U.S. patent application number 10/438551 was filed with the patent office on 2003-11-06 for portable system for detecting skin abnormalities based on characteristic autofluorescence.
This patent application is currently assigned to Xillix Technologies Corporation. Invention is credited to Cline, Richard W., Leduc, Pierre.
Application Number | 20030206301 10/438551 |
Document ID | / |
Family ID | 23864247 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030206301 |
Kind Code |
A1 |
Cline, Richard W. ; et
al. |
November 6, 2003 |
Portable system for detecting skin abnormalities based on
characteristic autofluorescence
Abstract
A lightweight hand-held skin abnormality detection system
includes a source of excitation light that causes tissue under
examination to produce fluorescence light. The fluorescence light
produced along with the beam of reference light is provided to a
beam splitter which divides the fluorescence light and the
reference light into separate optical channels. Each optical
channel produces an image of the tissue under examination. A
passive optical combiner superimposes the image produced by each
optical channel for viewing by a user.
Inventors: |
Cline, Richard W.;
(Vancouver, CA) ; Leduc, Pierre; (Surrey,
CA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
Xillix Technologies
Corporation
|
Family ID: |
23864247 |
Appl. No.: |
10/438551 |
Filed: |
May 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10438551 |
May 14, 2003 |
|
|
|
09469562 |
Dec 22, 1999 |
|
|
|
6603552 |
|
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Current U.S.
Class: |
356/417 |
Current CPC
Class: |
A61B 5/444 20130101;
A61B 5/0071 20130101; A61B 5/0059 20130101; A61B 5/0088
20130101 |
Class at
Publication: |
356/417 |
International
Class: |
G01N 021/25 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A skin abnormality detection system, comprising: a light source
for producing a concentrated beam of illumination light; an optical
excitation filter that receives the illumination light and creates
excitation light by passing light having selected wavelengths, the
excitation light generating reflected and fluorescence light when
directed onto a surface of interest; an optical splitter that
receives the reflected and fluorescence light from the surface of
interest and splits the fluorescence light into two wavelength
bands; a pair of optical channels that receive the light from the
optical splitter, each optical channel including: an optical
emission filter for passing light having selected wavelengths; an
optical assembly for forming an image of the surface of interest;
and an image intensifier tube with a long persistence phosphor
screen that amplifies the light passed by the optical emission
filter and produces an output image with the light passed; and a
passive optical combiner that receives the output image produced in
each optical channel and superimposes the output images to create a
combined image that is seen by a user.
2. The skin abnormality detection system of claim 1, wherein the
passive optical combiner comprises a dichroic mirror that is
positioned to direct the output image from each optical channel
into an eye of a user.
3. The skin abnormality detection system of claim 1, further
comprising a camera positioned to capture the combined output image
onto an image sensor.
4. The skin abnormality detection system of claim 1, wherein the
image sensor is photographic film.
5. The skin abnormality detection system of claim 1, wherein the
image sensor is a digital imaging sensor.
6. The skin abnormality detection system of claim 1, wherein the
system includes a pair of optical splitters which direct the light
into multiple optical channels and produces a pair of combined
output images for a binocular viewing.
7. A skin abnormality detection system comprising: a light source
for producing a beam of illumination light; an optical excitation
filter that receives the illumination light and creates excitation
light and reference light, the excitation light generating
fluorescence light when directed onto a surface of interest; an
optical splitter that receives the fluorescence light and reflected
reference light and directs the fluorescence light and reflected
reference light into separate optical channels, each optical
channel producing an image of the surface of interest; and a
passive optical combiner that combines the images of the tissue
produced with the fluorescence light and the reference light into a
single image that can be viewed by a user.
8. The skin abnormality detection system of claim 5, wherein the
reference light comprises the excitation light.
9. The skin abnormality detection system of claim 5, wherein the
light source produces both excitation light and reference light,
and the reference light comprises light having a different
wavelength than the excitation light.
10. The skin abnormality detection system of claim 5, wherein the
system includes a pair of optical splitters which direct the light
into multiple optical channels and produces a pair of combined
output images for a binocular viewing.
11. The skin abnormality detection system of claim 5, further
comprising a camera positioned to capture the combined output image
onto an image sensor.
12. The skin abnormality detection system of claim 9, wherein the
image sensor is photographic film.
13. The skin abnormality detection system of claim 9, wherein the
image sensor is a digital imaging sensor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the detection of skin
abnormalities and, more particularly, to the detection of cancerous
or precancerous skin tissue using autofluorescence.
BACKGROUND OF THE INVENTION
[0002] Whether due to increased awareness or a variety of
environmental factors, the incidence of detected cases of skin
cancer is increasing. Because most skin cancers are curable if
treated early, there is an increased emphasis on the detection of
malignant or premalignant skin tissue. The majority of skin cancers
are detected based on a visual observation of a patient's skin
under white light by a trained dermatologist. However, the success
of such a method relies heavily on the ability of the physician to
distinguish healthy skin from a potentially malignant lesion.
