as) United States
`a2) Patent Application Publication (0) Pub. No.: US 2008/0063998 A1
`(43) Pub. Date: Mar.13, 2008
`
`Liang etal.
`
`US 20080063998A1
`
`(54) APPARATUS FOR CARIES DETECTION
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`A6IC 3/00
`(2006.01)
`AGIC 5/00
`(52) US. Che ciecccccccccccccssscssssssssssssenneeseens 433/29; 433/215
`
`(57)
`
`ABSTRACT
`
`(76)
`
`Inventors:
`
`Rongguang Liang, Penfield, NY
`(US); Victor C. Wong, Rochester,
`NY (US); Michael A. Marcus,
`Honeoye Falls, NY (US); Mark E.
`Bridges, Spencerport, NY (US);
`Paul O, McLaughlin, Rochester,
`NY (US); Peter D. Burns,
`Fairport, NY (US); David L.
`Patton, Webster, NY (US)
`
`Correspondence Address:
`Carestream Health Inc,
`150 Verona Street
`Rochester, NY 14608
`
`An apparatus for obtaining an image of a tooth having at
`least one light source providing incidentlight havinga first
`spectral range for obtaining a reflectance image (122) from
`the tooth and a second spectral range for exciting a fluores-
`cence image (120) from the tooth. A polarizing beamsplitter
`(18) in the path of the incident light from both sources
`directs light having a first polarization state toward the tooth
`and directs light from the tooth having a secondpolarization
`state along a return path toward a sensor (68), wherein the
`second polarization state is orthogonal to thefirst polariza-
`tion state. A first lens (22) in the return path directs image-
`bearing light from the tooth toward the sensor (68), and
`(21) Appl. No.:—11/530,987
`obtains image data from the portion of the light having the
`second polarization state. A long-passfilter (15) in the return
`path attenuates light in the second spectral range.
`
`(22)
`
`Filed:
`
`Sep. 12, 2006
`
`22
`
`32
`
`Color
`
`Camera
`
`12
`
`
`
`15
`
`20
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 1 of 30
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`US 2008/0063998 Al
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`30
`
`22
`
`38
`Camera
`
`
`40
`
`Monochrome
`
`60
`
`26
`
`FIG. 1
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 2 of 30
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`US 2008/0063998 Al
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`22
`
`12
`
`4 14
`?xyor
`
`2
`
`32
` 40
`
`Color
`
`Camera
`
`60
`
`FIG. 2
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 3 of 30
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`US 2008/0063998 Al
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`
` Camera
`
`60
`
`FIG. 3
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 4 of 30
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`US 2008/0063998 Al
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`Camera (WV
`
`Color WC
`
`FIG. 4A
`
`FIG. 4B
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 5 of 30
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`US 2008/0063998 Al
`
`10
`
`12
`
`30
`
`22
`
`Color
`
`Camera
`
`44
`
`Ls
`Uy
`
`°
`
`14
`
`42
`
`20
`
`
`oN ft
`
`15
`
`12
`
`UV
`LED
`
`17
`
`FIG. 4C
`
`

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`Patent Application Publication
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`Mar. 13, 2008 Sheet 6 of 30
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`US 2008/0063998 Al
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`
`
`FIG. 5
`
`20
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 7 of 30
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`US 2008/0063998 Al
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`20
`
`58
`
`58
`
`58
`
`RS
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`54
`
`82
`
`60
`
`FIG. 6
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 8 of 30
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`US 2008/0063998 Al
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`52
`
`50
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`62
`
`58
`
`
`
`60
`
`58
`
`64
`
`FIG. 7
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`

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`Patent Application Publication Mar. 13, 2008 Sheet 9 of 30
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`US 2008/0063998 Al
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`
`
`FIG. 8
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`

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`Patent Application Publication Mar. 13, 2008 Sheet 10 of 30
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`US 2008/0063998 Al
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`
`
`FIG. 9
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`

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`Patent Application Publication Mar. 13, 2008 Sheet 11 of 30
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`US 2008/0063998 Al
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`24
`
`
`
`FIG. 10
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`

