a schematic drawing of a laboratory arrangement of a differential absorption detection device in accordance with a further aspect of the present invention.
• Figure 3 is a schematic drawing of a differential absorption detection device in accordance with an aspect of the present invention.
• dental decay can give rise to significant changes in the transmission characteristics of light through enamel and dentine. These changes occur in a spectral region not previously investigated in the prior art and are substantial enough to provide the basis for the selective imaging of tooth decay.
• Figure 1 refers to spectra recorded through relatively thin sections of teeth.
• This approach examines the difference in transmission between two wavelengths in the same region one of which shows the dominant changes due to caries, and the other of which acts as a less strongly affected reference.
• wavelengths are in the region 1.1 to 1.6 ⁇ m, and are most advantageously chosen to be between 1.4 and 1.5 ⁇ m, and between 1.2 and 1-3/zm.
• the absorption characteristics of the tissue mean that other wavelengths are chosen.
• the important criterion in selecting the wavelengths is that the relative absorptions of the tissue to be detected and its surrounding tissue must be related such that the relationship at the first frequency is different from the relationship at the second frequency.
• the absorption of the caries tissue at the first frequency (1.3 ⁇ m) is 50% greater than that of the dentine tissue, while at the second frequency (1.44 ⁇ m) it is 30% less.
• FIG. 2 illustrates a laboratory arrangement used to demonstrate that a practical step in realising this differential absorption detection in a simple fashion is to modulate the two light sources at the same frequency but in antiphase to each other.
• Light Emitting Diodes (LEDs) 20 and 22 operating with relatively narrow bandwidths of several ran at wavelengths within the regions previously noted, are the preferred sources.
• Light transmitted through a sample 24 is viewed with a detector 26 provided with an electronic filter 28. This electronic filter 28 is set to pass only the modulated frequency and thus the detector 26 "sees" only the differential signal, that is the signal corresponding to differences in absorption between the two wavelengths. This approach provides the basis for caries detection.
• any optical wavelength as opposed to an X- ray wavelength, has the added complication of the high level of light scattering in tissue. This scattering complicates the process of trying to retain detailed image information on objects buried within such scattering media.
• the longer wavelengths used in this method and device help to reduce the level of scatter but not to the point where even teeth become free of the problem.
• an additional feature of this invention is the inclusion of a means by which the effects of scatter can be significantly reduced. Specifically, the rays allowed to fall on the detector 28 are restricted to only those having direct or nearly direct paths through the sample 24 from the sources 20,22. This is accomplished through the use of appropriate optical spatial filtering 32 and a re-imaging lens 34.
• rays sometimes referred to as 'ballistic' rays, are those which pass through the sample 24 substantially unscattered and are therefore better able to preserve the information or the hidden detail associated, in this case, with differential absorption between caries and the surrounding sound tissue.
• the laboratory arrangement of Figure 2b is used to observe details of carious lesions.
• the detector used is a CCD camera 30. This arrangement provides two dimensional imaging of the ballistic rays.
• the phrase "ballistic shadowgram" has been used to refer to this 2D image.
• the use of a pair of wavelengths within a newly identified region provides a novel means for the detection of dental disease.
• Figure 3 illustrates a practical embodiment of a device 1 incorporating this principle wherein two modulated light sources 2,3 at 1.25 ⁇ m and 1.43 ⁇ m provide simultaneous illumination of a tooth 6.
• the output from these sources 2,3 is substantially collimated by means of lenses 10, 11 and a transmitting mirror 12 and combined along a single axis.
• the combined beams are transmitted along a first arm 4 of the device and reflected by a reflector 13 to an aperture 5 placed on one side of a tooth or teeth 6.
• a second arm 14 of the device has an aperture 15 which is disposed on the opposite side of the same tooth or teeth 6, and this second arm 14 contains lenses 7,8 and a reflector 16 such that a spatially filtered image of the tooth 6 is presented to a two-dimensional array detector 9.
• the image produced by the detector 9 is transmitted by cable 18 to a computer and/or visual display unit for display of the image.
• the resulting image could be scanned in one dimension across a line array of detectors, or scanned in both directions across a single point detector. Such arrangements may be required since two dimensional array detectors at these wavelengths are slow and expensive.
• the resulting image is displayed, in real time, on the screen of a video monitor (not shown) .
• the image may be subject to processing by software running on an associated computer or microprocessor (not shown) to electronically enhance the raw image, and means such as a printer may be provided for producing hard copies of images for maintaining patient records.
• the technique may be extended to include visualisation of normal dental structures such as root canals and pulp chambers .
• the embodiment described above offers significant advantages over currently available devices for the early detection of dental disease. Specifically it employs non-ionising radiation and its use is therefore intrinsically safer than the use of X-rays.
• the device as described offers real time images through teeth combined with the availability of hard copies of those images. Finally the device is constructed from relatively inexpensive materials and processes resulting in a diagnostic offered at a much lower price than current X-ray machines.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Heart & Thoracic Surgery (AREA)
• Medical Informatics (AREA)
• Physics & Mathematics (AREA)
• Dentistry (AREA)
• Biophysics (AREA)
• Pathology (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Audiology, Speech & Language Pathology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Molecular Biology (AREA)
• Surgery (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)

Applications Claiming Priority (3)

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• 1997
  • 1997-05-23 GB GBGB9710561.3A patent/GB9710561D0/en active Pending
• 1998
  • 1998-05-26 WO PCT/GB1998/001524 patent/WO1998052460A1/en not_active Application Discontinuation
  • 1998-05-26 EP EP98922975A patent/EP0984717A1/de not_active Withdrawn
  • 1998-05-26 AU AU75433/98A patent/AU7543398A/en not_active Abandoned

Non-Patent Citations (1)

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