[0003] One technique that can aid a physician in the detection of
cancerous or precancerous lesions is based on the difference in
autofluorescence light produced by healthy and non-healthy tissue.
All tissue will fluoresce or produce light within a well-defined
range of wavelengths when excited. It is known that the
autofluorescence light produced by healthy tissue has a spectral
profile that differs from that produced by non-healthy tissue. A
number of research groups have exploited this difference in the
spectral profile by recording the wavelength spectrum of a single
point. Although this provides interesting data, it is clinically
difficult to use.
[0004] One system for detecting cancerous tissue based on
differences in autofluorescence light is described in U.S. Pat. No.
5,507,287, which is assigned to the Xillix Technologies Corporation
of Richmond, B.C., Canada, the assignee of the present invention.
However, this and similar systems generally require a computer
monitor and image processing equipment in order to produce images
of suspect tissue and are not portable enough to be used outside a
hospital. In addition, these systems are relatively expensive and
require significant amounts of energy to operate.
[0005] A lightweight, portable system for the detection of
autofluorescence light of the skin is described in PCT application
PCT/CA97/00919, entitled "Fluorescence Scope System for
Dermatologic Diagnosis." However, depending on the embodiment, this
device either lacks sensitivity due to the lack of light
amplification, or is difficult to use due to the requirement for
the user to mentally combine images of different colors presented
to each eye.
[0006] To increase the ability of medical personnel to perform
screening tests on greater numbers of patients, there is a need for
a low-cost, lightweight, portable cancer detection system that can
aid physicians in the detection of potentially malignant lesions
based on differences in the autofluorescence light produced by
healthy and suspect tissue.
SUMMARY OF THE INVENTION
[0007] The present invention is a lightweight, hand-held skin
abnormality detection imaging system including a source of
excitation light which causes tissue under examination to produce
autofluorescence light. The autofluorescence light generated from
the tissue under examination along with reference light is directed
to a pair of optical channels that produce an image of the tissue
under examination. An optical combiner, which preferably comprises
a dichroic mirror, superimposes the images of the tissue to be
viewed by a user.
[0008] In one embodiment of the invention, the autofluorescence
light received in one channel has a wavelength selected such that
the autofluorescence intensity for healthy tissue differs from the
autofluorescence intensity produced for diseased or suspect tissue.
The reference light comprises autofluorescence light, wherein the
autofluorescence intensity for diseased tissue is substantially
similar to the autofluorescence intensity for healthy tissue. In
another embodiment of the invention, the reference light comprises
reflected excitation light. In yet another embodiment of the
invention, the reference light comprises light having wavelengths
that differ from the wavelengths of the excitation light.
[0009] The combined superimposed output images may be viewed by a
user or may be captured by an analog or digital camera. For viewing
by a user, these embodiments can all be implemented with monocular
or binocular viewing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0011] FIG. 1 is a schematic block diagram of a first embodiment of
a skin abnormality detection system according to the present
invention that detects abnormalities by providing a monocular,
false color view of the skin based on two detection wavelength
bands of autofluorescence light;
[0012] FIG. 2 is an example of a combined color view produced by
the present invention using a blue excitation filter, a first
autofluorescence optical channel with a green emission filter and a
green phosphor screen and a second autofluorescence optical channel
with a red emission filter and red phosphor screen;
[0013] FIG. 3 is a schematic block diagram of another embodiment of
a skin abnormality detection system according to the present
invention that detects abnormalities by providing a binocular,
false color view of the skin based on two detection wavelengths of
autofluorescence light; and
[0014] FIG. 4 is a schematic block diagram of yet another
embodiment of a skin abnormality detection system according to the
present invention that detects abnormalities by providing a camera
which captures a false color image of the skin based on two
detection wavelengths of autofluorescence light.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] The present invention is a lightweight, hand-held system for
detecting skin abnormalities based on the differences in
autofluorescence light produced by healthy and diseased tissue.
[0016] As shown in FIG. 1, a skin abnormality detection system 5
according one embodiment of the present invention is made up of
seven major subsystems: a light source 10 that produces excitation
light that will cause a tissue sample 12 under examination to
produce characteristic autofluorescence light. An optical splitter
13 divides the fluorescence light received from the tissue sample
12 into two beams of different wavelengths. The first beam is
directed into a first optical channel 14 that collects, amplifies,
and images the light in one fluorescence wavelength band, and a
second beam is directed into a second optical channel 15 that
collects, amplifies, and images the light in a second fluorescence
wavelength band. An optical combiner 16 combines the images from
the two optical channels 14 and 15 into one and presents the
combined image the user's eye 19. In addition, the system 10
includes a control module 17, and a power source 18. The system
described above is a monocular viewer that produces a combined
false color image that is made up of images from two fluorescence
wavelength bands.