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`Patent Application Publication Mar. 13, 2008 Sheet 12 of 30
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`US 2008/0063998 Al
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`
`
`20
`
`FIG. 11
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`

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`Patent Application Publication Mar. 13, 2008 Sheet 13 of 30
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`US 2008/0063998 Al
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`
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`20
`
`FIG. 12A
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 14 of 30
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`US 2008/0063998 Al
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`68
`
`20
`
`FIG. 12B
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 15 of 30
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`US 2008/0063998 Al
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`20
`49b 42a
`
`49c¢
`
`FIG. 12C
`
`

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`Patent Application Publication
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`Mar. 13, 2008 Sheet 16 of 30
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`US 2008/0063998 Al
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`SN
`
`FIG. 13
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`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 17 of 30
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`US 2008/0063998 Al
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`92
`
`FIG. 14A
`
`FIG. 14B
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`

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`Patent Application Publication
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`Mar. 13, 2008 Sheet 18 of 30
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`US 2008/0063998 Al
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`proto cc cc cc
`
`Witte— — — — —l
`
`106
`
`SN
`
`FIG. 15
`
`
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 19 of 30
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`US 2008/0063998 Al
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`104
`
`112
`
`108
`
`FIG. 16
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 20 of 30
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`US 2008/0063998 Al
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`
`
`122
`Software to
`Composite image
`Reflectance image
`
`
`correlate image
`
`120
`
`124
`
`130
`
`
`
`White light image
`
`
`
`FIG. 17
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 21 of 30
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`US 2008/0063998 Al
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`ten«¢=a 20
`
`.
`
`
`
`FIG. 18
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 22 of 30
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`US 2008/0063998 Al
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`
`
`20
`
`FIG. 19
`
`

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`Patent Application Publication Mar. 13, 2008 Sheet 23 of 30
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`US 2008/0063998 Al
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`202
`
`204
`
`206
`
`Read white light and
`fluorescence images
`
`Analyze the imagesin
`different color plane
`
`Apply image
`processing
`
`
`
`
`
`
`
`Extract and display information about
`regions, such as size, shape, and status
`
`Highlight suspicious
`region automatically
`
`212
`
`210
`
`g
`
`208
`
`FIG. 20
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 24 of 30
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`US 2008/0063998 Al
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`220
`
`20
`
`FIG. 21
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 25 of 30
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`US 2008/0063998 Al
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`
`
`240c
`
`240b
`
`20
`
`FIG. 22
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 26 of 30
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`US 2008/0063998 Al
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`110
`
`Out of focus
`
`On focus
`
`FIG. 23A
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 27 of 30
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`US 2008/0063998 Al
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`110
`
`20
`
`252a
`
`252a
`
`254
`
`Out of focus
`
`Onfocus
`
`FIG. 23B
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 28 of 30
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`US 2008/0063998 Al
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` 252a,
`
`20
`256
`
`,
`252b
`
`\')
`!
`VI
`
`FIG. 23C
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 29 of 30
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`US 2008/0063998 Al
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`
`
`450
`
`550
`
`700
`
`Wavelength (nm)
`
`FIG. 24
`
`

`

`Patent Application Publication Mar. 13, 2008 Sheet 30 of 30
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`US 2008/0063998 Al
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`40
`40
`
`83
`
`104
`
`122
`
`83
`
`104
`
`FIG. 25
`
`