[0017] The power source 18 could be batteries or the AC line. In
the preferred embodiment battery power is utilized for
portability.
[0018] The light source 10 provides light of the required
characteristics for exciting the tissue fluorescence. It consists
of a power supply 21, which is controlled by the control module 27
and which receives electrical power from power source 18. The power
supply outputs electrical power of the appropriate characteristics
to operate a lamp 22. The lamp, which may be a xenon flash lamp,
produces a broad spectrum output of visible light (e.g. white
light). The light is formed into a beam which uniformly illuminates
the tissue 12 by a reflector 23 and the combination of image
forming elements 24 and 25 (e.g. lenses). A region of collimated
light is produced between the two lenses. The region of collimated
light provides optimal conditions for the placement of an optical
band pass filter, excitation filter 26, designed for incident light
to be perpendicular to filter's surface. The excitation filter
characteristics are preferably selected such that the filter passes
light of wavelengths utilized to excite fluorescence (typically 400
nm to 450 nm) and blocks light of other wavelengths. The blocking
by the filter in the wavelength bands where fluorescence is
detected must be very good (i.e. in those bands, less than 1 in
10.sup.5 of the light from the lamp should be able to pass through
the filter).
[0019] Typically, the lamp 22 is operated in a pulsed mode similar
to a camera flash; however, it could be on continuously. The
advantages of operating in the pulsed mode are that it allows the
system to be utilized in an undarkened room and the power required
is reduced so battery operation is possible. The intensity and
duration of the light (when pulsed) are controlled by the control
module 17 as a means of adjusting the brightness of the image as
detected by the user's eye 19.
[0020] The result of illuminating the tissue 12 with excitation
light is the emission of characteristic autofluorescence light 31
by the tissue. If the excitation light is in the blue portion of
the spectrum, the emitted fluorescence typically spans wavelengths
from the green to the red (470 nm to 700 nm). The emitted
autofluorescence light 31 is collected and split into two
wavelength bands by the optical splitter 13. An image forming
element (e.g. lens assembly) 41 in the optical splitter 13 collects
the emitted fluorescence light and forms an image of the tissue at
infinity. The image can be focused at infinity via focus mechanism
44. The light is directed onto a dichroic mirror 42 resulting in
the autofluorescence light being split into two wavelength bands. A
portion of the light in one wavelength band passes straight through
the dichroic mirror 42 and enters the first optical channel 14. The
remaining light in the second wavelength band is reflected by the
dichroic mirror 42. Typically, the dichroic mirror 42 will pass
light having wavelengths less than 570 nm and will reflect light
having wavelengths greater than 570 nm. The light reflected by the
dichroic mirror is again reflected by a mirror 43 into the second
optical channel 15.
[0021] As mentioned previously, the autofluorescence light that
passes straight through the dichroic mirror 42 enters the first
optical channel 14. In this optical channel, autofluorescence light
with wavelengths within a defined band is amplified and formed into
an image. The optical channel 14 consists of an emission filter 52,
a lens assembly 53, an image intensifier 54 with phosphor screen 55
and power supply 56. Emission filter 52 passes only the
autofluorescence light in a band of wavelengths near the maximum in
the tissue spectral emission (typically 490 nm to 560 nm). The
emission filter 52 should have particularly good blocking
characteristics for light in the wavelength band utilized for
fluorescence excitation--typically less than 1 in 10.sup.5 of the
excitation light passes the emission filter 52. The lens 53 forms
an image with the autofluorescence light on the input of the image
intensifier 54. The image intensifier is a device that amplifies
the light by a gain determined by a bias voltage that is supplied
by power supply 56. The image intensifier produces an output image
on a phosphor screen 55 (actually an integral part of the image
intensifier). The power supply 56 is controlled by a controller 71
within the control module 17. The controller 71 controls the output
of the power supply 56 in such a way that the intensifier has the
appropriate gain for the light input into the system and is
protected from overexposure. The image intensifier phosphor screen
55 preferably has a long persistence so that the amplified image
would be visible for a few seconds. The phosphor screen 55 would
produce light of a specific wavelength band, for example green
light mainly in the band 500 nm to 560 nm. The light from the image
on the phosphor screen 55 is input to the optical combiner 16.
[0022] As mentioned previously, the autofluorescence light that is
reflected by the dichroic mirror 42 and mirror. 43 in the optical
splitter 13 enters into the second optical channel 15. The second
optical channel 15 consists of an emission filter 62, a lens 63, an
image intensifier 64 with phosphor screen 65 and power supply 66.
The second optical channel 15 is nearly identical to the first
optical channel 14 except that the emission filter 62 is different
than emission filter 52 in that filter 62 passes light of a
different wavelength band (e.g. passes red light in the band 630 to
750 nm). The phosphor screen 65 produces light of a different
wavelength (e.g. produces red light in the band 620 nm to 700 nm)
than the phosphor screen 55 does with long persistence, and the
gain of the image intensifier 64 as set by the controller 71 and
power supply 66 may be different than the gain of image intensifier
54. As a result of these differences, the image formed on phosphor
screen 65 is from a different autofluorescence band and may be of
different brightness. The light from the image on phosphor screen
65 is supplied as an input to the optical combiner 16.
[0023] The optical combiner 16 consists of a lens 81, a lens 82, a
dichroic mirror 83, a mirror 84, a lens 85, and a light sensor 86.
The lens 81 collects light from the image on phosphor screen 55,
and in combination with lens 85 relays the image from the phosphor
screen to the user's eye 19. Light from the image on phosphor
screen 55 in one wavelength band (e.g. green light) passes straight
through dichroic mirror 83. The dichroic mirror 83 has, for
example, characteristics such that light at wavelengths shorter
than 570 nm passes straight through and light at wavelengths longer
than 570 nm is reflected. Lens 82 collects light from the second
optical channel in a second wavelength band (e.g. red light) from
the image on phosphor screen 65. Lens 82, in combination with lens
85 relays the image from phosphor screen 65 to the user's eye 19.
The light from phosphor screen 65 is reflected both by mirror 84
and dichroic mirror 83. This results, in combination with the image
from phosphor screen 55 that passed straight through the dichroic
mirror 83, in the formation of a combined image a the user's eye 19
made up of the images from phosphor screens 55 and 65. The
magnifications of lenses 81 and 82 are chosen so that the images
from phosphor screens 55 and 65 are the same size at the user's
eye, even though the optical path lengths are different.
[0024] In addition to passing straight through dichroic mirror 83,
a small proportion of the light from phosphor screen 55 is
reflected by the dichroic mirror (typically 5%) onto sensor 86.
This light is converted into an electrical signal proportional to
the light amplitude, which is measured by the control module
17.
[0025] The control module 17 consists of the controller 71, acquire
image pushbutton 72, and brightness adjustment knob 73. The
controller 71 contains circuitry to control the light source power
supply 21 and image intensifier power supplies 56, 66, as well as,
circuitry that measures the output voltage of light sensor 86. The
acquire image pushbutton 72 is activated by the user to signal to
the controller to start the image acquisition sequence when the
device is operated in a pulsed mode.
[0026] The brightness adjustment knob 73 is utilized by the user to
communicate an adjustable reference point for the brightness of the
image to the controller. The brightness of the image seen by the
user is automatically controlled by the controller 71 based on a
combination of measurement of light intensity by the light sensor
86, the reference brightness from the brightness adjustment knob
73, and stored image intensifier calibration characteristics. The
controller 71 utilizes this information to control the light source
intensity and duration, as well as the gain of image intensifiers
54 and 64. In order to achieve the best image quality, the control
algorithm is designed to operate at the maximum possible light
source intensity and pulse duration and minimum intensifier gains.
The control algorithm first adjusts the light source intensity and
duration (when pulsed) to achieve the desired brightness. The
algorithm then adjusts the gain of image intensifier 54 to achieve
the target brightness and then adjusts the gain of image
intensifier 64 in such a way that the ratio of the gain of
intensifier 54 to the gain of intensifier 64 is constant, based on
the calibration parameters. In this way, the color of the combined
image is made to be independent of the brightness of the image and
independent of the distance between the tissue and the device.
[0027] Using the system 5 described above, two images of different
color and brightness originating from two autofluorescence
wavelength bands are overlaid for interpretation by the user as
illustrated in FIG. 2. The color of the resulting combined image
depends on the degree of abnormality of the tissue. The spectral
characteristics of autofluorescence light emitted by the tissue
depend on the degree of abnormality. Typically the autofluorescence
light emission of abnormal tissue is different in the green portion
of the spectrum compared to normal tissue. In contrast, the
autofluorescence light emission in the red portion of the spectrum
is essentially unchanged when comparing abnormal and normal tissue.
As a result, the brightness of the green component of the combined
image varies, depending on the degree of tissue abnormality. Tissue
with a degree of abnormality appears a different shade (redder or
greener) than normal tissue. Typically, users can easily discern
subtle color differences indicative of abnormal tissue, especially
when one area in the field of view is different than the rest.