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`US 2008/0063998 Al
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`Mar.13, 2008
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`APPARATUS FOR CARIES DETECTION
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] Reference is made to commonly-assigned copend-
`ing U.S. application Ser. No. 11/262,869, filed Oct. 31,
`2005, entitled METHOD FOR DETECTION OF CARIES,
`by Wonget al.; U.S. application Ser. No. 11/408,360, filed
`Apr. 21, 2006, entitled OPTICAL DETECTION OF DEN-
`TAL CARIES by Wonget al.; and U.S. patent application
`Ser. No.
`, filed herewith, entitled LOW COHER-
`ENCE DENTAL OCT IMAGING, by Liang et al.,
`the
`disclosures of which are incorporated herein.
`
`[0008] U.S. Pat. No. 4,479,499 (Alfano) describes a
`method to detect caries by comparing the intensity of
`the light scattered at two different wavelengths.
`[0009] US. Pat. No. 4,515,476 Ungmar) discloses use
`of a laser for providing excitation energy that generates
`fluorescence at some other wavelength for locating
`carious areas.
`
`[0010] US. Pat. No. 6,231,338 (de Josselin de Jong et
`al.) discloses an imaging apparatus for identifying
`dental caries using fluorescence detection.
`[0011] U.S. Patent Application No. 2004/0240716 (de
`Josselin de Jong et al.) discloses methods for improved
`image analysis for images obtained from fluorescing
`tissue.
`
`FIELD OF THE INVENTION
`
`[0002] This invention generally relates to methods and
`apparatus for dental imaging and moreparticularly relates to
`an apparatus for caries detection using fluorescence and
`scattering.
`
`BACKGROUND OF THE INVENTION
`
`[0012] Among commercialized products for dental imag-
`ing using fluorescence behavioris the QLF Clinical System
`from Inspektor Research Systems BV, Amsterdam, The
`Netherlands. Using a different approach,
`the Diagnodent
`Laser Caries Detection Aid from KaVo Dental GmbH,
`Biberach, Germany, detects caries activity monitoring the
`intensity of fluorescence of bacterial by-products under
`illumination from red light.
`[0013] U.S. Patent Application Publication 2005/0003323
`In spite of improvements in detection, treatment,
`[0003]
`(Katsuda et al.) describes a hand-held imaging apparatus
`and prevention techniques, dental caries remains a widely
`suitable for medical or dental applications, using fluores-
`prevalent condition affecting people of all age groups. If not
`cence imaging. The ’3323 Katsuda etal. disclosure showsan
`properly and promptly treated, caries can lead to permanent
`apparatus that receives the reflection light from the diag-
`tooth damage and evento loss of teeth.
`nostic object and/orthe fluorescence of the diagnostic object
`[0004]
`‘Traditional methods for caries detection include
`with different light irradiation. The disclosed apparatus is
`visual examination and tactile probing with a sharp dental
`fairly complicated, requiring switchable filters in the probe,
`explorer device, often assisted by radiographic (x-ray) imag-
`for example. While the apparatus disclosed in the Katsudaet
`ing. Detection using these methods can be somewhat sub-
`al. °3323 patent application takes advantage of combining
`jective, varying in accuracy due to many factors, including
`reflection light and fluorescence from the diagnostic object
`practitioner expertise, location of the infected site, extent of
`in the same optical path, the apparatus does not remove or