[0028] A second embodiment of the skin abnormality detection system
is also based on FIG. 1. The architecture of the system is the same
as the first embodiment and a combined view similar to that shown
in FIG. 2 is produced, but a different principle of operation is
utilized, necessitating different implementation details. In the
first embodiment, an image is produced by overlaying images from
two different wavelength bands of autofluorescence light. The color
of the composite image resulting from the first embodiment depends
on the health of the tissue, because the intensity of the
autofluorescence light forming one of the images (green) is known
to be a strong function of the health of the tissue, whereas the
intensity of autofluorescence light forming the second image (red)
depends weakly on the health of the tissue. In the second
embodiment, a composite image is formed based on one image from the
wavelength band of autofluorescence light that is a strong function
of the health of the tissue (green), and one image formed from
reflected excitation light (blue). As in the first embodiment, the
color of the combined image depends on the health of the tissue,
because the intensity of the autofluorescence light forming one
image utilized in the composite varies depending on the health of
the tissue, whereas the intensity of the reflected light forming
the second image of the composite depends only weakly on the health
of the tissue.
[0029] The implementation details for the second embodiment are
different from those of the first embodiment in the following ways:
The emission filter 62 for the second optical channel 15 transmits
light reflected from the tissue of the same wavelength band as the
light emitted by the light source (e.g. 400 nm to 450 nm). In
addition, because the reflected light is of much stronger intensity
than the fluorescence light utilized in the first embodiment, the
image intensifier 64 in the second optical channel 15 of the second
embodiment does not need to amplify the light as much and can be of
lower quality. Note that, although dichroic mirror 42 is designed
to transmit light with shorter wavelengths, for example <570 nm
in the first embodiment, there is no need to utilize a different
dichroic mirror for the second embodiment. This is because dichroic
mirrors typically reflect 5% of the incident light in region they
transmit, so the dichroic mirror 42 specified in the first
embodiment can be utilized to reduce the intensity of the light
reflected from the tissue going into the second optical channel 15.
Alternatively, a dichroic mirror that transmits in the green and
reflects in the blue (e.g. reflects wavelengths<470 nm and
transmits wavelengths>470 nm) in conjunction with a neutral
density filter or low gain image intensifier can be utilized.
[0030] Like the second embodiment, a third embodiment of the skin
abnormality detection system is also based on the architecture of
FIG. 1 and produces a combined view similar to that shown in FIG.
2. The third embodiment utilizes the same principle of operation as
the second embodiment, but differs in the implementation details.
Like the second embodiment, a combined image is formed from the
combination of a fluorescence image and a reflected image. The
difference is that instead of utilizing the excitation light as the
source of light for the reflected image, the light source 10
outputs light expressly for the purpose of producing a reflected
image, at a wavelength that is longer than that utilized for the
detection of fluorescence. To produce light both at the wavelength
required for the excitation of fluorescence and for the purpose of
producing a long wavelength reflected image, the excitation filter
26 in the third embodiment has two passbands, one passing short
wavelengths for fluorescence excitation (for example 400 nm to 450
nm), and one passing longer wavelengths for the reflected image
(for example 630 nm to 700 nm). The filter preferably has very good
blocking characteristics in the wavelength region where
fluorescence is detected (e.g. less than 10.sup.-5 of the incident
light should be transmitted between 470 nm and 600 nm). The
emission filter 62 passes light in the longer wavelength band which
is used for the reflected image (for example 630 nm to 700 nm).
This filter 62 should have good blocking of the light in the
excitation wavelength band (400 nm to 450 nm in this example). The
emission filter 52 must, in addition to the characteristics
described for the first embodiment, also have good blocking of
light in the band used for the reflect image (for example, in the
band 630 nm to 700 nm less than 10.sup.-5 of the light should pass
the filter). The balance of the system is similar to that of the
second embodiment.
[0031] A fourth embodiment of the skin abnormality detection system
according to the present invention is shown in FIG. 3. The fourth
embodiment is a viewer that produces a combined, binocular image
based on images either from two wavelength bands of emitted
autofluorescence light, or from one wavelength band of emitted
autofluorescence light and one wavelength band of reflected light.
The system described in the fourth embodiment can be obtained by
combining two of the systems (i.e., one for each eye) described in
one of the first three embodiments to obtain a binocular view. In
the example shown in FIG. 3, the imaging system 100 includes a
power source 102, a control module 104 and a light source 106 that
supplies light to excite a tissue sample 108 to produce
autofluorescence light. A left imaging system 5L provides a
superimposed autofluorescence image to a viewer's left eye in the
same manner as the system shown in FIG. 1 and described above. An
imaging system SR provides a superimposed autofluorescence image
for a viewer's right eye in the same manner as the system 5 shown
in FIG. 1.