`infection, viewing conditions, accuracy of x-ray equipment
`minimize specular reflection. Any unwanted specular reflec-
`and processing, and other factors. There are also hazards
`tion produces false positive results in reflectance imaging.
`associated with conventional detection techniques, includ-
`Moreover, with the various illumination embodiments dis-
`ing the risk of damaging weakened teeth and spreading
`closed, the illumination directed toward a tooth or other
`infection with tactile methods as well as exposure to x-ray
`diagnostic object is not uniform, since the light source is in
`radiation. By the time caries is evident under visual and
`close proximity to the diagnostic object.
`tactile examination, the disease is generally in an advanced
`[0014] U.S. Patent Application Publication 2004/0202356
`stage, requiringafilling and, if not timely treated, possibly
`(Stookey et al.) describes mathematical processing of spec-
`leading to tooth loss.
`tral changes in fluorescence in order to detect caries in
`[0005]
`In response to the need for improved caries detec-
`different stages with improved accuracy. Acknowledging the
`tion methods,
`there has been considerable interest
`in
`difficulty of early detection when using spectral fluorescence
`improved imaging techniques that do not employ x-rays.
`measurements, the ’2356 Stookeyet al. disclosure describes
`One method that has been commercialized employs fiuo-
`approaches for enhancing the spectral values obtained,
`rescence, caused when teeth are illuminated with high
`effecting a transformation of the spectral data that is adapted
`intensity blue light. This technique,
`termed quantitative
`to the spectral response of the camera that obtains the
`light-induced fluorescence (QLF), operates on the principle
`fluorescent image.
`that sound, healthy tooth enamel yields a higher intensity of
`fluorescence under excitation from some wavelengths than
`[0015] While the disclosed methods and apparatus show
`does de-mineralized enamel that has been damagedbycaries
`promise in providing non-invasive, non-ionizing imaging
`infection. The strong correlation between mineral loss and
`methodsfor caries detection, there is still room for improve-
`loss of fluorescence for blue light excitation is then used to
`ment. One recognized drawback with existing techniques
`identify and assess carious areas of the tooth. A different
`that employ fluorescence imaging relates to image contrast.
`relationship has been foundfor red light excitation, a region
`The image provided by fluorescence generation techniques
`of the spectrum for which bacteria and bacterial by-products
`such as QLF can bedifficult to assess dueto relatively poor
`in carious regions absorb and fluoresce more pronouncedly
`contrast between healthy and infected areas. As noted in the
`than do healthy areas.
`°2356 Stookey et al. disclosure, spectral and intensity
`changes for incipient caries can be very slight, making it
`[0006] Among proposedsolutions for optical detection of
`difficult to differentiate non-diseased tooth surface irregu-
`caries are the following:
`larities from incipient caries.
`[0007] U.S. Pat. No. 4,290,433 (Alfano) discloses a
`method to detect caries by comparing the excited
`[0016] Overall,
`it is well-recognized that, with fluores-
`luminescence in two wavelengths.
`cence techniques, the image contrast that is obtained corre-
`
`

`

`US 2008/0063998 Al
`
`Mar.13, 2008
`
`sponds to the severity of the condition. Accurate identifica-
`tion of caries using these techniques often requires that the
`condition be at a more advanced stage, beyond incipient or
`early caries, because the difference in fluorescence between
`carious and soundtooth structure is very small for caries at
`an early stage. In such cases, detection accuracy using
`fluorescence techniques may not show marked improvement
`over conventional methods. Because of this shortcoming,
`the use of fluorescence effects appears to have some prac-
`tical
`limits that prevent accurate diagnosis of incipient
`caries. As a result, a caries condition may continue unde-
`tected until
`it
`is more serious,
`requiring a filling,
`for
`example.
`[0017] Detection of caries at very early stages is of par-
`ticular interest for preventive dentistry. As noted earlier,
`conventional techniques generally fail to detect caries at a
`stage at which the condition can be reversed. As a general
`rule of thumb,
`incipient caries is a lesion that has not
`penetrated substantially into the tooth enamel. Where such a
`caries lesion is identified before it threatens the dentin
`
`portion of the tooth, remineralization can often be accom-
`plished, reversing the early damage and preventing the need
`for a filling. More advancedcaries, however, grows increas-
`ingly more difficult to treat, most often requiring some type
`of filling or other type of intervention.
`[0018]
`In order to take advantage of opportunities for
`non-invasive dental techniques to forestall caries, it is nec-
`essary that caries be detected at the onset. In manycases, as
`is acknowledgedin the ’2356 Stookeyet al. disclosure, this
`level of detection has been found to be difficult to achieve
`
`using existing fluorescence imaging techniques, such as
`QLF. As a result, early caries can continue undetected, so
`that by the time positive detection is obtained, the opportu-
`nity for reversal using low-cost preventive measures can be
`lost.
`
`[0021] As is described in one embodimentof the Everett
`et al. °407 patent disclosure, optical coherence tomography
`(OCT)has been proposedas a tool for dental and periodontal
`imaging, as well as for other medical imaging applications.
`For example:
`[0022] U.S. Pat. No. 5,321,501 (Swanson et al.)
`describes principles of OCT scanning and measure-
`ment as used in medical imaging applications;
`[0023] U.S. Pat. No. 5,570,182 (Nathelet al.) describes
`the use of OCT for imaging of tooth and gum struc-
`tures;
`[0024] U-S. Pat. No. 6,179,611 (Everettet al.) describes
`a dental explorer tool that is configured to provide a
`scanned OCT image;
`[0025] U.S. Patent Application Publication No. 2005/
`0024646 (Quadling et al.) describes the use of time-
`domain and Fourier-domain OCT systems for dental
`imaging;
`[0026]
`Japanese Patent Application Publication No. JP
`2004-344260 (Kunitoshi et al.) discloses an optical
`diagnostic apparatus equipped with a camera for visual
`observation of a tooth part, with visible light for
`illuminating a surface image, and an OCT device for
`scanning the indicated region of a surface image using
`an alternate light source.
`[0027] While OCT solutions, such as those described
`above, can provide very detailed imaging of structure
`beneath the surface of a tooth, OCT imagingitself can be
`time-consuming and computation-intensive. OCT images
`would be most valuable if obtained within one or morelocal
`
`regions of interest, rather than obtained over widespread
`areas. That is, once a dental professional identifies a specific
`area of interest, then OCT imaging could be provided for
`that particular area only. Conventional solutions, however,
`have not combinedvisible light imaging with OCT imaging
`in the same imaging apparatus.
`[0028] Thus,
`it can be seen that there is a need for a
`[0019] U.S. Pat. No. 6,522,407 (Everett et al.) discloses
`non-invasive, non-ionizing imaging methodfor caries detec-
`the application of polarimetry principles to dental imaging.
`tion that offers improved accuracy for detection of caries,
`One system described in the Everett et al. °407 teaching
`particularly in its earlier stages, with a reduced numberof
`providesafirst polarizer in the illumination path for direct-
`components and reduced complexity over conventional
`ing a polarized light to the tooth. A second polarizer is
`solutions.
`provided in the path of reflected light. In one position, the
`polarizer transmits light of a horizontal polarization. Then,
`the polarizeris oriented to transmit light having an orthogo-
`nal polarization. Intensity of these two polarization states of
`the reflected light can then be compared to calculate the
`degree of depolarization of light scattered from the tooth.
`The result of this comparison then provides information on
`a detected caries infection.
`
`[0020] While the approach disclosed in the Everett et al.
`°407 patent takes advantage of polarization differences that
`can result from backscattering of light, the apparatus and
`methods described therein require the use of multiple polar-
`izers, one in the illumination path, the other in the imaging
`path. Moreover, the imaging path polarizer must somehow
`be readily switchable between a reference polarization state
`and its orthogonalpolarization state. Thus, this solution has
`inherent disadvantages for allowing a reduced packagesize
`for caries detection optics. It would be advantageous to
`provide a simpler solution for caries imaging, a solution not
`concerned with measuring a degree of depolarization, thus
`using a smaller number of components and not requiring
`switchable orientation of a polarizer between one of two
`positions.
`
`SUMMARY OF THE INVENTION
`
`[0029] The present invention provides an apparatus for
`imaging a tooth comprising:
`[0030]
`(a) at least one light source providing incident
`light having a first spectral range for obtaining a
`reflectance image on the tooth and a second spectral
`range for exciting a fluorescence image ofthe tooth;
`[0031]
`(b) a polarizing beamsplitter in a path of the
`incident
`light,
`the polarizing beamsplitter directing
`light having a first polarization state toward the tooth
`and directing light from the tooth having a second
`polarization state along a return path toward a sensor,
`wherein the second polarization state is orthogonal to
`the first polarization state;
`[0032]
`(c) a lens positioned in the return path to direct
`image-bearing light from the tooth toward the sensor
`for obtaining image data from the portion of the light
`having the second polarization state; and
`[0033]
`(d)along-pass filter in the return path, to attenu-
`ate light in the second spectral range and to transmit
`light in thefirst spectral range.
`
`