[0032] A fifth embodiment of the skin abnormality detection system
is shown in FIG. 4. The fifth embodiment is an optical system that
produces a combined image based on images from two wavelength bands
of emitted autofluorescence light. The fifth embodiment is similar
to the first embodiment, except that it is intended to be utilized
with an instant camera or a digital camera instead of the user's
eye. A combined view, similar to that shown in FIG. 2 is recorded
and displayed by means of the camera.
[0033] As shown in FIG. 4, the fifth embodiment of a skin
abnormality detection system according to the present invention is
made up of eight major subsystems: a light source 10 that produces
excitation light that will cause the tissue 12 under examination to
produce characteristic autofluorescence light, an optical splitter
13 that divides the fluorescence light received from the tissue
into two beams, a first optical channel 14 that collects,
amplifies, and images the light in one fluorescence wavelength
band, a second optical channel IS that collects, amplifies, and
images the light in a second fluorescence wavelength band, an
optical combiner 16 that combines the images from the two
fluorescence optical channels into one and presents the combined
image to a digital or instant camera 120 which records the image
for viewing, a control module 17, and a power source 18.
[0034] The power source 18 could be batteries or the AC line. In
the preferred embodiment, battery power is utilized for
portability.
[0035] The light source 10 provides light of the required
characteristics for exciting the tissue fluorescence. It consists
of a power supply 21 which is controlled by the control module 17
and which receives electrical power from power source 18. The power
supply outputs electrical power of the appropriate characteristics
to operate lamp 22. The lamp, which may be a xenon flash lamp,
produces a broad spectrum output of visible light (e.g. white
light). The light is formed into a beam onto the tissue 12 by
reflector 23 and the combination of image forming elements 24 and
25 (e.g. lenses). In addition to forming a beam, a region of
collimated light is produced between the two lenses that provides
optimal conditions for the placement of an optical band pass
filter, excitation filter 26. This filter 26 is designed for
incident light to be perpendicular to the filter surface. The
excitation filter 16 characteristics are such that the filter
passes light of wavelengths utilized to excite fluorescence
(typically 400 nm to 450 nm) and blocks light of other wavelengths.
It is important that the filter block light in the wavelength bands
where fluorescence is detected (i.e. in those bands no more than 1
in 10.sup.5 of the light from the lamp can pass the filter).
[0036] Typically, the lamp 22 is operated in a pulsed mode similar
to a camera flash. The advantages of operating in the pulsed mode
are that it allows the system to be utilized in an undarkened room
and the power required is reduced so battery operation is possible.
The intensity and duration of the light (when pulsed) are
controlled by the control module 17 as a means of adjusting the
brightness of the image as detected by the camera 120.
[0037] The result of illuminating the tissue 12 with excitation
light is the emission of characteristic autofluorescence light 31
by the tissue. If the excitation light is in the blue, the emitted
fluorescence typically spans wavelengths from the green to the red
(470 nm to 700 nm). The emitted autofluorescence light 31 is
collected and split into two wavelength bands by the optical
splitter 13. An image forming element (e.g. lens) 41 in the optical
splitter collects the emitted fluorescence light and forms an image
of the tissue. The position of the lens 41 can be moved via focus
mechanism 44 to focus the image. The light is directed onto a
dichroic mirror 42 resulting in the autofluorescence light being
split into two wavelength bands. A portion of the light in one
wavelength band passes straight through the dichroic mirror and
enters the first optical channel 14. The remaining light in the
second wavelength band is reflected by the dichroic mirror 42.
Typically, the dichroic mirror 42 will pass light having
wavelengths less than 570 nm and will reflect light having
wavelengths greater than 570 nm. The light reflected by the
dichroic mirror is again reflected by a mirror 43 into the second
optical channel 15.
[0038] As mentioned previously, the autofluorescence light that
passes straight through the dichroic mirror 42 enters the first
optical channel 14. In this optical channel, autofluorescence light
with wavelengths within a defined band is amplified and formed into
an image. The optical channel 14 consists of a lens 53, an emission
filter 52, an image intensifier 54 with phosphor screen 55 and
power supply 56. The lens 53 forms an image at an infinite distance
to collimate the light. This results in an optimum location for the
emission filter 52 that is designed to filter incident light
perpendicular to the filter's surface. Emission filter 52 passes
only the autofluorescence light in a band of wavelengths near the
maximum in the tissue spectral emission (typically 490 nm to 560
nm). The emission filter preferably has good blocking
characteristics for light in the wavelength band utilized for
fluorescence excitation. Typically less than 1 in 10.sup.5 of the
excitation light passes the emission filter. The lens 53 forms an
image with the autofluorescence light on the input of the image
intensifier 54. The image intensifier amplifies the incoming light
by a gain determined by a bias voltage supplied by power supply 56.