`

`US 2008/0063998 Al
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`Mar.13, 2008
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`Itis a feature of the present inventionthatit utilizes
`[0034]
`both fluorescence and reflectance image data for dental
`imaging.
`It is an advantage of the present invention that it
`[0035]
`offers enhancementoverexisting fluorescence imaging tech-
`niques, useful for detection of caries in its incipient stages.
`[0036] These and other objects, features, and advantages
`of the present
`invention will become apparent to those
`skilled in the art upon a reading of the following detailed
`description when taken in conjunction with the drawings
`wherein there is shown and describedan illustrative embodi-
`mentof the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0037] While the specification concludes with claims par-
`ticularly pointing out and distinctly claiming the subject
`matter of the present
`invention,
`it
`is believed that
`the
`invention will be better understood from the following
`description when taken in conjunction with the accompa-
`nying drawings, wherein:
`[0038]
`FIG. 1 is a schematic block diagram of an imaging
`apparatus for caries detection according to one embodiment;
`[0039]
`FIG. 2 is a schematic block diagram of an imaging
`apparatus for caries detection according to an alternate
`embodiment;
`[0040]
`FIG. 3 is a schematic block diagram of an imaging
`apparatus for caries detection according to an alternate
`embodiment;
`[0041]
`FIG. 4A is a schematic block diagram of an imag-
`ing apparatus for caries detection according to an alternate
`embodiment using polarized light;
`[0042]
`FIG. 4B is a schematic block diagram of an imag-
`ing apparatus for caries detection according to an alternate
`embodiment using a polarizing beamsplitter to provide
`polarized light;
`[0043]
`FIG. 4C is a schematic block diagram ofan alter-
`nate embodimentusing a bandpass filter with a narrow band
`light source;
`[0044]
`FIG. 5isaview showingthe process for combining
`dental image data to generate a fluorescence image with
`reflectance enhancementaccordingto the present invention;
`[0045]
`FIG. 6 is a composite view showing the contrast
`improvement of the present
`invention in a side-by-side
`comparison with conventional visual and fluorescence meth-
`ods;
`FIG. 7 is a block diagram showing a sequence of
`[0046]
`image processing for generating an enhanced threshold
`image according to one embodiment;
`[0047]
`FIG. 8 is a schematic block diagram of an imaging
`apparatus for caries detection according to an alternate
`embodiment using multiple light sources;
`[0048]
`FIG. 9 is a schematic block diagram of an imaging
`apparatus for caries detection using polarized light in one
`embodiment of the present invention;
`[0049]
`FIG. 10is aschematic block diagram of an imaging
`apparatus for caries detection using polarized light in an
`alternate embodiment of the present invention;
`[0050]
`FIG. 11 is aschematic block diagram of an imaging
`apparatus for caries detection using polarized light in an
`alternate embodiment of the present invention;
`[0051]
`FIG. 12A is a schematic block diagram of an
`imaging apparatus for caries detection using polarized light
`from two sources in an alternate embodimentof the present
`invention;
`
`FIG. 12B is a schematic block diagram of an
`[0052]
`imaging apparatus for caries detection using a ring illumi-
`nator with LEDs in an alternate embodimentof the present
`invention;
`[0053]
`FIG. 12C is a schematic block diagram of an
`imaging apparatus for caries detection using a fiber ring
`illuminatorin an alternate embodimentofthe present inven-
`tion;
`FIG. 13 is a schematic block diagram of an imaging
`[0054]
`apparatus for caries detection using polarized light and OCT
`scanning in one embodiment;
`[0055]
`FIG. 14A is a plan view of an operator interface
`screen in one embodiment;
`[0056]
`FIG. 14 B is an example display of OCT scanning
`results;
`FIG. 15 is a block diagram showing an arrange-
`[0057]
`ment of a hand-held imaging apparatus in one embodiment;
`[0058]
`FIG. 16 is a perspective view showing an imaging
`apparatus having an integral display;
`[0059]
`FIG. 17 isa block diagram showing combination of
`multiple types of imagesin order to form a composite image;
`[0060]
`FIG. 18 is a block diagram showing a wireless
`dental imaging system in one embodiment;
`[0061]
`FIG. 19 is a block diagram ofan alternate embodi-
`ment for the imaging probe with two sensors;
`[0062]
`FIG. 20 is a logic flow diagram for image process-
`ing workflow;
`[0063]
`FIG. 21 is a block diagram showing an imagerelay
`arrangement used in one embodiment;
`[0064]
`FIG. 22 is a block diagram showing the path of