The image intensifier produces an output image on phosphor screen
55. The power supply 56 is controlled by the control module 17. The
control module controls the output of the power supply in such a
way that the intensifier has the appropriate gain for the light
input to the system. The image intensifier phosphor screen 55 has a
persistence of at least a few milliseconds, and produces light of a
specific wavelength, for example green light mainly in the band 500
nm to 560 nm. The light from the image on the phosphor screen is
input to the optical combiner 16.
[0039] As mentioned previously, the autofluorescence light that is
reflected by the dichroic mirror enters into the second optical
channel 15. The second optical channel 15 consists of a lens 63, an
emission filter 62, an image intensifier 64 with phosphor screen 65
and power supply 66. The second optical channel 15 is nearly
identical to the first optical channel 14 except that the emission
filter 62 is different than emission filter 52 in that filter 62
passes light of a different wavelength band (e.g. red light in the
band 630 to 750 nm), phosphor screen 65 produces light of different
wavelength (e.g. red light in the band 620 nm to 700 nm) than
phosphor screen 55, and the gain of the image intensifier 64 as set
by controller 71 and power supply 66 may be different than the gain
of image intensifier 54. As a result of these differences, the
image formed on phosphor screen 65 is from a different
autofluorescence band and may be of different brightness. The light
from the image on phosphor screen 65 is input to the optical
combiner 16.
[0040] The optical combiner 16 consists of lens 81, lens 82,
dichroic mirror 83, mirror 84 and lens 85. Lens 81 collects light
from the image on phosphor screen 55, and in combination with lens
85 relays the image from the phosphor screen to the camera's 120
optical system. Light from the image on phosphor screen 55 in one
wavelength band (e.g. green light) passes straight through dichroic
mirror 83. The dichroic mirror 83 has, for example, characteristics
such that light at wavelengths shorter than 570 nm passes straight
through and light at wavelengths longer than 570 nm is reflected.
Lens 82 collects light from the second optical channel in a second
wavelength band (e.g. red light) from the image on phosphor screen
55. Lens 82, in combination with lens 85 relays the image from
phosphor screen 65 to the camera's 120 optical system. The light
from phosphor screen 65 is reflected both by mirror 84 and dichroic
mirror 83. This results, in combination with the image from
phosphor screen 55 that passed straight through the dichroic mirror
83, in the formation of a combined image appropriate for the
camera's 120 optical system made up of the images from phosphor
screens 55 and 65. The magnifications of lenses 81 and 82 are
chosen so that the images from phosphor screens 55 and 65 are the
same size at the camera's optical system, even though the optical
path lengths are different.
[0041] The fifth embodiment of a skin abnormality detection system
attaches to a digital or instant camera 120 by means of the camera
lens mount 122, or by means of a screw in filter mount on the
camera's lens.
[0042] The control module 17 consists of a controller 71, and
brightness adjustment knob 72. The controller 71 contains circuitry
to control the light source power supply and image intensifier
power supplies. The shutter button 123 on the camera is activated
by the user to start the image acquisition sequence. The camera
sends a signal to the controller 71 through the flash
synchronization output jack 121 indicating that image acquisition
is to start and related to the image brightness. The controller
makes use of this signal in controlling the light source power
supply and image intensifier power supplies as described below. The
brightness adjustment knob 72 is utilized by the user to
communicate an adjustable reference point for the brightness of the
image to the controller.
[0043] The brightness of the image as seen by the user is
automatically controlled by the controller 71 based on a
combination of measurement of light intensity by the camera light
meter, the reference brightness from the brightness adjustment knob
72, and stored image intensifier calibration characteristics. The
controller 71 utilizes this information to control the light source
intensity and duration, as well as the gain of image intensifiers
54 and 64. The image intensifiers, controlled through their power
supplies, are turned on by the controller 71 only during the period
that the light source outputs light, plus an additional period
while the fluorescence decays (typically 100 microseconds). The
camera's shutter is opened for a time much longer than the duration
of the light source output (typically {fraction (1/125)} of a
second). In order to achieve the best image quality, the control
algorithm is designed to operate at the maximum possible light
source intensity and pulse duration and minimum intensifier gains.
The control algorithm first adjusts the light source intensity and
duration to achieve the desired brightness as indicated by the
camera light meter. Following this the algorithm adjusts the gain
of image intensifier 54 as further required to achieve the desired
brightness and then adjusts the gain of image intensifier 64 in
such a way that the ratio of the gain of intensifier 54 to the gain
of intensifier 64 is constant, based on the calibration parameters.
In this way, the color of the combined image is made to be
independent of the brightness of the image and independent of the
distance between the tissue and the device.