`emitted light within the apparatus of the present invention;
`[0065]
`FIGS. 23A and 23B are block diagrams of embodi-
`ments for image capture with auto-focusing capability;
`[0066]
`FIG. 23C is a diagram showing how focusing
`indicators operate;
`[0067]
`FIG. 24 is a graph showing characteristic curves
`for white light and for a long passfilter used in the apparatus
`of the present invention; and
`[0068]
`FIG. 25 is a diagram showingoperation of a toggle
`switch for obtaining separate images.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`[0069] The present description is directed in particular to
`elements formingpart of, or cooperating more directly with,
`apparatus in accordance with the invention. It
`is to be
`understoodthat elements not specifically shown or described
`may take various forms well known to those skilled in the
`art.
`
`[0070] As noted in the preceding backgroundsection,it is
`knownthat fluorescence can be used to detect dental caries
`
`using either of two characteristic responses: First, excitation
`by a blue light source causes healthy tooth tissue to fluoresce
`in the green spectrum. Secondly, excitation by a red light
`source can cause bacterial by-products, such as those indi-
`cating caries, to fluoresce in the red spectrum.
`[0071]
`In order for an understanding of how light is used
`in the present invention, it is important to give more precise
`definition to the terms “reflectance” and “back-scattering” as
`they are used in biomedical applications in general and,
`moreparticularly, in the method and apparatus of the present
`invention. In broadest optical parlance, reflectance generally
`denotes the sum total of both specular reflectance and
`scattered reflectance. (Specularreflection is that component
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`of the excitation lightthat is reflected by the tooth surface at
`the same angle as the incident angle.) In biomedical appli-
`cations, however, as in the dental application of the present
`invention, the specular component of reflectance is of no
`interest andis, instead, generally detrimental to obtaining an
`image or measurement from a sample. The component of
`reflectance that is of interest for the present application is
`from back-scattered light only. Specular reflectance must be
`blocked or otherwise removed from the imaging path. With
`this distinction in mind,
`the term “back-scattered reflec-
`tance” is used in the present application to denote the
`componentof reflectance that is of interest. “Back-scattered
`reflectance” is defined as that component of the excitation
`light that is elastically back-scattered over a wide range of
`angles by the illuminated tooth structure. “Reflectance
`image” data, as this term is used in the present invention,
`refers to image data obtained from back-scattered reflec-
`tance only, since specular reflectance is blocked or kept to a
`minimum. In the scientific literature, back-scattered reflec-
`tance mayalso bereferred to as back-reflectance or simply
`as backscattering. Back-scattered reflectance is at the same
`wavelength as the excitation light.
`[0072]
`It has been shownthat light scattering properties
`differ between sound andcarious dental regions. In particu-
`lar, reflectance of light from the illuminated area can be at
`measurably different levels for normal versus carious areas.
`This change in reflectance, taken alone, may not be suffi-
`ciently pronounced to be of diagnostic value when consid-
`ered by itself, since this effect
`is very slight, although
`detectable. For more advancedstages of caries, for example,
`back-scattered reflectance may beless effective an indicator
`than at earlier stages.
`[0073]
`In conventional fluorescence measurements such
`as those obtained using QLF techniques, reflectanceitself is
`an effect that is avoided rather than utilized. A filter is
`
`usually employed to block off all excitation light from
`reaching the detection device. For this reason, the slight but
`perceptible change in back-scattered reflectance from exci-
`tation light has receivedlittle attention for diagnosingcaries.
`[0074] The inventors have found, however, that this back-
`scattered reflectance change can be used in conjunction with
`fluorescence effects to more clearly and more accurately
`pinpoint a carious location. Moreover, the inventors have
`observed that the changein light scattering activity, while it
`can generally be detected wherevera caries condition exists,
`is more pronouncedin areas of incipient caries. This back-
`scattered reflectance change is evident at early stages of
`caries, even when fluorescent effects are least pronounced.
`[0075] The present
`invention takes advantage of the
`observed back-scattering behavior for incipient caries and