[0044] A sixth embodiment of the skin abnormality detection system
is also based on the embodiment shown in FIG. 4. The architecture
of the system is the same as the fifth embodiment and a combined
view similar to that shown in FIG. 2 is produced, but a different
principle of operation is utilized, necessitating different
implementation details. The sixth embodiment is similar to the
second embodiment except that the sixth embodiment utilizes a
camera to store the image whereas the second embodiment is a
viewer. In the fifth embodiment, an image is produced by overlaying
images from two different wavelength bands of autofluorescence
light. The color of the composite image resulting from the first
embodiment depends on the health of the tissue, because the
intensity of the autofluorescence light forming one of the images
(green) is known to be a strong function of the health of the
tissue, whereas the intensity of autofluorescence light forming the
second image (red) depends weakly on the health of the tissue. In
comparison, in this sixth embodiment a composite image is formed
based on one image from the wavelength band of autofluorescence
light that is a strong function of the health of the tissue
(green), and one image formed from reflected excitation light
(blue). As in the fifth embodiment, the color of the combined image
depends on the health of the tissue, because the intensity of the
autofluorescence light forming one image utilized in the composite
varies depending on the health of the tissue, whereas the intensity
of the reflected light forming the second image of the composite
depends only weakly on the health of the tissue.
[0045] The implementation details for the sixth embodiment are
different from those of the fifth embodiment in the following ways:
The emission filter 62 for the second optical channel transmits
light reflected from the tissue of the same wavelength band as the
light emitted by the light source (e.g. 400 nm to 450 nm). In
addition, because the reflected light is of much stronger intensity
than the fluorescence light utilized in the first embodiment, the
image intensifier 64 in the second optical channel 15 of the second
embodiment does not need to amplify the light as much and can be of
lower quality. Note that, although dichroic mirror 42 is designed
to transmit light with shorter wavelengths, for example <570 nm
in the first embodiment, there is no need to utilize a different
dichroic mirror in this embodiment. This is because typically
dichroic mirrors reflect 5% of the incident light in region they
transmit, so the dichroic mirror as specified in the fifth
embodiment can be utilized to reduce the intensity of the light
reflected from the tissue going into the second optical channel 15.
Alternatively, a dichroic mirror that transmits in the green and
reflects in the blue (e.g. reflects wavelengths<470 nm and
transmits wavelengths>470 nm) in conjunction with a neutral
density filter or low gain image intensifier can be utilized.
[0046] Like the sixth embodiment, a seventh embodiment of the skin
abnormality detection system is also based on the architecture of
FIG. 4 and produces a combined view similar to that shown in FIG.
2. The seventh embodiment utilizes the same principle of operation
as the sixth embodiment, but differs in the implementation details.
The seventh embodiment is similar to the third embodiment except
that the seventh embodiment utilizes a camera to store the image
whereas the third embodiment is a viewer. Like the sixth
embodiment, a combined image is formed from the combination of a
fluorescence image and a reflected image. The difference is that
instead of utilizing the excitation light as the source of light
for the reflected image, the light source 10 outputs light
expressly for the purpose of producing a reflected image, at a
wavelength longer than that utilized for the detection of
fluorescence. To produce light both at the wavelength required for
the excitation of fluorescence and for the purpose of producing a
long wavelength reflected image, the excitation filter 26 in the
seventh embodiment light source has two passbands, one passing
short wavelengths for fluorescence excitation (for example 400 nm
to 450 nm), and one passing longer wavelengths for the reflected
image (for example 630 nm to 700 nm). The filter preferably has
very good blocking characteristics in the wavelength region where
fluorescence is detected (e.g. less than 10.sup.-5 of the incident
light should be transmitted between 470 nm and 600 nm). The
emission filter 62 must also pass light in the longer wavelength
band which is used for the reflected image (for example 630 nm to
700 nm). This filter should have good blocking of the light in the
excitation wavelength band (400 nm to 450 nm in this example). The
emission filter 52 must, in addition to the characteristics
described for the fifth embodiment, also have good blocking of
light in the band used for the reflect image (for example, in the
band 630 nm to 700 nm less than 10.sup.-5 of the light should pass
the filter). The balance of the system is similar to that of the
sixth embodiment.
[0047] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention. For example, the present invention is not
limited to the detection of skin cancer but can be used to detect
other types of lesions that exhibit variations in autofluorescence
intensities. The invention may also be utilized in internal organs
such as the mouth or during surgical procedures. In addition, the
abnormality detection may also be coupled to a scope, such as an
endoscope or laproscope, used in the medical field to examine
internal tissues and organs. The embodiments described may also be
used with tissue where photodynamic agents, which enhance the
fluorescence response, have been introduced. Finally, the detection
system may be used not only on skin, but also on other surfaces,
such as the detection of abnormalities on plants, and the detection
of contaminants on non-living surfaces, such as surgical tools or
food. It is, therefore, intended that the scope of the invention be
determined from the following claims and equivalents thereto.
* * * * *