`uses this effect, in combination with fluorescence effects
`described previously in the background section, to provide
`an improved capability for dental imaging to detect caries.
`The inventive technique, hereafter referred to as fluores-
`cence imaging with reflectance enhancement (FIRE), not
`only helps to increase the contrast of images over that of
`earlier approaches, but also makes it possible to detect
`incipient caries at stages where preventive measures are
`likely to effect remineralization, repairing damage done by
`the caries infection at a stage well before more complex
`restorative measures are necessary. Advantageously, FIRE
`detection can be accurate at an earlier stage of caries
`
`infection than has been exhibited using existing fluorescence
`approaches that measure fluorescence alone.
`
`Imaging Apparatus
`
`there is shown one basic
`[0076] Referring to FIG. 1,
`optical arrangement for an imaging apparatus 10 for caries
`detection using the FIRE method in one embodiment. A light
`source 12 directs an incident light, at a blue wavelength
`range or other suitable wavelength range, toward tooth 20
`through an optional lens 14 or other light beam conditioning
`component. The tooth 20 may be illuminated at a smooth
`surface (as shown) or at an occlusal surface (not shown).
`Two components of light are then detected by a mono-
`chrome camera 30 through a lens 22: a back-scattered light
`componenthaving the same wavelength as the incidentlight
`and having measurable reflectance; and a fluorescent light
`that has been excited due to the incident light. For FIRE
`imaging, specular reflection causes false positives and is
`undesirable. To minimize specular reflection pick up, the
`camera 30 is positioned at a suitable angle with respectto the
`light source 12. This allows imaging of back-scattered light
`without the confounding influence of a specularly reflected
`component.
`[0077]
`Inthe embodiment of FIG. 1, monochrome camera
`30 has colorfilters 26 and 28. One ofcolor filters 26 or 28
`
`is used during reflectance imaging; the other is used during
`fluorescence imaging. A processing apparatus 38 obtains and
`processes the reflectance and fluorescence image data and
`forms a FIRE image 60. FIRE image 60 is an enhanced
`diagnostic image that can be printed or can appear on a
`display 40. FIRE image 60 data can also be transmitted to
`storage or transmitted to another site for display.
`[0078] Referring to FIG. 2, there is shownthe basic optics
`arrangement
`in an alternate embodiment using a color
`camera 32. With this arrangement, auxiliary filters would not
`generally be needed, since color camera 32 would be able to
`obtain the reflectance and fluorescence images from the
`color separations of the full color image of tooth 20.
`[0079] Light source 12 is typically centered around a blue
`wavelength, such as about 405 nm in one embodiment. In
`practice, light source 12 could emit light ranging in wave-
`length from an upper ultraviolet range to blue, between
`about 300 and 500 nm. Light source 12 can bea laser or
`could be fabricated using one or more light emitting diodes
`(LEDs). Alternately, a broadband source, such as a xenon
`lamp, having a supporting colorfilter for passing the desired
`wavelengths could be used. Lens 14 or other optical ele-
`ments may serve to condition the incident light, such as by
`controlling the uniformity and size of the illumination area.
`For example, a diffuser 13, shown as a dotted line in FIG. 2,
`might be used before or after lens 14 to smooth out the hot
`spots of an LED beam.Thepath of illumination light might
`include light guiding orlight distributing structures such as
`an optical fiber or a liquid light guide, for example (not
`shown). Light level is typically a few milliwatts in intensity,
`but can be moreor less, depending on the light conditioning
`and sensing components used.
`[0080] Referring to the basic optical arrangement shown
`in FIG.3, illumination components could alternately direct
`light at normal incidence, turned through a beamsplitter 34.
`Camera 32 would then be disposed to obtain the imagelight
`that is transmitted through beamsplitter 34. Other options for
`illumination include multiple light sources directed at the
`tooth with angular incidence from one or more sides. Alter-
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`nately, the illumination might use an annular ring or an
`arrangement of LED sourcesdistributed about a center such
`as in a circular array to provide light uniformly from
`multiple angles as shown in FIGS. 12A and 12B. Illumina-
`tion could also be provided through an optical fiber or fiber
`array as shown in FIG. 12C.
`[0081] The imagingoptics, represented as lens 22 in FIGS.
`1-3, could include any suitable a